Airplane on Conveyor Belt Mythbusters 12/12

[Rondo777]

Put an airplane (not a helicopter or a vectored flight airplane) on a treadmill that is bolted to the ground. There is no natural wind. Start up the plane's engine and increase the throttle to max. The plane will begin to move forward, BUT you start the treadmill and increase it's speed to keep the plane more or less in the same place relative to the solid ground. Will the plane lift off (or take off, if you will)?
My answer: It won't.

You are correct that it won't. But the point I think you are missing is, the treadmill can't do ANYTHING to keep the plane "more or less in the same place relative to the solid ground" unless there is something physically tethered from the ground (not the treadmill) directly to the plane. Well, unless the wheels are acting as a brake.
Even if the plane's propulsion system triggered the treadmill's speed, the thrust of the airplane isn't being derived from the treadmill or the plane's contact with the ground, it is being generated by the engines, which is using airflow, which is completely independent from the ground. Thus, when the propulsion system has enough thrust to move the plane 5 mph, and the treadmill starts to run at 5 mph, the plane will still move 5 mph in relation to the ground. The wheels of the plane on the treadmill will either skid (if there's enough propulsion) or the wheel speed will increase to 10 mph (5 mph for the thrust generated, and 5 mph additional for the treadmill speed).

WHAT?!?! - OK, I believe reading this just gave me a Cerebral Hemorrage IT HURTS! IT HURTS! :confusedsmiley:

 

[tinpusher]

This was from the Mythbusters site....There are some pissed off people over there.

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I have just received an email from Dan Tapster, executive producer of MythBusters.

Thanks to all the activity, he can't log in and asked me to post this for him.

quote:

"Adam? Jamie? Dan? Someone step up and tell us what happened tonight."

Dear all,

As wbarnhill called out, I thought I should step in to what is rapidly becoming a hornet's nest. I will try to calm things down but I don't hold out much hope!

First up, for those concerned that this story has been cancelled, don't worry, planes on a conveyer belt has been filmed, is spectacular, and will be part of what us Mythbusters refer to as 'episode 97'. Currently that is due to air on January 30th.

Secondly, for those very aggrieved fans feeling "duped" into watching tonight's show, I can only apologise. I'm not sure why the listings / internet advertised that tonight's show contained POCB. I will endeavour to find out an answer but for those conspiracy theorists amongst you, I can assure you that it will have just been an honest mistake. At one point

several months ago, POCB was going to be part of Airplane Hour. Somewhere, someone has mistakenly posted the wrong listing. It will have been a genuine mistake but nonetheless it was a mistake which is unacceptable. As said I will try to find out what went wrong and hope that you will see fit to forgive the team at Discovery.

Thanks in advance,

Dan

-------------------------

 

[madmike2]

I figured it was a programming error. It'll still be fun to watch!

 

[Scab]

Is this thread the internet version of a pissing contest?

We should pose this to the people at "Mythbusters":

"He who argueth the most fervent hath the larger penis."

 

[SouthernCruizer]

This has got to be the most amusing and ridiculous thread ever ! LOL...now I know why there are so few pilots around. There are 4 forces involved in flight...Thrust, Drag, Lift , and weight. Regardless of Thrust, Drag, or Weight ,without adequate air flow over a wing to create LIFT, that wing WILL NOT FLY...Ground speed means NOTHING. AIR SPEED is the determing factor to generate lift. Based on the assumption that a treadmill will spin at the same rate as the rolling landing gear, the plane remains motionless, both in ground speed and air speed(save for the little prop wash, which is not "clean" air flow over the entire wing). No air speed, no fly.

For the mathmatically challenged... L=CLV2p/2S

L = Lift

CL=Coeffieicent of lift

V = Velocity (in ft per sec)

p=Air Density

S = Wing surface area (Sq. ft.)

Jay

'04 FJR 1300

Private Pilot , Single Engine Land, PPC Land

 

[Bounce]

i recant my previous position. i'll wait to see the show.

 

[twowheelnut]

Edible panties. Strawberry or Wild Cherry are the best. I'm jus' sayin'...

 

[GunMD]

This has got to be the most amusing and ridiculous thread ever ! LOL...now I know why there are so few pilots around. There are 4 forces involved in flight...Thrust, Drag, Lift , and weight. Regardless of Thrust, Drag, or Weight ,without adequate air flow over a wing to create LIFT, that wing WILL NOT FLY...Ground speed means NOTHING. AIR SPEED is the determing factor to generate lift. Based on the assumption that a treadmill will spin at the same rate as the rolling landing gear, the plane remains motionless, both in ground speed and air speed(save for the little prop wash, which is not "clean" air flow over the entire wing). No air speed, no fly.
For the mathmatically challenged... L=CLV2p/2S

L = Lift

CL=Coeffieicent of lift

V = Velocity (in ft per sec)

p=Air Density

S = Wing surface area (Sq. ft.)

