Airplane on a Conveyor conundrum

[Apache]

if a plane landed on a conveyor belt would it be bumpy??

More to the point, would your plane be the last one to arrive on the conveyor belt, and would someone else lift it off without checking the tag to see if it was their plane?

[MOTRAV]

May I pick the bones outta that?

The CoG NEVER moves rearward, unless you want an unstable aeroplane...

Simply, lift becomes sufficient to outweigh gravity and drag and the wing acheives flight.

Bah! Armchair aerodynamicists!!!

Cof G moves rearwards then forwards apache on a fixed wing Concorde had active cOf G control as it was inherantly unstable . As for armchair aero dynamacists see my website www.aeml.co.uk


Mo

[Slugsie]

OK, it is my belief that the aircraft will fly. Here is my explanation, and some pointers as to why I believe so many of you got it wrong.

An aircraft flies by creating airflow over its wings. It does this by moving forward through the air. It does not move through the air by turning the wheels like a car. It does it by pulling air in from the front and forcing it out behind using its engine (be it jet or propeller it's the same effect). Thus the speed that it moves over the conveyor belt is irrelevant. If the engines generate enough thrust to power the aircraft forward at 10mph, then the conveyor will be moving backwards at 10mph. Now, if it was a car, then the thrust would be acting on the conveyor, and so the movement of the conveyor would cancel the thrust out and the aircraft would not move. However, the thrust acts on the air and not the conveyor, so the net result is that the aircraft has a movement of 20mph with respect to the conveyor. As a result, the aircraft is able to generate airflow over its wings, and will thus ultimately take-off.

As an analogy imagine this situation. You are standing on a skateboard, and have a rope in your hand that is secured at some distant point in front of you. You are able to excerpt enough force on the rope to pull yourself forward at 10mph. You now place a treadmill underneath the skateboard, set to run at 10mph. You excerpt the same force on the rope. It should be obvious to most people that you will move forward (relative to the surrounding area) at 10mph just as before. The only difference is that the wheels of the skateboard will be turning at 20mph because you are travelling at 20mph relative to the treadmill.

One other point to think about if you still think the airplane won't move. As I stated, the conveyor only moves at the same speed (but opposite direction) to the aircraft. If the conveyor was indeed able to stop the movement of the aircraft, then it has to logically follow that the conveyor belt has to stop too. You can therefore demonstrate that the conveyor can never move. Because the conveyor obviously can move the original assumption must be shown to be wrong.

One slight thing to point out is that because the wheels are running at twice the normal speed, there is increased friction from the bearings and rolling resistance of the tyres. However this must be insignificant against the thrust of the engine otherwise the original assumption (1) that the aircraft is capable of taking off would not hold true.

[drunkmonkeyboy]

sorry mate, i love mythbusters

I love mythbusters too, mainly cause carrie is just soooo damm hott!!! worth watching just for her! oh and the fact they do some really cool experements!

[Apache]

Cof G moves rearwards then forwards apache on a fixed wing Concorde had active cOf G control as it was inherantly unstable . As for armchair aero dynamacists see my website www.aeml.co.uk


Mo

No mate, I'll argue this til the cows come home. CoP moves depending on AoA (and airspeed in some cases), CoG is static. Are you telling me that gravity acts differently depending on lift? Sorry, it doesn't. Remind me never to fly in one of your planes.

Concorde moved fuel around because the CoP moved rearwards when it acheived supersonic flight. Gravity's effect remains the same throughout.

[Apache]

But Slugsie, you state yourself, that if the conveyor surface moves backwards at 10mph, the aircraft moves forward at the same speed. Net result is 0mph.

Now your saying that the plane moves forward at 20mph when the belt moves at 10mph? How? Aren't they suppose to be the same?

[Apache]

I love mythbusters too, mainly cause carrie is just soooo damm hott!!! worth watching just for her! oh and the fact they do some really cool experements!

What about 'Braniac' and How Hard is Your Thing?

[da SLUG man]

No mate, I'll argue this til the cows come home. CoP moves depending on AoA (and airspeed in some cases), CoG is static. Are you telling me that gravity acts differently depending on lift? Sorry, it doesn't. Remind me never to fly in one of your planes.

Concorde moved fuel around because the CoP moved rearwards when it acheived supersonic flight. Gravity's effect remains the same throughout.

i read that some of virgins new planes were having trouble, cos of all the kit in first class, they're flying nose down and using far more fuel trying to compensate...

[Apache]

I'm waiting for GWH to come along and break this discussion to down to a sub-atomic level

[da SLUG man]

But Slugsie, you state yourself, that if the conveyor surface moves backwards at 10mph, the aircraft moves forward at the same speed. Net result is 0mph.

Now your saying that the plane moves forward at 20mph when the belt moves at 10mph? How? Aren't they suppose to be the same?

hold on.... i voted yes, but i'm having a re-think...

the engines would thrust on the air to give forward motion.... the plane starts to move....

the conveyor moves at the same speed in reverse...

so, it would end up like having full thrust with the brakes on!

but then as there's no forward movement of the plane, the wheels wouldn't turn so the conveyor wouldn't move... so the plane would move forward... making the conveyor move and stopping the plane again!...


D'OH!!!

[tom222]

I'm waiting for GWH to come along and break this discussion to down to a sub-atomic level

you got your tarten blanket on?

[Apache]

No, figured I'd go for the red velvet smoking jacket tonight.

[Slugsie]

But Slugsie, you state yourself, that if the conveyor surface moves backwards at 10mph, the aircraft moves forward at the same speed. Net result is 0mph.

Now your saying that the plane moves forward at 20mph when the belt moves at 10mph? How? Aren't they suppose to be the same?

Not quite. The aircraft thrust is making it move forward through the air at 10mph. Because the aircraft is moving at 10mph the conveyor is also moving at 10mph backwards. In a system like a car, because the thrust force is directed through the wheels to the ground (or conveyor) the overall effect would indeed be a ground/air speed (the air is still, so they're the same) of zero. However, because the aircrafts thrust is directed at the air, it achieves an air speed of 10mph. The speed relative to the conveyor is 20mph, but that is of no relevance as the conveyor is not excerpting any force on the aircraft other than that necessary to overcome the friction in the wheel bearings.

Examine the scenario of the skateboard on a treadmill I mentioned. If the reverse movement of the treadmill was indeed capable of cancelling out your forward pull on the rope, then no matter how hard you pulled you'd never be able to move forward. Do you believe that that would be the case? And because you aren't moving, neither would the treadmill (it will always match your speed, so if you aren't moving, neither is it). But obviously the treadmill can move, so it follows that the treadmill cannot halt your movement.

[Slugsie]

hold on.... i voted yes, but i'm having a re-think...

the engines would thrust on the air to give forward motion.... the plane starts to move....

the conveyor moves at the same speed in reverse...

so, it would end up like having full thrust with the brakes on!

but then as there's no forward movement of the plane, the wheels wouldn't turn so the conveyor wouldn't move... so the plane would move forward... making the conveyor move and stopping the plane again!...


D'OH!!!

But think about this. The wheels on an aircraft are free to rotate at any speed they like (within the limits of the bearings and tyres etc). So, because the tyres can rotate freely, the conveyor is unable to excerpt any force on the aircraft, and thus will have no influence on its speed.

The only 'trick' is to understand that in this scenario the conveyor belt is nothing more than a distraction, and has no effect on the outcome.

[Apache]

You original premise did not state an airspeed differential, and it cant be assumed.

Broken down simply, if it has airspeed it will acheive lift. If it has groundspeed (relative to the conveyor) it need not.

Its a trick, or badly worded question.