Modified Frise style ailerons

[PMD]

One other plane that I'm very interested to hear more about is the Grumman Yankee, Tiger, etc. They have a simple semi circle nose with a concentric hinge that is centered vertically on the back of the airfoil. I would think that this would result in adverse yaw, and the need for extra rudder input to counter it. I can't seem to find any accounts of Grumman handling online though. Are there any Grumman pilots out there that can comment?

couple thousand hours in AA-1 and AA-5B, but few in AA-1A/B/C and AA-5. The aileron (and elevator/rudder) design of the AA-1 was done not so much with some incredible insight into aerodynamics, but in Jim Bede's attempt to make a simple and economical design where panels were interchangeable or simply modified in construction to become left or right (wings). The end result is that an AA-1 is infinitely nicer to fly that ANY of its contemporary 2 place trainers. It CAN be flown feet flat on floor (as can the AA-5A/B) but the control response is so delightful nobody in his right mind would do that.

The only thing I can fault their ailerons over is that if you lose a bearing (nylon sleeves that can slide out of place from the brackets, they will start an extremely low frequency "flutter" that tells me they are probably a bit short on counterbalance and damping - but otherwise if all in tact they work extremely well. Have not flown an assymetric wing 2 places to the kind of extremes I had done extensively on symmetric airfoil to compare but certainly have never heard a 1A/B/C person complain though.

 

[challenger_II]

Many hours in an AA-1 "fast wing": I have to concur with PMD. She's a delightful ship to fly. No hint of adverse aileron tendencies.

 

[luked]

Flitzerpilot, thank you for sharing the details of the later Frise design. It seems like there is a diminishing return (if any) when you go much past the established designs. The bulged aileron is something that always seemed like a good idea. In some cases it may not add much, but I would think it's unlikely to hurt much.

Also, the Flitzers always intrigued me. The basic original model looked like it would be so much fun to just go out and burn holes in the sky on a clear blue day. Unfortunately, I probably won't be able to own multiple planes, so I need more of a swiss army knife that can do several things relatively well.

 

[luked]

PMD and Challenger, thanks for the first hand accounts. Do you know if these planes incorporate differential? Also, do the ailerons seem as effective in slow flight as say Cessna ailerons? I know that's a strange question because they obviously are effective enough for safe flight, but what is your general impression about their effectiveness when slow?

 

[challenger_II]

Slow flight, in an AA-1? In the "Fast Wing" AA-1, you have relatively fast flight, and then poorly-thrown rock" flight.
But, in all sincerity, the ailerons are effective to the stall.

 

[flitzerpilot]

Thanks for your comment LukeD. Yes, the basic Flitzer is just that, a simple, no frills design with excellent stability, but with positive pitch input becomes a 'tiger' as the CP migrates forward on the excellent USA 35B section. The prototype has no brakes, no active trim, no starter, makes a 360 in 7 secs and is perfect for cloud-busting. There's enough built-in drag to avoid exceeding VNE in carefree manoeuvring but it's not a snail on an 1834cc VW, indicating 92 mph on a good day! :0)

A forward push for loop or stall turn entry sees 115 mph almost instantly but it takes a bit more force to hit 120-125 mph. Picture shows the prototype Z-1 with two Goblins now under construction.

 

[Dan Thomas]

I was having trouble intuiting this. As you get to the tip, you're basically just controlling the intensity of the tip vortex, like, you're controlling how hard the toilet flushes, and it doesn't accomplish anything useful. But... once you deflect the flap (i.e. aileron), then you're also changing the amount of lift produced. So, it's not accurate to visualize it as a nice giant ellipse from the textbook, right?

Yes, it's not intuitive. So much about aerodynamics is not intuitive. Look at this:



The airflow from front to back is not straight except right up near the fuselage. Since the pressure is low on top, the airflow is drawn inwards, at more of an angle farther out on the span. Higher pressure below forces the flow outward, again at more of an angle farther out. It's this phenomenon that creates the tip vortices; it's not simple "air spillage." The air is being forced out from the bottom and sucked up by the top.

In fact, there are small vortices generated all along the trailing edge by this spanwise flow:




So now: The spanwise flow means that the air, in travelling a farther distance across the airfoil, sees a gentler camber and so produces less lift farther out.

 

[luked]

This brings up a question I hadn't thought of before. When ailerons are used is the upgoing wing (aileron down side) not only increasing induced drag on that side, but also increased drag from a larger tip vortex?

I'm sure the answer is yes, but I guess the finer point is how much of a factor is this in practice usually?

 

[wsimpso1]

I was having trouble intuiting this. As you get to the tip, you're basically just controlling the intensity of the tip vortex, like, you're controlling how hard the toilet flushes, and it doesn't accomplish anything useful. But... once you deflect the flap (i.e. aileron), then you're also changing the amount of lift produced. So, it's not accurate to visualize it as a nice giant ellipse from the textbook, right? Because the wing at the tip is producing either much greater lift or much less, depending on the aileron deflection. So it's basically a separate ellipse with a different vertical axis. And in theory it could dwarf the other ellipse. So yes, there are tip losses, but it does not seem accurate to imply that the lift produced by the wing sans aileron is relevant in understanding the limit of aileron effectiveness.

