Airplane on a Conveyor - Post-Mythbusters-Mortem

[Greebo]

Ok, Mythbusters has done the test. They put a plane on a makeshift conveyor and got the conveyor going faster than the plane's takeoff speed, in the opposite direction. The plane flew, without a hiccup.

So - now that you've seen it for yourself, what is your position?

 

[Pi1otguy]

First I said it'd fly, but months later mistook the "equal and opposite speed" for "the conveyor will try its hardest to cancel forward movement". I voted for it flying before I voted for catastrophic tire failure (the plane still moved before said failure).

BTW, did anyone else find it discerting that a pilot expected his plane not to fly? It's kind like if an airline capt said "I expect to run out of gas over the Atlantic." right before "Prepare for takeoff."

 

[KennyFlys]

I will not be assimilated!

I will not join the Borg!

 

[TMetzinger]

I want option one AND option four!

 

[Greg Bockelman]

I want option one AND option four!

Me too.

 

[Greg Bockelman]

I will not be assimilated!

Why is it so hard for you to understand, Ken?

 

[ScottM]

I will not be assimilated!

I will not join the Borg!

Why is it so hard for you to understand, Ken?

You know from the Spin Zone that he can't be swayed by facts

 

[Greebo]

I want option one AND option four!

I know...I thought of that one second too late.

 

[mikea]

I want option one AND option four!

Ditto. I was gonna post exactly that.

 

[KennyFlys]

Why is it so hard for you to understand, Ken?

Show me a view of both the airplane and the truck, plus the full length of the tarp (conveyor). Then show me where the tarp (conveyor) had absolutely no give or stretch capability. Recall the holes torn in it just by running on it in shoes?

Last, let's have calibrated speed monitoring and throttle control.

Even after that, it seems the premise changed from the original question I first read a couple years ago.

For example, the throttle advances only to the point that equals the resulting speed equivalent to the conveyor. If a fixed prop is determined to effect 25 MPH with 2000RPM then that should be a calibrated setting. Then, calibrate the conveyor to be at a speed of 25MPH.

By what everyone is saying, with a "two-thousand foot" conveyor and that same STOL aircraft, you should be able to begin the conveyor rolling and at first the aircraft will move backward on the conveyor. But, then if the aircraft's throttle is advanced to the calibrated setting for that 25MPH, the plane should take off by what everyone is saying. It shouldn't matter that it's initially moving backward. Right?

It's gonna drive me to drinking. In fact, I'm gonna have a Coke for lunch!

 

[jason]

<sigh>

 

[KennyFlys]

<sigh>

I agree!

 

[gprellwitz]

I want option one AND option four!

Double-ditto!

 

[RMCN172RG]

By what everyone is saying, with a "two-thousand foot" conveyor and that same STOL aircraft, you should be able to begin the conveyor rolling and at first the aircraft will move backward on the conveyor. But, then if the aircraft's throttle is advanced to the calibrated setting for that 25MPH, the plane should take off by what everyone is saying. It shouldn't matter that it's initially moving backward. Right?

Right.

 

[jason]

Show me a view of both the airplane and the truck, plus the full length of the tarp (conveyor). Then show me where the tarp (conveyor) had absolutely no give or stretch capability. Recall the holes torn in it just by running on it in shoes?

Last, let's have calibrated speed monitoring and throttle control.

Even after that, it seems the premise changed from the original question I first read a couple years ago.

For example, the throttle advances only to the point that equals the resulting speed equivalent to the conveyor. If a fixed prop is determined to effect 25 MPH with 2000RPM then that should be a calibrated setting. Then, calibrate the conveyor to be at a speed of 25MPH.

By what everyone is saying, with a "two-thousand foot" conveyor and that same STOL aircraft, you should be able to begin the conveyor rolling and at first the aircraft will move backward on the conveyor. But, then if the aircraft's throttle is advanced to the calibrated setting for that 25MPH, the plane should take off by what everyone is saying. It shouldn't matter that it's initially moving backward. Right?

It's gonna drive me to drinking. In fact, I'm gonna have a Coke for lunch!

You should not need to be "shown" these things. You should be able to deduce by using your logic that you are wrong. Do you believe that wind exists? It has never been shown to you. You know that wind exists because you've seen the effects of it and you've used your logic to realize that there is validity in what you've been told about the atmosphere. Honestly, at this point, I think you're just trolling. You're having fun listening to people tell you the same thing over and over again in different ways and are amused by their reaction when you just "refuse to believe". There is no way that you can be this stubborn. It's not possible.

