7
$\begingroup$

As a passenger, I have always felt like the engine are not kept at take-off thrust/full throttle a few (tens of) seconds after take-off, and so for obvious reasons as fuel efficiency, engine wear prevention, noise control for population in airport area, and so on.

I have also read on this site or on excellent Twitter account of the A380 captain Dave Wallsworth lots of explanation about how to reduce the take-off thrust (eg. flex temp).

But I cannot find any information about the throttle level (N1 percentage may be more accurate) during cruise. My guess is it is not constant because of weight decreasing during flight due to fuel comsumption, but this is only a guess.

I know Airbus airliners have a "CLIMB" position on throttle which allow the autopilot to set N1 automatically to reach cruise speed, but I would like to know how N1 value evolves during cruise.

A320 throttle quadrant with lever at CLIMB position, with auto-throttle range:

A320
(source: skalarki-electronics.eu)

Improve this question
$\endgroup$
0

2 Answers 2

Reset to default
9
$\begingroup$

enter image description here
(Above is the max cruise limit in standard ISA for the A320.)

It's 80.4% - 86.5% for the different weights and altitudes. Do note that 81% does not mean 81% of the available thrust. The maximum continuous thrust (MCT) at standard temperature is between 86% and 89% for the different cruise flight levels.

The colder the air, the lower the values, and vice versa for hot temperatures. If too hot above ISA, max flight level is limited for the higher weights due to MCT being the limiting factor.

For the A320 example, the thrust levers remain in the CLimb detent from thrust reduction to just before landing in normal operations.

For the 777-200, the range varies from 69% - 96.8% depending on the flight level and weight (with 86.8% - 94.7% being the optimum range). The wider range is due to the 777's wider payload/fuel range when compared to the smaller A320.

Improve this answer
$\endgroup$
2
  • $\begingroup$ Just for clarification, does this mean that maximally loaded at FL350 the engines are essentially flat-out if N1 is 86.5% and the max is high 80s? $\endgroup$
    – Talisker
    Commented Nov 6, 2018 at 22:09
  • $\begingroup$ @Talisker: Sorry for the huge delay, I must have missed your comment: yes, that's basically correct. Higher thrust may be available but will be time-limited to avoid overheating, compared to the "maximum continuous thrust". $\endgroup$
    – user14897
    Commented Sep 23, 2021 at 15:51
1
$\begingroup$

From my experience in B767, the computer generated flight plan (with preset company settings) will give a Cruising Mach number, eg we used .80. At the initial cruise level the auto-throttle will set the power required to achieve that speed.

As the a/c burns off fuel, the required thrust and therefore N2, N1 and fuel flow will decrease to keep the same Mach number.

Improve this answer
$\endgroup$

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .