Stupid physics question

[Tom]

So the engines are throttled up to 100%, but the conveyor belt which cannot counteract the thrust from the engines somehow magically manages to keep the plane still.

So what are the engines pushing against then? That airframe must be pretty bent out of shape by now.

 

[Paradroid]

A question for the yes camp. How would this theoretical situation look to an observer standing in line with the plane at the side of the runway? Would he hear the engines spool up and see the plane's wheels begin to spin faster and faster (while the aircraft stays still in relation to him)? Then what? At some magical amount of thrust the aircraft would just jump into the air and fly off? Bollocks. If the surface beneath the aircraft changes it's speed to match that generated by the plane, then it will NEVER move forward. If it never moves forward and there's no wind, then it will NEVER have any air flowing over (and under) the wings. No wind over the lifting surfaces equals no lift.

I realise that aircraft wheels do not operate like automobile wheels, but neither do most aircraft propulsion units (whether prop or jet or whatever) provide lift. They push or pull the airframe through the air. Lift comes from the wings. No air over the wings - no flight.

The waterplane arguement doesn't work for me. The floats basically act like boat hulls once the plane reaches a certain speed through the water. Nothing at all to do with a theoretical plane with magic wheels on a magic surface as discussed throughout most of the thread.

Who the f**k started this anyway? It's annoying as f**k!

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For people trying to get their heads around this, try imagining the opposite scenario with the plane landing on the conveyor belt. According to some, the plane should stop dead as soon as it touches the runway - which would be impossible.
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The wheels don't supply the forward motion, you said it yourself:

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...aircraft propulsion units ... They push or pull the airframe through the air.
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The wheels are there merely to stop the undercarriage scraping along the runway (and obviously to allow a relatively frictionless conduit for the aircraft to reach its take-off velocity).


And to address your proposition:

...How would this theoretical situation look to an observer standing in line with the plane at the side of the runway? Would he hear the engines spool up and see the plane's wheels begin to spin faster and faster (while the aircraft stays still in relation to him)? Then what? At some magical amount of thrust the aircraft would just jump into the air and fly off?
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You'd see the wheels spinning before the engines were engaged, and you'd see the wheels spinning twice as fast as normal as the plane careered down the runway, taking off as you'd normally expect (probably with some smoke coming off the wheels).

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Bollocks. If the surface beneath the aircraft changes it's speed to match that generated by the plane, then it will NEVER move forward.
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The wheels aren't connected to the engines. This applies to cars, not planes.


...I'll draw a picture...

 

[Mofo8]

I've changed my mind after surfing about the interweb for a bit... and finding some much more helpful and insightful arguements that the ones in this thread

In THEORY it appears the answer is yes, as the conveyor belt has no way of influencing or counteracting the thrust.

In practice however, I'd be happy if someone could name an aircraft whose maximum gear down speed in flight (never mind the gears max speed on the ground which will be much lower) is equal to, or over twice the speed it normally rotated at (takes off).

http://www.avweb.com/news/columns/191034-1.html

 

[Louster]

Uhm, you do realise that that exact link was not only posted twice in this thread already, but was also largely quoted directly by Will? So much for having read through.

 

[Paradroid]

I've changed my mind after surfing about the interweb for a bit... and finding some much more helpful and insightful arguements that the ones in this thread

In THEORY it appears the answer is yes, as the conveyor belt has no way of influencing or counteracting the thrust.

In practice however, I'd be happy if someone could name an aircraft whose maximum gear down speed in flight (never mind the gears max speed on the ground which will be much lower) is equal to, or over twice the speed it normally rotated at (takes off).

http://www.avweb.com/news/columns/191034-1.html

Your question doesn't make any sense! You seem to be relating the flight dynamics (of the under carriage creating drag) to the spinning wheels?

The wheels will rotate at twice their normal rate. That's it. The plane takes-off as normal, at it's normal take-off speed. There's no extra drag created because the plane isn't travelling any faster or slower than normal. It's just a normal flight. (but with some smoke coming off the wheels, and huge boulders of concrete pilling up at the end of the fictional runway).


If you're asking does anyone know of any landing gear that can cope with 300kmh+ speeds, then the answer is no. But who's ever heard of a mile long concrete conveyor belt?

