Who's right?

squiffy · 20 Jan 2007 at 00:23

but to depart with no lift from the wings is nigh on impossible and extremely dangerous/careless.

Nigh on impossible and dangerous means it is possible, but it's dangerous and careless. But it still work, if the pilot so desires.

Isn't the "Bee Gee" a very difficult plane to fly, due to high stall speeds from the wings?

Vonhelmet · 20 Jan 2007 at 00:24

Scam said:
This is easy once you know it, heh/

@big_white_dog84 -- the wheels will 'freewheel'. Everybody who still cant understand it, think of it like this..

How easy is it to push a shopping trolley on a conveyer belt? Very easy. Now think of this. That trolley is a plane, and your force is now the plane's engines. The plane will move forward. Easy. Done. End of debate.

The wheels dont cause any major resistance to the plane moving forward because they 'freewheel'. Essentially, the conveyer belt makes no difference. The plane will move forward pretty much as normal, and eventually take-off.

The point of the conveyor belt is that the aircraft remains stationary. The belt moves backwards as fast as the wheels move forwards. You could just as well say "The plane is sat on a frictionless surface, so the wheels spin but it goes nowhere."

Scuzi · 20 Jan 2007 at 00:29

squiffy said:
Nigh on impossible and dangerous means it is possible, but it's dangerous and careless. But it still work, if the pilot so desires.

Not necessarily. If the wings, fin, rudder and ailerons have no effect due to lack of airspeed, an aircraft with an engine powerful enough to attempt such a manoeuvre will generate enough of a torque effect to flip the aircraft. If the wings are flying and the control surfaces have authority then the torque effect can be counteracted but since in the case you describe, there is no airspeed to have control authority, the aircraft will flip.

I'm not an engineer but I do have a good bit of flying experience and a sound understanding of the principles of flight.
EDIT: On re-reading that it came across as condescending, sorry!

Scam · 20 Jan 2007 at 00:29

vonhelmet said:
"The plane is sat on a frictionless surface, so the wheels spin but it goes nowhere."

It doesnt matter if the wheels turn or not on a frictionless surface does it? The engines provide thrust through the air, not through the ground it's sitting on.

Admittedly i hadnt clicked the link and forgot about the second sentence part, so was a bit rash in my post. But it doesnt matter anyway.

Think about it this way. The conveyer belt cannot put any force back into the wheel because they freewheel. They dont take that force from the conveyer belt and put into the plane, because they freewheel. Going back to the trolley.. if you were to hold a trolley still on a conveyer belt, then move the conveyer belt back and forth.. would the trolley move? No, because you're holding it. Now to the plane; the plane engines arent merely holding it.. they're pushing it forward. Just as you could push the trolley forward slowly, and the conveyer belt backwards (at whatever speed). You'd still be pushing the trolley forward though wouldnt you?

tim_enchanter · 20 Jan 2007 at 00:36

Scam said:
Think about it this way. The conveyer belt cannot put any force back into the wheel because they freewheel. They dont take that force from the conveyer belt and put into the plane, because they freewheel. Going back to the trolley.. if you were to hold a trolley still on a conveyer belt, then move the conveyer belt back and forth.. would the trolley move? No, because you're holding it. Now to the plane; the plane engines arent merely holding it.. they're pushing it forward. Just as you could push the trolley forward slowly, and the conveyer belt backwards (at whatever speed). You'd still be pushing the trolley forward though wouldnt you?

That is so right

EDIT; and oh yeah what a bunch of muppets on the other forum

Vonhelmet · 20 Jan 2007 at 00:37

Scam said:
It doesnt matter if the wheels turn or not on a frictionless surface does it? The engines provide thrust through the air, not through the ground it's sitting on.

Admittedly i hadnt clicked the link and forgot about the second sentence part, so was a bit rash in my post. But it doesnt matter anyway.

Think about it this way. The conveyer belt cannot put any force back into the wheel because they freewheel. They dont take that force from the conveyer belt and put into the plane, because they freewheel. Going back to the trolley.. if you were to hold a trolley still on a conveyer belt, then move the conveyer belt back and forth.. would the trolley move? No, because you're holding it. Now to the plane; the plane engines arent merely holding it.. they're pushing it forward. Just as you could push the trolley forward slowly, and the conveyer belt backwards (at whatever speed). You'd still be pushing the trolley forward though wouldnt you?

You might be right.

