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| Will the plane ever take off? |
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| Total Votes : 26 |
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flosho
Joined: 01 Jul 2004
Posts: 3160
Location: Eau Claire, Wisconsin
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 Posted: Sat Dec 03, 2005 6:40 am Post subject: OT- Airplane Riddle?!! |
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An Airplane propelled by a jet engine is on a runway that acts as a treadmill. The faster the plane puches it self the treadmill counteracts the motion. Therefore if the airplane is pushing at 100 mph north, then the runway is moving 100 mph south.
The Question:
Will the airplane take off?
Explain
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Ozzie
Joined: 12 Mar 2005
Posts: 4448
Location: Townsville, Qld. Australia
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| Posted: Sat Dec 03, 2005 7:18 am Post subject: |
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There is no air moving over the wings to create lift.
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morghen
Joined: 21 Jan 2005
Posts: 9095
Location: Romania
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| Posted: Sat Dec 03, 2005 8:29 am Post subject: |
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some jet airplanes get airborne and land verticaly 
all jet airplanes have a control jet direction sistems so the actual jet changes its angle compared to the plane itself...
the threadmill moves at 100mph...well that movment would move some air in its nearby space...
so there is some air moving under the plane...the jet can be pointed down...i guess it could actualy take off 
ALL THIS IGNORING THE INERTIA OF THE THREAMILL(MUST BE A HEAVY THING TO SUPPORT THE PLANE) AND FRICTION BETWEEN THE PLANE AND THE THREADMILL PLANE,WICH IS HIGH AND WOULD MAKE THE PLANE JUST SHOOT OFF IT
so...theoreticaly...maby the plane would stay on the threadmill....practicaly...NEVER
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chris24
Joined: 17 Jan 2005
Posts: 334
Location: boston/nottingham UK
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| Posted: Sat Dec 03, 2005 8:38 am Post subject: |
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Bernoulli effect ( fluid with higher velocity has a lower pressure) and Newton's 3rd Law (action-reaction is opposite but equal).
1. Bernoulli Effect: The wings of a plane are flatter on the bottom than the top. This means that there is a greater distance to travel on the top than the bottom. Giving rise to the popular theory that the increased velocity at the top gives a lower pressure above the wing and so a force upwards - lift. ((However, to get the acceleration you need a lower pressure to start with!))
2. Newton's 3rd Law: The air that flows over the top of the wing sticks to the wing (?Coanda effect) and as the top of the wing angulates downwards, once the air has reached the end of the wing it continues in its path of movement (conservation of momentum). This downward flow or force requires an opposite (upward) force that equal (Newton's 3rd Law).
And so it is a mix of these two that keep planes in the air and generate lift.
Right?
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WhoDak
Joined: 22 Mar 2005
Posts: 492
Location: Akron, OH
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| Posted: Sat Dec 03, 2005 8:38 am Post subject: |
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The engines would be moving the air through the turbines fast enough to displace enough air it wouldn't be able to stay in one spot on the runway would it?
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Mike
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chris24
Joined: 17 Jan 2005
Posts: 334
Location: boston/nottingham UK
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| Posted: Sat Dec 03, 2005 8:40 am Post subject: |
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a jumpjet...nice lateral (or vertical) thinking morghen.
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Andrew NZ
Joined: 22 Jun 2004
Posts: 744
Location: New Zealand
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| Posted: Sat Dec 03, 2005 9:11 am Post subject: |
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Of course it would, its just that the wheels would be spinning twice as fast as normal until it leaves the ground!
The last time I looked at a plane the wheels were'nt driven by the engine  so what speed the ground is going past is irrelevant - the jet engines push through the air.
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Andrew
1977 RX924 race car
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Khal
Joined: 26 Sep 2003
Posts: 4872
Location: Sunny and lovely interior BC, Canada
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| Posted: Sat Dec 03, 2005 9:25 am Post subject: |
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Agree with Ozzie.
If the 'plane is not moving forward through the air, it cannot take off.
