Airplane physics question

7 years later and people are still debating this question lol

 

Wheel speed is independent of forward speed and completely irrelevant. Nothing the conveyor belt does in the real World will keep the plane stationary. It's just how things work.

The plane flies every time.

 

This thread just makes me smile every time I read it. Especially since most of the people posting are much more intelligent in regards to physics than I am.
Good point on wheel speed, I understand your point, but in my mind, the person that originally wrote this question meant that wheel speed and conveyor belt speed Being equal at the point of contact implies no forward motion. For the plane to move forward and generate lift, the wheel speed of the plane must be greater than the speed of the conveyor belt.

 

I'm certainly curious as to whether anyone has changed their mind.

Disclaimer: I haven't.

 

I'm still right as well. What did you guys say? I said that it will fly.

GT

 

A tailwheel plane flies due to the increased angle of attack on the wings. A tricycle gear plane will not due to conveyer belt drag. So if you need to get somewhere, fly a B-17 and not a B-24

It takes off upside down with Denzel Washington at the controls.
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With zero forward motion, zero airspeed, and therefore no flight. Angle of attack doesn't matter.

 

Holy crap... STILL running .... wow!

 

Where does it say that the airplane doesn't have forward motion?

GT

 

Ask yourself these questions:

1. What is the ONLY way that the airplane's wheels are going to be able to start moving?
A: Forward motion derived from airplane engine thrust

2. Given the information in the quote above, how fast will the airplane wheels be spinning?
A: As the airplane increases ground speed, the speed of the tires will be double the speed that the wheels would normally be turning during a non-conveyered take-off.

3. Imagine the exact same scenario except that the conveyer is moving the SAME direction as the airplane taking off. Remember that the wheels of an airplane are on bearings and have no drive component to the aircraft. Will the airplane take off twice as fast??
A: No, as the conveyer has no effect on takeoff in either case.

GT

 

The all important pitot tube will be bored silly without wind, and as such, disallow progress in a manner which creates lift.


via rubber ducky

 

Not sure I understand this argument.

Wind is measured relative to the ground. If you stick your hand out of a car window you'll feel air, but the wind isn't blowing. The car is moving through the air.

GT

 

The wheels and conveyor can do whatever they want. As long as the plane isn't anchored to the ground it will fly every time.

 

I would like the no-fly believers to read my explanation post, process it, and post which part doesn't make sense.

GT

 

Good point.

Revise to assuming no forward motion.

 

In this case a glider is sitting on your conveyor belt.

 

I think the plane will fail to take off and will just stay at the same physical location similar to a person running on a treadmill.

In a regular scenario of a plane on a normal runway the thrust of the engine pulls the wing forwards forcing air over/under the wing creating lift. Its only when enough lift is produced to overcome the gravitational pull that the plane is under that it begins to move upwards.

Bearing the above in mind if your plane is sat on an travelator going backwards your already have a negative airflow over the wings (that's why planes cant fly backwards!) so you have to generate more thrust than normal to not only overcome the negative airflow but generate enough airflow to get the lift you want. All your thrust will do will counteract the backwards travel of the travelator.

Just as an aside its the reverse of the rams on an aircraft carrier which allows an aircraft to get airborne more quickly - imagine what would happen if you tried to take off with the ram working in reverse.

BTW If you fly a plane into a strong enough headwind there is enough air passing over the wing to create the lift you require but you my not be making any actual headway in movement

 

A plane (wing) does not fly but is lifted by differential pressure over/under the wing, the plane with attached wing flys only when thrusted forward by other forces to reach a speed of airflow enough to create a pressure differential enough to cause lift

 

The person has neither wheels nor a prop.

What is so difficult about this? One can easily calculate this (see above) and still half of the users deny the plane could take off!

Of course one could create a strange kind of plane (johngober's case) with thrust minimized to just equal the initial resistance of the wheels and thrust being permanently adjusted to match the wheels resistance when the belt is moving. But this kind of plane would not move without conveyor belt as well. Its thrust would be so minimal that it could not overcome the static friction of the wheels.

 

This.

If the given scenario of the OP, ANY situation where the thrust is applied to the ground (bike, car, walking etc) then that device / person wouldn't move.

But, with an airplane, the thrust is applied elsewhere and therefore, except for the bearing friction in the wheels, the existence of the conveyer has no effect on the airplane.

GT

 

User "name" is perfectly right:

"The lift generation comes out from the mathematical solution of the differential equations that describe the flight phenomenon. These are the so called Navier-Stokes equations. The Bernoulli principle is an ideal subset of Navier-Stokes that cannot fully describe the actual phenomena in a lifting body or airfoil or 3D-wing. By solving the Navier-Stokes in 2D or 3D one can actual see how pressure side and suction side of a wing co-operate in order to produce lift, together with the remaining aerodynamic field (temperatures, vector velocities, entropy etc. etc.). So, in conclusion there is no straightforward explanation of "how planes fly" and no wrong or correct school explanations, but incomplete explanations. Only by solving the above mentioned differential equations in an appropriate grid and with the appropriate solid & boundary conditions will understand flight."

Source: http://danielmiessler.com/blog/why-planes-fly-what-they-taught-you-in-school-was-wrong#comment-13436428

Only problem is most people have no clue what a Navier-Stokes equation is. But one can't blame them. It takes some time to study this.