Today's Message Index:
----------------------
1. 07:35 AM - Re: Re: Alternator vs Generator and Overvoltage (Brian Lloyd)
2. 09:13 AM - Rib stitching (Walt Murphy)
3. 09:17 AM - Re: TOGGLE SWITCH (Walter Lannon)
4. 09:27 AM - Re: TOGGLE SWITCH (doug sapp)
5. 09:33 AM - Re: Rib stitching (Dale)
6. 09:44 AM - Re: Rib stitching (Dr Andre Katz)
7. 10:25 AM - Cent. Florida RPA FAST Clinic news (Drew)
8. 12:11 PM - Re: What happend to Brian Lloyd's OV project? (Bitterlich, Mark G CIV Det Cherry Point, MALS-14 64E)
9. 12:21 PM - Re: Alternator vs Generator and Overvoltage (Bitterlich, Mark G CIV Det Cherry Point, MALS-14 64E)
10. 12:33 PM - Re: Yak n CJ Aircraft anniversaries and Oshkosh... (Bitterlich, Mark G CIV Det Cherry Point, MALS-14 64E)
11. 12:38 PM - Re: Yak n CJ Aircraft anniversaries and Oshkosh... (Bitterlich, Mark G CIV Det Cherry Point, MALS-14 64E)
12. 01:05 PM - Re: What happend to Brian Lloyd's OV project? (Brian Lloyd)
13. 01:13 PM - Re: Re: Alternator vs Generator and Overvoltage (Bitterlich, Mark G CIV Det Cherry Point, MALS-14 64E)
14. 02:29 PM - Re: Re: Alternator vs Generator and Overvoltage (Gill Gutierrez)
15. 03:11 PM - Re: Re: Alternator vs Generator and Overvoltage (Yak Pilot)
16. 07:06 PM - Re: Re: Alternator vs Generator and Overvoltage (Brian Lloyd)
17. 07:45 PM - US User Fees Are Back (Roger Kemp M.D.)
Message 1
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| Subject: | Re: Alternator vs Generator and Overvoltage |
On Feb 17, 2008, at 9:44 AM, Craig Winkelmann, CFI wrote:
> You mentioned that you would automatically replace the gen system
> and replace it with an alternator in any Yak/CJ you owned. I
> suspect it is more for the peace of mind in modern regulators/
> alternators/etc. or is there another benefit of the alternator that
> I am missing (other than weight).
Oh, be careful when you ask me a question. You may get more answer
than you want. ;-) More below.
> Also, I have not seen an alternator for the CJ on the B&C website.
> The one listed is for the M-14 not the Housai. I understand that
> the drive spline is different on these two engines.
I am not sure that the drive spline is different (Dennis?) but I do
know that the Huosai engine has the shaft seal in generator case
rather than in the engine accessory case as is more common. The M14
has the shaft seal in the accessory case. I have seen several
alternator conversions where someone makes an adaptor plate with the
necessary shaft seal for the Huosai engine. Most involve truck
alternators with the proper spline shaft welded to the alternator
shaft and then inserted through the adaptor plate.
As for alternator vs. generator, here goes the short and the long of it.
Short version:
If your airplane already has a stock generator and it is working,
leave it alone until it breaks. A working generator will do the job
just fine. If you have a broken generator or are doing a ground-up
restoration (as I am) you may want to consider an alternator
conversion, especially if, like me, you have completely removed and
discarded the stock electrical system. (Just the wire loom from a CJ6A
weighs 100lbs, mostly due to the 100% copper braid shield covering
every inch of the cable bundles.) If you want to add an OV protection
system, do so. Basically it will wire to the generator switch and
between the existing voltage regulator and the generator.
Long version:
Generators are a lot more complex than alternators. Since the
alternator has relatively few parts so I am going to describe it
first. After that I will describe all that has to be added to make a
generator and how it adds to all the interesting ways a generator can
fail.
An alternator has relatively few parts. First, there is the case. This
normally consists of two aluminum end pieces with a steel part in the
middle (more on this part later.) The shaft which transmits the
mechanical power from the engine to the alternator is supported by
bearings at either end of the alternator's case. On the shaft is the
armature which consists of an electromagnet of a single winding. This
winding is the field. Current for the field is provided by the voltage
regulator (more on this later) through a pair of brushes and slip
rings. The slip rings are just round contacts that rotate with the
armature. The brushes press against the slip rings to transfer
electrical current to the armature. When more current flows in the
field, the armature produces more magnetism. Less current means less
magnetism.
The center section of the alternator's case is a complex steel pole
piece. The three stator windings which produce the electrical power
output are wound on this pole piece. There are six diodes which
"steer" the power from the three stator windings. The negative side of
the six-diode array is usually connected to the alternator case. The
positive side of the diode array is connected to the battery or B-
lead. The diodes convert the alternating current from the stators into
the direct needed by the electrical system. They also serve to prevent
current from flowing through the alternator when its output is less
than the battery voltage. This is why an alternator's B-lead is always
connected to the battery in a car's electrical system. No on/off
switch is needed.
The output of an alternator varies depending on two things: the
current in the field and the RPM of the armature. The if field current
is held constant then the output of the alternator will increase as
RPM increases. Since we want constant output, something needs to
adjust the field current. That is the job of the voltage regulator.
The voltage regulator always assumes that the alternator is turning.
When the voltage on the bus is too low it increases the field current
(up to some maximum, usually about 3-4A). At low RPM a lot of
magnetism and a lot of physical force are needed to generate power so
the field current is high. At high RPM the opposite is true.
If the load on the alternator is increased, e.g. someone turns on the
landing lights or pitot heat, more output is needed from the
alternator. The VR sees the drop in bus voltage and increases the
field current until the voltage is again at the proper level. Reverse
that if the load is decreased.
That is how an alternator works.
BTW, an alternator is protected from delivering too much output by the
resistance of the stator windings. Bottom line is that a 60A
alternator can't deliver more than 60A so it is self-protected. (The
reason for making this point will be made clear later when describing
the generator.)
Only two things kill an altnernator: mechanical wear and heat. There
are only three wear points in an alternator: the bearings, the slip
rings, and the brushes. Since the brushes are made of carbon and the
slip rings are made of copper, almost all the wear is on the brushes.
Keep feeding the alternator new brushes and it will last almost
forever, modulo the bearings wearing out -- and good bearings should
last a long time.
Heat also kills alternators. If they get too hot the bearings can
fail, the stator windings can burn up, and the diodes can fail.
Remember that, if you are trying to draw full output from your
alternator, it is self protected by the resistance of the windings.
That protection comes at the expense of the stator windings getting
hot -- REALLY hot. They need a lot of air to get rid of that extra
heat. That is why most alternators have those little fans on the front
-- to force air through the alternator to cool the stator windings. If
you keep your alternator cool none of the bad things are likely to
happen. Simple.
As long as we are thinking of alternator failures it is time to talk
about how an alternator can produce an overvoltage condition. This is
not really an alternator failure, per se. It happens when the
regulator "runs away" and turns the field on full. At that point the
alternator produces full output. At first the battery accepts the
excess but that doesn't last. The voltage rises and battery boils and/
or explodes. Without the battery to absorb the excess, buss voltage
goes to the moon. Did you know that an alternator with the field
turned full on can hit over 100V? Kiss your avionics good-bye. To save
everything most aircraft have an OV relay that disconnects the
regulator from the field of the alternator. This shuts down the
alternator. Most OV relays open at around 16V/32V depending on whether
the electrical system is 14=10V or 28V.
Oh, and some alternators have internal regulators. The regulator is
inside the case. The only lead needed is the B-lead. Most of these are
"self exciting" which means that the residual magnetism in the
armature is enough to generate enough output to turn the voltage
regulator on and start the alternator working. All you have to do is
spin them fast enough to start up. Once that happens, you can slow
them to idle and they will work just fine. The only way you can turn
them off is to stop turning the armature. Virtually all automotive
alternators are of this type these days.
Of course, this leads to a very interesting failure mode. If the VR
fails in such a way that it turns the field on hard, the alternator
will "run away" and produce a serious OV condition. Since there is no
way to control the field circuit with this type of alternator there is
no way to add an OV protection relay short of modifying the
alternator. This type of alternator is therefore a time-bomb. The fact
that so few actually fail mens that you will likely never see this
failure should you equip your Yak or CJ with a modified truck
alternator with an internal regulator. But if it DOES fail, kiss your
electrical accessories and your avionics good-bye.
One last thing on this: some of these internally-regulated alternators
have a terminal that can be used to turn the alternator on or off.
Some think that this will save their bacon in the case of an OV event,
i.e. if you detect an OV event just manually turn off the alternator.
The only problem is, this on/off lead depends on the VR working
properly. If the VR's field-controlling device (a transistor inside
the VR) fails shorted, the field is turned on and the on/off switch
will have no effect.
The only way to make an internally-regulated alternator completely
safe is to remove the diode-trio (a separate set of diodes used to
power the regulator from the stator independent of the B-lead) and
feed power to the regulator from a separate wire to the buss that is
under your control. You can even use the on/off control terminal to do
this. Of course, this implies modifying your alternator in the first
place. Why not just start with an externally-regulated alternator and
do it right.
Permanent Magnet (PM) Alternators (Dynamos):
I know that some of you are using dynamos (PM alternators) in your
aircraft. The ones I am most familiar with are the units from B&C that
mount on a vacuum pump pad and produce 5A-10A max. These are great for
day VFR aircraft as the power requirements are very low, usually a
couple of instruments, a comm, an intercomm, and a GPS receiver.
The dynamo is always running at full output for its RPM since its
magnetic field is always full on. There is no control as with a field
winding where you can vary a current to vary the magnetic field. This
means that you need to provide brute-force regulation of the output of
the dynamo and that is what its VR does. Essentially it just burns up
the excess output as heat. Since the currents are relatively low, this
turns out not to be a big problem. This is just about the simplest and
most reliable electrical generating device you can have. If I had a
day VFR airplane that didn't need much electrical power, this the way
I would go.
Generators:
Generators add a LOT of monkey-motion to the power generating
equation. Before I get into the details let's go back about 200 years
to Michael Faraday playing with wire and magnets. He determined that
he could generate an electric current by either moving a wire within a
magnetic field or by moving a magnet past a stationary wire. The only
problem was (and is), when you move the wire or magnet one way the
current flows in one direction and then when you bring the magnet or
wire back to its starting point, the current moves in the other
direction. The only problem is, we want the current to always move in
one direction. Therefore, we need a way to reverse the wiring every
time the current reverses.
Since the 1950s we have had these nice silicon diodes that can do that
job for us. They are small, use very little power, and (almost) never
wear out. They made the alternator possible. But before then we had to
do things the brute-force way. We needed a physical switch to reverse
the connection at the right time to keep the current flowing in only
one direction. In a generator, this switch is called the commutator
and lives at the end of the armature. More on this in a second.
There is one big difference in the architecture of a generator and an
alternator. In the alternator the exciting magnetic field spins
(either a PM or a field winding) and the power-producing windings are
on the outside. In a generator the field windings (or PM) are on the
outside and the power-producing windings are on the spinning armature.
In the alternator the slip rings only have to handle the current of
the field, a few amps at most. Also, the slip rings don't have to
switch on and off. They are going to live a long time. In a generator
the commutator has to switch the full power output of the power-
generating windings of the armature. Every time this happens there is
a small spark which vaporizes a tiny bit of the commutator and its
brushes. Eventually the commutator and its brushes disappear. So the
commutator is the first achilles-heel of the generator. Because of the
commutator, your generator has a limited life. You can make it as long
as possible by making the contact area of the commutator and its
brushes as large as possible but you can never eliminate the problem
entirely. Now on to more of the required extra complexity.
Remember that the diodes in the alternator prevented the battery from
forcing power back through the alternator so we could leave the
alternator always connected to the battery? (They do that in cars.)
Well, you can't do that with a generator. If the generator is not
producing output and it is connected to the battery, current from the
battery will flow through the alternator turning it into an electric
motor. Needless to say the battery won't last long in that case. So
the generator controller has to have a low-output cut-off switch that
disconnects the output of the generator when its output is too low.
That is why generators drop off-line at low RPM. Oh, and that switch
is a possible point of failure, much more likely to fail and wear out
that the diodes in an alternator.
On the other end of the spectrum the commutator and its brushes can
only handle so much current. Unlike the self-protecting stator
windings in the alternator, if you try to get too much current out the
commutator and the brushes they will destroy themselves. So the
generator controller has a current-limiting switch (relay) that
disconnects the generator's output if the current gets too high. This
is another point of failure for our generator system. (Actually there
are some really clever generator voltage regulators that can recognize
the over-current state and actually reduce field current to accomplish
the same thing but they are not very common.)
Lastly, the make/break arcing of the commutator, the make/break arcing
of the field control relay (vibrator), and the make/break arcing of
the over-current relay all make electrical noise that could get into
your avionics. This requires one more thing that an alternator system
doesn't have: a filter at the output of the generator. This is a big,
clunky box full of coils and capacitors designed to get rid of that
noise so only "clean" DC gets to the system buss. It takes up space
and it weighs something, about 8 lbs if I recall, so it uses up useful
load.
So, as you can see, the generator is a LOT more complex than an
alternator. It has MANY more things that can and do break. It has a
lot more adjustments to keep it working properly. All that extra stuff
weighs more. This is why I won't put a generator back into a system I
already have apart.
So getting back to what I said at the beginning, if you already have a
generator, use it until it breaks. After all, it IS working. (If it
ain't broke, don't fix it.) But once it craps out and you find
yourself in the unenviable position of trying to figure out and then
fix what is wrong, it may be easier to just rip it out and start over
with an alternator. The alternator is much simpler, will last longer,
and be less trouble. Personally, I prefer flying my airplane to
troubleshooting. I already have a reciprocating engine and a pneumatic
system to capture and hold my attention. I don't need any extra
distractions.
--
Brian Lloyd 3191 Western Drive
brian HYPHEN 1927 AT lloyd DOT com Cameron Park, CA 95682
+1.916.367.2131 (voice) +1.270.912.0788 (fax)
I fly because it releases my mind from the tyranny of petty things . . .
=97 Antoine de Saint-Exup=E9ry
PGP key ID: 12095C52A32A1B6C
PGP key fingerprint: 3B1D BA11 4913 3254 B6E0 CC09 1209 5C52 A32A 1B6C
Message 2
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Does anyone have good illustrations on how the rib stitching is done on
the Russian and Chinese control surfaces?
The Western method crosses the ribs but the Eastern aircraft have the
rib stitch in line with the rib with the knots hidden, can't find any
reference to how this is done in the manuals that I have.
Thanks,
Walt Murphy
CJ-6A ( recovering elevators )
Reno, NV
Message 3
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| Subject: | Re: TOGGLE SWITCH |
Yes.
That information and many other things you need to know are contained in the
CJ6 Technical Specifications Manual. This and other CJ manuals are available
from Doug Sapp at 509-826-4610 or rvfltd@televar.com.
Walt
----- Original Message -----
From: "CZ" <chriszimmer2002@yahoo.com>
Sent: Sunday, February 17, 2008 9:47 PM
Subject: Yak-List: TOGGLE SWITCH
>
> Does anybody have a label list or illustration of the toggle switches for
> the cj cockpit
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=164758#164758
>
>
>
Message 4
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| Subject: | Re: TOGGLE SWITCH |
Page 160 of your Tech Spec Manual for the CJ6.
On Feb 17, 2008 9:47 PM, CZ <chriszimmer2002@yahoo.com> wrote:
>
> Does anybody have a label list or illustration of the toggle switches for
> the cj cockpit
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=164758#164758
>
>
--
Always Yakin,
Doug Sapp
Phone 509-826-4610
Fax 509-826-3644
Message 5
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| Subject: | Re: Rib stitching |
George Coy has the information.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=164818#164818
Message 6
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| Subject: | Re: Rib stitching |
contact me off line, I have drawings of the knots and techniques for european fabric
covering, you can tell by looking at the line, there are no transverse stitches
and there isnot full thickness material going under and over, the fabric
is usually attached to the ribs via a rib cover and stitched under the ribs.
a
Walt Murphy <waltmurphy@charter.net> wrote:
Does anyone have good illustrations on how the rib stitching is done on
the Russian and Chinese control surfaces?
The Western method crosses the ribs but the Eastern aircraft have the
rib stitch in line with the rib with the knots hidden, can't find any
reference to how this is done in the manuals that I have.
Thanks,
Walt Murphy
CJ-6A ( recovering elevators )
Reno, NV
Message 7
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| Subject: | Cent. Florida RPA FAST Clinic news |
Anyone hearing this transmission...
The first annual Okeechobee Formation Fly-In located on the north side of the
Okeechobbee lake in central Florida is March 7-8-9 and has some 16 folks on the
roster - we may be losing one of our IPs, so if any CPs or IPs want to help
establish this new event, it's in sunny Florida, we can arrange pick up from
major airline serviced domiciles such as KPBI/KMIA/KMCO/KTPA.
As well as anyone of any level of proficiency that wants to spend the weekend in Florida having some fun - more aviators the better. Register online at www.flyredstar.org under "Fly-Ins"
The airfield has a restrnt so no scrambling for lunch, cheapest gas they say
in FL - The hotel is a cut above and inexpensive - located right on the Okeechobee
lake with beer served on the deck after flying, they have a pool table equipped
bar (comes equipped with one white and one red ball for the RPAers).
Drew
---------------------------------
Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now.
Message 8
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| Subject: | What happend to Brian Lloyd's OV project? |
On the YAK's (not sure of the CJ's, but assume it is the same or close)
there is a very good over-voltage protection module that will disconnect
the generator from the main electrical bus by opening the main contactor
in the combination module.
Most aftermarket systems also include over-voltage protection. The only
one that I know of that does not come stock with this protection is the
B&C PMG Alternator, and with that particular one, it is an option..
Simple crowbar circuit.
Brian's project was much more than this, and I am curious as to what the
end result was as well. Just a reassurance that the stock electrical
systems include such a system... Huge as it is.
Mark Bitterlich
-----Original Message-----
From: owner-yak-list-server@matronics.com
[mailto:owner-yak-list-server@matronics.com] On Behalf Of Elmar
Hegenauer
Sent: Friday, February 15, 2008 23:38
Subject: Yak-List: What happend to Brian Lloyd's OV project?
What happend to Brian Lloyd's
Overvoltage Protection project
for the CJ?
IMHO, overvoltage is still a serious
issue on those planes, especially
with all the latest and expensive
avionics installed.
cheers
Elmar (C-FTKL)
Message 9
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| Subject: | Alternator vs Generator and Overvoltage |
I just wrote something on this Craig.... Our minds must have been in
sync.
Stock YAK's most certainly do contain over-voltage protection.
Mark Bitterlich
-----Original Message-----
From: owner-yak-list-server@matronics.com
[mailto:owner-yak-list-server@matronics.com] On Behalf Of Craig
Winkelmann, CFI
Sent: Saturday, February 16, 2008 21:36
Subject: Yak-List: Alternator vs Generator and Overvoltage
--> <capav8r@gmail.com>
Gang:
Can Brian or someone enlighten me on this topic. From what I recall,
both gen and alt systems can have an overvoltage situation. The
external regulator is supposed to control this. From what I gather, the
CJ/Yak electrical system does not provide protection for this?
Please enlighten me!
Craig
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=164497#164497
Message 10
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| Subject: | Yak n CJ Aircraft anniversaries and Oshkosh... |
I think the real answer is how you define the term "AKRO". If you are
talking about slow, lazy, low G type stuff, the CJ is obviously in the
running. If you are talking about competitive/judged aerobatics, the
answer is very simple. Look at the number of CJ's entered for ANY level
of competitive events and compare that to YAK-52's. I believe the CJ
will do very nice, very graceful stuff... Kind of like a T-34. However,
the YAK-52 was built to do every Arresti move in the book, and the CJ
simply was not.
Mark Bitterlich
-----Original Message-----
From: owner-yak-list-server@matronics.com
[mailto:owner-yak-list-server@matronics.com] On Behalf Of A. Dennis
Savarese
Sent: Sunday, February 17, 2008 10:16
Subject: Re: Yak-List: Yak n CJ Aircraft anniversaries and Oshkosh...
Rick,
I'll respond to the question AND start the debate - "....who does akro
best, Yak or CJ? in a while". Answer - no comparison. Yak 52 wins
hands down. :-)))) OK. Let the "debate" begin!
Dennis
----- Original Message -----
From: Rick Basiliere <mailto:discrab@earthlink.net>
To: yak-list@matronics.com
Sent: Sunday, February 17, 2008 5:35 AM
Subject: RE: Yak-List: Yak n CJ Aircraft anniversaries and
Oshkosh...
Drew;
Thanks for all you and the other organizers of Red Star have
done. I was one of the earlier originals with coming on board with Bud
in '96, so 12 years for me now. Wow. I have kept some of Bud's Yak
"magazines" crude in comparison to our slick color mag now but it
brings back great memories.
All of you out there...a big thanks - the organization is
working. We haven't had a good - who does akro best, Yak or CJ? in a
while - that one has hopefully died a gruesome death.
