Quick Physics Test..

[R Black]

After reading Ian C's i have changed my view, the plane is acting on the air around it, the runway is incidental apart from the fact the wheels will be working twice as hard, the plane will take off. The crux is what do the engines push against, not the wheels with no power.

[spidermonkey]

great thread this, it is a very badly worded question, i took it as the treadmill will counteract any MOTION, i take my hat off to some of you guys, i am now convinced the plane will take off

[hogmaw]

The lifting force on a plane's wings is a function of the air velocity

across the wing. If the plane has zero velocity with respect to the air

surrounding it there is no lift

 

OOPS yeh I getit now. Kind of a trick question

[spidermonkey]

After reading Ian C's i have changed my view, the plane is acting on the air around it, the runway is incidental apart from the fact the wheels will be working twice as hard, the plane will take off. The crux is what do the engines push against, not the wheels with no power.

 

yeah but if you read the question the treadmill will counteract the speed of the plane speed = motion, i think the question is not very clear

[Thorin]

Do bears poo in the woods?

[Gaz6002]

Actually I think there is a mythbusters episode readily viewable on youtube that does in fact discuss, quantify, and downright prove the treadmill has no effect at all on the plane taking off.

 

Someone must have a link to it?

 

The only increased effect is bearing and tyre friction on the wheels, the speed doubles so these will go up. Negligible in the scheme of things compared to the power required to get a 777 up in the air.

 

Er. Wow. Can't even begin to start on that one in this thread

 

Well, see above re understanding of physics

 

Your unconvincedness is to be admired. I'm certainly not going to turn that around with mere text - find the mythbuster thang, or failing that, a jetpack and a treadmill now that'd be a youtube hit

 

-Ian, entertained at work at last

 

I'm glad you find it entertaining. While I do understand what you are saying I still don't think it's as clear cut as the plane will just take off.

 

I still maintain that the plane won't go anywhere as the extra force required to get the plane to take-off speed would damage the landing gear (due to gravity acting on the plane). I see this as the weak link.

 

R.E. The gravity comment, what I meant was that you have to combat gravity in order to create lift. Bad phrasing by myself.

 

R.E. Mythbusters: I very much doubt they have done something similar that creates the forces we are talking about (777 on runway at take-off weight etc)

 

 

 

Can the plane take off?

 

 

IMO - no.

[Gaz6002]

yeah but if you read the question the treadmill will counteract the speed of the plane speed = motion, i think the question is not very clear

 

Thats the reason for playing devils advocate. Although the plane will indeed move in the direction of thrust from the jet engine, it won't necessarily take off due to the other factors involved in getting the thing into the air in the first place.

 

I'm not challenging physics - I'm trying to answer the question in my own opinion and still think the question is VERY MUCH open to interpretation.

[merckx]

The plane will take off.

 

The propellor or the jet engine pushes or pulls the plane forward through the air which isn't moving so you then get air moving over the wing and it produces lift.

 

The wheels are free to rotate and don't come into the equation at all.

[MrRalphMan]

yeah but if you read the question the treadmill will counteract the speed of the plane speed = motion, i think the question is not very clear

 

It only says it goes as fast in the opposite direction.

 

This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction).

[Thorin]

R.E. Mythbusters: I very much doubt they have done something similar that creates the forces we are talking about (777 on runway at take-off weight etc)

 

Well I haven't seen said Mythbusters episode but why would it have to be a 777? Should be easy enough to do with a remote control plane, the physics involved would be the same.

[tbourner]

What's take off speed for a plane? 180mph minimum? I'm sure at half that the gravity point is reduced somewhat (regardless of whether the lift on the plane at half take-off speed is exactly equal to half the mass of the plane or not, it'll still be lighter?).

So at take off speed the wheels will be spinning at 360mph ish?

Do the wheels of a plane get damaged and fall off at landing speed? What is landing speed? What factor of safety do Aerospace Engineers add when designing and testing aircraft?

[Kopite]

Not read all of this thread but it would take off with some tired-ass wheels

[Matt H]

Theres two chaps in my office, on over £80K per annum, calling me stupid because they think the plane wont take off

[Ian C]

 

and still think the question is VERY MUCH open to interpretation.

 

I don't think it is. It's a classic "thought experiment", and these are designed to be as simple as possible without a myriad or fiddly litte extraneous factors. You could go on about the additional loading of the tyres and bearings, friction generated, heat, fatigue stresses, the potential turbulence under the wing caused by the moving runway and that subsequently affecting lift, but that overcomplicates things and that's not the point at all.

