Brain Teaser

[Jamz72]

Randomly found this on the internet today, it's a good one

Let's have people's opinions without the use of Google


"A plane is standing on a runway that can move (some sort of conveyer belt). The plane moves in one direction, while the conveyer moves 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). Can the plane take off?"

 

[Chris]

Surely not? Im confused.

 

[Tree200]

No, it's not about a both how fast the plane is travelling on its wheels. It's about the wind flowing over the wings creating lift.

 

[Foxspeed]

yes it can

 

[mark_1873]

Im rather drunk and I without google I think NO it won't move. With the conveyor belt turning at the wheel speed the plane should stay stationary as it can't move forward to generate lift ???

like an F1 car on a dyno without a wind tunnel it'll still produce its amazing power etc but won't produce any down fore...

 

[Fernandez]

I'm saying no too. It will need airflow over and under the wing to create lift. Surely if the treadmill counteracts the forward inertia of the plane it'll be stood still relative with the ground

 

[Foxspeed]

could also be one of those "trick" answer question the "oh that's it" type of answers inky:

 

[Jamz72]

As the answers seem fairly one sided atm, I'll throw out there that wheels of a plane are freely rotating (so long as the brake is off!) and the force generated to move a plane comes from propellers/jet engines

I don't know the correct answer btw!

 

[mark_1873]

Regardless of the power of the jet engine if the wheel bearings can keep up with the rotation on a 'treadmill' it'll sit still/stay in the one position.

It needs airflow over/under the wing to create liftoff

 

[Craig211]

Wait a minute!! Treadmill counteracts the speed of the wheel not the plane! I was convinced the plane can't take off due to no lift blah blah but after a few beers and heated discussion and considering the jets propel a plane and not wheels I'm gonna go yes? Wheels could be turning at a million miles per hour but the jets/propellor can move the plane forward surely?

 

[Spiders_o.0]

depends how big the engines are surely, im thinking with a lack of air passing the wings once you have enough forward momentum to lift the nose and balance the weight of the aircraft its just a matter of getting the weight airborne, kick up the arse with a couple of rocket engines ala c130 should do the trick

 

[Mentalpen]

this was on mithbusters iirc and it took off

 

[smithandroper]

[video=youtube;01Q83yxdDaI]http://www.youtube.com/watch?v=01Q83yxdDaI[/video]

 

[smithandroper]

But in my opinion it would work with a front mounted propeller due to it forcing the air over the wings but not on a jet because they are normally mounted below or behind the wing !

 

[Tree200]

So what about planes that hold their brakes on and spin the prop on the front? They don't lift up an fly away, you still need the wind over the wings surely?

 

[smithandroper]

So what about planes that hold their brakes on and spin the prop on the front? They don't lift up an fly away, you still need the wind over the wings surely?

That would give them a shorter take off distance look at this video @ about 4.35 in there is 4 people holding the plane back to build up the prop wash over the wings ! It would also pull the plane apart with the brakes on at full power.
[video=youtube;pUdzVnZBaoY]http://www.youtube.com/watch?v=pUdzVnZBaoY[/video]

 

[Tree200]

Bear in mind that the ship is moving in that video creating lift on the wings, not much but some. I can see your point however the wind created by a propeller is not enough to generate enough lift to take off.

 

[smithandroper]

I think it all depends on the weight of the plane and efficiently other the wings and prop, it would be less likely to work on a c130 than on the plane used in the video.

 

[Tree200]

Also would the resistance on the wheels be the same no matter what speed the treadmill is moving. So the propeller will only need to move at a slow speed to overcome the resistance of the wheels/ bearings. Even if the treadmill was going 100mph the resistance will be the same so the propeller will not need to move 100mph.

 

[parkincj]

I remember seeing this one of myth busters, I can't remember the outcome but it was a fair old effort they did for it.

Something to chuck in there, the Bernoulli effect which is the theory behind why an airplane generates life isn't a law, it's just a theory that cannot be disproven yet. We dot actually know how a planes stays in the air for definite.