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+--- Thread: Will it fly? (/showthread.php?tid=6807)
Will it fly? - .RJ - 12-20-2007
You know the question.
![[Image: poguespan.jpg]](http://graphics8.nytimes.com/images/2006/12/11/technology/poguespan.jpg)
![[Image: diaf.gif]](http://rr-ax.com/bbs/images/emoticons/diaf.gif)
- HAULN-SS - 12-20-2007
The plane has to be moving for it to have air flowing over the wings. An infinite treadmill keeps the plane stationary, so no, won't fly
- Ginger - 12-20-2007
No fly as in the picture. Can we assume there's infinitely long treadmill - not the motor cover seen in the picture? In the pic it would just run straight into said cover.
The wheels aren't driven, the jets move the body of the plane, so you can't assume it goes nowhere. However, it's not long enough for the plane acheive sufficient speed, and therefore lift, to take off.
- .RJ - 12-20-2007
asteele2 Wrote:. Can we assume there's infinitely long treadmill - not the motor cover seen in the picture? In the pic it would just run straight into said cover
Yes - its a theoretical question. The 'treadmill' is infinitely long. And for theoretical discussion purposes, the wheels/treadmill are frictionless.
- BLINGMW - 12-20-2007
Ginger's got it. The plane will accelerate and takeoff just like normal. It's just that the wheels will consequently be spinning twice as fast.
- Ginger - 12-20-2007
.RJ Wrote:asteele2 Wrote:. Can we assume there's infinitely long treadmill - not the motor cover seen in the picture? In the pic it would just run straight into said cover
Yes - its a theoretical question. The 'treadmill' is infinitely long. And for theoretical discussion purposes, the wheels/treadmill are frictionless.
Then you bet it'll fly! I'll be gettin' my Mile High Club on in a treadmill takeoff plane!
- ViPER1313 - 12-20-2007
BLINGMW Wrote:Ginger's got it. The plane will accelerate and takeoff just like normal. It's just that the wheels will consequently be spinning twice as fast.
What he said
- Evan - 12-20-2007
.RJ Wrote:Yes - its a theoretical question. The 'treadmill' is infinitely long. And for theoretical discussion purposes, the wheels/treadmill are frictionless.well thats a completely different question.
the way it is phrased and illustrated above implies that the plane itself doesnt move.
the way you just changed it just means the runway is a big treadmill, which still means its a runway and will still take off with enough thrust, and isnt a particularly interesting problem.
- .RJ - 12-20-2007
Evan Wrote:the way you just changed it just means the runway is a big treadmill, which still means its a runway and will still take off with enough thrust, and isnt a particularly interesting problem.
Well I *ass-u-med* that everyone had seen this same question argued ad nauseum elsewhere on the internet and didnt need to 'splain it.
Edit: I grabbed the first pic I could find for 'plane treadmill' for illustration only
Mythbusters will be testing this (or already has tested it?). Either way it airs next month.
- CaptainHenreh - 12-20-2007
Cecil says yes, and it's a dumb question anyway.
If we're talking infinite runway, etc, even frictionless runway or whatever, the plane still takes off.
The only way to make the plane *not* take off is to continue to accelerate the treadmill as the plane accelerates. (at a greater rate, to overcome the force of the engines, rather than just the speed of the wheels)
Which is also stupid.
- Kaan - 12-20-2007
no it doesnt fly. its not indefinately long... if the "treadmill" moves as fast and the plane moves... it goes no where.
if its indefinately long... to take off the plane must reach take off speed + the speed of the treadmill to generate the same lift as a plane on ground that is not moving.
- Ginger - 12-20-2007
Kaan Wrote:no it doesnt fly.
Explain yourself.
- Kaan - 12-20-2007
planes need a take off speed... the speed doesnt make the plane take off... it causes the lift (due to wing shape and size)... Xmph moves X amount of air to move across X wing... if the ground moves in an equal and oposite direction of the plane, you never get air under the wing to produce lift.
btw you can calculate minimum take off speeds with crazy math... you need to know wing shape, size, and weight of the plane...
- G.Irish - 12-20-2007
CaptainHenreh Wrote:The only way to make the plane *not* take off is to continue to accelerate the treadmill as the plane accelerates.Nope. Remember, the wheels are turning freely. That means that the only force the wheels exert on the plane's body that prevents it from moving forward is the resistance on the wheel bearings. The airplane's thrust is what drives it forward so even if the wheels are turning backwards at 1000 mph it won't slow the plane down.
Which is also stupid.
- CaptainHenreh - 12-20-2007
G.Irish Wrote:CaptainHenreh Wrote:The only way to make the plane *not* take off is to continue to accelerate the treadmill as the plane accelerates.Nope. Remember, the wheels are turning freely. That means that the only force the wheels exert on the plane's body that prevents it from moving forward is the resistance on the wheel bearings. The airplane's thrust is what drives it forward so even if the wheels are turning backwards at 1000 mph it won't slow the plane down.
Which is also stupid.
The wheels are not frictionless. Angular momentum is imparted do them by the treadmill, some of which which will manifest itself as a linear backward force on the plane. Eventually, with enough acceleration by the treadmill the plane will *not* take off, as the linear force from the angular momentum of the wheels = the thrust force of the engines.
- Ginger - 12-20-2007
Kaan Wrote:planes need a take off speed... the speed doesnt make the plane take off... it causes the lift (due to wing shape and size)... Xmph moves X amount of air to move across X wing... if the ground moves in an equal and oposite direction of the plane, you never get air under the wing to produce lift.
Actually, planes need a specific air velocity moving under the wing to generate enough lift to take off. The fuselage of the plane doesn't actually have to moving across the gound. Take off can be achieved in this fashion.. I've actually seen it modeled in win tunnels. However, in the example, the fuselage will still move along the ground at whatever speed the engines propel it at. The treadmill does not effect this travel at all because the wheels are not driven.
Now, what would be really cool, is if it were a VTOL. ;
- ScottyB - 12-20-2007
G.Irish Wrote:CaptainHenreh Wrote:The only way to make the plane *not* take off is to continue to accelerate the treadmill as the plane accelerates.
friction of the tires notwithstanding, you get a plane thrust forward fast enough by it's jet engines and it can't do anything BUT fly.
if the wheels are goign fast enough to cause bearing and traction friction, it wil be like the plane is in sand and it won't get enough speed for takeoff.
- Kaan - 12-20-2007
Evan Wrote:the way you just changed it just means the runway is a big treadmill, which still means its a runway and will still take off with enough thrust, and isnt a particularly interesting problem.
right it would take off if the trust it produces is equal to its minmum take off speed + the speed the treadmill is moving.
the issue that ran around the internet says that the plane and the treadmill will always move at the same speed... so no it will not take off. it never achieves enough thrust to produce lift.
- stevegula - 12-20-2007
Yea, I'll go ahead and say I've never heard whatever question is not being posed because RJ thinks we've all heard it.
- Ginger - 12-20-2007
Kaan, I think you're missing that the wheels aren't "connected" to the movement of the plane. The frictional losses considered are marginal, at best. You could move the threadmill under the plane at whatever speed you wanted and hold the plane in place with a glorified chain. The moment the thrusters activate the plane begins to move forward and, proportional to foward velocity, lift is generated.