Today, experts from the War Thunder development team are going to be talking about the technical aspects of calculating the effect of overload of MANPADS missiles.
A significant number of reports recently refer to the available overload of MANPADS missiles: Igla, Stinger, Mistral and others. Comprehensive information about missiles isn’t always available, for example, on the zones of destruction of maneuvering targets. Because of this, we’d like to note that when analyzing the flight model of missiles, we carry out a comparative analysis with those structurally similar missiles where information is actually available.
All MANPADS missiles with an infrared seeker presented in the game are structurally made according to the “canard” aerodynamic design with control using a single-channel control scheme for a rolling airframe missile. A pair of rudders serves to alternately control the missile in pitch and yaw, and the second fixed pair serves as fixed destabilizers and is designed to shift the aerodynamic focus of the missile forward, closer to the center of mass.
This design solution is based on size and weight requirements and can significantly reduce the mass of the missile, which is why it has found application in MANPADS missiles and some ATGM missiles. However, the use of this design solution also leads to a decrease in the average available overload and imposes special features on the steering surface control scheme.
With a single-channel relay control of a rolling airframe missile, to create a control force in any direction of flight, the rudders are moved by the servomotor mechanism from one outermost position to another four times per revolution of the missile’s rotation. This rudder control scheme makes it possible to regulate the resulting overload and therefore ensure proportional guidance of the missile.
The duration of the control surfaces being in each position determines the magnitude of direction of the resulting missile overload.
If it’s necessary to create the maximum resulting force, the rudders are deflected twice per revolution of the missile.
The way the resulting force in the missile maneuver plane changes can be represented in a simplified form as a half-wave of a sine wave. The average resulting force in the maneuver plane over a half-period of rotation is equal to the integral of the change of the resultant force in the maneuver plane. Dividing it by the integral of the resulting force in the plane of the maneuver of a non-rolling airframe missile over the same time period, we obtain the ratio of maximum overload to the average overload over the rotation period.
Therefore, the average resulting force over half a rotation period for a missile with a single-channel control system in relay mode will be 63.66% compared to the same non-rotating missile performing a maneuver in the plane of the control surfaces. The ratio is also the same for the average available overload to the peak one when the rudders are in the maneuver plane.
Because of this feature, when analyzing the maneuvering capabilities of MANPADS missiles, we rely not only on the maximum overload indicated in the documents, but also on the weapon engagement zones and conduct a comparative analysis of missiles by mass and area of aerodynamic surfaces. For MANPADS missiles, we reliably know the maneuvering capabilities of the 9M39 with available overload of 10.2G, which is confirmed not only by the overload in technical documentation, but also by the size of the engagement and kill zones of maneuvering targets.
For other MANPADS systems, open sources indicate a higher overload such as 18, 20 and even 25g in the case of the Mistral 1 MANPADS. However, these MANPADS systems have only slight differences in the area of aerodynamic surfaces compared to the 9M39, so a multiple increase in average achievable overload compared to the 9M39 cannot be expected. We believe that the slightly higher overload of other MANPADS systems is mainly due to the slightly higher maximum speed of the missiles in comparison with the 9M39 MANPADS missile. Therefore, we assume that for the MANPADS FN-6, FIM-92 and Mistral, the documents indicate the peak overload achieved at the moment when the rudders are in the maneuver plane. With this assumption, the average available overload for the half-cycle of rotation of these MANPADS will be 63% of the peak and will be consistent with the data on the available overload of the 9M39 MANPADS.
Within the game, due to technical limitations, even in the case of single-channel relay control, we use two-channel proportional control of missiles. Therefore, the maximum overload for the autopilot of MANPADS missiles in the game was set to the average overload of a real missile over a half-period of rotation. In the missile’s stat card, we also display the average overload for the half-period of rotation of the missile, which gives players a greater understanding of the capabilities of the missile than the peak overload, which is achieved only at the moment the plane of the control surfaces coincides with the plane of the missile maneuver would have given.
With all of the above in mind, we have made the following changes:
- FIM-92 Stinger, ATAS(AIM-92) — available overload has been increased from 10G to 13G. Autopilot parameters have been adjusted, missile dynamics have been altered.
- Mistral, Mistral SATCP — available overload has been increased from 12G to 16G. Autopilot parameters have been adjusted, missile dynamics have been altered.
We hope that we were able to explain the principles of calculating the overload parameters for MANPADS missiles in War Thunder in general terms, the specifics of their implementation and explain the difference between the average and peak overload values on the flight trajectory. Thanks for reading.