Respectfully, Rick b
----- Original Message -----
From: Drew <mailto:lacloudchaser@yahoo.com>
To: yak-list@matronics.com
Sent: 2/16/2008 9:41:59 AM
Subject: Yak-List: Yak n CJ Aircraft anniversaries and
Oshkosh...
Folks,
I'm sitting here with my copy of a newsletter dated
Winter 1993 Vol 1, No 1. and titled "The CJ-6/Yak-18 Driver"
In that first edition, page 1, the editor Bud Harrell
asked this question:
"...Will there be a Yak association like the T-34
association? I cannot answer that question. For now, we may be too few,
and too far flung..."
He reffered to the CJ-6 as a Yak-18 in those days and
had some 23 pilots respond to this proposal to organize, out of a
distribution list of 47 owners.
For many of you, the founding of the Yak Pilots Club and
evolution to the RedStar Pilots Association, has been a positive
addition to your interest in these aircraft and this great past time.
The RPA (RedStar) is a unified all-aircraft aviators association, it was
about the pilots flying, and not about one type specific aircraft or
another - the name change proposal itself was done to cement that
concept not long after a Yak 52 pilot called up before coming to a
California fly-in we were forming in 2001 and said "This ain't one of
those *$#@ CJ club get togethers they just refer to as 'Yak' is it?".
No, this is RedStar...and we made it a goal to forever remove such an
incorrect perception among aircraft owners of Eastern Block aircraft
(and beyond, RPA membership is open to pilot-owners who simply commit to
the goals of training and fun).
I've heard that the Yak 52 is 30 years old this year?
The CJ is 50 or maybe more. Whats really important, as is being pointed
out by Condor [pres] to the volunteers and seen through the agressive
refocus of Oshkosh 2008, as you will read in this quarters Red Alert, is
the realization that the RPA is 15 years old - and this event is a
National RedStar Celebration of the ENTIRE associations membership and
it's collective accomplishments and evolution.
RPA ops at Oshkosh may highlight the CJ and Yak
anniversaries in specialty publications, mass formations and other
venues, but this event is getting a lot of planning effort (and RPA
treasury and sponsor money) to support the pilots and members equally,
doesn't matter what you fly or drive.
And yes Bud, the community did indeed grow their
association...from 23 in 1993 to well over 450 today.
Food for thought,
Drew
href="http://www.matronics.com/Navigator?Yak-List">http://www.matronics.
com/Navigator?Yak-List
href="http://forums.matronics.com">http://forums.matronics.com
href="http://www.matronics.com/contribution">http://www.matronics.com/c
Message 11
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| Subject: | Yak n CJ Aircraft anniversaries and Oshkosh... |
No way Doc. The 50 is far from being the best Aerobatic Mount... And I
say that owning one. For doing AIRSHOWS, it may very well be one of the
best. Hang a 400HP motor on it with a good three bladed prop and look
out! However for pure aerobatics I believe of all the Russian models,
the Sukhoi 31 would be the best, followed by the 26, and right there
equal with the 26, probably the 29. Just a tiny notch down, and this is
of course debatable... Would be the YAK-55, and close to that.. The 54.
The 54 is very hard to judge... Very few of them flying and you hardly
ever see one at anything other than airshows.
The difference between a 50 and a 31 is simply night and day. Of
course... So is the freaking price!
Getting the best bang for the buck, I would clearly put the 55 and 50
first.
Sadly, I think we are about to see the end of the day where Russian
designs dominate. A lot of models have either stopped production, or
are now asking SERIOUS prices.
Mark Bitterlich
-----Original Message-----
From: owner-yak-list-server@matronics.com
[mailto:owner-yak-list-server@matronics.com] On Behalf Of Roger Kemp
M.D.
Sent: Sunday, February 17, 2008 14:34
Subject: RE: Yak-List: Yak n CJ Aircraft anniversaries and Oshkosh...
Ohhhh.......Nooooo...YUUUUUU.....d'it'nntt!! Being one of the few and
the proud...the YAK-50!
Now lets hear from the YAK 54/55 and Sukio boys....a well...the girls
too!
Doc
From: owner-yak-list-server@matronics.com
[mailto:owner-yak-list-server@matronics.com] On Behalf Of A. Dennis
Savarese
Sent: Sunday, February 17, 2008 9:16 AM
Subject: Re: Yak-List: Yak n CJ Aircraft anniversaries and Oshkosh...
Rick,
I'll respond to the question AND start the debate - "....who does akro
best, Yak or CJ? in a while". Answer - no comparison. Yak 52 wins
hands down. :-)))) OK. Let the "debate" begin!
Dennis
----- Original Message -----
From: Rick Basiliere <mailto:discrab@earthlink.net>
To: yak-list@matronics.com
Sent: Sunday, February 17, 2008 5:35 AM
Subject: RE: Yak-List: Yak n CJ Aircraft anniversaries and
Oshkosh...
Drew;
Thanks for all you and the other organizers of Red Star have
done. I was one of the earlier originals with coming on board with Bud
in '96, so 12 years for me now. Wow. I have kept some of Bud's Yak
"magazines" crude in comparison to our slick color mag now but it
brings back great memories.
All of you out there...a big thanks - the organization is
working. We haven't had a good - who does akro best, Yak or CJ? in a
while - that one has hopefully died a gruesome death.
Respectfully, Rick b
----- Original Message -----
From: Drew <mailto:lacloudchaser@yahoo.com>
To: yak-list@matronics.com
Sent: 2/16/2008 9:41:59 AM
Subject: Yak-List: Yak n CJ Aircraft anniversaries and
Oshkosh...
Folks,
I'm sitting here with my copy of a newsletter dated
Winter 1993 Vol 1, No 1. and titled "The CJ-6/Yak-18 Driver"
In that first edition, page 1, the editor Bud Harrell
asked this question:
"...Will there be a Yak association like the T-34
association? I cannot answer that question. For now, we may be too few,
and too far flung..."
He reffered to the CJ-6 as a Yak-18 in those days and
had some 23 pilots respond to this proposal to organize, out of a
distribution list of 47 owners.
For many of you, the founding of the Yak Pilots Club and
evolution to the RedStar Pilots Association, has been a positive
addition to your interest in these aircraft and this great past time.
The RPA (RedStar) is a unified all-aircraft aviators association, it was
about the pilots flying, and not about one type specific aircraft or
another - the name change proposal itself was done to cement that
concept not long after a Yak 52 pilot called up before coming to a
California fly-in we were forming in 2001 and said "This ain't one of
those *$#@ CJ club get togethers they just refer to as 'Yak' is it?".
No, this is RedStar...and we made it a goal to forever remove such an
incorrect perception among aircraft owners of Eastern Block aircraft
(and beyond, RPA membership is open to pilot-owners who simply commit to
the goals of training and fun).
I've heard that the Yak 52 is 30 years old this year?
The CJ is 50 or maybe more. Whats really important, as is being pointed
out by Condor [pres] to the volunteers and seen through the agressive
refocus of Oshkosh 2008, as you will read in this quarters Red Alert, is
the realization that the RPA is 15 years old - and this event is a
National RedStar Celebration of the ENTIRE associations membership and
it's collective accomplishments and evolution.
RPA ops at Oshkosh may highlight the CJ and Yak
anniversaries in specialty publications, mass formations and other
venues, but this event is getting a lot of planning effort (and RPA
treasury and sponsor money) to support the pilots and members equally,
doesn't matter what you fly or drive.
And yes Bud, the community did indeed grow their
association...from 23 in 1993 to well over 450 today.
Food for thought,
Drew
href="http://www.matronics.com/Navigator?Yak-List">http://www.matronics.
com/Navigator?Yak-List
href="http://forums.matronics.com">http://forums.matronics.com
href="http://www.matronics.com/contribution">http://www.matronics.com/c
http://www.matronics.com/Navigator?Yak-List
http://forums.matronics.com
http://www.matronics.com/contribution
Message 12
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| Subject: | Re: What happend to Brian Lloyd's OV project? |
> Brian's project was much more than this, and I am curious as to what
> the
> end result was as well. Just a reassurance that the stock electrical
> systems include such a system... Huge as it is.
The CJ6A stock electrical system does not have any OV protection. The
module was completed by Bob Nuckolls and tested by Tom Elliot who has
it installed in his aircraft. Tom can answer how well it works and how
easy/hard it was to install. I didn't have an aircraft to work on at
the time.
FWIW, I strongly recommend Bob Nuckolls' book,
_The_Aeroelectric_Connection_. It talks about the design and
implementation of aircraft electrical systems. Bob has worked for both
Cessna and Beechcraft and knows what he is talking about. The book is
written for the layman just getting started and covers a lot of basic
electricity for people who have no previous experience. He gets into
everything from the simple to the complex. The book is aimed at people
building their own aircraft, everything from the simplest RV to the
most complex glass airplane with glass panel and dual electrical
systems.
Brian Lloyd 3191 Western Drive
brianl AT lloyd DOT com Cameron Park, CA 95682
+1.916.367.2131 (voice) +1.270.912.0788 (fax)
PGP key ID: 12095C52A32A1B6C
PGP key fingerprint: 3B1D BA11 4913 3254 B6E0 CC09 1209 5C52 A32A 1B6C
Message 13
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| Subject: | Re: Alternator vs Generator and Overvoltage |
Brian knows I have to respond to this.
I agree with everything he has said. Great explanations as well for the theory
between the two devices. Further, if you have some money hanging around in your
pocket that you need to get rid of, don't wait for the generator to fail...
Replace it right now. Figure around $1000 for on over the counter model, and
some hours for you're A&P to wire it in.
The Alternator system is very reliable. I don't follow their failure rates at
all, and I only know of one that failed (the bigger B&C model with external regulator
with field winding). The owner sent it back for repair, and B&C sent
him a replacement. $700 for the replacement.
As Brian said, the generator system is much more complicated, and it has come to
my attention that very few people really understand it. Even if you have Brian's
understanding of the theory of operation, you still have to cross-match
every piece you know HAS to be there by theory, to where the Russians actually
decided to put the thing, and what they decided to make it look like, and worse
yet, how they labeled it. This makes troubleshooting a Russian electrical
generation system one huge pain in the ass.
On the flip side... It is CHEAPER to maintain if you:
1. Learn how it works.
2. Buy some spare parts to keep handy.
Figure a spare generator... $100.
Spare over-voltage module, regulator, etc. Also around $50 to $100 for each.
The "Combination" relay is a SOB to get ahold of, so all bets are off there, but
it can be repaired.
That said, I have over 700 hours on my YAK-50 here are a list of my electrical
"issues".
Main fuse in forward electrical box failed internally. This is a pretty common
event and has happened to about 5 aircraft that I am aware of. You need to know
where this puppy is and how to replace it. It has nothing to do with generators
or alternators!
