Yes, in fact the helium balloon is bigger than the cabin by many times and the whole airplane is suspended from it on cables from it being above. If it explodes, the airplane falls from the sky. In a related matter, I read the paper novel Das Boot. The submarine had a fly on board which became their mascot. I submit that according to Cheesy physics, they would have had to very slightly retrim the sub every time the fly took off and buzzed around. I think my work here is done. I must now go feed my adopted cat.
Well, like most Americans who haven't studied science, cheesey and his supporters don't understand physics, but let's educate them, not insult them. James Woods et al. are right, the weight of the birds is supported by the air, and the downward force on the air is supported by the floor of the airplane. The weight is the same whether the birds are flying or perching. Note that the birds would have to be hovering to keep from from flying to the front of the airplane. The air in the cabin is moving with the airplane. As for the balloon question, a pressurized airplane maintains a selected pressure inside the cabin. Because the helium in the balloon is less dense than the air around it, and the air is part of the airplane's weight, the airplane will weigh less with the balloon on board than it would if the balloon were not there and its volume were occupied by air. (Because of the tension in the membrane of the balloon, the pressure inside the balloon is slightly greater than the pressure in the surrounding air, but I am assuming that the balloon would still rise to the ceiling if released.) If the balloon were to burst, the helium would still be there, just dispersed, and the airplane's weight would not change. Somebody wanted an authoritative answer to these questions. I have a PhD in nuclear engineering, and I have nearly 40 years of experience in fusion reactor plasma physics and fission reactor physics. These questions are the kind of thing you should understand after about the first month of freshman physics.
OldSlowpoke, I notice you put your address as Longmont, Colorado. I have a cabin just a few miles up the road (from Lyons) to Estes Park...but live in Dallas. Have not been up there since the flood. How is the flood recovery effort going?
I haven't driven that road since the flood. I have spent most of the time since then recovering from total knee replacement surgery. I understand that there was a lot of devastation along the St. Vrain River. A friend of ours barely escaped a total loss along the South St. Vrain. I hope your cabin escaped harm. I do know that all the roads are now open.
You're a nice guy, and qualified to answer. Keep in mind this is playful banter here and Cheesey doesn't seem to want to be educated. I quote him here as an example of how I came to that conclusion: "Lou and other like minds have it wrong." I can't decide if he believes what he says or he's just messing with us. I see you have a 360 and an Aerostar, what a great combo!
In case anyone still doubts that the airplane weighs the same whether the birds are perched or flying, I'll tell you how physicists analyze the problem. Physicists like to draw "free-body diagrams" to analyze forces and motions. Draw two diagrams of just the air in the cabin. In the first case, the birds are perching. Now draw all the external forces acting on the air. First, draw the weight, a downward force acting through the center of mass of the air. Newton's Third Law of Motion says that if a body A exerts a force on a body B, then body B exerts an equal and opposite force on body A. The air exerts a pressure on the cabin walls (including the floor and the ceiling), so the cabin walls exert an equal and opposite pressure on the air. This distributed pressure adds up to a net, or resultant, force also acting through the center of mass. Newton's Second Law of Motion, F=ma, applies here. The air is not accelerating, so a=0. Then the net force must be zero, and the resultant reaction force exerted by the cabin walls on the air must equal the weight of the air, but in the opposite direction (upward). Again by Newton's Third Law of Motion, the air exerts a downward force on the airplane equal to the weight of the air. Since the birds are perching, the air and the birds exert forces on the cabin walls equal to their respective weights. The total force on the cabin walls is equal to the combined weight of the birds and the air. Now draw your diagram with the birds flying (really, hovering). The forces on the air are now the weight of the air, the downward force equal to the weight of the birds, which the air is supporting, and the reaction force to the air pressure on the cabin walls. Again, the air is not accelerating, so the reaction force to the air pressure must equal the sum of the weight of the air and the weight of the birds. This is equal to the total downward force exerted by the air on the cabin walls. Since the birds are not perching, they do not exert a force on the cabin walls directly, and the total force on the cabin walls is the same in both cases. QED
When this thread first popped up, I confess that I was leaning toward "the plane gets lighter" argument. What changed my mind was thinking about a goldfish being dropped into a bowl sitting on a scale. Of course the additional weight of the fish will register on the scale. Whether it's a fish supported by buoyancy or birds flapping their wings (essentially creating their own buoyancy) is immaterial.
Indeed. Medium plus material has a certain weight. Material can be suspended in the medium, or sitting at the bottom of the medium. Weight stays the same. Or we could all save a bundle on shipping costs by floating Ferrari parts in some gel. Hmmm.
True, but, the cabin/airplane is submerged in air which exerts pressure on the external sides of the cabin. Therefore the airplane doesn't actually have to carry the weight of the air in the cabin (unpressurized) or all of the weight of the air (Pressurized.) In other words, the outside air does the work of carrying the inside air. Just like if we had truly flat feet, we couldn't walk on a flat glass floor with 14lbs/sq inch of atmosphere bearing down on us. Dave
Mass is another thing. Weight is a vectored force on the entire mass of an object. In the case of Gravity it is always toward the center of the earth but the frame of reference can change (initially in a descending elevator you weigh less to the elevator floor, but not to the earth). If you assume the wings carry the weight of the plane then the weight of the airplane includes the weight of the bird but not the air (unless pressurized) in the cabin. Due to the free support of the same density air underneath the wings and cabin. However, if the airplane performs an aggressive pull-up, the weight of the air and bird would momentarily increase and require the wings to carry the extra load of air and bird. I'm just trying to keep this thread going man! Dave
Still is. I've spent hours with some of my best friends calling each other morons. Worst I've ever seen is in a pilot lounge. dave
I was watching a bunch of union riggers put up some lighting gantries for a concert. The foreman walked in and yelled "Hey A$$h0l3!" Every single guy dropped what he was doing and yelled back "What?!" True love.
The outside air supports the airplane (including the inside air), but that doesn't have anything to do with the force analysis on the inside air that I presented. The weight of the inside air is supported by the inside surfaces of the cabin. It is no different from how passengers are supported. The weight of the passengers is part of the weight of the airplane that the outside air supports, but the passengers' seats support their weight, and the floor of the cabin supports the weight of the passengers and their seats.
Totally agree. I blame James for saying your explanation was beyond debate. I'll confess it was a stretch on my part. As a pilot, not an engineer, I think of the weight of an airplane as synonymous to what you would get if you put it on a set of scales. After all, that's what it will have to lift in flight. The scales don't measure the air in the cabin. Dave
Imagine if cheesey was right. On overloaded airplanes, the pilot would be announcing that everyone please jump at the count of 3 as the plane approached the end of the runway. Extra credit if could jump and fart at the same time!
