МиГ-21бис with fowler flaps????

[Котков Андрей]

Here is a scheme of SPS system from the technical manual MiG-21PFS, its showned how its work.

I know that the SPS system was used starting from MiG-21PFS version and mounted on PFS, PFM, R and S(SM). About 'bis' I can't say now, but tomorrow i'll try to find this information in the technical schemes of Mig-21bis.