Modified Frise style ailerons

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

luked

Member
Joined
Mar 27, 2013
Messages
21
Location
Albany
My understanding is that Frise type ailerons provide two main benefits. First, as the trailing edge rises, the leading edge dips down into the airflow below the wing, and increases drag to help counter adverse yaw. Also, that drag can help counter the hinge moment and decrease stick forces.

In most Frise type ailerons I've seen, the leading edge nose or point extends the full span of the aileron. I'm wondering if there are any examples where this feature is only on the outboard portion.

My thought was that the further outboard the drag is created, the more benefit it provides in terms of countering adverse yaw. Less helpful drag (inboard) could be eliminated. As for lightening stick forces, it wouldn't seem to matter (other than torsional stiffness maybe).

There must be a good reason this isn't common. My first thought is that it's not worth the trouble on most designs because the drag only occurs when ailerons are moved from the neutral position. Are there some negative effects I'm not thinking of?

Thanks,
Luke D.
 

bhooper360

Well-Known Member
Joined
Dec 9, 2021
Messages
145
Hi Luke,

Frise type ailerons are a simple solution to a problem that doesn't exist. You have two pieces of wing, and you have this piano hinge (extruded, not cast). Well, it has to go on one side or the other, so you pick the side with the most benefit. And, it was probably easier to make the edges flat anyway. It was never a legitimate aerodynamic feature to begin with, which is why nobody's concerned with improving the aerodynamics.

My thought was that the further outboard the drag is created, the more benefit it provides in terms of countering adverse yaw.

Yeah, and what else counters adverse yaw? The rudder. It's even more efficient. And, it's already at the very back of the plane.

I'm wondering if there are any examples where this feature is only on the outboard portion.

These are from the 330SC & NG. These are not frise-type ailerons.

SC060-b.jpg

C8B4BF81-3FDF-4804-9F15-C419589FC003.jpeg 65B282D4-46D7-48C2-9A1B-FCB415ADE468.jpeg
 
Last edited:

wsimpso1

Super Moderator
Staff member
Joined
Oct 18, 2003
Messages
9,168
Location
Saline Michigan
If you were starting with all control surfaces simply hinged at their leading edges and big enough to give all the control authority you wanted, you would find that the rudders and elevators felt fairly nice but that the ailerons felt really heavy. And then we humans are less strong in side-to-side pushing than in pushing or pulling... And then there is that adverse yaw thing going on when you don't apply enough rudder with the ailerons...

So, you start looking for aerobalance on those ailerons to give better control harmony, and maybe balance the drag on the two ailerons too. What do you find? Well, extend the aileron forward of the hinge and the forces to move and hold aileron get smaller.

There is a limit as to how far you can extend the front edge. Airload is roughly triangular on the aft edge of the wing, so the center of the lifting forces about 1/3 back from the leading edge of the aileron. If the hinge approaches that line, the forces can get close to zero, which is not pleasant - we usually like to have some centering forces on our ailerons or the airplane becomes difficult to fly with precision.

Then there is aileron lock. Under some alpha and delta angles, the hinge moment can go through a reversal. Now the aileron wants to go hard over - full deflection. You might have enough strength to hold the stick on center, but frequently, this will be "aileron lock". Never good. So folks do stuff like soften or radius the forward part of the aileron and only move the hinge line to about 25% of the aileron chord. These reduce the rate at which the aero balance and drag build up.

If you want to beat adverse yaw, you can start playing around with putting the hinge above or below the chord line. On some airplanes the hinge is on the top surface. On other airplanes the hinge may actually be below the wing slightly. Configure the portion of the aileron ahead of the hinge properly and it only sticks out into the air for drag when the trailing edge is up.

Now you have a lighter feel on the ailerons, giving much improved control harmony between the axes, you have some restoring moment on the controls giving some feel and a tendency to return to center, and some correction for adverse yaw. But you may want a little more tendency to stay centered, so you may thin the forward part of the aileron a bit, so it does not stick out at the tiniest deflection.