Sheared generator shaft coupling (reason unknown, but would have just as easily
happened with an Alternator in my humble opinion). I replaced the whole generator.
Cost... Zero, a guy with an old ugly one laying in the corner gave it
to me. I put it on, it has worked perfectly every since.
Failed Combination Device. This contains the main contactor relay. I fixed it
by replacing the defective internal Russian relays with American made ones.
Took a week to figure out the electrical circuit involved. Another few hours
to try and explain it with an article posted here (a fair but not GOOD job), and
then about 3 hours to actually repair it. Cost, $10 for the relays.
One friend of mine was sure he has a bad generator system. All he had was bad
batteries.
So thus my conclusion. Original system. Cheap to repair. Complicated to understand.
Alternator System. Easy to fix, easy to understand, not cheap for the average
guy.
Mark Bitterlich
P.s. Another little tidbit between Alternators and Generators.
1. If your batteries ever go totally dead in the air or on the ground... I mean
zero or really LOW battery voltage.... And the alternator is not already on-line...
It will never turn on. It needs a little juice to get it going so to
speak. For example, you're flying along and think you may have a battery problem,
so you turn off your alternator to check the battery. If the battery has
indeed failed and gone to zero... Turning your alternator back on will NOT restore
power. Basically you're screwed. Something to keep in mind before turning
off the alternator!
2. Do the same thing with a generator and it will come back on line and operate
and power your aircraft.
A small thing, but part of the overall picture.
-----Original Message-----
From: owner-yak-list-server@matronics.com [mailto:owner-yak-list-server@matronics.com] On Behalf Of Brian Lloyd
Sent: Monday, February 18, 2008 10:32
Subject: Re: Yak-List: Re: Alternator vs Generator and Overvoltage
On Feb 17, 2008, at 9:44 AM, Craig Winkelmann, CFI wrote:
You mentioned that you would automatically replace the gen system and replace
it with an alternator in any Yak/CJ you owned. I suspect it is more for the peace
of mind in modern regulators/alternators/etc. or is there another benefit
of the alternator that I am missing (other than weight).
Oh, be careful when you ask me a question. You may get more answer than you want.
;-) More below.
Also, I have not seen an alternator for the CJ on the B&C website. The one listed
is for the M-14 not the Housai. I understand that the drive spline is different
on these two engines.
I am not sure that the drive spline is different (Dennis?) but I do know that the
Huosai engine has the shaft seal in generator case rather than in the engine
accessory case as is more common. The M14 has the shaft seal in the accessory
case. I have seen several alternator conversions where someone makes an adaptor
plate with the necessary shaft seal for the Huosai engine. Most involve truck
alternators with the proper spline shaft welded to the alternator shaft and
then inserted through the adaptor plate.
As for alternator vs. generator, here goes the short and the long of it.
Short version:
If your airplane already has a stock generator and it is working, leave it alone
until it breaks. A working generator will do the job just fine. If you have
a broken generator or are doing a ground-up restoration (as I am) you may want
to consider an alternator conversion, especially if, like me, you have completely
removed and discarded the stock electrical system. (Just the wire loom from
a CJ6A weighs 100lbs, mostly due to the 100% copper braid shield covering every
inch of the cable bundles.) If you want to add an OV protection system, do
so. Basically it will wire to the generator switch and between the existing
voltage regulator and the generator.
Long version:
Generators are a lot more complex than alternators. Since the alternator has relatively
few parts so I am going to describe it first. After that I will describe
all that has to be added to make a generator and how it adds to all the interesting
ways a generator can fail.
An alternator has relatively few parts. First, there is the case. This normally
consists of two aluminum end pieces with a steel part in the middle (more on
this part later.) The shaft which transmits the mechanical power from the engine
to the alternator is supported by bearings at either end of the alternator's
case. On the shaft is the armature which consists of an electromagnet of a single
winding. This winding is the field. Current for the field is provided by
the voltage regulator (more on this later) through a pair of brushes and slip
rings. The slip rings are just round contacts that rotate with the armature.
The brushes press against the slip rings to transfer electrical current to the
armature. When more current flows in the field, the armature produces more magnetism.
Less current means less magnetism.
The center section of the alternator's case is a complex steel pole piece. The
three stator windings which produce the electrical power output are wound on this
pole piece. There are six diodes which "steer" the power from the three stator
windings. The negative side of the six-diode array is usually connected to
the alternator case. The positive side of the diode array is connected to the
battery or B-lead. The diodes convert the alternating current from the stators
into the direct needed by the electrical system. They also serve to prevent
current from flowing through the alternator when its output is less than the
battery voltage. This is why an alternator's B-lead is always connected to the
battery in a car's electrical system. No on/off switch is needed.
The output of an alternator varies depending on two things: the current in the
field and the RPM of the armature. The if field current is held constant then
the output of the alternator will increase as RPM increases. Since we want constant
output, something needs to adjust the field current. That is the job of
the voltage regulator. The voltage regulator always assumes that the alternator
is turning. When the voltage on the bus is too low it increases the field current
(up to some maximum, usually about 3-4A). At low RPM a lot of magnetism
and a lot of physical force are needed to generate power so the field current
is high. At high RPM the opposite is true.
If the load on the alternator is increased, e.g. someone turns on the landing lights
or pitot heat, more output is needed from the alternator. The VR sees the
drop in bus voltage and increases the field current until the voltage is again
at the proper level. Reverse that if the load is decreased.
That is how an alternator works.
BTW, an alternator is protected from delivering too much output by the resistance
of the stator windings. Bottom line is that a 60A alternator can't deliver
more than 60A so it is self-protected. (The reason for making this point will
be made clear later when describing the generator.)
Only two things kill an altnernator: mechanical wear and heat. There are only three
wear points in an alternator: the bearings, the slip rings, and the brushes.
Since the brushes are made of carbon and the slip rings are made of copper,
almost all the wear is on the brushes. Keep feeding the alternator new brushes
and it will last almost forever, modulo the bearings wearing out -- and good
bearings should last a long time.
Heat also kills alternators. If they get too hot the bearings can fail, the stator
windings can burn up, and the diodes can fail. Remember that, if you are trying
to draw full output from your alternator, it is self protected by the resistance
of the windings. That protection comes at the expense of the stator windings
getting hot -- REALLY hot. They need a lot of air to get rid of that extra
heat. That is why most alternators have those little fans on the front --
to force air through the alternator to cool the stator windings. If you keep
your alternator cool none of the bad things are likely to happen. Simple.
As long as we are thinking of alternator failures it is time to talk about how
an alternator can produce an overvoltage condition. This is not really an alternator
failure, per se. It happens when the regulator "runs away" and turns the
field on full. At that point the alternator produces full output. At first the
battery accepts the excess but that doesn't last. The voltage rises and battery
boils and/or explodes. Without the battery to absorb the excess, buss voltage
goes to the moon. Did you know that an alternator with the field turned full
on can hit over 100V? Kiss your avionics good-bye. To save everything most
aircraft have an OV relay that disconnects the regulator from the field of the
alternator. This shuts down the alternator. Most OV relays open at around 16V/32V
depending on whether the electrical system is 14V or 28V.
Oh, and some alternators have internal regulators. The regulator is inside the
case. The only lead needed is the B-lead. Most of these are "self exciting" which
means that the residual magnetism in the armature is enough to generate enough
output to turn the voltage regulator on and start the alternator working.
All you have to do is spin them fast enough to start up. Once that happens, you
can slow them to idle and they will work just fine. The only way you can turn
them off is to stop turning the armature. Virtually all automotive alternators
are of this type these days.
Of course, this leads to a very interesting failure mode. If the VR fails in such
a way that it turns the field on hard, the alternator will "run away" and produce
a serious OV condition. Since there is no way to control the field circuit
with this type of alternator there is no way to add an OV protection relay
short of modifying the alternator. This type of alternator is therefore a time-bomb.
The fact that so few actually fail mens that you will likely never see
this failure should you equip your Yak or CJ with a modified truck alternator
with an internal regulator. But if it DOES fail, kiss your electrical accessories
and your avionics good-bye.
One last thing on this: some of these internally-regulated alternators have a terminal
that can be used to turn the alternator on or off. Some think that this
will save their bacon in the case of an OV event, i.e. if you detect an OV event
just manually turn off the alternator. The only problem is, this on/off lead
depends on the VR working properly. If the VR's field-controlling device (a
transistor inside the VR) fails shorted, the field is turned on and the on/off
switch will have no effect.
The only way to make an internally-regulated alternator completely safe is to remove
the diode-trio (a separate set of diodes used to power the regulator from
the stator independent of the B-lead) and feed power to the regulator from a
separate wire to the buss that is under your control. You can even use the on/off
control terminal to do this. Of course, this implies modifying your alternator
in the first place. Why not just start with an externally-regulated alternator
and do it right.
Permanent Magnet (PM) Alternators (Dynamos):
I know that some of you are using dynamos (PM alternators) in your aircraft. The
ones I am most familiar with are the units from B&C that mount on a vacuum pump
pad and produce 5A-10A max. These are great for day VFR aircraft as the power
requirements are very low, usually a couple of instruments, a comm, an intercomm,
and a GPS receiver.
The dynamo is always running at full output for its RPM since its magnetic field
is always full on. There is no control as with a field winding where you can
vary a current to vary the magnetic field. This means that you need to provide
brute-force regulation of the output of the dynamo and that is what its VR does.
Essentially it just burns up the excess output as heat. Since the currents
are relatively low, this turns out not to be a big problem. This is just about
the simplest and most reliable electrical generating device you can have. If
I had a day VFR airplane that didn't need much electrical power, this the way
I would go.
Generators:
Generators add a LOT of monkey-motion to the power generating equation. Before
I get into the details let's go back about 200 years to Michael Faraday playing
with wire and magnets. He determined that he could generate an electric current
by either moving a wire within a magnetic field or by moving a magnet past
a stationary wire. The only problem was (and is), when you move the wire or magnet
one way the current flows in one direction and then when you bring the magnet
or wire back to its starting point, the current moves in the other direction.
The only problem is, we want the current to always move in one direction.
Therefore, we need a way to reverse the wiring every time the current reverses.
Since the 1950s we have had these nice silicon diodes that can do that job for
us. They are small, use very little power, and (almost) never wear out. They made
the alternator possible. But before then we had to do things the brute-force
way. We needed a physical switch to reverse the connection at the right time
to keep the current flowing in only one direction. In a generator, this switch
is called the commutator and lives at the end of the armature. More on this
in a second.
There is one big difference in the architecture of a generator and an alternator.
