Today's Message Index:
----------------------
1. 03:30 AM - Re: Yak 52 Questions (Rob Rowe)
2. 06:06 AM - Re: Yak 52 Questions (cjpilot710@aol.com)
3. 06:38 AM - Re: Yak 52 Questions (Bill Geipel)
4. 07:13 AM - Re: Yak 52 Questions (tjyak50)
5. 08:39 AM - Over square (sajdds@comcast.net)
6. 09:06 AM - Re: Yak 52 Questions (Brian Lloyd)
7. 09:36 AM - Re: Over square (Brian Lloyd)
8. 10:13 AM - Re: Over square (Jj)
9. 10:34 AM - Re: Yak 52 Questions (RICHARD VOLKER)
10. 01:12 PM - Re: Over square (sajdds@comcast.net)
11. 01:14 PM - Re: Yak 52 Questions (Brian Lloyd)
12. 01:46 PM - Re: Yak 52 Questions (RICHARD VOLKER)
13. 06:18 PM - Re: Over square (Brian Lloyd)
14. 07:03 PM - Re: Yak 52 Questions (CD 2.0)
15. 08:54 PM - Re: Over square (DAVID STROUD)
16. 09:59 PM - Re: Over square (Brian Lloyd)
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| Subject: | Re: Yak 52 Questions |
Grayson wrote:
>
> First, is there any consensus for V speeds on the Yak 52.
> ...
> Any consensus on the best throttle and prop setting for max range?
Hi Grayson,
FWIW the attached (partially translated) document from the Russian Ministry of
Transport is dated 1990 and is the latest I've been able to find.
It appears to supersede figures for all YAK-52s, not just later built ones.
The stall speeds have been revised as follows (power off / max weight);
In a landing configuration - 110 km/h (Vs0)
In direct flight - 120 km/h (Vs1)
In inverted flight - 150 km/h (previously 140 km/h)
As always treat these as theoretical, from my own 1991 aircraft last (triennial)
flight test gave a Vs0 of 105 km/h & Vs1 of 114 km/h ... yours may (will) vary.
Interesting the inverted stall has been revised up ... recall the aerobats amongst
us commenting a while back on the list that the original 140 km/h was understated.
Also note the widely mis-quoted stall speed of 100km/h (landing configuration at
NOMINAL 1 power - short field?) has been deleted entirely from this 1990 document.
As to range even in this document there are minor discrepancies ... so caution
advised. Section 1.2.2 quotes fuel range calculation based on 120 litres is 465km,
yet table 3 uses 118 litres & 460km ... both look generous, literally YMMV.
The max range calculation is based on flying at 190 km/h IAS (195 km/h CAS) at
an altitude of 500 metres, using 55% RPM and manifold as required to produce the
stated IAS.
It allows for 118 litres of fuel available at take-off (so after start, taxi ,
power check) ... again generous, but maybe DOSAAF usage assumes a ground crew
has warmed oil etc.
>From this 118 litres a 10% reserve (not 'unusable' as often mis-quoted) of 12
litres is subtracted plus another 7 litres for take-off, climb to 500 metres and
for a circuit to land (from their own figures in table 2 another 0.5 litre
should have been added for the descent phase); leaving 99 litres available for
en-route fuel.
Using the stated power / CAS apparently gives a fuel burn of 42.51 litres/h giving
an en-route range of 454 km, plus another 5.5 km in the circuit (from table
2) to give (rounded up) a 460 km distance travelled. Enabling an en-route flight
time of 2h 20mins and total flight time (including circuit) of 2h 30min (although
table 2 suggests this should be 2h 28min).
So while these purport to be the official (theoretical) figures they look rather
generous from a practical perspective. So advisable to supplant your aircraft's
data (based on experience) into this calculation and then factor a personal
additional safety margin on top ... as stated above YMMV!
FYI - my comments in green were from submitting this to the UK CAA in May 2010
requesting clarification on Permit to Fly limitations and flight manuals in circulation
... I'm still awaiting a response (gentle hint).
brgds, Rob R
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=352117#352117
Attachments:
http://forums.matronics.com//files/caa_yak_52_1990_specs_208.pdf
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| Subject: | Re: Yak 52 Questions |
I can only add one thing to Brain's post. Keeping an engine 'over square'
can help with the longevity of the engine. You want the engine to be
driving the prop - not the prop driving the engine. This is known as "back
loading" for which the bearings and such in the engine are not really design
for. This is particularly bad for bigger engines (W1820 & PW1830). The
HS6a and M14p are somewhat "beef-e-er" for their size/hp so they are not quite
as critical for the occasional backloading. A few cycles in an 1830 and
you'll be changing an engine way before that 1,000 hours mark.
As Brain pointed out the IAS at stall is what it is. It is the instrument
you will be using for reference. It can read in any units of valve of
what ever you want to call them. And they are only good in your airplane.
There are a great many errors from the real TAS at stall to that of ASI
simply because of system design. You can even see this in a Cessna or Piper.
Have you ever seen an ASI with one (1) kt/mph increments? Also remember
that a stall is really defined by the critical angle of attack of that
particular airfoil not a speed.
Jim "Pappy" Goolsby
In a message dated 9/13/2011 1:25:52 A.M. Eastern Daylight Time,
brian@lloyd.com writes:
On Mon, Sep 12, 2011 at 6:21 PM, Grayson <_grayson50@hotmail.com_
(mailto:grayson50@hotmail.com) > wrote:
(mailto:grayson50@hotmail.com) >
Any input is appreciated,
First, is there any consensus for V speeds on the Yak 52. I know there can
be a bit of confusion since they come in 3 flavors (mph, knots, km/h) but
it seems like every site I visit has a different number. I've seen Vne from
226mph to about 275mph, and stall clean from about 60 mph up to 75 mph and
dirty from about 60 mph to 70 mph. The stall numbers are what I'm most
interested in. My 'POH' has clean at 69mph and dirty at 63mph (my indicator is
mph) I believe. But the my POH isn't even the original.