 

The point of a thought experiment is, that there is a right answer and a wrong answer, and it provokes a lot of careful thought to get to one of them. In this case (will the plane take off), No is wrong and Yes is right

 

And anyway, the worst that happens to the suspension is that the wheels turn twice fast as they normally would, so if takeoff speed is say 170mph, they go at 340mph for a few seconds. I doubt they would a) collapse or b) cause so much drag a 777 couldn't take off. I don't know why gravity has appeared, unless you are attempting to use it to add weight to your argument chortle

 

-Ian

[MrRalphMan]

Theres two chaps in my office, on over £80K per annum, calling me stupid because they think the plane wont take off

 

What do you do in your office? I really hope it's not aero engineering..

[Ian C]

Theres two chaps in my office, on over £80K per annum, calling me stupid because they think the plane wont take off

 

Depressing, isn't it. 10,000lbs of aero thrust negated by parking the plane on some gym equipment.

 

Aircraft carriers should have these instead of the arrester hook system - land on a treadmill going the same speed backwards, stop dead, chaching

[MrRalphMan]

Depressing, isn't it. 10,000lbs of aero thrust negated by parking the plane on some gym equipment.

 

Aircraft carriers should have these instead of the arrester hook system - land on a treadmill going the same speed backwards, stop dead, chaching

 

Give you a bit of a nose bleed though.

[Rob]

yeah but if you read the question the treadmill will counteract the speed of the plane speed = motion, i think the question is not very clear

 

People always say that, when they've been proved wrong about this question. The question is worded perfectly, but people jump to the wrong conclusion before thinking it through thoroughly.

[Gaz6002]

People always say that, when they've been proved wrong about this question. The question is worded perfectly, but people jump to the wrong conclusion before thinking it through thoroughly.

 

I'd hold my hand up to this.

 

Every answer I've given in this thread has been a bit of a reaction to what was posted rather than me thinking about it logically. I've been talking on the phone whilst typing most answers and trying to fix peoples internet at the same time.

 

I've now had a 10 minute break and come back to realise that I am in fact wrong - the plane will take off.

 

I'd have thought my physics would have been better than this - I guess it's a mixutre of lack of concentration and Ians inflamitory comments

 

Still - good game, good game

[Gaz6002]

I don't think it is. It's a classic "thought experiment", and these are designed to be as simple as possible without a myriad or fiddly litte extraneous factors. You could go on about the additional loading of the tyres and bearings, friction generated, heat, fatigue stresses, the potential turbulence under the wing caused by the moving runway and that subsequently affecting lift, but that overcomplicates things and that's not the point at all.

 

The point of a thought experiment is, that there is a right answer and a wrong answer, and it provokes a lot of careful thought to get to one of them. In this case (will the plane take off), No is wrong and Yes is right

 

And anyway, the worst that happens to the suspension is that the wheels turn twice fast as they normally would, so if takeoff speed is say 170mph, they go at 340mph for a few seconds. I doubt they would a) collapse or b) cause so much drag a 777 couldn't take off. I don't know why gravity has appeared, unless you are attempting to use it to add weight to your argument chortle

 

-Ian

 

See above post.

 

chortle.

[rpslaughter1982]

The plane would take off. Such as a plane that takes off from water moving in the opposite direction. The runway does not effect the air around the plane. The thrust is caused by the equal and opposite force caused by the engine pushing out air.

 

If the air speed increased at the same rate that the thrust was generated then the plane would not take off.

 

The difference between ground speed and air speed is demonstrated in the question.

[rpslaughter1982]

also take off speeds vary greatly depending on various factors such as the weight, shape, wings span/area etc.. A paper plane takes off at a far lesser speed than a eurofighter

[Thorin]

and Ians inflamitory comments

 

Shocking behaviour from a mod isn't it. You know, if I'd have been made a mod....

[Kranz]

So the plane's ground speed is zero???

 

If it is then the plane will not take off as it is the airspeed that it requires to produce lift.

 

If the conveyor runway was moving in the same direction as the plane, therefore doubling its ground speed, it would take off quicker.....much like a plane on an aircraft carrier, hence why they have to take off into wind from the read to front of the ship.

 

Edit: To clarify, the engines would produce thrust that would accelerate the plane along the runway, but as the runway matched the speed of the plane its actual speed relative to the environment around it would be zero. Its air speed would be the same as the wind speed at the time, which would be insufficient to produce any lift.

However, the laminar flow developed by the moving runway MAY produce some ground effect on the underside of the wing, producing a little lift, but still not enough to get airbourne.

[Ian C]

I wasn't making any inflamatory comments The gravity thing was a terrible pun though, I admit to that.

 

Right, sorted then. Next up - the perennial non-question "what happens if I drive at the speed of light and turn on my headlights..."