This is basically the history of ailerons on airplanes. Some folks will go add spades, which add aileron area forward of the hinge and are easily adjusted for angle and size and shape to get whatever feel you want. Why do spades instead of adjusting the size of the part of the aileron forward or move the hinges? Because you can easily adjust in small increments if you want to. And they may have less tendency to aileron lock.

Now did we talk anywhere about ailerons being too heavy? Not usually... Most of the time, the manufacturer makes the ailerons lighter until the feel relative to the elevator and rudder is about right, and then they stop adding aerobalance.

Now let's get into the rest of the issues. Wing lift is usually distributed along the span in a nice elliptical shape. High pressure air on the bottom "leaks" around the tip toward the lower pressure air above the wing, giving us that elliptical lift distribution, and this shape does not care much about the planform of the wing. Really. The local lift at the root looks like the lift of a foil in a wind tunnel. But go half way out the wing and the local lift is dropping off. By the very tip there is no local lift at all. And the air being accelerated downward by the wing extends many feet up and down from the wing. If all that air were accelerated uniformly, the air moved would be a cylinder of wingspan in diameter. We are moving a lot of air.

Deflect the flaps, and they are where the local lift (Cl) is strong, and this changes pressure and diverts flows, not just through the part of the span where the flaps are, but out beyond them too, although to a lesser extent, what with the "leak" around the tip. So, flaps work great on the inner half of the span. Put ailerons on what is left, outboard. Now you are trying to make local lift outboard, where the local lift is getting smaller and smaller as we get near the very tip. Hmm, ailerons out at the tip might have longer arms for more leverage, but they also have less and less pressure difference being made out there too. That lowers how effective ailerons can be.

So, we have a gadget that tends to feel heavy and not be as effective as we might like, then we add area to it that increase effectiveness while it reduces the forces to move and hold the surfaces, and also tends to reduce adverse yaw. But does it ever get too light? Most of the time, it does not. Most of the time, we want lighter ailerons than we have. So we design a nice simple aileron with area forward of the hinge that also comes down into the airstream when the trailing edge is raised but we rarely get the forces too light unless we tilt to them going hard over... And if we are close, you can always stick a spade on each aileron and play with its angle, area, and shape.

But make only half the aileron have too much forward and the rest too little? Hmmm. Usually, that gives heavier feeling ailerons, is harder to build and make behave well, is either less stiff torsionally or adds weight than if the whole thing was one shape, and reduces aileron size for less effectiveness. Why would you want to do that? The world has gravitated to the common design.

Now let's look at that spectacular akro bird above. The ailerons there have a great big aero horn at the outer end rather than smaller aero extensions of a Frise, and it is shaped to minimize drag when deflected. Hmm, when you buy an Extra, they expect you to know how to use the rudder to set whatever yaw angle you want.

Billski
 

luked

Member
Joined
Mar 27, 2013
Messages
21
Location
Albany
Frise type ailerons are a simple solution to a problem that doesn't exist. You have two pieces of wing, and you have this piano hinge (extruded, not cast). Well, it has to go on one side or the other, so you pick the side with the most benefit. And, it was probably easier to make the edges flat anyway. It was never a legitimate aerodynamic feature to begin with, which is why nobody's concerned with improving the aerodynamics.



Yeah, and what else counters adverse yaw? The rudder. It's even more efficient. And, it's already at the very back of the plane.


I guess adverse yaw isn't a problem if you don't mind it. I know there are quite a few pilots that learned in planes with lot's of adverse yaw, and just chalk the extra rudder input up to pilot skill. Fair enough.

I learned in a 152. Like you say, they just attached the hinge at the top, and let the bottom stick out enough to make Frise style ailerons. Not much extra work. It does seem to help though. I won't say you don't need to use rudder to turn, but it doesn't take much.

Interesting pictures of the Extra. I didn't know they had those horns like that.
 

luked

Member
Joined
Mar 27, 2013
Messages
21
Location
Albany
Thanks for the detailed explanation. It's a lot do digest. Of course the difficult part is the fact that we're talking about general theories Here, and not a specific aircraft design, so one assertion could be true for some plane, but not another. I appreciate your examples in general terms though. It helps for the sake of learning concepts.

