troopernflight
Well-Known Member
I'm just going to say NO for the record, since I know the plane's not going to take off.
Poll: Mythbusters - Will the plane take off?
- Thread starter TheAlchemist
- Start date
BobDDuck
Island Bus Driver
That's the common misconception. An airplane does not use it's engine to move across the ground like a car. An airplane's engine moves it through the air. It may be in contact with the ground, through the wheels, but that just creates a little friction and that's it.
GatorFC
Well-Known Member
You should have made the poll public so that we know who to mock afterwards.
(Just Kidding, Mods!
Put away the stick.)For the record, I voted YES.
(hopefully Adam and Jamie don't screw it up)
FlyingPoke
I'm here to help...
I've been thinking about this all day, and I now realize the other side's point of view... I'm changing my answer to a resounding I HAVE NO IDEA, but im leaning towards - yes it will fly.
granlistillo
Well-Known Member
My guess is if the airspeed makes it into the white arc, it would lift off.
I think a better test would be to borrow the nimitz from the Navy put it at flank speed and see if a piper cub would take off chocked.
Firebird2XC
Well-Known Member
The real answer to this question is whether or not groundspeed equals airspeed.
Airspeed is what makes an airplane fly. If you had a suitable strong enough headwind you could theoretically maintain airspeed suitable for flight and actually have zero groundspeed. Actually, you could even have NEGATIVE groundspeed!
Beyond that, what we're dealing with is confusion over the point of application of force. A treadmill operates as it does because force used to create forward motion using 'equal and opposite' reaction concepts. ie, when a runner on a treadmill uses forward moving force with his feet to run forward, the rearward directed force is harnessed by the treadmill to move backward.
Because the force is equaled, the runner's relative position in space does not change. As long as force applied equals force negated, you can apply more and more energy and never really change relative position.
In an airplane (I'll use a jet, because the physics are simpler) you have THRUST being leveraged against the airplane, not the ground. The fact that the airplane rolls over the ground is irrelevant. No actual force is being applied (horizontally speaking) to the ground opposite the direction of travel. It's being leveraged against the ENGINES>
This is why you can lock up the brakes on an icy runway and still accelerate if you applied thrust. The wheels turn freely (or rather, apply no friction or rearward reaction)- there is no force being applied through them.
Since an airplane's forward motion is caused by the engines and not its wheels, a treadmill would not move if an airplane were on it, assuming normal operating conditions. The airplane would accelerate and take off once it had accelerated fast enough through the surrounding air flowing over the wings.
Now, if the treadmill were moving rearward under its own power, the airplane would first have to excede the treadmill's readward pace (ie, accelerate to a groundspeed of the treadmill + required indicated airspeed) in order to takeoff.
Assuming that were timed correctly, that'd reduce ground roll.
In a sense, that's how a carrier's catapult works. Depending on perspective, you could say the F-18 being launched is stationary to a point, and the carrier is being accelerated backwards relative to the jet.
Perspective is key.
Airspeed is what makes an airplane fly. If you had a suitable strong enough headwind you could theoretically maintain airspeed suitable for flight and actually have zero groundspeed. Actually, you could even have NEGATIVE groundspeed!
Beyond that, what we're dealing with is confusion over the point of application of force. A treadmill operates as it does because force used to create forward motion using 'equal and opposite' reaction concepts. ie, when a runner on a treadmill uses forward moving force with his feet to run forward, the rearward directed force is harnessed by the treadmill to move backward.
Because the force is equaled, the runner's relative position in space does not change. As long as force applied equals force negated, you can apply more and more energy and never really change relative position.
In an airplane (I'll use a jet, because the physics are simpler) you have THRUST being leveraged against the airplane, not the ground. The fact that the airplane rolls over the ground is irrelevant. No actual force is being applied (horizontally speaking) to the ground opposite the direction of travel. It's being leveraged against the ENGINES>
This is why you can lock up the brakes on an icy runway and still accelerate if you applied thrust. The wheels turn freely (or rather, apply no friction or rearward reaction)- there is no force being applied through them.
Since an airplane's forward motion is caused by the engines and not its wheels, a treadmill would not move if an airplane were on it, assuming normal operating conditions. The airplane would accelerate and take off once it had accelerated fast enough through the surrounding air flowing over the wings.
