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aileron stick force

fredbauerjr

Well Known Member
We are looking for someone who would have aerodynamic knowledge of the fit between ailerons and the wing.

Our aircraft has fairly stiff ailerons and we are wondering if this is because we have very tight clearances, (we added some pieces to fill the gap better) between the top wing skin to the top of the aileron and between the bottom wing skin to the bottom of the aileron.

We thought that if we closed the aileron to wing gap as tight as possible we would be getting a better handling aircraft.

We notice that the Germans in WWII, (and Chris Heinz) design the ailerons to have a large gap between the wing and the aileron and we are wondering if this makes the ailerons "fly" better and with less stiffness.

Allowing airflow up from the bottom of the wing, over the aileron leading edge to the top of the wing might make the aileron less stiff??

What do you think??:confused:

It may be that we have a 160 HP engine in the aircraft and our cruise speed is higher than the aircraft was designed for?
 
Hi Fred,

I first want to thank you for the pictures on your web site! Since we are currently building a -3B, and there are only about five web sites with construction pics, every one is a gem.

I don't know if I have an answer for you, but I do have a couple of thoughts. First, are you saying that the ailerons are heavy in flight? if you move them on the ground, do they feel normal? In that case, you may be seeing something that i have been collecting information on with the various models - any convexity in the ailerons tend to make the feel of the airplane heavier in roll. So far, i have observed and correlated this on several different RV's. The effect is VERY subtle - a very minor bowing of the aileron can have considerable effect. to check, run a straight edge down th upper and lower surface, and see if it ends up perfectly tangent to the "final" trailing edge radius. Please report back!

On "gap fillers", I must say that I am extremely cautious about such things. Control surface leading edge design is a fairly involved science, and what works on one design is not always transferable to another. Gap fillers are very effective in lowering drag when applied where appropriate - and they can have very adverse effects on handling if applied where they were not designed to be. In short, you can't just slap them on any design and see improvements. Although trained as an aeronautical engineer, I would not attempt to add them to a design without significant input from the original designer. Could they explain what you are describing? Quite possibly, but I can't say for sure.

Hope you get some more input.

Paul
 
Its because you attempted to fair the top and bottom skins flush to the ailerons. The ailerons are Frise (sp?) type and require airflow over them for proper fucnction. Another RV4 builder tried that with the same exact results.
 
We thought that if we closed the aileron to wing gap as tight as possible we would be getting a better handling aircraft.

We notice that the Germans in WWII, (and Chris Heinz) design the ailerons to have a large gap between the wing and the aileron and we are wondering if this makes the ailerons "fly" better and with less stiffness.

The Friese ailerons use a gap to help keep the boundary layer excited, which helps keep the flow of air attached to the aileron. Closing the gap will make the ailerons heavier. On the 3B wing it uses a 1:1 ratio on the wing bellcrank. This can be changed by shortening and rewelding the arm connecting the pushrod to the aileron. Friend of mine did this on his RV-3B to improve handling.
 
Hi Fred (et al)

One would assume that by "filling the gap" you are trying to "smooth" the airflow over the ailerons / prevent turbulence cause around / through the "gap".

As Paul says, this is a complex area, and given the RV-3 design is maintained all the way through to the RV-8 (and probably beyond), I would consider it "optimal". When Van's wants a tight seal, he gets it (flap upper surface). So my instinct would be to follow the design as closely as possible.

In practical / testing terms, a wind tunnel is probably not an option. But when we fly the RV-8 through a rain shower, it still amazes how at 150K+, the rain drops remain undisturbed around the aileron leading edge i.e. there appears very little flow through that gap - which again would indicate to me it is a complex / pretty good design and I would not try to second guess it.

As per Paul again - thanks for the website and advice eMails, a precious resource ;)

Andy
 
Build them to plans!

Friese ailerons must have the gap as shown in the plans. The gap allows for flow around the leading edge of the aileron which aerodynamically balances the aileron to reduce stick force. The main design goal at the time (1930's) was reduce hinge moment and counteract adverse yaw, which was contributing to stall/spin accidents in their day.

The gap geometry on the Friese aileron is critical to proper operation. Take a close look at your plans, and build in the gap geometry exactly as depicted. Note the gap isn't a constant dimension from bottom to top surface. Be sure to get the left/right gap geometry exactly the same: asymmetric ailerons will produce asymmetric hinge moment, which will show up as an out of trim condition.
 
light aileron

Mine has a 160hp also, and the stick forces are very light. My opinion, remove the gap seals, Friese ailerons were designed to work that way.
BTW, could we be related?
 
:)

Thanks to all for your input. We will be removing our aileron to wing gap fillers very soon and will post our results. We have about 200 hours on the -3B and should be able to get a good read on the difference.

Ironflight.
Our ailerons are flat and true, no bow to them, also ---
our aileron linkage is smooth and friction free.

BOY!
I can REALLY overcook, (over think) a project with very little effort.:eek:
 
Mine has a 160hp also, and the stick forces are very light. My opinion, remove the gap seals, Friese ailerons were designed to work that way.
BTW, could we be related?

Mike,
I don't think so, our entire family line is from Minnesota.
Fred
 
Friese ailerons must have the gap as shown in the plans. The gap allows for flow around the leading edge of the aileron which aerodynamically balances the aileron to reduce stick force. The main design goal at the time (1930's) was reduce hinge moment and counteract adverse yaw, which was contributing to stall/spin accidents in their day.

The gap geometry on the Friese aileron is critical to proper operation. Take a close look at your plans, and build in the gap geometry exactly as depicted. Note the gap isn't a constant dimension from bottom to top surface. Be sure to get the left/right gap geometry exactly the same: asymmetric ailerons will produce asymmetric hinge moment, which will show up as an out of trim condition.

Bill,
We will be correcting this soon, see reply to Ironflight.
Fred
 
This is a unique opportunity for a before and after Fred - can't wait to hear a report on the difference without the gap seals!

Oh....what part of Minnesota?! (Born in Bemidji myself....)

Paul
 
Also check your airspeed difference...

...carefully, before and after. Quite a few really fast guys install gap seals for speed and tolerate the heavy controls.

Let us know if the speed falls off afterwards,

Thanks,
 
aileron gap fillers

First we will only remove the lower gap filler, fly the aircraft and see what takes place.

Our upper gap filler does not completely close the gap untill the aileron is deflected almost to its up limit so normally there is clearance for airflow to move from the bottom of the wing, past the nose of the aileron, to the top of the wing (aileron).

We will advise everyone on our results.

Fred
 
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