bloody hell, how are you guys surviving this? It is DAMN cold! ... and I missed the worst of it. I don't want to go outside and try my car... one cold vehicle is enough... and I'm loathe to find out how my roomie has treated the place in my absence.

blech. At least it's February now.



actually, I lied... it's not bad outside right now. heck, I didn't mind shovelling for that matter. ... at my parents' place. I don't wanna go back to my place just yet.

Ahhh... thank-you Paras, I can finally see a fallacy in my previous statement! You're right when you say since the thrust isn't coming from the wheels that the forward velocity of the plane won't be affected by the wheels on the treadmill. My confusion though lies in what I thought they were trying to argue:

that a plane can take off without moving forward. I thought the whole reason for putting it on a treadmill was to prove that the forward movement of a plane is not necessary for flight. I thought they were trying to get the plane to take off from a stationary ground position. I think my initial misunderstanding came from my inability to decipher what they were trying to prove. That's why in my earlier post when I watched the video I didn't think the test proved their point so I said: "why does the plane drive forward for quite some distance before it takes off? That's not impressive at all. It honestly doesn't look like they proved shit in that video." But now I think I understand what the question was SUPPOSED to be: will a conveyer belt under the wheels of a plane counteract its forward acceleration? And NOT: will counteracting a plane's forward movement not affect its ability to fly?

I guess sometimes to understand the answer you've got to understand the question.

their thrust is useless because it's being counteracted by a treadmill

Turbines (as al stated) aren't for air flow, they're for thrust, and the air flow comes from the thrust pushing the plane forward through the air (initially on a runway). So if it's a plane with turbines and the turbines aren't propelling it forward (ie: their thrust is useless because it's being counteracted by a treadmill) then what's causing the air flow that's making the pressure differential necessary for lift?

That's my question.

You're totally out to lunch :)

It doesn't matter if it's a prop plane or turbines, the thrust is independent of the wheels which makes the conveyor belt inconsequential. What they proved on the show is that a plane will take off from a conveyor belt moving the same speed as the plane. If the plane was driven by the wheels then of course it wouldn't take off, but the force pushing the plane forward and forcing the air over the wings is completely independent of the wheels.

I don't think they were trying to prove anything specific about the necessity of runways, just simply the statement that "a plane cannot take off from a conveyor belt running in the opposite direction".

Or maybe I'm misunderstanding your question Tay?

oops, I keep saying turbines when I mean to say "propeller". In that last post I used the word turbine once instead of propeller. But since Al made a good point of explaining the distinction between the two, this only furthers my argument that they didn't "prove" anything on the show:

The plane they tested was an ultra-light which utilized a propellor to create air flow. But most modern commercial jets use turbines, and turbines (as Al previously mentioned) don't serve the same purpose; they are intended to create THRUST. It is that thrust which makes a plane accelerate down a runway, and it is the speed of the plane moving down the runway which creates the air movement which provides the LIFT. So if you used a normal commercial plane, there's no fucking way it will take off from a stationary position.

Am I making any sense? This just seems so obvious and yet the myth busters show seems to be making a ridiculous assertion based on a ridiculous test that ultimately proves nothing.

Al, am I getting everything right here? Please tell me if I'm totally out to lunch on something.

see, I understand exactly everything you guys are saying, but I still don't think they proved anything with their test. I understand the bernoulli effect and why/how it works, (it creates a pressure differential on the two sides of the wings which creates lift) but it seems to me like they "myth" they're tring to "bust" is that driving down a runway doesn't cause (in combination with the turbines) the air flow necessary to lift the plane. OF COURSE DRIVING FAST DOWN A RUNWAY CAUSES LIFT ON THE WINGS, EVEN IF THE PROPELLER ISN'T GOING. Why do you think F1 cars have those big fins? Those fins are actually just upside-down plane wings which PUSH the car onto the ground so that it can make very sharp turns without flipping over (the cars themselves are very light), and I'm pretty sure F1 cars don't have propellors... only wheels. So here's my problem with the whole thing:

What exactly is the myth? If you have air flowing around the wings of a plane it will fly. That's pretty much common knowledge to anyone who took junior high science classes. I don't understand what they're trying to prove by putting it on a conveyer belt. It seems to me they're trying to prove that runways don't actually serve any purpose to helping a plane take off when in my mind they clearly do. It just seems really fucking retarded. Am I still missing something?

Jamie said it right at the end... the motor drives the propeller not the wheels. So the plane may take off at 25 mph air speed. Putting a conveyor belt under it at -25 mph means that the planes wheels are turning at a rpm equivalent to 50 mph, but the plane still moves at 25 mph air speed to take off. The conveyor belt does nothing but make the wheels turn faster under the plane. That is why runways are necessary, the distance it takes the plane to reach that 25 mph stays the same with or without the conveyor belt.

Sorry for the lack of Mec input on this discussion, I was bedridden with flu/strep throat for the last 3 days. Anyways to start:

A turbine forces thrust or a force to propel a plane forward not force air over a wing... well they're related in a way, the more thrust you have the faster your plane goes, the faster your plane goes the more air is forced over the plane of the wings. Enough force and you get lift and suprise, suprise you fly.

So a runway is used so a plane's turbine can build up enough thrust so you can get the force required to propel a plane at enough sped to get lift. VTOL aircraft can actually land VTOL but taking off is another matter. Due to their ducting engines and a lack of turbine build up, (if you are taking off straight up) this severly drains the fuel as they are forced to provide all the lift, none are provided by the wings. So this is why we don't have all VTOL planes, not very fuel efficent and very mechanically dificult to maintain.

Now as for the long build up before flight well think of it this way, Lets say you're in my car and say I turn to you and say I'm going to make this thing go to 220 km/h. If I just floor it and we get to 220 in 45 seconds you'll feel a ton of gees. But if I wuss out and get there in 5 minutes you won't feel jack, you'll see a build up of speed but you won't notice the acceleration. Same speed but different level of gees for the passenger. That's why commercial planes take so long to build up speed to take-off, I mean they could throw on these monster engines which can build up the required thrust and speed in say a 100 meters, but I don't think anyone would enjoy the ride.

As for the point of the myth I think they are trying to say the plane won't build up the necessary speed to get lift. The conveyor built idea is like you on a thread mill, you maybe running at 15 km/h but the threadmill is going in the opposite direction at 15 km/h therfore you aren't moving anywhere. I guess this proves the idea wrong. I'm wondering if the thrust or in this case pulling force of the propeller was strong enough to build the lift even though the observed speed should of been zero. Sounds like too much math and engineering, probally need to do a free body diagram too, I'll assume they are correct