Mig-21-Flight Model - Check six

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Time (s) Time (s) Mig-21-FM-Identification-Rev. 14 The diagrams are (t,Mach), i.e. time requested to reach a given mach number. The continuous black curves are computed from the flight model described here and standard atmosphere (ISA). The heavy colored segments delimit the time required to reach a given mach number in ISA and ISA+10°C condition in the L-15/Mig-21M manual. The length of the segment also describes the potential dispersion of the measures, and consequently the admissible error in forecast. All data are related to a configuration where gross weight is 8,000 kg and Drag index is 12 (2 K-13 missiles): 180 1,640 Acceleration (Max A/B Thrust) ISA Conditions 165 150 135 120 105 9,843 16,404 L-15 Manual 500m L-15 Manual 3,000m L-15 Manual 5,000m ISA + 10°C ISA 90 75 60 45 30 15 0 0.30 0.40 0.50 0.60 0.70 Acceleration 0.80 0.90(Max 1.00 A/B Thrust) 1.10 1.20 1.30 1.40 1.50 1.60 ISA Conditions Mach 180 165 150 135 120 105 22,966 32,808 39,370 L-15 Manual 7,000m L-15 Manual 10,000m 90 75 60 45 30 15 0 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 1.10 1.20 1.30 1.40 1.50 1.60 1.70 1.80 1.90 2.00 2.10 2.20 Mach Page - 10
Mig-21-FM-Identification-Rev. 14 Lift laws. This section deals with the definition of the maximum lift, maximum lift can be reached by reaching the incidence value that give the maximum lift coefficient, or by reaching the maximum possible incidence due to the lack of efficiency of the pitch command. Our first step will be to define the Lift coefficient law along incidence angle. Figure 7 The high subsonic (M=0.7) lift coefficient curve on the following figure (supposed coming from Mig-21bis / L-17 Manual) show that: C z is null for AoA=0 deg C z variation is linear from 0 to 16 deg Maximum value reached around AoA=35deg But this curve should not be considered as accurate in term of value, in order to determine C z values along AoA, I do use the next figure (8). The variation of the maximum C z value along mach number is described by the following figure (once again extracted from the Mig-21bis/L17 manual). The diagram mix the limitation of incidence (stab efficiency) and variation of the C z-max . I have redrawn the green and pink curve to represent the C z values for AoA=33 and AoA=28 along Mach number. Mach Cz(33) Cz(28) 0.2 0.812 0.698 0.4 0.812 0.698 0.6 0.810 0.698 0.8 0.846 0.736 1.0 0.894 0.759 1.2 0.826 0.696 1.4 0.777 0.658 1.6 0.759 0.648 1.8 0.759 0.648 Figure 8 The figure is translated in values described in the following table. We can see that the ratio between C z (33) and C z (28) is quite constant and equal to 85%. If we compare fig.7 and fig.8, we can see that Cz values for M=0.7 are not the same: Cz(33) = 0.94 in fig.7 and 0.83 in fig.8, Cz(28) = 0.89 in fig.7 and 0.72 in fig.8. Page - 11
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Mig-21-Flight Model - Check six

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