Airplane on a treadmill!

[Zorba]

https://m.youtube.com/watch?v=Sr5YRuGYmKo

Imagine if the car was an airplane. In order for an airplane to lift off the ground it must produce lift. The amount of lift produced is based on wing area, coefficient of lift, and velocity of air over the wing, so if the car in the video had wings, there would not be enough airflow over the wings to creat enough lift to overcome the weight of the aircraft.

Assuming a perfect treadmill. Otherwise you would need an aircraft like a Maule.

http://www.controller.com/listingsd...AULE-M7-420AC/2000-MAULE-M7-420AC/1389113.htm

Those planes are light, have huge engines, bug Hersey bar wings and can lift into the air with a very short roll down a runway. A jet aircraft would never take off.

The problem never mentions a "perfect treadmill." I think people have a hard time thinking of a treadmill being used to mean a conveyor belt as opposed to a piece of gym equipment.

 

[sdifox]

The problem never mentions a "perfect treadmill." I think people have a hard time thinking of a treadmill being used to mean a conveyor belt as opposed to a piece of gym equipment.

It's a theoretical problem, like all physics problems you did back in school.

 

[WelshBloke]

Think of it this way. If you put a(n unbraked) dyno under each set of wheels would the plane take off?

 

[sdifox]

Think of it this way. If you put a(n unbraked) dyno under each set of wheels would the plane take off?

Plane takes off and dyno reports over 9000 whp :awe:

 

[sdifox]

WHP, stupid autocorrect

 

[Phanuel]

Speed doesn't matter, but acceleration does. A continuously accelerating wheel becomes a flywheel and stores the energy input by the force of the engines as inertia. Friction continuously bleeds away this energy.

Infinity is a concept that is only achieved by those who oversimplify the initial problem.

Then any of the current generation of KERS systems used in racing right now would mean the cars would never go anywhere after braking once and spinning the flywheel up.

A SPINNING WHEEL DOES NOT GENERATE ADDITIONAL WEIGHT. It only generates a gyroscopic force that causes said gyroscope to stabilize in the axis that it is spinning.

The plane still takes off.

https://m.youtube.com/watch?v=Sr5YRuGYmKo

Imagine if the car was an airplane. In order for an airplane to lift off the ground it must produce lift. The amount of lift produced is based on wing area, coefficient of lift, and velocity of air over the wing, so if the car in the video had wings, there would not be enough airflow over the wings to creat enough lift to overcome the weight of the aircraft.

What plane in the world puts power down to the ground and actually flies with this as its sole source of movement generation?

You use physics terms for how a wing functions and then completely blow past how a plane generates thrust in the same medium, air.

 

[jagec]

Then any of the current generation of KERS systems used in racing right now would mean the cars would never go anywhere after braking once and spinning the flywheel up.

A SPINNING WHEEL DOES NOT GENERATE ADDITIONAL WEIGHT. It only generates a gyroscopic force that causes said gyroscope to stabilize in the axis that it is spinning.

If you don't know the difference between speed and acceleration, you probably shouldn't participate in physics threads.

You even brought up a great example: the use of KERS to store energy otherwise dissipated in braking. Note that the vehicle must be accelerating or decelerating to transfer energy to and from the flywheel. At a constant speed, KERS does nothing.

 

[Darwin333]

https://m.youtube.com/watch?v=Sr5YRuGYmKo

Imagine if the car was an airplane. In order for an airplane to lift off the ground it must produce lift. The amount of lift produced is based on wing area, coefficient of lift, and velocity of air over the wing, so if the car in the video had wings, there would not be enough airflow over the wings to creat enough lift to overcome the weight of the aircraft.

Assuming a perfect treadmill. Otherwise you would need an aircraft like a Maule.

http://www.controller.com/listingsd...AULE-M7-420AC/2000-MAULE-M7-420AC/1389113.htm

Those planes are light, have huge engines, bug Hersey bar wings and can lift into the air with a very short roll down a runway. A jet aircraft would never take off.

It doesn't matter how perfect the treadmill is, cars produce power at the wheels so a treadmill could work to keep them stationary. Airplanes produce thrust with their engines, the wheels basically just spin freely. The plane will move forward no matter what, increasing the speed of the treadmill will increase the speed that the wheels are traveling but will have absurdly little effect (friction) on the planes forward momentum. Either the plane takes off or the wheels move so fast that shit breaks while the plane is moving forward.

Think about this, assume you have rollerblade with wheels that are almost completely free of friction. You hold it on a treadmill and set it at 50mph, how much energy will it take you to keep the rollerblade in the same spot on the treadmill? In this hypothetical you could do it with a single finger, now how much force will you have to exert to move the rollerblade a foot forward on the treadmill?

A planes thrust does not come from its wheels so barring structural failure it's irrelevant how fast they are going. Assuming perfect wheels that have zero friction and won't structurally fail under any circumstance the treadmill could go 100 times faster than the planes take off speed backwards and the plane still freaking takes off.

 

[Darwin333]

Think of it this way. If you put a(n unbraked) dyno under each set of wheels would the plane take off?

Either the plane skips off of the dyno and takes off just fine or the wheels of the plane never turn and eventually the landing gear will rip off the plane. No matter what the plane will move forward, it's just a question of it having it's landing gear still attached or not.

Edit: I'm thinking of bit jets. Maybe a really small prop plane won't rip the gear off but if it doesn't the wheels will not move at all, the dyno reads 0. The only reason the plane doesn't take off is because you have immobilized it no differently than tying it to a big ass tree.

