will it take off?

[RonMar]

Re: Mythbusters/airplane/treadmill

But, that is not possible, right?
Is this another one of those "moot point doesn't matter" discussions?

If not impossible, certainly very impractical. It just dosn't take that much energy to spin up the wheels. Minor fractions of the prop thrust moving the plane forward, and the belt going to the rear. And if you are talking about super accelerations of the conveyor belt, Any rapid acceleration of the plane to the rear caused by inertial drag of accelerating the tires, would also be resisted by the planes greater mass. Kind of like the person ripping the tablecloth out from under the dishes on the table. A quick acceleration overcomes the friction and the mass of the dishes keeps them relatively stable and pretty much in the same position. The same thing can be done with a toy car or plane setting on the table. The tablecloth can be jerked right out from under them.

Do the wheels take energy to accelerate? YES. Did it impede the aircrafts ability to take off? I am sure it did to some degree, but it was by such a small margine as to be extremely difficult, if not impossible to measure accurately... The belt went backward, the plane accelerated forward and took off in what appeared to be normal distance... Myth Busted.

 

[SPYDERLK]

Re: Mythbusters/airplane/treadmill

But, that is not possible, right?
Is this another one of those "moot point doesn't matter" discussions?

It matters because it is theoretically possible and thereby worth an understanding of the physics making it so. The theory has the math to determine whether it could be done within material strength of presently available materials. My guess is that any wheeled plane that has a thrust to weight ratio below 1/2 could be held completely still or even pulled backward under full thrust for a second or so before something in the wheel or the conveyor system failed. The engineering involved in such a demonstration would be prodigious. What a big deal to show doubters the validity of what physics and math describe. And no, the plane probably wouldnt be able to take off due to the damages inherent in the mechanical failure.
larry

 

[MossRoad]

Re: Mythbusters/airplane/treadmill

Thread closed. Please continue this discussion in the original thread, as this one has the potential to become a huge monster post as well. We will try to merge this post into the other one. Wish us luck.

Here's the link to the original thread.

Click here please.

 

[MossRoad]

Looks like it worked. The two threads should now be merged. Please continue this most fascinatiing discussion.

 

[RobJ]

Maybe its just me but sometimes its hard to tell what side people ore on.

BTW, the helo will take off to...same reason the plane takes off. :d

 

[RobS]

Maybe its just me but sometimes its hard to tell what side people ore on.

BTW, the helo will take off to...same reason the plane takes off. :d

I'm going to disagree on the helo. Assuming the turntable rotates at the same speed as the rotor shaft, the helo body will be spinning but the rotor will be stationary. Stationary rotor = no lift.

 

[RobJ]

I'm going to disagree on the helo. Assuming the turntable rotates at the same speed as the rotor shaft, the helo body will be spinning but the rotor will be stationary. Stationary rotor = no lift.

But the rotor will be spinning, turntable spinning at the same speed as the rotor shaft equals spining rotors connected to rotor shaft, like the prop on the plane. The question is if the turntable is spinning at the same speed as the rotor, will it take off. Answer yes, if the turntable is spinning at a speed where the rotor will produce lift to overcome the weight of the helo, yes it will lift.

Like the plane, the key here is the rotor IS spinning and producing a low pressure on top and high pressue air below...equal lift.

So RobS, will the plane fly on the conveyer?

When a helo loses a tail rotor, it still flys while it's spinning, just hard to control and somebody is gonna get motion sickness!!

Do we need a new thread on this one Moss? hehe

 

[RobS]

But the rotor will be spinning, turntable spinning at the same speed as the rotor shaft equals spining rotors connected to rotor shaft, like the prop on the plane. The question is if the turntable is spinning at the same speed as the rotor, will it take off. Answer yes, if the turntable is spinning at a speed where the rotor will produce lift to overcome the weight of the helo, yes it will lift.

Like the plane, the key here is the rotor IS spinning and producing a low pressure on top and high pressue air below...equal lift.

So RobS, will the plane fly on the conveyer?

When a helo loses a tail rotor, it still flys while it's spinning, just hard to control and somebody is gonna get motion sickness!!

Do we need a new thread on this one Moss? hehe

I'll wait for the new thread to continue the helo discussion...

See the early pages of this thread for my opinion on the airplane. I think I weighed in about mid-stream as well though my opinion did not change.

 

[RobJ]

I think I weighed in about mid-stream as well though my opinion did not change.

OK you could have just said Yes, it'll fly. But why would the helo be different. What about the airboat? there's another one to ponder.

I was a convert on the plane...from no to yes after some thought.

Ever seen one of these fly?

 

[ray66v]

If your lucky enough to have good froward speed when you loose a tail rotor in your heli you can keep it from spinning.

 

[rback33]

If your lucky enough to have good froward speed when you loose a tail rotor in your heli you can keep it from spinning.

There you go educating me again. I would not have guessed that was possible.

OMG I just realized how that sounded! I see you knew I mean the part about keeping it from spinning that I did not guess was possible... not the part about educating me. I am not THAT big of a narcicist to think I know EVERYTHING.

 

[ray66v]

Knowing this crowd, someone will want to have a death match over it. But, it can be done.
As describe to me by my HCFII
From forward flight: Down on cyclic, forward on collective, While maintaining forward motion, raise cyclic as necessary to softly impact the ground, slide on the skids along the ground. The wind will keep the tail behind you.
Even more interesting, there is a way to stop rotation of the aircraft with a stuck rudder pedal (also spinning).