Go out and find out for yourself. Here:
1. Calibrate your airspeed indicator. I have a spreadsheet that uses
three GPS track and groundspeed pairs to calculate TAS and winds aloft. I
then use pressure altitude and temperature to convert TAS to CAS. From that
you can build your own airspeed indicator calibration card.
2. Load the airplane to the gross weight you want to use.
3. Go out and carefully fly a stall series. Use very slow deceleration
so you can carefully read the IAS when the break occurs.
Now you know the real stall speed, not some number that someone else wrote
down that may or may not be correct.
BTW, once you know the stall speed, you can properly calculate
maneuvering/cornering speed for your airplane. Take the square-root of the maximum
load factor, 7 G's in the case of the Yak-52 (2.65), and multiply it by the
stall speed. The result is Va.
Unfortunately, you have to get Vne from the designer.
Also, I'm doing a long cross-country soon. Is there any problem with
filling the oil reservoir all the up to 16L so I don't have to add oil as often?
I know not to turn it upside down like this as a lot will come out.
But you don't get a higher oil burn rate because you have the reservoir
filled do you?
You can do that but you need to know how much drains back into the engine
sump when the aircraft is sitting. Once you get going, the engine sump oil
pump will keep the sump scavenged and will raise the level of oil in the
tank. The best way to know what your maximum fill point is is to check the
level cold, fly a very short hop, and then immediately check the oil level on
landing.
And..
Any consensus on the best throttle and prop setting for max range? 60
units throttle and 60% prop? Oversquare 65 throttle, 60% prop? Any limit to how
much is safe to oversquare by? And is the reason for oversquaring because
a higher rpm results in higher fuel consumption more so than a high
manifold setting?
Generally speaking, running "over square" is not going to hurt an engine
that is not boosted (turbocharged or supercharged). But the M14P does have a
supercharger. The boost used in the standard 360hp motor is not all that
great but there MAY be a maximum MAP for a lower RPM in the PF. You need to
get that info from the engine manufacturer.
As for fuel consumption, lower RPMs result in lower frictional losses in
the engine. So if you reduce RPM and increase MAP to get the same hp out of
the engine, you will have lower frictional losses and thus slightly lower
fuel burn.
If you want to get carried away (and I usually do) there is one more thing
to think about and that is the RPM, torque (proportional to MAP) and TAS
for maximum prop efficiency. Prop blades have twist because the velocity of
the tips is greater than the velocity near the hub. So the angle of attack
of the prop blades is changing from hub to tip. There is an optimal
combination that will result in the maximum conversion of hp into IAS.
Frankly, I doubt anyone has done the flight testing to determine the most
efficient operating point for the Yak-52. I did a lot of this kind of work
with the CJ6A and determined how to safely get 400+nm legs on the stock
42gal fuel. (I made a couple of cross-country cross-countries in the CJ6A and
wanted to be able to save gas, save time, AND save gas stops. I routinely
flew 450nm legs when I had a 10kt or greater tailwind and still landed with
legal reserves.) You can do it in the Yak-52 but it will take flights at
different altitudes and power settings to determine what works best. If you
are planning a long cross country you can use the trip to try different
altitudes and power settings to determine the effect on fuel efficiency.
But generally speaking, altitude is your friend when it comes to
efficiency. If you need to reduce MAP, do it by climbing, not by pulling the
throttle back. Take an O2 bottle with you and see how the airplane works at
13,000-16,000 feet. I think you will be pleasantly surprised. Hopefully you have
an aux tank so you can spend more time at altitude and less time climbing
and descending.
So don't worry that you don't have a POH with this information. Go figure
it out for yourself. You will be happy you did because you will KNOW that
the numbers are accurate.
--
Brian Lloyd, WB6RQN/J79BPL
3191 Western Dr.
Cameron Park, CA 95682
_brian@lloyd.com_ (mailto:brian@lloyd.com)
+1.767.617.1365 (Dominica)
+1.916.877.5067 (USA)
(http://www.matronics.com/Navigator?Yak-List)
(http://www.matronics.com/contribution)
Message 3
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| Subject: | Re: Yak 52 Questions |
Brian,
Why do you fill it to gross weight?
Bill
On Sep 13, 2011, at 8:02 AM, cjpilot710@aol.com wrote:
> I can only add one thing to Brain's post. Keeping an engine 'over square'
can help with the longevity of the engine. You want the engine to be drivi
ng the prop - not the prop driving the engine. This is known as "back loadi
ng" for which the bearings and such in the engine are not really design for.
This is particularly bad for bigger engines (W1820 & PW1830). The HS6a an
d M14p are somewhat "beef-e-er" for their size/hp so they are not quite as c
ritical for the occasional backloading. A few cycles in an 1830 and you'll b
e changing an engine way before that 1,000 hours mark.
>
> As Brain pointed out the IAS at stall is what it is. It is the instrument
you will be using for reference. It can read in any units of valve of what
ever you want to call them. And they are only good in your airplane. Ther
e are a great many errors from the real TAS at stall to that of ASI simply b
ecause of system design. You can even see this in a Cessna or Piper. Have y
ou ever seen an ASI with one (1) kt/mph increments? Also remember that a st
all is really defined by the critical angle of attack of that particular air
foil not a speed.
