Brett
That is why you have to static balance it.
The flap has nothing to do with it.

Minisota
I did not know combat planes were sensitive, unless something is amiss.
Quick but not sensitive.
You should be able to fly the fuel out with your eyes closed.
Need to have them open during launch and landing when line tension is low.
The hing at the LE was quick and easy.

Static Balance will also cure or at least help reduce flutter.
If you hear a buzz with a leaned out setting it is probably flutter even on conventional setup.
This can be fixed with a control horn mounted at hinge line and attaching a wire to horn that extends some distance (1in?) ahead of hinge line and adding weight to forward end of wire until surface balances slightly nose heavy at the hing line.
Flutter is destructive.

David
51336

I suppose "quick" is the more descriptive word. To me that relates more to airspeed; "sensitive" to me doesn't mean "unstable", but that it will jump with minimal control input. My combat wings would fly "eyes-off" of course, by feel, and go where you pointed them--right now.

I experimented with counterbalanced tails (hinged behind the LE), as did many others, and concluded there was no advantage, for me anyway.  Perhaps there would be for stunt ships, I don't know.

Hi Ray
I did set my controls up where allot of hand movement was required and did not limit the controls with stops.
Never know when that extra speed killing turning radius might be needed!
The balanced surface kept the drag down with less total movement required.
I used Hot rock small handle and 1-1 1/2 tall control horns set up so that several inches of line movement would give something like 1/4 inch at the elevator.Just ball park guess on these linkage ratios--been a long time--34 years!

On stunt planes with the higher polar moment of inertia (bar bell effect?)I would think that the flying stab would be an advantage.
With more power to start and stop rotation and less drag to reduce slowing in the corners.
only experiments and development will  tell.

I am just now getting into stunt for the first time and will probably wind up designing something in next few years
And being a guy that tries wild wacky stuff the flying tail will probably get included somewhere along the way.

Now to go see how cantankerous this Fox .35 in the Smoothie wants to be!

David
51336

Brett
My limited knowing of things---

Depends on the center of pressure of the stabilizer airfoil.
25 % or forward would be a good starting place that's for sure.
If it was me I would probably start at 20% with any, even a selected airfoil because there is no way I am going to do the Reynolds number math!
Picking an airfoil that the Center of pressure moves the least is a good starting place also.

Playing with different nose heavy settings might help also.
To much may make it pull to the inside of turn. Just shy of that point might be a good setting?
The C/P may even counter this as the C/P moves back with added angle of attack.
I may have the last backwards on the movement /angle) can look if you need.

Just my opinion from playing with toys! (the jumping smiley face thing goes here when its not broken)

David
51336

Brett
My limited knowing of things---

Depends on the center of pressure of the stabilizer airfoil.
25 % or forward would be a good starting place that's for sure.
If it was me I would probably start at 20% with any, even a selected airfoil because there is no way I am going to do the Reynolds number math!
Picking an airfoil that the Center of pressure moves the least is a good starting place also.

   Exactly right - but if you look at almost any conventional airfoil, the CP is very close to 25%. So I don't think we are disagreeing.

     Brett

David,


Long elev horn radii help, but do not cure a basic negative: without a fixed stab, YOU hold the model to its path, every instant and all the way.

An interesting "balance" or compromise problem involves stabilator area. If anywhere near the tail area of a stab+elev model, it will be hard to restrain motion in a way that prevents overcontrol. If only of enough area to do everything you need in calm air conditions, tail power may not be enough to make a high-g recovery like inthe bottom turns in the Triangles, Hourglass or even the Vert 8. There, you can too easily "dirt-track" right into the ground.

There are easier ways to fly CLPA....

Not quite true, Lou.  The area of the surface, whether it is a stab/elevator or stabilator, is what contributes the stability.  If you wiggle your hand, the plane will wiggle, whether is has a stab/elevator or stabilator.

