Something to think about

[Guest enave]

>The aircraft uses the props (or jets, rockets, whatever) to>provide momentum to the wheels which cause the aircraft to>exert a force upon the ground which in turn causes the>aircraft to move along that ground."The aircraft uses the props (or jets, rockets, whatever) to provide momentum"ok, good so far."to the wheels"bzzz. wrong."which cause the aircraft to exert a force upon the ground"wrong. No force is exerted upon the ground except the weight of the aircraft. The wheels just support the aircraft. Unlike a car, the wheels have no part in moving it forward."which in turn causes the aircraft to move along that ground."an aircraft moves along the ground for the same reason it moves through the air* because of its engine, not because of its wheels. The wheels have nothing at all to do with this.It is true, a car on a conveyor belt could be held motionless by the turning of the conveyor. A person on a treadmill could also be held motionless. In both cases, the reason the person or the car doesn't move is because a person or a car attempts to move by pushing on the ground. This is not true of an aircraft, and as a result, the motion of the conveyor has a negligible effect on an aircraft.*note that I didn't say, "for the same reason it lifts off the ground" I'm not talking about the lift from the wings, I'm talking about thrust.

[michal 44]

I completely agree with you - I am a physicist (MS) and absolutely see nothing that will stop the takeoff (provided the tires can take increased rotation). The aircraft doesn't need the ground (or wheels) to propel itself forward - it needs the Newtonian 3-rd law to propel itself relative to the inertial platform- the earth.Michael J.http://www.precisionmanuals.com/images/forum/pmdg_744F.jpghttp://www.hifisim.com/images/asv_beta_member.jpg

[michal 44]

>If it's matching your speed exactly, but in the opposite>direct as you say, no, it could not. There'd be no airflow>over the wings.Its is a falacy. The aircraft is not a car and its power is not delivered to tires. If aircraft engines were spinning the wheels in order to gain speed - yes, the takeoff in this case would be imposssible. But the jet engines use exhaust to take advantage of Netwon's 3-rd law and due to preservation of momentum the aircraft starts moving forward - regardless what is happening with the tires. Of course the tires will be spinning like crazy in this case and assuming they won't burst - the take off will happen normally.It is easy to modify this experiment slightly and see why this is the case. Replace tires with snow skis, replace concrete with snowy/icy treadmill and think again ...Michael J.http://www.precisionmanuals.com/images/forum/pmdg_744F.jpghttp://www.hifisim.com/images/asv_beta_member.jpg

[Guest oyvindhansen]

I'm shocked that this is even considered problematic. To think that a such threadmill could prevent the aircrfat from gaining any forward momentum, you would have to totally lack any sense of physics and understanding of the principles of how the the engines propels the aircraft forward to get an airflow over the wings that makes it fly.Now, if this threadmill somehow could move the air around the aircraft in addition to the ground a takeoff on the spot would be possible.-

[michal 44]

>point is that the rubber bands don't become any less tense as>the speed of the treadmill increases. This shows that there>is no forward motion of the aircraft relative to the air, and>thus no lift/flight.Mistake in reasoning. The rubber bands will keep the same tension - regardless of the speed of the treadmill - once the rolling friction is overcome it makes no difference if the treadmill moves with 5 mph or with 500 mph. So really the moving treadmill creates no significant force that prevents the aircraft to accelerate and take off. The treadmill and its friction on the tires is the same obstacle for the aircraft as the stationary runway.Michael J.http://www.precisionmanuals.com/images/forum/pmdg_744F.jpghttp://www.hifisim.com/images/asv_beta_member.jpg

[michal 44]

>I'm shocked that this is even considered problematic. To>think that a such threadmill could prevent the aircrfat from>gaining any forward momentum, you would have to totally lack>any sense of physics Tha sad part is that few people have any concept of physics regardless how elementary it might be ...Michael J.http://www.precisionmanuals.com/images/forum/pmdg_744F.jpghttp://www.hifisim.com/images/asv_beta_member.jpg

[Guest oyvindhansen]

>Tha sad part is that few people have any concept of physics>regardless how elementary it might be ...>Yes, probably right. And I'm also a physicist myself, so perhaps I am a little blind about the difficulties.-

[AlaskanFlyboy 7]

Bah, I knew my mind was goin', now there's the proof. Not that I was ever good at these sorta puzzles. Hehe----------------------------------------------------------------John MorganReal World: KGEG, UND Aerospace Spokane Satillite, Private ASEL 141.2 hrs, 314 landings, 46 inst. apprs.Virtual: MSFS 2004"There is a feeling about an airport that no other piece of ground can have. No matter what the name of the country on whose land it lies, an airport is a place you can see and touch that leads to a reality that can only be thought and felt." - The Bridge Across Forever: A Love Story by Richard Bach

[dmaher 0]

LOL... Did everyone take a crazy pill?

[Guest]

The movement relative to the ground provides the airflow which gives lift.If the aircraft is held stationary by the runway being a treadmill (as in this example) that lift is never generated, ergo the aircraft will never take off.That's where your logic is flawed, you don't take into account that the aircraft never gets enough speed to provide airflow over the wing and therefore never generates the required lift for takeoff.It may get forward momentum, but no forward speed.

[Guest]

I'm a physicist myself...The aircraft in this case is not moving relative to the earth, it's held stationary by the treadmill.It IS moving relative to the treadmill surface, but that surface is stationary relative to the earth because of its construction.Therefore the aircraft has forward momentum but no forward speed, thus no airflow over the wing.If you were to place the whole thing into a wind tunnel providing an airflow over the wing at the same speed as the wheels provide to the treadmill the aircraft would indeed take off.

[michal 44]

>I'm a physicist myself...wow, that's a serious case of incompetence .. sorry. That's almost as bad as a doctor not knowing on which side of the body the heart is.Michael J.http://www.precisionmanuals.com/images/forum/pmdg_744F.jpghttp://www.hifisim.com/images/asv_beta_member.jpg

[victorwest2 0]

>The movement relative to the ground provides the airflow>which gives lift.>>If the aircraft is held stationary by the runway being a>treadmill (as in this example) that lift is never generated,>ergo the aircraft will never take off.>>That's where your logic is flawed, you don't take into account>that the aircraft never gets enough speed to provide airflow>over the wing and therefore never generates the required lift>for takeoff.>It may get forward momentum, but no forward speed.Exactly my point. The aircrfaft has to have a certain velocity in relation to the air around it in order to achieve lift. If the surface the aircraft is on is achieving an equal but opposite speed to that echieved by the engines, how can the aircraft increase its relative speed in relation to the airflow over the wings?

[Guest]

the incompetence is yours, Michael.I may have worded it a bit sloppy (blame 10 years working in another field because there's no money to be made in physics here), but I do get the ideas correct.You're the one who is seriously incompetent in not recognising that the aircraft would never pick up an airflow and thus never get the wing to generate lift.As the aircraft starts to gain forward momentum the wheels transfer that momentum to the runway surface which counteracts that movement by moving in the opposite direction, thus preventing the aircraft from over gaining forward speed.If you can't see that as a physicist you should seriously consider another line of work.

[Guest oyvindhansen]

>It may get forward momentum, but no forward speed.How is that possible, momentum being the product of mass and velocity? The only kind of momentum the aircraft will get on the threadmill is the rotational momentum of the wheels, that is if aircraft actually relied on the wheels for acceleration.-