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Helicopter in a box....

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Helicopter in a box....

Old 3rd Dec 2004, 22:22
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The box will weigh the same as if it were full of air. The balloon displaces a similar mass of air as itself and has no effect on weight.
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Old 3rd Dec 2004, 22:23
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Do some work Barotrauma!

Fay
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Old 3rd Dec 2004, 23:21
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Just worked out the boat and rock one. Those in small boats should not throw rocks - the CoG will go up and the boat will capsize
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Old 4th Dec 2004, 04:55
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if a boodle beetle battles on a bottle with a noodle
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Old 4th Dec 2004, 08:47
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How would you plan the flight???
I wouldn't. It's pointless. The dispatcher will call with a change of destination anyway, so why bother to plan. I flew on a contract for a drilling company for about 2 years, and when I started I would call up each day and find out where I was going so I could plan fuel stops, etc. I never, not even once, flew what I had planned. The only thing to do is load on all the fuel you can, (it will fly over gross, but not without fuel) and head south, and wait for the radio call.
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Old 4th Dec 2004, 08:57
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Are we talking 'MASS' or 'WEIGHT'??

The mass of the total body will never change whether it is in flight or in space, but the weight will??

In this case, the 'weight' (because of 'G') of the helo displaces that same amount of air downward and exerts a force on the scales. Hence no 'weight' change in readout.

If the air could escape thru cracks in the box, then the 'weight' would indicate less.

The mass never changes.
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Old 4th Dec 2004, 10:36
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Well this one got me thinking, in the first few minutes I managed to convince myself that the scales would measure the weight of the box only and then I convinced myself that they would measure both the box and helicopter, then I wasn’t sure Ahhhhhh!!!

However several hours later, I think this explanation answers it for me: -

As TC stated, the downwash will strike the bottom of the box and exert a force on it. However, that is an oversimplification because the air will now dissipate sideways, strike the side of the box deflect upwards hit the top of the box and then get sucked back down through the rotor system. At this point there will be a reduction in pressure on the ‘inside’ of the top of the box and an increase in pressure on the base of the box, hence there will be a greater force exerted by the air on the bottom of the box than on the top of the box. The resultant of these two forces will be a force downward (onto the scales) equal to the weight of the helicopter.

The scales will show the weight of the helicopter and the box.

That’s my theory for what it is worth.

Cheers

TeeS
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Old 5th Dec 2004, 05:29
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When the helicopter is not running and sitting on the floor of the box, all the force, or potential energy, is on the floor of the box and being read by the scales.

When the aircraft is hovered the air is being forced down to the floor then out to the walls of the box and up to the roof to be recirculated. It would make sense to me to say that now some of this force, or energy, is being aplied sideways to the walls of the box and therefore would not bear pressure down on the scales thus the scales would read lighter in the hover.

Now though, what effect, if any, would changing the size of the box so that now non of the sideways air movement ever reaches the sides of the box?

Now my head hurts.
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Old 5th Dec 2004, 19:25
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............and what if the box were tall enough to allow the helicopter to hover OGE
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Old 5th Dec 2004, 20:37
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Or transitions into forward flight?

I think the scales won't weigh the same figure in either case as some of the rotor thrust will cause vortices to form, which won't bear down on the scales.

Anyone got a big box? Now don't be rude.....
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Old 5th Dec 2004, 23:36
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You guys crack me up - you really do.

I'm going to make a statement: the box is airtight.

So it doesn't matter whether the box has a helicopter, a balloon or a duck in it, nor does it matter whether whatever is in the box is being supported by skids, rotors, heated air or flapping wings.

Whatever mass you put into the box before you sealed it will remain there. The mass of the air will remain unchanged whether it is still or being swirled or heated. Since weight is a function of gravity acting on mass, if the mass stays the same, the weight stays the same.

Actually, I crack myself up - I can't believe I'm actually getting concerned about this! Time for a nice hot cuppa...
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Old 5th Dec 2004, 23:54
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Mmmm;
The box is airtight.
The box is cardboard.

From the start point of the experiment, a vacuum will be created due to the engine and pilot consuming the fixed volume of air.

This vacuum will increase in strength ultimately causing the box to collapse in on itself, resulting in the weight of the wreckage + box + pilot being the same as at the start of the experiment.

However, assuming the integrity of said box has not been compromised, ie is still airtight, the resultant carbon dioxide that was produced, being heavier than the air it has replaced, would cause the resultant wreckage on the scales to weigh more than at the start.


Just a thought.
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Old 6th Dec 2004, 00:07
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Sid, You should know better than that, certainly, a vacuum will be created due to the enignes intake however this will be offset due to the pressure of the exhaust gases. Like Flingwing said, the mass will remain unchanged. The box will not collapse. The first law of thermodynamics, Energy cannot be created nor destroyed. This does not answer the original question however it may point you in the right direction.
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Old 6th Dec 2004, 00:11
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Sounds like a recipe for vortex ring and carbon monoxide poisoning to me.


You actually dont need the box for this scenario.

Does the world weigh the same when my Enstrom takes off????
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Old 6th Dec 2004, 00:50
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Sir HC,

The reason my vacuum is caused, is by the burning of the air by the engines and by the pilots lungs, (albeit minutely compared to the engines consumption).

Nothing to do with the complicated dynamic properties associated with a jet engine, but simply the conversion of fossil fuels to carbon dioxide.