In the alternator the exciting magnetic field spins (either a PM or a field
winding) and the power-producing windings are on the outside. In a generator
the field windings (or PM) are on the outside and the power-producing windings
are on the spinning armature. In the alternator the slip rings only have to handle
the current of the field, a few amps at most. Also, the slip rings don't
have to switch on and off. They are going to live a long time. In a generator
the commutator has to switch the full power output of the power-generating windings
of the armature. Every time this happens there is a small spark which vaporizes
a tiny bit of the commutator and its brushes. Eventually the commutator
and its brushes disappear. So the commutator is the first achilles-heel of
the generator. Because of the commutator, your generator has a limited life. You
can make it as long as possible by making the contact area of the commutator
and its brushes as large as possible but you can never eliminate the problem
entirely. Now on to more of the required extra complexity.
Remember that the diodes in the alternator prevented the battery from forcing power
back through the alternator so we could leave the alternator always connected
to the battery? (They do that in cars.) Well, you can't do that with a generator.
If the generator is not producing output and it is connected to the battery,
current from the battery will flow through the alternator turning it into
an electric motor. Needless to say the battery won't last long in that case.
So the generator controller has to have a low-output cut-off switch that disconnects
the output of the generator when its output is too low. That is why
generators drop off-line at low RPM. Oh, and that switch is a possible point of
failure, much more likely to fail and wear out that the diodes in an alternator.
On the other end of the spectrum the commutator and its brushes can only handle
so much current. Unlike the self-protecting stator windings in the alternator,
if you try to get too much current out the commutator and the brushes they will
destroy themselves. So the generator controller has a current-limiting switch
(relay) that disconnects the generator's output if the current gets too high.
This is another point of failure for our generator system. (Actually there
are some really clever generator voltage regulators that can recognize the over-current
state and actually reduce field current to accomplish the same thing
but they are not very common.)
Lastly, the make/break arcing of the commutator, the make/break arcing of the field
control relay (vibrator), and the make/break arcing of the over-current relay
all make electrical noise that could get into your avionics. This requires
one more thing that an alternator system doesn't have: a filter at the output
of the generator. This is a big, clunky box full of coils and capacitors designed
to get rid of that noise so only "clean" DC gets to the system buss. It
takes up space and it weighs something, about 8 lbs if I recall, so it uses up
useful load.
So, as you can see, the generator is a LOT more complex than an alternator. It
has MANY more things that can and do break. It has a lot more adjustments to keep
it working properly. All that extra stuff weighs more. This is why I won't
put a generator back into a system I already have apart.
So getting back to what I said at the beginning, if you already have a generator,
use it until it breaks. After all, it IS working. (If it ain't broke, don't
fix it.) But once it craps out and you find yourself in the unenviable position
of trying to figure out and then fix what is wrong, it may be easier to just
rip it out and start over with an alternator. The alternator is much simpler,
will last longer, and be less trouble. Personally, I prefer flying my airplane
to troubleshooting. I already have a reciprocating engine and a pneumatic system
to capture and hold my attention. I don't need any extra distractions.
--
Brian Lloyd 3191 Western Drive
brian HYPHEN 1927 AT lloyd DOT com Cameron Park, CA 95682
+1.916.367.2131 (voice) +1.270.912.0788 (fax)
I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupry
PGP key ID: 12095C52A32A1B6C
PGP key fingerprint: 3B1D BA11 4913 3254 B6E0 CC09 1209 5C52 A32A 1B6C
Message 14
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| Subject: | Re: Alternator vs Generator and Overvoltage |
I believe the Yak generator is like the CJ generator is type 'B' and it is
powered like an alternator. That is power is supplied by the battery to the
fields. So I would be careful about checking poor battery condition in
flight.
Gill
-----Original Message-----
From: owner-yak-list-server@matronics.com
[mailto:owner-yak-list-server@matronics.com] On Behalf Of Bitterlich, Mark G
CIV Det Cherry Point, MALS-14 64E
Sent: Monday, February 18, 2008 2:10 PM
Subject: RE: Yak-List: Re: Alternator vs Generator and Overvoltage
MALS-14 64E" <mark.bitterlich@navy.mil>
Brian knows I have to respond to this.
I agree with everything he has said. Great explanations as well for the
theory between the two devices. Further, if you have some money hanging
around in your pocket that you need to get rid of, don't wait for the
generator to fail... Replace it right now. Figure around $1000 for on over
the counter model, and some hours for you're A&P to wire it in.
The Alternator system is very reliable. I don't follow their failure rates
at all, and I only know of one that failed (the bigger B&C model with
external regulator with field winding). The owner sent it back for repair,
and B&C sent him a replacement. $700 for the replacement.
As Brian said, the generator system is much more complicated, and it has
come to my attention that very few people really understand it. Even if you
have Brian's understanding of the theory of operation, you still have to
cross-match every piece you know HAS to be there by theory, to where the
Russians actually decided to put the thing, and what they decided to make it
look like, and worse yet, how they labeled it. This makes troubleshooting a
Russian electrical generation system one huge pain in the ass.
On the flip side... It is CHEAPER to maintain if you:
1. Learn how it works.
2. Buy some spare parts to keep handy.
Figure a spare generator... $100.
Spare over-voltage module, regulator, etc. Also around $50 to $100 for
each.
The "Combination" relay is a SOB to get ahold of, so all bets are off there,
but it can be repaired.
That said, I have over 700 hours on my YAK-50 here are a list of my
electrical "issues".
Main fuse in forward electrical box failed internally. This is a pretty
common event and has happened to about 5 aircraft that I am aware of. You
need to know where this puppy is and how to replace it. It has nothing to
do with generators or alternators!
Sheared generator shaft coupling (reason unknown, but would have just as
easily happened with an Alternator in my humble opinion). I replaced the
whole generator. Cost... Zero, a guy with an old ugly one laying in the
corner gave it to me. I put it on, it has worked perfectly every since.
Failed Combination Device. This contains the main contactor relay. I fixed
it by replacing the defective internal Russian relays with American made
ones. Took a week to figure out the electrical circuit involved. Another
few hours to try and explain it with an article posted here (a fair but not
GOOD job), and then about 3 hours to actually repair it. Cost, $10 for the
relays.
One friend of mine was sure he has a bad generator system. All he had was
bad batteries.
So thus my conclusion. Original system. Cheap to repair. Complicated to
understand.
Alternator System. Easy to fix, easy to understand, not cheap for the
average guy.
Mark Bitterlich
P.s. Another little tidbit between Alternators and Generators.
1. If your batteries ever go totally dead in the air or on the ground... I
mean zero or really LOW battery voltage.... And the alternator is not
already on-line... It will never turn on. It needs a little juice to get it
going so to speak. For example, you're flying along and think you may have a
battery problem, so you turn off your alternator to check the battery. If
the battery has indeed failed and gone to zero... Turning your alternator
back on will NOT restore power. Basically you're screwed. Something to
keep in mind before turning off the alternator!
2. Do the same thing with a generator and it will come back on line and
operate and power your aircraft.
A small thing, but part of the overall picture.
-----Original Message-----
From: owner-yak-list-server@matronics.com
[mailto:owner-yak-list-server@matronics.com] On Behalf Of Brian Lloyd
Sent: Monday, February 18, 2008 10:32
Subject: Re: Yak-List: Re: Alternator vs Generator and Overvoltage
On Feb 17, 2008, at 9:44 AM, Craig Winkelmann, CFI wrote:
You mentioned that you would automatically replace the gen system
and replace it with an alternator in any Yak/CJ you owned. I suspect it is
more for the peace of mind in modern regulators/alternators/etc. or is there
another benefit of the alternator that I am missing (other than weight).
Oh, be careful when you ask me a question. You may get more answer than you
want. ;-) More below.
Also, I have not seen an alternator for the CJ on the B&C website.
The one listed is for the M-14 not the Housai. I understand that the drive
spline is different on these two engines.
I am not sure that the drive spline is different (Dennis?) but I do know
that the Huosai engine has the shaft seal in generator case rather than in
the engine accessory case as is more common. The M14 has the shaft seal in
the accessory case. I have seen several alternator conversions where someone
makes an adaptor plate with the necessary shaft seal for the Huosai engine.
Most involve truck alternators with the proper spline shaft welded to the
alternator shaft and then inserted through the adaptor plate.
As for alternator vs. generator, here goes the short and the long of it.
Short version:
If your airplane already has a stock generator and it is working, leave it
alone until it breaks. A working generator will do the job just fine. If you
have a broken generator or are doing a ground-up restoration (as I am) you
may want to consider an alternator conversion, especially if, like me, you
have completely removed and discarded the stock electrical system. (Just the
wire loom from a CJ6A weighs 100lbs, mostly due to the 100% copper braid
shield covering every inch of the cable bundles.) If you want to add an OV
protection system, do so. Basically it will wire to the generator switch and
between the existing voltage regulator and the generator.
Long version:
Generators are a lot more complex than alternators. Since the alternator has
relatively few parts so I am going to describe it first. After that I will
describe all that has to be added to make a generator and how it adds to all
the interesting ways a generator can fail.
An alternator has relatively few parts. First, there is the case. This
normally consists of two aluminum end pieces with a steel part in the middle
(more on this part later.) The shaft which transmits the mechanical power
from the engine to the alternator is supported by bearings at either end of
the alternator's case. On the shaft is the armature which consists of an
electromagnet of a single winding. This winding is the field. Current for
the field is provided by the voltage regulator (more on this later) through
a pair of brushes and slip rings. The slip rings are just round contacts
that rotate with the armature. The brushes press against the slip rings to
transfer electrical current to the armature. When more current flows in the
field, the armature produces more magnetism. Less current means less
magnetism.
The center section of the alternator's case is a complex steel pole piece.
The three stator windings which produce the electrical power output are
wound on this pole piece. There are six diodes which "steer" the power from
the three stator windings. The negative side of the six-diode array is
usually connected to the alternator case. The positive side of the diode
array is connected to the battery or B-lead. The diodes convert the
alternating current from the stators into the direct needed by the
electrical system. They also serve to prevent current from flowing through
the alternator when its output is less than the battery voltage. This is why
an alternator's B-lead is always connected to the battery in a car's
electrical system. No on/off switch is needed.
The output of an alternator varies depending on two things: the current in
the field and the RPM of the armature. The if field current is held constant
then the output of the alternator will increase as RPM increases. Since we
want constant output, something needs to adjust the field current. That is
the job of the voltage regulator. The voltage regulator always assumes that
the alternator is turning. When the voltage on the bus is too low it
increases the field current (up to some maximum, usually about 3-4A). At low
RPM a lot of magnetism and a lot of physical force are needed to generate
power so the field current is high. At high RPM the opposite is true.