>
> Jim "Pappy" Goolsby
>
> In a message dated 9/13/2011 1:25:52 A.M. Eastern Daylight Time, brian@llo
yd.com writes:
>
>
> On Mon, Sep 12, 2011 at 6:21 PM, Grayson <grayson50@hotmail.com> wrote:
>
> Any input is appreciated,
>
> First, is there any consensus for V speeds on the Yak 52. I know there can
be a bit of confusion since they come in 3 flavors (mph, knots, km/h) but i
t seems like every site I visit has a different number. I've seen Vne from 2
26mph to about 275mph, and stall clean from about 60 mph up to 75 mph and di
rty from about 60 mph to 70 mph. The stall numbers are what I'm most interes
ted in. My 'POH' has clean at 69mph and dirty at 63mph (my indicator is mph)
I believe. But the my POH isn't even the original.
>
> Go out and find out for yourself. Here:
> Calibrate your airspeed indicator. I have a spreadsheet that uses three GP
S track and groundspeed pairs to calculate TAS and winds aloft. I then use p
ressure altitude and temperature to convert TAS to CAS. =46rom that you can b
uild your own airspeed indicator calibration card.
> Load the airplane to the gross weight you want to use.
> Go out and carefully fly a stall series. Use very slow deceleration so you
can carefully read the IAS when the break occurs.
> Now you know the real stall speed, not some number that someone else wrote
down that may or may not be correct.
>
> BTW, once you know the stall speed, you can properly calculate maneuvering
/cornering speed for your airplane. Take the square-root of the maximum load
factor, 7 G's in the case of the Yak-52 (2.65), and multiply it by the stal
l speed. The result is Va.
>
> Unfortunately, you have to get Vne from the designer.
>
>
> Also, I'm doing a long cross-country soon. Is there any problem with filli
ng the oil reservoir all the up to 16L so I don't have to add oil as often? I
know not to turn it upside down like this as a lot will come out.
> But you don't get a higher oil burn rate because you have the reservoir fi
lled do you?
>
> You can do that but you need to know how much drains back into the engine s
ump when the aircraft is sitting. Once you get going, the engine sump oil pu
mp will keep the sump scavenged and will raise the level of oil in the tank.
The best way to know what your maximum fill point is is to check the level c
old, fly a very short hop, and then immediately check the oil level on landi
ng.
>
>
> And..
> Any consensus on the best throttle and prop setting for max range? 60 unit
s throttle and 60% prop? Oversquare 65 throttle, 60% prop? Any limit to how m
uch is safe to oversquare by? And is the reason for oversquaring because a h
igher rpm results in higher fuel consumption more so than a high manifold se
tting?
>
> Generally speaking, running "over square" is not going to hurt an engine t
hat is not boosted (turbocharged or supercharged). But the M14P does have a s
upercharger. The boost used in the standard 360hp motor is not all that grea
t but there MAY be a maximum MAP for a lower RPM in the PF. You need to get t
hat info from the engine manufacturer.
>
> As for fuel consumption, lower RPMs result in lower frictional losses in t
he engine. So if you reduce RPM and increase MAP to get the same hp out of t
he engine, you will have lower frictional losses and thus slightly lower fue
l burn.
>
> If you want to get carried away (and I usually do) there is one more thing
to think about and that is the RPM, torque (proportional to MAP) and TAS fo
r maximum prop efficiency. Prop blades have twist because the velocity of th
e tips is greater than the velocity near the hub. So the angle of attack of t
he prop blades is changing from hub to tip. There is an optimal combination t
hat will result in the maximum conversion of hp into IAS.
>
> Frankly, I doubt anyone has done the flight testing to determine the most e
fficient operating point for the Yak-52. I did a lot of this kind of work wi
th the CJ6A and determined how to safely get 400+nm legs on the stock 42gal f
uel. (I made a couple of cross-country cross-countries in the CJ6A and wante
d to be able to save gas, save time, AND save gas stops. I routinely flew 45
0nm legs when I had a 10kt or greater tailwind and still landed with legal r
eserves.) You can do it in the Yak-52 but it will take flights at different a
ltitudes and power settings to determine what works best. If you are plannin
g a long cross country you can use the trip to try different altitudes and p
ower settings to determine the effect on fuel efficiency.
>
> But generally speaking, altitude is your friend when it comes to efficienc
y. If you need to reduce MAP, do it by climbing, not by pulling the throttle
back. Take an O2 bottle with you and see how the airplane works at 13,000-1
6,000 feet. I think you will be pleasantly surprised. Hopefully you have an a
ux tank so you can spend more time at altitude and less time climbing and de
scending.
>
> So don't worry that you don't have a POH with this information. Go figure i
t out for yourself. You will be happy you did because you will KNOW that the
numbers are accurate.
>
> --
> Brian Lloyd, WB6RQN/J79BPL
> 3191 Western Dr.
> Cameron Park, CA 95682
> brian@lloyd.com
> +1.767.617.1365 (Dominica)
> +1.916.877.5067 (USA)
>
>
>
> ="http://www.matronics.com/Navigator?Yak-List">http://www.matronics.com/
Navigator?Yak-List
> s.matronics.com/">http://forums.matronics.com
> p://www.matronics.com/contribution">http://www.matronics.com/contribution
>
>
>
==========================
=========
==========================
=========
==========================
=========
==========================
=========
>
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| Subject: | Re: Yak 52 Questions |
Grayson is this a new airplane for you?
Hopefully you have done some 1 hour X-crountry legs first to get an idea on where
oil consumption will be and how well the rest of the airplane works. The oil
returned to the tank gets to sit there for a minute and de-bubble some more
so I never felt good about overfilling.
