Myth busters

[toprob]

Apparently this Discovery Channel show finally got around to busting the aeroplane-on-a-conveyer-belt myth. From the posted comments, though it seems they didn't manage to convince a lot of folk, so this may go on for a while...
Mythbuster Results

[victor_alpha_charlie]

I read the comments and thought they made sense, but when you think about it the thrust from the engines is going to the air, and the wings generate lift from air, so the conveyor belt would have no effect whatsoever. Jamie and Adam did get it right

[HardCorePawn]

At first glance, it would appear that like a human on a treadmill, the aircraft should achieve some sort of 'equilibrium' and therefore would be stationary relative to the ground/air and thus have no airflow over the wings to generate lift.

However, what is causing people problems is they are used to the wheels of a car (or legs on a human) being used as the driving force. That is, the parts that have contact with the treadmill are what drives the object forward.

However, as far as a aircraft is concerned, the wheels are essentially free spinning and are not the driving force. It is the prop (or jet) that is pushing it through the air. So what would happen is that the wheels would just spin faster than the treadmill, while the aircraft accelerated through the air to its takeoff airspeed.

Another way to think of it is that a treadmill would not prevent an aircraft from moving forward... (assuming the wheel bearings had low enough friction so that the aircraft could accelerate past the treadmill speed).

To prove this, they should put a big jet engine on a car, and put the car on a treadmill... it will move forward as well.

Myth busted as far as I am concerned.

[Charl]

Betcha this wouldn't work with my front-wheel-drive Elerka 3 Convertiplane.
It has to get to 38 mph before you can start flapping the wings...

[toprob]

QUOTE (Charl @ Feb 1 2008, 11:32 AM) <{POST_SNAPBACK}>

Betcha this wouldn't work with my front-wheel-drive Elerka 3 Convertiplane.
It has to get to 38 mph before you can start flapping the wings...

Which helps prove the theory. The Convertiplane is so named because it converts to a plane -- as you said, around 38mph. Until then it is a normal kid's trike, and we are not talking about trikes...

[Charl]

Yeah, didja know that if you wear #5 red-coloured braces and long flannels, and you reach round behind your head, with your right hand, so you get a good grip on both of 'em, just above where they cross over...you can PICK YOURSELF UP!

[toprob]

QUOTE (HardCorePawn @ Feb 1 2008, 09:36 AM) <{POST_SNAPBACK}>

To prove this, they should put a big jet engine on a car, and put the car on a treadmill... it will move forward as well.

Myth busted as far as I am concerned.

Simpler than that - there is something you can actually do without upsetting your normal daily routine:
The next time you go to the gym, hop on the treadmill and dial it right up so that you are running for dear life. Now -- carefully! -- reach into your pocket and pull out a toy plane. Wind up the rubber band as tight as you can. Hold it up -- as still as you can -- and let it go.
Will it fly?

[Charl]

QUOTE (toprob @ Feb 1 2008, 11:56 AM) <{POST_SNAPBACK}>

Simpler than that - there is something you can actually do without upsetting your normal daily routine:
The next time you go to the gym, hop on the treadmill and dial it right up so that you are running for dear life. Now -- carefully! -- reach into your pocket and pull out a toy plane. Wind up the rubber band as tight as you can. Hold it up -- as still as you can -- and let it go.
Will it fly?

Know what? Our home treadmill is fitted with a large cooling fan, so you can actually feel as if you are going somewhere into the cooling breeze, instead of going absolutely nowhere and bulding up a sweat.
This little aeroplane, provided you were smart enough to point it frontward, will fly along just next to your ear.
(Note: I love these daffy science things, but I am going to force myself to stop this, now. Sorry Robin)

[toprob]

QUOTE (Charl @ Feb 1 2008, 11:52 AM) <{POST_SNAPBACK}>

Yeah, didja know that if you wear #5 red-coloured braces and long flannels, and you reach round behind your head, with your right hand, so you get a good grip on both of 'em, just above where they cross over...you can PICK YOURSELF UP!

Funnily enough I was already dressed that way this morning.

[HardCorePawn]

I actually just watched the episode (gotta love the internet ) and I'm struggling to understand why people are still arguing... they explained it pretty well

They had a toy car on the treadmill... running at the same speed so it was staying in position relative to the ground... then they cut the power to the car and sure enough it went backwards into the backstop...

Adam then pointed out that if he now used his hand to act like the propeller force there was almost no resistance as the wheels were just free spinning...

[deaneb]

QUOTE (HardCorePawn @ Feb 1 2008, 09:36 AM) <{POST_SNAPBACK}>

At first glance, it would appear that like a human on a treadmill, the aircraft should achieve some sort of 'equilibrium' and therefore would be stationary relative to the ground/air and thus have no airflow over the wings to generate lift.

However, what is causing people problems is they are used to the wheels of a car (or legs on a human) being used as the driving force. That is, the parts that have contact with the treadmill are what drives the object forward.

