Plane with the engine connected to the wheels
 

Plane with the engine connected to the wheels. Will it take off?

Do you believe that a plane without propellers or jet engines will be able to take off and fly a short distance (leave the ground for a few meters) if the engine is connected only to the wheels?

Yes.

It would have to be accelerated to beyond flight speed on the ground, and then it's momentum (negative inertia for the pedants:rolleyes:) would carry it into the air for a few moments.


MJ:ok:

Yes indeed - pretty much the same principle as a chuck glider (and, indeed, the occasion racing car).
http://www.pprune.org/data:image/jpe...tKm5qVWgf/2Q==
http://img.gawkerassets.com/img/18sc.../ku-xlarge.jpg

http://www.pprune.org/data:image/jpe...tKm5qVWgf/2Q==


To be fair to pedants, a pedant would probably point out that the unit of inertia is mass, (eg kilogram in SI units), whereas the unit of momentum is mass*velocity, so one is extremely unlikely to be the "negative" of the other :E

Yes but can the plane really accelerate to beyond the flight speed supposing a powerful engine, coupled to the wheels, is available?
It appears that the moment the plane is about to take off the thrust will be zero. As the plane gets more and more speed, running on the runway, the force with which the wheels press on the ground decreases and less and less thrust is available.

I've been told several times that I use the word 'momentum' incorrectly in this context, and that I should refer to 'negative inertia'.

Perhaps it's me being the pedant!;)

So long as the wings are held at an angle of attack that produces 0 lift during the acceleration to above flight speed, the weight on the wheels will remain constant, until 'rotation'.


MJ:ok:

Yes if one keeps the angle of attack zero or slightly negative and then, after the plane gets enough speed, suddenly changes the angle of attack and make it positive, the plane will fly a bit. However, if the plane has no flaps, no ailerons, no other moving control surface and can not modify its initial shape in any way or suddenly drop ballast, then will it take off?

I've experienced it, so definitely.

The incident in question was a big Chevrolet truck with nitrous injection that had an instrumented pylon on top for testing whole aeroplane wings that could not for various reasons be scaled and put in a wind tunnel.

It wasn't supposed to happen, but on one occasion we did get airborne for 10 metres or so down the runway at Rufforth in Yorkshire during safety testing of a microlight wing.

It was a bit disconcerting. There were five of us in the vehicle at the time, 2 from the CAA observing, driver, operator, and myself in the back seat as test conductor. This is a picture of a similar (but not quite identical) vehicle I found online:-

http://www.willswing.com/images/Eagl...st_vehicle.jpg

(The wing could have it's AoA changed from controls within the vehicle.)

G

Did the Chevrolet take off when the AoA was changed and did it leave the ground with all four wheels?

simplex just what are you on about?

yes a vehicle can accelerate to a speed where it can lift off and trade momentum for thrust to continue flying a little while, yes it can have all its wheels off the ground.
what is so difficult to understand???
the previous posters have given the correct answers. why do you ask them?

If the angle of attack remains constant, then no, because as soon as it reaches a speed where the wing develops enough lift to support the weight, it will loose traction and slow down.

However, if the positions of the C of G, C of P, and mainwheels were adjusted correctly, you could arrange for the aircraft to pitch it's own nose up when it reached a certain speed, and fly a few metres before it ran out of 'momentum'.


MJ:ok:

It was some years ago and it was labelled a "failed" test point, so I don't have any notes to look up - although I'm sure something's tucked away in a file still at my formal employer.

Either we were at target AoA and accelerating to condition, or we were on speed condition and pitching the wing up onto AoA conditon. I honestly couldn't tell tell you which now.

It seemed, so far as we could tell, to leave the ground with all four wheels at once, pitching very slightly nose-up.

G

Another example is the Rutan BiPod which "flew" :hmm: just for a little while.
It had no propeller, just an electric motor connected to the wheels.
http://stargazer2006.online.fr/aircr...bs/bipod03.jpg

Ah! but if the wheels were on a conveyor -belt.........:E

It certainly worked for the Harrier - I was once asked by an Senior Army Officer passenger in the T-bird how we got the drive down those narrow legs to the wheels, ho-ho-ho..........

Genghis' picture reminded me of my hang-gliding tuition.

Running on a flat field (no slope) legs going like the clappers, wing pitch angle at neutral, once up to 'speed' ease the bar out and up we go, a short hop as airspeed degraded very quickly and we all end up in a big heap in the nettles/cow pats.

Happy days but it proved the point, if not with powered wheels. :ok:

I was once at an air show standing by my Puma. A young lad of about five years old was asking me various questions about my aircraft and others nearby. A two seat Harrier taxied past. The lad asked me why it had two seats and I explained that it was used for training new pilots.

He nodded wisely. "Aha", he said. "So when the pilot is good enough to fly by himself, they'll take off those little stabiliser wheels, just like my daddy will do with my bike!"
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To answer the original question:

Yes it is quite possible. Look up the Mercedes Le Mans racer from a few years back. It took off, did a complete back flip and managed to fly completely out of the race track in the process. The driver was extremely lucky to survive intact.