1. When engineers design the power management of the FADEC, how do they set the required thrust when the pilot pushes the throttle to the TO/cruise/idle position?

  2. I have read some papers, and I found that the demanded thrust is related to the inlet environment, but I don't know how to calculate the influence of the environment, and how to correct the thrust.

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    Welcome to Aviation.SE! "How did they set the required thrust when the pilot pushes the throttle to TO/Cruise/Idle position": This would be a good base for a good question. The environment part is less clear, and maybe should be treated separately in a later question when you have the answer about the settings. – mins Sep 27 '16 at 10:59
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    Yes, you are right .I would change the order of the questions. – LMerCy Sep 29 '16 at 2:12

All modern engine control systems take 'environment' (most importantly inlet total pressure and temperature) into account.

Takeoff and maximum continuous thrust are normally limited by the turbine temperature (which is controlled internally) and N2 (high-pressure rotor) RPM. So such settings on the throttle usually preset a certain N2, and then the thrust will be whatever the engine develops in present conditions. However, this limiting N2 may, and often does, depend on the environmental conditions. The max max (takeoff) is usually a hard limit, but the max cruise N2 may increase with altitude (falling temperature/pressure). Thus when you are climbing with a constant throttle setting, the control system may increase the RPM - even though the actual thrust will be falling due to engine physics.

Idle thrust is limited by stability of the flame. Idle RPM on the ground may be substantially lower than what can be sustained in the air (at speed). Thus the engine control systems often have a weight-on-wheels input signal and apply different control on the ground, primarily with regards to idle power.

Idle can also be significantly affected by the amount of bleed air taken from the engine, but this is not quite the 'environment', I suppose.

Of course, real control systems are a lot more complicated, even if we consider just the environmental parameters. For example, they can have numerous logical rules like: "if idle is selected after having maximum thrust for more than X seconds, ignore the pressure sensor and hold its value for Y seconds", or some such.

  • what i say is "required thrust",which maybe given by aircraft, not the thrust produced by aircraft engine. – LMerCy Sep 27 '16 at 8:25
  • @LMerCy, then I don't quite understand what you are asking. When pilots set, say, TO thrust, they in fact request ~100% RPM (sometimes 101% or some such value) from the engine. What thrust actually develops depends on many environmental factors. Before takeoff, pilots should consider all these factors, and their manuals/computers may advise to use reduced thrust. But in this case they (or the autopilot) will set a reduced setting on the throttles, so it won't be a TO power. Even if autopilot does it, this is generally not the domain of engine control system. – Zeus Sep 27 '16 at 8:36
  • Thanks for your reply. I think when pilots set TO thrust ,the aircraft engine should produce the required thrust to ensure the plane can take-off safely which is defined by aircraft ,I am not sure whether the RPM is 100%(maybe when they design the aircraft engine to ensure when the aircraft engine produce the TO thrust the RPM is 100%).Then that's my opinion is the requirement of aircraft is first which the FADEC must meet . – LMerCy Sep 29 '16 at 2:09
  • @LMerCy, generally, no, the engine controller doesn't know much about what the airplane needs. It usually doesn't know its weight, let alone drag or runway length. It is the job of the aircraft designers to match the engine to the airframe so that enough thrust was produced in the defined set of conditions. It may happen (say, in hot weather) that even TO thrust will not produce enough, and takeoff won't be possible. It is then responsibility of the pilots to set throttles (or program autopilot to do so) to the most appropriate setting, or in some cases not to attempt takeoff. – Zeus Sep 29 '16 at 4:27
  • Could u please give me the source about you said " engine don't know what the airplane needs" ? – LMerCy Sep 29 '16 at 7:36

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