hiflyer45

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I'm building a pattern plane. Actually, it's going to be a modified Curari. My question is can I add flaps to the wing, which will be a fully symetrical airfoil. I've read that flaperons could cause an unstable condition by adding negative washout. So would flaps cause unstable conditions at low speed (landings)? The original Curari had a spoiler type flat setup which I want to eliminate and just go with the flaps. Also, the anhedral stablizer I would like to keep (looks cool). Does this have any unfavorable flight stabilities or positive flight characteristics?

Thanks

pimmnz

You can use the original flap set up without the spoiler bit added. You will need to mix down elevator with flap if you do this. (Mine pitches up even with the spoiler bit added). Without flaps it lands fast, even with the tail dragging before the mains touch and mine is light (6.75lb). There is no problem with the wing section, the flapped area just changes camber and adds drag, which this model really does need. Slow flight with flaps down is very stable and needs just a trickle of power to maintain height. If you need to go around, open the throttle slowly and add just a little power, if you bang the throttle open the nose will pitch up real steeply. The anhedral tailplane has no detectable differences from a straight tail, but it does look neat. What I find is that the model does need to be very deliberately flown, but responds like a arrow when you do, i.e. it goes exactly where you point it, whether you meant it or not. Once trimmed you will enjoy the thing.
Evan.

mulligan

A little more feedback on flapersons and the washout aspect...

With typical wings, they can be designed such that the inboard portion of the wing will stall before the outboard portion- this is done either by using different airfoil sections at the root and tip or by twisting the wing such that the root always has a slightly higher angle of attack. This allows the ailerons to still be effective when the wing begins to stall (as the outboard of the wing is still "flying" while the inboard portion is stalled).

When you add flaps to the inboard portion of a wing, this simply adds to the above condition. Of course, the flaps greatly reduce stall speed and enables slower landings/steeper descents; and they do not take away from the desired early inboard stall characteristic.

Adding a flap mix to your ailerons upsets this desired early stall characteristic. By using flapersons, you increase the angle of attack of the outboard portion of the wing relative to the inboard portion (unless the ailerons run the full length of the wing). So, it is possible to cause the reverse of what is desired... the outboard portion of the wing will stall early. If this "tip-stall" occurs, the ailerons lose their effectiveness, and the plane may be uncontrollable once the stall begins.

Having said all this, it may or may not affect your plane significantly depending on how much flap is used, the geometry of the wing to begin with, etc. I am not familiar with your plane, but as it's a pattern ship, I would guess everything is symmetrical and no washout is built into the wing... which means your are starting with everything neutral... so you would certainly be adversely affected by adding flaperons. It is not a great idea if you can avoid it. Use flaperons only if you can't land without flaps, you cannot add traditional inboard flaps, and/or if your ailerons are the full length of the wing.

hiflyer45

My Feedback: (2)

George, Thanks for the reply. I would like to discuss further with you. Could you give me your email address so I can email you? Thanks.

Tom