There is a limit as to how far you can extend the front edge. Airload is roughly triangular on the aft edge of the wing, so the center of the lifting forces about 1/3 back from the leading edge of the aileron. If the hinge approaches that line, the forces can get close to zero, which is not pleasant - we usually like to have some centering forces on our ailerons or the airplane becomes difficult to fly with precision.

Then there is aileron lock. Under some alpha and delta angles, the hinge moment can go through a reversal. Now the aileron wants to go hard over - full deflection. You might have enough strength to hold the stick on center, but frequently, this will be "aileron lock". Never good. So folks do stuff like soften or radius the forward part of the aileron and only move the hinge line to about 25% of the aileron chord. These reduce the rate at which the aero balance and drag build up.

I understand your caution about moving the hinge line to far aft. It's something that I've thought quite a bit about because the consequences could be severe. I had two thoughts in mind here. First be conservative in moving the hinge line. Better to have heavier ailerons that behave as expected than the alternative. Second, sizing the surface large enough to provide adequate control authority with lower angles of displacement. It would seem that this problem would become more exaggerated with more deflection. Does this seem reasonable?

If you want to beat adverse yaw, you can start playing around with putting the hinge above or below the chord line. On some airplanes the hinge is on the top surface. On other airplanes the hinge may actually be below the wing slightly. Configure the portion of the aileron ahead of the hinge properly and it only sticks out into the air for drag when the trailing edge is up.

Now you have a lighter feel on the ailerons, giving much improved control harmony between the axes, you have some restoring moment on the controls giving some feel and a tendency to return to center, and some correction for adverse yaw. But you may want a little more tendency to stay centered, so you may thin the forward part of the aileron a bit, so it does not stick out at the tiniest deflection.

The aileron designs that I have gotten the most inspiration from are probably the Piper Cub, and the RV. The RV in particular is known for it's handling qualities. I think this is owed to it's aileron design, but maybe also to it's all pushrod control system.

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?

I appreciate the discussion of spades, and they do seem like the ultimate in ease of "tuning", but they seem like the highest drag proposition the way they're always hanging out there in the breeze.

Your comments about lift distribution got me thinking quite a bit though. I'll have to do some more reading and thinking about that interaction before I'll even ask any follow up questions. Thanks again.

Luke D.
 

bhooper360

Well-Known Member
Joined
Dec 9, 2021
Messages
145
Now let's get into the rest of the issues. Wing lift is usually distributed along the span in a nice elliptical shape.(...)
Now you are trying to make local lift outboard, where the local lift is getting smaller and smaller as we get near the very tip. Hmm, ailerons out at the tip might have longer arms for more leverage, but they also have less and less pressure difference being made out there too. That lowers how effective ailerons can be.
(...)
And if we are close, you can always stick a spade on each aileron and play with its angle, area, and shape.
(...)The ailerons there have a great big aero horn at the outer end rather than smaller aero extensions of a Frise, and it is shaped to minimize drag when deflected.

The aileron spades are easy to adjust, and they provide a convenient place for anti-flutter weights. Aerodynamically, they're not in a great place. Low aspect ratio, and they operate near the flow from the wings.

On the modern aerobatic aircraft the spades are moved out to the wingtips instead. The biggest advantage is that they increase the AR of the wing, so when you pull Gs you can hold on to more energy. There are downsides -- increased rotational inertia, and decreased roll rate. Because most of the airplane's mass is on the centerline, the difference in weights is less important. A more efficient wing may allow for a smaller wing, partially offsetting the effects. Also, longer wings are easier to judge from the ground. The two-seat aircraft like the NG prioritize cross-country performance to reach a wider market share, so the pros outweigh the cons.
 

bhooper360

Well-Known Member
Joined
Dec 9, 2021
Messages
145
In general, you will always sacrifice performance in order to get the convenience of hands-off flight. If you optimize your aircraft for hands-off cruise flight, you will have to use lots of rudder in the pattern. At that point, the easiest way to make the airplane safer is to make it stable, i.e. stall resistant. This will cut into cruise performance. Canard aircraft are the exception, because the front wing is very efficient.

