Let's say you had a giant treadmill with an airplane on it

[FR8mastr]

Yea everyone knows the faster you run on a treadmill the more wind you feel in your face

 

[regionaltard]

The only way the plane wouldn't take off would be if the tires blew before it reached flying speed.

 

[PCL_128]

Yea everyone knows the faster you run on a treadmill the more wind you feel in your face

And that might actually be relevant if an airplane produced forward thrust through its wheels instead of a prop/jet.

 

[The Drizzle]

And that might actually be relevant if an airplane produced forward thrust through its wheels instead of a prop/jet.

seriously, don't get involved beyond ridicule.

 

[Flyer1015]

If I understand this correctly, as the engines spool up and the airplane starts to roll on this giant treadmill, then does the treadmill start and match the speed of the rolling wheels?


If it does, then there is no relative motion of the airplane with respect to the ground.

As in, if you step five feet away off the treadmill, and look at the airplane, it will be stationary.


Lift is created by airflow over/under the wings, via Bernoulli's principle. High speed over the wing creates low pressure, low speed under the wing creats high pressure. This pressure differential creates lift.

But in this case, there is no wind flowing over the wing... just as you don't feel wind flowing over your body when you run on a treadmill as fast as you can.

Relative to some point on earth, you're stationary.


So, you will not takeoff.

 

[YourPilotFriend]

The question is whether or not the belt can provide enough backwards force though friction to equal the force applied by the engines. The answer is: YES. You can see this by placing a rollerblade on a treadmill. As you increase the speed of the treadmill, the force applied by your hand to keep the rollerblade stationary increases. The belt could potentially spin the wheels fast enough in the opposite direction to hold the plane stationary. If you neglect friction in the wheel bearings, the plane takes off.

 

[Flyer1015]

The belt could potentially spin the wheels fast enough in the opposite direction to hold the plane stationary.

Exactly my point.

Are we assuming this treadmill can match the wheels spinning, exactly?

If that's the case, when the engines spool up, the wheels start rolling forward. BUT, if the treadmill exactly matches it in the other direction, then your forward motion is countered.

Relative to a point on earth outside of the treadmill, you are still stationary even at takeoff thrust.

You won't takeoff.

 

[AdSo81]

Ya...but your in a prop...so its not take off thrust...its take off power! Who manufactures that big of a treadmill anyways.

 

[Flyer1015]

I mean, really this is common sense. It's just like you running on a treadmill.


Imagine standing on the wing of this airplane. Engines spool up, wheels start rolling forward.

BUT, the treadmill goes in the opposite direction, exactly countering the wheel motion forward. And at takeoff thrust, the treadmill still goes fast enough to keep the aircraft from rolling forward.

You, standing on the wing, won't feel a thing. No wind flowing over/under the wing.

Imagine standing on the shoulders of a guy running full speed on a treadmill.

You won't feel any wind in your face.... since you have no forward motion relative to some point on earth besides the treadmill.

 

[YourPilotFriend]

You can actually derive an equation for belt speed of this question. So if there is an actual belt speed, the plane does not have any forward motion relative to its position in space. There is no takeoff.