Something to think about

[mgh 89]

The aircraft will accelerate and take off. All that is needed is an understanding of basic physics.Newton's 2nd Law states ensures that if the engines apply a thrust T Newtons to an aircraft of mass M kg then the aircraft must accelerate at T/m metres/sec unless there is an exactly equal and opposite force to stop it. With the brakes off, there is no way in which such a force -T can be generated.

[bob.bernstein 0]

There you go! but of course folks were earlier disputing science based on their intuition, I was trying to help folks synch their intuition up with science that they may not have been exposed to yet.I thought my experiement with friend helping pull a bar on a wheel over the treadmill did a good job of resetting folks intuition.Its about teaching, not just being accurate.

[Guest wyoming]

The error in the above is the "by hypothesis". The hypothesis doesn't imply that the space coordinates do not change. They do change because the A/C has...wheels.

[Guest airbus2]

The best solution to this that i have heard is this:Imagine a rocket flying close to the 'treadmill runway' no matter how fast that treadmill goes, the rocket will still go forward. Now imagine that the rocket has a lightweight roller skate attached to it. the wheels simply roll, no enigines in them at all. The rocket will still move forward, the wheels on the roller skate will just move at the speed of the rocket, plus the speed of the treadmill. Thats it, solved! In a plane its exactly the same. the propeller or jet pushes the plane along and is acting on the air around it, not on the treadmill, the wheels are simply there to hold it up.Dave

[Guest wyoming]

You can take off with the wheels motionless or even turning backward if the speed of the treadmill is equal to, or higher than, that of the A/C.

[Guest Adrian Wainer]

Since in this scenario the treadmill can allways match the forward speed of the aircraft the aircraft can not use airflow from forward motion to take off so unless the aircraft is a helicopter or similar VTOL aircraft it's ability to take-off is negated by its inability to achieve forward motion, assuming unlimited adhesion between the aircraft's wheels and treadmill, if on the otherhand the adhesion between the aircraft wheels and the treadmill was limited and the power available to the aircraft was very large, the aircraft could take off e.g. a rocket powered aircraft. Alternatively with a very powerfull engine producing airflow over the wing and a lightly loaded airframe, the aircraft might be able to take off by producing sufficent air-flow over its wing.Best and Warm RegardsAdrian Wainer

[bob.bernstein 0]

read my post #179. Then think about it again. The "motive" force, that force that produces motion is based on a seperate reference. What's happening below the cabin of the aircraft has no effect on the relative motion between the body of the airplane and the air.you could say anything you want about speeds, directions, etc of the treadmill, makes no difference. Airplane wheels are free spinning. They don't have a transmission that could transfer load between the treadmill to the a/c body. The a/c body is moved by the propellor ONLY.So, if you want to know whether the Airplane flys, investigate if there is relative motion between the a/c and the air. Since the a/c gets it propulsion from the propellor "pulling" thru the air, you don't have to understand, hear about, learn, or know anything about what's happening below, as long as the a/c CAN move, that is its not nailed down. The wheels can spin as fast as you like, its irrelevant to the relative motion between a/c and air.Again, the intuitive similarity is the guys walking beside the treadmill, as in our case with the a/c the motive force is not affected by the treadmill.

[mgh 89]

Also read my post #180Consider, say a B747 with some 200,000 lb of static thrust. If it doesn't move then there must be an equal and opposite force of -2050,000lb. Please explain where this additional force comes from and how it changes to match the thrust if the thottle position is changed?

[kerosene31 349]

How about this?What if you printed out all the posts from all the treadmill threads here, and dumped all that paper in an airplane? Would any aircraft be able to leave the ground then?

[mgh 89]

It was said in the earlier days of the 747 (before electronic documentation) that a a 747 couldn't carry all the documentation needed by an airline to operate and maintain it!

[Cee-Jaay 0]

>>Consider, say a B747 with some 200,000 lb of static thrust. If it doesn't move then there must be an equal and opposite force of -2050,000lb. Please explain where this additional force comes from and how it changes to match the thrust if the thottle position is changed?<

[Guest PARADISE]

Actually, we already have something that resembles what the original poster was refering to....it's called a catapult.....search "aircraft carrier" to see how it works.:-) John M

[Guest CowlFlapsOpen]

deja vue. Have been away from this forum for more than 6 months and return today to find this thread, which covers the same issue an a thread about 6 months ago. Anyways, as I posted back then and several here have already mentioned--the wheels and track are a red herring. Aircraft fly because of their movement thru the air. At the risk of oversimplifaction, the wheels you are likely to find on a conventional ac are a convenience to avoid dragging the fuselage along the ground as airspeed builds. As long as the propeller can burrow into the air ahead and the ac is not fixed to the ground it will pull the ac through the air mass and, when speed is sufficient, it will fly. In fact, an aircraft at altitude is in the same position. The ground underfoot is giving way with no resistance at precisely the speed the ac and air mass is traveling across the ground. The puzzle is ill defined and somewhat tautological.

[jagabom 21]

I think it is time to lock this thread and get rid of it.JimCYWG

[Guest airbus2]

>I think it is time to lock this thread and get rid of it.>Jim>CYWGYeah, kill it nowpleaseDave