The question is, how are leading edge flaps deployed with respect to other control surfaces, particularly flaps? I am building an SU-27 which uses LE flaps-not slats- and flaperons. I'm told on the full scale, the tailerons provide the basic roll control. From photos, the LE flaps appear to be lowered at times, while the flaps are in what appear to be neutral. Again from photos, the LE flaps are lowered for T/O and landings. The literature I've read says they deploy automatically; and again, photos, suggest they appear lowered in high AOA maneuvers. At first, I considered coupling them to the flaps. I know these things are used on Big Jets from other discussions here, Any thoughts on the subject? Why you ask? Because they are on the full size and I want it to look, and fly as scale as I can.

What are tailerons? do you mean elevons? Are you sure there are flaps on the leading edge, are you not talking about drooped leading edge?

Leading edge flaps add lift in slow-speed high-alpha situations.. takeoff and landing.
As these two areas are fraught with peril for a model.....
as well as being difficult to fabricate..
Unless you can have a flight control computer as in the full-scales control the deployment of these things (it monitors angle of attack, airspeed, g, and airplane weight), it's better to takeoff and land fast, with the leading edge flaps artfully represented by panel lines.

I've attached an image of the wing configuration for the F-16.

Bob Fiorenze and Larry Wolfe have both used leading edge flaps with success on their models. In Bob Fiorenze's case (on a Yellow Aircraft F-18) the leading and trailing edge flaps were operated by one servo in each wing.

Larry Wolfe's method for building the leading edge flaps is to have a "leading edge within a leading edge". He will send you the info, or you can find it in one of the Model Airplane News "400 tips" books.

I've created a set of pages, including many contributions by RCU readers, specifically devoted to flaps, slats, and leading edge flaps. You can find it at http://homepage.mac.com/mikejames/rc...ite/index.html

Hope this helps.

Mike: what a cool collection of these devices! I guess it's all about the craft of miniaturization in trying to incorporate all the full size stuff. How far can we be from a true 'fly by wire' system. I think the flaps would be easier to model than, e.g., movable slats. Thought about that for my Skyray, but I understand they welded those shut in the full size as they were problamatic in a dogfight-had a habit of sticking open, I guess. The 'tailerons' or elevons I think differentiate the aileron function from a stabilator or 'all moving elevator' which functions only as an elevator. I'll have to spend some time digesting Mike's info.

I am wondering, Mike, if you can explain -F-16 wing configuration dwg-how the air flow operates in the 'reflex' configurations? I must admit I never heard of it. and it completely destroys my limited knowledge of lift. Is this same group of configs.used on all or some jets? I would personally never attempt anything like that on a model, are any of the RC aircraft using such a setup.

I'm not one of the aerodynamic gurus here... but here's what I believe is happening.

With the F-16 using a super critical airfoil, two things happen:

1. At high speed, (and only at high speed) drag is reduced.

2. At low speed, it serves as a "lift dumper", allowing the plane to accelerate more readily on takeoff, and to "stick" to the ground on landing. (According to some F-16 pilots, this helps keep the plane from bouncing (ballooning ) if you're a little fast on approach. )

PS> I assume that at model size Reynolds numbers, you would skip the reflex, but keep the other configurations.

Would have been nice to have that reflex feature on the few full sized I've flown! Not that I've bounced really, really, high, but......... I note that the max maneuver configuation looks very similar to the pics I've looked at on the SU in flight at higher AOA. Also, the pictures of the SU-27 show the LE flaps in the down position when static, and there is what looks like a pin with a ball end in the root which appears to keep the flap from 'reflexing'. So, I think you're right, I'll go for the two 'down' positions.

wsmalley,

The bottom line is that flaps, both trailing edge and leading edge, allow the camber of the wing to varied in flight to improve performance under various conditions. The most familiar case of this is using trailing edge flaps to dramatically increase camber for landing. The large camber allows high CL, which allows slower, steeper landings. At very high speeds, the wing is operating at very low CL, so that very little camber is needed. I am assuming that the reflexed position shown in the diagram corresponds to the amount of camber which is most efficient for high speed cruise.

banktoturn