Jay

'04 FJR 1300

Private Pilot , Single Engine Land, PPC Land

I'm not buying it. In the case of an airplane the propulsion mechanism is the prop (or jet engine). Since propulsion is independent of the wheels / tires it isn't altered by the speed of the conveyor. The plane will move forward because the props are going to make it move. It makes no difference how fast the wheels are going...they don't provide the propulsion like they would on a car. The plane takes off.

 

[JimLor]

True, depends on the speed of the "conveyor" belt. If the belt is free wheeling and will match the thrust of the A/C (equal and opposite reaction), that conveyor belt can go 200mph and the A/C ground speed will be zero and A/C airspeed will be zero. A/C will not move, will not fly, but that ole' conveyor belt will be going at the speed of heat.

Whaddya think of that!?

 

[GunMD]

True, depends on the speed of the "conveyor" belt. If the belt is free wheeling and will match the thrust of the A/C (equal and opposite reaction), that conveyor belt can go 200mph and the A/C ground speed will be zero and A/C airspeed will be zero. A/C will not move, will not fly, but that ole' conveyor belt will be going at the speed of heat.
Whaddya think of that!?

Not buying that argument really. The a/c applies enough thrust to move the a/c forward at 100mph (relative to the motionless air and motionless ground) then this magical conveyor will match that speed and be going backwards at 100mph. That means (let's see...carry the nine...oh, ok) the wheels are spinning (free-wheeling) at 200mph (relative to the conveyor) and the a/c is moving forward at 100mph (relative to both the motionless air and the motionless ground). Assuming that this particular a/c can generate enough lift at 100mph to get off the ground, the plane takes off.

To summarize, the airplane's exerted energy is acting on the air, not on the ground. Therefore it will still move relative to the air.

 

[markjenn]

This has got to be the most amusing and ridiculous thread ever ! LOL...now I know why there are so few pilots around. There are 4 forces involved in flight...Thrust, Drag, Lift , and weight. Regardless of Thrust, Drag, or Weight ,without adequate air flow over a wing to create LIFT, that wing WILL NOT FLY...Ground speed means NOTHING. AIR SPEED is the determing factor to generate lift. Based on the assumption that a treadmill will spin at the same rate as the rolling landing gear, the plane remains motionless, both in ground speed and air speed(save for the little prop wash, which is not "clean" air flow over the entire wing). No air speed, no fly.
For the mathmatically challenged... L=CLV2p/2S

L = Lift

CL=Coeffieicent of lift

V = Velocity (in ft per sec)

p=Air Density

S = Wing surface area (Sq. ft.)

Jay

'04 FJR 1300

Private Pilot , Single Engine Land, PPC Land

Stop being so condescending.

The problem is with the "treadmill spinning at the same rate as the rolling landing gear." As has been discussed over and over, this constraint doesn't make any sense. It presumes that the airplane is generating its forward motion in the air via some form of friction with the treadmill, like a car, but the airplane is generating it's thrust by "pulling" on the air, not the treadmill.

Unless you assume some kind of fantastically high wheel-bearing friction, there is nothing the treadmill can do to constrain the airplane. The treadmill can spin a million miles an hour forward, backward, etc. - it doesn't matter as the wheels just spin.

The treadmill constraint must be expressed in some common frame of reference. One way is to put both with respect to the ground. In this case, if the airplane is rolling straight ahead at X mph with respect to the ground, then the treadmll would roll backwards at the same linear speed with respect to the ground. In this case, the wheels of the airplene would roll at double their normal rate - X mph due to the airplane moving forward + X mph for the treadmilll rolling back or 2X total. But again, unless the wheels can exert some form of drag on the airplane, it wouldn't be constrained from taking off.

And FWIIW, I'm a pilot also with 2K+ hours.

- Mark

 

[SouthernCruizer]

True, depends on the speed of the "conveyor" belt. If the belt is free wheeling and will match the thrust of the A/C (equal and opposite reaction), that conveyor belt can go 200mph and the A/C ground speed will be zero and A/C airspeed will be zero. A/C will not move, will not fly, but that ole' conveyor belt will be going at the speed of heat.
Whaddya think of that!?

Not buying that argument really. The a/c applies enough thrust to move the a/c forward at 100mph (relative to the motionless air and motionless ground) then this magical conveyor will match that speed and be going backwards at 100mph. That means (let's see...carry the nine...oh, ok) the wheels are spinning (free-wheeling) at 200mph (relative to the conveyor) and the a/c is moving forward at 100mph (relative to both the motionless air and the motionless ground). Assuming that this particular a/c can generate enough lift at 100mph to get off the ground, the plane takes off.

To summarize, the airplane's exerted energy is acting on the air, not on the ground. Therefore it will still move relative to the air.

