It's been a while - and we have new blood...

[Apache]

if the props caused the air flow over the wings prop planes could take off on the spot merely on the air flow the prop would create over the wings

Well actually it could work.

The prop provides 'lift' in the horizontal plane (you're correct in suggesting propellers 'suck') but a byproduct of this is a huge draught of air from front to back of the aircraft and therefore (assuming a conventional layout) over the wing. The wing is now acting to convert some of the horizontal forces from the prop to a vertical force which in turn produces a lifting force (or, again, suction above the wing surface) so if enough of the wing is exposed to this airflow from a big enough propeller, or several spread along the wing, there will come a theoretical point where the lifting force of the wing is greater than the weight of the aircraft, and the aircraft will take off.

Obviously, the aircraft would need to be horizontally tethered because most of the force is still horizontal.

I had an Aerobatic RC plane once which was quite light and very overpowered which used to take off in a few feet, in part due to lift provided by airflow from the prop. If you held it in your hand, you could feel a very significant lifting force if you opened the throttle wide.

[Mork]

Ignore taking off for a moment, let's just look at moving.
In fact, let's assume it's not a plane at all.

It's a Surf. A big red one.
The surf has a winch on the front.
The winch is attached to an immovable object in front of the conveyor.
The gearbox is in neutral so the wheels can spin freely.

Now, turn the conveyor up to 5mph.
The surf won't move. The wheels will turn backwards, but the car won't move.
There will be a little pressure on the winch, but not much because the wheels spinning is dropping most of the pull of conveyor.
(assuming you don't have knackered bearings.)

If you then turn the winch up to 5mph then the surf will pull itself forwards.
It doesn't matter that the conveyor is going backwards because the pull of the conveyor is being absorbed by the freewheeling wheels.
The speedo in the car will show 10mph, because the wheels are spinning at 10mph.*
But the car will be moving at 5mph forwards relative to the world.
The car moved because the propulsion system (rope) isn't attached to or influenced by the conveyor.

I take it you agree with that, please say if you don't.

If we assume all that to be true, then it's just a short mental step to swap the rope for a jet engine or prop.
The jet or prop act on the air, which isn't attached to the conveyor – just like the rope.

Once it's understood that the vehicle can move then all it has to do is move fast enough to achieve take off speed.


*assuming it's wired up that way. I've no idea if the speedo will register if the cars in neutral, It's just an example anyway.

[Koi]

Ignore taking off for a moment, let's just look at moving.
In fact, let's assume it's not a plane at all.

It's a Surf. A big red one.
The surf has a winch on the front.
The winch is attached to an immovable object in front of the conveyor.
The gearbox is in neutral so the wheels can spin freely.

Now, turn the conveyor up to 5mph.
The surf won't move. The wheels will turn backwards, but the car won't move.
There will be a little pressure on the winch, but not much because the wheels spinning is dropping most of the pull of conveyor.
(assuming you don't have knackered bearings.)

If you then turn the winch up to 5mph then the surf will pull itself forwards.
It doesn't matter that the conveyor is going backwards because the pull of the conveyor is being absorbed by the freewheeling wheels.
The speedo in the car will show 10mph, because the wheels are spinning at 10mph.*
But the car will be moving at 5mph forwards relative to the world.
The car moved because the propulsion system (rope) isn't attached to or influenced by the conveyor.

I take it you agree with that, please say if you don't.

If we assume all that to be true, then it's just a short mental step to swap the rope for a jet engine or prop.
The jet or prop act on the air, which isn't attached to the conveyor – just like the rope.

Once it's understood that the vehicle can move then all it has to do is move fast enough to achieve take off speed.


*assuming it's wired up that way. I've no idea if the speedo will register if the cars in neutral, It's just an example anyway.

Nah because its fixed to something so will be pulled towards that fixed point by the winch because its winding in the rope, its not free standing in the true sense as its attached to something.

[Mork]

Nah because its fixed to something so will be pulled towards that fixed point by the winch because its winding in the rope, its not free standing in the true sense as its attached to something.

The plane with its jets or props running is not free standing either though.
It's pushing itself along by pushing or pulling the air, and the air isn't being moved backwards by the conveyor.