Will the plane take off?

[Kelvin]

airsick,

 

I finally got it without going back to the BAK. Wonder if I can change my vote and go with the strength? I'd probably sleep a lot better knowing I have righted a wrong.

 

Kelvin (with along way to go, but no turning back onto the conveyor).

 

 

[Admin]

And I thought we had a problem trying to solve the conveyor belt question...

 

Have a look at this Physics website forum...they are up to 618 pages of posts

 

PhysForum Science, Physics and Technology Discussion Forums -> Plane on conveyor... Will it ever take off?

 

 

[Guest mike_perth]

 

If Adam and Jamie can do it then of course it will take off!!

 

 

[Thx1137]

Hmm. it is obvious when I thought about it again. The prop is pushing through the parcel of air, not the conveyor belt so of course it takes off! and as mentioned, the wheels get a good work out :-)

 

Oh well, I never claimed I was smart :-)

 

 

[facthunter]

Arrival.

 

At least you got there!. Nev

 

 

[Guest Walter Buschor]

I might be a late starter on this one. My wife and I argued for some time over this theorie . I say it will not take off. She argues that it will. Just watched the video of the mythbusters and it cements my believe!

 

No argument - the plane did take off - but let's be honest - it barrelled forward as is so obvious when looking at the cones moving backwards and yes - since it is moving forward it will fly.That's what planes do. I thought the plane had to remain stationary relative to the surroundings. This one was not. Therefore the test is null and void.

 

The only way it will take off is if the plane is capable of delivering more thrust than it's weight. Ie: it does not rely on lift from its wings for flight.

 

I for one am not ready to accept this one yet.

 

Imagine this cenario: an aircraft carrier moves at 30knots. All the planes on deck move at the same speed. Let's now push a plane EVER SO GENTLY over the edge at the back of our carrier. The plane will fall into the water at an angle in line with the forward speed of the carrier ie: it has a momentum given by the forward motion of the carrier.

 

If now the same was repeated again but this time the plane was rolling under it's own power against the carrier at the same speed it would simply fall down vertically once it comes to the end since relative to the surrounding air it has not moved an inch.

 

This is doing my brains in as I'm typing this .

 

The coin just dropped . Yes - it will fly. !! Of course ! stupid me .

 

fly safe - off the runway or conveyor belt.

 

 

[Guest mudjeep]

I think those that thought the plane wouldn't fly - pilots and physicists alike - misread or skimmed over a critical part of the question and infered an implication that simply wasn't there. The question said the conveyor would MATCH the speed of the aircraft. That's all. Not that it would adopt whatever speed necessary to try and keep the aircraft stationary.

 

Therefore, as has been stated by others, if the aircraft is moving forward at 50 knots (and the only possible frame of reference is the airframe to the earth - anything else is clutching at straws) then the convoyor must be moving backwards at 50 knots. SO, if the aircraft is actually moving, and capable of accelerating (and freewheeling undercarriage isn't going to stop that!) then sure as hell it's going to take off regardless of what the conveyor is doing under its feet.

 

Having missed that critical point the NO crowd went off into irrelevant questions of lift and friction to try and understand the question. Well done to those who at first said no but continued to think critically and change their answer when they saw their mistake rather than dig their heels in and try to justify their position. This is the difference between a scientific approach and a blind faith approach.

 

It's also much harder as a thought experiment than it would be in real life. What beats me is how the pilot in the Mythbusters experiment, when faced with the reality of it right in front of him, could still think he wasn't going to accelerate along the ground when he pushed the throttle forward and subsequently take off! I think he needs to go back to ground school and study whats happening to the air when his prop is spinning!

 

 

[Guest Decca]

You put that together pretty well Mudjeep. My reaction to the pilot's assumption was same as yours (couldn't believe it) but I do wonder if that wasn't scripted to gain some suspense and effect.

 

I made one post way back on P.6, which only got one comment (from Ian).

 

Walter I had a bit of a chuckle over your awakening.

 

It's been an entertaining thread.

 

Regards, Decca.

 

 

[Yenn]

Has this thread run longer than the never ending story?

 

Time to think up another brain teaser.

 

 

[facthunter]

Contribution.

