Mythbusters to take on "the plane and the treadmill" conundrum?

[JDub02]

Originally posted by: LeiZaK
The plane will not take off, but will crash due to its landing gear being ripped off by the treadmill.

Probably.

But assuming the plane was strong enough, it would take off.

Since the forward propulsion comes from props or jet turbines, the aircraft would head down the runway (treadmill) as any normal takeoff, except that the wheels would be spinning incredibly fast. The treadmill would do nothing other than cause the wheels to rotate. Additionally, the treadmill would have to be just as long as a normal runway because the aircraft would still need that distance to get it's speed relative to the ground (not treadmill) high enough to create lift on the wings.

 

[Number1]

Originally posted by: randay
i just set up a treadmill and a model airplane and tried this and the airplane didnt move at all! it just sat there motionless while the treadmill held it back! pretty cool.

You glued the RC plane on the treadmill?
No, now I get it, you removed the wheels from the RC plane.

 

[Atheus]

I didn't read the thread, but I think there's no chance of them doing this 'myth', because it's not a myth. It's not even a worthwhile experiment - there is no doubt about the outcome.

 

[gsellis]

Originally posted by: chrisms
More importantly, planes need to land. Good luck landing on a conveyor belt.

This would be a money saver. Match the runway to the airplane. Plane sets down and then the treadmill slows to a stop. No big tire wear as the plane hits the ground! Remember that the tires have to 'skid' to a start on impact. Burning rubber in reverse. It would make landings with a flat or blown gear safer too.

Bring it ON!

 

[JS80]

How does a jet on an aircraft carrier going X miles per hour fly off the ship?

The plane flies.

 

[gsellis]

Originally posted by: BoomerD
"Splain this to me...if the treadmill moves in reverse fast enough to counter the plane's forward thrust, where is the lift going to come from? Yes, the plane's motors/engines may move it in a forward direction (now countered by the treadmill, the there would be no forward movement through the air to generate the necessary lift....so, everyone who says the plane takes off, what am I missing?
(/me knows zip about physics, but understands mechanics)

It can't as it only matches the groundspeed of the aircraft. Groundspeed <> airspeed. And the wheels have no effect on airspeed. If they did, landings would be really harsh as when the wheels contact the runway, the plane would stop. Instead, the spin up to what was groundspeed (airspeed is still independent, which is why they land into the wind as much as possible.)

The flaw in all the "won't take-off" folks is not grasping groundspeed vs airspeed and assuming that groundspeed can trump airspeed. It only does in a crash.

 

[nweaver]

is this still alive?

Look, in theory, there isn't enough speed/energy to keep the treadmill from stopping forward movement of the plane, because if the engines pushed the plane forward at 1MPH, then the treadmill would have to go insanely fast (much much faster then 1 MPH) in order to create enough friction to overcome the engines.

In practice, the plane would not stay stationary, and would take off like normal, except the wheels would be spinning at a crazy fast rate (not that wheel speed has ANYTHING to do with taking off)

 

[exdeath]

Originally posted by: randay
i just set up a treadmill and a model airplane and tried this and the airplane didnt move at all! it just sat there motionless while the treadmill held it back! pretty cool.

Something is screwy here...

What kind of plane?

What kind of wheels (cheap plastic discs punched into wire 'axles' or good solid ball bearing free spinning wheels, etc)

Was the treadmill inclined? If so then you have two things going on, 1) gravity + normal force on an incline aids in pulling the plane back toward the negative XY axis, and 2) some of the engines thrust is directed on the positive Y axis instead of horizontally so some of the engine power is spend countering weight instead of moving forward and letting the wings lift all the weight.

Lots of variables that need to be constrained that aren't present in a real runway with a real plane (ie: cheap wheels with high rolling resistance, low thrust, inclined runway, etc)

 

[exdeath]

Originally posted by: gsellis

Originally posted by: chrisms
More importantly, planes need to land. Good luck landing on a conveyor belt.

This would be a money saver. Match the runway to the airplane. Plane sets down and then the treadmill slows to a stop. No big tire wear as the plane hits the ground! Remember that the tires have to 'skid' to a start on impact. Burning rubber in reverse. It would make landings with a flat or blown gear safer too.

Bring it ON!

And the maintenence and power bill for that would be less than tires...

 

[LeiZaK]

Originally posted by: ScottMac
OK, I read the whole thread. I'm amazed.

There was almost the right thing posted once ... the missing explanation:

You (non take-offers) are on a skateboard, which is located on a treadmill. You have a rope around your waist that is attached to a '57 Chevy's rear bumper.

