Well let me know if you think this idea is worth a darn for a 3D type plane. I will get around to trying it on a foamy this winter when I get some time off from school. I am also tinkering with another idea I have had with a, one servo per aileron setup, where the inboard portion would have more throw than the outboard portion of the aileron. Lack of flying just gets the gears turning.

Dave

dang, the preview doesn't show if my attachment worked. hope it does...

I don't see what this would do other than act like a spoiler...

Dave,

That will work but it has some basic inefficiencies:

1 – When deflected this arrangement creates a “zigzag� airfoil shape. Not the most effective use of available surface area.

2 – Movement slop resulting from linkage slop adds up from servo to final movement of the hinged leading edge.

3 – The hinged leading edge faces the airflow and will want to deflect on its own. Proper and sufficient linkage is critical for commanding and restraining the movement of the forward surface.

4 – All loads from the forward surface are transferred through the aft surface compelling it to move in response. Flutter or simply ability to hold trim may be significantly reduced.

There is a better solution for what you are trying to achieve. You can see this by optimizing what you have drawn. The basic weakness in your arrangement comes from the distance between the 2 hinge lines. As the hinge lines are moved closer together (width of fixed center piece reduced) the zigzag in the airfoil when deflected is reduced. If the distance is reduced to zero the zigzag is eliminated. Also the length of the upper linkage from rear surface to front surface is reduced to zero. It can then be eliminated altogether, greatly reducing linkage slop. The last thing to eliminate is any imbalance of forces and tendency to flutter resulting from the front surface driving the rear. This will happen when the width of the front surface is shortened to ¼ or less of the overall chord.

What results from these changes is the well known “stabilator,� a single piece horizontal tail surface that is hinged to let the entire thing rotate for pitch control.

Now if you wanted to do something really effective, you could use a 3 piece surface as in your drawing to make a variable airfoil section that varies in the optimum way for a stabilator. This means that the articulated surface creates a “cambered� airfoil shape cup-up for up elevator, and reverses camber to cup-down for down elevator. This would increase stablator effectiveness by whatever the difference in max lift coefficient is between the articulated cambered airfoil shape and a symmetrical shape that would have to be used otherwise.

I have heard of glider fliers using a moveable leading edge for variable camber of the main wing. I haven’t heard of anyone using variable camber on a horizontal tail. My guess is for model building, due to the added complexity and weight of construction, a better solution would be simply building a larger single stabilator surface?

Multiflyer

WOW, nice post. Everything you stated sounds good and true. I like the idea of a full flying stab but to get a system on a forty size plane I think would be rather hard. I think you would need to use a bushing or a bearing and a good and strong CF or metal rod to reduce the flexing to a minimum and I "think" that might get heavy fast.

Thanks for your replies, they have brought up some things to think about.

Dave

I agree that a stabilator would be a better solution and in fact that looks like what you have designed with the leading edge down and the trailing edge up. (or vice versa)
A stabilator would be far simpler and much more efficient and if you used it for 3d and perhaps something like a Funtana where we fly very slow anyway, it could be designed to be strong enough. Glider guiders used them for years but they too fly slow for the most part.
Full size jets use them so why not a model?
In hover, it would have tremendous power compared to a regular elevator/stab mode.
I wonder if anyone else has tried a stabilator on a 3d ship?

3dbob

I think what you're looking for is what is known as compound surfaces where two movable portions are used to produce a more highly cambered and smoother surface.

What you did is forming an S curve when what you really want to do is form a proper airfoil shape.

Here's basically how it's done......

Actually with a carbon tube as the carry through spar and a couple of plastic or plywood bearing plates a full flying stabilizer could be done easily and probably quite lightly. But if you do that I would suggest you plan on a thick built up airfoiled stabilizer. Something like the E474 for a section that tends to avoid the super deep stall of the typical flat plate section.

Cambering the way Bruce shows is done on the Grumman S2 Tracker's vertical, for better control single engine.
For a horizontal it would be better than a stabilator on a 3D.
Better flow control in the prop blast at zero airspeed.
The middle section could be the fixed part, with the leading and trailing edges movable...