With an unknown Yak I find an hour leg is a good place to start, then you can expand
from there. Typically the things that become problems are fuel tanks not
feeding right, air not working right and mag coil surging. These problems help
take your mind off the issue of adding oil at the next stop.
In the past I found that some RPM between 66 and 73 will feel smoothest depending
on the prop and balance. Put the throttle adjacent to the Prop lever and thats
usually a pretty decent setting.
Higher is better when seeking "Maximum efficiency" in a Yak 52.
Tom Johnson
Yak 50
Phoenix, AZ
www.airpowerinsurance.com
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=352135#352135
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Please excuse my ignorance but I have never been able to understand the concept
of over square . First, since over square is a relationship between two numbers
it would seem the specific units of measurements would have to be specified.
Our airplanes have a variety of different units so I do not see how the rule
can be valid. Secondly, it seems to me that the concept of engine pushing the
plane or plane pushing the engine is a function of attitude, speed, power setting,
and prop setting. I can understand that for some engines using the prop
to slow you down puts stress in areas that receive no direct oil and consequently
can produce problems. I just do not see the connection with under/over square.
I can be either under or over square and still have the engine pulling the
plane. Can anyone enlighten me? Also, I believe George Coy once told me that
back loading was not really a problem for a Yak 52. Is that not the case?
Steve Johnson
Yak-52 N9900X
0B5
413 522-1130 Cell
----- Original Message -----
From: cjpilot710@aol.com
Sent: Tuesday, September 13, 2011 8:02:58 AM
Subject: Re: Yak-List: Yak 52 Questions
I can only add one thing to Brain's post. Keeping an engine 'over square' can help
with the longevity of the engine. You want the engine to be driving the prop
- not the prop driving the engine. This is known as "back loading" for which
the bearings and such in the engine are not really design for. This is particularly
bad for bigger engines (W1820 & PW1830). The HS6a and M14p are somewhat
"beef-e-er" for their size/hp so they are not quite as critical for the occasional
backloading. A few cycles in an 1830 and you'll be changing an engine way
before that 1,000 hours mark.
As Brain pointed out the IAS at stall is what it is. It is the instrument you will
be using for reference. It can read in any units of valve of what ever you
want to call them. And they are only good in your airplane. There are a great
many errors from the real TAS at stall to that of ASI simply because of system
design. You can even see this in a Cessna or Piper. Have you ever seen an ASI
with one (1) kt/mph increments? Also remember that a stall is really defined
by the critical angle of attack of that particular airfoil not a speed.
Jim "Pappy" Goolsby
In a message dated 9/13/2011 1:25:52 A.M. Eastern Daylight Time, brian@lloyd.com
writes:
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| Subject: | Re: Yak 52 Questions |
On Tue, Sep 13, 2011 at 6:35 AM, Bill Geipel <czech6@mesanetworks.net>wrote:
> Brian,
>
> Why do you fill it to gross weight?
>
Well Bill, every airplane ALWAYS flys at gross weight. That is the
definition. But we change the gross weight depending on what we take with
us. (Or what we had for breakfast -- BURP. :-) Or were you asking about
maximum gross weight? Most manufacturers specify stall speed at max gross
weight for the airframe. But we rarely fly our airplanes at max gross
weight. So doesn't it make sense to find the stall speed at the weights we
normally use?
Stall speed varies with loading. As you increase the gross weight, static
loading increases, and so does stall speed. (You need a greater airspeed to
produce more lift at the critical angle of attack.)
So, when you want to find the stall speed under static load conditions, you
have to specify AND test at a particular gross weight. In fact, it might be
worthwhile to do the testing under typical conditions, e.g.:
1. me,
2. me and Fred,
3. me and Fred with our chutes,
4. me and Fred after a big lunch,
5. me and Fred after a big lunch, wearing chutes, carrying all the crap
we will need at Oshkosh.
I don't know about you guys but I find flight testing to be pretty fun. I
have also found that it is easy to do and quickly shows up the errors in the
POH. It also gives you a much greater feeling for the characteristics of
your particular airplane.
I had a student that decided to buy his own airplane not long after we
started his primary training. He wanted a Comanche 250 and I offered him
mine. He declined because I wanted too much money so he went out and found
one that was a "good deal". When we went out to fly it the first time the
speeds seemed wrong. I assumed that the pitot-static system was leaking but
I did what I usually do with a new airplane -- I built an airspeed
calibration table as I mentioned in my earlier post.
Turns out that the airspeed indicator was dead-nuts accurate. The airplane
was actually stalling at the wrong speed. This prompted me to suggest that
the plane go into the shop for a look-over.
Turns out that the airplane had been wrecked. (Now we know why he got such a
good deal.) Someone had put different wings on the plane and the wings had
broken ribs. So not only was the wing rigged wrong, it wasn't holding its
design airfoil shape under air loads. In the end it cost him WAY more to fix
his "good deal" than it would have to have purchased my plane in the first
place. (heh)
But the key is that some simple flight testing quickly showed up the
characteristics of that particular airplane. This is the kind of thing that
every pilot should do when he/she first contemplates acquiring an airplane.
Just because it goes up and comes back down again without killing you
doesn't necessarily mean it is a good deal. ;-)
--
Brian Lloyd, WB6RQN/J79BPL
3191 Western Dr.
Cameron Park, CA 95682
brian@lloyd.com
+1.767.617.1365 (Dominica)
+1.916.877.5067 (USA)
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On Tue, Sep 13, 2011 at 8:36 AM, <sajdds@comcast.net> wrote:
> Please excuse my ignorance but I have never been able to understand the
> concept of over square. First, since over square is a relationship between
> two numbers it would seem the specific units of measurements would have to
> be specified. Our airplanes have a variety of different units so I do not
> see how the rule can be valid.