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Neil924
Joined: 18 Mar 2003
Posts: 4225
Location: Canada
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| Posted: Sat Dec 03, 2005 9:58 am Post subject: |
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| It would probably lift {taking weight off the wheels} but I don't know if it has enough eumphh! to actually leave the ground. And if it did, it would be a very short and bouncey trip. |
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Paul
Joined: 02 Nov 2002
Posts: 9491
Location: Southeast Wisconsin
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| Posted: Sat Dec 03, 2005 10:19 am Post subject: |
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| Andrew NZ wrote: | Of course it would, its just that the wheels would be spinning twice as fast as normal until it leaves the ground!
The last time I looked at a plane the wheels were'nt driven by the engine so what speed the ground is going past is irrelevant - the jet engines push through the air. |
I agree with Andrew as long as the treadmill or the runway at the end of the treadmill is long enough for the plane to achieve lift off speed. (I hope my years of Aerospace Engineering at Penn State helped me make the right decision....)
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Neil924
Joined: 18 Mar 2003
Posts: 4225
Location: Canada
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| Posted: Sat Dec 03, 2005 10:40 am Post subject: |
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| Paul wrote: | | Andrew NZ wrote: | Of course it would, its just that the wheels would be spinning twice as fast as normal until it leaves the ground!
The last time I looked at a plane the wheels were'nt driven by the engine so what speed the ground is going past is irrelevant - the jet engines push through the air. |
I agree with Andrew as long as the treadmill or the runway at the end of the treadmill is long enough for the plane to achieve lift off speed. (I hope my years of Aerospace Engineering at Penn State helped me make the right decision....) |
They taught you Areospace Engineering in a State Penitentiary? Wow! |
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tj924
Joined: 15 Jul 2004
Posts: 957
Location: Toowoomba, Queensland, Australia
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| Posted: Sat Dec 03, 2005 11:43 am Post subject: |
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| Andrew NZ wrote: | Of course it would, its just that the wheels would be spinning twice as fast as normal until it leaves the ground!
The last time I looked at a plane the wheels were'nt driven by the engine so what speed the ground is going past is irrelevant - the jet engines push through the air. |
| Paul wrote: | | I agree with Andrew as long as the treadmill or the runway at the end of the treadmill is long enough for the plane to achieve lift off speed. (I hope my years of Aerospace Engineering at Penn State helped me make the right decision....) |
But the point is that the plane is remaining stationary (not physically possible, but thats not the point). It needs significant forward movement to achieve flight, so I'd think it would remain on the tradmill.
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Silver '82 924 NA 5-Speed Manual |
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Andrew NZ
Joined: 22 Jun 2004
Posts: 744
Location: New Zealand
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| Posted: Sat Dec 03, 2005 11:49 am Post subject: |
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| tj924 wrote: | | Andrew NZ wrote: | Of course it would, its just that the wheels would be spinning twice as fast as normal until it leaves the ground!
The last time I looked at a plane the wheels were'nt driven by the engine so what speed the ground is going past is irrelevant - the jet engines push through the air. |
| Paul wrote: | | I agree with Andrew as long as the treadmill or the runway at the end of the treadmill is long enough for the plane to achieve lift off speed. (I hope my years of Aerospace Engineering at Penn State helped me make the right decision....) |
But the point is that the plane is remaining stationary (not physically possible, but thats not the point). It needs significant forward movement to achieve flight, so I'd think it would remain on the tradmill. |
Perhaps it should have been worded differently then?? There's nothing there that says the plane isn't, or can't move, is there?
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Andrew
1977 RX924 race car
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tj924
Joined: 15 Jul 2004
Posts: 957
Location: Toowoomba, Queensland, Australia
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| Posted: Sat Dec 03, 2005 11:52 am Post subject: |
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| Andrew NZ wrote: | | ...There's nothing there that says the plane isn't, or can't move, is there? |
How about:
| Flosho wrote: | | ...The faster the plane pushes it self the treadmill counteracts the motion...if the airplane is pushing at 100 mph north, then the runway is moving 100 mph south |
I thought that implied no forward motion.
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TJ
Silver '82 924 NA 5-Speed Manual |
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Paul
Joined: 02 Nov 2002
Posts: 9491
Location: Southeast Wisconsin
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| Posted: Sat Dec 03, 2005 11:55 am Post subject: |
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That doesn't matter, unless the pilot has full brakes applied!
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