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Improving PA-11 takeoff perf

S2D

S2D

MEMBER
Montana
Got a PA-11 thats a dog. Anybody know the best prop combination for an 85 HP PA-11? I've got an 85 HP Chief that will beat it off the ground bya bunch. Friend has a PA-11 with an 0-200 that is a dog also, (although his could be a weak engine). Thought of trying a 74 inch flatter prop, but don't want to spend a bunch of money to find out it doesn't work any better.
We are considering these dogs because we are comparing them to his old 85 hp j3 that was a rocket and my Chief that shouldn't come close to a cub.
Admittedly both have two tanks that add weight and 25" tires, but other than that they are stock.
 
Don't know if I should repeat second hand info (theorys) about this subject but what the heck.
I was told by an individual (old timer) who used to really be into the short field thing here in Alaska who had operated both J-3s and PA-11s from his cabin which had a 450 ft strip. He said that the PA-11 was a dog right from the start. He said he noticed a difference between the two airplanes when they were sitting side by side and looking at the propeller angles in relation to the centerline of the airplane.
He claimed that the PA-11 has a different engine mount which caused the engine centerline to angle "downhill" as compared to the J-3. He experimented by installing spacers behind the lower engine mount cones which raised the nose of the engine to the same as the J-3 . He claimed that it improved the takeoff performance. He suspected the change was made to try and gain some speed with the PA-11
This may be totally BS but always thought that it was interesting. Like to hear if theres any truth to it.
 
Was always told by my old boss that a 90 hp pa-11 was the best performing cub ever made. Haven't seen that yet. Mines an 85 that I'm gonna convert back to 90 when this engine is runout, but still haven't seen anything perform with the 85 cub we used to have here.

I'll try the washer trick sometime and see if there is any difference.
 
I have an '11 with the C-90 and it's a great performer. After flying all the cubs mine still is off the ground as quick as any of them. Mind you it doesn't have electrics and it has clipped wings. Don't know if that makes a diff.
 
The J3 engine is mounted higher than a PA11. That is one of the biggest differences between the two models.
 
11 Perf

The 11 is a far better performer with the C-90-8. It is, in my opinion, the best flying of the Cubs. It's light, yet it has some oomph with the 90. You will notice a considerable difference between the 85 and the 90. My 11 is in for a recover and I'm going to put micro VGs on and have upgraded to the 90. That will add an additional margin of safety and from what I've observed on other Cubs it will increase the takeoff and landing performance. Keep them light--the other 11 on our field just pops off the ground and climbs like a homesick angel. 11's are great. :lol:
 
Hello, I owned at 90hp, J3 for several years with a sensnitch prop 74-40 pitch, it out performed everything at sea level, it was stock, no electric, supercub tail, 735lbs....very sweet excellent performing plane, my only complaint was, it wouldn't go over 75mph. Good luck! :D
 
T.J. Hinkle said:
S2D:
My 11 has a M76AK-2 prop on a 90 engine. .
Click to expand...

I've been wanting to try one of those on mine but best I can tell it is legal on about everything but an 85 hp PA-11. Its legal on the 85 and 90 j3 and the 90 pa-11. haven't figured that one out yet, unless I'm missing something. Might get one anyway so when I convert it back to 90 hp I'll have the right prop.
 
I've always liked the little McCauley on a 90, (I forget the exact model #). It seems to have more initial thrust on the takeoff roll. I always thought it may be because the McCauley has higher pitch, and/or longer cord on the inboard blade sections, (It won't lay flat on the bench because the inboard blade trailing edges are behind the hub). A flat pitched 76AK Sensenich, which is actually only 74", will spin up, but just doesn't seem to have the inital "oomph" that the McCauley has. This is based only on "feel" and "opinion", so take it as such.

There was a long prop that was used on Cessna 150 seaplanes that works well on Cubs.
 
The McCauley 1B90CM7443 is a good prop to try. This model is approved on the engine but, not on the airframe. You are limited to 72" diameter.
You may want to try and get a field approval for the 74" McCauley.

Matt
 
PA-11 Performance

Hi,
I think the seaplane prop that is being refered to is the ;
I A 90 CF 7535, but it is for the 0-200.
Dave.
 
PA12driver said:
Ask Jerry Burr? I don't think the White Hawk would fit the bill as a "Dog"??

Tim
Click to expand...

Nor is Jerry's an 85 hp or even close to stock. I'm just trying to get this one to perform close to what a "slightly" modified PA-11 should.

Wayne did notice that one rear spar is bent slightly but main problem might be the pitch "71 x 48"
 
Re: PA-11 Performance

D. Davis said:
Hi,
I think the seaplane prop that is being refered to is the ;
I A 90 CF 7535, but it is for the 0-200.
Dave.
Click to expand...



