So... I hear Mythbusters are doing the plane on a conveyor belt thing.

[cultureofdoubt]

You have a plane.

It sits on a conveyor belt.

This conveyor belt is rather unusual. It moves backwards at the same speed the plane moves forwards.*

Poll Does the plane take off?

*there's some ambiguity there. I'm deliberately leaving it ambiguous

Comments

[cultureofdoubt]

Whoops. I should learn how to use font size tags. Fixed anyway.

[azureskies]

With my admittedly limited knowledge of science, I voted no, because if it's not moving (or, er, not in a wind tunnel), then there's no air being pushed underneath the wings to lift it off the ground. And if it WAS possible to make planes take off without a runway (um, not counting Harriers), wouldn't it have been done by now?

[cultureofdoubt]

Well, I'll leave it a bit longer before posting a discussion. But I must say I'm a little surprised I'm on my lonesome on this one so far.

[chrisvenus]

I'm surprised you're on that side of the fence to be honest. It seems like a really obvious answer to me so I can't really see where teh question is so I look forward to your reasons for saying it will take off.

[cultureofdoubt]

Well, I can see both sides of the fence. But I'd choose to read the question in the way that it can.

Unless you think there's no way of reading it that it can take off, in which case I look forward to the resulting discussion too :-)

[chrisvenus]

Oh, yeah, I guess I hadn't read the ambiguity there before. :)

I can see how you could read it in a way that lets the plane take off but it seems like a strange reading to me. I suspect I'm just not thinking about it in the right way or something...

[beingjdc]

I think 'it depends on the plane', and on your ambiguity, but in the case of most actually-existing planes, rather than thought-experiment possible-planes, it's a no.

[cultureofdoubt]

Interesting. How do you think it depends on the plane?

[beingjdc]

Well, see your ambiguity which is mainly that the plane is not defined as moving forward relative to any thing, so the plane and the conveyor belt might be moving relative to the earth. That does require the plane to be able to move twice as quickly relative to the ground it's sitting on than its normal take-off speed. If it's being pushed by jets, that can still happen I imagine, since the wheels are merely an unwelcome distraction.

Also if it's a Harrier.

[cultureofdoubt]

Conveyor belt fixed relative to the earth on a day with no wind.

No vertical thrust applied (so no harriers or the like)

Beyond that I'll hold off on discussion.

[hsenag]

I voted no for the obvious air reasons, but on reflection there's a significant momentum issue here; since planes are powered by pushing air around rather than turning their wheels, it'd be quite hard to stop the plane from simply skidding forward (relative to the earth).

[evath]

why should the wheels not turn? You don't take off with the breaks on ;)

[hsenag]

Yes, good point.

OK, I see the ambiguity now. If the conveyor belt is light or unpowered, then no matter how fast it moves the plane's wheels will turn fast enough to keep the plane moving forward relative to the earth. (If it accelerates a lot the wheels will skid).

However if the belt is heavy and powered, it should be able to accelerate the plane backwards to counteract the plane's acceleration. The forward momentum from the jets will be applied to the entire earth via the belt, instead.

[cultureofdoubt]

Yeah, I'm thinking more in terms of the friction of the wheel bearings of the landing gear, but I think it's essentially the same ambiguity in terms of the ability of the belt to apply force.