Principles of flight?

[RedMist]

no the conveyer in moving
in order to stop the wheels from spinning the conveyer is rotating in the oposite direction to there rotation

this means that the conveyer is rotating in the same direction the plane is moving


remeber the conveyer matches the wheelspeed not the ground speed of the plane

==================>>>> planes moving this way

=================<<<<< bottom of the wheels would need to move in this direction for the plane to move forward

================>>>>> coveryer would have to move in this direction (the same way the plane need to go to take off to stop wheel motion


==================>>>> planes moving this way

=================<<<<< bottom of the wheels would need to move in this direction for the plane to move forward

================>>>>> coveryer would have to move in this direction (the same way the plane need to go to take off to stop wheel motion

Okay, been discussed before in regards to point linea and rotational speed.

Point linea. A rotating wheel never ever travels in reverse. At its slowest speed, its contact patch, has 0 point linea speed. It then accelerates forward to max speed at 180 degrees from contact patch in a forward direction, then slows to the point, where it is still traveling forwards but slowing to just before the contact patch. Where again it has 0 velocity. Remember these wheels are freewheeling. So push the plane forward the wheels rotate forward.

==================>>>> planes moving this way

bottom of the wheels don't move


conveyor doesnt move.


Wheels are forced to skid.


Rotational. Are you telling me that when you push a trolley forward the wheels rotate backwards? In my experience all wheels rotate in line with the direction of travel.

==================>>>> planes moving this way

=================>>> wheels would need to move in this direction for the plane to move forward

================<<<<< coveryer would have to move in this direction

[igor]

Remember that the conveyor rotates in the opposite direction to the wheels.

[igor]

Point linea. A rotating wheel never ever travels in reverse. At its slowest speed, its contact patch, has 0 point linea speed. It then accelerates forward to max speed at 180 degrees from contact patch in a forward direction, then slows to the point, where it is still traveling forwards but slowing to just before the contact patch. Where again it has 0 velocity. Remember these wheels are freewheeling. So push the plane forward the wheels rotate forward.

So according to that, the wheels can still rotate, and the conveyor never move, as the contact patch between the two has 0 linear speed.

It's an epiphany!!!

[vvega]

Imagine a plane is sat on the beginning of a massive conveyor belt/travelator type arrangement, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.
There is no wind.
Can the plane take off?

Explain why it can, or cannot, take off?

so again

wheel moves clockwise and teh conveyer attempts to rotate the wheel in the oposite direction

if it turned counter clockwise then as soon a you get movement the wheel would just keep acellerating till it exploded
because as it attempts to match the speed it will cause the wheel to spin faster

and finally the wheels cannot skid there freewheeling
you seam to think they have some sort of conection to the plane...aside from the tapered rollers the plane has no way of offering any motive orce to them aside from the brakes

so now as a experiment go out and grab ya bogy wheel off your trailor move it backwards and tri to make it ......skid in a straight line


v

[RedMist]

Remember that the conveyor rotates in the opposite direction to the wheels.

Which is exactly as I have stated it.

[RedMist]

so again

wheel moves clockwise and teh conveyer attempts to rotate the wheel in the oposite direction

if it turned counter clockwise then as soon a you get movement the wheel would just keep acellerating till it exploded
because as it attempts to match the speed it will cause the wheel to spin faster

and finally the wheels cannot skid there freewheeling
you seam to think they have some sort of conection to the plane...aside from the tapered rollers the plane has no way of offering any motive orce to them aside from the brakes

so now as a experiment go out and grab ya bogy wheel off your trailor move it backwards and tri to make it ......skid in a straight line


v

Your right of course. When I push the buggy, the wheels dont rotate, IE there is no connection between movement and wheels moving. And aagin when a plane takes off I've never seen wheels rotate. They somehow just skid down the runway. I fail to see why people continue to think that I believe the wheels to be powered. I really dont give a shyte. Other than the fact that if they were powered, which they are not, skiding would only power the plane BACKWARDS.

I have no idea why you continue to think that when the wheels rotate, they rotate backwards.

Clockwise, would depend on which side of the buggy I'm standing on. However I still think you have the concept that somehow when I push the buggy forward the wheels rotate in reverse. They dont.

I whole heartedly agree with the explosion statement. "because as it attempts to match the speed it will cause the wheel to spin faster
" You got it babe.

Your last statement I semi agree with. I also have no idea as to why you think that thrust operates in a backwards direction. IE move the buggy backwards. I should be pushing the buggy forwards to simulate thrust. However you can't skid in a straight line, as such the plane will not take off.

If I push a trolley, the wheels travel 200m and a conveyor is setup to operate in the opposite direction at exactly the same speed what happens?
I guess your going to say BUT the wheels freewheel and it travels 300 meters in reverse? But doesnt that change the original distance traveled? IE havent I now traveled 300m forwards and 300m in reverse?