*head asplode*

Scam · 20 Jan 2007 at 00:39

vonhelmet said:
You might be right.

*head asplode*

And without the need for any mention of maths, physics or aeronautical engineering

clv101 · 20 Jan 2007 at 00:48

Scratch that!

Scam · 20 Jan 2007 at 00:50

clv101 said:
That plane isn't going anywhere - no forward motion relitive to the air - there is no lift - it's going to sit stationary on the (rapidly moving) ground.

Please read above :\

Although it doesnt specifically say the plane moves, it clearly will: "The plane applys full forward power and attempts to take off."

EDIT: Too slow i already quoted ya

Scuzi · 20 Jan 2007 at 00:51

clv101 said:
Scratch that!

You WERE wrong

clv101 · 20 Jan 2007 at 00:55

Scam said:
EDIT: Too slow i already quoted ya

Scuzi said:
You WERE wrong

Ha! That'll learn me.

Scuzi · 20 Jan 2007 at 00:56

clv101 said:
Ha! That'll learn me.

I was about to go into the whole spiel again until I noticed your ninja edit.

tim_enchanter · 20 Jan 2007 at 00:57

LOL thats a good one

divine` · 20 Jan 2007 at 01:05

This question makes me cry when people don't understand how planes provide themselves with thrust and thus forward motion

Digital Punk · 20 Jan 2007 at 01:07

OK, I'm a bit drunk so forgive me.

If the plane's forward thrust is equal to the backward speed of the treadmill, then it wouldn't go anywhere.

It would sit on the spot on full power.

The plane would actually need to move forward to get enough lift to take off.

clv101 · 20 Jan 2007 at 01:15

Digital Punk said:
If the plane's forward thrust is equal to the backward speed of the treadmill, then it wouldn't go anywhere.

What the wheels are doing is irrelevant. Just think about the body of the plane and the thrust of the engines - for the body of the plane to stay still there would have to be an equal and opposite force acting on the body - that ain't coming from the ground/wheels so the plane goes forward, picks up speed and up up and away.

Macro · 20 Jan 2007 at 01:15

It won't take off as it won't make any forward motion to generate lift from air moving over the wings via a longer route than under. The key is this:

conveyer has a control system that tracks the plane's wheel speed and tunes the speed of the conveyer to be exactly the same but in the opposite direction, similar to a treadmill.

Clearly to generate lift the plane must move forward. To move forward it's wheels must rotate on the ground propelled forward by the force of the engines (in order to make progress down the runway forcing the stationairy air over & under it's wings). In this case the treadmill is moving in a equal and opposite direction to the force being applied by the engines (i.e. if the engines should in theory be propelling the plane down the runway at 120knots to take off, the treadmill running at 120knots in the opposite direction means in effect the plane is not moving and so there is no lift).

Yes the plane has in effect 120knots ground speed but airspeed is 0

This can be seen all the time for example by airspeed being different from groundspeed. If the plane was racing down the runway at 120 knots with a 120knots tailwind it would not take off as the effective speed of the air moving over the wings would be 0.

Alternatively imagine a boat on a fast flowing river. The boat (or plane) via it's engine is doing what would be 20knots on a still river. However the river (treadmill) is running against the boat at 20 knots so the boat is in effect standing still.

I'm off to bed now - my work here is complete

Macro · 20 Jan 2007 at 01:16

Digital Punk said:
OK, I'm a bit drunk so forgive me.

If the plane's forward thrust is equal to the backward speed of the treadmill, then it wouldn't go anywhere.

It would sit on the spot on full power.

The plane would actually need to move forward to get enough lift to take off.

Spot on

Jotun · 20 Jan 2007 at 01:17

Digital Punk said:
OK, I'm a bit drunk so forgive me.

If the plane's forward thrust is equal to the backward speed of the treadmill, then it wouldn't go anywhere.

It would sit on the spot on full power.

No. The speed of the planes wheels forward is equal to the backward speed of the treadmill. The wheels will just spin freely. Then when apply thrust the plane will move forwards, as the wheels spinning will cause very little resistance.

Digital Punk said:
The plane would actually need to move forward to get enough lift to take off.

Yes, and it would be moving forwards due to the thrust from the engines. The treadmill moving backwards will only cause the wheels to spin, and so will not cause any resistive force on the plane, and the engines will create a force going forwards.

Shock · 20 Jan 2007 at 01:18

Athanor read a few posts up!