If you want a high-performance aircraft that's easy-to-fly, the best option is an autopilot servo connected to the rudder. You can use either a lookup table or a gyroscope to make yaw inputs.

What are your goals? "Minimize unhelpful drag" is a good start, but not very specific.
 

BJC

Well-Known Member
Supporting Member
Joined
Oct 7, 2013
Messages
15,421
Location
97FL, Florida, USA
At that point, the easiest way to make the airplane safer is to make it stable, i.e. stall resistant.
Please explain the connection between stall resistance and stability.
If you want a high-performance aircraft that's easy-to-fly, the best option is an autopilot servo connected to the rudder.
All the high performance aircraft autopilots that I am familiar with drive the ailerons to control either track or heading. Please tell me which aircraft drive the rudder.

Thanks,


BJC
 

bhooper360

Well-Known Member
Joined
Dec 9, 2021
Messages
145
Please explain the connection between stall resistance and stability.

An aircraft with a high degree of static longitudinal stability has the center of gravity far ahead of the center of lift. The horizontal stabilizer (in a conventional aircraft) exerts comparatively more downwards force. The stall speed increases. In an absurd example, let's take a Piper Cub with a large amount of nose ballast. The aircraft dives in level flight. If you pull the stick all the way back, the aircraft still continues to dive, until it reaches 90 mph. At that point, there is only enough elevator effectiveness to maintain level flight. You cannot achieve the trim speed where the main wing will reach critical AoA. This is a stall-proof airplane.

All the high performance aircraft autopilots that I am familiar with drive the ailerons to control either track or heading.

So... based on context I'm inferring from your reply, the purpose of adverse yaw correction is to provide an acceptable ride quality in an aircraft without a rudder servo. The more correction you introduce, the higher roll rate you can set the autopilot to. If you don't have any adverse yaw correction, you can only roll very slowly, otherwise you will notice the nose swinging. If the correction is too high, you will have to use opposite (backwards) rudder on enroute descents.
Please tell me which aircraft drive the rudder.

T-6 Texan II. Google "trim aid device."
 

BJC

Well-Known Member
Supporting Member
Joined
Oct 7, 2013
Messages
15,421
Location
97FL, Florida, USA
If you want a high-performance aircraft that's easy-to-fly, the best option is an autopilot servo connected to the rudder.

So... based on context I'm inferring from your reply, the purpose of adverse yaw correction is to provide an acceptable ride quality in an aircraft without a rudder servo.
Sounds like you are referring to a yaw dampener rather than an autopilot.


BJC
 

Pops

Well-Known Member
Supporting Member
Joined
Jan 1, 2013
Messages
11,007
Location
USA.
On the SSSC the ailerons are hinged by piano hinges on the top surface . More up than down, ( don't remember the amount without digging through the plans). Has 28' of span with a 48" cord , 24" wide fuselage. Each aileron is 7' long by 12" cord. You can bank the wings up to 20 degrees with your feet on the floor and the ball will stay centered. Over that you need just a little rudder. Ailerons are light and responsive. Same for the elevator and rudder. Everyone that has flown it, loves it.
 

BJC

Well-Known Member
Supporting Member
Joined
Oct 7, 2013
Messages
15,421
Location
97FL, Florida, USA

bhooper360

Well-Known Member
Joined
Dec 9, 2021
Messages
145
On the SSSC the ailerons are hinged by piano hinges on the top surface . More up than down, ( don't remember the amount without digging through the plans). Has 28' of span with a 48" cord , 24" wide fuselage. Each aileron is 7' long by 12" cord. You can bank the wings up to 20 degrees with your feet on the floor and the ball will stay centered. Over that you need just a little rudder. Ailerons are light and responsive. Same for the elevator and rudder. Everyone that has flown it, loves it.

I guarantee you that even in a level turn the ball staying centered has nothing to do with bank angle.
 
