Fuel economy

[boeing boeing.. gone]

Hello all, just a quick question that has been bothering me.. do pilots achieve different levels of fuel economy? I know some car pilots (yes i know) acheive differing levels of economy based on how heavy their right foot is... i was just wondering if the same applied to pilots!? (based on the same plane/route/load/temp etc)

Thanks in advance

[de facto]

Of course.

[autoflight]

Fuel economy needs to be considerered alongside other considerations that could have far greater impact on overall efficiency of flights. ATC shortcuts can save fuel. I am sure high speed descents in A320 can save heaps of gas.

Missing a departure slot could cost hundreds of Kgs of APU fuel waiting for another slot. Being in a position to take a slot missed by another aircraft can save fuel, parking fees etc and can get your aircraft home early to maximise company choices for next operation. If you know company is sweating on this, select a faster level and cost index and hang the extra burn.

A320 taxi fuel flow is similar to cruise rate. If taxi time can be less, however it is arranged, this can save fuel.

How some of these things can be arranged is the subject of a previous autoflight post.

I would like to see pilots comments on a wide angle look at total efficiency rather than simple flight fuel.

[Lord Spandex Masher]

A320 taxi fuel flow is similar to cruise rate.

Err...Really?

[BOAC]

I suppose if you taxi with 90% N1 or so it will be.

[CelticRambler]

Originally Posted by autoflight

Fuel economy needs to be considerered alongside other considerations that could have far greater impact on overall efficiency of flights. ATC shortcuts can save fuel.

Missing a departure slot could cost hundreds of Kgs of APU fuel waiting for another slot. Being in a position to take a slot missed by another aircraft can save fuel ...

Doesn't this come within the OP's question? Being easy with the "right foot" in this environment includes understanding these factors and some individuals will be better able than others to judge the right time or turn of phrase to ask for that ATC shortcut or grab the slot that's just become available, won't they?

[BOAC]

Originally Posted by js

Quote:
A320 taxi fuel flow is similar to cruise rate. If taxi time can be less, however it is arranged, this can save fuel.
How on earth do you work that one out?

- maybe Autoflight's parking brake is on?

[Tapshi]

I suggest taxi with the gear down and locked

[autoflight]

I am waiting for the doubters or others to provide some actual Kgs/hour fuel flow during taxy and also at cruise level. Perhaps we could also have some figures for other jet aircraft types.

I will eat humble pie if I'm wrong but I ask for the same from those who are too quick to be critical, if they are wrong.

[Cough]

During taxy 440kg/hr+100kg/hr apu burn (single engine). During cruise 1100kg hr per engine, so about 4 times the burn. A320, approx.

[bex88]

I second Cough's figures, most flight plans allow for about 42-44kg per min fuel burn (trip fuel) so about 1200kg per engine per hour. Fuel flow at idle during taxi is about 400 ish. I recently had a 50 min taxi (no I did not get lost but I did use up my daily allowance of enthusiasm. Net result was 700kg of fuel gone. On the fms2 aircraft, certainly on the IAE equipped ones on the fuel page you can see the fuel flow in kg per min.

[autoflight]

Please consider the humble pie eaten

[peter kent]

Jerky throttle movements

heavy their right foot is

I suppose heavy handed may conjure up pictures of unnecessary slams or perhaps Bodies if you are trying to discover some shortcoming of the engine/installation.
However, necessary jerky throttle movements were quantified with the introduction of EUMS recorders. I remember, about 1977, processing tapes from 2 Red Arrows Gnats. The shaft speed/time histories were converted into accumulated LCF damage and useage of fatigue life. The revelation was that the wingman accumulated damage at 25X the rate of the leader. In fact, the leader didn't even, for the whole display flight including TO, get in one reference stress cycle, whatever that was.

In the context of this post I wonder whether the wingman's fuel used correlated in any way with the mass of throttle excursions required to maintain position 3 planes removed from the smooth leader.

Any ideas?

[BOAC]

n the context of this post I wonder whether the wingman's fuel used correlated in any way with the mass of throttle excursions required to maintain position 3 planes removed from the smooth leader.

- formating a/c always burn more fuel than the lead but not, I think, 25x as much (not that much fuel on board!) so I suspect there is no direct correlation between throttle movement and fuel burn. Constantly accelerating and decelerating the rotating mass will always be less efficient than steady state running.

Move out from lead to 'outside' wing and throttle movement becomes more extreme. As an example, in the line abreast barrel roll as an 'outsider' the throttle goes from full to idle/idle to full at least once to maintain position although the engine of course does not have time to fully respond to the demands. Many of the formation changes also call for extreme throttle movements and 'slams' were frequent during rejoins and other movements and very much part of the airtest requirement for the individual airfame/engine combo. The synchro pair's consumption was occasionally 'very interesting'.