Hey Guys,

Just curious, What would be the effect of instead of having full span flaps? If they where moved to say the Alieron area on the plane. Near the wingtips.

I have seen where some Europeans and Chinese have been flying 1/2 flaps near the inboard wing area. Next to the fuseluge.

Issue I could see that could cause a problem. Would be the torqueing of the flap horn needed to reach the outboard section. And create an alieron roll effect. If one flap torqued slightly. Other than that, what else?

Wingtip turbulance?

Thanks
(Just tossing around new ideas/ or very old thoughts)

Apart from the aileron roll affect (which would be quite likely) flaps are only used to gain lift from the wing so in theory they could be mounted anywhere along the span of the wing if they were large enough to give whatever increase in lift you needed. On an RC model the ailerons are out close to the tips because that's where the greatest leverage is to roll the model.

What's really needed with flaps is to have them large enough to give just enough extra lift needed to overcome any tendency to stall in the hardest of corners but with the smallest movement possible because any deflection adds drag which slows the model down right when you don't want it to slow down.

Downunder,

What about the amount of deflection ? I have plans that show equal deflection for flaps and elevator, others show far less for flaps (which makes more sense to me). Presumably it would depend on the amount of flap area but is there an ideal ?


Luke S

Generally flaps are use only on the inboard section of the wing. The reason is that while flaps increase a wing sections maximum coefficient of lift, that maximum is achieved at a LOWER angle of attack. A wing section that, when clean, may stall at 16 deg AOA may now stall at 14 degs with flaps; however, at 14 deg with flaps it will be producing more lift than when at 16 deg clean.

What this means in practical purposes is that while you may achieve more lift for slower flight with outboard flaps, you run the risk of stalling the outboard section of the wing first and thereby loose roll control (the dreaded tip stall). You would not want a wing that stalls the tip section 2 deg before the root section.

As a side note, slots and slats are just the opposite. That is, they increase the maximum lift (like flaps) but they INCREASE the stalling AOA. That is why you generally see them near the tips of a wing.

Bill Vail

Additionally, consider that the increased lift is to help achieve a smooth but tight turn (the old unattainable 5' radius turn) and would impose a tremendous stress on the wingtips which could (would?) make the wings break and fold in flight.

I think there is a reason why the guys who are much more knowledgeable than me put them close to the center if using partial flaps.

Another consideration is that flap tweaking is a means of adjustment. It may be a bit harder (more sensitive) if done at the ends.

I would not recommend it, but if you give it a try, let us know your findings. Good luck.

George

Obviously the deflection needed is going to vary from model to model but from what I've found the ideal seems to be to start off with a very low wing loading and then use quite large but adjustable flaps to do the final tweaking to get rid of any perceptible stall in the hardest possible turn. The flap adjustment I use is completely seperate from the elevator so if I adjust the flaps then it has no affect on anything else.

The first time I used this system I set the flaps for zero movement and did a few test flights gradually reducing the elevator movement until it felt comfortable to me. I ended up with +-17 degrees but there was a trace of stalling in the triangle and hourglass so I started dialling in a bit of flap movement. With only +-5 degrees of flap it was perfect. So for my model an elevator to flap ratio of about 3.5:1 was all that was needed.

What really surprised me was how much the effort at the handle increased by adding just that tiny bit of flap compared to no flap movement. As a guess I'd say it increased by 2-3 times but it was still very easy to turn.

This is the model I was using. About 830 sq inch, 59 ounces with a tail moment of 21.5" and an ST G51. The other photo shows how I adjust the controls through an access hatch under the fuselage (a different model but same design).