The weight of birds in airplanes
 

A 100 ton cargo aircraft is loaded with 50 tonnes of birds, sitting on the floor of the cargo room, and the aircraft is flying straight and level at cruising altitude. The total weight of the aircraft is 150 tonnes, and thus the aircraft wings produces a total lift of 150 tonnes.

Suddenly all he little birds start flying around in the cargo room.

How much lift must the wings produce now to keep the aircraft flying straight and level?

Nick.

......and a follow up question.....

If we tethered their feet to the floor with a short leash, is it possible for them to beat their wings even faster so that we may shut down the engines and still climb???? :)

On a vaguely related theme;
Describe the behaviour of a helium filled balloon tethered by a length of string to the floor of an aircraft whilst performing various manoevres. Would it be useful as an instrument?

In the same vein - a goldfish weighing 25 grams is placed into a bowl of water. The weight of the bowl plus water is 975 grams.

If the goldfish floats, what is the combined weight of fish plus bowl+water?

same question - same answer.

You'll have to specify whether the aeroplane is in a normal or inverted spin.

TW

1. Same as before.

2. No.

3. No.

Reasons? Mass, weight, gravity and Newtonian Physics.

Theres a similar question to this in this months FHM believe it or not - so obviously the answer was 100% correct ;) !?!? The only difference being that the example used a truck rather than an aircraft. The answer that was given was that if the birds were all flying, a truck would indeed weigh less if placed on scales . Some people claim that the force of the air pushed down by the birds' wings counteracts the loss of weight imparted on the base of the truck by the birds - but this is blag because the weight of each bird is being supported by the lift in it's wings (roughly) and not imparted onto the a/c and downforce through bird wings compared to a/c lift is negligible. (I'm sure someone will give you a better, more detailed explanation including Newton's Laws of why this is not the case !). Therefore for straight and level flight I reckon the lift would simply have to equal the empty weight of the a/c. Of course I'm probably completely wrong and someone will correct my incredibly poor logic and reasoning !! But hey... ;)

... and I thought talking outta my jacksie would spark an lengthy debate... ;)

Hey, Good name you have chosen.

There was a thread I started on the instructors forum a few months back titled (I think) "Pilot mag quiz".

I still maintain that this is not the same question as the goldfish as with the fish we are talking about two different fluids with differing Viscocity.

Oh Er

Oh God,
Not this one again! I remember the one back in March and it caused all sorts of answers to come up. ie, what if all of the birds(geese) were tame and asked to sit still for a while to weigh the aircraft then all takeoff when asked. Or something like that. It was reckoned that the down force from the wings (lift) would exert the same force as the weight of the birds, hence leaving the aircraft same weight.What if the aircraft was pressurised when all of this was going on then someone opened a window? Would it make any difference? Apart from the geeses being sucked out at altitude to fly on their own.
:confused: :confused: :confused:

This one's far too easy- if the dowforce of air generated by the birds' wings is less than the weight of the bird then the birds will hit the floor. This is due to the no. 1 law of physics which states, "There is no such thing as a free lunch." The only way you'd be lightening the A/C would be to remove the floor of the cargo hold, in which case the plane would'nt be carring the birds but flying in formation with them.

Are the birds African or Indian? :D :D :D

Smoketoomuch:
Yes, the balloon would be just as useful as a pendulum.

Caution: In aircraft not certified for inverted flight, special certification is required to conduct IFR operations using helium filled balloons in place of faulty pendulums in the instrumentation!

compressor stall:
Very interesting issue. However, the first question to be raised should be "how far could a swallow carry a coconut?" (*)

I guess you're familiar with the rest?

"Would that be an african or a european swallow?"

"I don't know.... YAAAAAAGH!"

Gotta love british humour. If you lot in the UK just get the food and the weather sorted out, I'm moving! :D

Cheers,
/ft

(*) Or was it "how many coconuts..."?

Both africans and europeans swallow? :cool:

With those long bangled necks those incredible African tribal women have.... :eek:

Okay then, along the same line, what happens if.........

You are carrying 200 passengers, and every passenger jumps up off the cabin floor at once, so they are not touching any part of the aircraft, and while holding all their cabin baggage??????????

:rolleyes: :eek: :D

lame,
just action/reaction - no downwash making things tricky. They push off upwards creating a downward force on the plane which reacts accordingly, then for a moment the plane has to produce the weight of passengers + cabin luggage kilos less lift while they are in freefall inside the cabin and will rise. Then floor and passengers reunite happily and everything is back to normal, same energy state as before.

You were joking I guess but someone probably is wondering... :)

Then again, there's PFIL(*) and that can be empirically proven... eh... sorta... :D

Cheers,
/ft

(*) Passenger Fear Induced Lift, short version: Passengers hold the plane up by clinging onto their armrests and pulling. The more scared they are, the more they pull. The take off roll is necessary to produce noise and vibration enough to scare them. Flaps create additional noise/fear/lift. It's pretty scary to see the ground swoosh by a few feet below so we get ground effect... :D :D

(Editd fot typos)

[ 15 August 2001: Message edited by: ft ]

PFIL - it all makes sense now :D

ft
See, it's the "noise" (or sound discussed in another thread) that produces the means of so called "lift", as you said the more "noise" the more fear etc. etc.

ft,

That explains a lot.

So then during the flight you feed the pax a nice meal and get a few drinks into them, so that they relax, and you can land again......

:rolleyes: :eek: :D

Best regards,

"lame"