>
Bingo. It isn't valid. But it is an old wive's-tale that doesn't seem to die
no matter how many stakes we drive through its heart.
> Secondly, it seems to me that the concept of engine pushing the plane or
> plane pushing the engine is a function of attitude, speed, power setting,
> and prop setting.
>
That is correct also. And it depends on engine design as well.
> I can understand that for some engines using the prop to slow you down puts
> stress in areas that receive no direct oil and consequently can produce
> problems. I just do not see the connection with under/over square.
>
There isn't one.
> I can be either under or over square and still have the engine pulling the
> plane. Can anyone enlighten me? Also, I believe George Coy once told me that
> back loading was not really a problem for a Yak 52. Is that not the case?
>
I believe you and George to be correct.
Here is the real scoop on "over square" operation.
An engine is designed for some maximum loading on the pistons, connecting
rods, and the crankshaft. These loads are relatively independent of RPM but
*ARE* a direct function of combustion pressures. And combustion pressure is
a function of manifold absolute pressure (MAP) because MAP tells you how
much fuel/air charge is going to enter each cylinder on each cycle. When you
light a fuel/air charge of a certain mass, you will get a fixed amount of
heat released and a certain amount of expansion into the volume of the
cylinder. That in turn produces a specific pressure on the top of the
piston, which in turn produces a specific force on the con rod and the
crank. OK? Good.
Now there are some variations that occur as a result of RPM because the fuel
burning process takes time. When the fuel/air charge in the cylinder is
ignited by the ignition, it begins to burn, release heat, and expanding. At
the same time the piston is coming to top-dead-center (minimum volume) and
then moving downward. As the crank moves through its rotating the
downward-moving piston increases the volume in the combustion chamber. The
farther the piston has moved when the fuel/air charge has completed
combustion, the larger the volume to hold the expanded gasses, the lower the
peak pressure on the top of the piston and, hence, the lower the force on
the con-rod and crank.
If you reduce RPM too far, the volume in the combustion chamber hasn't yet
increased enough and you get higher peak pressures in the cylinder. If you
run a high enough MAP (fuel/air charge entering the cylinder) and a low
enough RPM (piston not increasing the cylinder volume fast enough) you CAN
reach the critical pressures needed to cause piston, rod, and crank damage.
This is the real, dreaded, "over-square" condition. But generally this
requires really low RPMs and really high MAPs. You aren't going to achieve
this with a normally-aspirated engine but you can get there with an engine
that is running with a high level of boost.
The big radial engines used on older warbirds actually came from the
manufacturer with peak MAP numbers that could be used at a particular RPM.
As RPM was increased, you were allowed to run a higher MAP without damage to
the engine. In addition, those numbers also varied with the presence of
things that slowed down combustion, e.g. higher octane fuel, water
injection, alcohol injection, etc. Unfortunately this "knowledge" was held
over by people who didn't understand even after we got engines for which
this didn't apply. That is where this whole "don't run oversquare" stuff got
started.
(And before someone jumps on me, I understand about detonation margins. They
are also affected by the changing volume of the cylinder as the piston moves
downward during the power stroke. The discussion is the same.)
--
Brian Lloyd, WB6RQN/J79BPL
3191 Western Dr.
Cameron Park, CA 95682
brian@lloyd.com
+1.767.617.1365 (Dominica)
+1.916.877.5067 (USA)
Message 8
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Nice work Brian Lloyd!
Jj
Sent from my iPhone
On Sep 13, 2011, at 11:33 AM, Brian Lloyd <brian@lloyd.com> wrote:
>
>
> On Tue, Sep 13, 2011 at 8:36 AM, <sajdds@comcast.net> wrote:
> Please excuse my ignorance but I have never been able to understand the co
ncept of over square. First, since over square is a relationship between two
numbers it would seem the specific units of measurements would have to be s
pecified. Our airplanes have a variety of different units so I do not see ho
w the rule can be valid.
>
> Bingo. It isn't valid. But it is an old wive's-tale that doesn't seem to d
ie no matter how many stakes we drive through its heart.
>
> Secondly, it seems to me that the concept of engine pushing the plane or p
lane pushing the engine is a function of attitude, speed, power setting, and
prop setting.
>
> That is correct also. And it depends on engine design as well.
>
> I can understand that for some engines using the prop to slow you down put
s stress in areas that receive no direct oil and consequently can produce pr
oblems. I just do not see the connection with under/over square.
>
> There isn't one.
>
> I can be either under or over square and still have the engine pulling the
plane. Can anyone enlighten me? Also, I believe George Coy once told me tha
t back loading was not really a problem for a Yak 52. Is that not the case?
>
> I believe you and George to be correct.
>
> Here is the real scoop on "over square" operation.
>
> An engine is designed for some maximum loading on the pistons, connecting r
ods, and the crankshaft. These loads are relatively independent of RPM but A
RE a direct function of combustion pressures. And combustion pressure is a f
unction of manifold absolute pressure (MAP) because MAP tells you how much f
uel/air charge is going to enter each cylinder on each cycle. When you light
a fuel/air charge of a certain mass, you will get a fixed amount of heat re
leased and a certain amount of expansion into the volume of the cylinder. Th
at in turn produces a specific pressure on the top of the piston, which in t
urn produces a specific force on the con rod and the crank. OK? Good.
>
> Now there are some variations that occur as a result of RPM because the fu
el burning process takes time. When the fuel/air charge in the cylinder is i
gnited by the ignition, it begins to burn, release heat, and expanding. At t
he same time the piston is coming to top-dead-center (minimum volume) and th
en moving downward. As the crank moves through its rotating the downward-mov
ing piston increases the volume in the combustion chamber. The farther the p
iston has moved when the fuel/air charge has completed combustion, the large
r the volume to hold the expanded gasses, the lower the peak pressure on the
top of the piston and, hence, the lower the force on the con-rod and crank.