Much the same as the old candle in an up turned jam jar.
As the flame burns the air, the candle gradually goes out, as there is no further air to burn.
The smoke produced follows the draught created by the carbon dioxide falling to the lowest point.
Should the jar be sat upon a dish with water in, the effects of the vacuum can be seen by the rise in water level within the jar.

OK, so in reality the engines will flame out and the pilot will die before any reasonable vacuum is produced, but the conversion of the air to a heavier than air gas will cause the scales to show, if sensitive enough, an increase in the weight of the total contents of the box.


edited to avoid the use of atomic weights

Last edited by SilsoeSid; 6th Dec 2004 at 01:09.
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Old 6th Dec 2004, 01:47
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Einstein would like a word with you

Neither mass nor energy can be created or destroyed. They can be exchanged for one another, but this typically happens (on a macroscopic scale) inside a nuclear bomb and not a helicopter. The helicopter and human expel the same amount of gas over time that they ingest. It might be a different gas, but weight is a function of mass and not volume. The energy comes from chemical reactions and not breakdowns on the atomic level

The scale only cares about the direct force that it has to apply to keep the box from accelerating downward. In this case, the force depends on the weight of the box and whether or not the helicopter (and thus the system, in physical terms) is accelerating up or down.

A more abstract explanation of the experiment can be found here.
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Old 6th Dec 2004, 02:43
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csmorris,

In your experiment with a rock in a boat then thrown into the pool, the water level in the pool will go down. This is because the boat had displaced the water's volume equivalent to the weight of the rock, which is more volume than the dense rock will displace when tossed out of the boat. When the rock is tossed into the water, the boat floated up to stop displacing the water weight of the rock, and the rock displaced less water when it sank to the bottom. In fact the pool water went down by an amount equal to the difference between the specific gravity of the rock and the SG of the water times the weight of the rock.


Your points about the box are right on! Guys, regarding the box experiment, remember that the helo flies by exchanging momentum with the earth system. Inside the box, the rotor allows the helo to fly, but the entire sealed box/helo system is constant weight, forever. Even as the engine and pilot consume the oxygen, it is mearly recombined in the H2O and CO2 expelled in the exhaust. The weight of the entire system stays constant (conservation of energy and mass.)

A great science show 20 years ago performed this exact experiment. "The Ring of Truth" with Philip Morrison weighed the box and then ran little cars, rockets and such inside the box, then re-weighed it, to the gram. Here is a reference to the video tape, which some libraries might have (there are 13 copies in Connecticut, for example):
Ring of Truth, Morrison, Program 2: Change
Summary: Using everyday examples that are dramatic, exciting & entertaining, Philip Morrison devotes an entire program to this subject, demonstrating in simple experiments that it is true that matter is equivalent to energy. 060 Min. VIDEO 1987 Subject: PHYSICS, ASTRONOMY Series: RING OF TRUTH, THE

Last edited by NickLappos; 6th Dec 2004 at 03:06.
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Old 6th Dec 2004, 04:18
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Hey all, lets keep it simple. Please remember the question, and I quote:

"Picture this - A Bell 206 in a huge cardboard box. The box, with the aircraft inside it is sitting on a massive pair of bathroom scales which show the weight of the helicopter plus that of the box. Now, the pilot is already inside the aircraft inside the box and lifts into a hover.

What do the bathroom scales show now??? "

I am not going back on the threads, but someone did mention earlier about flight planning off shore. I agree with you. Nothing is confirmed until you land back home.

Fay Slag: You have brought up a topic, that I have heard of, and been asked many times before. On one flight off shore we had a fly in the flight deck, and started an hours discussion on exactly the same topic. Everything has mass, no matter dimension. What you are asking in simple terms is weight. Now, in a sealed box, for a simple explanation, should be the same as mass. Mass has many factors affecting, weight fewer. If anybody can remember when we start our flight training, Newtons law: For every action, there will be an equal and opposite reaction. The aircrafts weight is displacing air to counter its weight to overcome gravity. Mass is involved, but not considered in this discussion. In theory, the weight indicated on the scale should remain the same, right??? I still don't know, but think about it. We don't want to know about exhaust gases, and vortex ring, and, and ,and... Simply, lift, opposes weight, the same as thrust is opposite to drag. In a 'sealed' box, with no other influences, nothing should change.

I would like to see how far this is gonna go. Keep it up all of you, some good thinking going on here. Once we answer this one, we can solve anything, maybe time travel.... This is not an easy one.
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Old 6th Dec 2004, 05:38
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chopperdude,

This is dirt simple and about 20 people have answered it. The scale does not change. See my post just above your last.

Try to imagine this one as a swimming pool:

You are sitting on the bottom of a swimming pool wearing scuba gear, slightly negitively bouyant so you must paddle to stay off the bottom. The pool is mounted on a big scale. The water, pool and you are all registered on the scale. Now you swin lazily off the bottom and paddle around for a while. While off the bottom, does the scale show less total weight?

This is exactly the same question as the helicopter question, but the answer is more obvious. The scale does not change in either case.
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Old 6th Dec 2004, 09:40
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"Even as the engine and pilot consume the oxygen, it is mearly recombined in the H2O and CO2 expelled in the exhaust."

But surely the newly produced elements of Hydrogen and Carbon add their weight to the volume of the box.

Atomic weights of ;
Hydrogen = 1.00794
Carbon = 12.011
Oxygen = 15.9994

Let's say,
A 'unit' of oxygen = 16
A 'unit' of H20 = 1+1+16=18
A 'unit' of CO2 = 12+16+16=48

Total exhausted gases = 18+48=66

Doesn't the weight of exhausted gases therefore exceed original gases weight?

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