Also, did my browser change or was there some kind of editor update? It erases my last newline when I press backspace.

I know that it is difficult to use intuition on flaps and ailerons, which is why I was making an attempt at a better explanation... So trying again from a different end of the same commentary...

Imagine the elliptically distributed lift, and then add flaps. The height of the lift distribution tries to go up more where there are flaps, but the "leaks" around the ends pretty much make it still look elliptical, just more gain through flapped portion then on the aileron equipped part.

Now imagine the elliptically distributed lift, then deflect one aileron down and the other up. The height of the distribution tries to change where the deflected ailerons are, but the "leaks" drive the distribution toward elliptical too. Yes, the distribution is raised - percentagewise - more through the aileron part of span than inboard, but total changes are smaller out at the ailerons because the outer parts start out smaller.

Now let's look closer at the part of the wing near centerline. We have already seen that the lift tries to change softly as we go from tip to root to tip. Make more lift out near one tip and less at the other and the rest of the distribution gets skewed between them.

The ailerons have a bunch of leverage because they are outboard, so even though they have weaker influence than flaps, they still work pretty well.

I hope that helps....

Billski

 

[wsimpso1]

This brings up a question I hadn't thought of before. When ailerons are used is the upgoing wing (aileron down side) not only increasing induced drag on that side, but also increased drag from a larger tip vortex?

I'm sure the answer is yes, but I guess the finer point is how much of a factor is this in practice usually?

Sure is. The interesting thing is the difference between deflecting ailerons while going straight and when rolling has gone steady state.

Straight flight, no rolling - Deflect the ailerons, one up, one down. Alpha for the wing has not changed yet. The wing immediately makes more lift on one wing and less lift on the other, which accelerates the airplane in roll.

Now roll has gone steady state - The wing tips are now describing a helix. The tip with the up aileron is now seeing a positive alpha angle and the down aileron is now seeing a negative alpha... When the lift added (or subtracted) by the deflected aileron equals the lift subtracted (or added) by the alpha changing in the opposite direction, the rolling moment approaches zero, so the forces making it change roll rate also approach zero, and the roll rate steadies up...

With roll at some rate and ailerons deflected, then we center the stick, what happens? Hmm. Now the ailerons are not making lift in the rolling direction, but the helix the wing tips are describing is making angle of attack opposite to the roll direction, making a rolling moment opposite the roll, and it tries to stop the rolling motion. Center the ailerons at the right place and the moment runs out as the airplane hits your desired bank angle. Otherwise you might do what we see the aerobatic guys sometimes do: They are trying to go from high roll rate to a particular bank angle with zero rate. If they just center the stick, the roll rate decreases at ever slowing rate - called an asymptotic approach - And you don't really know where it will really stop. Well, if you drive the stick through neutral to deflection a little opposite the roll, roll rate comes down even faster. As you approach desired bank angle the stick might then get wiggles across neutral to drive the bank angle and rate to the desired angle and rate together.

This is not just important to impressing the judges in an aerobatic competition. Being able to hit a desired bank angle and roll rate while also hitting a heading and centerline alignment is what we do to land or shoot at something or just keep the passengers comfortable. Easy to see why we like light responsive ailerons, neutral stability (or close to neutral) in roll, and linear feeling between stick force and control response...

Billski

 

[luked]

Billski, thanks for another detailed discussion. The distinction between straight ahead flight and an aircraft that has entered a steady state roll is another interesting case to think about. There are so many ways to think about the effects of flow around a wing and how they interact with aircraft mass and acceleration. When you consider cases that pertain to aerobatics it can seem endless. It's definitely interesting to think about though.

My main interest has to do with aircraft in the utility category, and really the questions about experimental aileron designs are mostly idle curiosity because I will probably end up using something that follows very tried and true design.

I will say that I had all but decided I would be using a Frise style aileron, but I'm giving serious consideration to a Grumman style aileron (for lack of a better name, maybe there is a proper name) with a slightly fat leading edge radius, and a healthy bit of differential. I'd still be happy to hear from anyone who things that's a bad idea. Still not completely sure it's appropriate for a utility style aircraft that needs to handle well in slow flight. That's my main concern.

another factor that plays into this discussion is washout, or even a change in airfoil in the outboard wing portion. That might be a little controversial. Just thinking out loud.

 

[bhooper360]

deleted

 

[Dan Thomas]

but I'm giving serious consideration to a Grumman style aileron (for lack of a better name, maybe there is a proper name) with a slightly fat leading edge radius, and a healthy bit of differential. I'd still be happy to hear from anyone who things that's a bad idea. Still not completely sure it's appropriate for a utility style aircraft that needs to handle well in slow flight. That's my main concern.