Now, if the treadmill were moving rearward under its own power, the airplane would first have to excede the treadmill's readward pace (ie, accelerate to a groundspeed of the treadmill + required indicated airspeed) in order to takeoff.
Assuming that were timed correctly, that'd reduce ground roll.
In a sense, that's how a carrier's catapult works. Depending on perspective, you could say the F-18 being launched is stationary to a point, and the carrier is being accelerated backwards relative to the jet.
Perspective is key.
Duck_Twacy
Well-Known Member
During takeoff, the engine moves the airplane across the ground. If you can overcome friction, and the additional movement of the treadmill in this case, the object - plane, me, R/C car, cat, whatever - moves forward. (Actually, the cat usually shoots off the back....or so I've heard) Throw some wings in with the forward motion, and you have take off.
I guess I need to watch, I thought they were going to prove/disprove that a stationary aircraft on a moving treadmill would lift off (which as someone said they just could hold it in place with a rope or something if that were the experiment).
:yeahthat:
I'm still watching Lost....
caliginousface
Frank N. Beans
The guy on youtube did a second test:
[yt]4owlyCOzDiE[/yt]
[yt]4owlyCOzDiE[/yt]
SlumTodd_Millionaire
Most Hated Member
No, the engine does not move the airplane across the ground, it moves it through the air. The propeller/jet engine doesn't react in any way to the ground. The wheels are in contact with the ground, but they are free-moving with bearings. The only thing the engine has to overcome is the tiny amount of friction in the bearings. You could do that with 100 RPM, probably. Once the friction in the bearings is overcome, the wheels move freely and the airplane is propelled forward. The treadmill's speed is completely irrelevant. You compare it to an RC car, cat, etc... but those are not analogous, because the force that propels them forward acts against the ground and not the air (wheels propel the RC car and legs propel the cat). With the plane, the wheels don't propel it, the prop/jet engine does.
Berkut
Well-Known Member
Only as a side effect of it moving through the air. As long as the interface between the ground and the aircraft is through a free-spinning wheel, it doesn't matter what the ground is doing. With a strong enough headwind, it doesn't have to move over the ground at all.
That's a redundant statement; if the aircraft overcomes friction, it is already overcoming the motion of the treadmill. the only way the treadmill can inhibit the aircraft is through wheel bearing friction, which as has already been pointed out, does not increase with speed.
KC Jake
Well-Known Member
Berkut
Well-Known Member
That is accurate, but it doesn't agree with your later statement:
If airspeed makes an airplane fly, why do you say it must accelerate to groundspeed + required airspeed? Like you said before, all it needs is the required airspeed. Groundspeed is irrelevant.
Assuming flank speed is greater than the takeoff speed of a Piper Cub, of course it would. The Cub does not care what the ground under its wheels is doing, only the airflow over its wings.granlistillo said:
troopernflight
Well-Known Member
1 and 1/2 hours to go, oh the suspense is killing me! 
iamapilot94
New Member
no the plane will not take off
i hope u people realize that there are more drag force acting on the plane than rolling friction and air resistants. you people miss the backward force the treadmill act on the plane even if the wheel are free bearing with the treadmill moveing backward the plane will do the same at the same speed without engine
condsider this
lets say the force to the left is negtive and the force to the left is positive
treadmill + alll other drag moving <---- at -70knot and plane moving forward -----> 70 knots
so this come to the equation -70+70=0
0 equal ground speed on a calm day 0gs=0tas no airspeed no lift no lift no flight end of story thank you every much
i hope u people realize that there are more drag force acting on the plane than rolling friction and air resistants. you people miss the backward force the treadmill act on the plane even if the wheel are free bearing with the treadmill moveing backward the plane will do the same at the same speed without engine
condsider this
lets say the force to the left is negtive and the force to the left is positive
treadmill + alll other drag moving <---- at -70knot and plane moving forward -----> 70 knots
so this come to the equation -70+70=0
0 equal ground speed on a calm day 0gs=0tas no airspeed no lift no lift no flight end of story thank you every much
SlumTodd_Millionaire
Most Hated Member
You're going to be proven wrong in 23 minutes.