calcapt

An airplane is preparing to takeoff and is ten pounds over MGTOW. There is a one pound bird in each of the airplanes ten seats. If the ten birds took flight in the cabin, would the airplane weigh ten pounds less and therefore be legal to takeoff weight wise? I don't know what the FAR's have to say about the birds keeping their seatbelts on, but what would the answer be?

Newguy85

Now I'm no scientist but.... If the bird is not connected to the mass being weighed because they are in flight, and becausethe birds should be considered in flight under thier own power then yes I would say you caould legally take off. However there is the other question. If the birds are flying in the cabin of the airplane thats is flying 400 mph and the birds are flying at 20 mph are the birds actually flying 20mph, 400 mph or 420mph?

NE_Pilot

It depends on what you are comparing their speed to, relative to the ground or the plane?? If they are flying 20 mph inside the plane, then relative to the plane they are going 20 mph. Relative to the ground they are going 420 mph.

As for would it be legal to takeoff, only considering weight, well yes, the birds will no longer count toward the weight of the plane.

tomgoodman

But the birds ARE connected---supported by a cushion of higher-pressure air below their wings than above, and that cushion rests on the cabin floor. The air migrates around their wings to equalize the pressure, but another flap of the wings re-pressurizes it. It would be the same if, instead of birds, little helicopters or Harriers were flying around in the cabin--no weight reduction.

Newguy85

Yah I wondered if Air pressure had something to do with the weight. Like I said, Not a scientist.

calcapt

Intersting debate going on. I will post the answer and explanation in a few days.

tomgoodman

Sure there is, although that's a simplified way of describing it. Any heavier-than-air object can maintain level flight only because the atmospheric pressure under it is greater than the pressure above it. (We're excluding ballistic flight and reaction motors which don't need atmosphere.)

Anything is capable of being SHOVED at the speed of sound (or greater) if enough force is applied, but its mass resists the shoving. That's why parachutes work, wings produce lift, and compressor blades get hot. If air were a massless, frictionless fluid, it would instantly "get out of the way" as you suggest. But nothing could become "airborne"; only shot, thrown, or rocketed.

That's not a "closed" system, (with the entire vertical thrust vector confined to your palm), so you'd only feel part of the bird's weight. Look at what a hovering helicopter does to tall grass and plants right below it---and now imagine a vertical cylinder around the helicopter (forming a "ducted fan"). The difference in pressure between the top and bottom of the cylinder would equal the weight of the helicopter.

NE_Pilot

Yea, you're right, didn't even think about the air pressure from the bird staying aloft.

dhc8fo

Of course the answer is NO....because all of the birds would be pooping all over everything thereby adding some more weight to the plane even if THEY were airborne.

calcapt

Wouldn't the weight of the birds decrease as the poop exited the bird? The combined weight should equal one pound. Right? I talked to a flight attendant recently and she wondered if the plane got heavier as all the passengers used the lavs. I told her I thought it made no difference as the passengers weight decreased by a proportionate amount to what was deposited in the toilets. You were simply redistributing weight that was already on the airplane. This thinking stuff wears me out.