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Puzzling question for the scientific minds!

post #1 of 19
Thread Starter 
DH and I have been puzzling over this:

A plane is standing on the equivalent of a plane sized treadmill. The plane moves in one direction while the belt moves in the opposite direction going at the same speed of the plane. Will the plane take off?

I'm saying no, because it's the airflow over the wings that gives the plane lift. The plane can sit in one spot with the engines going and the wheels turning, but that won't give it the lift it needs.

What do you guys think?
post #2 of 19
I would say no because you wouldn't have the proper forces to propel it. I could be wrong though.
post #3 of 19
Sarahp, you are correct.
post #4 of 19
Yes, it will take off. Mythbusters did this already you can see it here... http://mythbustersresults.com/episode97
post #5 of 19
the pane is moving, means it is getting lift., yes it will take off if they get enough air flow over the wings.

i have seen small aircraft break, there tie down rope and take off, or just flip over from very strong winds.
post #6 of 19
Quote:
Originally Posted by twstychik View Post
Yes, it will take off. Mythbusters did this already you can see it here... http://mythbustersresults.com/episode97
or that .....
post #7 of 19
Quote:
Originally Posted by twstychik View Post
Yes, it will take off. Mythbusters did this already you can see it here... http://mythbustersresults.com/episode97

I love that show!

It seems that several people there disagree with their findings though.
post #8 of 19
Not only that, but if there's a strong enough tailwind, the plane can get up to its normal takeoff speed and still not get enough lift. It's all about the airflow.

On the other hand... if there's enough of a headwind, a plane can stay in flight with everything seemingly normal, except that it moves backwards! Sliding, so to speak, being pushed back by the very air current its wings are using for lift. This happened to my father in a little L-4 (military version of the old Piper Cub) in a mountain valley in the Philippines.
post #9 of 19
The plane would take off. After all, it's not the tires on the plane that are bringing it to take-off speed, it's the engines on the wings. The engines suck in air and create the air flow under the wing which makes the plane take off. The tires don't have any purpose other than: A) driving the plane to the docking bay, B) keeping the body of the plane off the ground, and C) slowing the plane down when it lands.
post #10 of 19
Quote:
Originally Posted by CarolPetunia View Post
Not only that, but if there's a strong enough tailwind, the plane can get up to its normal takeoff speed and still not get enough lift. It's all about the airflow.

On the other hand... if there's enough of a headwind, a plane can stay in flight with everything seemingly normal, except that it moves backwards! Sliding, so to speak, being pushed back by the very air current its wings are using for lift. This happened to my father in a little L-4 (military version of the old Piper Cub) in a mountain valley in the Philippines.

very true. hehe i used to bet people on very windy days, that i could fly backwards.

drop the flaps, go to right above stall speeds, and the winds will push you backwards.

have seen piper cubs, just sitting there, they where moving forward so slow, that it looked like they where not even moving at all.
post #11 of 19
Quote:
Originally Posted by TigerOnTheProwl View Post
The plane would take off. After all, it's not the tires on the plane that are bringing it to take-off speed, it's the engines on the wings. The engines suck in air and create the air flow under the wing which makes the plane take off. The tires don't have any purpose other than: A) driving the plane to the docking bay, B) keeping the body of the plane off the ground, and C) slowing the plane down when it lands.
You'd be surprised at the long discussions of this, which is, of course, why Mythbusters did it.

Airplanes fly purely by airspeed. That is, the speed of the air both over AND under the wings. Sitting on a treadmill, the plane has zero airspeed, no matter how fast the engines or tires run.

As another poster noted, if the airspeed of an airplane (say, a Piper Cub, which can do something like 60 mph airspeed) is slower that the wind speed, say, 65 mph, the Cub would actually move backward if it was heading into the wind, having a ground speed of 60-65. However, if it turned around and flew with the wind, it would have a ground speed of 60+65, or 125 mph.

Understanding this scientific principal is obviously difficult for many people.

Consider this, however. A wind tunnel is essentially a treadmill in which the air moves, but the ground doesn't. A treadmill is a situation where the ground moves, but the air doesn't. An airplane can have its engines off and be tethered to the ground, but when they turn the big fans on, it can still "fly," that is, lift off the ground to the extent its tethers allow.

So, an airplane sitting on a treadmill with its engines running will never take off, since it has NO airspeed, only groundspeed.
post #12 of 19
Thread Starter 
Quote:
Originally Posted by twstychik View Post
Yes, it will take off. Mythbusters did this already you can see it here... http://mythbustersresults.com/episode97
I just found the episode - the plane is moving forward on the tarp. You're supposed to have the thing moving underneath it going the same speed as the plane, in which case the plane wouldn't move at all.

I don't think it's a valid experiment.
post #13 of 19
Im having a great time thinking about this!
I think it will take off. Planes are not like cars, they dont use their wheels against the ground to accelerate, they use their engines to generate thrust using air.
I say the thrust generated by the planes engines can and will overcome the groundspeed issue, causing the plane to accelerate forward, and eventually lift off.
I dont see how spinning wheels on the treadmill could overcome this forward acceleration, unless we are discussing a treadmill that could run at impossibly fast speeds thus keeping the entire energy of the aircraft occupied in wheel friction?
post #14 of 19
The Straight Dope did a piece on this:
http://www.straightdope.com/columns/...plane-take-off

I don't think I know enough about aeronautics, myself
post #15 of 19
Oh god, not this again! *runs away*
post #16 of 19
Quote:
Originally Posted by StarryEyedTiGeR View Post
I would say no because you wouldn't have the proper forces to propel it. I could be wrong though.
Yes, you could be wrong.
I do not know the correct answer but I would appreciate being seated right by the emergency exit, thank you.
post #17 of 19
Quote:
Originally Posted by Natalie_ca View Post
I love that show!

It seems that several people there disagree with their findings though.
There's always a critic (20,000) It's to the point now where they KNOW they will get contrary believers no matter how exact their experiment is.
Quote:
Originally Posted by theimp98 View Post
very true. hehe i used to bet people on very windy days, that i could fly backwards.

drop the flaps, go to right above stall speeds, and the winds will push you backwards.

have seen piper cubs, just sitting there, they where moving forward so slow, that it looked like they where not even moving at all.
Now that sounds like fun!
Quote:
Originally Posted by sarahp View Post
I just found the episode - the plane is moving forward on the tarp. You're supposed to have the thing moving underneath it going the same speed as the plane, in which case the plane wouldn't move at all.

I don't think it's a valid experiment.
Good point... I wonder if they'll revisit this myth in the future?
post #18 of 19
Quote:
Originally Posted by TigerOnTheProwl View Post
...The engines suck in air and create the air flow under the wing which makes the plane take off...
The airflow created by the turbines (or the prop) propels the plane forward -- but it's the air moving across both the upper and the lower surfaces of the wings as the plane moves forward that creates lift and allows takeoff. The reason both surfaces matter is that, for takeoff, air pressure has to be greater under the wing than above it -- so the upper surface of the wing is curved more than the lower surface, creating a longer path for the air to travel across the top than across the bottom. That makes the relative speed of the air across the upper surface faster -- which lowers the air pressure on that surface and allows the plane to lift off.
post #19 of 19
Quote:
Originally Posted by CarolPetunia View Post
The reason both surfaces matter is that, for takeoff, air pressure has to be greater under the wing than above it -- so the upper surface of the wing is curved more than the lower surface, creating a longer path for the air to travel across the top than across the bottom. That makes the relative speed of the air across the upper surface faster -- which lowers the air pressure on that surface and allows the plane to lift off.
wing camber, along with Bernoulli's principle or what you said hehe.
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