Game Development Reference
In-Depth Information
Table 10-1.
Atmospheric Density and Power Drop-Off Factors
Density (
kg/m
3
)
Altitude (
m
)
Power Drop-Off Factor (
F
)
0.0 (sea level)
1.225
1.0
1500
1.058
0.845
3000
0.909
0.707
4500
0.819
0.623
The input parameters are inserted into Equation (10.18), and thrust values are computed
as a function of velocity up to the maximum rated velocity of the plane of 63
m/s
. The results are
shown in Figure 10-16. Because the
b
coefficient in the curve fit equation is negative, the calcu-
lated thrust generated by the engine is highest when the airplane velocity is zero and decreases
in a parabolic fashion with increasing velocity. As predicted by the power drop-off factor, the
thrust generated at an altitude of 4500 meters (close to the maximum altitude for the plane) is
only 62% of the thrust generated at sea level.
Figure 10-16.
Computed thrust profiles for the Cessna 172 Skyhawk
The most recent Cessna 172 Skyhawk models feature an engine with better performance
than earlier versions of the airplane. Previous Skyhawks featured an engine that delivered 160
hp
at 2700
rpm
. Because the current Skyhawk engine delivers the same power with a lower propeller
turnover rate, it delivers about 10% more thrust than the earlier models.
