One-piece all-moving tails?

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cluttonfred

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Alberto Santos-Dumont's Demoiselle used an all-moving cruciform tail.

1652693177155.png

Mike Whittaker used a similar approach for his MW4, which worked very well but made the PFA engineering folks nervous so the production MW5 kits and plans had two separate but still all-moving tail surfaces.

1652693266113.png 1652693308444.png

I find the idea of making *one* tail very appealing for a simple, low and slow design. Yes, the universal joint needs to be designed carefully with plenty of reserve strength and duplicate load paths. You, you need to take into consideration mass and aerodynamic balancing. Yes, you might even need one or more anti-servo tabs like the Volksplanes. These are all design challenges, but once that's all worked out, the build becomes very appealing. It need not be cruciform, you could use an X-tail or an H-tail as well, that latter better for a low wing because of ground clearance issues.

Thoughts? Appealing idea or "no way I would fly something like that"?

Cheers,

Matthew
 

wsimpso1

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Here is this vibe guy's take on it.

With fixed stabilizers, elevator, and rudder, you have two half-sized moving surfaces, each moving independantly with one degree of freedom, making two dof for movement and vibe management. The two axes may have some coupled effects, some of us offset vertical and horizontal surfaces to reduce drag and decouple control responses. P51 and forward.

With hinged vertical and horizontal tailplanes, you have two full sized surfaces, each moving independently with one dof, also making two dof for movement and vibe management. Decoupling by offsetting is also beneficial.

The Hooke jointed all flying tail also has two full sized surfaces, but now the two control axes inevitibly have some coupling of movement (try designing a linkage to run them where elevator only movement does not put in some rudder and vice versa). The control responses of deflecting even one surface will cause some airflow changes to the other, so you have response coupling too. And now while it looks we still have 2 degrees of freedom for movement, the inevitable movement and response coupling makes it 3 to 4 dof that we now have to manage, mass balance, and prevent from fluttering - the elevator pivoting on its hinges is also rotating the rudder in pitch and rudder pivoting is rotating the elevator in yaw. This engineer knows it can be done and folks have done it. But the problem becomes another order of magnitude more involved to make it all work safely.

Then, besides novelty, what benefit does this bring? It is neither a weight save nor a control improvement. With the inevitable coupling in both actuation and responses and the increased drag, it looks like all downsides to me.

Billski
 
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cluttonfred

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All good points, Billski, but I wonder if some of those issues are really non-issues in a simple puddlejumper rather than a high-performance sailplane or a competition aerobat. Here is how Mike Whittaker did it on the MW-4 using what I believe we would call in the USA the universal joint from a Ford Cortina driveshaft. I suspect you could find an off-the-shelf automotive or commercial component that would suit and be far stronger than necessary.

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TFF

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Mark Stull designed one right here in HBA. His round tail. I find while in early aviation you tried everything, we have already tried it and it’s not the best way unless you just want to do it for the fun of it. Not as crisp of control. Changing pitch can change the effectiveness of yaw input, and vice versa. You can move a control surface out of its best aero position while using the other. Also way more is required to keep it from falling off over a simple hinge.
 

Vigilant1

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M. Colomban's one piece stabilator on the Luciole facilitates its quick removal for trailering and storage, which is a plus. On the other hand, a mere mortal would probably have an easier time designing a safe, rigid stabilizer that clips into place on top of the tailboom with two pins and a hinged elevator that attaches to the control rod. No, not as elegant or quick.
 

wsimpso1

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All good points, Billski, but I wonder if some of those issues are really non-issues in a simple puddlejumper rather than a high-performance sailplane or a competition aerobat. Here is how Mike Whittaker did it on the MW-4 using what I believe we would call in the USA the universal joint from a Ford Cortina driveshaft. I suspect you could find an off-the-shelf automotive or commercial component that would suit and be far stronger than necessary.

The designer of an airplane with such a gadget should go in knowing that it gives no advantage and has the potential for a number of issues. As I said, it has been done. But that does not mean it will work without a bunch of fuss. Flutter can be dragged down into even low speed ops, and I do not even know how to analyze for it with these added DOF...

Billski
 
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ragflyer

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yeah +1 Billski....It can of course be done but not sure what the benefit would be. Nightmare to analyze with coupled modes and I am not convinced it is easier to build than a traditional tail. I guess the only thing going for it is novelty and the appearance of ease of construction.
 

wsimpso1

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The annular all flying tail is the best,
I'd stick with Boom models until the
forces and pilot feel are well known.
If one were to do a ring tail, I would think that it would be an ellipse - not a circle - as the required area of vertical tail is generally less than the required area of horizontal tail. While it might seem interesting, if we already know going in that it is not an advantage, so why bother?
 

bhooper360

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These are all design challenges, but once that's all worked out, the build becomes very appealing.

Depending on the depth the length and the width of the puddle in question, you're talking about a regular ,quarter inch drill bit, two heavy-duty pliers, a threaded rod with two nuts, two washers and something* to attach some steel cable to. (e.g. a sixteenth inch drill bit and a crimping tool) And some duct tape. But if you want to get fancy, you can use extruded (certainly not cast!) door hinges.

Considering that the result in either case is a fluttering deathtrap, this tried-and-true, conventional approach has the advantage of not putting a vintage car drive component at station 9,999.
 
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bhooper360

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Aileron Aerodynamics
Since the ailerons are relatively short, they need to be very effective. Constant chord Sukhoi-type ailerons, hinged near their aerodynamic centers, are used. Spades may be used if required to increase rolling moments and tailor control forces.

For roll control at low and zero airspeeds, such as in the hover, two options present themselves:



  • “Statorons” (small control surfaces on the stators connected to the aileron control system) would provide roll control at low and negative airspeeds, power on, as well as assist the ailerons in forward flight.
  • The aileron controls could be linked through a mixer device to the elevators and/or rudders. Thus, with roll input the elevators/rudders would move differentially though small deflections.
Statorons are preferred due to their simplicity, reliability, and proximity to the propellers, ensuring roll control under all flight conditions (power on). Fortuitously, the aft stator spars are required to be moved forward from the stator trailing edges to establish sufficient cross-section for structural stability, thus leaving room for optimally sized statorons.


Tail Surface Aerodynamics
 
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