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Wing Incidence experts, need your help,,,

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Old 03-30-2014, 02:58 PM
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raron455
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Default Wing Incidence experts, need your help,,,

I am still learning, and want to seek some advice,,
I have a great planes pitts that I am flying, this is my 3rd one and it flies terrible compared to the others. So I figure it is a thrust alignment issue or wing incidence. I decided to check the wing incidences.
First I set the plane on the level ground, then propped the plane up on a box until it looked like it was perfectly level. I then put my incidence meter on it and got the numbers,,
I do not know much about wing incidence and do not know what the numbers are supposed to be, these numbers may be fine, or may be terrible, that is why I am asking for help. And any help advice would be greatly appreciated, thanks fellas

Top Wing +3 degrees
Bottom Wing +1 degrees
Horizontal Stab +2 degrees I used some clamps and wood to hold the elevator flush with the stab while I took the reading

took a couple of pics to show how I was doing it,,
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Old 03-30-2014, 05:27 PM
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dbacque
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Could you describe "flies terrible"? What is the problem?

I have no experience with this particular model but a degree or so of incidence increase of the top wing over the bottom wing is pretty standard stuff with conventional wing stagger. Top wing stalls first, bottom wing still lifting now is nose heavy, nose drops and prevents unwanted snap.

When you checked the incidence, did you also test for wing twist? Check that the incidence at each wing tip matches the incidence of that wing at the root.

Dave
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Old 03-30-2014, 07:03 PM
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raron455

Things you wll need a good small level, 4ft. stright edge, your incidence meter, sand or heavy bean bags to hold the bird in position, a good square.

Frist I am not an expert, But I will tell you how I would set it up.
1. Detrmine the horizontal thrust line fwd and aft, down one side of the bird, with that established, Level the fuse to that line. ( tape the small level to the fuse) so that you know you dont move it.
Now check the horizantal stab to see if it that is in line with the thrust line (clamp a flat stick across the stab and elevators) check the stab with your incidence meter, with luck you should have 1 to 1 1/2 deg positive inicdence.
2. now check the lower wing, at best it should be 0 incidence,
do what ever you have to do the make these 2 items so.
3. with the upper wing installed check the Incidence it should be 2 deg's negitive (this lets the upper wing stall after the lower wing)
Again do what ever you have to make this so.

Now establish a line donw the center looking down on the fuse. check the fire wall for square, with luck it will have 1 to 2 deg's right thrust a protracter helps hear. Now with the bird still in a level position check the fire wall for down thrust with luck it will have 1 or 2 deg's down,

4. With the engine installed shim under the mount's or stand off's to get 1 or no more than 2 deg's right and down thrust.
Once you have this check your balance, for a maiden be a little nose heavy dry 2 deg's max

This set up will get you flying, and with no bad habbits in landings, you will most likely have to adjust the nose heavyness for your stile of flying

I know this sound like a lot of B/S but once you have done it you will find it easy and a good place to start.

Cheers and good luck

As you are flying pitts you should know that 3 piont landings are nearly imposable, so go for wheel landings

Last edited by rt3232; 03-30-2014 at 07:05 PM.
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Old 03-30-2014, 07:10 PM
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PS this is how I set up my pipes weeks special's
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Old 03-31-2014, 06:46 AM
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I've done many tests on many bipes and ALL model bipes I tested flew best with the upper wing at about 1 to 2 degrees LESS angle of attack than the lower wing. This was on 6 Aeromasters (60 size), one super Aeromaster, two 1/4 scale Moths, 2 large Lazy Aces, 2 Phaeton 90's and two Phaeton 40's. Play with lowering the incidence on your upper wing, there will be a point where the plane starts to grove and do what you tell it to do.
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Old 03-31-2014, 07:01 AM
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one third scale GP pitts?? (I LOVED that bipe!)

Correct incidence for the G/P Pitts and Christen Eagle as follows;

Top Wing: negative 1/2 to 1-1/2 degrees
Bottom Wing: Zero
Horizontal Stab: Zero
Engine: Zero up and down, right per manufacture installed firewall.

at minimum, zero incidence everywhere EXCEPT the top wing

I'll bet it'll be more fun to fly this way
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Old 03-31-2014, 08:08 AM
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AMA 74894

good numbers, The numbert I quoted are what I have used on both of my 1/3 weeks built from kits, and what my flying buddy havs used on his 3, 1/3 pitts ARF all came from the box different I don't know if they were GP

So the OP should have enough info to get a good flying bird

Cheers Bob T
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Old 03-31-2014, 01:52 PM
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Thanks for all the info Fellas,, I will get started on making sure these lines are true, and getting the incidence where it is supposed to be. I really do appreciate all the help, I had no Idea what they were supposed to be.
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Old 04-05-2014, 04:32 PM
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The incidence Jim is giving you are pretty much what I use on all the bipes I have built. Only one I had a problem with was an Aeromaster 60 I built. It would balloon up every time I shut down the power. My bad, I had added in engine down thrust without noticing. It can be something that simple that can bite you.
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Old 04-06-2014, 03:50 AM
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Rodney
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Originally Posted by Gray Beard View Post
The incidence Jim is giving you are pretty much what I use on all the bipes I have built. Only one I had a problem with was an Aeromaster 60 I built. It would balloon up every time I shut down the power. My bad, I had added in engine down thrust without noticing. It can be something that simple that can bite you.
All of my Aeromasteres (7 of them) required about 1.5 degrees of down thrust to fly nicely.
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