Imagine a plane is sitting on a treadmill

OOOH! Where from?

left & right is done with the treadmill.

Forwards and backwards is done by that imaginary piece of rope..

Fischer on Sonnenstr. had had them for 35 but was all sold out by Saturday. A little shop off of Lindwurmstr. has them for 26 - I'll note down the address when I go by today.


Larger RC choppers are all 5-channel (4+1 i.e. the collective is mixed with the throttle so 1. collective 2. roll 3. pitch 4. yaw 5. throttle). This little one uses one channel for altitude control (collective in a real heli but just more RPMs in this case) and the other for yaw control. As such there's no cyclic roll or pitch. A bit of weight on the nose results in the center of gravity being ahead of the center of lift thus it pitches forward and picks up speed. The rest is stabilized by pendulum and gyroscopic forces.

All things considered it's amazing how well they fly.

Thanks.

Edit: have you reserved one just in case?

Just had a thought, if the conveyor was perfectly frictionless with the air above it, then it would also be perfectly frictionless with the tyres

So even allowing for impossible conveyor and wheel speeds, it still debunks itself. So you cannot agree with him on that by definition

Geek.

Let's imagine it the other way round: landing on a giant conveyor. Let's use a short landing plane so we don't need to worry about exploding tyres etc. - landing speed of 30 mph. Would it be a normal landing? Answer: yes, until the brakes were applied, in which case the plane would slow down much more quickly than normal.

Exactly my point - it's totally impossible for this to work at all for several reasons, so in the original question it *must* mean the conveyor speed is the same as the plane's *air* speed, ie the plane doesn't stay stationary.

Anyone want to help me try and build experimental proof of this? We need someone with a treadmill that has variable speed, and a plane that can take off in about 1metre. There are some slow-fly planes that should do the trick...

Also need some accurate low-speed measuring devices to get the planes speed...

I'm pissed off! I paid 30€ for mine from amazon and it'll only get here when I'm away and it comes in crap DHL colours (the box and the toy...). The plane looks pretty sweet too. I saw the helicopter on cnn last night - it's one of the super toys for christmas (ie all sold out).

or you use the travelator at the airport late at night when security is asleep. Ask for a security tape as proof of experiment.

Lets let this die. Or least see if w can get this thread on page 2 for the first time since it was created.

Tom17, I don't think anyone is still saying the plane won't take off if the conveyor runs at the same speed as the planes *air speed* are they? If they are, they aren't worth building a rig for!

I hope not..

So its agreed then that its just ambiguity in the question, right?

I don't think anybody dares to.

lol

Even if there is ambiguity, it still will always take off no matter what you assume. If you assume the the plane stays stationary (and has very sticky tyres to allow the conveyor to do this) then after a few seconds the conveyor will be creating enough wind for the plane to take off anyway. Or the plane crashes somehow and hits the deck of a 10000mph conveyor belt, which is not going to be pretty, and the plane will probably take off, just not all in one piece

It would be interesting to hear DW's answer as this thing appears to be still sitting on the threadmill.

Next, let's get an expensive camera and take a bunch of pictures of stuff to prove that black is not white. Seriously, anyone claiming to need to see "proof" of this to believe that the plane would actually take off needs to have their head examined.

I'll answer for DW:

"Howdy. I'm DW and I'm fucking cool and I know fucking everything about planes, R/C helicopters and space. The plane would fly. Now if you'll excuse me I'm off to waste some taxpayers' money on firing monkeys into orbit".

No, I'm off to put a deuce in Jimbo's pillowcase!

Ahh course.. I had forgotten about that even though I mentioned it a few posts(for me) earlier... DOH!

you kidding it sounds like jolly good fun. what do you think myth busters do on discovery channel...

This must be trolling when he says:


Do what?

This will for sure appear on mythbusters.

I saw one the other week when they tested to see if a Chinese guy with 4,000 fireworks up his bum really managed to be the first ever astronaut. I think we can be pretty confident that about 25% of people on this forum reckon he got there before Yuri.

Cmon guys. No more replies? !

No, everyone now realises that it will indeed take off.