In slow flight, you use the ailerons fairly gingerly, and you need more rudder to keep the ball centered. You'll already need more rudder due to prop slipstream effect and AoA differentials between the upgoing and downgoing prop blades.

In slow flight you are near the stall, and too much aileron could stall the upgoing wing and get a spin. That's just a fact of geometry: the angle of attack of the wing increases when you deflect an aileron downward, and AoA is what stalls the wing.

Remember:
-The angle between the wing's chordline and the relative wind is the angle of attack;

-The chordline moves as the aileron's trailing edge moves, and camber changes as well

-The aileron (or flap) deflection affects the airflow over the entire wing ahead of it. Lowering an aileron or flap increases the wings camber, increasing the airspeed over the top of the wing and increasing the lift. Raising an aileron slows the airflow and reduces the lift. Ailerons and flaps aren't just deflecting air like a ping-pong table deflects the ball.

This website is excellent: See How It Flies

 

[TFF]

The Grumman aileron is just a plain aileron. It has unique hinges and torque tube, but those have nothing to to do with aerodynamics. The Tailwind has the same general ailerons. Plans have fabric covered steel, but just about everyone makes aluminum ailerons like the Grumman ones, now.

 

[luked]

Dan, I agree about rudder in slow flight, and logically I guess aileron design probably doesn't make a big difference in maintaining control in that speed range. Some washout or other similar wing feature that delays the onset of stall on the outer wing section is probably more important. I just have this nagging feeling that a plain aileron isn't the best option since you mostly see Frise type on so many designs.

Great link by the way. I'll be going through that for sure. Thanks!

 

[luked]

The Grumman aileron is just a plain aileron. It has unique hinges and torque tube, but those have nothing to to do with aerodynamics. The Tailwind has the same general ailerons. Plans have fabric covered steel, but just about everyone makes aluminum ailerons like the Grumman ones, now.

TFF, I guess what I was getting at when I referenced Grumman style ailerons was the specific details of how Grumman implemented plain ailerons. They're a little more tightly fitting than some plain ailerons that have a gap that opens and closes (also similar to some RC planes).

Maybe this implementation is just more common that I realized. I have seen it on the Tailwind like you mentioned, and also the Team Mini Max. Maybe I should be calling them Wittman style if anything since the Tailwind probably predates the other designs that used that style.

I just liked the way they seem cleaner aerodynamically, and allow the little trick of crowning the aileron leading edge. They also provide a nice radiused surface when actuated.

 

[PMD]

Since the subject came up, just a few memories of Grumman control response. The AA-1 supposedly had a shortage of elevator authority and a bit of deficiency in rudder power. Well, anything with enough rudder for a crisp sn.....shite I can't say that out loud... is more than enough. I always found its pitch authority exactly to my liking, but not in any way overpowering. The Tiger on the other hand had HUGE elevators and while it didn't bother stuff in flight it could do one handy thing that a Yankee could not: lift the nosewheel on takeoff. Even with full fuel and two up front I could start a gentle roll on gravel strips, yank that massive elevator up (sometimes needed to bounce with forward CofG) and when the prop was clear firewall it to hold the nose well off with enough prop clearance to prevent blade damage. I don't recall being able to do that with a Pa28 or C177.

 

[flitzerpilot]

LukeD, I erroneously reported that the Hartshorn aileron was more susceptible to rigging errors than the standard Frise. On re-reading the data I see that the original Frise was more likely to be incorrectly rigged, but the Hartshorn, although considered in some ways better than the standard (not specified), did suffer some anomalies such as a slight indication of adverse yaw at low speeds and a reduced rate of roll for a given aileron deflection. As a result it was abandoned in favour of the standard type. Sorry for my error.

 

[TFF]

The gap is up to the designer. Some materials it is easier to implement and how you design the cove. Aluminum sheet can go right up to the aileron. Some planes have wear strips designed in so they can touch. Ply or wood will usually have covering; making a guess how close you can go. Most don’t want to recover if there is a mistake, so gaps are bigger. Of course there can be hybrid like aluminum cove on wood wing.

 

[Pops]

Since the subject came up, just a few memories of Grumman control response. The AA-1 supposedly had a shortage of elevator authority and a bit of deficiency in rudder power. Well, anything with enough rudder for a crisp sn.....shite I can't say that out loud... is more than enough. I always found its pitch authority exactly to my liking, but not in any way overpowering. The Tiger on the other hand had HUGE elevators and while it didn't bother stuff in flight it could do one handy thing that a Yankee could not: lift the nosewheel on takeoff. Even with full fuel and two up front I could start a gentle roll on gravel strips, yank that massive elevator up (sometimes needed to bounce with forward CofG) and when the prop was clear firewall it to hold the nose well off with enough prop clearance to prevent blade damage. I don't recall being able to do that with a Pa28 or C177.

Maybe the difference in lifting the nose wheel could be in the difference in the fore or aft placement of the main LG.