I hope I’m not too early with this, but tomorrow, 1/30, Jamie and Adam finally test one of our pet myths, Airplane on a conveyor belt. Any bets as to the results? Will this be busted? Plausible? Will it be the definitive answer? Or do you think they’ll have to revisit this one?
And just to get it out of the way:
I HAVE HAD IT WITH THESE MOTHER EFFIN’ PLANES ON THIS MOTHER EFFIN’ TREADMILL!
Oh, they’ll have to revisit it. Nobody’s going to be happy.
I predict that if Adam or Jamie or any of their underlings attempt anything with aviation they will piss me off to no end. I predict that the experiment will fail horribly due to their inexperience with aviation and prove nothing about the experiment at hand.
I’ve seen their aviation work twice. First was the concrete glider. They couldn’t get one to fly - but they proved nothing. Their inexperience screwed them more than their building materials.
Then was the postage stamp on a heli blade stunt. They destroyed an RC Heli that was worth close to $1,000 to see if a 1lb weight on one of the rotor blades of a 5lb helicopter would do anything. WTF Mate? That one had me cringing.
But, if they get qualified people and setup the experiment with any basis in science I’ll at least be entertained.
Brewha - who is otherwise a huge fan of Mythbusters and an Aerospace Engineer by trade.
The one where they got to play with a jumbo-jet simulator to see if a complete moron with no experience could land it using verbal instructions from the control tower was pretty cool.
There was also the oen where they got to blow over a car, a bus, and a small plane with the exhaust from a large jet. I alos remember them using a mslal propeller prop plane to cut gouges into another plane. Those seemed pretty successful.
They also tried to build a one-man ducted-fan helicopter and failed at that.
To me, the conveyor belt problem is very simple:
if you put an aircraft on a conveyor belt, and the wheels had zero friction, the conveyor belt would do nothing, and the aircraft could start its engine and take off normally.
Since the wheel does have friction, the conveyor belt is going to impart a rearward force to the axle. The aircraft engine will have to use some of its power to counteract that force., so takeoff distance will be longer.
If you put a sensor on the conveyor belt that detects aircraft motion and tries to prevent it from moving forward by speeding up the belt, the following will happen:
The conveyor belt will go faster and faster until the force generated on the axle overcomes the force of the engines, and stay at that speed. Then the airplane will just sit there at full throttle and do nothing. To the airplane, the conveyor ‘feels’ like a rope strong enough to hold it back.
The conveyor belt will continue to increase in speed until it hits its physical limits, at which point the aircraft will begin to move forward but may/may not have enough excess power left to take off.
The conveyor belt will continue to increase in speed until the bearings in the wheels burn out, at which point disaster ensues.
The conveyor belt will increase in speed until IT fails. Disaster ensues.
Those are the only options. This isn’t a hard question, or a myth, or anything else. It’s a question of what will break first. On any real-world airplane, there’s never going to be enough friction imparted through the wheels to oppose the engines, because the bearings will burn out long before. And it’ll take one hell of a conveyor belt to be able to spin fast enough to burn out the wheels.
So all they are going to be able to do is either break the wheels or break the conveyor.
Now, one interesting thing they could do - put a set of aircraft wheels/axles on the conveyor with an airplane-sized weight on them, and hook the thing up to a force gauge. Then plot the rearward force on the thing for varying belt speeds. Doing that, assuming you get a reasonable curve you could plot how fast your conveyor would have to go to keep the airplane from moving.
I predict disaster and carnage, or an experiment with equipment so incapable of getting near the speeds they’d need that they learn nothing at all.
What was the result of this one, any simulated survivors?
With guidance from the tower, they both successfully landed. (The results were… poor without help of any kind.)
Remember that episode of the Simpsons where Homer caused an actual meltdown in a simulator. It was kind of like that without guidance.
Unfortunately for viewers, the simulator didn’t render realistic destruction of the plane. That would have been spectacular.
That’s a spectacular understatement.
Oh don’t forget the hair gel one. (Basically they wanted to test the myth of fighter pilot setting his head on fire because of too much hair gel in a pure oxygen atmosphere but they confused absolute pressure with gauge pressure. So they pressurized the mock up cockpit to 20 psi of pure oxygen instead of doing it correctly and pressurizing to 5 psi of pure oxygen which is what they were supposed to do.)
Sam Stone, you’re assuming in both point 2 and point 3 that the frictional force depends on the relative speed. To a good approximation, it doesn’t. If the plane can take off against the frictional force from an ordinary runway, then it can take off against the frictional force from a treadmill, too, no matter how fast the treadmill is going.
Really? The relative force applied to the axle won’t change as the speed of the wheels increases? I would have thought that for a constant coefficient of friction that it would. Isn’t it the same as the rolling resistance from the wheels in a normal landing, which is proportional to speed?
Oh, for God’s sake, let’s NOT erupt that stupid debate again here!!!
We debated it recently talking about Mythbusters
We debated it at length this month where someone called Cecil out on it
We debated it late last year when someone else tried to correct Cecil
And endless other times ad nauseum. (I’m too lazy to bother with the links)
zut does a good job of summarizing the possibilities in the recent threads with what is probably by now a cut and paste posting.
Why is it every single time we talk about this, I feel like I’m playing a game of Mornington Crescent? 
So what is the difference? Just wondering.
Regarding the postage stamp on the helicopter rotor… I would cut them some slack. I’m sure that they knew full well that this stunt wouldn’t work, just as they knew that Tesla’s earthquake machine would be a bust. Sometimes though, they just have to go through with the test for the sake of good television.
The difference is atmospheric pressure (14.7 psi at sea level).
0 psi (gauge) = 14.7 psi (absolute)
Go ahead and cut them some slack. I won’t. I’m sure they knew what would happen when they strapped the weight on the RC heli’s rotor blade - but it still pissed me off. First of all, you don’t strap a helicopter to the ground - ever. Ground resonance will destroy even a perfectly balanced helicopter. Secondly, why did they have to use an expensive, scale, RC heli?It didn’t need to be radio controlled - it never left the shop. It didn’t have to be an expensive scale version of the MD500 either - anything with rotors would have worked. I know that they were looking for entertaining TV - it just annoyed me since I am an avid RC pilot and I didn’t like seeing such a nice model get wrecked.
There’s always the best possible outcome too: The plane rolls backwards off the treadmill and crushes Jaime or Adam, and somehow manages to blow Kari’s clothes off.