It is a known fact that a heavier aircraft will take longer for a given descent at the same speed than a lighter aircraft. Our rule-of-thumb clipboard data for the early 747s indicated that for every
extra 10 tonnes, the descent distance would
increase by approximately 2nm - and this was consistently borne out in practice.
The question is, why? I still think it must be to do with the increased energy (P.E. - not K.E. as I erroneously said earlier
) retained in the heavier aircraft at altitude.
Perhaps we should be analysing the converse to reach a conclusion and consider why a heavier aircraft takes longer to climb to a given altitude than a lighter one ... ? That must be to do with greater energy required, surely ...? If that is so, then there is more P.E. available in the heavier aircraft at altitude to be released in the form of work on the descent (as
TOD most eloquently says), is there not ... ?
JD
