Author Topic: Flap to elevator ratio? (Read 888 times)

Gary Anderson · « **on:** September 16, 2008, 11:50:09 PM »

Hi guys,

I'm bench trimming one of my junkers and someone told me to trim a touch of down in the elevator. We never used to do this but a lot of the different system had a little slop in the system and your plane would find neutral. I use all ball joint type hook up's and there isn't any slop. I flew my Stiletto set up this way and she seemed to love it. Fuse looked level both ways. I just can't remember the reason for doing the controls this way. Does it have something to do with the torque of the engine? Is each plane different? Would appreciate any input, thank you Gary

Mark Scarborough · « **Reply #1 on:** September 17, 2008, 09:33:15 AM »

To my knowledge, the reason behind this has to do with the fact that our planes have symetrical wings and require some angle of attack to generate lift. Hence on a flapped airplane by setting the elevator with a bit of down relative to the flaps when you neutralize the elevator the flap now is down a touch which creates some positive angle of attack on the wing while the airplane is still level relative to direction of flight. I beleive this is where the stabilizing affect comes from. I do know on several of my flapped planes, this trick has helped calm it down in level flight. However, I do beleive that what Ty says is also a factor.

Gary Anderson · « **Reply #2 on:** September 17, 2008, 10:11:59 AM »

Quote from: Ty Marcucci on September 17, 2008, 08:57:19 AM

From what I remember, it has to do with how the air coming off the prop will hit the stab and want to push it down, thus the nose up. By putting in a trim amount of down in the elevator, it counteracts this force. Also the stab has its own asirfoil and most tend to lift, as they should, and again, that little trim amount of down will counteract this as well.

Engine torque or prop precession tends to make the plane roll more than climb or dive. Or so that is how I undestand it.

Hi Ty,

You're probably correct, the only thing that keeps going through my mine is, when the plane is upright you have a little down but when you're inverted you have a little up. It seems to work both ways, so I wonder if what you state is correct but maybe has something to do with the location of the stab section to the wing! I know it works, just an interesting set up. I know Ted or Brett could explain the reason. I do a lot of different things cause they work, just don't alway understand why. Just me, Gary

Dick Fowler · « **Reply #3 on:** September 17, 2008, 08:49:59 PM »

Current Theory... The plane flying in a circle about the pilot is undergoing angular acceleration. The gyroscopic effect of the prop combined with the angular acceleration creates "gyroscopic precession" which generates a nose up pitching force when flying CCW (upright) and a nose down pitching force when flying CW. Thus a little down creates a counteracting force for either direction.

Steve Helmick · « **Reply #4 on:** September 23, 2008, 06:43:08 PM »

I can tell you from personal experience that 1/2 turn of a 4-40 ball joint or clevis at the elevator can change a model from barely flyable to a sweetie pie, so go slow and keep twiddling with the beast until it works!

Steve

Air Ministry . · « **Reply #5 on:** September 23, 2008, 07:25:56 PM »

Apparently . . . .

Theres a bit of downwash off the wing.
A low mounted Stab. would require a bit of up elevator ?

Author Topic: Flap to elevator ratio? (Read 888 times)

Gary Anderson

Flap to elevator ratio?

Mark Scarborough

Re: Flap to elevator ratio?

Gary Anderson

Re: Flap to elevator ratio?

Dick Fowler

Re: Flap to elevator ratio?

Steve Helmick

Re: Flap to elevator ratio?

Air Ministry .

Re: Flap to elevator ratio?