I'm not a scientist, nor and eingineer so I have some questions. (I haven't been able to read through all 29 pages. Please excuse me if this has already been asked or pointed out)

I read some comments that the jet "pushes" against the air. This doesn't make sense to me, I thought jets provide the majority of their thrust simply by exhaust exiting the engine? (why would a jet work in space if it had to push against something?)

If the above is true, then the forwards thrust seems to be happening only relative to the plane itself, has nothing to do with the happenings on the ground.

Now rip me apart...as usaully seems to be the case with people who don't know what they are talking about...

My vote is for the plane to take off...

I was lucky enough to be present when DW flew his RC Helicopter. well, when I say flew...

What a lovely little riddle (back online after 4 hours sleep and head cleared of snot).

Does everybody agree that the plane requires airflow to the wings to gain lift and take off?

How does it get the airflow?

It has take-off thrust, the brakes are off, but for every mm it tries to go forwards... to gain airflow to the wings... the conveyor belt brings it back at the same speed to the same position.

The wheels are irrelevant, apart from contact to the conveyor belt. If the rotation of the free-spinning wheels increases due to the take-off thrust, the conveyor belt matches this acceleration to keep the plane stationary. The plane remains stationary (it's engine/s and wheels will be going like fuck mind).

How does it get the necessary airflow to gain enough lift to take off?

It doesn't.

Lovely! Thanks DW. Now I am starting to appreciate the riddle.

There is no conveyor belt.

@Sin:

That's the flaw in your logic, the conveyor cannot "bring back" the plane because it is just pulling against freely-spinning wheels on the plane. OK there's a bit of bearing friction, but it's tiny compared to the force of the engine.

If you can't visualise this, imagine trying to pull a skateboard towards you very gently while it is sat on a treadmill. No matter how fast the treadmill goes away from you, you will still easily be able to pull the skateboard towards you.

Me troll? Never!


Not just exhaust. Jets throw LOTS of exhaust but also drive the turbines which throw lots more air backwards. They function solely by Newton's Third Law.


Nope, relative to the ground and surrounding air.


Oh shit! You agree with me as well!

For those here who thought I'd had a lobotomy before posting to the thread, try this: Get a pair of rollerblades and go to the airport. You know those people-movers they have? The horizontal "escalators"? Get on and match their speed and note that once you're stationary with resppect to the wall, you're moving as fast forwards as they are in the other direction. Note that despite the force your legs exert, there is NO wind.

If there were ropes hanging from the ceiling like vines from a jungle you could pull yourself forward and the speed of your wheels wouldn't matter, but there aren't. Now consider that the thing started speeding up as you did while trying to get to the end.

Unlike the Flash animation, neither a plane nor a rollerblader have anything solid to grab onto, unlike the car with wheels above and below (see pg 24 or thereabouts). All thrust comes from the point of contact with the ground. Ground which is moving in an opposite direction to the vehicle's motion and negating any forward progress.

The wheels on a plane won't move until thrust is applied. As soon as the thrust is applied and the wheels move, the conveyor moves to match the speed. I'm trying to figure out if the wheels will ever move beyond SIGMA x=0->1 as a result of this. But whatever speed the wheels turn, the belt moves the same speed in the opposite direction, holding the mass of the plane stationary.

Relativity:
The plane moves relative to the surface it's on.
The conveyor belt moves relative to the surface it's on.
The plane moves relative to the conveyor (twice as fast as the conveyor is moving, in the opposite direction) but as a result of a conveyor which can match the speed of the airplane in the opposite direction, remains stationary. Because there's a canceling out, the plane remains stationary relative to the ground and the air above it.

Trying to say that at a high enough speed the conveyor will generate sufficient wind is at best disingenuous and demonstrates a severe lack of understanding about how much wind is necessary to provide lift.

woof.

Sorry, but to speak to you in your own language that is total bollocks from the university of makeshitup. Imagine a jet plane hovering due to magnetics or whatever, it will still accelerate forwards even if it isn't touching the ground. How the fuck do planes accelerate once they are airborn?

