frets24

My Feedback: (15)

I have been all through the various posts and threads on aileron differential and have seen widely varying and conflicting responses and nothing that really served to answer my query, so here goes:

Two main parts.

1. a. It is my understanding that the rising wing(down ail) has greater drag due to the creation of lift thus requiring us to "step into the turn", as I learned in fullscale, to co-ordinate the turn and over-ride the opposit yaw.

b. We can use differential, in that we create greater relative deflection (and drag) in the "up aileron" (low wing) than in the "down aileron"(rising wing) to help balance the drag co-efficient and reduce the yaw tendency.

??? Does this apply in friese type ailerons where the bottom LE of the rising aileron protrudes into the underwing airstream thereby creating drag intended to offset the opposing lowering aileron or is there still a typical
need to add differential as well??? (This may seem self evident but it ties into the main question below.)



2. I have been working on a freise aileron setup on an A6M5 Zero that is bottom hinged with a topside control horn on a plane with 72" span x 895sq/in wing area. The aileron is @ 18' long and when fully deflected, 7/8", in the up position, the bottom edge has just under 3/8" sticking into the underwing airstream. That yeilds almost 6 sq/in of perpendicular to the chord line surface. To me that seems HUGE, even if a small percentage of the wing area.(do they evenrelate?) Does it really make a lot of difference that this surface is relatively tight to the wing surface, or is it really no different than taking a 2.5" x 2.5" slab of balsa and mounting it under a wing flat faced into the relative wind?

In other words, "Am I in for a plane that is crap in the air?" Or is this in the realm of typical numbers?

Lnewqban

I believe that the aileron is going to work as well as you have explained it.
It could work better, if when fully deflected, there is a constantly decreasing channel or nozzle formed between the TE of the wing and the LE of the aileron.
Through that nozzle, air from the bottom would accelerate onto the top surface of the aileron, increasing the velocity there and the control effect of the aileron.

A 2.5x2.5 would not work the same since the AR would be different an also the shape aft.

A flat piece that is perpendicular creates a huge amount of turbulence behind it, and so much drag (the coefficient of drag (Cd) is the highest).

The shape of the aileron leads the flow to re-attach to the bottom of the aileron (as some Coanda effect remains), but disturbing it enough to reduce lift on 18" of the half-span and to increase drag (both useful effects when banking).
Some Frise ailerons have a sharp LE, which creates even more drag.

This video explains how air flows around disturbances better:

http://www.youtube.com/watch?v=6UlsA...369B28D0ED19CB

Copied from http://en.wikipedia.org/wiki/Aileron

"Frise Ailerons
Engineer Leslie George Frise (1897–1979) developed an aileron shape that is often used due to its ability to counteract adverse yaw. The Frise aileron is pivoted at about its 25 to 30% chord line and near its bottom surface. When the aileron is deflected up (to make its wing go down), the leading edge of the aileron dips into the airflow beneath the wing. The moment of the leading edge in the airflow helps to move up the trailing edge, decreasing the stick force. The down-moving aileron also adds energy to the boundary layer by the airflow from the under-side of the wing that scoops air by the edge of the aileron that follows the upper surface of the aileron and creates a lifting force on the upper surface of the aileron aiding the lift of the wing. That reduces the needed deflection angle of the aileron. If the leading edge of the aileron is sharp or bluntly rounded, that adds significant drag to that wing and help the aircraft to yaw (turn) in the desired direction, but adds some unpleasant or potentially dangerous aerodynamic vibration (flutter)."

jester_s1

Sounds like a really fancy way to avoid using aileron differential! It does sound like it would work though as you've described. It also sounds like the control response will be hotter than with normal ailerons, which might mean your throws become too sensitive.

Lone Star Charles

Because of your question, I measured the protrusion and the interference of the Friese ailerons on my full sized Acroduster II.  At full deflection, the protrusion is about 1-1/2".  Each aileron is about 52 inches long.  This makes about 78 square inches, or a total of 156 square inches of interference for both the upper and lower wing.  The wingspan is 21'-5" and the wing area is 130 sqft.  I don't even pretend to be able to make a guess as to how that would translate to your model, but it's begining to sound like 6 square inches will not amount to much and that you are on the right track.  Seriously, If your effort is directed toward achieving a scale like appearance, just go for it. 

kenh3497

I had a Sig Zlin 526 with the same aileron set up. It flew fine though I did have spades on the ailerons per the full scale aircraft. I'm currently building a 20% Zlin 526 and it will also use the Friese ailerons, again with spades. The Sig version was a very nice flying airplane and I don't remember ever having any problems with ailerons flutter.