I A 90 CF 7535, That sounds like the right number to get it off the ground.
 
mark, your bringing up something interesting, the a model mccauleys have a rounded tip were as the B model has a clipped tip, ive always been told to use a clipped tip, but have had no etched in stone reason, what are the pros and cons of clipped or rounded tip props
 
I did a quick search of the STC database, and here's the best option I could find:

STC: SA65EASA65EA
Description: One Aerojet-General 15NS-250 aircraft rocket engine on underside of fuselage on airplane centerline

Looks like a winner. If you go this route please be sure to post pictures. :D :D
 
I did a quick search of the STC database, and here's the best option I could find:

STC: SA65EASA65EA
Description: One Aerojet-General 15NS-250 aircraft rocket engine on underside of fuselage on airplane centerline

Looks like a winner. If you go this route please be sure to post pictures. :D :D
 
PA-11 Performance

Hi tempdoug,
Since I brought up the "A" prop and you have some knowlege
of the "B" prop I will expand a little. I use both on my 0-200;
the "A" for a take-off prop, "Boar",and,the "B" for a standard
prop. If you look at the spec.'s you will see a big difference besides
the tips, weight for one, length for the other. For the application
on the typed engine I don't think Mc. could do much else.
Now I could be wrong.
Dave.
 
Dave:
Thought I read in Univairs catalogue that the only difference was the square verses rounded tips. Length on both is normally 71" . I have the square on my PA-11 and the rounded on my Chief.


PA12_ pilot if I could figure out how to post a picture here, I'd show you a picture of what happens when you put a rocket on a cub!!
 
PA-11 Performance

Hi S2D,
The I A 90 CF7535 is 75" a bit longer than 71". Again this is for my
0-200, the standard prop is 69".
Dave.
 
Dave
I think we are comparing apples and oranges.
A 1A90CF7144 would be the same as a 1B90CM7144 except tip shape I believe. Both were made in various lengths and pitch. Specs show weight of both as 21 lbs at maximum length.
Your 1A90CF7535 would definitely be better than either a 1A90CF71xx or a 1B90CM71XX for takeoff, but I don't think it has anything to do with the A or B.
According to the specs from a vibration standpoint, the 85 should only have a 71 inch propeller and the 90 should only have a 73 inch propeller.
 
S2D according to Piper TCDS on the PA-11 the C-90 with the McCauley prop the limit is not over 71" or under 69.5". (See item 311(D)(5). The C-85 with the McCauley prop the length limit is not over 72" and not under 70" ( Item 311(D)(4). The 73" limit is on the Koppers propeller. More than likely the limit on length isn't due to vibration, but due to ground clearance. The 1A90-1B90 series of propellers are approved out to 78" on the C-90 according to the prop TCDS. ( I know they might have done specific vibration analysis on the PA-11 and that is the reason for the length limit but I doubt it.) I would think you could present a good argument for a FA on the 74" prop on the 85 or 90, seeing as how it is approved on the engine, as long as you have the ground clearance.

Matt
 
Matt:
I kinda agree with part of what you say but I was refering to the Prop TC vibration analysis. Obviously Piper must have done their own because all their props are 1" longer than what the prop TC lists.
 
S2D sorry about that I was just looking at the prop application chart on McCauley's TCDS and didn't read the all of the notes. Now that I see what your saying in your previous post. I still think Piper cut them down for ground clearance. You would have a hard time convincing me that the harmonics are all that different between a C-85,C-90 or O-200 when mounted to a cub airframe. At least that is the argument that I would pose for the basis for a FA.


Matt
 
Legal installation issues (which are interesting) aside, I guess I always thought the square "clip" tip would be better because of more surface area. But who knows? There is a lot more aerodynamic voodoo happening to a spinning airfoil that is moving forward through the air at various speeds than this big dumb farm boy can ever hope to comprehend.

How about "Q" tips? I've never seen those used on a Cub, (exept those unfortunate "ground altered" props).

I looked at a McCauley Clip Tip on a J3 yesterday, stamped on the hub it said something like "Limited to 85hp and 2600 rpm".
 
My response to most guys that fly cubs that want to improve takeoff performance. Lose some weight fat azz. That is the best thing you can do for your own health and your aircraft's takeoff performance.

Torch
 
PA12_Pilot said:
I did a quick search of the STC database, and here's the best option I could find:

STC: SA65EASA65EA
Description: One Aerojet-General 15NS-250 aircraft rocket engine on underside of fuselage on airplane centerline

Looks like a winner. If you go this route please be sure to post pictures. :D :D
Click to expand...

OK PA-12_Pilot--- I got my Rocket installed!!! Sure wish you'd of said something about putting air brakes on this thing!!
http://www.supercub.org/upload/jetassist.jpg
 
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