If the load on the alternator is increased, e.g. someone turns on the
landing lights or pitot heat, more output is needed from the alternator. The
VR sees the drop in bus voltage and increases the field current until the
voltage is again at the proper level. Reverse that if the load is decreased.
That is how an alternator works.
BTW, an alternator is protected from delivering too much output by the
resistance of the stator windings. Bottom line is that a 60A alternator
can't deliver more than 60A so it is self-protected. (The reason for making
this point will be made clear later when describing the generator.)
Only two things kill an altnernator: mechanical wear and heat. There are
only three wear points in an alternator: the bearings, the slip rings, and
the brushes. Since the brushes are made of carbon and the slip rings are
made of copper, almost all the wear is on the brushes. Keep feeding the
alternator new brushes and it will last almost forever, modulo the bearings
wearing out -- and good bearings should last a long time.
Heat also kills alternators. If they get too hot the bearings can fail, the
stator windings can burn up, and the diodes can fail. Remember that, if you
are trying to draw full output from your alternator, it is self protected by
the resistance of the windings. That protection comes at the expense of the
stator windings getting hot -- REALLY hot. They need a lot of air to get rid
of that extra heat. That is why most alternators have those little fans on
the front -- to force air through the alternator to cool the stator
windings. If you keep your alternator cool none of the bad things are likely
to happen. Simple.
As long as we are thinking of alternator failures it is time to talk about
how an alternator can produce an overvoltage condition. This is not really
an alternator failure, per se. It happens when the regulator "runs away" and
turns the field on full. At that point the alternator produces full output.
At first the battery accepts the excess but that doesn't last. The voltage
rises and battery boils and/or explodes. Without the battery to absorb the
excess, buss voltage goes to the moon. Did you know that an alternator with
the field turned full on can hit over 100V? Kiss your avionics good-bye. To
save everything most aircraft have an OV relay that disconnects the
regulator from the field of the alternator. This shuts down the alternator.
Most OV relays open at around 16V/32V depending on whether the electrical
system is 14V or 28V.
Oh, and some alternators have internal regulators. The regulator is inside
the case. The only lead needed is the B-lead. Most of these are "self
exciting" which means that the residual magnetism in the armature is enough
to generate enough output to turn the voltage regulator on and start the
alternator working. All you have to do is spin them fast enough to start up.
Once that happens, you can slow them to idle and they will work just fine.
The only way you can turn them off is to stop turning the armature.
Virtually all automotive alternators are of this type these days.
Of course, this leads to a very interesting failure mode. If the VR fails in
such a way that it turns the field on hard, the alternator will "run away"
and produce a serious OV condition. Since there is no way to control the
field circuit with this type of alternator there is no way to add an OV
protection relay short of modifying the alternator. This type of alternator
is therefore a time-bomb. The fact that so few actually fail mens that you
will likely never see this failure should you equip your Yak or CJ with a
modified truck alternator with an internal regulator. But if it DOES fail,
kiss your electrical accessories and your avionics good-bye.
One last thing on this: some of these internally-regulated alternators have
a terminal that can be used to turn the alternator on or off. Some think
that this will save their bacon in the case of an OV event, i.e. if you
detect an OV event just manually turn off the alternator. The only problem
is, this on/off lead depends on the VR working properly. If the VR's
field-controlling device (a transistor inside the VR) fails shorted, the
field is turned on and the on/off switch will have no effect.
The only way to make an internally-regulated alternator completely safe is
to remove the diode-trio (a separate set of diodes used to power the
regulator from the stator independent of the B-lead) and feed power to the
regulator from a separate wire to the buss that is under your control. You
can even use the on/off control terminal to do this. Of course, this implies
modifying your alternator in the first place. Why not just start with an
externally-regulated alternator and do it right.
Permanent Magnet (PM) Alternators (Dynamos):
I know that some of you are using dynamos (PM alternators) in your aircraft.
The ones I am most familiar with are the units from B&C that mount on a
vacuum pump pad and produce 5A-10A max. These are great for day VFR aircraft
as the power requirements are very low, usually a couple of instruments, a
comm, an intercomm, and a GPS receiver.
The dynamo is always running at full output for its RPM since its magnetic
field is always full on. There is no control as with a field winding where
you can vary a current to vary the magnetic field. This means that you need
to provide brute-force regulation of the output of the dynamo and that is
what its VR does. Essentially it just burns up the excess output as heat.
Since the currents are relatively low, this turns out not to be a big
problem. This is just about the simplest and most reliable electrical
generating device you can have. If I had a day VFR airplane that didn't need
much electrical power, this the way I would go.
Generators:
Generators add a LOT of monkey-motion to the power generating equation.
Before I get into the details let's go back about 200 years to Michael
Faraday playing with wire and magnets. He determined that he could generate
an electric current by either moving a wire within a magnetic field or by
moving a magnet past a stationary wire. The only problem was (and is), when
you move the wire or magnet one way the current flows in one direction and
then when you bring the magnet or wire back to its starting point, the
current moves in the other direction. The only problem is, we want the
current to always move in one direction. Therefore, we need a way to reverse
the wiring every time the current reverses.
Since the 1950s we have had these nice silicon diodes that can do that job
for us. They are small, use very little power, and (almost) never wear out.
They made the alternator possible. But before then we had to do things the
brute-force way. We needed a physical switch to reverse the connection at
the right time to keep the current flowing in only one direction. In a
generator, this switch is called the commutator and lives at the end of the
armature. More on this in a second.
There is one big difference in the architecture of a generator and an
alternator. In the alternator the exciting magnetic field spins (either a PM
or a field winding) and the power-producing windings are on the outside. In
a generator the field windings (or PM) are on the outside and the
power-producing windings are on the spinning armature. In the alternator the
slip rings only have to handle the current of the field, a few amps at most.
Also, the slip rings don't have to switch on and off. They are going to live
a long time. In a generator the commutator has to switch the full power
output of the power-generating windings of the armature. Every time this
happens there is a small spark which vaporizes a tiny bit of the commutator
and its brushes. Eventually the commutator and its brushes disappear. So the
commutator is the first achilles-heel of the generator. Because of the
commutator, your generator has a limited life. You can make it as long as
possible by making the con!
tact area of the commutator and its brushes as large as possible but you
can never eliminate the problem entirely. Now on to more of the required
extra complexity.
Remember that the diodes in the alternator prevented the battery from
forcing power back through the alternator so we could leave the alternator
always connected to the battery? (They do that in cars.) Well, you can't do
that with a generator. If the generator is not producing output and it is
connected to the battery, current from the battery will flow through the
alternator turning it into an electric motor. Needless to say the battery
won't last long in that case. So the generator controller has to have a
low-output cut-off switch that disconnects the output of the generator when
its output is too low. That is why generators drop off-line at low RPM. Oh,
and that switch is a possible point of failure, much more likely to fail and
wear out that the diodes in an alternator.
On the other end of the spectrum the commutator and its brushes can only
handle so much current. Unlike the self-protecting stator windings in the
alternator, if you try to get too much current out the commutator and the
brushes they will destroy themselves. So the generator controller has a
current-limiting switch (relay) that disconnects the generator's output if
the current gets too high. This is another point of failure for our
generator system. (Actually there are some really clever generator voltage
regulators that can recognize the over-current state and actually reduce
field current to accomplish the same thing but they are not very common.)
Lastly, the make/break arcing of the commutator, the make/break arcing of
the field control relay (vibrator), and the make/break arcing of the
over-current relay all make electrical noise that could get into your
avionics. This requires one more thing that an alternator system doesn't
have: a filter at the output of the generator. This is a big, clunky box
full of coils and capacitors designed to get rid of that noise so only
"clean" DC gets to the system buss. It takes up space and it weighs
something, about 8 lbs if I recall, so it uses up useful load.
So, as you can see, the generator is a LOT more complex than an alternator.
It has MANY more things that can and do break. It has a lot more adjustments
to keep it working properly. All that extra stuff weighs more. This is why I
won't put a generator back into a system I already have apart.
So getting back to what I said at the beginning, if you already have a
generator, use it until it breaks. After all, it IS working. (If it ain't
broke, don't fix it.) But once it craps out and you find yourself in the
unenviable position of trying to figure out and then fix what is wrong, it
may be easier to just rip it out and start over with an alternator. The
alternator is much simpler, will last longer, and be less trouble.
Personally, I prefer flying my airplane to troubleshooting. I already have a
reciprocating engine and a pneumatic system to capture and hold my
attention. I don't need any extra distractions.
