Since ambient conditions vary in a wide range within the full flight envelope

the existing piecewise linear model (PLM)

which is based on sea-level static condition with use of corrected parameters for other points in the flight envelope

cannot meet the accuracy for replacing the nonlinear model. To obtain more accurate linear models

a method of partitioning the flight envelope over a grid of Mach number and altitude boxes was suggested. Then

a set of linear models for a given operating condition was selected by picking the nearest (Mach number

altitude) box in the flight envelope. Through the selected set of linear models

interpolating for power level based on a weighted sum of corrected rotor speeds can obtain a linear model with acceptable accuracy. Simulation results of different points within the full flight envelope showed that the maximum error between nonlinear model and the existing PLM was more than 50%

while the maximum error between nonlinear model and the improved PLM was within 8%. It is concluded that the improved PLM performs accurately

especially under the non-standard conditions. In addition

the improved PLM can satisfy the real-time requirement better than the existing PLM.