 

[stingray]

By what everyone is saying, with a "two-thousand foot" conveyor and that same STOL aircraft, you should be able to begin the conveyor rolling and at first the aircraft will move backward on the conveyor. But, then if the aircraft's throttle is advanced to the calibrated setting for that 25MPH, the plane should take off by what everyone is saying. It shouldn't matter that it's initially moving backward. Right?

It's gonna drive me to drinking. In fact, I'm gonna have a Coke for lunch!

Where do you come up with this stuff? The problem said (Just like they explained it on the show) "As the plane MOVES in one direction the belt MOVES in the opposite direction matching the PLANES speed." The question never said anything about throttle position of the plane or the belt moving first. Your trying to make an argument that the plane won't fly, not SEEING that it will. It would be far easier if you said that the plane won't fly because you forgot to release the parking brake.

Dan

 

[TMetzinger]

Look closely at the demo they did with the model car on the treadmill, where the wheels are allowed to turn freely (just like an airplane). That should help fix the mental disconnect.

In fact, go get a kids toy car (non motorized) and take it to the gym, and feel for your self how little variation there is in the amount of force it takes to hold the car in one spot over a treadmill, regardless of treadmill speed. This force is friction in the wheel bearings and tires , and is the ONLY coupling between the car and the earth.

It should then be obvious that as long as the airplane generates takeoff thrust + the friction amount, it will move forward at normal rate of acceleration and lift off at normal speed.

 

[Greg Bockelman]

I should let this go.

Show me a view of both the airplane and the truck, plus the full length of the tarp (conveyor).

You think they played TV magic with it?

Then show me where the tarp (conveyor) had absolutely no give or stretch capability.

Not sure why that matters.

Last, let's have calibrated speed monitoring and throttle control.

To what end?

Even after that, it seems the premise changed from the original question I first read a couple years ago.

Well, here is the scenario as I have always seen it.

An airplane is standing on a runway that can move (some sort of big conveyor belt). The airplane moves in one direction, while the conveyor moves in the opposite direction. The conveyor has a control system that tracks the airplanes speed and matches the speed of the conveyor to the speed of the airplane, but in the opposite direction.

Will the airplane ever be able to take off?

What premise changed and what premise do you want to defend?

For example, the throttle advances only to the point that equals the resulting speed equivalent to the conveyor. If a fixed prop is determined to effect 25 MPH with 2000RPM then that should be a calibrated setting. Then, calibrate the conveyor to be at a speed of 25MPH.

Just curious. What do you think the result of this would be?

By what everyone is saying, with a "two-thousand foot" conveyor and that same STOL aircraft, you should be able to begin the conveyor rolling and at first the aircraft will move backward on the conveyor.

Ok, but that isn't part of the original scenario.

But, then if the aircraft's throttle is advanced to the calibrated setting for that 25MPH, the plane should take off by what everyone is saying.

That is only true if the airplane's stall speed is less than 25 MPH. Otherwise, no it won't.

It shouldn't matter that it's initially moving backward. Right?

Well you can take it to an extreme, but correct.

It's gonna drive me to drinking. In fact, I'm gonna have a Coke for lunch!

Me too, but for me it is Diet Mountain Dew.

Ken, I am just trying to figure out where we are diverging on the understanding of this.

 

[stingray]

I am begining to think we need one more option for Ken. "I didn't think it would fly and I still don't". I don't believe what I saw. It is impossible. It just cannot happen. They used two camera's and spliced the film together.

Just kidding Ken Sometimes it is better to be wrong, than to just look....

Dan

 

[TangoWhiskey]

By what everyone is saying, with a "two-thousand foot" conveyor and that same STOL aircraft, you should be able to begin the conveyor rolling and at first the aircraft will move backward on the conveyor. But, then if the aircraft's throttle is advanced to the calibrated setting for that 25MPH, the plane should take off by what everyone is saying. It shouldn't matter that it's initially moving backward. Right?

Ken, this is the first time I've jumped into this conversation. Bear with me for a minute. Imagine this variation on the Mythbuster's / treadmill scenario, and tell me what you think would happen:

The airplane is sitting on the treadmill, with its nose pointed opposite the direction the treadmill's belt will run. The aircraft's engine is NOT RUNNING. A rope is tied around the prop, and attached to the hitch of a truck on the ground off the far end of the treadmill--the truck is not on the treadmill belt.

The treadmill starts up, and the truck with the rope tied to the front of the airplane starts driving away, at the same MPH as the treadmill is running. What happens to the airplane? Does it stay still and spin it's wheels, or does it move forward?

 

[Greebo]

Show me a view of both the airplane and the truck, plus the full length of the tarp (conveyor). Then show me where the tarp (conveyor) had absolutely no give or stretch capability. Recall the holes torn in it just by running on it in shoes?

Last, let's have calibrated speed monitoring and throttle control.

