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Discussion in 'Hangar Talk' started by SixPapaCharlie, Jan 15, 2019.
What do you think will happen? Then watch the video. I totally guessed wrong.
My guess, the drone may drop a skitch but it continues to hover. After all, the elevator is moving the air up along with the person and drone. Now I'll watch and see if I guess correctly...
Really? Elevator up drone will hit the floor... Elevator down, drone will hit the ceiling... wow I was right... imagine that...
I was right for the reasons the guy described at the end of the video.
If he had more than 8 floors he could have put drone on the floor, started the elevator up or down, taken off, and it would hold until the elevator stopped. Just like his bus/airplane examples.
Next video: "What happens to the bullet when a gun is fired in an elevator"
"teeheehee it went UP". /endwatchingvideo
I was going to say it should stay more or less in hover until I saw that he wasn't using something with down-looking optic stabilization. Lacking that, yeah its going into the floor or the ceiling son.
This is what I thought.
I am still not 100% sure why. Does all the air suddenly go to the floor in an elevator when it ascends? I know air is compressible and I would have expected a brief dip / bump but not that much.
If the drone is using some sort of inertial sensor to maintain hover, then you get the behavior seen in the video. It's reference point doesn't move when the elevator moves. If it used a proximity sensor then (assuming sufficient power, which this one apparently did not have-he tried full throttle and it still settled when the elevator was going up) it would follow the elevator. Which it didn't.
You pays your money and you takes your frame of reference.
open a can full of butterflies in the elevator and try again!
I think there is something at play here that most are not considering: even these simple drones, like the one he is using, have internal sensors, like sensitive barometers, or motion/inertial sensors, to help them stay stable...
Run a separate test, with a "balanced" helium balloon.
Edit, @jsstevens beat me to it!
If the drone didn't move up or down in relation to the elevator when the elevator accelerates/decelerates then there would also be no reason for us to wear seat belts in vehicles. It's a simple inertia problem.
The issue here is that elevators aren't sealed and there's acceleration. Air moves through them vertically as the elevator moves up and down. The drone will remain fixed relative to the air its in, which will move some as the elevator goes up and down. Even if it were sealed, there'd be some movement (but less) due to inertia and the acceleration.
Not quite the taking-off-on-a-treadmill "scenario" lol
See post #9, @jsstevens has the answer.
Wouldn't even matter if it was sealed. Put a ping pong ball in a sealed glass jar and shake it around. I bet it rattles. And a ping pong ball will be more affected by air movement (or lack of) than a drone will. Density and all that.
Sure, but that's a bit too simple. If the drone is powered off, sure... But shaking the ping pong ball induces far more acceleration, so of course it'll rattle around, and the ping pong ball isn't producing lift, doesn't have a computer providing stability control with 3D gyros, and won't eventually enter ground effect as the elevator climbs.
Even a drone in a sealed container is bound by Newton's Laws.
Acceleration? Aren't those drones just using sensitive accelorometers?
Except for when the elevator first starts to move and when it stops, it's traveling at a constant speed. As an unaccelerated frame, it's as if it was not moving.
If you have the drone hovering at the time the elevator first starts to move, it will need to compensate to remain at the same "altitude" within the elevator frame. After that, it's just as if it was sitting in an unmoving box.
Correct. Once acceleration ceases and inertia has done its thing, it will find homeostasis and will move with the mass containing it. A ping pong ball being rattled never gets that opportunity.
Damaged hearing, arrest, court date, jail time.
Dry cleaning. Don't forget the dry cleaning.
We are in agreement. The way I read your first post was that the drone shouldn't move up or down at all when the elevator accelerated because the air would 'encase' it like it was in the middle of a jello mold.
Gotcha... and I sure hope not. I wouldn't want to be in that elevator, at least
By the way, Welcome to POA EdFred
I dunno. Depends on the flavor of Jello.
Why why why do I keep getting sucked into these threads..???
What would the results be if the elevator was in zero gravity as in the space station.??
Why would you need an elevator in zero gravity?
Same result actually! I know it was a rectorical question.
Fair point... but think of the implications.
Because I'm lazy. Beam me up, Scotty... not make me climb.
What would happen if the drone were on a treadmill in the elevator?
We all die.
I'm not watching that. You are not my supervisor.
Forget the air... It's not having the greatest effect on things. It's all about acceleration.
If we use the elevator as our frame of reference, essentially what we're doing when we start down is we're turning gravity down, to maybe 0.8 or 0.9 G. Since the drone is pushing enough air down to counteract exactly 1 G before the elevator starts moving, and now we're subjecting it to less than 1 G, it goes up. Same is true if the elevator is going up, and then stops at its destination.
The opposite is true when we stop going down, or start going up - We're effectively turning gravity up a little bit, to maybe 1.1 or 1.2 G. Since the drone was pushing enough air down to counteract only 1 G and now it's "heavier" it will go down.
Now, let's say you're riding an elevator up the Burj Khalifa, all the way from the ground floor to the 163rd floor, and that it's a normal-speed elevator that just accelerates for a couple seconds and then goes at a steady speed until decelerating for a couple of seconds. If you wait to start the drone until after the elevator is finished accelerating, you'll have a significant amount of time where the drone will fly completely normally, as if you're just in a small room rather than an elevator. It won't act different until the elevator starts to decelerate.
This all has to do with Density Altitude. Elevator goes up, air is thinner...less lift, drone goes down.
Elevator down, thicker air, drone goes up.
All I know is that it’s more fun to fly quad copters outside the elevator than inside.
We are not subjecting it to less than 1 G unless it is touching the elevator and the elevator moves.
This guy does a video where he puts a hair dryer on its back, on a scale and turns it on so we can see the weight of the hair dryer with the opposite force of the air flow.
He asks now if I put a ping pong ball on top of the air flow will the scale register the weight of the ping pong ball. I thought for sure it would.
It didn't though. Now if the dryer was off and you put the ball directly on the dryer obviously it would register on the scale.
I forget where I was going with this but I don't think you are changing the G force by moving the elevator unless the drone is resting on the elevator floor.
Oh yeah, the drone is not pushing itself off the floor, it is just climbing the air molecules.
This kid only plays with toys and has no basic understanding of the laws of nature. Maybe if he didn't flunk physics 101, he could have saved his toy.
Next video request: airplane on a conveyor belt runway that's matching its takeoff speed.
To stay fixed in relation to the elevator, the drone has to accelerate (or decelerate) at some factor other than 1G. The drone stays fixed in space (relative to the earth, to be clear) and the elevator accelerates around it. So you are correct in that we are not subjecting the drone to greater than 1G and that's why, from the frame of reference of the elevator (which is accelerating at 1.1G or some such) it falls to the floor.
The drone is fixed to a different frame of reference than the elevator.
I wanted to see him launch the drone while the elevator was already moving, was disappointed.