AK200Guy
21st Feb 2001, 20:41
I am sure i was taught this at LEAST once...In the planning and performance section of the FHB for the 747 classic it shows a minimum assumed temp. What is the reason for a MINIMUM assumed temp?
Thanks in advance
HighSpeed
21st Feb 2001, 20:52
ak,
most jet engines are flat-rated at ISA+15 which is 30 deg at sealevel. therefore, you will get the max thrust at ISA+15. if you select a temp greater or less than ISA+15, then you have less than max thrust.
say you are taking off at 0 deg and sealevel and finds your selected temp to be 20 deg then you should use 30 deg (ISA+15) or not select any assumed temp at all as selecting 20 deg will actually cause you to takeoff with less than required thrust.
on the b777, some intellegence have been built into it cos the thrust will not reduce below ISA+15 even if one 'accidently' enter an assumed temp of less than ISA+15.
HS