Eviation Alice prototype fire

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BoKu

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Just spitting into the wind here, but isn’t it likely that the tail motor is lighter duty in order to avoid weighty motors and batteries (or heavy cables) behind the CG? They can carry the bulk of the battery weight in the wings where it would be closer to the tip motors and not impose a penalty in terms of long cables, CG arm or bending moment at the wing root.
I have seen promotional content for Alice that strongly implies that the tail is a lifting surface, resulting in an airframe that is inherently unstable. Their story seems to be that all stability will be synthesized by the flight management computer.
 

Dan Thomas

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I have seen promotional content for Alice that strongly implies that the tail is a lifting surface, resulting in an airframe that is inherently unstable. Their story seems to be that all stability will be synthesized by the flight management computer.
The original configuration was a trike. Perhaps a massive CG shift explains the switch to taildragger and lifting tail.
 

lr27

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I have seen promotional content for Alice that strongly implies that the tail is a lifting surface, resulting in an airframe that is inherently unstable. Their story seems to be that all stability will be synthesized by the flight management computer.
In the pictures I've seen, the tail looks very large. If so, it could lift a little without making the aircraft unstable. No numbers here, so I could be wrong. I imagine a v-tail isn't terribly efficient as lifting surfaces.
 

aeromomentum

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They need an aeronautical engineer that understands finite wing trailing edge vorticity. We need to stop calling it "wing tip vortex" or other incorrect and misleading terms.
 

bmcj

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They need an aeronautical engineer that understands finite wing trailing edge vorticity. We need to stop calling it "wing tip vortex" or other incorrect and misleading terms.
Yep, vorticity can be generated anywhere along the span, but I do think that controlling the tip vortex might mitigate some of the spanwise flow/vorticity.
 

Dan Thomas

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In the pictures I've seen, the tail looks very large. If so, it could lift a little without making the aircraft unstable. No numbers here, so I could be wrong. I imagine a v-tail isn't terribly efficient as lifting surfaces.
A lifting tail is naturally unstable and was outlawed a long, long time ago. The regs demand static stability, which means that as speed decays the nose will fall and maintain speed instead of the airplane stalling. A lifting tail will let the nose rise as speed decays and the airplane will stall. Some WW1 airplanes were built this way and they'd stall and enter an unrecoverable spin.
This thing would require software that prevents the stall. Great.
 

proppastie

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They need an aeronautical engineer that understands finite wing trailing edge vorticity. We need to stop calling it "wing tip vortex" or other incorrect and misleading terms.
Are we talking about the same thing. ......is there a difference, if so perhaps you could explain?
 

BoKu

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A lifting tail is naturally unstable and was outlawed a long, long time ago...
The relative lift gradients of the wing and tail are where stability comes from. There are actually some corner cases in which the tail of a conventional aircraft can be lifting up instead of down, and yet the aircraft is stable. High-performance sailplanes in particular are usually like this; at the lower end of the speed range the tail actually lifts up slightly. But it's still stable because the relationships between the rates of change of lift of the wing and the tail. My aero engineer friends explain it a lot better than I can.

It is somewhat paradoxical that in most airplanes, the tail is producing the most down force at the high end of the speed range when the elevator is deflected down, and the least amount of down force, and sometimes some upward lift, at the lowest end of the speed range where the elevator is deflected up. But that's pitching moment for you.
 

cluttonfred

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One caveat...there are examples of stable aircraft with lifting tails (essentially all canards and tandem wings) and it can work with a larger forward wing and smaller lifting tail *if* the relative wing loading is substantially higher on the front surface than on the rear one. (Airfoils matter, too, but wing loading matters more.)

The danger with any fore-and-aft, two-wing system is that it’s tempting to move the CG aft to improve efficiency by sharing the load and that works well right up to the point that the rear wing is too highly loaded and stalls first, which is often unrecoverable.

It can be fun to play around with drugstore balsa gliders and I have done so, mixing and matching parts and using a paper clip to vary CG. With patience you can get canard, tandem, and lifting tails all to work.

A lifting tail is naturally unstable and was outlawed a long, long time ago. The regs demand static stability, which means that as speed decays the nose will fall and maintain speed instead of the airplane stalling. A lifting tail will let the nose rise as speed decays and the airplane will stall. Some WW1 airplanes were built this way and they'd stall and enter an unrecoverable spin.
This thing would require software that prevents the stall. Great.
 

lr27

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A lifting tail is naturally unstable and was outlawed a long, long time ago. The regs demand static stability, which means that as speed decays the nose will fall and maintain speed instead of the airplane stalling. A lifting tail will let the nose rise as speed decays and the airplane will stall. Some WW1 airplanes were built this way and they'd stall and enter an unrecoverable spin.
This thing would require software that prevents the stall. Great.
You should explain that to some of my free flight models with large horizontal stabs. They don't seem to understand. One of them is stable with the cg at around 75 percent MAC, another at something like 125 or 150 per cent. It's a very light model and I can actually see the tail boom flex upwards slightly in flight.

You should also explain it to Prof. Mark Drela*. He has produced a nice chart/graph about cg vs configuration, which, as I recall, puts conventional configurations, flying wings, and canards on a continuum. I just can't find it on the web using my phone. Maybe someone else has a link.

* I don't often argue from authority, but it's definitely a nice chart. If you're familiar with the Aurora D8, Daedalus airplane, Decavitator, Bubble Dancer and many other aircraft, you've seen some of his work (some of these are collaborations. )
 

Victor Bravo

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But high performance free flight models are designed to be stable in one fairly narrow range, and most of the time IIRC you are using thrust angle to keep some of the pitching tendency (up or down) under control.
 

Vigilant1

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If a design depends on software/active stability, the aerodynamic challenges will pale in comparison to the software engineering/certification challenges.
And, apparently, fire safety might need to be bumped up on the priority list.
At a time like this, there are lots of investors to be found, the bar is not high. Heck, Dr Moller always managed to find 'em regardless of his track record or the general economic environment.
 
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cluttonfred

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I looked online for this quickly, no luck, and I am about to jump in the car but I would love to see this chart and the source document!

You should also explain it to Prof. Mark Drela*. He has produced a nice chart/graph about cg vs configuration, which, as I recall, puts conventional configurations, flying wings, and canards on a continuum. I just can't find it on the web using my phone. Maybe someone else has a link.
 

cluttonfred

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Thanks! Since it was posted by Drela on an open forum, I don’t think it’s a problem to reproduce the graph here, but I’ll start another thread.
 
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