conveyor belt and plane answered at last ??

[Mw Roofline]

Be interesting to see what the general opinion is out there - how many reckon it'll take off vs the ones who think it won't.

//www.diynot.com/forums/genera...nts-just-vote-yes-take-off-no-it-wont.334135/

 

[securespark]

Cheers, MWR!

So if i put a model plane on a dining table and pulled the table cloth out from under it are you suggesting the wheels would not rotate the opposite way?

Just had a big think about the plane thing and I've come up with this:

Imagine starting the belt without the plane's engines on.

Would the plane remain stationary (because the wheels freewheel backwards)?

 

[misterdubya]

It cannot take off.

Lets reverse it... an F1 car cannot corner at the speed it does without airflow. Well.... can it, if its on a conveyor belt? No bleedin chance.

 

[securespark]

But we've been there.

A car is different because the engine drives the wheels. That's not the case on a plane.

The conveyor is not moving the aircraft, it's simply spinning its wheels.

 

[misterdubya]

Secure... Ive gone back to basics. If a conveyor belt is running in the opposite direction to the vehicle at the same speed (thus effectively leaving it stationery), it (the vehicle) cannot do what it is designed to do, no matter how its powered. Am I missing something here? This is the most basic of physics surely?

 

[doitall]

Just had a big think about the plane thing and I've come up with this:

Imagine starting the belt without the plane's engines on.

Would the plane remain stationary (because the wheels free wheel backwards)?

If the plane is sat on the conveyor with no engine it will move at the same speed as the belt it the direction of flow.

The wheels will not be turning.

It's only when you apply energy to hold or move the plane in the opposite direction to the belt that the wheels turn.

This is where myth busters is wrong, the plane on the dust sheet would not go backward if you pulled it and if it did the wheels would turn, as the weight is being transferred to the ground and not a conveyor.

 

[Deleted member 63160]

If a conveyor belt is running in the opposite direction to the vehicle at the same speed (thus effectively leaving it stationery), it (the vehicle) cannot do what it is designed to do, no matter how its powered. Am I missing something here?

Yep.

 

[securespark]

The wheels are not connected to the engine as in a car.

While I agree the car and plane are not driven in the same way, if we go back to the car on a treadmill, floored it and the belt speed matched that of the car, you would go nowhere.

Now, attach a rocket onto the back of the car. Fire it up. The car will move forward.

Talking of tyres and rotation, since the main tyres are bigger than the nose ones, the nose tyres are turning faster.

Does that mean the nose is moving faster than the rest of the plane?

 

[misterdubya]

Now, attach a rocket onto the back of the car. Fire it up. The car will move forward.

Of course it bloody will! Stick the car in reverse, and it will move backwards pretty damn fast if the conveyor is in reverse wont it? Whats your point?

 

[securespark]

Think about it! What is my point?

 

[misterdubya]

For my own piece of mind secure.... if a vehicle is stationery (due to a conveyor belt neutralising the speed of that vehicle, no matter how many rockets you stick on the bugger) will it...

a: create 'lift'?
b: create 'downforce'?

 

[crank39]

Cheers, MWR!

So if i put a model plane on a dining table and pulled the table cloth out from under it are you suggesting the wheels would not rotate the opposite way?

Just had a big think about the plane thing and I've come up with this:

Imagine starting the belt without the plane's engines on.

Would the plane remain stationary (because the wheels freewheel backwards)?

Yes IMO it would but if you really wanted to split hairs you could argue that with friction within the bearings the plane would roll backwards, slowly at first because the wheels were going forward at the same speed as the belt was going backwards but eventually with friction the wheels will slow down, the slower they go the faster the plane will go backwards till eventually the wheels stop turning and the plane will be travelling backwards like a sack of spuds at the same speed as the belt.

The exact reverse of the wheels slowing and the plane going backwards is the wheels speeding up i.e when thrust is applied, in which case the plane would do........GO FORWARDS

But then the wheel rpm isn't equal to what the belt mph say the wheels should be doing

 

[misterdubya]

Think about it! What is my point?

Your point is different to mine. I view it simply.... ie. the vehicle is staitionery. You seem to be of the the view that you can increase the speed of the vehicle to enable it to take off. As I typed earlier, I just viewed it as a basic case of physics.

 

[securespark]

Hi 39 & MrW

I believe that if you started the belt with the plane's engines off, the plane would remain stationary. The wheels would move, but not the plane, thus leaving the plane free to propel itself along the belt and take off.

To explain: my point is that the planes engines act on the air, not the wheels.

If we then agree that the moving belt acts on the wheels, not the plane and the plane would remain stationary if the belt was moving, then it would be free to move forwards and take off simply by applying thrust.

 

[doitall]

If the weight of the plane is on the conveyor belt, then the plane has to move with the belt, unless the plane s tied to a big tree first.

Take a toy plane next time you go shopping and test the theory.

If you have a young kid it will be less embarrassing.