 

Mine was very little. I didn't enter the thread till #17. It certainly went for a good run. I thought some had already put the case well enough, and that the facts would speak for themselves, but it was a right royal battle. It's great to see people work it out and change their minds publicly. The situation was presented in a "trick" way but those of you who have done a lot of exams should be able to separate the "essential elements of the problem" from the "throw you off the scent" parts. Nev.

 

 

[Guest Redair]

Nope, I've gone back over the fence... it wont fly, well not off the express way... they'd have to put the wings on it first!

 

Redair.

 

 

[Admin]

Well, will it fly?

[hihosland]

Quote "Ok all, seeing we have a zillion pages about an aircraft on a conveyor belt I thought I would start a never ending story. "

[joew49]

It's quite simple. The aircraft is not anchored to the runway. The air that it is in is stationary (assuming nil wind). The propeller will pull the aircraft forward through the air. The aircraft will move forward as usual but the wheels will be turning twice as fast as normal because the runway is moving backwards.

 

The runway could be going backwards at light speed and assuming the wheels have friction-less bearing the plane will still fly.

 

The conveyor will increase it's backwards movement to match the plane's forward movement, so the plane is still not moving and will not fly.

 

(This conveyor has a control system that tracks the plane speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction). Can the plane take off?"

[joew49]

How about this?

 

Let's place our plane on that treadmill and see what happens. If the wheels were perfect - that is, there is no friction in the bearings (and no deformation of the wheels as they spin) - then something interesting happens. When we turn on the treadmill, the plane stays stationary on its own. The wheels simply spin along the track, and impart no force to the plane. If you had a car with frictionless axles, and you disconnected the whole drive train, the same thing would happen to your car.

 

The only reason that a plane or a car moves backwards on a treadmill is that the wheels are somehow partially locked to the axles. In a plane, this is because of minor friction in the bearings. In a car, it's because of the drive train. If you want the car to stay still, you have to turn the drive train at the proper speed. If you want the plane to stay still, you have to overcome the minor bearing friction. And again, since friction does not change with speed, you don't have to exert any more force at higher speeds. If you run the treadmill at 5mph and turn on the plane's engines just slightly, they will provide enough thrust, pushing against the air, to keep the plane still. If you then increase the treadmill speed to 500 mph, you won't need to adjust the throttle on the airplane - it will remain stationary. That's because it's seeing the same frictional force that it was at 5mph. Thus, it doesn't matter how fast the treadmill is moving - if the pilot does not want to remain stationary, then he won't. It only uses the very first bit of power from the engines to keep the plane stationary. As the throttle is increased from that point, it moves forward just as it would on any other runway. It's pushing against the stationary air!

 

If you don't believe me, imagine this (or even try it at home): you're standing on a skateboard on a treadmill. You hold onto the handrails of the treadmill and turn it on. Of course, you'll remain stationary (relative to the ground). In fact, you only need to use a very light touch to stay stationary - perhaps a few fingers pressed against the handrails. Crank up the treadmill speed as high as you like. You'll still only need the same light touch to remain stationary. At any time you like, you can move forward - closer to the treadmill console - by simple pulling on the handrails. If you had a jet engine, or super-strong hairdryer, you could use this to propel yourself forward instead of holding onto the handrails. In fact, if you're really careful, you might be able to do this at home with a skateboard and a leafbower, but I doubt you'll have a sensitive enough control of your leafblower thrust to get yourself to remain stationary.

 

So you see (oh please tell me you see), the conveyor operator cannot force the plane to remain stationary. And if the plane isn't stationary, it can take off.

 

There's a dedicated website for this!

 

Airplane on a Treadmill

 

 

The question is NOT asking you to insert heat, friction against treadmills, etc!

It is asking you to"HYPOTHETICALLY" accept that the "CONVEYOR BELT" is perfect and can maintain the exact speed of the plane's momentum even under changes to forward or backward movement.Then, the plane will NOT take off!

 

Take the analogy of the wheel brakes being on and irregardless of whether the propeller is at full speed, full pitch or just idling, the plane will NOT take off! (unless the brake is released)

 

In real life, there is no perfection and "hypothetical". Natural forces come into play and the plane will take off!