How are you planning to hinge your ailerons? My plans suggest something like what you have constructed.

Ken

frets24

My Feedback: (15)

I will probably hinge them using 3/32 Printed Circuit Board for the fixed hinge arm. The PCB is fairly inexpensive, readily available at Radio Shack and very strong.

The fixed arm will be very much like the one in the photos above, though longer and with better shaping. Also in the pics there is a small crescent cut out at the bottom of the arm that won't be on the real part...it's just a viewing cutout for the mock-up.

On the aileron itself there will be a plastic tube from the outboard end to just inboard of the inboard most hinge as a guide for a full length wire hinge pin that can be removed for aileron removal/service. There will be PCB plates each side of the hinge arm in the ail as well...much like the bread on a sandwich with the hinge arm being the meat.



THANKS to all who responded and for the real world reports on flight characteristics of models and 1:1 with similar setups.

Lnewqban, there actually is a small channel from bottom to top when the ail is raised so as Jester observed from your reply I will be forewarned that this could have a pretty sensitive response. Your explanation will likely save me from being ill prepared for how "hot" the ail effectivenes may be. I enjoyed the link and found the addendum to be very informative also!

kenh3497

For what it's worth I don't remember the Zlin 526 being "hot" on the ailerons at all. In fact I remember it being responsive yet controlled, if that makes any sense. The Zlin does have kind of a long wing though so that may be a factor. The later versions of the full scale 526 shortened the wing somewhat to improve roll response. Personally, I would not fret over the "hotness". Set up for normal throws and go for it.

Good luck on your quest!!

Ken

I like the PCB idea. I was thinking about making my own G10. But if I can purchase it, that is better. Thank you!!

FBaity

My Feedback: (2)

Question to the group:

As a general rule of thumb, how much more up deflection than down defection is needed to prevent yaw in rolls? My question refers to Pilot 30 % Sbach flown in IMAC style.

Thanks

pimmnz

It depends. Different aiplanes need different amounts, you will have to SIAS. (Suck It And See). So far as the Friese discussion is concerened, most of the WW2 fighters used them, without any noticeable flutter. The forward protrusion is useful as you can add the mass balance weights in the leading edge, which further reduces any flutter propensities. It is to be noted that testing of FW190's revealed that rudder was not needed to perform a balanced turn, so the idea really works. It does not, necessarily, make the ailerons more responsive, but the slotted variety in Jodels allowed the aileron to work even when the airplane was stalled. Just FWIW.
Evan, WB #12.

gerryndennis

G'day Frets,

Every set of Frise ailerons I've seen incorporate a bit of differential as well ie more up than down. I don't know why you've designed yours to have reverse differential ie more down than up! I would suggest that you don't do that. Make yours with equal deflection or a small amount of conventional differential and I'm sure they will work just fine.

Don't worry about them being more effective than conventional ailerons, they won't be. While its true that they are lighter in feel that is totally irrelevant for an RC model (unless you are trying to use weaker servos). You would have to be holding on to the control column of a full size aeroplane to feel lighter ailerons, not a radio set. Someone's got the wrong end of the stick there.

Incidentally did you know that the adverse yaw is probably at least as much due the diffence in drag between the wings due to the roll rather than the actual aileron deflection? The descending wing has less drag than the climbing one. Makes no odds though, we still need to 'step into the turn' as you say. Even the best designed ailerons won't exactly balance the adverse yaw for all rates of roll at all speeds or angles of attack.

Congratulations on putting some thought into your ailerons instead of just bunging some triangular lumps of balsa on the back.

Cheers

Dave H

frets24

My Feedback: (15)

Thanks for the compliment Dave.

It took me a minute to figure out where you got the idea that I was programming more down throw that up; Then I saw my labeling on the mock-ups[&:]

The distances on the mock-ups are just the total available before interference. I am programming them at 3/4''(20mm) up & 5/8''(16mm) down on high rate (100%). For normal flying on low rates they are set at 70% of those values.

Thanks also for pointing out a confusing implication in my labeling too.

da Rock

Frets, have you tried other settings for the differential?

The friese might be the reason you are satisfied with what my experience with simple hinged ailerons seem to suggest, that the up really needs to be UP and less down is enough.

