Mythbusters: Can an airplane take off from a conveyor belt??

What do YOU think?

I seen comerricals after nipt tuck... yesterday but the website says some james bond thing is playing........

Anyways

Can an airplane take off from a conveyor belt?

[335i4u2nv]

no!

[Spool]

No, it needs to generate lift

[O-cha]

That's the dumbest question ever.

[Hawkeye]

YES
with it's engine working it can. If the belt is going in the same direction as the plane it will be able to take off a bit faster, if not then it will take a bit longer (wheels will be rotating at a much faster speed than needed to take off but they have to have significant lift.)

You people that said no are probably picturing a plane on a treadmill aren't you?

[Spool]

Oh forgot to ask which direction the conveyor belt is moving...


If it's moving backwards like on a treadmill then no...

[SoYank]

If the conveyor belt was propelling the aircraft fast enough that enough aerodynamic lift was produced by the wings and overcame drag, yes, the airplane can take off, that is, the wheels will leave the surface of the conveyor belt. It will land pretty much as soon as it does though because the thrust used to gain that lift is eliminated once the airplane separates from the belt and aerodynamic drag takes over.

On the other hand, if the airplane had engines providing thrust and it was situated on a conveyor belt, then it can take off under the engine's thrust and remain aloft provided the conveyor belt was stopped or moving towards the nose of the aircraft [the aircraft would have "taken off from a conveyor belt", would it not?]. But if the conveyor belt was moving towards the tail, the aircraft's engines would have to overcome the backwards motion imparted on the aircraft by the conveyor in order to produce the needed lift.

If you took a quality scale model airplane -- not a flat balsawood glider (do they even make these anymore?) -- and held it out a car window while someone was driving the car you would probably feel, through your fingertips, some bit of lift imparted on the model. When you let go and watch it, besides quickly retreating behind your car it will rise a bit before crashing into the highway. It will also startle the driver behind you so much she drops her cellphone or mascara or lipstick or Starbuck's coffee into her lap causing her to steer into the side of a Chevy forum member triggering a massive multicar pileup that blocks the freeway for hours. For that reason alone I wouldn't suggest trying this little experiment, not that I have anything against Chevy's, cellphones, mascara, lipstick, or even Starbuck's coffee. OK, maybe on a backroad where there's less traffic but a Chevy or two.

Can an airplane take off from a moving ship's deck without assistance? Yes, as long as the airflow over the airfoil (wings) is fast enough to produce a difference in pressure between the upper and lower surfaces in excess of the weight of the airplane. However, since contact with the ship's deck provided some forward motion to the airplane, as soon as this is removed (by lifting the airplane) this "thrust" is eliminated and the ship will move forward from beneath the airplane. I doubt if it would get very high except in extremely high speed winds. This is one reason aircraft carriers will turn into the wind, i.e., the wind is directed down the length of the flightdeck, when launching/catapulting aircraft. The speed of the ship added to the natural windspeed is the actual windspeed over the wings and this allows aircraft to use less fuel to get airborne. On the other end of the ship, the landing aircraft benefit from the flying into the wind with having a lower airspeed. If the ship weren't into the wind, but sailing with the wind, the aircraft would have to fly faster in order to keep the same amount of airflow over the wings to prevent the airfoil from stalling. This is similar in effect as the backwards conveyor belt.

Of course, Jamie and Adam will probably prove me wrong in all aspects, I'll be embarrassed beyond all comprehension, and I will have to leave E90post.com in shame. Please tell me you didn't have this in mind when you posed the question.

Betcha didn't expect all this, did ya?

[SoYank]

Originally Posted by Hawkeye

YES
with it's engine working it can. If the belt is going in the same direction as the plane it will be able to take off a bit faster, if not then it will take a bit longer (wheels will be rotating at a much faster speed than needed to take off but they have to have significant lift.)

You people that said no are probably picturing a plane on a treadmill aren't you?

I don't think you're gonna get much lift from wheels.

[MadDog]

Originally Posted by SoYank

If the conveyor belt was propelling the aircraft fast enough that enough aerodynamic lift was produced by the wings and overcame drag, yes, the airplane can take off, that is, the wheels will leave the surface of the conveyor belt. It will land pretty much as soon as it does though because the thrust used to gain that lift is eliminated once the airplane separates from the belt and aerodynamic drag takes over.

On the other hand, if the airplane had engines providing thrust and it was situated on a conveyor belt, then it can take off under the engine's thrust and remain aloft provided the conveyor belt was stopped or moving towards the nose of the aircraft [the aircraft would have "taken off from a conveyor belt", would it not?]. But if the conveyor belt was moving towards the tail, the aircraft's engines would have to overcome the backwards motion imparted on the aircraft by the conveyor in order to produce the needed lift.

