Wee brain teaser

[Burdekin]

A friend posted this on facebook and I found it interesting the number of folk that struggled with this. So what do you guys reckon and why?

 

[lazybones51]

No because it's not moving so there's no airflow, therefore the wings won't provide any lift.

 

[Burdekin]

Why can't it move?

 

[lazybones51]

I'm so thick at times.. those ruddy great jets hanging off the wings won't give a toss about what the wheels are doing.

 

[ms08]

If you were on a gym treadmill running at the same speed the belt is travelling in the opposite direction do you move?
No air flow over wings, no lift, no take off.

If, however the wind was blowing at around 250 knotts (unlikely!) from the front of the air craft - we have lift off.

 

[Burdekin]

Loads of folk missed that and one of the girls on facebook still can't get that.

 

[Burdekin]

It's your legs that are propelling you via contact with the treadmill but if someone came along and shoved you you'd move.

 

[ms08]

It's your legs that are propelling you via contact with the treadmill but if someone came along and shoved you you'd move.

Yes, but that would require the thrust from the engines to be greater than the backwards motion of the belt runway.....

 

[Hood]

If the engines are being used then surely it will move forward no matter what speed the conveyor moves as the wheels on a plane do not propel it, they free wheel.

 

[ms08]

Newton's third law I think it is...?

 

[rtbcomp]

This could be end of airport noise problems - run the conveyor in the forward direction (very quickly), apply the handbrake and switch the engines on once in the air and away from populated areas.

 

[ms08]

This could be end of airport noise problems - run the conveyor in the forward direction (very quickly), apply the handbrake and switch the engines on once in the air and away from populated areas.

Steam launch - its done on aircraft carriers(though engines still on full chat)...though i think the energy required to haul a 747 into the air......

 

[rtbcomp]

There'll be more drag but the engines should overcome that.

 

[rtbcomp]

Steam launch - its done on aircraft carriers(though engines still on full chat)...though i think the energy required to haul a 747 into the air......

Back to the drawing board

 

[Burdekin]

This could be end of airport noise problems - run the conveyor in the forward direction (very quickly), apply the handbrake and switch the engines on once in the air and away from populated areas.

Turn the wheels backward while flying along to slow down for landing as well. ;-)

 

[atomant48]

The problem is constrained by the question itself. Because they have put a constraint that the treadmill always moves at the same speed as the wheels, they are constraining the maximum power that can be used. So the engines will likely never get above idle no matter how fast the treadmill runs, and it cannot takeoff with such low power set.

 

[rtbcomp]

Turn the wheels backward while flying along to slow down for landing as well. ;-)

That'll leave a huge skidmark on the runway, and quite a few in the cabin too.

 

[gg280t]

Hi All, Long time lurker here,but can't resist sticking my two peneth in at this one !! I see it as the wheels are only there to keep the plane from digging in the floor, and have no effect on anything other than landing and takeoff. Look at the planes that land and take off from the water. The thrust will move the plane forward until its going fast enough to produce uplift then take off. The wheels will just spin faster.

 

[WorkshopChris]

If this worked they wouldn't need to keep building more runways at Heathrow just a huge rolling road mot brake test type machine for all takeoffs leaving the runways clear for landings.
But if the wheels don't move along the horizon the plane is not moving , doesn't mater what the engines are doing no movement = no lift.

 

[Shox Dr]

This has been on mythbusters