Whether you use a stab/elevator or stabilator, the force on the pushrod is determined by the position of the stab hinge line or the stabilator hinge line, relative to the chord.  Wild Bill's articles detail the calculation.  You can set the pushrod force using the same graph for both configurations.  On a stabilator setup I just used the % ahead of the hinge to offset a similar percentage behind the hinge and it worked out fine.  If the plane doesn't turn as well when it speeds up you've run into the Netzeband wall.  You have to use a larger bellcrank and horns to reduce the pushrod forces until you always can generate more than enough force to move the surface.  Or move the balance point back so less force is needed(which can make the plane twitchy).  A combat style stabilator, hinged at the front, is very sensitive to speed and balance point.  Moving the hinge back to 15-20% of chord is much easier to manage.

The biggest advantage of a stabilator is that, if you have the correct hinge position and control geometry, you can adjust the sensitivity for a wider range of CG positions.  The stab/elevator can run out of oomph if it is too small, to the point where you may not be able to get both stabilty and turns.  The newer 25%+stabs don't have that problem.

The biggest problem with a stabilator on a bigger plane is, as Brett pointed out, it's hard to build a strong, light, tight bearing setup when the plane gets much over 48 in.   And a sloppy hinge will give less precise flying, obviously.

Not quite true, Lou.  The area of the surface, whether it is a stab/elevator or stabilator, is what contributes the stability.  If you wiggle your hand, the plane will wiggle, whether is has a stab/elevator or stabilator.

Whether you use a stab/elevator or stabilator, the force on the pushrod is determined by the position of the stab hinge line or the stabilator hinge line, relative to the chord.  Wild Bill's articles detail the calculation.  

    The same point I was trying to make above, although mine was not as clear. The area has to be the same for stability reasons. If it's too sensitive, cut down on the throw. That was the mistake most people made early on - moving the whole thing instead of half makes it about 3x as effective, or conversely, you get the same rotation rate/torque from ~1/3 the deflection.

    The airplane at the top of this thread, as I recall the sequence, originally had the elevator at 1:1 and pivoted around the 50% point (which is about what it shows there). That didn't work too well, for all the reasons delineated in this thread. Eventually, it got extensions on the TE of the elevator to move the CP to the pivot, and the throw cut in about half, and then it flew pretty well, at least as good as it would have with a conventional tail.

    I saw it fly in about 1999-2000 at the WAM El Cerrito Flying Dons "Eat Chili and Fly day", by David W. "Bill" Fitzgerald himself, and it flew just fine. May have been Bill's last model airplane flight.

    Brett

Note:

If I ever build an electric plane it will have a flying stab, not sure but could have a forward canard too?  Ouch, I think I would have to reinforce the wing center section.  I could see it pulling 25+ G's.

Jim Pollock

Note:

If I ever build an electric plane it will have a flying stab, not sure but could have a forward canard too?  Ouch, I think I would have to reinforce the wing center section.  I could see it pulling 25+ G's.

Jim Pollock

Maybe instead of a canard you could put leading edge slats on the wing for more lift to complete that scary fast turn.  Either that, or I wonder if chines (ala F-18, etc) would add lift for the very high aoa maneuvers the tail would drive the wing to.....

This is one amazing piece of art with what appears to be a flying stab. Nice photo....but take a close look at this stab

Looks like pivot(hing) line is around 25-30%?

Who's and what is it?

David,

Appreciate your comments, and as a practical - not just theoretical - approach, think you have it about nailed.

However, check several of the above posts for other considerations. My personal preference was to use the axiom that symmetrical sections have center of pressure at 25%, with no change at different AoA ( no moments about the cp ), which led me to hinge at 20% MAC. SOME, but not overpowering, return to 'trail' tendency. Ted F's comments are valuable. What I tried was to use the smallest total tail area sufficient for the needed 'turn.' That worked, for several - but not all - conditions. It made a model that went where it was aimed, but needed to be aimed there at all times. Fun, but tiring...

For modern CLPA demands, it is at least as important that a model LOCK into the exit direction, hard and instantaneously. All-flying stabilators are not good at that, particularly in severe wind conditions.

It IS theoretically less than the best to carry tail surface area that opposes the needed turn potential - EXCEPT when tracking out of a severe turn is just as important as achieving the needed, severe turn. All aerodynamic design is compromise: the stab+elevator solution is a win/win solution...