 

[Maljonic]

I don't see why people are so fixated by the conveyor belt, it's just a modal example to illustrate that the craft wont move forwards. It could just as easily be big steel rollers under the wheels that match the speed of the plane, not that it makes any difference to the outcome.

 

[Scouse]

You'd see the wheels spinning before the engines were engaged

No you wouldn't. If I park a shopping trolley on one of those moving airport floors it won't stay in the same place spinning it's wheels freely.

But yup, the plane would still take off.

 

[old.user4556]

I've thought about it long and hard; I have deliberated with my colleagues at work, i've run it past my extremely brainy dad.

I have come to the conclusion that the plane would indeed take off.

What made me think about it more was the snow this morning when I tried to drive away, my rear wheels (with traction control off) just kept spinning and spinning. So I thought "what if i put a jet engine on the back, would I start to move forward?" and of course I would start to move forward.

And then I thought about a plane on totally frictionless ice; if you apply maximum thrust then the plane would just roll forward as normal. Now if you were to start to move the ice in the opposite direction (assuming the friction is zero), it wouldn't matter - the plane would start to roll forward as normal.

Again, it's all very hypothetical, but for a given frictionless environment - the plane would take off .

 

[tris-]

aahh G, i wish i could fist you up the arse just for that. you should of been convinced 20 pages ago

 

[Xgkkp]

Here is another link which convinced people on another forum; just for the record:

http://www.straightdope.com/columns/060203.html

 

[ECA]

Here is another link which convinced people on another forum; just for the record:

http://www.straightdope.com/columns/060203.html

Why do you care so much about peoples opinion on a shittily phrased question?

 

[old.user4556]

aahh G, i wish i could fist you up the arse just for that. you should of been convinced 20 pages ago

Probably because i'm not a knee-jerk decision maker; i like to hypothesise and mull it over, discuss it with others, evaluate every possibility, scenario and outcome before making a decision.

The original scenario was too vague and too badly worded to make an instant decision, although some people did and it was a correct decision - although when it's a 50:50 question you have a good chance of knee-jerking the right way .

 

[itcheh]

I like knee-jerking (off?)

I've changed my mind too - plane takes off.

YAY!

Right - now that I've repented you are free to close the thead

 

[ECA]

BUMP!

Mythbusters is officially covering this !

I think its airing on the 30th!

 

[ECA]

There is also a preview!

Video - Discovery Channel Videos Online - News, Science, Space, History, Engineering


( the link just takes you to the latest preview, but go to mythbuster 70 clips> planes on a conveyor belt ).

 

[Tilda]

Why does the US military not use this on carriers?

 

[Frizz]

There are so many "No" votes in this thread.

 

[Sharma]

This will be interesting.

 

[Chilly]

oh ffs...

 

[old.user4556]

Toilet Roll Goes Over K?

 

[nath]

Am I missing something or did that video end before anything happened...? (looking at the plane on a conveyor belt clip)

 

[nath]

Actually, doesn't matter - it's going to take off anyway

 

[ECA]

Am I missing something or did that video end before anything happened...? (looking at the plane on a conveyor belt clip)

maybe reread my post/s?

 

[nath]

Aye - it was a fairly long preview though, figured that it might actually go somewhere.

 

[TdC]

I should bad all of you for defibrillatoring this thread

 

[Chilly]

PLEASE kill it teedles

 

[SawTooTH]

NO as the plane needs to generate lift from air passing over the top wing slower than the bottom wing. This creates upward drag and the plane takes off.

If the plane were stationary there is no wind and hence it doesnt take off.

A better question would be what if you put giant fans in front of it blowing air over the wings.

Then the answer maybe yes

 

[Will]

Oh for fucks sake. Can we not do this again? The answer is yes, because the plane is driven by gigantic jet engines on its wings, not by its wheels.

If anyone else posts up an answer, I'm locking the thread, because this fills me with teh rage!!!

 

[Insane]

If anyone else posts up an answer, I'm locking the thread, because this fills me with teh rage!!!

Sure just set the zombies onto them instead, it would be more fun to watch the carnage

either that or you got bit by the rabid monkey

 

[TdC]

Will's so angry these days