I use aluminum tubing from the LHS, with a bamboo skewer poly glued inside for my stabilators, both pivots and levers. Strong & light.

What you show in your first post is exactly what is used for boost tabs. However, the boost tabs need to be limited to 10% or less of the moveable surface else severe hunting occurs when you are near neautral position. This is used quite often in many of the larger models, both on elevator and aileron as the servo load is reduced a great deal permiting weaker servos to fly large planes. I frequently use this on some of my bigger planes and on the quarter scale Facetmobile to allow 30 inch/oz dervos to replace the 100 inch/oz ones. I am told that Burt Rutan used this same principle to show that our little 30 inch/oz servos could fly one of his full scale canards by flying the boost tab on ailerons with electronic control (an RC servo only) and no other input.

Well if Burt Rutan can use them I must give them a try!! LOL Well I think I will like I said on a foamy first.

Bruce,

Your sketch in post #6 is way cool! I have a foamy on the bench right now that needs to have that treatment added ... maybe not on elevator but on rudder f'sho.

Tall Paul,

Hmmm, your sketch (post #8) shows leading edge down, trailing edge down. No question, that will generate a ton of upward lift (down elevator) as long as the airplane is level and moving forward. But won't it be self-limiting after a few degrees of nose-down pitch? Seems like the traditional flat airfoil/flying stabilizer arrangement, or Bruce's arrangement, would be better for Lomcevaks or other maneuvers where you want the airplane to keep rotating nose-over-teakettle.

But I'm not an aerodynamicist -- just a serial airplane abuser.

Duane Gall
RCPRO

Beats me.. I just posted that as an alternative solution.. especially for the flutter problem when you have all that mass hanging off two sets of hinges as in Bruce's variation..
Aerodynamically making the middle part the support stiffens the structure, while not affecting the controliability... I think.
I've used a boost tab system on a flying tail, but only the trailing edge flap moved as the slab itself was moved by the servo.
About like Bruce's drawing.
Put it on a foamie and try it... ???

A lot of the 3D elevator designs that I've seen are really just stabilators in disguise. The horizontal stab is nothing more than just a narrow stub to hinge the heavily counterbalanced elevator to. I have seen examples where the elevator was 90% of the whole assembly. For lightness and simplicity, this is a design that's hard to beat for 3D.

Paul, I believe part of the equation to an elevator's response is the angle of attack change that comes along with the elevator deflection. The hinged leading edge will certianly increase the camber but it reduces the amount of AoA change. But a conventional elevator or the compound elevator maintains the AoA change as well as adding the camber to the equation.

DHG, do yourself and the rest of us a favour and start with a standard rudder and then pull the hingepins and mount up the compound rudder and let us know how it works out. If you need a sketch for a swappable hinge system let me know. I've done some using music wire hinges to allow for replaceable rudders in the past and they worked out great. A bit more work for sure but damn it man, THIS IS SCIENCE!

Light weight stabilator pivot: A high temper aluminum knitting needle [stub] can be glued into ply plates [on both sides of the fuselage] for the axle, and greased up for matching aluminum tubing to slide over [the bearings]. For a .40 sized 3D plane, build your balsa stick style stabilator and then sew the pivot bearings to the framework. 1/8" Aluminum welding rod that has been annealed makes a fine "elevator half" joiner. Carbon kite tubes can be used for the pivot too, just make sure they are greased where they rub.

Bruce,

Swappable hinge system? Thanks, but that's the beauty of trying this stuff on a 3D foamy: the hinge is just a strip of tape!

OK, I'll investigate this SCIENTIFICALLY, but it may take a little while. I have to eat turkey tomorrow ... just hope I don't end up eating crow later.

I had a GP YAK 55 for a short while (too many "arrivals" did in the front end of the fuselage).
It featured a full-flying stab. It was really a handful.
I've heard some guys go to fixed horizontal and elevator on that one.
My E-Flite Tribute has a large elevator with large aerodynamic balances.. stabilizer just large enough to carry the hinges.
It's a good flier.