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What are you smoking?? The plane RESTS on its wheels...the wheels are the LINK between the plane and the ground (treadmill)...as the engine spools up and the prop/turbine creates THRUST, the plane starts to move forward, but since it RESTS on the treadmill and the treadmill registers forward movement, it counters that movement by running the opposite direction at EXACTLY the same speed as the rotating wheels....thus, NO RELATIVE MOVEMENT from the plane...as the prop/turbine produce more and more thrust, the treadmill goes FASTER AND FASTER to match the speed of the tires spinning. Air speed = 0 Ground speed = 0

NO LIFT

geeze, my 15 yr old just checked out this thread and can't belive that this concept is that difficult to grasp.

The tires are going at a rate that would be 100mph on flat ground, then the treadmill is going 100 mph to counter. There is NO 200 mph in that equation. For every action, there is an OPPOSITE and EQUAL reaction! :blink:

Jay

'04 FJR 1300

 

[Rondo777]

Put an airplane (not a helicopter or a vectored flight airplane) on a treadmill that is bolted to the ground. There is no natural wind. Start up the plane's engine and increase the throttle to max. The plane will begin to move forward, BUT you start the treadmill and increase it's speed to keep the plane more or less in the same place relative to the solid ground. Will the plane lift off (or take off, if you will)?
My answer: It won't.

You are correct that it won't. But the point I think you are missing is, the treadmill can't do ANYTHING to keep the plane "more or less in the same place relative to the solid ground" unless there is something physically tethered from the ground (not the treadmill) directly to the plane. Well, unless the wheels are acting as a brake.
Even if the plane's propulsion system triggered the treadmill's speed, the thrust of the airplane isn't being derived from the treadmill or the plane's contact with the ground, it is being generated by the engines, which is using airflow, which is completely independent from the ground. Thus, when the propulsion system has enough thrust to move the plane 5 mph, and the treadmill starts to run at 5 mph, the plane will still move 5 mph in relation to the ground. The wheels of the plane on the treadmill will either skid (if there's enough propulsion) or the wheel speed will increase to 10 mph (5 mph for the thrust generated, and 5 mph additional for the treadmill speed).

Ponyfool, untill an airplane actually leaves the ground (unless theres a headwind) it is all about ground speed. If you put the plane on a treadmill set at 5mph with out the plane running at all then the plane is going to move with the treadmill, no wheels turning, no propulsion from the plane at all but it will be moving at 5mph relative to you if your not standing on the treadmill with it. Now if you fire up the plane and give it enough thrust to just compensate for the 5mph treadmill the plane will become stationary. Resulting in 0 airspeed, thats what you need to fly. How fast the wheels are turning is irrelevent. If the treadmill speed is increased to 500 mph and there plane is only given enough thrust to maintain a 500 mph groung speed you still have 0 airspeed and your not getting off the ground. There is nothing powering the wheels, there just going along for the ride and you cant add the wheel speed to the treadmill speed to come up with anything.

I cant believe that I just can't leave this alone, my g-d, I'm getting even less then usual done at work today! mg2:

 

[germany]

My only question is...does the plane have a Power Commander? 'Cuz I just put one on my bike and it's freaking awesome!

 

[SouthernCruizer]

My only question is...does the plane have a Power Commander? 'Cuz I just put one on my bike and it's freaking awesome!

***************************

:clapping: :clapping:

 

[xviper]

I cant believe that I just can't leave this alone, my g-d, I'm getting even less then usual done at work today! mg2:

Same here. Like I said before. I always get sucked into these sorts of things. I'm done with this till the show airs. Too many people who don't quite understand the concept of such an experiment.

 

[GunMD]

If you don't believe me, go try this out. Put a pair of rollerblades on and go stand on a running treadmill (you can hold on to the sides if you want). Your feet will move backwards due to some frictional force of the rollerblades' axles, but they won't move backwards at anywhere near the velocity of the treadmill. You'll even find that you can pull yourself forwards with your arms (kind of like an airplane's engine, huh?) Now, take the rollerblades off and stand on the treadmill in bare feet. I guarantee you that you're going to be moving backwards a whole lot more quickly because now the force of the treadmill is acting on your body much more efficiently than it was when you were wearing the rollerblades.

Shamelessly stolen from here.

 

[GunMD]

Ooooooo....here is a much better way to look at it.

This helps clear it up (I think so anyway).

 

[JimLor]

JIMLOR - you're a dolt!

Just back from the gym where I do my best thinking. Bottom line, the tires/wheels of an aircraft to not provide any motive or driving force and therefore the movement of the a/c will not xfer to the belt. The wheels are nuetral and are there so the A/C doesn't fall over when stopped and you can move it around. Thereforeheretounder, I now think an a/c on a freewheeling conveyer belt will takeoff pretty much as normal. The only force from the a/c to act on the belt is the weight of the a/c on the wheels and that's basically straight down and won't impart any movement to the belt (all of this is in a "perfect" world).

And BTW JimLor, I'm sleeping with your wife tonight.

 

[GunMD]

The gym was good to you, Jim. :lol: