Has anyone had experience with leading edge flaps? I am doing a Byron F-18 and am trying to create a scale wing. Any information on the subject would be greatly desired. Thanks,

Matt J

Get ahold of BVM, they have them on there F100

Hi Matt, I remember a few years back, Bob Fiorenze put them on a Yellow Hobbies F-18 and they worked really well, just be sure that they both come ou equally, and use enough servo power to get them out there the same. Also, use a mechcanical stop in the up position so that they are locked in in high speed flight. Bill Harris

I would contact Larry of JHH [email protected] He's done leading edge flaps on a number of his airplanes.

John, the F-100 actually has leading edge slats as opposed to leading edge flaps. Slats physically detach from the wing by sliding on rails (or something similar) where the flaps are typically hinged on the lower surface to allow the leading edge to just drop downward.

OOps, my slip up

Ya know what would be a perfect servo for these? As Bill said "use a mechcanical stop in the up position so that they are locked in in high speed flight". I use programmable MPX digitals on the Isobar flaps and re-program them for 180 degree total throw. Then I set them up so that in the flaps up position, the servo arm is parallel to the push rod. Therefore, at full flap when the servo has rotated 180 degrees, the output arm is again parallel to the pushrod and there is zero load on the servo's gear train. Works great! You could do the same for leading edge flaps.

Hi Jetputz (great name) and John, If I remember right, the Hun has areodynamic slats that come out on speed and AOA like the A-4. I guess were kind of cheating with the servo thing, but they still look really neat. They have a C model Hun inside at the Air Force Museum and you can push on them to see how they work. Pretty cool. Bill Harris

NAA learned about slats from the F-86. PRobably whatever is on the F-100 is very close to what is on the Sabre.

For LE flaps, the hinge moments could be high, which means the servo loads could end up being high, even when at 0 deg. That idea about the over center arm is a good one. That flap will always be trying to deflect up, even past 0, especially at high AOA. Be aware of that, watch your Rx battery power consumption etc.

LE flaps will allow you to go to higher AOA before stall, similar to a slat but not as good. At low AOA they won't make a difference in lift - they really just extend the lift curve.

They are useful for landing approach, getting that nose up to create drag. You could also mix them with elevator and TE flaps for high g turns, not unlike the control line stunt models of old.

So, if you do this, you need a mechanical up-stop where the flap contacts fixed structure directly, so the servo is not straining for the whole flight. Also, using a jackscrew setup would be alot more secure and reduce the force seen by the actuator.

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They are useful for landing approach, getting that nose up to create drag. You could also mix them with elevator and TE flaps for high g turns, not unlike the control line stunt models of old.

You could mix them in with elevator. But using them at high speed, you would probably end up ripping the wings off if you don't strip the gears and spiral in. Combining enhanced lifting power with speed is a recipe for structural failure.

I have an F-18 that I would like to do this with as well, but I would only deploy them at low speed - maybe linked with the gear switch.

You do not necessarily "need a mechanical up-stop where the flap contacts fixed structure directly". As mentioned before, you can use programmable servos programmed for 180 degree rotation. That way you can set it up so that the servo's output arm is parallel to the pushrod load, thereby negating gear train loads at the full up and full down positions.

The fighters use them at high speed for dog fighting, to increase the amount of G they can pull. But they are stressed accordingly. They are limited by the pilot for the most part, but there are places in the envelope where they need the extra lift to turn.

I have a pal who flys the T-33 in the Canadian Forces (stop laughing please! ) and he told me there are speeds and altitudes where he can out turn an F-18. Simply a question of max lift and wing loading. No matter how much thrust you have, your turn radius is a function of lift, so the LE flaps come in handy.

As for structural failure, it all depends how strong your airframe is. You would be increasing max lift of your wing by maybe 20 or 30%. Chances are you are not using anywhere near the max lift of your wing at high speed, the way we fly models, so there is not much point in doing it I suppose.

A jack screw would reduce servo loads but it would be more work to set up.

I tried them this weekend on a F-22 and they work fine, no attitude change at all as long as the trailing edge flaps come down twice as far as the leading in degrees, otherwise the aircraft will generally pitch down slightly.