Even after that, it seems the premise changed from the original question I first read a couple years ago.

For example, the throttle advances only to the point that equals the resulting speed equivalent to the conveyor. If a fixed prop is determined to effect 25 MPH with 2000RPM then that should be a calibrated setting. Then, calibrate the conveyor to be at a speed of 25MPH.

By what everyone is saying, with a "two-thousand foot" conveyor and that same STOL aircraft, you should be able to begin the conveyor rolling and at first the aircraft will move backward on the conveyor. But, then if the aircraft's throttle is advanced to the calibrated setting for that 25MPH, the plane should take off by what everyone is saying. It shouldn't matter that it's initially moving backward. Right?

It's gonna drive me to drinking. In fact, I'm gonna have a Coke for lunch!

You failed physics, didn't you?

 

[ScottM]

I'm gonna have a Coke for lunch!

Stay off of the nose candy, I think it is rotting your brain and you cannot think logically.

 

[KennyFlys]

I'm taking this same scenario...

An airplane is standing on a runway that can move (some sort of big conveyor belt). The airplane moves in one direction, while the conveyor moves in the opposite direction. The conveyor has a control system that tracks the airplanes speed and matches the speed of the conveyor to the speed of the airplane, but in the opposite direction.

and envision the following experiment using concise calibrated means:

For example, the throttle advances only to the point that equals the resulting speed equivalent to the conveyor. If a fixed prop is determined to effect 25 MPH with 2000RPM then that should be a calibrated setting. Then, calibrate the conveyor to be at a speed of 25MPH.

Will the airplane ever be able to take off?

I still say... plausible but I'm yet to be convinced given the very non-scientific means used.

Mythbusters has put a lot more into a lot less on that show. I'm rather disappointed in their method as well as the lack of view. I would like to see an elevated view of the entire event.

Me too, but for me it is Diet Mountain Dew.

Gosh, the hard stuff! Just remember the "Twelve hours, bottle to throttle" rule!

Ken, I am just trying to figure out where we are diverging on the understanding of this.

Me too!

 

[KennyFlys]

Ken, this is the first time I've jumped into this conversation. Bear with me for a minute. Imagine this variation on the Mythbuster's / treadmill scenario, and tell me what you think would happen:

The airplane is sitting on the treadmill, with its nose pointed opposite the direction the treadmill's belt will run. The aircraft's engine is NOT RUNNING. A rope is tied around the prop, and attached to the hitch of a truck on the ground off the far end of the treadmill--the truck is not on the treadmill belt.

The treadmill starts up, and the truck with the rope tied to the front of the airplane starts driving away, at the same MPH as the treadmill is running. What happens to the airplane? Does it stay still and spin it's wheels, or does it move forward?

I picture what you're saying. This scenario is the same as a vehicle on the conveyor with it's internal motor running against the conveyor direction. But, it's not really solving what I have issues with.

 

[KennyFlys]

I am begining to think we need one more option for Ken. "I didn't think it would fly and I still don't". I don't believe what I saw. It is impossible. It just cannot happen. They used two camera's and spliced the film together.

Just kidding Ken Sometimes it is better to be wrong, than to just look....

Dan

I have honest and sincere questions on how the experiement was conducted. I'm saying flight is certainly plausible but without more conclusive controls on the experiment, I'm not yet convinced it will indeed fly.

 

[Ken Ibold]

My wife (a non pilot) also was convinced the airplane would not take off. The disconnect comes from the fact that the treadmill "moving at the same speed as the airplane" is irrelevant. The treadmill may be moving at 50 mph in one direction, and the airplane may be moving at 50 mph in the other direction, but the two are not comparable because one is airspeed and one is groundspeed. The two cannot cancel each other out because they are measuring different things.

She went to bed mad.

 

[KennyFlys]

You failed physics, didn't you?

What is the meaning of "physics"?

Actually, I didn't take physics in college. In high school, I took a single biology course and spent the rest of my time in business classes and architectural drafting classes.

 

[KennyFlys]

She went to bed mad.

I'm not mad about it. But, I'm not convinced.

To quote Gilligan...

"You can't make me! You can't make me! You can't make me!"

 

[KennyFlys]

Stay off of the nose candy, I think it is rotting your brain and you cannot think logically.

I think I snorted my Wheaties this morning!

 

[Greebo]

Ken,

One last time, please - explain to me why you think an airplane with a takeoff speed of 25kts sitting on a treadmill moving in the opposite direction at exactly 25kts will not take off.

Lets see if we can't resolve whatever confusion has got hold of you...

 

[TangoWhiskey]

I picture what you're saying. This scenario is the same as a vehicle on the conveyor with it's internal motor running against the conveyor direction. But, it's not really solving what I have issues with.