>
> If you reduce RPM too far, the volume in the combustion chamber hasn't yet
increased enough and you get higher peak pressures in the cylinder. If you r
un a high enough MAP (fuel/air charge entering the cylinder) and a low enoug
h RPM (piston not increasing the cylinder volume fast enough) you CAN reach t
he critical pressures needed to cause piston, rod, and crank damage. This is
the real, dreaded, "over-square" condition. But generally this requires rea
lly low RPMs and really high MAPs. You aren't going to achieve this with a n
ormally-aspirated engine but you can get there with an engine that is runnin
g with a high level of boost.
>
> The big radial engines used on older warbirds actually came from the manuf
acturer with peak MAP numbers that could be used at a particular RPM. As RPM
was increased, you were allowed to run a higher MAP without damage to the e
ngine. In addition, those numbers also varied with the presence of things th
at slowed down combustion, e.g. higher octane fuel, water injection, alcohol
injection, etc. Unfortunately this "knowledge" was held over by people who d
idn't understand even after we got engines for which this didn't apply. That
is where this whole "don't run oversquare" stuff got started.
>
> (And before someone jumps on me, I understand about detonation margins. Th
ey are also affected by the changing volume of the cylinder as the piston mo
ves downward during the power stroke. The discussion is the same.)
>
> --
> Brian Lloyd, WB6RQN/J79BPL
> 3191 Western Dr.
> Cameron Park, CA 95682
> brian@lloyd.com
> +1.767.617.1365 (Dominica)
> +1.916.877.5067 (USA)
>
>
>
==========================
=========
==========================
=========
==========================
=========
==========================
=========
>
Message 9
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| Subject: | Re: Yak 52 Questions |
Also worth testing stall speed with prop stopped and in the coarse prop cond
ition your plane returns to with mags off. With the MTV 9-29-260'cm prop on m
y SU26, stall speed with mags off ( zero oil pressure) gives me a stall spee
d about 15km an hour less than book value.
Rick VOLKER
Sent from my iPhone
On Sep 13, 2011, at 12:03 PM, Brian Lloyd <brian@lloyd.com> wrote:
>
>
> On Tue, Sep 13, 2011 at 6:35 AM, Bill Geipel <czech6@mesanetworks.net> wro
te:
> Brian,
>
> Why do you fill it to gross weight?
>
> Well Bill, every airplane ALWAYS flys at gross weight. That is the definit
ion. But we change the gross weight depending on what we take with us. (Or w
hat we had for breakfast -- BURP. :-) Or were you asking about maximum gross
weight? Most manufacturers specify stall speed at max gross weight for the a
irframe. But we rarely fly our airplanes at max gross weight. So doesn't it m
ake sense to find the stall speed at the weights we normally use?
>
> Stall speed varies with loading. As you increase the gross weight, static l
oading increases, and so does stall speed. (You need a greater airspeed to p
roduce more lift at the critical angle of attack.)
>
> So, when you want to find the stall speed under static load conditions, yo
u have to specify AND test at a particular gross weight. In fact, it might b
e worthwhile to do the testing under typical conditions, e.g.:
> me,
> me and Fred,
> me and Fred with our chutes,
> me and Fred after a big lunch,
> me and Fred after a big lunch, wearing chutes, carrying all the crap we wi
ll need at Oshkosh.
> I don't know about you guys but I find flight testing to be pretty fun. I h
ave also found that it is easy to do and quickly shows up the errors in the P
OH. It also gives you a much greater feeling for the characteristics of your
particular airplane.
>
> I had a student that decided to buy his own airplane not long after we sta
rted his primary training. He wanted a Comanche 250 and I offered him mine. H
e declined because I wanted too much money so he went out and found one that
was a "good deal". When we went out to fly it the first time the speeds see
med wrong. I assumed that the pitot-static system was leaking but I did what
I usually do with a new airplane -- I built an airspeed calibration table a
s I mentioned in my earlier post.
>
> Turns out that the airspeed indicator was dead-nuts accurate. The airplane
was actually stalling at the wrong speed. This prompted me to suggest that t
he plane go into the shop for a look-over.
>
> Turns out that the airplane had been wrecked. (Now we know why he got such
a good deal.) Someone had put different wings on the plane and the wings ha
d broken ribs. So not only was the wing rigged wrong, it wasn't holding its d
esign airfoil shape under air loads. In the end it cost him WAY more to fix h
is "good deal" than it would have to have purchased my plane in the first pl
ace. (heh)
>
> But the key is that some simple flight testing quickly showed up the chara
cteristics of that particular airplane. This is the kind of thing that every
pilot should do when he/she first contemplates acquiring an airplane. Just b
ecause it goes up and comes back down again without killing you doesn't nece
ssarily mean it is a good deal. ;-)
>
> --
> Brian Lloyd, WB6RQN/J79BPL
> 3191 Western Dr.
> Cameron Park, CA 95682
> brian@lloyd.com
> +1.767.617.1365 (Dominica)
> +1.916.877.5067 (USA)
>
>
>
==========================
=========
==========================
=========
==========================
=========
==========================
=========
>
Message 10
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Brian
Thanks for taking the time to give such complete explanation. The explanati
ons I have gotten in the past just never made sense to me.
