Mig-21-Flight Model - Check six

Mig-21-FM-Identification-Rev. 14
Maximum After-Burner Power, Altitude of 3,000m
Vcas
(Km/h)
Vcas
(Kts)
Mach
Sustained
Ng
(read)
Sustained
Ng
(computed)
Error
500 270 0.489 2.33 2.64 13%
550 297 0.538 2.70 2.95 9%
600 324 0.587 2.97 3.25 9%
650 351 0.634 3.23 3.53 9%
700 378 0.682 3.50 3.78 8%
750 405 0.730 3.80 4.11 8%
800 432 0.778 4.12 4.52 10%
850 459 0.826 4.41 4.74 7%
900 486 0.874 4.61 4.74 3%
The error relative values are greater for 3,000m/9,843ft than for other altitude, I have no idea why. For
other altitudes (1,000m and 5,000m), thrust law deduced from level flight acceleration combined with
a unique aerodynamic model (independent from altitude) give the same range of values for relative
error.
Please note also that, even in the worst case, sustained load factor error remain less than 0.31G
Let’s try to analyze the solving of one of this configuration (Vcas=650Km/h)
We start from thrust definition by level flight acceleration at 3,000m, assuming that a Vcas of
650Km/h is equivalent to a mach number of 0.634 (ISA at 9,843ft), we will use section b) data (raw)
and the values after curve smoothing (fig.15),:
Mach number Raw Ps Raw Thrust Smoothed Ps Smoothed Thrust
0.600 309 ft/s 11,113 lbs 306 ft/s 11,114 lbs
0.634 317 ft/s 11,118 lbs
0.700 337 ft/s 11,127 lbs 334 ft/s 11,124 lbs
The smoothed thrust values are computed in solving equation (3.3) for Mach=0.634 and Ps=317 ft/s
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