Extra margins with assume thrust

[Gysbreght]

The whole point of this discussion is that if the thrust is constant for flat-rated temperatures, or with the assumed temperature method, the gradient is constant (i.e. does not change with TAS). If the thrust is not constant, the gradient is not constant.

[Meikleour]

Gysbreght: As others have pointed out - although the STATIC thrust in the flat rated regime may be constant, it changes by a variable amount with temperature during the takeoff roll. Hence thrust variation. Add to that, ref. to the Boeing paper (Vilas posting) shows also that there is a thrust difference at FLEX with respect to the ambient temperature.
Thus the consensus seems to be that, yes there is a variation in gradient!
Which I think is what you said.

[Gysbreght]

Originally Posted by Meikleour

Thus the consensus seems to be that, yes there is a variation in gradient!
Which I think is what you said.

Correct, there is a variation in gradient due to the variation in thrust.

[vilas]

Gysbreght
CFM document on smart cockpit gives better explanation. According to that:


If performance is limited by the one engine inoperative minimum climb gradient requirements, the higher actual thrust will result in a higher climb gradient
If performance is limited by obstacle clearance, the higher climb gradient combined with the shorter takeoff distance will result in extra clearance margin

[vilas]

Gysbrehght
The CFM document on smart cockpit gives clearer explanation according to that:
Due to lower ambient air temperature and higher air density in the actual take off conditions, actual TAS is lower and actual thrust is higher and
• If performance is limited by the one engine inoperative minimum climb gradient requirements, the higher actual thrust will result in a higher climb gradient


• If performance is limited by obstacle clearance, the higher climb gradient combined with the shorter takeoff distance will result in extra clearance margin