Help! High lift devices for rc planes

[.WARHAWK.]

Hi , I am designing a rc ground attack-trainer jet ( edf ) (1.2 meter length) and I want it to be highly manueverable and to be controllable at high angles of attack ( < 30deg )
I also want it to be relatively fast ( 100 km/h ( for some this is slow.. ) )
the wings are slightly swept with straight trailing edge, and aspect ratio is 6.
CFD will be used

Currently I am thinking of using LERX , 4deg washout and vortex generators.
What kind of high lift devices are most suitable for this role ( preferably not moveable and not mechanically complex ) ?

 

[leaded50]

Vortex generators, or stall fences, even a "dog-tooth" at the trailing edge , or a few leading-edge cuffs could be of help on charateristics. 4 degree washout is perhaps too much (?) mainly 2-3 degress seems best for rcplanes, depending on type. LERX does help impoving on wingload.
Vortex, and leading edge slats is mainly recognized as good support for high lift./slow speed manueverabillity.

 

[Monte.C]

Vortex generators, or stall fences, even a "dog-tooth" at the trailing edge , or a few leading-edge cuffs could be of help on charateristics. 4 degree washout is perhaps too much (?) mainly 2-3 degress seems best for rcplanes, depending on type. LERX does help impoving on wingload.
Vortex, and leading edge slats is mainly recognized as good support for high lift./slow speed manueverabillity.

I agree, a few differential cufflinks 3-4 degrees wash dry & fold Lexus resperometer Flux Capacitator Vortex Spiral In through the out door What's your clearance Clarence?

Just kidding. I'm bored.

 

[Pieliker96]

Washout makes it structurally easier by decreasing load on the wingtips, A bit more than usual for something that'll be pulling a lot of Gs is fine, although it will hurt span efficiency a tad. I can attest that VGs are wonderful for delaying flow seperation at high AoA.

You'll probably want some large (possibly all-moving) tail feathers for decent control at low speeds - remember, EDFs don't have any propwash to artificially increase control authority, airspeed is life. Adding thrust vectoring would be neat but probably isn't necessary unless you plan on having good control during post-stall maneuvering.

leaded50 has got a good list of static devices which will likely improve high-alpha performance. Due to how aerodynamics tend to work, moveable systems tend to be much better for high-lift. They can be configured for both high and low speed flight, improving performance in both regimes (as opposed to coming to a compromise). Something like a simple offset-hinge slotted flap is just slightly more complex than a traditional control surface but provides a much more significant change to the coefficient of lift than any of the static methods. A simpler option (less effective than a slotted flap but miles better than nothing) is to just turn the inboard bit of the trailing edge that isn't aileron into a flap.

 

[L Edge]

Agree with Pieliker96 that movable systems can be configured for high and low speeds.

Another device for an EDF is the 2D gimbal thrust vectoring nozzle. I have used this device where you can shut it down doing high speed and when engaged, gives excellant control at high alphas. If used in forward flight, adds tighter acrobatic maneuvers.

 

[Fluburtur]

I know flaps are technically movable parts but so are ailerons so adding flaps wouldnt be much more trouble and they will help a great deal.
I plan on eventually making some plane with leading edge slats, they would be somewhat easy to make with a 3d printer.

 

[L Edge]

I know flaps are technically movable parts but so are ailerons so adding flaps wouldnt be much more trouble and they will help a great deal.
I plan on eventually making some plane with leading edge slats, they would be somewhat easy to make with a 3d printer.

That is another approach. To reduce drag for high speed, throttle controls position of slats where past 1/2 throttle, flaps retract to reduce drag. To get high alpha, slower landing speeds plus high manueverabillity , less than 1/2 throttle to a low idle it increases the slats and foots the bill.
Now in the process of automating the slats so anytime pitch is added, down come the slats and improve the tightness of turns, takeoffs and landing. Now want to combine slats and flaps to see what happens.


This is one of the videos that started my quest for automation. First played with fixed down slats, then variable with throttle and as technology improved, now into automation.

Watch closely the leading edge, see it change when only pitch is applied, to/turns/landing.

 

[MacTuk777]

The LERX will provide alot of added maneuverability even with no additional modifications........They will probably be the best bang-for-the-buck solution. I built a Steve Shumate F-18 many years ago and added leading edge flaps and full span flapperons to it. It was almost 1/3 heavier than the design specs but after I figured out the mixing it would turn ridiculously tightly and land at a walking pace.

Also if your model has nose up pitch tendencies with flaps extended (like Zephyr1’s MiG21) it is easy to fit plain flaps and mix flap to elevator to improve pitch rate and tighten turns. Plain flaps have always worked well for me for this and they help keep landing speeds down to boot!

You might also try a “paddle” placed directly in the EDF eflux. Slave its servo to either elevator or rudder and it’ll give you a thrust vectoring effect without the need for any complex gimbal - like the X-31 (not pretty - but REALLY effective in both yaw and pitch. I only tried this once, but it was impressive). This setup allows for control even when the conventional control surface the paddle slaves to is stalled/blanked by the wing or operating at such low airspeed that its ineffective. It’s a cruder, uglier option than L Edge’s edf nozzle, but easy to build and remove if you don’t like it.

Also a saw-tooth notch and outboard droop configuration like the F-106 or the EE Lightening will give an effective under-camber with wash-out at the tip and act as an aerodynamic “stall fence” allowing you to pull harder in turns with less chance of tip stalling. I figured this configuration would create alot of drag but best I can tell from tinkering with the 106 it really had little effect on level flight speed.

good luck, Mate!

 

[Fluburtur]

You can do spring loaded automatic slats, past a certain airspeed they will be pushed into the closed position.

 

[.WARHAWK.]

You can do spring loaded automatic slats, past a certain airspeed they will be pushed into the closed position.

I really like this idea but this would work for a bigger plane
at this size , such mechanisms are very difficult to create and fit

Another Idea I had , was to connect flaps to a spring. When airspeed is low , the spring overcomes the force from the air , and the flaps go down . When airspeed is high , the force of the air is bigger than that of the spring , so the flap goes up.
This however may be a false concept and to validate it , I need some experiments.

 

[MacTuk777]

I think that would be a fun project! maybe try to use the spring out of a pen? It may require some kind of bus system to prevent differential deployment.......maybe a popsicle stick connecting the inboard flap sections together somehow?? Only downside I can see is you may get unexpected pitching moments as the flaps change position that might catch you by surprise - especially since you wouldn’t know when or by how much they were going to deploy......

 

[Fluburtur]

If you have a plane that isnt too short coupled the automatic flaps could work, worth investigating