 

[patrick_g]

After reading all these replies?
I would suggest all of you to get a real Pilots license and read your book very good
and go from there
This whole thing has been misrepresented to all of us big time
Jim

Oh Mr. Jimi, My USAF job was instrument flying instructor on a flight simulator, I have a pilots lisc, and before I got into computers, software and training I was a physicist, briefly, before I found that a BS in Physics qualified me to be an electronics technician to a PhD in physics.

The RIGHT answer is dependent on the problem statement and precise definition of terms. That is what made the topic so interesting as well as frustrating. Depending on the problem statement and definition of terms you can argue either way, take off or no take off AND BE RIGHT. The pity was that so many folks made their own (often unwarranted and unstated) assumptions and or were close minded and filed to explore any idea contrary to their preconceived notion.

Whether or not a real airplane will take off from a real conveyor belt was never in question and is trivially obvious to even the most casual observer with a modicum of experience or physical theory (with exception of the idiot pilot on Myth Busters) but that wasn't the problem stated here, WHETHER OR NOT SOME FOLKS NOTICED IT.

Again, depending on the definitions of terms and ignoring the current state of the art in building conveyors and airgraft wheels/tires/axles, you picks your definitions and you gets your answer. Either contention can be supported, depending on your assumptions.

Somehow I am reminded of a room full of folks in a marlinespike seamanship class I taught. At break time I sent half of the class out of the room and showed the remaining half how to tie a bowline knot. Then swapped class halves and showed the other half of the class a completely different way to do it. At the next break as students were practicing the knots they had been shown there were heated discussions just short of fights in some instances as many thought the other guy was just too wrong and had to be straightened out and shown the PROPER way to tie a bowline.

Pat

 

[rback33]

Somehow I am reminded of a room full of folks in a marlinespike seamanship class I taught. At break time I sent half of the class out of the room and showed the remaining half how to tie a bowline knot. Then swapped class halves and showed the other half of the class a completely different way to do it. At the next break as students were practicing the knots they had been shown there were heated discussions just short of fights in some instances as many thought the other guy was just too wrong and had to be straightened out and shown the PROPER way to tie a bowline.

Pat

LMAO and the best thing is knowing you did that to them on purpose. I would have paid money to see that. I can't for the life of me remember how to tie a bowline, but I can tie a great anchor line bowline.

 

[RobS]

The RIGHT answer is dependent on the problem statement and precise definition of terms. That is what made the topic so interesting as well as frustrating. Depending on the problem statement and definition of terms you can argue either way, take off or no take off AND BE RIGHT. The pity was that so many folks made their own (often unwarranted and unstated) assumptions and or were close minded and filed to explore any idea contrary to their preconceived notion.

Somehow I am reminded of a room full of folks in a marlinespike seamanship class I taught. At break time I sent half of the class out of the room and showed the remaining half how to tie a bowline knot. Then swapped class halves and showed the other half of the class a completely different way to do it. At the next break as students were practicing the knots they had been shown there were heated discussions just short of fights in some instances as many thought the other guy was just too wrong and had to be straightened out and shown the PROPER way to tie a bowline.

Pat

You nailed it Pat. I've seen a number of these sorts of problems. All built with sufficient vaguaries to allow for two sides to easily form. It's all fun.

I love your bowline example!

It's all about opening the mind, which I admit sometimes I have a hard time doing.

 

[jsborn]

Mythbusters tested the question this week and the plane took off from the conveyor just like it did from a concrete non moving runway CASE CLOSED !!

 

[RobS]

OK you could have just said Yes, it'll fly. But why would the helo be different. What about the airboat? there's another one to ponder.

I was a convert on the plane...from no to yes after some thought.

Ever seen one of these fly?

Rob, I have not seen one of those fly, but I do have a retirement dream of mastering an RC helo (with actual rotor lift). I saw a video years back and got an impression of how difficult they are to fly, thus my wait 'til later in live where I hope to have more time on my hands.

Regarding the helo and airboat questions, I never saw the actual problem statement for either, only can assume how they were worded. Refer now to PatrickG's statement about these sorts of problems. They make for fun discussion/debate as there are intentionally two sides to argue. Another one I've been involved in is the stranded (pick your place, desert, ocean, mountain) situation where the team has to agree on the priority of a list of items they have. There is often no "correct" answer, but plenty of lively discussion/debate.

Oh, sorry for not answering you directly. Only trying to add to the vagueness of this whole thread...

BTW, if a tree falls in the woods and no one is there to hear...

 

[SPYDERLK]

I'm going to disagree on the helo. Assuming the turntable rotates at the same speed as the rotor shaft, the helo body will be spinning but the rotor will be stationary. Stationary rotor = no lift.

You got it. I can tell I know a lot less about hcops than others here, but I can dicipher reference frames and physics. Rotor motion wrt air produces lift. Here you have wings sitting still wrt atmosphere. You could get some lift if you could aim the tail rotor forward to blow over the main, but that would be modifying the chopper and it would only affect one or 2 blades at a time anyway....... Vibration and not much lift.
larry

 

[SPYDERLK]

You nailed it Pat. I've seen a number of these sorts of problems. All built with sufficient vaguaries to allow for two sides to easily form. It's all fun.

I love your bowline example!

It's all about opening the mind, which I admit sometimes I have a hard time doing.

There are at least 3 sides. Two of them seem unable to understand the valid points of the opposed view.
larry

 

[turnkey4099]

Just to throw a stick in the ocean of theoretics:

Replace the wheels with skis (or ice skates) and ice the belt. There just went all the energy being applied to spinning up wheels, etc.

Harry K