Something to think about

[Guest Charlie]

The treadmill doesn

[Guest Charlie]

That's right. The propulsion method is irrelevant here. In either case, be it a person running or an aircraft's thrust, the forward motion simply offsets the backward motion of the treadmill.

[Guest]

Not so.The propulsion provided by the engines imparts momentum on the aircraft structure.This is passed through the wheels into the treadmill as a force which provides an equal but opposite force on the aircraft holding it in place.Of course assuming the treadmill is a perfect design which exactly counters any force it is subjected to (else the treadmill would propel the aircraft itself either forward or back).

[LAdamson 240]

>What all you "takeoff" folks seem to be negating is that the>treadmill

[Guest oyvindhansen]

>Not so.>The propulsion provided by the engines imparts momentum on the>aircraft structure.>This is passed through the wheels into the treadmill as a>force which provides an equal but opposite force on the>aircraft holding it in place.>That is rubbish. The threadmill cannot hold the aircraft in place because the wheels rotate freely.-

[Guest oyvindhansen]

>The treadmill doesn

[Guest Charlie]

Proved? How? I understand what you

[Guest Adverse Yawn]

That's what I wrote ages ago. It would be like taking off in a tailwind. Those who think there is no airflow will kick themselves when the penny drops ;)

[michal 44]

>force which provides an equal but opposite force on the>aircraft holding it in place.>if you are capable of such crap you are not a physicist.Michael J.http://www.precisionmanuals.com/images/forum/pmdg_744F.jpghttp://www.hifisim.com/images/asv_beta_member.jpg

[RobertVA 0]

As long as the aircraft's wheel brakes are released, the treadmill's ONLY relavence would be the ability of the wheel bearings and tires to handle the doubled RPM.Let's not forget, an aircraft is propelled when the engines force mass backwards. This mass can be air propelled backwards by a propeller, the combustion products from rockets or the combination of combustion products and air flow through turbojets and fanjets. The reaction (EVERY action has an EQUAL and opposite reaction) propells the engine and the attached aircraft forward. The acceleration of the aircraft is in proportion to the mass and velocity of the expelled air and combustion gases. Don't forget that the aircraft's engines continue to propell the vehicle after it leaves the ground! Tire friction has NOTHING to do with propelling the aircraft.For an aircraft the equivelent of a treadmill would be a wind tunnel like headwind. Under those conditions the aircraft's forward progress would be restricted by the added drag. If the appropriate angle of attack was maintained, lift would be consitant with the speed of the airflow relative to the wings.Of course in space you wouldn't have that troublesome atmospheric drag, but tossing something out the back AT HIGH VELOCITY still propells the vehicle in the opposite direction. The best way to increase thrust is to increase exaust velocity.

[Guest Charlie]

Oh yes it does. There is plenty of wheel friction

[Guest oyvindhansen]

I think it is a complete short circuit of thought to focus on the wheels at all. Aircraft can take of with floats or skis or whatever, the only thing that matters is its velocity relative to the air.-

[mgh 89]

Yes it will take off.Consider the basic physics. If a thrust is applied to the aircraft it must accelerate in the direction of the thrust unless there is an equal and opposite force to stop it. (Newton's Second Law of Motion). There isn't such an equal and opposite force. The only source could be the rolling resistance of the wheels and, in any, realistic aircraft, this will be a fraction of the thrust. The wheels will rotate twice as fast as they would normally. This would absorb a little more rotational energy reducing the acceleration a little. However, the rotational energy in the wheels will be fraction of the energy in the rest of the aircraft so the take off would be only slightly delayed.Sorry, but you can't get away from Newton's Laws of Motion.

[Guest Charlie]

It is not a short circuit at all, as wheel speed could be used to define forward speed while the aircraft is on the ground. Prior to take-off, any movement of that aircraft is as a rolling object. Thus, I believe it is natural for wheel rotation speed to come to mind. Not suggesting at all that the wheels have anything to do with propulsion, just that it is natural and logical for their rotation speed to come to mind. This is really quite simple when you boil it down. Speed is always relative and in the original message we are not told what the aircraft

[kerosene31 349]

No takeoff. The only relevant variable is airflow over the wings. On a treadmill there is no airflow since the wings are not moving. A small GA plane taking off into a 50 knot headwind will lift off the runway early. A plane landing in a strong tailwind will have to keep its speed up to avoid stalling.