ZeroWorld

I really hate it when a 5-year-old asks me a question that I cannot answer.

Here's the question... should a plane weigh the same before and after the flight? Obviously fuel is excluded from this question, since fuel gets burned off by the engines during flght. And, no, nobody parachuted out during the flight.

WillR

- quantum of nuclear decay (trivial amount)
- conversion of carbohydrates and fat to carbon dioxide in the humans on board
- If it was raining at the origin, and there was water sitting on the fuselage, that weight could be lost by arrival
- Flushing of water through the toilets
- Consumption of water by humans which is then perspired or otherwise excreted


I can't think of any other ways weight might be lost.

Mr H

It would weigh less if it landed at a higher altitude than take off - although its mass would remain the same.

uk1

Own up ..... no 5 year old involved ... the sort of question we all wonder about ... and then can't let it go ......

sbm12

It is going from one tank to another, right? It isn't vented out of the plane AFAIK.

VivoPerLei

Don't forget loss of paint, however miniscule it might be

WillR

My mistake. I assumed that liquid waste was vented when at altitude. Happy to stand corrected!

BLI-Flyer

Yuck! Just don't stand underneath the plane when it "vents!"

WillR

Ah of course. Nicely put.

BTW, there can't be many BD Gold members based in MEL!

cordelli

Well there have been more then a few cases of "blue ice" falling from the sky because of leaks.

Not counting fuel, there will probably be a slight difference from the amount of moisture we give off in breathing, assuming that's vented out of the plane and not just absorbed in the fabrics.

I also believe that the air introduced into the plane is humidified a bit, so there would be some water vapor added to it, as that circulates and is exchanged some moisture may escape, causing the weight to drop a bit.

There may be some fluids like oil and grease that also burn off a bit, friction and that, again probably trivial amounts.

But besides that, I would assume that everything is a closed system.

In reality though on planes that have in flight internet, all those extra electrons from people downloading videos may actually add to the weight when it lands.

Kidding about that part.

B747-437B

The ZFW (Zero Fuel Weight) of an aircraft is assumed to be the same upon landing as it was at takeoff.

In addition to fuel, there is also consumption of hydraulic fluid, engine oil, lubricants, etc... during the flight but the quantity is negligible in this context.

MisterNice

..............and dont forget the occasional wheel-well stowaway who unfortunately loses his grip.

MisterNice

buckeyefanflyer

Here is one exception. The NW 727 that DB Copper jumped out of that plane would be less by approximently 200 lbs.

ZeroWorld

don't know about planes... but I miss the good old days when passenger trains used to dump human wastes on railroad tracks.

nbs2

Walk down the tracks in Union Station sometime, and you'd think they still do it.