Ken,

No, it's NOT the same scenario... An airplane on the treadmill being towed by a vehicle that is not on the treadmill IS NOT THE SAME "as a vehicle on the conveyor with it's internal motor running against the conveyor direction".

We have to get past this misconception first before we'll make progress. How do you think this is the same scenario? In the scenario I describe, the source of power is external to the treadmill and not affected by it--the wheels of the towing vehicle are tractioned with the stationary ground. In the scenario you describe, the vehicle (car or truck) on the conveyor with it's internal motor running against the conveyor direction is fighting the conveyor belt's motor.

Do you see the difference?

 

[TangoWhiskey]

Actually, I didn't take physics in college. In high school, I took a single biology course and spent the rest of my time in business classes and architectural drafting classes.

That explains it... no shame in that, either... but since you didn't take the class, you have to be willing to listen and learn from those that did. Your reply to my scenario (with the engine off) shows where the disconnect is. Read my reply and we'll go from there.

 

[Richard]

Silly me, I thought this thread was simply to say, "Yeah I watched Mythbusters last night." when in fact it is another reincarnation of that stupid thread.

 

[Greg Bockelman]

and envision the following experiment using concise calibrated means:

That is the part I don't understand and you haven't explained adequately to me. How does that fit into the scenario?

 

[Dave Siciliano]

Guys, I did understand this, but didn't understand the manner in which this was presented.

The plane accelerates as normal. If one was standing on the ground next to the treadmill observing, the plane would accelerate as if the treadmill wasn't there while the wheels spin the other way.

What screwed me up was the Myth Busters folks seems to say to me, the plane would stay still relative to the ground because the treadmill was going the other way.

So, part of the reason I wasn't on board with this thing in my mind was the way I perceived it was being explained. Perhaps I fixated on the wrong point. But I didn't think they showed the plane would stay still relative to the ground; and they didn't. It accelerated normally.

Anyway, I think part of the problem was the manner in which this was presented. Couple other folks seem to agree.

Best,

Dave

 

[KennyFlys]

Ken,

One last time, please - explain to me why you think an airplane with a takeoff speed of 25kts sitting on a treadmill moving in the opposite direction at exactly 25kts will not take off.

Lets see if we can't resolve whatever confusion has got hold of you...

I don't know how to explain it any better than I have.

 

[KennyFlys]

Ken,

No, it's NOT the same scenario... An airplane on the treadmill being towed by a vehicle that is not on the treadmill IS NOT THE SAME "as a vehicle on the conveyor with it's internal motor running against the conveyor direction".

We have to get past this misconception first before we'll make progress. How do you think this is the same scenario? In the scenario I describe, the source of power is external to the treadmill and not affected by it--the wheels of the towing vehicle are tractioned with the stationary ground. In the scenario you describe, the vehicle (car or truck) on the conveyor with it's internal motor running against the conveyor direction is fighting the conveyor belt's motor.

Do you see the difference?

Yes, an external rope (static hold) verus internal power limited to within the confines of the conveyor.

 

[KennyFlys]

Silly me, I thought this thread was simply to say, "Yeah I watched Mythbusters last night." when in fact it is another reincarnation of that stupid thread.

Hush and go enjoy a bikini or something... or, whatever you find in one.

 

[KennyFlys]

That is the part I don't understand and you haven't explained adequately to me. How does that fit into the scenario?

My response is the same as to Chuck. I don't know how I can explain my opposing view any better than I have.

 

[midlifeflyer]

I've had very little interest in the past in the "controversy," really only having read enough posts to get a general idea what it was about. Like most everyone here, though, I was interested in watching the "experiment." Even now, I'm much more interested in the quality of the experiment than I am in the myth itself.

My own view of the experiment is that I was disappointed. I thought the "myth" involved an airplane with wheels turning as fast as but no faster than a treadmill heading in the opposite direction at or above takeoff speed - a scenario where, at least in one version of the theory, you have an airplane incapable of developing sufficient air speed for takeoff.

That's not what I saw since (1) the airplane began moving forward with respect to the Earth as soon a power was applied and (2) I did not see any indication of the speed of the aircraft's wheel being measured.

Instead, I saw the answer to a question more akin to the one Greebo posed above to Kenny: Will an airplane capable of producing enough power to move forward relative to the air and produce lift while on a treadmill heading the opposite direction at or above takeoff speed, be able to take off. Frankly, I always though the answer to that was, "Duh, of course," and never thought that was particularly "controversial."

Reading the post mortem comments has led me to the conclusion that there is a basic disagreement of what the question is to begin with. And it's really hard to agree on an answer when you can't agree on the question.