Today's Message Index:
----------------------
1. 06:27 AM - Re: Bent whip "radiators" question (Robert L. Nuckolls, III)
2. 06:34 AM - Effects of feedline length on Standing Wave Ratio - Corrected (Robert L. Nuckolls, III)
3. 07:41 AM - Re: Modified Z-12 comments (Robert L. Nuckolls, III)
4. 07:41 AM - Re: Z13a Pre-flight alt test procedure? (Robert L. Nuckolls, III)
5. 08:30 AM - Apex (Raleigh) NC Seminar Date Set (Robert L. Nuckolls, III)
6. 08:55 AM - Re: Microlight battery sizing (Robert L. Nuckolls, III)
7. 09:20 PM - Rotary Switch- solution found (Bonnie & August Lehmann)
Message 1
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| Subject: | Re: Bent whip "radiators" question |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 09:59 PM 1/20/2005 -0500, you wrote:
>--> AeroElectric-List message posted by: "Turbo Tom" <turbotom@mindspring.com>
>
>
> >
> > See: http://www.aeroelectric.com/Pictures/DummyLoad.jpg
> >
> > . . . this is a VERY poor antenna but the transmitter
> > doesn't know it. SWR is 1:1 but it radiates little or
> > nothing.
> >
>That was very well-explaned, Bob! The super-low SWR but non-radiator
>illustration was outstanding.
>
>I for one, would like to know just what effects the bending of the typical
>1/4-wave whip 'aft' would have on radiation [transmission and reception].
>How do those composite streamlined "Commant" [sp] stack up against a
>straight or bent wire on the bottom of the fuselage of the typical RV?
>
>They all seem to work "OK", but do you have an opinion on which is best, or
>worse. I've seen quite a few bent wires lately that were swept completely
>aft, and not all that far from the belly. Are there practical differences?
Not many. The WORKING portion of the antenna is where the greatest
currents are flowing in the radiator. For the 1/4-wave whip, this
is at the base. Current diminishes to zero at the tip.
The antenna needs to look ELECTRICALLY like a full 1/4-wave conductor
for it to match the feedline and accept power. However, it may be
PHYSICALLY shorter and still function well.
For example, my first mobile radio installation in a '41 Pontiac
used an 11' whip with a loading coil about 3' up from the bottom.
The loading coil made the antenna look 32' long ELECTRICALLY
while keeping the physical length much less. As for functionality,
the bottom 3' section was doing most of the work. I could have made
the coil larger and the top section much shorter and not materially
impact efficiency.
The laid-back whips on comm antennas are fine. They don't even
use loading (rubber ducks get so small by doing CONTINUOUS loading.
Most of the antenna is coiled wire wraped around a core).
>One last related question; if the antenna is mounted between the gearlegs,
>[mine are aluminum] does that have a real-world effect?
Sure. You don't event want to know what it does to the radiation
pattern of your antenna. But does it prevent the antenna from
doing what you need it to do? Probably not and only in occasional
instances that go away when you change course.
Bob . . .
Message 2
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| Subject: | Effects of feedline length on Standing Wave Ratio - |
Corrected
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
The first paragraph of my reply was incomplete. I've added the
necessary words in THIS version:
At 08:20 PM 1/20/2005 -0600, you wrote:
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
<b.nuckolls@cox.net>
> > What is the smallest ground plane you'd recommended for a COM antenna
> > and does the antenna have to be mounted in the middle of it?
>
>mounted my antennas to the outside carbon, but attached 4
>copper radials (striped house wire) to the nut plates... the
>length of the ground planes isn't nearly as critical as
>the vertical. what matters is the SWR, or reflected energy
>back into the radio, this can be adjusted by coax feed
>length if you can't cut your floxed in radials like me.
>http://mars.comportco.com/~w5alt/antennas/notes/ant-notes.php?pg=22
>
> > The writer is not "wrong" but he's making a mountain out of
> > a molehill. An airplane is not a perfect world for antennas.