If I travel one inch forward and one inch in the opposite direction how far have I travelled?
If I travel one inch backwards and one inch in the opposite direction, how far have I travelled?

[RedMist]

So according to that, the wheels can still rotate, and the conveyor never move, as the contact patch between the two has 0 linear speed.

It's an epiphany!!!

Unfortunately its not. If your taking point linea speed from a point on the contact patch, then that point shifts as it circum navigates the tyre. Any point on the circumferance will travel exactly the same distance as the conveyor. 0 wheel rotation = 0 conveyor movement

You could take point linea speed from something else on the plane and the solution would be simple, the plane would take off easily. But thats not the question.

[Sanx]

OK. A friend pointed me in the direction of this thread, and after wading through most of the pages, it's time for my $0.02, mainly as I could feel a RedMist descending whilst reading.

The first question that must be asked is are we dealing with theoretical or real-world physics. Ignoring the fact we're dealing with a runway-sized conveyor belt with a capacity for infinite speed, there is nothing within the question on which to base as assumption either way, so we must look at both options. Real-world physics throws in all sorts of added extras like mechanical weaknesses, etc.

So, theoretical physics model first:

In this theoretical model, bearings have no friction, tyres cannot skid and nothing falls apart at insane speeds.

Immediately after the plane engine was set to a level sufficient to overcome the static air resistance of the plane itself, the plane would start to move forward and the wheels would begin to rotate.

How does the conveyor react? As the question is vague, and any assumptions based upon the wording come down to semantics, we'll look at all options.

Wheel speed = axle speed = ground speed of plane. The conveyor would simply match the speed of the plane as it accelerated as normal. The plane would take off. The wheels would be rotating at 2x the ground speed of the plane throughout.

Wheel speed = rotational speed = velocity of the part of the tyre that makes contact with the runway. The conveyor (and therefore the wheel) would accelerate exponentially until both were travelling at speed of light (as nothing can be accelerated through the speed of light). Whilst the conveyor and wheels accelerated, the plane would continue to accelerate as normal, as the thrust exerted on the plane is independent of wheel speed - although this period would be infinitessimally short. Once the speed of the conveyor reached light speed, it would be impossible for the wheels and conveyor to accelerate further. At this point, the plane would effectively stop, i.e. ground speed = 0. It wouldn't take off.

Now onto the real-world physics model:

Wheel speed = axle speed = ground speed of plane. The conveyor would simply match the speed of the plane as it accelerated as normal. The plane would take off. The wheels would be rotating at 2x the ground speed of the plane throughout. The wheel bearings would get a bit hot and you'd risk a tyre blowing out, but other than that, nothing unusual would happen.

Wheel speed = rotational speed = velocity of the part of the tyre that makes contact with the runway. As in the theoretical model, the conveyor and wheels would accelerate exponentially until something broke. Assuming the conveyor is indestructible, the things that'd break would be either the wheel bearings or the tyres themselves. As the destruction of either of these would essentially render the wheel inoperable, the wheel would stop turning and the conveyor would slow down to zero.

What happens then depends on the plane. Should the thrust generated by the engines be sufficient to overcome the additional drag created by a broken landing gear, the plane would accelerate and take off. Should it not be sufficient, it'd either slow down and stop or carry on along the ground at whatever speed the plane was capable of until it ran into something.

Can a plane take off with no landing gear? Depends on the plane. Each plane has a different Vr - in pilot's parlance - rotate speed. This is the air speed of the plane at which the pilot pulls back on the stick, and makes the plane lift off. Should the thrust of the engine be sufficient to allow the plane to hit Vr, then yes, it could take off. There are some fighter planes (they have lots of thrust and lower weight, meaning less drag when scraping along the ground) that can do that. A Cessna 152 however, doesn't have enough power to pull the skin off a rice pudding.

So, to sum up? Does the plane fly? From that question, it's impossible to say, as not enough information is given.

[RedMist]

Agreed wholeheartedly.

There is several pages on the discussion of wheelspeed being linea or rotational. I searched the web in an attempt to find any reference to "speed of the wheels" being linea, all references were rotational. In addition I searched for wheel speed in an aviation sence. Most hits refered to wheelspeed sensors for slip control, again metering in a rotational sence. All references, again, were in a rotational sence.

You also have to think of the context of the wording. This question was designed to challenge people. If it had no reference to wheels then there would simply be no debate. Or if there had meant to be a reference to wheelspeed in a linea sence, why not simply state groundspeed, which is a more common term used in every day flight?

So I have to swing to the rotatoinal side of either real world or non- real world physics.