Snap flaps - RC Groups
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May 29, 2002, 12:31 AM
Tragic case
davidleitch's Avatar

Snap flaps

Getting ahead of myself as usual.

Is anyone using snap flaps on a hotliner and care to share some of the benefits?

I read that some of the slope flyers do this. Ie upelevator is coupled to down flaps and vice versa, in the sports plane forum its fairly common.

I plan to try it on my cheap foamie first (crazee max) and then work it through to the Spiro.

What would the benefit be over just increasing the elevator travel?
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May 29, 2002, 10:28 AM
around Colombia
ShredAir's Avatar

Snap flap is effective only for a few gliders, such as F3F/B type models. Even there, it is imperative to first dial in the plane properly in terms of CG.

It'll have no beneficial effect on your Crazee Max.
Your 10-cell Spiro has an airfoil and planform, and relatively light loading where experimenting with snap flap starts making some sense. First though, make sure you get the plane to fly as neutral as possible, by moving the CG back as we discussed. Only then can you determine if snap flap on this plane actually does something for you.

May 29, 2002, 05:57 PM
Tragic case
davidleitch's Avatar
Thanks Dieter

Actually the crazee max will have a lot lower wingloading than the Spiro.

I calculate the Spiro at around 15 0z sq ft. Crazee max (a toy foamie 8 0z) Its interesting that over in the sports plane forum a lot of the new hovering geared aerobatic planes have wing loadings not that dissimilair to hotliners. for instance one of the Cap 232 s I was looking at is around 19 0z. I worked out Vijay Rams new wonder toy at about 14 0z

Clearly getting the Spiro trim fully dialed in is number one priority. Like I say just get ahead of myself.

In terms of aerobatic performance, snap flaps are supposed to give square and tighter loops, and I was just trying to understand what the advantage was over more elevator travel.

They certainly don't seem to be in common use in the hotlining field.
May 29, 2002, 06:26 PM
Registered User

Just a Guess


I'd seen this idea of using flaps in combination with the elevator as well. I don't fly any model planes with flaps, but can take a guess as to why people use this technique.

With real planes, flap deployment to about 20 degrees typically gives extra lift, beyond that you also get a lot more drag! As you deploy the flaps, you get a pretty good nose up on the aircraft and typically have to trim it back down again. This, as I understand it is because you're getting a lot more lift from the wing (hence the reason your stall speed decreases since the wing is more effective at slower speeds).

If you combine more lift from the wing with a down force on the tail, your basically hitting the plane with up in the front and down in the back to change directions that much faster.


May 30, 2002, 10:55 AM
around Colombia
ShredAir's Avatar
I'm wondering if you're thinking of snap flap as used in an aerobatic power plane; It won't work like that in a glider.

In a glider, you first have to have an airfoil that won't just add drag when camber changing at high speed, and then you will use only a few degrees down-flap and almost none up.
On the Stratos SR F3F racer, for example, the most radical snap flap I've seen is 5 mm down-flap and 3mm down-aileron measured at the trailing edge and at the tips. Reflex (up-aileron and flap) is minimal, less than 1 mm.

This snap flap business is a rather personal thing. I always ALWAYS first get my plane to handle as well as possible (the way I like it; it's personal), and them I may experiment with snap flap.

May 30, 2002, 11:14 AM
high-speed freak
opualuan's Avatar
ok, I give up. what is a snap flap? are we talking about a standard flap, one in a different location, deploying a flap quickly, what? I figured I'd understand by listening in, but I'm a bit confused...

sailplane nut in training.
May 30, 2002, 07:45 PM
around Colombia
ShredAir's Avatar

You're asking the wrong guy... but the idea behind snap flap in slope racers is to help turn the plane rapidly without loosing speed. As such, it is programmed to rapidly deploy when the pilot really yanks on the elevator. The flap does not deploy in normal flying with gentle elevator inputs.


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