>4 radials of "close" size are easy to glass in (3 would work, but
>more than 4 is overkill) and fine tune SWR with feed length.. no
>math required... one would notice loss of impedance fuel level
>converters for 30secs long before the tower asks you to "say again"
Antenna feedline length has no effect on SWR. When SWR is very
poor, the transmitter may be HAPPIER attempting to transfer
energy to the antenna/feedline system by adjusting the
length of the feedline. This simply means that you've moved
the transmitter's position on a "standing wave" from a
low current, high voltage point to a higher current, low
voltage point. But SWR is SWR is SWR.
The PRIMARY effect on SWR is overall length of the radiating
element . . . i.e. the antenna itself. SECONDARY effects
that stack on top of each other is the sum of the reactances
of what purports to be a 'ground plane' combined with any
attempts with lumped constant inductors and capacitors to
optimize the 1/4-wave antenna feed-point impedance to 50 ohms.
It naturally falls close to 35 ohms.
It's always a good thing to do an SWR plot of a multi-frequency
antenna (COMM runs 118-135 MHz) and see if the SWR is MINIMUM
near the center of the range of interest (126.5) and that it doesn't
get outrageously high at the ends. SWR of 3:1 is generally quite
acceptable. It may be that minimum occurs somewhere OTHER than
right in the middle but as long as it's less than 3:1 over
the range, the antenna is at least a reasonable LOAD for
energies put out by the transmitter. This says NOTHING
about the antenna's efficiency as a radiator (and conversely
a receptor) of radio frequency energies. One WISHES that
the whole 50 ohms impedance of a 1:1 antenna also represents
its RADIATION resistance as well. Never quite so. Very sad
antennas can have RADIATION resistances in the 1-10 ohm range
while the rest is resistive losses. A 50 ohm resistor has
an impedance of 50 ohms but a radiation resistor in the
milliohms range. This is why they make good "DUMMY LOADS".
See: http://www.aeroelectric.com/Pictures/DummyLoad.jpg
. . . this is a VERY poor antenna but the transmitter
doesn't know it. SWR is 1:1 but it radiates little or
nothing.
Be very suspicious of any instructions suggesting that
you adjust the length of the feedline for "improved
matching" or "reduction of SWR". This is a big red flag
that says something is seriously wrong with the
design of the antenna and/or feedline system.
Bob . . .
--------------------------------------------------------
< Throughout history, poverty is the normal condition >
< of man. Advances which permit this norm to be >
< exceeded -- here and there, now and then -- are the >
< work of an extremely small minority, frequently >
< despised, often condemned, and almost always opposed >
< by all right-thinking people. Whenever this tiny >
< minority is kept from creating, or (as sometimes >
< happens) is driven out of a society, the people >
< then slip back into abject poverty. >
< >
< This is known as "bad luck". >
< -Lazarus Long- >
<------------------------------------------------------>
http://www.aeroelectric.com
Message 3
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| Subject: | Modified Z-12 comments |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 06:18 PM 1/12/2005 -0800, you wrote:
>--> AeroElectric-List message posted by: "Scott Winn (Matronics List)"
><swmat@cox.net>
>
>I had a similar response to a very similar question a few weeks back. I
>wanted to know if my method if integrating the Z-30 dual battery with
>the Z-13 'All Electric Airplane on a Budget' would work well or not.
>
>See:
>AeroElectric-List: RE: Schematic Review
>It's message number 21455.
>I don't know how to link to it.
>
>I got one response from another list user but it seemed pretty clear
>that 'battery failure' has been discussed before and isn't a topic that
>needs to be rehashed. The batteries are infallible and failure is as
>likely as the prop coming off.
> Your question isn basically the same how
>is it best to integrage Z-30 with the various diagrams?
>
>I'm still curious why Z-30 exists if properly maintained RG batteries
>never fail. A dual alternator, single battery system should be just as
>reliable as a dual battery dual alternator system. With the exception
>of a twin engine which could use dual batteries for cabling reasons, I
>don't know what reasons could be construed for a dual battery
>installation.
A PROPERLY MAINTAINED battery has a very low probability of
failure. Properly maintained means making sure that a battery
is not taxed to duty beyond some minimum value of capacity . . .
LOOOOONNNNGGG before it stops cranking the engine. This is
done by either (1) periodic and frequent change-out or
(2) periodic capacity testing. The philosophy you choose
is driven by your perceptions of $time$ invested in
reliability.
Dual batteries allow one to mitigate probability
of CONNECTION failure to a perfectly good battery. If you
have an electrically dependent engine with TWO sets of
electrically driven support hardware, you MAY wish to mitigate
single points of failure in common wiring by having two
independent batteries supplying power to EACH of two
systems.
The concept of installing two batteries has little to
do with gross battery reliability. We've had cases where
wiring has become disconnected and battery posts were broken
off (stiff 2AWG 22759 jumpers). THESE are greater risks easily
handled with dual batteries and dual battery busses to
support dual engine support systems.
>In the particular aircraft configuration I am working with, we have dual
>electronic ignitions and limited weight carrying capability aft of the
>firewall (canard). I can't slap an SD-20 on there as a backup, it's
>simply getting too heavy. An SD-8 is the lightest backup I can get, but
>it doesn't meet the current requirements to power both ignitions (6A)
>plus the essential bus.
Why run BOTH ignitions in the endurance mode? The engine
runs just fine with ONE ignition . . . when the main alternator
is unavailable, I'd shut down one of the ignition systems too.
Remember, all you need to have running are the gizmos that keep
you airborne and pointed in the right direction until time for
approach to landing. With an SD-8, 99% of airplanes flying should
be able to keep 100% of the battery's capacity in reserve for
approach to landing.
> I need a large battery up front to supplement
>current to provide electrical power for the long range the aircraft is
>capable of. I would also like to add 'Replace and Rotate batteries' to
>the annual maintenance task list. This will simplify maintenance for
>myself or whoever else may own the aircraft.
How large is "large"?
>If the aircraft was ever sold, and had one battery, it would be much
>easier for a third party to later rationalize not replacing a large
>battery after only 1 year. It also seems likely to me that even though
>I would stress how important proper battery maintenance is, that the
>battery would might not be properly maintained with bi-annual capacity
>checks and timely replacement. I see two batteries as a simplification
>of maintenance. Two, smaller batteries also provide protection in the
>event that some future user replaces them with some other type of
>battery that is more prone to failure.
Why agonize over a future buyer's PERCEPTIONS of a design
and established operating/maintenance requirements. If it's
in the POH and maintenance procedures and has served one well
for many years, (1) the new owner can either accept it without
understanding it (that's how 90% of the spam can drivers do it)
or (2) one can explain how and why the system was designed this way
and offer him UNDERSTANDING or (3) he can get out the hammers-n-saws
and make it work any way he likes. Let's hear it for liberty and the
freedom to do dumb things.
>In the configuration that you are describing James I think that having
>to use the circuit breakers as switches to perform battery isolation
>complicates things from a usability point of view. When I integrated
>Z-30 with Z-13 I didn't eliminate any switches, and it is a very simple
>system to use, although it does take a bit more panel space.
Can we backtrack and see what mission requirements and equipment
compliments drove the architecture decision in the first place?
Then start with a Z-13/Z-30 combo and discuss whatever shortcomings
have been discovered? A discussion on total battery weight would
be useful too. I'm mystified by the term "large" battery to support
mission requirements when there are two alternators.
Bob . . .
Message 4
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| Subject: | Re: Z13a Pre-flight alt test procedure? |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 09:45 PM 1/20/2005 -0800, you wrote:
>--> AeroElectric-List message posted by: "Mike Holland" <hollandm@pacbell.net>
>
>Bob, I have the SD8, with indicator light and wired per Z13. What problem
>is there with having both alternators active?
No, won't hurt a thing.
> If the SD8 will come on-line at idle speed the indicator light would go
> out and that would indicate it was active without having to shut down the
> main alternator.
The light goes out when you flip the switch to ON and there
is no OV condition present. The absence of that light is NOT
and indicator of PROPER operation but the presence of the light
is solid indication of alternator OFF.
