This might be a totally dumb question.... but i'm just here learning so no one be mean lol..
I am wondering can you place an elevator or rudder on the leading edge of a stab instead of how it's commonly done connected to the trailing edge of the stab. I've seen some aircraft like this.. or what i thought was this .. like the russian Sukhoi i think it's the SU-27 forward swept wing aircraft. But maybe those were spoilers and not alierons on the front.

Is there anything to be gained or lost on an aircraft by putting elevators or rudders sweeping off the leading edge of their respective tail surfaces. Also what about Alierons on the leading edge. Or does just not make any kind of practical sense??

PA

Oh PS.. can you rush an answer hehe.. cause i'm kinda trying to figure out if I should mess around with this or scrap the idea right away.. thanks...

Paul

I suspect it would try to tear itself apart. On a normal elevator when it is deflected downward, the air loads try to push it back up, ie., it tries to return to neutral. Another term for this tendency is that the surface is stable. Now imagine an elevator on the leading edge. When it deflects down the air load will try to push it further down. If the air load is great enough,and the control linkage weak enough, the elevator will flip clear over backwards. Note that an all flying stab, the stabilator, has more area behind the pivot point to provide the stability. I used to own a full size Cessna 170. It had a warning placard that prohibited "whip stalls." These are close to tail slides. Cessna didn't want pilots to rip that great big rudder off by "flying" backwards.

Hey, experimentation is what it's all about-within reason, of course! I think R8893 has pretty well summed up this concept, but if it doesn't compromise safety or your wallet too much, EXPERIMENT!
My friend Pete ("jmupilot" on here) once made a plane with a "T" tail , (stab sitting on top of the vertical stab), and it was a "full flying stab". No elevators, the whole thing changed incidence. I saw the first flight of it. The linkage wasn't quite stiff enough to hold the stresses imposed on the stab when it changed incidence. It would fly fine up to a certain speed, then the stab would start occillating up and down at a very rapid rate, and the plane responded accordingly, jumping up and down about 5ft. very quickly. Cutting the power would stop the problem. It was funny as hell to watch. I was amazed that everything stayed together in the plane. Pete and I also had a joint space shuttle combo we flew successfully. I flew a Telemaster with his shuttle atop it, complete with Estes rocket assisted take off. I'd take him to altitude, disconnect and he would fly the shuttle back. We even have that on video tape. Two successful flights. We won't talk about the third. Pete also has a plane with forward swept wings, but I think the ailerons are on the back of the wing. It appears to fly well. Hey, go for it!
Randy

There are a few reasons why this hasn't been used.
First, as has been mentioned, the air loadings tend to make the surface deflect more.
Second, if there is even the slightest amount of slop in the system, since the control tends to deflect, you will probably be hunting around neutral. In inedxperienced hands this could lead to an uncontrolled porpoise.
Third, I have used the full flying stab before. Works fine. You do have to be careful on the pivot point. As I recall, about a quarter of the way back is a good pivot location. It could be that your friend had the pivot point too far back.

The T-tail plane you mention, there are reasons why you do not see vary many of this configuration. First, the stab is in an easy-to-break location. Next, the T tail configuration tends to barrel roll. As the plane rolls about its longitudinal axis, the stab moves in a circle, scooping air as it does causing the barreling out of the roll. People prefer a plane that looks nice in a roll so 99% of the planes don't have them. The T-tail does get the elevator out of the wing wash, making is more sensitive than a conventional tail.

so i'm still a little confused curious.. then why does the Sukhoi S-37 have alierons or something on it's front leading edges of the wings? Are these control spoilers?


ViperRed

Many planes as far back as the F-86 had leading edge slats or high lift devices for maneuvering to prevent high speed stall. These weren't for control, but for added lift. I also recall the Messerschmidt Me-262 had these. Swept wing planes tend to have bad stall characteristics and the slats help keep this under control.

The early jets had the slats balanced where g forces would deploy them and normal level flight air pressure on the leading edge would retract them. They had to be checked, and maybe adjusted, every flight or they could hang up.

Later planes used hydraulics. You'll find modern planes have a triple or four times redundant computer system to make sure these things don't get out of control. Our servos are not as powerful or as tight as hydraulics. Neither do we know the forces on the control surfaces. I suspect they would go up at least exponentially with deflection. It would be nice to have telemetry from the servo and graph force vs. deflection.

We are also limited to what we can see. Modern jets take the control stick pressure and do what you want. It's like the computer is saying, "My little buddy in the cockpit wants the plane level so I'm going to move the surfaces to level it." It can dampen out oscillations and it can hold a forward control surface right where it is supposed to be. With our RC planes, you stand a chance of getting in a position where the servo does not have enough force to move the control back to neutral.

If you have a control linkage failure, and I have had several in my many years of RC and CL flying since 1950. I have yanked servos out of the wing doing snap rolls at very high speed and I've nad every part fail at one time or the other. I will say that the hardware you can buy now is a great imprevement over what we had. If you have a failure, a normal control tries to streamline. With a forward control, it will go to full deflection. This is the reason why the pivot for a full flying control like a stabilator is forward of the aero center.

But, if you do try this, please let us all know how the experiment comes out.

The aircraft you have pictured has leading edge slats. as Ed stated they are for additional lift in high angle of attack manuevers. The aircraft pictured I am sure has computer controlled slat deployment. Puting control sufaces on the leading edge of the elevator or rudder would be almost impossible with the material used in our hobby. I'm sure that the newer digital servos would have enough power to move them but the structure needed to keep the movable surface in place would be heavy and and hard to build. As randy (rryman) said I like to experiment with all kinds of models and configurations. Some worked and some didnt. The swept forward wing airplane i have does fly nicely, but roll rate is allmost a blurr. When first built it 15 years ago, I didnt have the opption of a computer radio to help with mixing and exponential rates. These features have tamed the beast to a very nice flying aiplane. The germans had swept forward wing jets on the drawing boards at the end of the WWII , but they didnt have the materials needed to keep the wings on the airplane at that time. A forward swept wing wants to rip right off the at the tip. Carbon fiber and titanium extrusions used by the Russians and the US in there respective sweep forward designs have made these aircraft possible today. But they too have to be flown by a pilot that inputs the controls into a computer and the computer moves the control surfaces needed in the correct direction to make the airplane flyable. i have pics of the forward swept wing plane, but this is twins and multis so i'll not post pics of it here unless asked to do so by the group.


Pete