Begin: the car is stationary. The treadmill starts up moving however fast you want it to go. The rope tightens and you remain stationary on the treadmill, relative to the surrounding air. The skateboard wheels match the speed of the treadmill belt.

Later: The greaser sitting at the wheel of the '57 Chevy (327, blower, pipes, upper/lower work) pops the clutch and zooms off to the burger stand. The rope will pull you off the front of the treadmill (trust me). Even if the treadmill speeds up to match the speed of the wheels on your skateboard, the rope (which would correspond to the prop of an airplane as a motivational force) is going to pull you forward and off the front of the treadmill. Your "airspeed" - how fast you are going relative to the surrounding air - will increase.

Later still: The Greaser gets a cheesburger, fires, and malt *and* a date with Suzy the Cheerleader.... and you end up looking like Grandma's dog in Lampoon's Summer Vacation movie.

Disclaimer: *Never* tie yourself to the bumper of a car, especially a '57 Chevy driven by a hungry Greaser, with out without a skateboard ...

FWIW

You are making an assumption that the treadmill can not create the exponential, but necessary amount of force to counteract the pull of the '57 Chevy.

 

[LeiZaK]

Originally posted by: nweaver
is this still alive?

Look, in theory, there isn't enough speed/energy to keep the treadmill from stopping forward movement of the plane, because if the engines pushed the plane forward at 1MPH, then the treadmill would have to go insanely fast (much much faster then 1 MPH) in order to create enough friction to overcome the engines.

In practice, the plane would not stay stationary, and would take off like normal, except the wheels would be spinning at a crazy fast rate (not that wheel speed has ANYTHING to do with taking off)

In theory, we have all of the speed/energy our minds can imagine. Reality is another case, however.

 

[smack Down]

Originally posted by: gsellis

Originally posted by: BoomerD
"Splain this to me...if the treadmill moves in reverse fast enough to counter the plane's forward thrust, where is the lift going to come from? Yes, the plane's motors/engines may move it in a forward direction (now countered by the treadmill, the there would be no forward movement through the air to generate the necessary lift....so, everyone who says the plane takes off, what am I missing?
(/me knows zip about physics, but understands mechanics)

It can't as it only matches the groundspeed of the aircraft. Groundspeed <> airspeed. And the wheels have no effect on airspeed. If they did, landings would be really harsh as when the wheels contact the runway, the plane would stop. Instead, the spin up to what was groundspeed (airspeed is still independent, which is why they land into the wind as much as possible.)

The flaw in all the "won't take-off" folks is not grasping groundspeed vs airspeed and assuming that groundspeed can trump airspeed. It only does in a crash.

Groundspeed is equal to windspeed unless there is wind. There is no wind in this case so they are equal.

 

[HeroOfPellinor]

Originally posted by: JS80
How does a jet on an aircraft carrier going X miles per hour fly off the ship?

Steam.

 

[jimbob200521]

Originally posted by: HeroOfPellinor

Originally posted by: JS80
How does a jet on an aircraft carrier going X miles per hour fly off the ship?

Steam.

Wrong, mostly. The only reason they have steam powered take off on aircraft carrier's is because they can't make the runway long enough for the plane to take off under it's own power.

 

[QuantumPion]

I think the confusion comes from people thinking of two separate examples.

The example that the "won't take off" crowd think of is a plane running its wheels with 0 airspeed and 0 relative ground speed. To them, saying the plane would take off doesn't make sense because that means the plane would be hovering in mid-air with 0 airspeed. But this isn't what actually happens.

The plane will take off, given a treadmill runway that is as long as a regular runway. The force of the engines will push the plane faster then the treadmill's speed, causing the plane to accelerate relative to the actual ground, gaining positive airspeed. The reason why it is able to do so is because it is the force of the engines pushing the plane forward through the air, not the friction of the wheels on the ground.

Once it has accelerated enough, it will reach its liftoff airspeed and take off just as if it was a traditional runway. But the plane is not stationary relative to the treadmill, it is accelerating along it due to the force of the engines.

So, can a plane take off from a person-sized treadmill? No, it will not have enough room and it will run off the track. But if you have a runway-length treadmill, the plane will take off along it just as if it was on a regular runway. The assertion that engines provide forward thrust and not upward lift is correct. The assertion that an airplane cannot take off with 0 airspeed is also correct. But you have to realize that the force of the engine pushes the plane forward regardless of what the wheels or ground is doing.

