The MiG 21 had all-moving tailplanes or stabilators. When rolling, did one stabilator pitch up and the other down to act as secondary ailerons and help the main ones on the wing?
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$\begingroup$ This video should at 6.35 gives a good view of a roll - no tailplane activity. youtube.com/watch?v=uePIzbYI7BU $\endgroup$– Party ArkJun 20, 2020 at 11:58
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$\begingroup$ Spoiler alert - no, the stabilisers didn't pitch when rolling in the video. $\endgroup$– Harshil SharmaJun 20, 2020 at 12:56
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$\begingroup$ "Spoiler alert - no, the stabilisers didn't pitch when rolling in the video"-because is 1 G rolling maneuver. $\endgroup$– George GeoJun 20, 2020 at 13:05
1 Answer
No.
MiG-21 (any modification) didn't need it and didn't have it. With its low-aspect-ratio delta wing and most mass concentrated in the centre, it was agile enough with standard ailerons.
The elevator had a single hydraulic booster driving both halves of the stabiliser.
Differential stabiliser was used on MiG-21's successor, MiG-23. That one had no ailerons at all; it had full-span flaps on its swing wing instead. Roll was controlled by the spoilers and the differential stabiliser.