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September 6th, 2010 • 18:09

Another Jet Engine Question! How Does N1 And Thrust Vairy With Altitude And Temperature?

For the same , what is the difference between N1 and when an is taken from sea level to a hot and high airfield?
I think if N1 is constant thrust must reduce and if thrust is constant, N1 must increase? Am I on the right lines here? Thanks.

4 Comments

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  • Sep 6th 2010 • 19:09
    by Benji

    For the same engine, what is the difference between N1 and thrust when an engine is taken from sea level to a hot and high airfield?
    I think if N1 is constant thrust must reduce and if thrust is constant, N1 must increase? Am I on the right lines here? Thanks.

  • Sep 6th 2010 • 21:09
    by Ben

    At sea level your atmosphere is compressed to about 14.7psi as you increase in altitude the pressure decreases.
    The lower your air temperature the denser the air is and as it raises it becomes less dense.
    Therefore at sea level or when it is cold your engine gets more Oxygen to burn and produces more power. When it is hot out or you are at higher elevations you have less air to work with and it starves the engine making it produce less power.
    N1 simply refers to the Low Compressor Speed which is measured in percentages or RPMs. Depending on the temperature and altitude you will create different amounts of thrust.
    When doing a performance run to check efficiency on an engine you always figure in altitude or barometric pressure and temperature to calculate efficiency. The difference in 5 degrees can change an engines efficiency by as much as 10 percent depending on what engine it is and the altitude.
    In Afghanistan you can only be pulling 60% of the engines power on a hot day.

  • Sep 6th 2010 • 23:09
    by Jimmbbo

    In cruise, N1 is constant with density altitude. With higher DA, (lower density) air flow decreases, and fuel flow is reduced accordingly, reducing thrust.

  • Sep 6th 2010 • 23:09
    by Techwing

    Thrust diminishes with increasing altitude and temperature, but so does aerodyanmic drag. This is why airplanes can fly faster at high altitudes even though their engines are producing less power than they would at sea level: the drag decreases faster than the thrust decreases. However, there’s a point at which the thrust diminishes so much that it can no longer support the aircraft (i.e., it can’t propel the aircraft fast enough to generate enough lift to support it), and that is the ceiling of the aircraft (with respect to density altitude).

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