How does it fly, btw?

rmh

All a matter of leverage n drag
Take a soaring glider and simply switch the aileron geometry such that ailerons work same throw - or proverse or adverse differential
you will easily see results

hinge em however you like as long as both sides are the same
Theory is fine to discuss
results are hard to ignore .

frets24

My Feedback: (15)

Still on the bench and have yet to glass the wing. As has been stated above, the proof will be in the performance. I have the throws and rates set according to past experience...3/4 deflection as the high rate/ full throw and 25-35% reduction for the low. In the past on other a/c this has been docile and smooth yet responsive in the low throws and can be made a bit more "snappy" on the high rates(though I rarely switch over to high rate).

The differential in the set up was reached by studying numerous posts and chatter on the subject here on the boards as I have yet to play with frise ailerons. This was a projest undertaken to expand my building and design scope as well as to see how it works out in the air. Also influencing the decision was how much of the upper ail surface was visible compared to the lower on the full scale Zero...Like a 5 to 3 difference(less on top). I wanted to model that effect and this was the logical choice due all factors involved. Top mounted control horn really makes a difference on this setup too, as far as necessary force applied to operate.

I'm looking forward to flying it and will undoubtedly tweak the set up to see what effect different throws, rates and off-sets or lack there of have on it.

I'll certianly post my results here and then be able to join more discussions of the topic from an experienced point of view rather than as one in search of info.

Thanks guys!

gerryndennis

Hi Frets,

Your ailerons are looking great.

Don't worry too much about the theory v practice argument. The idea of Frise ailerons is that they deal with adverse aileron yaw with less drag penalty than other methods (differential or rudder for eg). Obviousely we will never see that efficiency in model flying, however they still work to reduce adverse aileron yaw. So the theory is they are more efficient and as RMH points out that's only theory. But the result is that they work, and they work at least as well as any others.

So given that they aren't that hard to build and rig, and most importantly they are correct for your scale model....

We had a large Zero turn up at our field last week, nicely weathered, cockpit detail etc, but huge gaps in all the control surfaces due to the standard 'model' control surface design. After the first flight he said the ailerons were very soft, and he ran out of elevator in the flare. He's talking about adjusting the throws, but I couldn't help thinking if his ailerons looked like yours, and if the tail surfaces where shrouded (instead of 'V' leading edge) then they might have worked better as well as looking more scale.

Yes it was the labeling of your diagram that led me to assume you were thinking more down than up, my apologies.

Best of luck.

Dave H

invertmast

My Feedback: (23)

In all of the airplanes I have built with Frise aileron style hinging (over a dozen) nearly all of them have never required differential aileron. Only one of them did and it was a slower flying airplane that required lots of aileron deflection for the turns anyways.

pimmnz

And yet, all the full size rigging diagrams of the popular WW2 fighters, Spits, 109's and 190's all with Frise ailerons, all show some differential in the aileron movement. Go figure.
Evan, WB #12.

da Rock

I believe that's not a real surprise. A lot of them actually carried design problems into the air because everyone back then was feeling their way into new territory and stuck with "what everyone knew to be true" design concepts. The P40 was basically unstable in yaw at power up for example. They designed the plane by what they knew to be safe and it wasn't. They added more rudder area and it didn't help enough. They lengthened the tail and it did. You know they didn't choose the original areas and moments knowing they were insufficient. They thought they were sufficient for some reason.

You know your list of examples has 3 of the most successful fighters of the war. That would suggest that differential is a good thing to have with ailerons.

There are lots of puzzles, aren't there.

rmh

Those old fighters had high wing loadings and flew , for the most part -upright
A natural choice would be differential.
Good, lightly loaded fully aerobatic stuff?
little if any is more desireable
No mystery here -It has to do with effective AOA of the wing during most flying.
The lower the aoa -the less the need
an exception is in some soaring craft - the relatively long spans -with ailerons on outer panels - produce more leverage (from aileron applictaion) and greater adverse yaw
I set these models such that turns with ailerons are similar to rudder turns - The ailerons have quite a bit of differential.
A basic trainer I had long ago - a Klemm 25- demonstrated the issue very well.

da Rock

And the pilot often died if the roll rate wasn't fast enough, or the roll killed the speed, or yawed the sucker.

Good thing you mention wingspan. You're spot on about gliders versus aerobatic planes.

There are lots of answers to all the puzzles aren't there.

1scalebldr

Invert,
You seem 2 B the expert on all this. I want to build scale Frise ailerons on a 60 size P-51. I'm unable to find ANY photos of scale or full size P-51 ailerons (cross sectional photo) & the hinging. Can you direct me to any sources please?
Thanks
Scale Rookie