--
Brian Lloyd 3191 Western Drive
brian HYPHEN 1927 AT lloyd DOT com Cameron Park, CA 95682
+1.916.367.2131 (voice) +1.270.912.0788 (fax)
I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupry
PGP key ID: 12095C52A32A1B6C
PGP key fingerprint: 3B1D BA11 4913 3254 B6E0 CC09 1209 5C52 A32A 1B6C
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| Subject: | Re: Alternator vs Generator and Overvoltage |
That is incorrect Gill. With no battery installed in the aircraft at all,
the generator will come on line at 20 volts. With a battery installed, it
will connect to the aircraft mains within a few volts of the battery. The
generator voltage regulation system is completely self contained. If you w
ant an explanation of how the whole system works, please read the article I
wrote on the YAK system. =0A=0AMark Bitterlich=0A=0A=0A----- Original Mess
age ----=0AFrom: Gill Gutierrez <Gill.G@gpimail.com>=0ATo: yak-list@matroni
cs.com=0ASent: Monday, February 18, 2008 5:24:47 PM=0ASubject: RE: Yak-List
: Re: Alternator vs Generator and Overvoltage=0A=0A--> Yak-List message pos
ted by: "Gill Gutierrez" <Gill.G@GPIMail.com>=0A=0AI believe the Yak genera
tor is like the CJ generator is type 'B' and it is=0Apowered like an altern
ator. That is power is supplied by the battery to the=0Afields. So I woul
d be careful about checking poor battery condition in=0Aflight.=0A=0AGill
=0A=0A-----Original Message-----=0AFrom: owner-yak-list-server@matronics.co
m=0A[mailto:owner-yak-list-server@matronics.com] On Behalf Of Bitterlich, M
ark G=0ACIV Det Cherry Point, MALS-14 64E=0ASent: Monday, February 18, 2008
2:10 PM=0ATo: yak-list@matronics.com=0ASubject: RE: Yak-List: Re: Alternat
rlich, Mark G CIV Det Cherry Point,=0AMALS-14 64E" <mark.bitterlich@navy.mi
l>=0A=0ABrian knows I have to respond to this. =0A=0AI agree with everythin
g he has said. Great explanations as well for the=0Atheory between the two
devices. Further, if you have some money hanging=0Aaround in your pocket
that you need to get rid of, don't wait for the=0Agenerator to fail... Repl
ace it right now. Figure around $1000 for on over=0Athe counter model, and
some hours for you're A&P to wire it in. =0A=0AThe Alternator system is v
ery reliable. I don't follow their failure rates=0Aat all, and I only know
of one that failed (the bigger B&C model with=0Aexternal regulator with fi
eld winding). The owner sent it back for repair,=0Aand B&C sent him a repl
acement. $700 for the replacement. =0A=0AAs Brian said, the generator sys
tem is much more complicated, and it has=0Acome to my attention that very f
ew people really understand it. Even if you=0Ahave Brian's understanding o
f the theory of operation, you still have to=0Across-match every piece you
know HAS to be there by theory, to where the=0ARussians actually decided to
put the thing, and what they decided to make it=0Alook like, and worse yet
, how they labeled it. This makes troubleshooting a=0ARussian electrical g
eneration system one huge pain in the ass. =0A=0AOn the flip side... It is
CHEAPER to maintain if you: =0A=0A1. Learn how it works. =0A2. Buy some
spare parts to keep handy. =0A=0AFigure a spare generator... $100. =0ASpa
re over-voltage module, regulator, etc. Also around $50 to $100 for=0Aeach
. =0AThe "Combination" relay is a SOB to get ahold of, so all bets are off
there,=0Abut it can be repaired. =0A=0AThat said, I have over 700 hours on
my YAK-50 here are a list of my=0Aelectrical "issues".=0A=0AMain fuse in f
orward electrical box failed internally. This is a pretty=0Acommon event a
nd has happened to about 5 aircraft that I am aware of. You=0Aneed to know
where this puppy is and how to replace it. It has nothing to=0Ado with ge
nerators or alternators! =0A=0ASheared generator shaft coupling (reason un
known, but would have just as=0Aeasily happened with an Alternator in my hu
mble opinion). I replaced the=0Awhole generator. Cost... Zero, a guy with
an old ugly one laying in the=0Acorner gave it to me. I put it on, it has
worked perfectly every since. =0A=0AFailed Combination Device. This cont
ains the main contactor relay. I fixed=0Ait by replacing the defective int
ernal Russian relays with American made=0Aones. Took a week to figure out
the electrical circuit involved. Another=0Afew hours to try and explain it
with an article posted here (a fair but not=0AGOOD job), and then about 3
hours to actually repair it. Cost, $10 for the=0Arelays. =0A=0AOne friend
of mine was sure he has a bad generator system. All he had was=0Abad batt
eries. =0A=0ASo thus my conclusion. Original system. Cheap to repair. C
omplicated to=0Aunderstand. =0A=0AAlternator System. Easy to fix, easy to
understand, not cheap for the=0Aaverage guy. =0A=0AMark Bitterlich=0A=0AP
.s. Another little tidbit between Alternators and Generators. =0A=0A1. I
f your batteries ever go totally dead in the air or on the ground... I=0Ame
an zero or really LOW battery voltage.... And the alternator is not=0Aalrea
dy on-line... It will never turn on. It needs a little juice to get it=0Ag
oing so to speak. For example, you're flying along and think you may have a
=0Abattery problem, so you turn off your alternator to check the battery.
If=0Athe battery has indeed failed and gone to zero... Turning your alterna
tor=0Aback on will NOT restore power. Basically you're screwed. Something
to=0Akeep in mind before turning off the alternator! =0A=0A2. Do the
same thing with a generator and it will come back on line and=0Aoperate an
d power your aircraft. =0A=0AA small thing, but part of the overall pictur
e. =0A=0A=0A=0A=0A=0A-----Original Message-----=0AFrom: owner-yak-list-s
erver@matronics.com=0A[mailto:owner-yak-list-server@matronics.com] On Behal
f Of Brian Lloyd=0ASent: Monday, February 18, 2008 10:32=0ATo: yak-list@mat
ronics.com=0ASubject: Re: Yak-List: Re: Alternator vs Generator and Overvol
tage=0A=0A=0A=0AOn Feb 17, 2008, at 9:44 AM, Craig Winkelmann, CFI wrote:
=0A=0A=0A You mentioned that you would automatically replace the gen sys
tem=0Aand replace it with an alternator in any Yak/CJ you owned. I suspect
it is=0Amore for the peace of mind in modern regulators/alternators/etc. o
r is there=0Aanother benefit of the alternator that I am missing (other tha
n weight).=0A=0A=0AOh, be careful when you ask me a question. You may get m
ore answer than you=0Awant. ;-) More below.=0A=0A=0A Also, I have not se
en an alternator for the CJ on the B&C website.=0AThe one listed is for the
M-14 not the Housai. I understand that the drive=0Aspline is different on
these two engines.=0A=0A=0AI am not sure that the drive spline is differen
t (Dennis?) but I do know=0Athat the Huosai engine has the shaft seal in ge
nerator case rather than in=0Athe engine accessory case as is more common.
The M14 has the shaft seal in=0Athe accessory case. I have seen several alt
ernator conversions where someone=0Amakes an adaptor plate with the necessa
ry shaft seal for the Huosai engine.=0AMost involve truck alternators with
the proper spline shaft welded to the=0Aalternator shaft and then inserted
through the adaptor plate.=0A=0A=0AAs for alternator vs. generator, here go
es the short and the long of it.=0A=0AShort version: =0A=0AIf your airplane
already has a stock generator and it is working, leave it=0Aalone until it
breaks. A working generator will do the job just fine. If you=0Ahave a bro
ken generator or are doing a ground-up restoration (as I am) you=0Amay want
to consider an alternator conversion, especially if, like me, you=0Ahave c
ompletely removed and discarded the stock electrical system. (Just the=0Awi
re loom from a CJ6A weighs 100lbs, mostly due to the 100% copper braid=0Ash
ield covering every inch of the cable bundles.) If you want to add an OV=0A
protection system, do so. Basically it will wire to the generator switch an
d=0Abetween the existing voltage regulator and the generator.=0A=0ALong ver
sion:=0A=0AGenerators are a lot more complex than alternators. Since the al
ternator has=0Arelatively few parts so I am going to describe it first. Aft
er that I will=0Adescribe all that has to be added to make a generator and
how it adds to all=0Athe interesting ways a generator can fail.=0A=0AAn alt
ernator has relatively few parts. First, there is the case. This=0Anormally
consists of two aluminum end pieces with a steel part in the middle=0A(mor
e on this part later.) The shaft which transmits the mechanical power=0Afro
m the engine to the alternator is supported by bearings at either end of=0A
the alternator's case. On the shaft is the armature which consists of an=0A
electromagnet of a single winding. This winding is the field. Current for
=0Athe field is provided by the voltage regulator (more on this later) thro
ugh=0Aa pair of brushes and slip rings. The slip rings are just round conta
cts=0Athat rotate with the armature. The brushes press against the slip rin
gs to=0Atransfer electrical current to the armature. When more current flow
s in the=0Afield, the armature produces more magnetism. Less current means
less=0Amagnetism.=0A=0AThe center section of the alternator's case is a com
plex steel pole piece.=0AThe three stator windings which produce the electr
ical power output are=0Awound on this pole piece. There are six diodes whic
h "steer" the power from=0Athe three stator windings. The negative side of
the six-diode array is=0Ausually connected to the alternator case. The posi
tive side of the diode=0Aarray is connected to the battery or B-lead. The d
iodes convert the=0Aalternating current from the stators into the direct ne
eded by the=0Aelectrical system. They also serve to prevent current from fl
owing through=0Athe alternator when its output is less than the battery vol
tage. This is why=0Aan alternator's B-lead is always connected to the batte
ry in a car's=0Aelectrical system. No on/off switch is needed.=0A=0AThe out
put of an alternator varies depending on two things: the current in=0Athe f
ield and the RPM of the armature. The if field current is held constant=0At
hen the output of the alternator will increase as RPM increases. Since we
=0Awant constant output, something needs to adjust the field current. That
is=0Athe job of the voltage regulator. The voltage regulator always assumes
that=0Athe alternator is turning. When the voltage on the bus is too low i
t=0Aincreases the field current (up to some maximum, usually about 3-4A). A
t low=0ARPM a lot of magnetism and a lot of physical force are needed to ge
nerate=0Apower so the field current is high. At high RPM the opposite is tr
ue.=0A=0AIf the load on the alternator is increased, e.g. someone turns on
the=0Alanding lights or pitot heat, more output is needed from the alternat
or. The=0AVR sees the drop in bus voltage and increases the field current u
ntil the=0Avoltage is again at the proper level. Reverse that if the load i
s decreased.=0A=0AThat is how an alternator works.=0A=0ABTW, an alternator
is protected from delivering too much output by the=0Aresistance of the sta
tor windings. Bottom line is that a 60A alternator=0Acan't deliver more tha
n 60A so it is self-protected. (The reason for making=0Athis point will be
made clear later when describing the generator.)=0A=0AOnly two things kill
an altnernator: mechanical wear and heat. There are=0Aonly three wear point
s in an alternator: the bearings, the slip rings, and=0Athe brushes. Since
the brushes are made of carbon and the slip rings are=0Amade of copper, alm
ost all the wear is on the brushes. Keep feeding the=0Aalternator new brush
es and it will last almost forever, modulo the bearings=0Awearing out -- an
d good bearings should last a long time.=0A=0AHeat also kills alternators.
If they get too hot the bearings can fail, the=0Astator windings can burn u
p, and the diodes can fail. Remember that, if you=0Aare trying to draw full
output from your alternator, it is self protected by=0Athe resistance of t
he windings. That protection comes at the expense of the=0Astator windings
getting hot -- REALLY hot. They need a lot of air to get rid=0Aof that extr
a heat. That is why most alternators have those little fans on=0Athe front
-- to force air through the alternator to cool the stator=0Awindings. If yo
u keep your alternator cool none of the bad things are likely=0Ato happen.
Simple.=0A=0AAs long as we are thinking of alternator failures it is time t
o talk about=0Ahow an alternator can produce an overvoltage condition. This
is not really=0Aan alternator failure, per se. It happens when the regulat
or "runs away" and=0Aturns the field on full. At that point the alternator
produces full output.=0AAt first the battery accepts the excess but that do
esn't last. The voltage=0Arises and battery boils and/or explodes. Without
the battery to absorb the=0Aexcess, buss voltage goes to the moon. Did you
know that an alternator with=0Athe field turned full on can hit over 100V?