Steve Johnson
Yak-52 N9900X
0B5
----- Original Message -----
From: "Brian Lloyd" <brian@lloyd.com>
Sent: Tuesday, September 13, 2011 11:33:20 AM
Subject: Re: Yak-List: Over square
On Tue, Sep 13, 2011 at 8:36 AM, < sajdds@comcast.net > wrote:
Please excuse my ignorance but I have never been able to understand the con
cept of over square . First, since over square is a relationship between tw
o numbers it would seem the specific units of measurements would have to be
specified. Our airplanes have a variety of different units so I do not see
how the rule can be valid.
Bingo. It isn't valid. But it is an old wive's-tale that doesn't seem to di
e no matter how many stakes we drive through its heart.
=C2-
Secondly, it seems to me that the concept of engine pushing the plane or pl
ane pushing the engine is a function of attitude, speed, power setting, and
prop setting.
That is correct also. And it depends on engine design as well.=C2-
=C2-
I can understand that for some engines using the prop to slow you down puts
stress in areas that receive no direct oil and consequently can produce pr
oblems.=C2- I just do not see the connection with under/over square.
There isn't one.
=C2-
I can be either under or over square and still have the engine pulling the
plane. Can anyone enlighten me? Also, I believe George Coy once told me tha
t back loading was not really a problem for a Yak 52. Is that not the case?
I believe you and George to be correct.=C2-
Here is the real scoop on "over square" operation.=C2-
An engine is designed for some maximum loading on the pistons, connecting r
ods, and the crankshaft. These loads are relatively independent of RPM but
ARE =C2-a direct function of combustion pressures. And combustion pressur
e is a function of manifold absolute pressure (MAP) because MAP tells you h
ow much fuel/air charge is going to enter each cylinder on each cycle. When
you light a fuel/air charge of a certain mass, you will get a fixed amount
of heat released and a certain amount of expansion into the volume of the
cylinder. That in turn produces a specific pressure on the top of the pisto
n, which in turn produces a specific force on the con rod and the crank. OK
? Good.=C2-
Now there are some variations that occur as a result of RPM because the fue
l burning process takes time. When the fuel/air charge in the cylinder is i
gnited by the ignition, it begins to burn, release heat, and expanding. At
the same time the piston is coming to top-dead-center (minimum volume) and
then moving downward. As the crank moves through its rotating the downward-
moving piston increases the volume in the combustion chamber. The farther t
he piston has moved when the fuel/air charge has completed combustion, the
larger the volume to hold the expanded gasses, the lower the peak pressure
on the top of the piston and, hence, the lower the force on the con-rod and
crank.
If you reduce RPM too far, the volume in the combustion chamber hasn't yet
increased enough and you get higher peak pressures in the cylinder. If you
run a high enough MAP (fuel/air charge entering the cylinder) and a low eno
ugh RPM (piston not increasing the cylinder volume fast enough) you CAN rea
ch the critical pressures needed to cause piston, rod, and crank damage. Th
is is the real, dreaded, "over-square" condition. But generally this requir
es really low RPMs and really high MAPs. You aren't going to achieve this w
ith a normally-aspirated engine but you can get there with an engine that i
s running with a high level of boost.=C2-
The big radial engines used on older warbirds actually came from the manufa
cturer with peak MAP numbers that could be used at a particular RPM. As RPM
was increased, you were allowed to run a higher MAP without damage to the
engine. In addition, those numbers also varied with the presence of things
that slowed down combustion, e.g. higher octane fuel, water injection, alco
hol injection, etc. Unfortunately this "knowledge" was held over by people
who didn't understand even after we got engines for which this didn't apply
. That is where this whole "don't run oversquare" stuff got started.
(And before someone jumps on me, I understand about detonation margins. The
y are also affected by the changing volume of the cylinder as the piston mo
ves downward during the power stroke. The discussion is the same.)
--
Brian Lloyd, WB6RQN/J79BPL
3191 Western Dr.
Cameron Park, CA 95682
brian@lloyd.com
+1.767.617.1365 (Dominica)
+1.916.877.5067 (USA)
========================
Message 11
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| Subject: | Re: Yak 52 Questions |
On Tue, Sep 13, 2011 at 10:29 AM, RICHARD VOLKER <rick@rvairshows.com>wrote:
> Also worth testing stall speed with prop stopped and in the coarse prop
> condition your plane returns to with mags off. With the MTV 9-29-260'cm prop
> on my SU26, stall speed with mags off ( zero oil pressure) gives me a stall
> speed about 15km an hour less than book value.
>
Now that surprises me. I wouldn't have thought that stall speed would be
much affected by the drag of a windmilling prop. Did you get the aircraft
into a steady-state descent and then very slowly increase AoA until it
stalled?
--
Brian Lloyd, WB6RQN/J79BPL
3191 Western Dr.
Cameron Park, CA 95682
brian@lloyd.com
+1.767.617.1365 (Dominica)
+1.916.877.5067 (USA)
Message 12
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| Subject: | Re: Yak 52 Questions |
The problem with the air show only prop that I use is that, even at 82%rpm, t
he blades are so flat that with manifold pressure at idle, it disturbs airfl
ow over the wing and tail. Losing oil pressure, It goes to your coarse stop a
nd changes the airflow over the inner third of the wing. Flip the mags off o
n short final at normal approach speed and you will float at least 500 feet w
ithout the prop to break you combined with lower stall speed. The flat prop
also shields the rudder on roll out enough to make it require the use of br
akes for directional control, unless the prop is pulled way back. Idle Glide
ratio at max rpm is 2.5 :1 which feels like someone threw out a drag chute d
uring the flare. This is useful for carrier approaches and short field landi
ngs.
I also leave at full power for all spin and tumble exits, given much Qui
cker and more benign recoveries. I would not suggest this practice with a ya
k 52 .