Last edited:

bhooper360

Well-Known Member
Joined
Dec 9, 2021
Messages
145
So an autopilot servo connected to the rudder is not a yaw damper but is fly-by-wire?


BJC
A fly-by-wire system converts pilot inputs into control surface deflections. Right now you all have decided that the ailerons cause coordinated rolls into and out of level turns, which is absolutely not what ailerons do at all, so if you care about efficiency your best option is to let a computer work around the discrepancy.

A yaw damper involves dynamic stability. The oscillations on longer (passenger) aircraft occur at a lower frequency, and structural considerations are important. This is not automatically relevant to small aircraft.
 
Last edited:

luked

Member
Joined
Mar 27, 2013
Messages
21
Location
Albany
In general, you will always sacrifice performance in order to get the convenience of hands-off flight. If you optimize your aircraft for hands-off cruise flight, you will have to use lots of rudder in the pattern. At that point, the easiest way to make the airplane safer is to make it stable, i.e. stall resistant. This will cut into cruise performance. Canard aircraft are the exception, because the front wing is very efficient.

If you want a high-performance aircraft that's easy-to-fly, the best option is an autopilot servo connected to the rudder. You can use either a lookup table or a gyroscope to make yaw inputs.

What are your goals? "Minimize unhelpful drag" is a good start, but not very specific.
I'm not shooting for hands off flying, but I would like decouple roll and yaw inputs somewhat.

I'm working on a wing design for a future project, and aileron design plays into the overall structural layout. So, I'm just weighing the pros and cons of different styles.

Although I'm not trying for a particularly fast cruise speed, I'm trying to watch drag in the details where possible if it doesn't add too much complexity. Power will be limited, so I don't want to squander it.
 

Dan Thomas

Well-Known Member
Joined
Sep 17, 2008
Messages
7,228
Hi Luke,

Frise type ailerons are a simple solution to a problem that doesn't exist. You have two pieces of wing, and you have this piano hinge (extruded, not cast). Well, it has to go on one side or the other, so you pick the side with the most benefit. And, it was probably easier to make the edges flat anyway. It was never a legitimate aerodynamic feature to begin with, which is why nobody's concerned with improving the aerodynamics.
How many types have you flown? I have flown lots of Cessnas, everything from the 150 to the 185, all with Frise ailerons. Flew Cherokees with them. I have flown lots of other designs, most without the Frise. The airplanes with the Frise could be flown with the feet flat on the floor unless you were on takeoff and climb. The one without? Better get used to using your feet.

it's not just the Frise. The differential aileron travel figures into it as well. Cessna typically has up travel of around 20° and down of 15°. Cherokees were up 30° and down 15°. This is common in an awful lot of airplanes. Those that had the cables working the ailerons directly, no bellcranks, had no differential and needed lots of rudder. The down aileron generates a lot of drag. My Jodel, Cubs, and many other old designs are like that.

Some airplanes use aileron-rudder interconnects to reduce adverse yaw. 172s with the floatplane conversion kits have light springs and interconnecting cables to move the rudder a bit when the ailerons are moved. The TriPacer does, too, but with stronger springs. Some Maules had a servo tab on the rudder that is actuated by the aileron control system to move the rudder in the direction of the bank.

So, all of these OEMs spent money and time building systems for a problem that doesn't exist? What are you talking about? They wanted to sell airplanes that were easy to fly, and reducing adverse yaw was one way of doing that.
 

Dan Thomas

Well-Known Member
Joined
Sep 17, 2008
Messages
7,228
Although I'm not trying for a particularly fast cruise speed, I'm trying to watch drag in the details where possible if it doesn't add too much complexity. Power will be limited, so I don't want to squander it.
Eliminate Frise and now you need more rudder. More drag there, maybe not as much as the Frise, but drag nonetheless. It's not so simple.

My Jodel needed rudder to stay coordinated, but its rudder and fin were all one piece, and the whole thing moved. It had a symmetrical airfoil section and some aerodynamic balancing, and was extremely powerful. Didn't need a lot of effort or movement at all. It could do awesome slips because of that power and the non-differential ailerons that had a lot of travel.
 
Top