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Whilst watching a video of a Beechcraft Premier A1 Jet whilst in the cruise at FL330 I noticed the N1 on both engines were at 104.4%.

Can anyone explain why they can go over 100%?

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    $\begingroup$ related, if not a dupe. $\endgroup$ – Manu H May 31 at 20:11
  • $\begingroup$ this answer explain what 100% actually designate (for another engine). $\endgroup$ – Manu H May 31 at 20:15
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100% is the designed speed - sometimes it can be proven, that slightly more is still safe to operate on. Now: Change all scales, so that the new full power is once again 100% - or allow more than 100% on the scale? As a matter of fact, this is much easier to do, as the software does not have to be changed a lot, dependencies to other components are still valid, the recertification mostly is also easier, ... This also has been done for the Space Shuttle Main engines, routinely operating at >100% nominal ( = design) thrust.

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100% isn't a design limit. It's not any kind of limit. Engine RPM's in turbine engines are quite high; the percentage is just a reference number, and nothing more.

Different components of turbine engines operate at different speeds: a compressor section vs. the power section and fan, for example. Different names or terms are given for the various speed and component values, such as N1, N2, Ng, etc. Each will have their own speed limits, but in all cases, 100% has nothing at all to do with a limitation. It's only a reference value for power management, trend recording, etc.

Actual limitations are calculated based on temperature and desired power. Most turbine operations are conducted with a reduced power on takeoff, for extended engine life, and for safety. A takeoff runway safety analysis takes into account airport elevation, ambient temperature, wind, slope, aircraft weight, obstacles, runway length, etc, and the takeoff power value is determined at that time.

100% does not represent 100% thrust. Percentage of RPM does not equate to a linear change in thrust, and the higher one gets in percentage, the steeper the power curve goes: small incremental changes at high power settings produce considerably more thrust than larger changes at lower power settings. 100% N1, N2, or Ng doesn't represent a fixed thrust value, fuel flow value, temperature value, or actual power value. It's just a reference system for that section of the engine.

Because different engine sections operate at different speeds relative to one another, one component may be operating at 100%, while another might be at a completely different value: they turn independently, and the engine parameters that count aren't so much the RPM, but the temperatures. Only when maximum values are to be exceeded are the RPM's relevant, other than as reference numbers when setting power.

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