[Flying Binghi]

I woulda thought all them bush pilot tundra tyre water landing YouTube videos would have made the treadmill scenario redundant..?

 

 

 

 

.

[Student Pilot]

Then we don't need wings to fly just a conveyor belt?

If there is no airflow over the wing the aircraft will not fly, no if's buts or maybe's.

[facthunter]

Can't follow either of those comments..Are the on the principle of , If I don't say much I can't be far wrong? Nev

[Student Pilot]

Aircraft on conveyor belt, no matter how fast the wheels go round, propeller producing thrust, if there is no airflow over wing = Aircraft no fly.

Can't put it any simpler.

[Thruster88]

Aircraft on conveyor belt, no matter how fast the wheels go round, propeller producing thrust, if there is no airflow over wing = Aircraft no fly.

Can't put it any simpler.

Not understanding your position SP, if the propeller is producing thrust the resulting acceleration will cause airflow over the wing unless the park brake has been left on.

[Student Pilot]

The premise is the aircraft is in a stationary position (Hence no airflow over the wing) on a moving conveyor belt. If you power up the aircraft it will then accelerate to take off speed thereby getting airflow over the wing, the aircraft is no longer stationary relative to it's resting position and has a normal take off roll.

An aircraft cannot fly without airflow over the wing.

The only video I have seen was the Mythbuster rubbish where they accelerated on a moving belt being towed by a car or something. The aircraft powered up and did a normal takeoff while the car pulled the rug out. The aircraft moved and took off normally, it was a Zenith or similar and had a very slow take off speed anyhoo.

[Thruster88]

The premise is the aircraft is in a stationary position (Hence no airflow over the wing) on a moving conveyor belt. If you power up the aircraft it will then accelerate to take off speed thereby getting airflow over the wing, the aircraft is no longer stationary relative to it's resting position and has a normal take off roll.

An aircraft cannot fly without airflow over the wing.

The only video I have seen was the Mythbuster rubbish where they accelerated on a moving belt being towed by a car or something. The aircraft powered up and did a normal takeoff while the car pulled the rug out. The aircraft moved and took off normally, it was a Zenith or similar and had a very slow take off speed anyhoo.

 

Ok I see what you are saying. The premise has never been that the aircraft remains in a stationary position but rather can it take off while the rug is pulled out from under it. The original scenario was only designed to confuse non pilots.

[Jerry_Atrick]

Deleted... Thought I was posting against a late pst.. Sorry chaps

[hihosland]

if the propeller develops sufficient air flow over the wings the craft will fly, the conveyor belt be it locked, running forward or running backward is just a distraction for the mythbusters audience.

[kasper]

The original throught experiment is:

"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?"

 

As pilots we know that flying works on airspeed and not groundspeed and that airspeed at takeoff is from thrust being greater than drag so ... why worry about a runway thats moving?

 

The misapprehension that confuses 'people' - not pilots, we are not mere 'people' - is that you link in your mind the conveyor belt moving against you to when you walk the wrong way on a travelator (or against the travel of an escalator) and can 'stand still' with reference to the world around you while walking.

The probelm applying the walking view of standing still to an aircraft taking off is that unlike feet being carried backwards at the same rate as the forward steps the tires of the aircraft are able to spin provided there is thrust equal to the drag of the aircraft on the belt ... the belt runway does not carry the aircraft backwards at all if the engine is delivering take-off power ... it just increases the drag of the spinning wheel bearings ... and that drag is VERY small compared to thrust from engine/prop - thrust > drag = accelleration.

 

So the pilots answer is ABSOLUTELY YES the aircraft will take off. It matters not if the belt runway is trying to 'pull' the aircraft backwards at takeoff airspeed or even greater speed ... all that happens is the wheel in contact with the belt runway will spin up to a speed equal to takeoff speed + belt speed ... and so long as that spinning does not disintergrate the wheel you are fine.

 

If you turn the throught experiment around and make the converyor belt run in the same direction as the aircraft your wheels will spin at airspeed - conveyor speed = 0 but you will still reach takeoff airspeed and it will be fine ... and youtube provides many examples of this when aircraft take off or land on moving trucks ... they fly on/off at airspeed but the aircraft tyres do not rotate.