 

[ScottMac]

Originally posted by: smack Down

Originally posted by: gsellis

Originally posted by: BoomerD
"Splain this to me...if the treadmill moves in reverse fast enough to counter the plane's forward thrust, where is the lift going to come from? Yes, the plane's motors/engines may move it in a forward direction (now countered by the treadmill, the there would be no forward movement through the air to generate the necessary lift....so, everyone who says the plane takes off, what am I missing?
(/me knows zip about physics, but understands mechanics)

It can't as it only matches the groundspeed of the aircraft. Groundspeed <> airspeed. And the wheels have no effect on airspeed. If they did, landings would be really harsh as when the wheels contact the runway, the plane would stop. Instead, the spin up to what was groundspeed (airspeed is still independent, which is why they land into the wind as much as possible.)

And it doesn't matter in this case. The airplane generates it own thrust through the airmass, the wheels and groundspeed are still irrelevent.


The flaw in all the "won't take-off" folks is not grasping groundspeed vs airspeed and assuming that groundspeed can trump airspeed. It only does in a crash.

Groundspeed is equal to windspeed unless there is wind. There is no wind in this case so they are equal.

....and it still doesn't matter at all. The airplane still generates its own thrust against and through the air mass. Wheels & groundspeed are irrelevent.

 

[Kev]

why do you morons keep arguing about this.

 

[gsellis]

Originally posted by: smack Down

Originally posted by: gsellis

Originally posted by: BoomerD
"Splain this to me...if the treadmill moves in reverse fast enough to counter the plane's forward thrust, where is the lift going to come from? Yes, the plane's motors/engines may move it in a forward direction (now countered by the treadmill, the there would be no forward movement through the air to generate the necessary lift....so, everyone who says the plane takes off, what am I missing?
(/me knows zip about physics, but understands mechanics)

It can't as it only matches the groundspeed of the aircraft. Groundspeed <> airspeed. And the wheels have no effect on airspeed. If they did, landings would be really harsh as when the wheels contact the runway, the plane would stop. Instead, the spin up to what was groundspeed (airspeed is still independent, which is why they land into the wind as much as possible.)

The flaw in all the "won't take-off" folks is not grasping groundspeed vs airspeed and assuming that groundspeed can trump airspeed. It only does in a crash.

Groundspeed is equal to windspeed unless there is wind. There is no wind in this case so they are equal.

WRONG! Groundspeed is the speed of the aircraft in relation to the treadmill. You can be flying with an airspeed of 150mph and have 0 groundspeed. Or in this case, 300mph groundspeed. But no point in telling you as you have proven you just cannot grasp the physical universe.

 

[SSSnail]

Originally posted by: jimbob200521

Originally posted by: HeroOfPellinor

Originally posted by: JS80
How does a jet on an aircraft carrier going X miles per hour fly off the ship?

Steam.

Wrong, mostly. The only reason they have steam powered take off on aircraft carrier's is because they can't make the runway long enough for the plane to take off under it's own power.

Basically, you just reiterate his word with a buncha mumble jumble. Steam! Oh, and if you want to get technical, there are pulleys, steel cables, deflectors and such.

 

[Linflas]

Originally posted by: HeroOfPellinor

Originally posted by: JS80
How does a jet on an aircraft carrier going X miles per hour fly off the ship?

Steam.

When I was on the Independence my squadron participated in a test the Navy called "Flanchoring" where we launched one of our S-3's while the ship was anchored off of Greece.

 

[jimbob200521]

Originally posted by: SSSnail

Originally posted by: jimbob200521

Originally posted by: HeroOfPellinor

Originally posted by: JS80
How does a jet on an aircraft carrier going X miles per hour fly off the ship?

Steam.

Wrong, mostly. The only reason they have steam powered take off on aircraft carrier's is because they can't make the runway long enough for the plane to take off under it's own power.

Basically, you just reiterate his word with a buncha mumble jumble. Steam! Oh, and if you want to get technical, there are pulleys, steel cables, deflectors and such.

 

[MasonLuke]

the plane will not fly.

 

[sao123]

Originally posted by: MasonLuke
the plane will not fly.

you bumped a week old thread to prove that you're a moron?
Congratulations...

 

[Toastedlightly]

Originally posted by: jimbob200521

Originally posted by: SSSnail

Originally posted by: jimbob200521

Originally posted by: HeroOfPellinor

Originally posted by: JS80
How does a jet on an aircraft carrier going X miles per hour fly off the ship?

Steam.

Wrong, mostly. The only reason they have steam powered take off on aircraft carrier's is because they can't make the runway long enough for the plane to take off under it's own power.

Basically, you just reiterate his word with a buncha mumble jumble. Steam! Oh, and if you want to get technical, there are pulleys, steel cables, deflectors and such.

Steam is the ONLY reason those planes get off that flight deck

 

[Squisher]

I was in a plane doing 200mph, I hung out and affixed a treadmill to wheels and spun them at 200mph backwards and the plane fell out of the sky and we all died.

So there.