Attention Tailless Nerds!

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Norman

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Although this represents additional thread drift, can any of our more educated folks offer an opinion as to whether an unswept (Fauvel style) wing is or is not prone to the same kind of tumbling problems that the trike in the video had? The Fauvel gliders do not have that reputation that I am aware of, but they have the mass pretty much in the center... and a forward GC... and if there is a likely pitch tumble issue with the Fauvel configuration I would like to know about it.
I haven't heard that Fauvels had a tumble problem but there is something mentioned in "Tailless aircraft in theory and practice" that's interesting. Apparently once in a while the AV-37 would do a singe flip at the top of a loop.

There are two tumble criteria that I know of.
One is Irv Culver's crotch depth to MAC ratio. Using paper models of varying sweep and tapper Culver found that the models with crotch depth (the distance from the root TE to a line connecting tip TEs) to MAC ratio of less than 2:1 could tumble if the static margin was too short.

The other is from some WWII spin research the NACA did with fighters with bombs or external fuel tanks mounted on the wings. They found that the spin axis depends on the mass moment of inertia. Basically after a stall the plane will try to spin around the axis with the highest inertia. Normally in a conventional plane the heaviest axis is the longitudinal axis but when you put a heavy bomb load on the wings the lateral axis gains a lot of inertia, usually not enough to overcome the horizontal stabilizer but sometimes enough to cause a flat spin (especially if the static margin is too short). In the absence of a horizontal stabilizer a wing-heavy airplane is free to spin around the lateral axis (tumble).

So the solution from a design standpoint is to keep the wings as light as possible, especially outboard, and distribute the mass in the pod as far apart as practical.
 

Aerowerx

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Been wondering when you would check in on this, Norm.

Here we are on page 4 of this thread, and all I did was say that the 'Tailless' book was available at a reasonable price!
 

Sockmonkey

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So the solution from a design standpoint is to keep the wings as light as possible, especially outboard, and distribute the mass in the pod as far apart as practical.
That makes me wonder about the construction of the wing itself. As in where along the wing chord most of the mass of the wing structure is. A heavy main spar VS a pair of smaller fore and aft spars.
That's going to make more a difference in a Fauvel as opposed to a tailed design isn't it?
 

pictsidhe

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I was reading a paper on lateral control characteristics when stalled recently. Though it was about tailed aircraft. One major point was that higher yaw inertia would often help keep an aircraft from being autorotationally stable. The ones being analysed, it made little difference if that inertia was in the z axis rather than the x axis, ie weight at the wing tips. There was quite a bit of maths involved.
 

Norman

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[W]here along the wing chord most of the mass of the wing structure is. A heavy main spar VS a pair of smaller fore and aft spars.
The lightest spar design is a tapered I-beam at the maximum thickness of the airfoil. Splitting the load between two beams won't save you any weight.
 

Sockmonkey

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The lightest spar design is a tapered I-beam at the maximum thickness of the airfoil. Splitting the load between two beams won't save you any weight.
No, I'm not talking about the amount of weight. I'm asking how much splitting the load like that would affect the pitch handling.
 

RPM314

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There's probably more mass and moment arm to play with in the central pod/fuselage, so I'd imagine the effect to be relatively weak.
 

lvaero

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Sep 23, 2018
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Spring, TX
Amazon is listing several copies of "Tailless Aircraft in Theory and Practice', for under $90. Although old, this is the best reference book on tailless design available as far as I know.

Just ordered copy. They may be print-on-demand, used, or new. Can't tell for sure. Will keep you posted.
That's a great price. I cannot remember what I paid for my copy from the UK, but this book is probably the #1 book in our library, and worth multiple times its weight in gold!! Totally worth it!
 
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