I don’t have any info on what this ‘SPS’ system in the MiG-21 is other than the limited Google references…but it sounds similar to the boundary layer control system in the F-104.
In the F-104, this system was used with the landing flap only. It was ineffective when used to maneuver with…the low speed limit of 240KIAS and the limited g available at that speed made that a poor choice.
Here is a picture of the system.
The soviet SPS(sduv pogranichnogo sloja) system with the Mig-21 uses the same principle of course, probably with some more or less technical differences. You can judge by your self when looking at pictures below. The SPS system was engaged after fulfilling following conditions.
1. The flap switch to “Landing” position, max. 45° flaps deflection, The SPS system starts acting when flaps reach 30° deflection, that`s about 390-400km/h IAS.
2. Engine throttle settings between SPS and MILITARY POWER, AB is disengaged when SPS is ON.
3. The circuit breaker “SPS Upravlenie” and “SPS VKL” switches are ON.
I do not remember to hear that deploying flaps(0-25° range flap deflection, flap switch to take-off position) was ever thought during an A2A combat, but perhaps there was a “little room” in the Mig-21 envelope where flaps could be utilized. It is rumoured by some soviet airforce official in various aviation sources, a special fighter pilot excercises called “500s” underwent on some training bases in order to master maneuvers when flying the Mig-21 on the edge. However, how much advantage they might gain from those slow-speed maneuvers is unknown, but the Mig-21 never liked slow speeds in general.
As already pointed out, the Mig aircrafts are using the “floating type” of flaps on almost all types Mig-21,23,25,29. The flap slowly deploys to max. deflection with decreasing dynamic pressure and vice versa. Look at the diagram below, though it is from a similar Mig flap system.
The question I`d like to have is whether the F-104 had the same flap system or not. Thanks
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