It's fucking 1st year physics, there are two horizontal forces on the plane a huge fuck off forwards one from the engines and tiny backwards one from the friction in the wheel bearings. These forces do not change with the speed of the conveyor. Use Newton's 2nd law and you will see the plane accelerates forwards.


On the contrary, it demonstrates that you don't understand how quickly the conveyor would need to move to keep the plane stationary.

Pamela T&A (aka Barbed Wire) is on IT4, now all you geeks shut up and go watch it.

I am really surprised at BD & Sin getting this so wrong.. They must be trolling. tut tut you two

@BD - you contradicted yourself in your last post. You stated that the jet's thrust is relative to both the plane itself and the air around it. Thus, the plane's thrust is not relative to the speed of the conveyor belt...

If that is true, then you can essentially eliminate the conveyor belt as a variable to the equation, because it just insn't "relevant" or relative...

I'm pissed and my teorll o meter isn't working properly.

I have something else for the "flat earthers" to consider.

In their scenario at the start the plane and the conveyor are doing 0 mph. Then the plane starts up his engine and tries to move forwards, but the conveyor then starts to run the other way and halts his progress.

So the plane increases his gas, producing the same power as normal takeoff, enough for say 200mph usually, but the conveyor counteracts this and does 200mph in the other direction, so that the plane is held in the same position and fails to take off.

Um...errrrrrrrrrr. So now the plane is doing 0 mph, not going anywhere, and being held back by the conveyor doing 200mph in the other direction.

But that ain't allowed in the original question is it? The conveyor is only allowed to match the plane's speed which is 0 mph. Hmmmmmmmmmm. In theory for the flat-earthers they would say the WHEELS are doing 200mph the other way - but that was NOT what the original question stated. Conveyor is only allowed to match the plane speed.

Even if you choose to twist the original question:


and say that "speed of the plane" actually means "speed of the plane's wheels" ('cos plane is doing 0 mph in your scenario), do you honestly think that the conveyor belt moving the freewheeling wheels is gonna stop the thrust from a plane's engines?

Yes. See my post around #240, it calculates how fast the belt would need to accelerate to stop the plane moving. It is about 40g, or 800mph per second, essentially the belt needs to put the same amount of force into the spinning the wheels as the engines generate.

As if I care.

@ BD

Wrong frame of reference.

If a vehicle produces thrust by driving its wheels e.g. a car, the correct frame of reference is to relate the speed of the vehicle and the speed of the treadmill. In this case the backward moving treadmill would prevent the car from moving. Luckily, because this is how power is measured on a dyno.

If a vehicle produces thrust by acting on the atmosphere e.g. a plane, the correct frame of reference is to relate the speed of the vehicle and the speed of the atmosphere.

If you wanted to measure the thrust produced by a plane, you wouldn't see how fast the wheels could do on a dyno because they aren't driven - you'd attach the plane securely with straps and measure the pull with the engines running.

Special Bob the interesting part for me is no longer the problem - that is history - it has been solved.

The fascinating bit now is the inability of the flat-earthers to open their minds to the truth. I think their attitude is very interesting, and will reflect on many aspects of their personalities and success or failures in life etc.

Being open-minded I think is an essential quality. But that is only my wankey opinion, and like an arsehole - everyone has got one!

They simply cannot get past the idea that the wheels don't produce thrust like a car. Get that and the rest is easy.

Edit: isn't BD a pilot? He should be able to work this out.

I guess I have always struggled to respect someone that ends every posting they make with "woof" but this takes the biscuit:


What? When it is "thrusting" through the air it is considered traditional for a plane to no longer be in contact with the ground. The technical term for this I think is "flight".

But I must accept you are just winding us up now.

Miaow.

Can I change my vote?

It will take off, I see it now, just a bit late.

Yes, we forgot to tell you it was a Ryanair flight.

But the discussion is true even if you replace the plane with a car.

Exactly, as I have already said, it doesn't matter where the propulsion is coming from. The conveyor belt is not matching the speed of the wheels.

The only difference for the case of car is that it will move with half of the speed compared to the case of stationary ground.