Rick VOLKER
Sent from my iPhone
On Sep 13, 2011, at 4:11 PM, Brian Lloyd <brian@lloyd.com> wrote:
>
>
> On Tue, Sep 13, 2011 at 10:29 AM, RICHARD VOLKER <rick@rvairshows.com> wro
te:
> Also worth testing stall speed with prop stopped and in the coarse prop co
ndition your plane returns to with mags off. With the MTV 9-29-260'cm prop o
n my SU26, stall speed with mags off ( zero oil pressure) gives me a stall s
peed about 15km an hour less than book value.
>
> Now that surprises me. I wouldn't have thought that stall speed would be m
uch affected by the drag of a windmilling prop. Did you get the aircraft int
o a steady-state descent and then very slowly increase AoA until it stalled?
>
> --
> Brian Lloyd, WB6RQN/J79BPL
> 3191 Western Dr.
> Cameron Park, CA 95682
> brian@lloyd.com
> +1.767.617.1365 (Dominica)
> +1.916.877.5067 (USA)
>
>
>
==========================
=========
==========================
=========
==========================
=========
==========================
=========
>
Message 13
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On Tue, Sep 13, 2011 at 1:09 PM, <sajdds@comcast.net> wrote:
> Brian
>
>
> Thanks for taking the time to give such complete explanation. The
> explanations I have gotten in the past just never made sense to me.
>
You are welcome Steve. This is why it is important to understand the physics
of flight. Once you really understand how the things are working, you can
make a much better guess at what is going to happen when you do something
different. And sometimes you just have to get in the plane and go try it.
(Engine excluded.)
The problem with engines is finding someone who truly has a clue. I have
found that, 99% of the people who think they have a clue about engines,
really don't. It can be very difficult to get good information. I have had
good luck with persistent calling to Lycoming, Continental, and the overhaul
shops who specialize in mods. On the M14P and Huosai ... not so much. :-)
What you WILL find is people who will fight to the death about their
opinions but then, it is just religion, not science.
So, we have to go back to the basic physics and make the best guesses we
can.
--
Brian Lloyd, WB6RQN/J79BPL
3191 Western Dr.
Cameron Park, CA 95682
brian@lloyd.com
+1.767.617.1365 (Dominica)
+1.916.877.5067 (USA)
Message 14
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| Subject: | Re: Yak 52 Questions |
Grayson,
Adding to what Tom said, if you have the stock fuel system, you should definitely
not go beyond a 1.5 hour maximum leg until you have flown enough to determine
how much fuel is left after this.
Another thing to consider is that its important to have a good understanding of
how the pneumatic design works on these airplanes. In a long cross country flight,
you might want to carry an extra bottle of compressed air and the appropriate
fittings to recharge the airplane's bottle.... Otherwise if you manage to
lose air, you won't be able to start the engine and you dont want to put yourself
in the position of not being able to find anyone able to help at an airport
along your route. You might want to bring along your own metric tools as well
for that same reason.
Carl
tjyak50 wrote:
> Grayson is this a new airplane for you?
>
> Hopefully you have done some 1 hour X-crountry legs first to get an idea on where
oil consumption will be and how well the rest of the airplane works. The
oil returned to the tank gets to sit there for a minute and de-bubble some more
so I never felt good about overfilling.
>
> With an unknown Yak I find an hour leg is a good place to start, then you can
expand from there. Typically the things that become problems are fuel tanks
not feeding right, air not working right and mag coil surging. These problems
help take your mind off the issue of adding oil at the next stop.
>
> In the past I found that some RPM between 66 and 73 will feel smoothest depending
on the prop and balance. Put the throttle adjacent to the Prop lever and
thats usually a pretty decent setting.
>
> Higher is better when seeking "Maximum efficiency" in a Yak 52.
>
> Tom Johnson
> Yak 50
> Phoenix, AZ
> www.airpowerinsurance.com
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=352222#352222
Message 15
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So we shouldn't ask you about MMO then, Sparky ? 8-)
David Stroud
Ottawa, Canada
Christavia C-FDWS
Fairchild 51 replica
under construction C-FYXV and survior of Sparky's Waterfront Bar, St.
Thomas, USVI
----- Original Message -----
From: Brian Lloyd
To: yak-list@matronics.com
Sent: Tuesday, September 13, 2011 9:15 PM
Subject: Re: Yak-List: Over square
On Tue, Sep 13, 2011 at 1:09 PM, <sajdds@comcast.net> wrote:
Brian
Thanks for taking the time to give such complete explanation. The
explanations I have gotten in the past just never made sense to me.
so much. :-) What you WILL find is people who will fight to the death
about their opinions but then, it is just religion, not science.
So, we have to go back to the basic physics and make the best guesses
we can.
--
Brian Lloyd, WB6RQN/J79BPL
3191 Western Dr.
Cameron Park, CA 95682
brian@lloyd.com
+1.767.617.1365 (Dominica)
+1.916.877.5067 (USA)
-------------------------------------------------------------------------
-----
Checked by AVG - www.avg.com
09/12/11 18:35:00
Message 16
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On Tue, Sep 13, 2011 at 8:53 PM, DAVID STROUD <dstroud@xplornet.com> wrote:
> **
> So we shouldn't ask you about MMO then, Sparky ? 8-)
>
Sure, ask me about anything. You'll either get a good answer or, "I don't
know." :-)
Personally, I use it in my oil but I don't use it in my fuel.
--
Brian Lloyd, WB6RQN/J79BPL
3191 Western Dr.
Cameron Park, CA 95682
brian@lloyd.com
+1.767.617.1365 (Dominica)
+1.916.877.5067 (USA)
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