Flaperons

How are flaperons used? Are they as good as seperate flaps and ailerons?

David Bradley

Flaperons is the term generally applied to wing trailing edge surfaces that combine the area normally occupied by flaps and ailerons, and that move as a unit. A Flaperon system will generally have a mechanical mixer that takes input from the roll control system and flap control system, and deflects the right and left flaperons according to the combined input.

You use flaperons just like you'd use a system that has separate flaps and ailerons. When you want to bank, you move the stick right or left. When you want to re-camber the wing to make it more effective at different speeds, you move the flap control. The mixer takes these inputs and makes the wing surfaces do the rest.

Basically, when you move the stick right and left, the entire flaperon surface goes up on one side, and down on the other. And when you move the flap control, it moves the neutral point of both flaperon surfaces up or down. And when you make both a roll input and and a flap input, the mixer combines the two.

Flaperons are in most respects better than separate flaps and ailerons. Because the entire trailing edge deflects on roll inputs, they provide more effective aileron area, and consequently better roll control, than separate ailerons. And because they entire trailing edge deflects on flap inputs, they allow for a more effective spanwise lift distribution than seperate flaps.

The one area in which flaperons are an operational issue is on takeoff and landing. In many flaperon-equipped ships, the flap control should be set in the negative range at the start of the takeoff run, and moved into the positive range once aileron control is established. This places the wing at a lower effective angle of attack during takeoff and landing, resulting in improved roll control. The problem is that having to move the flap control gives you one more thing to do during very busy parts of the flight. Many pilots just select a neutral setting and leave the control there during the takeoff, tow, and landing. That's great when it works.

Good examples of modern implementations of flaperons are the PIK-20D and the LS-6. On both of these ships, the entire trailing edge of the wing moves as a unit. However, I think that both of those ships have separate inboard and outboard flaperon surfaces. But that's just an accommodation to the fact that the hinge axes for the inboard and outboard sections aren't along the same line.

Another implementation that might be called flaperons is the ASW-20. Flap inputs reflex the entire trailing edge surface, and roll inputs move the entire trailing edge surface in opposite directions. However, the surfaces are connected through a complicated differentiating mixer that mives the inboard and outboard portions according to different ratios. That ship also allows for flap deflections of up to 60 degrees; however at deflections greater than about 10 degrees the ailerons decouple from the flaps and return to near the 0 degree portion. Or something like that. I believe that different versions of ASW-20 also have slightly different implementations of the mixer system.

There are similar systems that offer what is called 'interconnected flaps and ailerons,' which is like flaperons but not the same. A good example is the Schreder HP-18. When you move the flap control, it moves the neutral point of the ailerons to follow the flap setting. However, when you move the stick right or left, it does not cause the flaps to deflect with the ailerons. This system offers the same effective spanwise lift distribution as flaperons, but does not have the flaperons' improved roll control. It also has the same operational issue on takeoff as ships with flaperons.

Hope that helps.

Bob K.

ailerons. Are they as good as seperate flaps and ailerons? No. The separate flaps are much better. The flaperons are a cheap version of separate flaps. George

Bye

I don't believe this 'improved roll control'. The inner portion of flaperons is rather ineffective in roll control due to its short lever arm, it merely add drag. This is why non flapped gliders have ailerons limited to the outer part of the wing. However the best disposition would be what was used on the first flying ships at the beginnig of aviation, i.e. spanwise twist where every portion of the wing contribute in its best way to the roll control. But for many other reasons always valid now this has been abandonned.

Then tell me, why in the Earth do most of the aerobatic sailplanes have full-trailing-edge-long ailerons? Swift for excample, as seen here: http://www.sailplanedirectory.com/PhotoOriginal.cfm? PhotoName=279_2_B...

The roll is the effect of the force, applied to one wing. To be excact, it's the result of the opposite forces, applied to the opposite wings. Which is result of a camber change. The bigger is the camber change, the faster is the roll rate and vice versa. Yes, the inner section of the wing is not as effective to generate the rolling force as outer section, but it is still adding pretty much for it.

Regards,

I don't say flaperons are a bad solution nor that the inner section of wing don't contribute, only that any surface of aileron/flaperon in the inner section is more efficently replaced by the same surface added to a classical aileron at the outer section. This especially when flaperons are made of one piece with the same deflection along the whole wingspan. Flaperon made of multiple pieces with different deflections increasing from the inner to the outer section are much better, since they are near the optimal case of twisted wings. On the 3 views of the Swift you mentionned above, it seems that this disposition is used there. However on many flapped modern gliders, one piece flaperons seem to be the best tradeoff in cost, simplicity and efficency.

Hi George,

that's not correct. Any Flap with aileron function is a flaperon. At first, flap-movement normally shall have the same deflection on any span-position (but it is possible to have a design, that have different deflection). Second, the designer may want to have aileron only on the outer flaperons, but it maybe, that he want's to have an aileron deflection on the inner flaps too (so they are flaperons) Due to the skip of circulationdistribution of the left and right wing at deflection, Flaperons hav a vortice near the fuselage, which improve rudder (e.g. www.eta-aircraft.de/en/technology/control.html)

So from outside the design process, you can't say if a flaperon is better or not.

Ciao, Steffen

Hi Steffen, acc.to your definition, I have to change my statement as follows: The one piece flaperons (e.g. DG-800) are a cheap version of flaperons with separate flaps and ailerons (e.g. ASW-20). Plese execute a couple of landings with an 'old' ASW-20 and than with a 'new' DG-800. I hope you will than understand what I mean by this statement. Regards, George