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Using flaperons......need help

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Using flaperons......need help

Old 06-27-2002, 01:23 AM
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kgetch
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Default Using flaperons......need help

OK...I want to start experimenting with flaperons. My question relates to how the plane will pitch when the flaperons are deployed. When the flaperons are down, will the plane pitch up or down. Bottom line, should I mix up or down elevator.

I know I can count on you all for the right answer. Thanks.

Ken
Old 06-27-2002, 01:48 AM
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tinman
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Default flaperons

hard to say till ya try em with no mix to see what plane does. some will pitch down some up. most likely tho you will need between 5 and 10 percent down elev. -Tin-
Old 06-27-2002, 06:13 AM
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AirplaneDan98
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Default Using flaperons......need help

I agree with tinman, try it with 15% down and test it at altitude. I flip it on and see what happens, then flip it off and adjust when I land. As for which way it will pitch, I think most will pitch up. My modified Uproar will pitch down though, so beware and expect the unexpected. Good luck. Dan
Old 06-27-2002, 01:11 PM
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mscic-RCU
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Default Using flaperons......need help

The theory of flaps is to increase the wing surface area thus increasing lift which will lower your stall speed. The downside is that they also substantially increase the aircraft's drag, which then needs an increase in power to overcome the drag. Contrary to popular opinion, flaps are not speed brakes. If the flaps are applied at too low an airspeed, the aircraft will pitch down. If they are applied at an airspeed above stall speed, the aircraft will pitch up. It just takes practice to figure out what is enough airspeed and what isn't. I have a Telemaster 40 with flaps that is setup for funflys. With the flaps down and in a slight breeze, I can hover the plane and land it like a helicopter.
Old 06-27-2002, 01:21 PM
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AirplaneDan98
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Default Using flaperons......need help

Mscic,

I don't want to start a fight or anything, and I will also say that I don't know a lot about the physics of flight. However, I can put the flaps down on my Uproar when it's at full throttle and it will still pitch down. Like I said before, it's a modified Uproar. I cut the last rib bay out of each panel. Now it has a 38" wingspan instead of a 48". Would this cause it to pitch down with flaps no matter what the speed is? Flaps are almost mandatory with this bird now, and it will slow down super slow with them. Dan
Old 06-27-2002, 04:19 PM
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MinnFlyer
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Default Using flaperons......need help

I think in the case of those Fun-Fly models, the wing is so wide (thereby putting the flaps farther back than a regular plane) that they tend to act a little like elevators, and will make the plane pitch down at higher speeds. I have flaps on my Ultra Sport 40, and regardless of what speed I'm flying, it NEVER pitches down. So, I think a lot of it has to do with the design of the plane itself, and that all planes will act differently.

But I will say this... Put the flaps on! I just love a plane that can slow down to a crawl on landings. With my US40, with full flaps, you can jog next to it and keep up with it! It is a sight to behold!
Old 06-27-2002, 08:13 PM
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Geistware
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Default Using flaperons......need help

A lot depends on the airfoil shape, If the center of lift moves ahead of the center of gravity the nose will pitch up. If the center of lift does not move, the increased drag will hold the nose stable or let it drop.

This is what I have always been told. I trust the information, but I do not have any data to support it. I have experienced both situation with my present and past planes.
Old 06-28-2002, 08:40 PM
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HarryC
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Default Using flaperons......need help

Flaps do not increase wing area, unless they are specially designed to slide out from the trailing edge like most airliners. On models, full size light aircraft, most fighters, etc., flaps make no change at all to area.

Flaps work by increasing the wing's camber thereby increasing the lift co-efficient.

Camber is responsible for the nose down pitching that wings create. That is why symmetrical sections with no camber have no negative pitching, unless flaps are lowered of course. The greater the camber, the greater the negative pitch co-efficient. Applying the flaps makes every wing increase its nose down pitching. That is how tailless planes maintain pitch control. But for a plane with a tail there is the wing's downwash to consider. A high wing, low tail like a Cessna blasts the tail with a powerful downwash when it lowers flaps. If the increased downforce on the tail, with its leverage arm, is able to exert more force than the wing's increase in nose down pitch, the plane will pitch upwards. Where the tailplane is high enough to be little affected by downwash, then the increase in the wing's negative pitching wins the fight and the plane pitches nose down.

So a good rule of thumb is that high wing low tail models will pitch nose up when flap is applied, if the tail is level or above the wing then it will probably pitch nose down.

If the model pitches nose down when flaps are applied, it is pointless using elevator to flap mixing to help in violent 3d manouvres, since the flap is reducing the pitch rate and you get a faster pitch rate from elevator alone!

Harry

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