toby1234abc:
A mathematical question foe Freight Dog .
What calculations or formula is used for using fuel and the aircraft becomes lighter in the flight plan ?
With the weight of the fuel becoming less, do you increase speed or maintain it, and does a commercial airline make a profit as less fuel is used as it becomes less heavy ?
And could a four engine aircraft fly halfway across the Atlantic with one engine working, what are the stress factors put on the fueselage and other parts ?
With a total loss of avionics, where you flying blind, how do you calculate the glide slope to an emergency airfield, I saw the co pilot do the maths on a back of an envelope, in a true story of landing on a shut down airfield with no power, in a movie ?
Eh up up Tobe, I might as well stick this in before I toddle
Yeah actually dead right. The fuel is burnt off and we do step climb as we go along. You start out at maybe 400 tonnes, only able to achieve 34000ft. Its roughly 10 tonnes an hour burn in cruise on the 74. The aircraft is stepped up when its light enough to achieve an optimal flight level. The optimal level depends on a combo of favourable winds, temperature, fuel burn and speed. The speed depends if you want to get there quickly to make a time restriction, or save as much jungle juice as possible. Most airlines want to strike a balance. They calculate a useable figure to represent this called a cost index. It’s a number that’s then input into the flight guidance computers during on the ground. You can change it if you wish in flight.
Generally we keep going higher and actually fly slower Mach numbers as we go along.
A four engined aircraft even on two engines wouldn’t be able to carry on if halfway across the ponds it would have to divert. On one engine, you’re aiming somewhere quite close. We have a variety of diversion airports we use in Iceland, Greenland and Nova Scotia.
You don’t actually need to calculate a glide slope angle. The glide slope beam from the instrument landing system is fixed and radiates from the ground. It’s published on the approach charts, it’s normally 3 degrees. It’s about 300 feet drop per mile.
Cheers mate