Blimey – haven’t heard this one before but it’s amazing how confused people can get themselves on something relatively straight forward. “Wood” and “trees” spring to mind.

Oh, and yes it would take off 😉

this has confused me for years.

i just ‘got it’ thanks to GrahamS’ point about the conveyor needing to be as long as the runway

boy do i feel stupid

OK, I think I get this….the question is written such that it makes you reason that the plane will remain stationary.
But actually it says that the plane will move at a certain speed in one direction, while the conveyor will move in the opposite direction at the same speed. So, both the plane and the conveyor are moving in opposite directions down the runway.

It’s all about RELATIVE velocity.

To an observer on the ground in between the two vehicles, they are both going at takeoff speed, but in opposite directions. However, an observer on the pick-up truck is stationary RELATIVE to the truck and will see the plane move away from him at 2x the takeoff speed; hence it can takeoff.

If the question was worded so that the pilot applied the normal power required for takeoff speed to be attained and the pick-up truck drove at takeoff speed in the opposite direction, then the plane would remain stationary, as all the thrust is going into pushing the plane at +v m/s but the conveyor is cancelling that out with it’s -v m/s.

stumpy… you were so so close, but then you mucked it all up in the last paragraph…

If the question was worded so that the pilot applied the normal power required for takeoff speed to be attained and the pick-up truck drove at takeoff speed in the opposite direction, then the plane would remain stationary, as all the thrust is going into pushing the plane at +v m/s but the conveyor is cancelling that out with it’s -v m/s.

You were doing so well up until that last paragraph. The extra power needed from the plane is minimal, just enough to overcome the slight increase in friction in the wheel bearings.

Oh yeah……bollocks!! I see where I have made my blunder and I am now going to stub my toe by way of punishment.

😳

http://www.airplaneonatreadmill.com/

Will it bollocks. The plane is effectively stationery, therefore no lift under the wings from air rushing past.

I’m 3 years old btw

The confusion on this comes from one of two sources:

1) people being thick and not understanding how planes work and
2) some versions of the original question being worded in such a way as would render the plane unable to take off despite the required situation being impossible in the real world.

I fully understand all facets of the problem. I have full grasp of every possible angle and can see everything at once.

I have reached Nerdvana.

When the question is explained as in the cases below it’s simple:
1) An airplane is sitting at rest on a very powerful treadmill. You are at the controls of the treadmill, while I am at the controls of the airplane. On some signal, I begin to attempt to take flight in the plane, and you attempt to match my speed to try to keep me stationary. Will the plane take off?

2) An airplane is sitting at rest on a very powerful treadmill. You are at the controls of the treadmill, while I am at the controls of the airplane. On some signal, I throttle up the airplane and you turn on the treadmill, and we conspire by our joint effort to try to keep the plane stationary relative to the ground. Will the plane take off?

3) An airplane is sitting at rest on a very powerful treadmill. You are at the controls of the treadmill, while I am at the controls of the airplane. On some signal, I attempt to take flight in the plane, but you match my speed with the treadmill and keep me stationary relative to the ground. Will the plane take off?

In case 1 it will take off providing the treadmill is long enough. Too much confusion and interpretation over the question. Nice to see the really intelligent people explaining their viewpoints with such clarity in terms such as “you’re thick.”
What if the ac wheel bearings were from Superstar?

devs.

it doesnt matter how powerful the tredmill is.

the only force holding the plane back is the friction in the wheel bearings.
which is a tiny amount, and in no way be noticable.
heck even a man can pull a jet plane along the apron.

The point you are missing devs is that in case 3 there is nothing the treadmill operator can do to prevent the plane taking off. No matter how powerful the treadmill there is no way he can keep the plane stationary relative to the ground.

It will, of course, take off. However it will then hit a flock of birds, and crash. Hope you’ve positioned the treadmill near a river, and have a pilot named Cheeseburger?

