Yes, of course the plane moves relative to the air, because the wheels aren’t providing the force to move the plane forward, the engine is.
Are you asking whether a huge windstorm can pick up a small plane and blow it around? Because of course it can. It doesn’t even need to be precisely angled to induce laminar airflow over the airfoils. It just needs to be a huge windstorm. There’s no mystery here: I’ve seen smaller windstorms pick up trash barrels, and they’re about as aerodynamic as a… trash barrel.
I think the notion with a conveyor belt is you have the conveyor belt moving under the plane towards the back (like a jogger on a treadmill). You are not pulling the plane forward but rather (in theory) allowing the plane to take off without a long runway. Instead of moving down a long runway the runway moves under your wheels so the plane stays in place. If it worked this would save a lot of space (although I guess you’d still need a long runway for landing).
Well, it doesn’t work. Regardless of what the ground is doing under the wheels the plane will move forward same as it always does.
You can see this tested by the Mythbusters. They pull a very long tarp out from under a plane trying to take off. The plane moves forward same as it always does and takes the same distance to take off as it always does despite the ground moving backwards under it (i.e. the plane is not held in place but moves forward).
Yes, all that happens on the treadmill is that the wheels free spin twice as fast. That has no effect on the movement of the plane relative to the air or the non-treadmill-ground.
The purpose of the airplane’s wheels is to reduce friction between the airplane and the ground. This can also be accomplished by skis or pontoons. As long as the friction between the airplane and the ground is minimal it doesn’t matter which way the ground is moving.
It’s not so much that the nose is being lifted by the wind, but the wind blowing over the horizontal stabilizer is pushing it downward, which makes the nose come up. And the engines have already been removed so the plane would be a bit tail-heavy to begin with.
But the basic point stands; a stationary plane in a strong enough wind behaves like a plane rolling down a runway on a calm day.
Plus the planes are loaded with one or two guys who are being paid big bux* to get their eyeballs pushed back into their heads for a few seconds, not a granny who just wants to get to Chicago to see her grandkids.
*I’d bet a lot of them would do it for free.
Remember, to get a swallow to carry a load, you have to have a decent airspeed over a laden swallow’s wings.
Sorry to bring this question up, but I don’t get this. If the conveyor belt moves 1 ft, and say the plane wheel’s circumference is 1 ft, it makes 1 rotation, how does the plane ever move forward? I realize that the wheels are not propelling the plane forward, but I can’t imagine how they actually move forward at all even when all the thrust is coming from the jets.
The wheels would make one rotation if the plane was stationary (relative to the ground). But as the plane gets propelled by the jets, the wheels will rotate faster. Imagine that instead of a propelled, the plane is being move by someone pulling it on a rope.
We already have this in a much more efficient form
Steam Catapult
I dont think your average 747 has being catapulted built into it’s stress design though
Do you buy the notion the ground is not moving? Thus if the wheels don’t turn the speed is the same. Replace the wheels with skis and throw some snow on the ground. Same thing? Yet the plane can take off.
About the only way I can see is if the plane on the conveyor is moving backwards at take off speed before the plane attempts to take off. Is there enough push in the engines to stop the plane from moving backwards (yes) plus accelerate forward. Most likely since once the plane stops, it is as if the conveyor belt is not there.
It is not something most passengers would enjoy.
Not sure something as big as a 747 could be launched by catapult anyway. The catapult strength needed to move something that big and making something that big strong enough to handle it (which would make it even heavier)…I doubt it can be done. Or maybe it could be done in principle but not something you would ever want to do.
Moved to Comments on Cecil’s Columns.
Colibri
General Questions Moderator
Flying motionless or backward with respect to the ground due to a significant headwind, the RC model would react to control inputs in just the same way as it would when flying forward. It would be maintaining a normal airspeed and there would be no important control differences from flight in no-wind conditions.
I’ve heard this explained a lot in many different ways and I choose to accept it because, well, I guess it’s the consensus, but I still can’t imagine it.
I went so far as to put a quality ball-bearing on a rod and place it on my belt sander. If I hold it in place, the bearing is spinning more-or-less the same speed as the belt. I can easily move the rod forward and backward while the belt is rotating with really no more discernable effort than if the belt is stationary.
But of course, in my experiment the linear speed of the belt is not keeping up with the rotational speed of the bearing if I’m moving it’s position. I want to think that if I had a device that could do this, I would not be able to move the bearing forward or backward along the spinning belt due to an infinite force that is summoned when you have this magical device where the two linear speeds of the bearing and belt are always equal. In reality, there would be some, even if near-infinitesimally small, lag so this couldn’t ever be tested so I guess I remain somewhat skeptical the plane would ever move forward with respect to ground. But maybe someone could just show the math somehow.
In WWII, I think they had aircraft take off from carriers without using the catapults. With the carrier going 30Kt into a 30Kt wind, you couldn’t stand up on the flight deck.
especially now that Chris Farley is dead. “Remember that time you took off? That was awesome”.
It might help to realize that the frictional force doesn’t depend on the speed, so magically speeding up the belt won’t do any more than leaving it at its original speed.
The friction does depend on the acceleration, albeit only extremely weakly. So it’s theoretically possible for the belt to have a high enough acceleration to hold the plane in place. But in this case, the plane still takes off, because a belt going at that kind of ludicrous acceleration would very quickly (in a matter of less than a second) reach ludicrous speeds, speeds high enough that the belt would act like the afore-mentioned giant fan and move enough air to lift the plane off.
Also, the question states that the treadmill keeps up with the (negative) speed of the plane, not the rotational speed of the wheels. Cecil even addressed that at the end, right? It’s a paradox to have the treadmill keep up with the rotational speed of the wheels – you end up with A=A+5.
I predict these last two posts will answer the question completely and this will not be a multi-page thread rehashing the same points over and over again. Now, is 0.999… really equal to 1?
Cecil never considered a plane on skies.