#BizarreLumpyTwinsTuesday

"RamblinRover Luxury-Yacht" (ramblininexile) 08/06/2013 at 10:33 • Filed to: twins tuesday

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#BertRutanLOL

ttyymmnn > RamblinRover Luxury-Yacht 08/06/2013 at 10:41

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No LOLs, really, for that asymmetrical design. Burt Rutan designed the Boomerang specifically to make it easier, and safer, to fly if one engine quits. Pretty damned brilliant, actually.

Air & Space Magazine had an excellent article about " Burt Rutan's Favorite Ride " back in September of last year.

Thunder > RamblinRover Luxury-Yacht 08/06/2013 at 10:44

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Gotta love Rutan.

Here's one of the original hypermilers. Also a twin.

dsigned001 - O.R.C. hunter > RamblinRover Luxury-Yacht 08/06/2013 at 10:53

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?itok=oTlJM67C

Rutan seems to have a thing for twins, and not always identical ones.

BoxerFanatic, troublesome iconoclast. > RamblinRover Luxury-Yacht 08/06/2013 at 12:14

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Not twin engines, not twin props...

Two sets of WINGS.

The Rutan-designed Quickie.

I have some ideas that started from this plane, to make one with joined wings. The front with dihedral and sweep, aft with slight anhedral and forward-sweep, with joining assemblies at the end that serve as a common winglet for both wings. Possibly with outrigger landing gear wheels in the bottom, and a tandem/bicycle undercarriage main landing gear (like a Harrier)

Other fun things that come to mind... a high-axis line pusher prop behind a ventral tail rudder, with the engine mounted near the center of gravity. (pilot and engine mass centralized in the middle of the fuselage)

Theoretically, on a scaled-up size, it could be a twin engine, with a tractor prop, and a pusher prop.

BoxerFanatic, troublesome iconoclast. > dsigned001 - O.R.C. hunter 08/06/2013 at 12:18

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That looks like the the logical evolution of a P38 Lightning successor into a race plane, and it is fantastic.

RamblinRover Luxury-Yacht > BoxerFanatic, troublesome iconoclast. 08/06/2013 at 12:23

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I love the Quickie.

The X-29 stopped a ways short of joining its surfaces. It could have, but forward sweep ideally has to allow for more wing flex than that would have permitted, and insofar as a little wing flex is advantageous for performance (but only a little), it wouldn't have served well.

Other planes have played with near surfaces as well, but having the two surfaces physically joined probably died with German prototypes in the 40s.

BoxerFanatic, troublesome iconoclast. > RamblinRover Luxury-Yacht 08/06/2013 at 12:51

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Those planes have their surfaces in the same geometric plane, and the down-wash would be an issue.

Plus, the Quickie's forward wings act similarly to canards, in that they are full-flying, and do control pitch as elevators (ailerons are on the upper rear wings)

The big difference that makes Quickie into a tandem-wing plane, rather than a wing + canard configuration, is that the forward wing actually provides a significant portion of the airframe's lift... I've read it as even 60%... more lift than the aft wings.

But another aspect is that the front wings are low mounted, and the aft-wings are shoulder mounted, so the are decidedly not in the same geometric plane, and the down-wash of the front wings doesn't directly influence the leading edge of the aft wing. It is almost a biplane, other than the wings aren't located at the same point on the length of the fuselage.

Another joined-wing experimental aircraft that I came across, is the Ligeti Stratos.

This is similar to what I was thinking, but this aircraft has very little anhedral or dihedral to the wings, and the aft high wing has nearly no sweep, the front low wings has all of the sweep to meet tall joining vertical spars at the end.

I was thinking more along the lines of Rutan's design, with slimmer wings, and using more of a diamond configuration to make the wing joining ends more compact, by bringing the wingtips much closer together by design.

The thought of LongEZ-like wingtip rudders, and a tailless fuselage occurred to me, but with the wing tip location near, or even a bit forward of the aircraft's center of gravity, I am not sure how much yaw authority they would have.

I like the pusher-prop idea, like the Stratos pictured, the LongEZ, and others... but I was thinking that to avoid tail prop strikes, a high-axis prop, and a ventral tail with a landing wheel in it, like the Bugatti 100P Reve Bleu (ventral tail with a wheel, but no pusher prop), and the pusher-prop Lear Fan (no tail wheel with traditional tricycle gear), would help avoid it.

I even like the idea of a Y tail, like 100P and Lear Fan, but with double wings, joined at the ends with winglets, and front elevator control, the upper V-tail surfaces may be redundant, not required for elevator control, and just add airframe weight.

RamblinRover Luxury-Yacht > BoxerFanatic, troublesome iconoclast. 08/06/2013 at 12:55

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Could always, I suppose, use a twin-engine setup to avoid needing a real tail. Fore/aft like the Do-335, but at sufficiently different axes of pull that you'd get some stability control through fly-by-wire acting on the throttles. Hmmm.

BoxerFanatic, troublesome iconoclast. > RamblinRover Luxury-Yacht 08/06/2013 at 13:16

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That would be the way I would go to seek more power with such a design, and it probably would have a longitudinal stabilizing effect.

But if the wing tips join together at a point near the center point of the length of the plane, would rudders on the winglets have yaw control authority? Seems like they would just slide the aircraft sideways, so to speak, and wouldn't serve to change the aircrafts' heading, at least not much.

I would think there would still need to be some sort of tail surface to leverage a heading change, like Quickie's small vertical tail without elevators... I was just thinking that ventral, rather than dorsal, would be something interesting, especially for a pusher-prop to go with it.

I suppose a rudder in the prop-wash like an air-boat or a hovercraft could use prop thrust vectoring to provide yaw control, and allow a truncated tail. That could be done with something similar to Ligeti Stratos' ducted fan.

RamblinRover Luxury-Yacht > BoxerFanatic, troublesome iconoclast. 08/06/2013 at 13:29

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The best way for wingtips to have yaw control would be for them to be non-vertical, and above the centerline of the plane in action, though they would also contribute to roll there. Since, after all, the point of a rudder is less to initiate the turn, but control attitude therein and keep the plane in it. Here's the thing, though: the present anhedral/dihedral of the wings would serve to have control over that also. If the forward plane is in elevator use and dihedral, it might in slip push the nose out, and the aileron action on the dihedral rear plane would push the tail out, but only as long as roll control was in use. Reverse it to elevator control aft, and you might have some margin of natural rudder impulse.

Also, the rudders on wingtips would have some varying amount of drag influence on yaw: it might be possible to bias their movement (i.e. have them actuate in a non-parallel manner) to have a drag-steering yaw control like a B-2.

BoxerFanatic, troublesome iconoclast. > RamblinRover Luxury-Yacht 08/06/2013 at 13:52

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Interesting. I didn't think of that... basically differential wingtip speed brakes as yaw control.

I think the reason the elevators are on the front wings, is to have more pitch effect authority. The rearward wing would truly have to be at the aft end of the airframe to have elevator control, not near-center like the Quickie's upper wing.

Hopefully, with a small experimental plane, with one or two seats, the vertical height differential between the low mounted front wing, and the high mounted aft wing, the front dihedral, and the aft anhedral angles would hopefully not be too steep. And there would be a bit of vertical element between them, even at the tips, to serve as a winglet, and probably some amount longitudinal staggered distance remaining, as well.

I figured that the front lower wing would be closer to neutral, in terms of wash-in or wash-out, and that the upper forward-swept wing would be a bit more wash-in, where the wing would be thicker and stronger toward the root, and where the leading edge of the upper wing would sort of funnel the airflow toward the fuselage a bit, anyway.