If you had all read the link above which explains why people get the wrong idea about the question, only a complete idiot would try to attempt 3. Case 1 is the only question which has the answer yes the ac will take off. It’s a good one though and has certainly had the old grey matter ticking over. The main problem with this one is getting everybody to see the same question. Now I have had it explained it really is simple.
LS, your statement is a bit daft if you think about it. I have pulled a 20 ton ac along the ground. The effort just about gave me piles. The treadmill would have to be very powerful. Your average gym jobber need not apply

devs, no matter how powerful the treadmill, there is no way it can stop the plane taking off. Ever.

devs… sorry for being so ignorant, but can you explain to a relative moron like myself exactly how you plan to keep an aircraft stationary by just using a rolling treadmill?

Superglue in the wheel bearings, or square wheels, would do it 🙂

aaaaaaggggggggghhhhhhhhhhhhhh

IF PLANE HAS AIR GO OVER WING FAST IT TAKE OFF

IF NO AIR GO OVER WING IT NO TAKE OFF

Pook… muuuuaaaaahahahahahaha

Yes Pook we know.

miketually… maybe a stick through the spokes would work too..

Okay, i think i can provide an explanation that might help those who are still confused.

A plane on a conveyor belt/treadmill is not like a human on a conveyor belt/treadmill. The human has to move their legs to stay still, and if the speed was increased enough they wouldn’t even be able to do that, and would fly off the back.

HOWEVER the plane doesn’t have legs. It has wheels. And (providing these have frictionless bearings) it can stay still on the conveyor belt/treadmill WHILE USING NO POWER – its wheels will just spin round underneath it. If it turns its engines on, it will move forward, and its wheels will spin even faster.

The idea of the plane on a treadmill of short length just doesn’t work. It wouldn’t take off, but it would hit the front of the treadmill straight away.

while we are dredging up the past, has anyone got any opinions on cheap disc brake pads?

Okay, i think i can provide an explanation that might help those who are still confused.

Another one that might help:

Strap a rocket to a shopping trolley and put that on the conveyor belt. Would that move along it?

Ooh, anyone got a YouTube video for that one?

TL:DR, but the aircraft going the opposite way to the conveyor theorey is arse!
that would apply if the power was being driven through the wheels, but its not, so it wont :s
as long as the engines apply enough power to overcome the inertia of the plane (the inertia causing it to move backwards on a backwards moving conveyor), the plane will move at the speed the engines dictate, the wheels will just spin, freely, twice as fast as on a static runway.

the engines, apply force to the static air around them, not to the surface the plane is resting on.

GOSH!

But what if it was in a river?

<insert new level of complication here>

in your FACE beardface!

simon wanders off muttering to find the sniper rifle and large box of hollow points

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miketually – Member

devs, no matter how powerful the treadmill, there is no way it can stop the plane taking off. Ever.
Posted 1 hour ago #
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funkynick – Member

devs… sorry for being so ignorant, but can you explain to a relative moron like myself exactly how you plan to keep an aircraft stationary by just using a rolling treadmill?

MT misses my point entirely. Scenario 3 which I pasted directly from a website that explains the whole thing would only be attempted by an idiot because of the reason you are trying to point out. The treadmill would need to be “powerful” to start the whole thing moving in the first place.

FN Are you taking the piss? Are we still in frictionless wonder land or the real world? In frictionless wonderworld the ac will stay still on a treadmill. In real world you would have to use enough forward thrust to counter the friction of bearing and weight on wheels on ground.
Any more thrust would give forward motion relative to the ground and air and lift would be produced.

What about if a helicopter is weighed in a box and then takes off and hovers. It’s still inside the enclosed box so does the box weigh the same?

*becomes unsure as to whether devs is actually a post-ironic troll*

devs… sorry, I must be really thick or something, but are you really saying that the friction in the wheel bearings is enough to keep an aeroplane stationary when it’s throttled up to try and take off?

No. Have you tried the fish?

In answer to your helicopter q yes the box should weigh the same as the helicopters rotors will be pushing air down.

How about a BIG fan blowing air at the plane!

How about a BIG fan blowing air at the plane!

From what direction?

Infront and not on a tredmill!

warm air or cold air?

Mmmmm…I’m thinking tepid air