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The quad-wing?

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Dr. Slack

Sun Nov 11 2012, 10:31PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

I've read other threads about getting much longer flight time from a quad-rotor, and this occured to me. I don't really want to hijack those threads, so here goes with an idea that I've not seen anywhere else in this form.

A quad-rotor generates all its lift like a helicopter. An aeroplane on the other hand generates lift from wings, and the props only have to overcome the drag from the wings. A good design of wing can achieve 30:1 or more lift/drag ratio, and 5:1 is really no trouble to exceed at all. If the flight time of a quad could be extended by a factor of 5, would that be worth it?

For some type of application, a quad needs to hover continuously, but there may be many others, aerial photography of large areas, or aerial inspection where getting to/from the target is a considerable part of the flight, where winged flight like a plane could be tolerated instead of helicopter/hover flight.

To avoid the mechanical complexities of a tilt rotor or tilt wing, how about a tilt craft. The wing is perhaps rigid foam, for light weight, cheapness, easy to profile. The quad would take off, land, loiter exactly as before, but it may not cope quite as well with cross winds in certain directions. For extended energy saving flight, it could just tip over. The four rotors are now driving it forwards. Used in pairs, they completely obviate the need for any control or stability surfaces on the wing, as they can apply roll, pitch and yaw. The controller may not need too much re-writing, if the gravity-sensing accelerometer had its axis rotated.

My apologies. I didn't want to crank up Povray, or spend more than a minute in Paint, so the illustration here is a suggestion at best, but if you want to, you can see what I mean.

There would be a significant rotor design compromise for a craft of this type. For the most efficient hover, the blades need to be wide and turn slowly, to reduce the speed of the air / increase the mass of the air driven downwards for the same momentum change (lift), thus reducing the kinetic energy of the downdraft, and so the power needed to create it. For high speed forward flight, the blades need to be small and use a higher airspeed. So it could be built for best flight, or best hover, but not both. I wonder if there's a good compromise?

What do you think?

Chip Fixes

Sun Nov 11 2012, 10:37PM

Registered Member #3781 Joined: Sat Mar 26 2011, 02:25AM
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Posts: 701

Really cool idea, what about making it more of a car shape than wing? It would create a bit more drag but would provide enough room for all the electronics. Although, I suppose you could make the wing hollow and put everything inside of it

Bjørn

Sun Nov 11 2012, 10:51PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Kickstarter got one

Pinky's Brain

Sun Nov 11 2012, 11:13PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837

For compromise you can use pitch control ... the size of the prop isn't the big problem, the RPM difference in hover and forward motion is.

BigBad

Sun Nov 11 2012, 11:50PM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
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Posts: 600

I don't think it works.

The problem is the aspect ratio of the wing; you want a high aspect ratio, and you've got a low aspect ratio.

You certainly can get a shed-load of lift with that kind of wing, but not efficiently.

Efficient wings are like glider wing, long and thin; that's nearer a Concorde wing.

Actually, that's why Helis are as they are, they have a longish, thin wing to give pretty good hover time.

I mean it could quite possibly fly (although it lacks a tail!), but as you've drawn it, it's not efficient. That may or may not matter.

BigBad

Sun Nov 11 2012, 11:57PM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600

BjÃ¸rn wrote ...

Kickstarter got one

Yes. that's got a much better aspect ratio.

Patrick

Mon Nov 12 2012, 01:26AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

really cool! just dont know how kickstarter allowed them to raise so much money? 84000 /293 =286 avg donated dollars per donation. (im sure there were some large donors too)

OH god i need money, lidars arnt cheap...

Pinky's Brain

Mon Nov 12 2012, 01:45AM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

How do Lidar's in UAV's work BTW? Are they true time of flight systems, or simply a mix of stereoscopy + structured light? (The latter seems cheaper.)

Patrick

Mon Nov 12 2012, 03:35AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Everyone tells me the hokoyu lidars 1200-6500 US$ are time of flight, but im suspicious, super fast clocks and lasers are not easy or cheap to make. Or every dumb idiot would be doing it.

i was told there is a way to use phase-amplitude (or some such term) to develop a latency differetnially proportional to distance (i think). the Neato robotic vacuum uses a right triangle spinning mirror and trig to do it cheap and at 115kbps through a normal serial connection.

If ive done the math right, 300,000,000 m/s divided by 1 second = 4ns pS per meter, i know the hykoyous start reading as close as 0.1 m and 0.06 m so thats less than 10 nS and they read +/- 1% out to 4m. real time of flight lidars go out a 1000m or more (even with a weak beam power)...

if they are true time of flight, im doubly impressed, a nano-second capability, precision optics, Electro-optical detection all for 1200$, in a commercial product...

Dr. Slack

Mon Nov 12 2012, 06:32AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

I like the quadshot. It's towards the other end of the spectrum of planes I was envisaging. It is a VTOL airplane, what I've drawn is a range-extended quad rotor. You can shoot for wing size and rotor size anywhere along that line, and beyond the ends of it if you so wish.

BigBad mentioned a tail. That's for pitch stability. Pitch is probably the hardest one to get right, in terms of speed of the control loop and control authority needed, so a tail for additional stability would be be a big plus. Unfortunately, a non-retractable tail is where it has to land. There are alternatives to a tail or control via differential thrust control (look up UA Flight 232 for pitch control via thrust!) which are a canard wing, or a special wing profile which is less efficient than a normal profile, but is stable in pitch.

BigBad mentioned wing aspect ration. Of course that's the easiest degree of freedom to exercise when attaching a wing. Something long and thin like a sailplane for efficient low speed flight, or shorter and wider that will be less of a problem in a cross wind hover. Bear in mind that a fabric wing like a high performance 'chute can get 5:1 lift to drag, anything rigid you make should get 10:1. There will be a law of diminishing returns because of all the other cruft hanging off the craft, there's no point in crafting a 35:1 glider wing when the drag from the quadrotor structure reduces that to 10:1 overall anyway. I used to fly gliders, and one of the last things to do before rolling it out was to tape up the joints between fuselage and wings to avoid air-leakage induced drag.

To make the source of the lift cryptic, and to improve hover stability through symmetry, how about the quad-duct-wing? Perhaps a bit more difficult to make?

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