Quad flying in a sealed box

[Toolman]

See this Youtube Vid which shows a Quad copter flying inside a sealed container,

When the quad lifts up the weight goes down to that of the container!

Who feels clever this morning & can explain this?

Tim.

[james_2k]

what else did you expect?

[trillian]

Hmmmm, not sure what's going on there. 'Common sense' would be no change in the weight because the quad is still inside the box whether it is supported by a column of air or something solid.

They did a bigger version of this experiment on Mythbusters with birds flying inside a room and an RC helicopter (not at the same time! )

[james_2k]

well any air deflected down is getting pushed around back to the top of the box anyway. so i imagine the net result is 0.

[Mark_T]

People expect the mass of air being pushed down to equal weight of heli so say scales should not change.

Heli doesn't just push itself up by blowing air mass down, it pulls itself up due to pressure difference over blades.

So force of air hitting box does not equal weight of heli.

[p4ddy]

People expect the mass of air being pushed down to equal weight of heli so say scales should not change.

fork me!! The blades would have to be big to do that wouldn't they?? That quad couldn't blow a pube from a bed sheet

[pgkevet]

People expect the mass of air being pushed down to equal weight of heli so say scales should not change.

Heli doesn't just push itself up by blowing air mass down, it pulls itself up due to pressure difference over blades.

So force of air hitting box does not equal weight of heli.

I expect the quad to be exerting a downward force equal to it's weight in the hover: whether that is due to pressure differentials, air blown down etc doesn't matter.. to lift itself up there has to be a force down - so something is screwy here such as a servo in the scales lifting from inside?

[David Drew]

Ok. So we have all seen when astronauts try out being weightless by being in an aircraft that is diving.

Just say the aircraft is 100 tons and the passengers 5 tons. When it takes off it is 105 tons. When the passengers are floating does the total weight now reduce to 100 tons?

[trillian]

Ok. So we have all seen when astronauts try out being weightless by being in an aircraft that is diving.

Just say the aircraft is 100 tons and the passengers 5 tons. When it takes off it is 105 tons. When the passengers are floating does the total weight now reduce to 100 tons?

That's fundamentally different because the plane is flying in an arc where it is essentially dropping away from the astronauts inside. A bit like if you were in a lift at the top floor of a building and the lift broke and started a freefall, the floor may well pull away from you for a moment.

With a aircraft or a bird flying inside a container, the weight does not change. All that has changed is that the pressure of the air has been redistributed to support the object. From a weight standpoint it makes no difference, so there's something wrong with this Youtube container thing. I would expect the scale to move at first simply because the weight inside the container is shifting around, but if the quad would stay put long enough I would expect the scale to get back to where it was before (the exception being that if the weight of the quad is way over to one side or the other it could throw off the scale's reading because the platform on the scale may sense unevenly, like if you put a weight at the edge rather than in the middle.)

[Red3]

That's fundamentally different because the plane is flying in an arc where it is essentially dropping away from the astronauts inside. A bit like if you were in a lift at the top floor of a building and the lift broke and started a freefall, the floor may well pull away from you for a moment.

parabolic flight hope this helps

[gazmk2]

Tell you what, let me grab a container and I'll try the same thing with my little hubsan x4!

[Toolman]

Well I have been scratching my head & I have watched it 3 times.

The thing I notice is that the box is wide but not very high,
Thinking about the down wash (imagine the air is made up of particles) they will hit the bottom of the box in theory with an equal force to the weight if the quad. But then bounce upward & then hit the top of the box which is very low. Some of the momentum will be imparted downwards, but some will be left to impact the top of the box.

If you are going to try this experiment, try it with a box that is bigger (taller) relative to the size of the quad if you can?

Tim.

[gazmk2]

Here is your answer!

https://www.youtube.com/watch?v=dCY9...Y6JX924n7UfOcw

[Toolman]

Nice, that answers that then!

I still wonder what was going on in that other video though.
One difference here is that the first Vid was a plastic box with flexible (springy) sidewalls, while a metal container isn't.

Tim.

[PeteStewardson]

Here is your answer!

https://www.youtube.com/watch?v=dCY9...Y6JX924n7UfOcw

I don't believe anything on that youtube feed after noticing the next one was showing a Trex 150 flying. Now I know they don't fly and just crash and destroy themselves so I can't see how any of the other videos are factual either