Tattoo

I've been flying for 26 years...and for the first 21 I simply built my planes and flew them, and if there were pitch trim problems...usually ballooning at hight power settings...it was very common and general knowledge to add down thrust to the engine. I never really paid much attention to the aileron neutral setting...I simply rigged them to look right as they followed the contour of the top slope of the wing. Then one day about 5 years ago I wanted to fly bad...and my plane was almost completed...but I only had two pushrods left from a previous plane...and they were just sliiiiiiightly too short for the ailerons. I installed them anyways...and my ailerons had about 3 degrees of reflex in them. Being impatient, I went and flew anyways. The model I was flying was my third of the same design, so I knew it charicteristics very well. When it flew I was shocked. It was on rails like no other plane before it. Rolls were dead on axial. Not a touch of elevator trim was needed for inverted straight and level...there were no trim changes needed for different power settings. This floored me, and the lightbulb came on about aileron neutral setting. All these years I've hassled with engine thrust to get pitch trim just right...and it was just a couple aileron clevis turns away all along. What I also couldn't is believe is how long I had been flying, and never heard this addressed before. I've seen people go to incredable lengths from adding shims, to ripping out firewalls, to changing wing and tail incedence...in an attempt to get a greaser on rails flying airplane...when it could have been as simple as moving the aileron neutral postition. Well, I've been testing this theory for 5 years now on my own planes, and helping guys at the field trim theirs. I now contend that if an airplane is built correctly, and the CG is in the right location, pitch trim problems are 100% the fault of miss-rigged ailerons at neutral. Almost evey time someone has an airplane that begins to climb at higher power settings, or needs excessive down trim to fly level inverted...or does a barrell looking roll instead of an axial roll...it's due to drooping ailerons, either visually obvious or they may look right but are stil too low aerodynamically. Rigged beautifully to follow the countour of the top slope of the wing...but not the bottom...and it only takes a little bit to throw the trim off. If you think about it, the wings incidence is the line drawn from the LE to the trailing edge. The ailerons are the trailing edge. If their neutral rig is a degree off...so is your incidence. The reason I'm bringing this up, is because it's come up twice here in the last week. I've had countless times at the field where I've heard someone recommend down thrust to someone, and I'll ask if I can try something first...bring the ailerons up a degree or so...and walla...a completely different flying airplane. I have also seen where ailerons "look" perfectly rigged with no droop at all...but exibit all the same symptoms. I can only contend that aerodynamically they are still to low, as a degree or two of reflex in many cases have solved any pitch trim problems. I might also add that for 5 years now I've built all my planes with a straight away engine thrust line...and have not added down thrust to an engine since. Any thoughts?

G19Man

Tattoo,

Great suggestions. My plane climbs when the power is added quite a bit.

So, to try to your fix, how do you best determine which way to turn the clevis? Put a straight edge on the wing (leading edge to trailing)?

I guessing I'd want to move my nuetral position up so that the ailerons trailing edges raise up. Sound right?

Again.. thanks for the great tip.. can't wait to give it a try.

Kevin

da_man

My Feedback: (30)

If my bipe rises then I guess the aieleron goes this way in the pic.

Now nothing makes sense to me anymore. You would be adding "up elevator" in a sense to make the plane go in the down direction.

I don't mean to say your wrong, Its just I don't understand it.

G19Man

Da Man,

I see your point and it makes sense. I am thinking of it backwards I guess. Thank's for the correction.

Kevin

im_a_rcav8r

I'm not an aerodynamics major, but that makes sense to me! By changing the position of the aileron, you are in effect changing the camber of the wing itself. The same effect a flap has on an airfoil. Bring the aileron up high enough and I suppose you would get the opposite effect as your aerodynamic incidents would be negative.

Tattoo

Yes, this would be correct.

On a conventionally configured airplane, the direction the ailerons or flaps deflects...has exactly the opposite reaction on the aircraft's direction as the elevator's deflection direction and how it moves the aircraft.

Simply look at what direction your ailerons go, and what direction it makes your airplane roll. Left down/right up= right roll...in other words the left aileron going down caused the left wing to rise...the opposite happened on the right side...up aileron caused the right wing to go down.

Now... think about what happens to the whole wing when you move both ailerons in the same direction? Both down (as in drooping) and the wing (whole airplane) goes up.

This is why I contend that pitch trim problems can be solved by aileron neutral position. I've been able to turn some real dogs into real sweet flyers at the field. So far it's worked 100% of the time and can even compensate for miss-built aircraft.

This has actually been the biggest "I can't believe I didn't realize this before" break through in all my R/C flying, and the simplicity of a few clevis turns solving what some field "experts" thought was all kinds of incidence, GC and/or thrust problems is great. I know very little about aerodynamic formulas, and have zero formal education on it...so all I have to go by is trial and error and LOTS of field experience. I've seen this turn crappy flying, miss built, and some downright unflyable airplanes into dream fliers. That's why I posted here, to hopefully get some comments from guys who do know all the formulas and maybe even have some formal education on it...as well as give someone who my read this, a simple fix at the field before they go adding shims to engines or rebuilding an airplane that really doesn't have anything wrong with it...or even worse, miss-diagnose the problem and change something like CG/thrust/incidence only to make things worse and see the plane splattered (I've seen this happen too many times to count).

G19Man

Thanks Tattoo.. I guess my thinking was right afterall. Thanks for the clarification.

Tonight, I turned in my clevises 1 full turn which brought my ailerons trailing edges up. I didn't get an opportunity to give it a try, but I'll post back to let you know on the next flight.

Kevin

bentgear

Tattoo,
I always thought thats what the flap knob on my 8103 was for. Raising or lowering the ailerons to find the best flight position. I lower the default 30% setting down to about 10% so it can't move them very far.
Let me add a word of caution, if you set it for something like 50 % or more, DO NOT reach up and rotate it to the extreme during high speed flight. You may be in for a very wild ride.
Ed M.

Tattoo

Thanks Bentgear!

This is my point exactly. If you were at the field, and someone needed help with a pitch trim problem, especially if he has a single aileron servo, or non computer radio, what would do? I make sure the CG is correct, and there is no obvious building errors, and then concentrate on aileron neutral position. It's proven successful 100% of the time on aircraft that are built and balanced to plans.

KadetBuilder

Hmmm maybe that is the problem with my irvine tutor 40...now that u mention it, my ailerons are a lil bit droopy....I have the plane balanced as per instructions, and it flies horribly....specially in aileron turns it just doesn't seem to want to go where i point it....I will check it out tomorrow...

rogwabbit

just an fyi to you all... this is also essentially putting a diferential in your ailerons... which helps many planes turn better as well.. not only are you correcting thrust or incedence problems you are also helping the plane turn better a little bit so in does make a huge diferance on some modles.

Flintlock28

I'm going to try this out on my trainer. I think I remember reading about Russian engineers and aviators doing this on full size aircraft for the same reasons, besides I think that this does slightly increase top speed, at the expense of slightly less lift.