>If it matters I have Hall effect sensors on both B leads.
Does your alternator have a built in regulator. Are you wired
per Z-24? IF NOT . . . then there's nothing at risk for turning
the main alternator OFF and aux alternator ON during runup to
check your ignition system(s). If you have Z-24 and internally
regulated alternator, turn the main alternator OFF and aux alternator
ON at engine idle before runup . . . after run up and at engine idle,
turn aux alternator OFF and main alternator back ON. Don't
concern yourself with voltage readings while aux alternator
is ON . . . just not that the current output comes up. You might
want to consider running BOTH alternator leads through ONE
hall-effect sensor. Since the alternators are tested/used
independently from each other, the one current sensor can be
used to monitor functionality of both alternators.
Bob . . .
Message 5
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| Subject: | Apex (Raleigh) NC Seminar Date Set |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
We've just concluded preparations for offering a weekend
seminar in the facilities of EAA Chapter 1114 in Apex
NC near Raleigh. Interested individuals are invited to
check out the details at:
http://aeroelectric.com/seminars/ApexNC.html
Bob . . .
--------------------------------------------------------
< Throughout history, poverty is the normal condition >
< of man. Advances which permit this norm to be >
< exceeded -- here and there, now and then -- are the >
< work of an extremely small minority, frequently >
< despised, often condemned, and almost always opposed >
< by all right-thinking people. Whenever this tiny >
< minority is kept from creating, or (as sometimes >
< happens) is driven out of a society, the people >
< then slip back into abject poverty. >
< >
< This is known as "bad luck". >
< -Lazarus Long- >
<------------------------------------------------------>
http://www.aeroelectric.com
Message 6
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| Subject: | Re: Microlight battery sizing |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 07:49 AM 1/20/2005 +1300, you wrote:
>--> AeroElectric-List message posted by: Frank & Dorothy
><frankv@infogen.net.nz>
>
>Hi
>
>I have recently bought a microlight project which includes a Kawasaki
>440 (26 cu in) engine with alternator and electric start.
>
>I'm trying to figure out what size battery I should buy... The
>documentation I've found on the engine says that I need a battery
>capable of delivering 18A or so cranking current.
That seems a little light in spite of the engine's small size.
Was the document suggesting an 18 a.h. battery? These are plentiful
in MANY brands. They're about 3 x 6 x 6 inches, weigh about
15 pounds and are very reasonable in cost. Some folks sell these
for $40 or less.
> I guess that's
>reasonable, since BobN uses a figure of 250A for (I guess) something
>like an O320, which is 10 times as big.
>
>BobN recommends a RG type as providing better cranking current than a
>standard flooded cell battery.
>
>There's really no essential electrical load... the only electrical
>equipment is a handheld radio, perhaps a GPS, perhaps an MP3 player...
>all of them can run off batteries.
>
>I've found a cheap CGB brand (made in China, 12V 7Ah) RG battery for
>sale. A Net search showed up 25 milli-ohms internal resistance for this
>battery. Is this going to be suitable?
Suitability is in the experience of the beholder and
difficult to predict given what we DON'T know about
the battery you're referring to. Try it. If you don't
like it get a different one.
Bob . . .
Message 7
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| Subject: | Rotary Switch- solution found |
--> AeroElectric-List message posted by: Bonnie & August Lehmann <blehmann@pris.bc.ca>
Just to say thank you to Leo Corbalis, Rob Prior, and Sigmo for their leads
and suggestions to a replacement of a 25A, 120VAC rotary selector switch.
None of the sources had anything of a high enough capacity, and as a total
greenhorn in electrical or electronic matters, I hesitated going the
relay/contacter route.
Then my better half came up with a solution after she examined the broken
switch, and that was to use parts of a sheet of Lexan I happen to have
laying around to replace the broken face of the switch. A full day later,
and voila, its repaired and working! Now we will survive the early stages
of the 37th ice age this year.
Many thanks to the List and the rapid responses it created to our dilemma.
August
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