However, as far as a aircraft is concerned, the wheels are essentially free spinning and are not the driving force. It is the prop (or jet) that is pushing it through the air. So what would happen is that the wheels would just spin faster than the treadmill, while the aircraft accelerated through the air to its takeoff airspeed.

Another way to think of it is that a treadmill would not prevent an aircraft from moving forward... (assuming the wheel bearings had low enough friction so that the aircraft could accelerate past the treadmill speed).

To prove this, they should put a big jet engine on a car, and put the car on a treadmill... it will move forward as well.

Myth busted as far as I am concerned.

Totally agree HC Pawn - myth busted. I doubt the wheel bearing friction would be very high. Lets assume a light aircraft like a Cessna 152 - a single person can push or pull one of those and I'd hazard a guess and say they could propably hold onto the front of the plane and keep it in place whilst it was sitting on the treadmill while running.

Of course the biggest problem with taking off - you would need a treadmill / conveyer as long as the take off length required for the aircraft !!

Deane

[kiwibarguy]

Slightly off the subject.

The other week while fiddling around with fsx i entered in a very strong headwind. My cessna started to quickly roll back in reverse due to the wind's force. I put the throttle on full and she started to stop to meet the headwind. Then she began to lift off and hover above the ground in a stationary position.

Can this be done? i imagine you would have to have a straight head on wind and a very experienced pilot to maintain the balance.

i got up to 1000feet and then turned to go with the wind. the force of the wind and the drop let her build up enough speed to fly.

Alot of fun.

[deaneb]

I have read anecdotes from the old topdressing days where some tiger moths were see to be moving backward and in at least one case, the pilot maged to set down in a field while still going backward slowly. Luckily he had managed to attract a small crowd, some of whom held onto the plane so it did not come to grief !!

Deane

[greaneyr]

QUOTE (kiwibarguy @ Feb 1 2008, 04:32 PM) <{POST_SNAPBACK}>

Slightly off the subject.

The other week while fiddling around with fsx i entered in a very strong headwind. My cessna started to quickly roll back in reverse due to the wind's force. I put the throttle on full and she started to stop to meet the headwind. Then she began to lift off and hover above the ground in a stationary position.

Can this be done? i imagine you would have to have a straight head on wind and a very experienced pilot to maintain the balance.

i got up to 1000feet and then turned to go with the wind. the force of the wind and the drop let her build up enough speed to fly.

Alot of fun.

Yup it can, because of the same phenomenon as the mythbusters experiment. Forget about the ground. What's the airspeed doing? 60 knots of head wind will always be 60 knots of head wind, regardless of whether you experience it on the ground or in the air. I've flown some interesting final approaches before like that. You have to sit on an insane amount of throttle just to make sure you're actually moving towards the runway. You can't land it by stalling either. I find it's just easier to hover directly to your tie-down location. The other one I love is getting a 737 up to 80+ knots of downwind on the ground, then turning a hard 90 degree turn and watching the thing drift sideways.

Totally unrealistic but oh so much fun.

[victor_alpha_charlie]

I did that in a 707 at Seattle. Set 200 knot winds and just pulled up..
I mustve had an awesome GS downwind..

[HardCorePawn]

QUOTE (kiwibarguy @ Feb 1 2008, 04:32 PM) <{POST_SNAPBACK}>

Slightly off the subject.

The other week while fiddling around with fsx i entered in a very strong headwind. My cessna started to quickly roll back in reverse due to the wind's force. I put the throttle on full and she started to stop to meet the headwind. Then she began to lift off and hover above the ground in a stationary position.

Can this be done? i imagine you would have to have a straight head on wind and a very experienced pilot to maintain the balance.

I saw a piper cub out at Ardmore the other day when the wind was about 25kts down the runway... it looked almost stationary! Even in the mighty 152 climbing out at 70kts, our groundspeed was ridiculously slow... i could see the cars on the road below were just leaving us behind like we were almost standing still...

One of the grey beards was talking the other day about watching tiger moths do circuits by taking off in strong headwinds, then closing the throttle and flying backwards and then cranking the throttle up again to make the approach!

This is why you tie light aircraft down... although theoretically you could get a heavy off the ground in the same fashion if the wind was blowing hard enough... but I dont think even Wellywood blows that hard!

[chickenman]

QUOTE (HardCorePawn @ Feb 1 2008, 12:29 PM) <{POST_SNAPBACK}>

I actually just watched the episode (gotta love the internet ) and I'm struggling to understand why people are still arguing... they explained it pretty well

They had a toy car on the treadmill... running at the same speed so it was staying in position relative to the ground... then they cut the power to the car and sure enough it went backwards into the backstop...

Adam then pointed out that if he now used his hand to act like the propeller force there was almost no resistance as the wheels were just free spinning...

Just watched it as well (eztv.it)

Simple explanation done well. The conveyor belt was a long tarp towed by a ute & the plane was an ultralight but the principles worked perfectly. The ultralight took off in the same length of run - despite the tarp running underneath it. Doesn't matter what's on the ground - it's all to do with the thrust as there is no resistance grom the ground.

Good watching,

On a completely different matter - damn kari byron is hot!