 

[SKORPI0]

Given enough air density and runway (treadmill/conveyor) length to generate/build up lift, the plane will take off.

https://en.wikipedia.org/wiki/Density_altitude

Air density is perhaps the single most important factor affecting aircraft performance. It has a direct bearing on:[2]

• The lift generated by the wings — reduction in air density reduces the wing's lift.
• The efficiency of the propeller or rotor — which for a propeller (effectively an airfoil) behaves similarly to lift on wings.
• The power output of the engine — power output depends on oxygen intake, so the engine output is reduced as the equivalent "dry air" density decreases and produces even less power as moisture displaces oxygen in more humid conditions.

Aircraft taking off from a "hot and high" airport such as the Quito Airport or Mexico City are at a significant aerodynamic disadvantage. The following effects result from a density altitude which is higher than the actual physical altitude:[2]

• The aircraft will accelerate slower on takeoff as a result of reduced power production.
• The aircraft will need to achieve a higher true airspeed to attain the same lift - this implies both a longer takeoff roll and a higher true airspeed which must be maintained when airborne to avoid stalling.
• The aircraft will climb slower as the result of reduced power production and lift.

Due to these performance issues, a plane's takeoff weight may need to be lowered or takeoffs may need to be scheduled for cooler times of the day. Wind direction and runway slope may need to be taken into account.

http://www-mdp.eng.cam.ac.uk/web/library/enginfo/aerothermal_dvd_only/aero/perf/to/index.html

 

[DrPizza]

How is this thread still going? The question was answered correctly, early on in the first thread, and it was answered correctly, early in this thread.

 

[sdifox]

How is this thread still going? The question was answered correctly, early on in the first thread, and it was answered correctly, early in this thread.

This is ATOT, where stubbornness rule supreme :awe:

 

[Darwin333]

How is this thread still going? The question was answered correctly, early on in the first thread, and it was answered correctly, early in this thread.

Mythbusters even did it with a real friggen plane FFS but as the above poster said, this is ATOT.

 

[Paratus]

How is this thread still going? The question was answered correctly, early on in the first thread, and it was answered correctly, early in this thread.

I think we're going to have to add people who don't understand the plane takes off to same group that contains anti-vaxxers, moon hoaxers, climate change deniers and people who talk at the theater.

 

[Zorba]

It's a theoretical problem, like all physics problems you did back in school.

Yeah, I remember engineering school, people that made up constraints on problems and ignored given data generally did very poorly. Answer the question asked, not a question not asked. This question clearly says the treadmill is moving in reverse at the same speed as the aircraft is moving forward. Assume the treadmill holds the aircraft stationary is a bad assumption because it violates the given data in the question.

 

[ImpulsE69]

What about a plane on a treadmill and someone yells "bomb". Does it take off?

 

[Zorba]

Either the plane skips off of the dyno and takes off just fine or the wheels of the plane never turn and eventually the landing gear will rip off the plane. No matter what the plane will move forward, it's just a question of it having it's landing gear still attached or not.

Edit: I'm thinking of bit jets. Maybe a really small prop plane won't rip the gear off but if it doesn't the wheels will not move at all, the dyno reads 0. The only reason the plane doesn't take off is because you have immobilized it no differently than tying it to a big ass tree.

I'm a landing gear engineer. There is no aircraft in the world that has enough thrust to pull off its own landing gear. Aircraft routinely do max power engine runs while braked. Braked max power isn't even the highest load on the gear.

Though most large aircraft landing gear are designed to break away if the aircraft hits something, see Asiana Flight 214 when the gear hit the sea wall.

I agree with you that the dyno wouldn't spin, either the plane would jump it (most likely, aircraft can jump chocks) or just sit there with no wheel movement.

 

[Suspicious-Teach8788]

Yeah, I remember engineering school, people that made up constraints on problems and ignored given data generally did very poorly. Answer the question asked, not a question not asked. This question clearly says the treadmill is moving in reverse at the same speed as the aircraft is moving forward. Assume the treadmill holds the aircraft stationary is a bad assumption because it violates the given data in the question.

Also honestly the friction that people keep talking about in terms of rolling friction is not what the problem is getting at.

 

[Bubbleawsome]

Mythbusters even did it with a real friggen plane FFS but as the above poster said, this is ATOT.

To be fair, I don't trust some of mythbuster's methods.

 

[Pacfanweb]

For those that can't get past the "wheels spinning on the treadmill" thing, try thinking of it this way:

Imagine the plane has skis on it instead, so it can take off from the snow.

Then imagine a treadmill that is either made of ice, or is lubed up so the skis will slide easily.

Now, you don't have to consider the wheels spinning....the plane IS going to move, and it IS going to take off. Whether the treadmill of ice is moving the opposite way is irrelevant.

If the plane wasn't moving forward from the thrust of its engine, it'd be moving backwards because of the treadmill's movement, right? So if the plane isn't going backwards, it's obviously creating forward thrust, correct?

Anyone still not get it?

 

[ElFenix]

can we do the monty hall problem next?

 

[IronWing]

Now put the plane on a merry-go-round.

Now put the plane on a Ferris wheel.

Put it on a hamster wheel.

Have Delta operate the plane.

Does it take off?

 

[master_shake_]

What about a plane on a treadmill and someone yells "bomb". Does it take off?

No they return to the gate for 5 hours then turn off the air conditioning

 

[Humpy]

can we do the monty hall problem next?

Is that the two sparrows and a coconut quandary?

 

[ElFenix]

No they return to the gate for 5 hours then turn off the air conditioning

Gate? Heck no, there's not enough gate slots. You'll sit out on the apron and like it

Is that the two sparrows and a coconut quandary?

I don't think so but we can do that one too