Fuel Flow Discrepancies

Over the last couple of months flying around the world, I have noticed that there are a few issues regarding fuel consumption amongst some aircraft.

B757

I recently flew two legs with the 752, EWR-MCO and MCO-SEA, both times, I had to run the engines between 40-50% N1 just to maintain taxi speed to the runway, so whereas a 737 may use 100kg taxiing to the runway, the 757 uses > 300kg.

I also find it odd that while the 757 using roughly 4.5t of fuel per hour in cruise, the 767, which is a bigger airplane, only uses 3.8-3.9t per hour, I feel like the 767 should definitely use more fuel than it’s smaller cousin.

A330/A350

I’ve flown both aircraft a number of times, and find it interesting that when both engines are set to 104% N1 (101% for the A330), the max fuel consumption is around 11t per hour. Whereas the actual aircraft I believe uses something like 24t per hour at takeoff, which befits an appropriate rate given how much thrust the engines produce.

To enforce the point, the 757 (mentioned earlier) will use about 13t per hour at normal takeoff settings, even though it is half as big and has less than half the range of the A350.

As a side note, the A330 consumes fuel at around 5.5t per hour, not the 4.6 listed on the weight and balance sheet, and the A350 has a rate of 5.5t per hour.

The A380 and A340 also have unrealistic fuel flows, but I’m sure those will be targeted when those aircraft go in to the shops for their rework. Same for the 747, which flies best when flaps are set to 10 for the whole flight (fuel flow is 7,6t per hour with flaps 10, 10.5t per hour flaps zero).

Just some thoughts for you all. Happy flying!

The A340, A380, 747, 767 and 757 are old models with old physics and unrealistic fuel flow values, etc…!

When these aircraft eventually get reworked- the fuel flow issues will be fixed (like the A330 was when it had its mini rework last year)

Also fuel flow depends on weight among many other factors (winds, etc…) so it can vary massively…which is most likely why you experienced discrepancies with the A330/A350 - which have updated fuel flow physics

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There were a similar problem with the F/A18

They need real numbers from a reliable source to start their work on fuel consumption. If have them they might be able to do the change.

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