WING ELEVATORS

[raby fink]

Can someone explain the physics behind wing elevators. I know they work opposite of the elevator. Someone told me that they cause the front of the plane to stall allowing the back to go up or down faster. I am curious as to how they work and the physics behind them.
Thanks
Raby

[John Stiles]

Can someone explain the physics behind wing elevators. I know they work opposite of the elevator. Someone told me that they cause the front of the plane to stall allowing the back to go up or down faster. I am curious as to how they work and the physics behind them.
Thanks
Raby

It has been my experience that anytime I added wing flaps, it decreased the radical[sharp] reaction of the plane. One plane that I noticed was a great trainer for my beginning pilots was the Nobler! When in flight, it was like on a rail.....we never saw a loop out of this plane, and we were using 65' of leads. The plane lit down as soft as a butterfly, and we made thousands of laps before the fox .15 gave up its piston. I have a sportsterized Ringmaster now that I added flaps to, and I have noticed the same result.....just a very stable flight....it does inverted flight as well, but so far....no loops have been attempted by me, noone in my bunch wants to try the plane, they rather like radical transitions. This may be correct, or maybe not, it is just my experience.

[George]

Can someone explain the physics behind wing elevators. I know they work opposite of the elevator. Someone told me that they cause the front of the plane to stall allowing the back to go up or down faster. I am curious as to how they work and the physics behind them.
Thanks
Raby

Raby,

The ones on the wings are referred to as flaps and are used to increase lift on sharp maneuvers to provide a sharper turn.

George

[Steve Helmick]

The deal is what Ty said...the flaps cause a "negative pitching moment" opposite the desired direction (the direction the elevators make the model turn). This is why large flaps used to be thought to make for soft corners (i.e., Nobler) while small flaps were thought to make for more acute corners (i.e., Thunderbird). 

The actual fact is that the tail moment (distance from wing center to horizontal tail center) was too short, and the horizontal tail was too small for the flap size. Modern designs have bigger flaps, but also longer aft fuselages, and larger horizontal tails. They will do extremely hard corners without stalling. The flaps function to increase lift, to make the corners smaller, at the expense of more drag. The drag is overcome by more power and low pitch propellers, which will accellerate the model back to cruisin' speed quicker.

The ImpAct is an excellent example of such a design...I haven't flown one, but I have judged them many times, under the control of many pilots. It's on my "to build" list...they work well for everyone!  Steve

[Brett Buck]

It has been my experience that anytime I added wing flaps, it decreased the radical[sharp] reaction of the plane. One plane that I noticed was a great trainer for my beginning pilots was the Nobler! When in flight, it was like on a rail.....we never saw a loop out of this plane, and we were using 65' of leads.

     It decreases the speed of the pitch rotational motion if you don't change anything else. But to tight corners,  you have to have two things - a rotation rate AND enough lift to change directions. The flaps help create more lift, and more importantly, more lift at a relatively low angle of attack. That's why you relatively few competitive stunt planes without flaps.

   The flaps tend to make the airplane pitch the wrong way, and the Nobler was always noted for rather soft cornering. That's mostly an illusion, because it doesn't pitch the nose around as fast. Other airplane *look* like they turn quicker because they aim the nose a different direction sooner, but they actually keep sliding for a while after you get aimed the right direction.

     The flaps tend to inhibit the pitch rate, but compare the tail length and area of current airplanes to the Nobler. The Nobler tail is relatively tiny compared to current airplanes. The reason is that we are trying to giver ourselves more torque to overcome the flap pitching us the other way. My airplane (Infinity) and the Impact, have relatively large flaps by current standards but much more tail volume than most and I can assure you they turn WAY tighter than you need them to!

     Brett

[Joe Yau]

It has been my experience that anytime I added wing flaps, it decreased the radical[sharp] reaction of the plane. One plane that I noticed was a great trainer for my beginning pilots was the Nobler! When in flight, it was like on a rail.....we never saw a loop out of this plane, and we were using 65' of leads. The plane lit down as soft as a butterfly, and we made thousands of laps before the fox .15 gave up its piston. I have a sportsterized Ringmaster now that I added flaps to, and I have noticed the same result.....just a very stable flight....it does inverted flight as well, but so far....no loops have been attempted by me, noone in my bunch wants to try the plane, they rather like radical transitions. This may be correct, or maybe not, it is just my experience.

Just wondering if you have tried adding tail weight to move the CG back or not?  My first test flight on my flapped Flite Streak felt very nose heavy..  (CG was about 2" from the LE)  It was till after I moved the CG further back on the FS before it could do the tight corners.

[John Stiles]

Just wondering if you have tried adding tail weight to move the CG back or not?  My first test flight on my flapped Flite Streak felt very nose heavy..  (CG was about 2" from the LE)  It was till after I moved the CG further back on the FS before it could do the tight corners.

Thanks Joe, no I had,nt thought of that[none of my planes have ever had weight added except for a "Dallas Doll" kit I built that couldn't land at all without a chunk of lead glued to the underside of the fuse]....see, I'm a rank amateur...I came here to learn, and you have made my day!! Thank you very much Sir

[Neville Legg]

I have a an aerobatic slope soarer fitted with flaperons, coupled to operate like a C/L stunter and it didn't turn any tighter than with only elevators! I then tried them as flaps, disconnected from the elevators, when they were drooped the nose dropped and the model tried to bunt! when raised the model just staggered around with its nose pointing skywards. So why don't we have the flaps and elevators moving in the same directions? I never did try this on the slope soarer!
This slope soarer had a fully symmetrical section!

Cheers     Neville

[Brett Buck]

So why don't we have the flaps and elevators moving in the same directions?

   Because you will create a situation where you are trying to turn corners using airfoils cambered the wrong way.

       Brett