Calculating an aircraft's weight
I've always wondered this, but never been able to find the answer. Sorry if this has been asked before.
Do the pilots need to know:
(a) how many passengers are on-board;
(b) how many bags are in the hold
in order to calculate the take-off performance data? What weight difference would be required to affect V1, Vr? I'm thinking B737 / A320.
A friend recently argued that the reason checked-in bags are weighed is so that the pilots know the weight in the hold. I disagreed, saying that this information does not go to the flightdeck; rather it is used to check compliance with the maximum weight allowance (and make the airline extra revenue). Plus, you can never know what the hand-luggage weighs, so that can't be relevant? Then I thought I should check this...
Sorry if there's a really simple answer to this, but I'd be interested to know.
Nick