Kiss your avionics good-bye. To=0Asave everything most aircraft have an OV
relay that disconnects the=0Aregulator from the field of the alternator. Th
is shuts down the alternator.=0AMost OV relays open at around 16V/32V depen
ding on whether the electrical=0Asystem is 14V or 28V.=0A=0AOh, and some al
ternators have internal regulators. The regulator is inside=0Athe case. The
only lead needed is the B-lead. Most of these are "self=0Aexciting" which
means that the residual magnetism in the armature is enough=0Ato generate e
nough output to turn the voltage regulator on and start the=0Aalternator wo
rking. All you have to do is spin them fast enough to start up.=0AOnce that
happens, you can slow them to idle and they will work just fine.=0AThe onl
y way you can turn them off is to stop turning the armature.=0AVirtually al
l automotive alternators are of this type these days.=0A=0AOf course, this
leads to a very interesting failure mode. If the VR fails in=0Asuch a way t
hat it turns the field on hard, the alternator will "run away"=0Aand produc
e a serious OV condition. Since there is no way to control the=0Afield circ
uit with this type of alternator there is no way to add an OV=0Aprotection
relay short of modifying the alternator. This type of alternator=0Ais there
fore a time-bomb. The fact that so few actually fail mens that you=0Awill l
ikely never see this failure should you equip your Yak or CJ with a=0Amodif
ied truck alternator with an internal regulator. But if it DOES fail,=0Akis
s your electrical accessories and your avionics good-bye.=0A=0AOne last thi
ng on this: some of these internally-regulated alternators have=0Aa termina
l that can be used to turn the alternator on or off. Some think=0Athat this
will save their bacon in the case of an OV event, i.e. if you=0Adetect an
OV event just manually turn off the alternator. The only problem=0Ais, this
on/off lead depends on the VR working properly. If the VR's=0Afield-contro
lling device (a transistor inside the VR) fails shorted, the=0Afield is tur
ned on and the on/off switch will have no effect. =0A=0AThe only way to mak
e an internally-regulated alternator completely safe is=0Ato remove the dio
de-trio (a separate set of diodes used to power the=0Aregulator from the st
ator independent of the B-lead) and feed power to the=0Aregulator from a se
parate wire to the buss that is under your control. You=0Acan even use the
on/off control terminal to do this. Of course, this implies=0Amodifying you
r alternator in the first place. Why not just start with an=0Aexternally-re
gulated alternator and do it right.=0A=0APermanent Magnet (PM) Alternators
(Dynamos):=0A=0AI know that some of you are using dynamos (PM alternators)
in your aircraft.=0AThe ones I am most familiar with are the units from B&C
that mount on a=0Avacuum pump pad and produce 5A-10A max. These are great
for day VFR aircraft=0Aas the power requirements are very low, usually a co
uple of instruments, a=0Acomm, an intercomm, and a GPS receiver.=0A=0AThe d
ynamo is always running at full output for its RPM since its magnetic=0Afie
ld is always full on. There is no control as with a field winding where=0Ay
ou can vary a current to vary the magnetic field. This means that you need
=0Ato provide brute-force regulation of the output of the dynamo and that i
s=0Awhat its VR does. Essentially it just burns up the excess output as hea
t.=0ASince the currents are relatively low, this turns out not to be a big
=0Aproblem. This is just about the simplest and most reliable electrical=0A
generating device you can have. If I had a day VFR airplane that didn't nee
d=0Amuch electrical power, this the way I would go.=0A=0AGenerators:=0A=0AG
enerators add a LOT of monkey-motion to the power generating equation.=0ABe
fore I get into the details let's go back about 200 years to Michael=0AFara
day playing with wire and magnets. He determined that he could generate=0Aa
n electric current by either moving a wire within a magnetic field or by=0A
moving a magnet past a stationary wire. The only problem was (and is), when
=0Ayou move the wire or magnet one way the current flows in one direction a
nd=0Athen when you bring the magnet or wire back to its starting point, the
=0Acurrent moves in the other direction. The only problem is, we want the
=0Acurrent to always move in one direction. Therefore, we need a way to rev
erse=0Athe wiring every time the current reverses. =0A=0ASince the 1950s we
have had these nice silicon diodes that can do that job=0Afor us. They are
small, use very little power, and (almost) never wear out.=0AThey made the
alternator possible. But before then we had to do things the=0Abrute-force
way. We needed a physical switch to reverse the connection at=0Athe right
time to keep the current flowing in only one direction. In a=0Agenerator, t
his switch is called the commutator and lives at the end of the=0Aarmature.
More on this in a second.=0A=0AThere is one big difference in the architec
ture of a generator and an=0Aalternator. In the alternator the exciting mag
netic field spins (either a PM=0Aor a field winding) and the power-producin
g windings are on the outside. In=0Aa generator the field windings (or PM)
are on the outside and the=0Apower-producing windings are on the spinning a
rmature. In the alternator the=0Aslip rings only have to handle the current
of the field, a few amps at most.=0AAlso, the slip rings don't have to swi
tch on and off. They are going to live=0Aa long time. In a generator the co
mmutator has to switch the full power=0Aoutput of the power-generating wind
ings of the armature. Every time this=0Ahappens there is a small spark whic
h vaporizes a tiny bit of the commutator=0Aand its brushes. Eventually the
commutator and its brushes disappear. So the=0Acommutator is the first achi
lles-heel of the generator. Because of the=0Acommutator, your generator has
a limited life. You can make it as long as=0Apossible by making the con!
=0Atact area of the commutator and its brushes as large as possible but you
=0Acan never eliminate the problem entirely. Now on to more of the required
=0Aextra complexity. =0A=0ARemember that the diodes in the alternator preve
nted the battery from=0Aforcing power back through the alternator so we cou
ld leave the alternator=0Aalways connected to the battery? (They do that in
cars.) Well, you can't do=0Athat with a generator. If the generator is not
producing output and it is=0Aconnected to the battery, current from the ba
ttery will flow through the=0Aalternator turning it into an electric motor.
Needless to say the battery=0Awon't last long in that case. So the generat
or controller has to have a=0Alow-output cut-off switch that disconnects th
e output of the generator when=0Aits output is too low. That is why generat
ors drop off-line at low RPM. Oh,=0Aand that switch is a possible point of
failure, much more likely to fail and=0Awear out that the diodes in an alte
rnator.=0A=0AOn the other end of the spectrum the commutator and its brushe
s can only=0Ahandle so much current. Unlike the self-protecting stator wind
ings in the=0Aalternator, if you try to get too much current out the commut
ator and the=0Abrushes they will destroy themselves. So the generator contr
oller has a=0Acurrent-limiting switch (relay) that disconnects the generato
r's output if=0Athe current gets too high. This is another point of failure
for our=0Agenerator system. (Actually there are some really clever generat
or voltage=0Aregulators that can recognize the over-current state and actua
lly reduce=0Afield current to accomplish the same thing but they are not ve
ry common.)=0A=0ALastly, the make/break arcing of the commutator, the make/
break arcing of=0Athe field control relay (vibrator), and the make/break ar
cing of the=0Aover-current relay all make electrical noise that could get i
nto your=0Aavionics. This requires one more thing that an alternator system
doesn't=0Ahave: a filter at the output of the generator. This is a big, cl
unky box=0Afull of coils and capacitors designed to get rid of that noise s
o only=0A"clean" DC gets to the system buss. It takes up space and it weigh
s=0Asomething, about 8 lbs if I recall, so it uses up useful load.=0A=0ASo,
as you can see, the generator is a LOT more complex than an alternator.=0A
It has MANY more things that can and do break. It has a lot more adjustment
s=0Ato keep it working properly. All that extra stuff weighs more. This is
why I=0Awon't put a generator back into a system I already have apart. =0A
=0ASo getting back to what I said at the beginning, if you already have a
=0Agenerator, use it until it breaks. After all, it IS working. (If it ain'
t=0Abroke, don't fix it.) But once it craps out and you find yourself in th
e=0Aunenviable position of trying to figure out and then fix what is wrong,
it=0Amay be easier to just rip it out and start over with an alternator. T
he=0Aalternator is much simpler, will last longer, and be less trouble.=0AP
ersonally, I prefer flying my airplane to troubleshooting. I already have a
=0Areciprocating engine and a pneumatic system to capture and hold my=0Aatt
ention. I don't need any extra distractions.=0A=0A--=0ABrian Lloyd
3191 Western Drive=0Abrian HYPHEN 1927 AT lloyd DOT com C
ameron Park, CA 95682=0A+1.916.367.2131 (voice) +1.270.912.0788
(fax)=0A=0AI fly because it releases my mind from the tyranny of petty thin
gs . . .=0A- Antoine de Saint-Exup=E9ry=0A=0APGP key ID: 12095C52A
32A1B6C=0APGP key fingerprint: 3B1D BA11 4913 3254 B6E0 CC09 1209 5C52 A32
=============
Message 16
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| Subject: | Re: Alternator vs Generator and Overvoltage |
> P.s. Another little tidbit between Alternators and Generators.
>
> 1. If your batteries ever go totally dead in the air or on the
> ground... I mean zero or really LOW battery voltage.... And the
> alternator is not already on-line... It will never turn on.
Not entirely true. Self-exciting alternators will. Even a regular
alternator will come on line if you can get all the loads off the bus
first.
> It needs a little juice to get it going so to speak.
That is true. OTOH the reason that the generator comes on-line without
the battery is the residual magnetism in the field. The alternator has
the same thing. You can see this by disconnecting the 'B' lead,
putting a voltmeter on it, and spinning up the alternator. You will
get some output. It should be enough to excite the field to bootstrap
the alternator to full output as long as nothing else is using that
output. As I said, that is how a self-exciting alternator gets going.
And most internally-regulated alternators are self exciting.
But there is another issue. Neither a generator system nor an
alternator system should be operated without a battery in the circuit.
The battery is needed to stabilize the voltage. Without it you have
nothing to absorb the excess output when you load-dump. Neither an
alternator nor a generator can change its output suddenly. It takes
time for the magnetism in the field to ramp up or ramp down with a
field current change. (Current lags voltage in an inductor if you want
to get technical.) That means that, without a battery, turn off the
landing light and watch the alternator or generator create an
overvoltage event.
Now we have said WAY more about alternators and generators than anyone
else wanted to hear. ;-)
--
Brian Lloyd 3191 Western Drive
brian HYPHEN 1927 AT lloyd DOT com Cameron Park, CA 95682
+1.916.367.2131 (voice) +1.270.912.0788 (fax)
I fly because it releases my mind from the tyranny of petty things . . .
Antoine de Saint-Exupry
PGP key ID: 12095C52A32A1B6C
PGP key fingerprint: 3B1D BA11 4913 3254 B6E0 CC09 1209 5C52 A32A 1B6C
Message 17
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| Subject: | US User Fees Are Back |
Time to Wake Up again fellow US aviators. Call or write your congressman and
senators. This time it is buried in the upcoming budget request!
Doc
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