If you took a quality scale model airplane -- not a flat balsawood glider (do they even make these anymore?) -- and held it out a car window while someone was driving the car you would probably feel, through your fingertips, some bit of lift imparted on the model. When you let go and watch it, besides quickly retreating behind your car it will rise a bit before crashing into the highway. It will also startle the driver behind you so much she drops her cellphone or mascara or lipstick or Starbuck's coffee into her lap causing her to steer into the side of a Chevy forum member triggering a massive multicar pileup that blocks the freeway for hours. For that reason alone I wouldn't suggest trying this little experiment, not that I have anything against Chevy's, cellphones, mascara, lipstick, or even Starbuck's coffee. OK, maybe on a backroad where there's less traffic but a Chevy or two.

Can an airplane take off from a moving ship's deck without assistance? Yes, as long as the airflow over the airfoil (wings) is fast enough to produce a difference in pressure between the upper and lower surfaces in excess of the weight of the airplane. However, since contact with the ship's deck provided some forward motion to the airplane, as soon as this is removed (by lifting the airplane) this "thrust" is eliminated and the ship will move forward from beneath the airplane. I doubt if it would get very high except in extremely high speed winds. This is one reason aircraft carriers will turn into the wind, i.e., the wind is directed down the length of the flightdeck, when launching/catapulting aircraft. The speed of the ship added to the natural windspeed is the actual windspeed over the wings and this allows aircraft to use less fuel to get airborne. On the other end of the ship, the landing aircraft benefit from the flying into the wind with having a lower airspeed. If the ship weren't into the wind, but sailing with the wind, the aircraft would have to fly faster in order to keep the same amount of airflow over the wings to prevent the airfoil from stalling. This is similar in effect as the backwards conveyor belt.

Of course, Jamie and Adam will probably prove me wrong in all aspects, I'll be embarrassed beyond all comprehension, and I will have to leave E90post.com in shame. Please tell me you didn't have this in mind when you posed the question.

Betcha didn't expect all this, did ya?

Sounds like a reasonable argument, but I'll be sorry to see you go.....

[AndrewAZ]

This has been beaten to death.. What it comes down to is a poorly worded question which over the years have split into 2 different poorly worded questions.

But it comes down to this a CB will not cancel out the thrust of an airplane engine as it would the power from the wheels of a car. If you want to get technical the CB will match the speed of the tires and the tires will heat up and explode thus causing a catastrophic accident, but in perfect physics land you know the answer but in the real world it would end in a fire ball.

This question is somewhat along the lines of the old argument about being able to swim faster in syrup than in water and various other questions like this.

[mpimping]

my guess in no but...

[mpimping]

what happened I missed the show...

[mds82]

damn, i missed the show too

[Kiemyster]

im so lost... i also missed the show lol

[SteveMD]

Hah! I have been a member of a community known as 'The Straight Dope' for several years. It is a website where you can get real, no BS, answers to pretty much anything. It is a great site despite the membership fee.

The airplane on a treadmill thing is one of their long standing 'debates'. Clearly Adam and Jamie are getting their ideas from the 'Dope'.

Which is good.

[TurboFan]

It goes one of two ways.....

If the conveyor is traveling in the direction of take off for the airplane, and assuming it is pulling the plane forward just like a catapult on an aircraft carrier, the plane will lift off when the air speed over the wings produces enough lift. It's not hard for the engines to spool to that thrust, so the plane will remain in the air - the conveyor is just helping the engines move the mass of the plane forward, in a sense acting like a JATO, steam catapult or other take-off assist. It's also similar in concept to how a carrier turns into the wind for takeoff and landing operations. But it still does not matter because a plane is not a wheel-driven machine. The conveyor only helps if there is an anti-freewheel mechanism in the wheels. The conveyor, with that level of acceleration, would roll forward and the wheels would counter rotate, so the plane would not move. If the conveyor rolled forward with acceleration low enough not to overcome the friction in the wheels, then the plane would move forward.

The bigger question is if the conveyor is traveling in the direction OPPOSITE of takeoff. If the conveyor were theoretically brought to a speed equal to the negative of takeoff, then the engines would likely not have sufficient airflow to ignite, and it's all a moot point.

If the conveyor were to be sped backward as the plane accelerates forward, the plane would not care. As stated above, the plane is not wheel driven. The engines would continue to accelerate the plane forward, but the wheels would just spin twice as fast as normal. Plane would lift off.

[335i4u2nv]

so what happened? did it take off or not?

[Hawkeye]

Originally Posted by SoYank

I don't think you're gonna get much lift from wheels.

I meant they as in the aircraft itself. The wheels would probably present more... dang whats the word for it.... it's what you dressed up in last Friday before you hit the bars...

Did it take off or not. I need to download the show.