Fuel Efficiency

[Maverick]

Considering two A320-200 aircrafts with different All Up Weights

1. 60,000 kgs
2. 75,000 kgs

Considering the max cruising altitude ceiling of 39,000 feet, more specifically FL 390. ( with 1013.25 hpa set on the subscale)

Will the best technique of climbing to FL390 be a straight climb for both aircrafts / either one aircraft?
Will Step climb be a more fuel efficient way of climbing for both / either one aircraft?
Will a colder temperature at any one particular level decrease fuel consumption. If Yes, then WHY?

I do understand that flying higher means a faster TAS and thus meaning that if you fly faster, for the same amount of fuel burn, you can travel further and thus on the whole burn lesser fuel.
Any other reasons / explainations of choosing a higher flight level for fuel efficiency is welcome / requested.
Thankyou!
Mav.

[Kiwiguy]

Well you can't just zoom up to 39,000ft in one hit. It would be the same as pulling away from traffic lights with your foot flat to the floor.:}

The best analogy for a step climb is like changing gears in a manual car. You go through lower gears and at each gear you build up speed until it is easy to change up a gear. With each higher gear, one builds speed before attempting the next gear. (probably makes no sense to people raised on automatics)

Higher gross weights limit your ceiling in any case. As you unburden fuel it becomes easier to step up to another altitude. Just trying to zoom straight up uses excessive fuel.

[chornedsnorkack]

The best analogy for a step climb is like changing gears in a manual car. You go through lower gears and at each gear you build up speed until it is easy to change up a gear. With each higher gear, one builds speed before attempting the next gear. (probably makes no sense to people raised on automatics)

Is it correct that step climb is essentially imposed by ATC on subsonic planes, and is NOT a most efficient way to climb? Concordes used to have cruise climb from FL460 to FL600 or so...

[Kiwiguy]

Concorde is a whole different beast. Concorde was massively inefficient at subsonic speeds and had to get to altitude fast to gain fuel efficiency. True it used lots of fuel to get to altitude, but that was so it could then cruise supersonic.

Of course one seeks ATC clearance to climb on a segment, but it is related to aircraft ceilings increasing as fuel weight is burned off.