|Quoting Pihero (Reply 2):|
Vast subject !
I'll start with a few pointers and the rest of us will elaborate, I'm sure.
1/- If by fuel economy, you refer to the trip burn-off, yes , a lower speed wiil improve your consumption.Up to a point. The main parameter is the aircraft incidence/AOA.You will then fly an incidence that would maximize your fuel flow.That incidence, identified on the "polar" graph means thatr your speed will decrease along with your weight. The catch is the bottom of that graph is a hard limit, flying slower means increasing your AOA,thus increasing the drag,thus your fuel burn-off.
On a 744, that speed normally gives you a .86/87 Mach at max weight, going down to .81/82 at the end of your flight.
2/-Economics are a balance of costs....Direct operating cost takes in all the expenses incurred for an average hour of flight.And very often, flying too slow will in fact increase your expenses (maintenance,crew,....). That's the reason why we'd input a cost index into our flight computers (its a formula that balances fuel price with DOC -and that statement is very simplistic).
That's the bulk of it, without going too far into flight aerodynamics and economy.
|Quoting Mrocktor (Reply 7):|
however the minimum fuel burn rate does not mean minimum fuel burn for the trip (if you burn 4% less fuel per hour and fly 5% slower, you are actually spending more fuel).
|Quoting 777236ER (Reply 8):|
the maximum range speed, which is marginally higher than the maximum range speed (max L/D speed).
|Quoting Rendezvous (Reply 9):|
believe the FMC on Boeing aircraft has two options: LRC (long range cruise) and ECON (economy cruise). The LRC burns the minimum fuel per distance I believe, whereas the ECON burns slightly more furl but takes less time. Is that correct?