Frederf Posted December 4, 2021 Posted December 4, 2021 I attempted to takeoff according to MiG-21bis Pilot Flight Operating Instruction, Day Circuit Flying, Concrete-Runway Takeoff without much success. ISA atmosphere, no wind, no stores, 50% fuel (7500kg) as assumed to day circuit flying training. Expected Engine stabilized at takeoff power setting before brakes release Upon 150-200 km/h control stick back 75%. Upon 250-270 km/h nose wheel unstick. Rotate to takeoff attitude: base of pitot at horizon, UUA-1 11-13°. Upon 340-360 km/h main wheels unstick. Retain liftoff pitch angle without airplane tendency to balloon or stall Retract landing gear at 10-15m height Retraction of flaps below 100m involves a controllable nose down moment No significant difference is expected with ventral tank, and up to two missiles or two UB-16 pods Unstick speed and takeoff length increases with heavier loads Manual Chart 8500kg, 11°, 760mmHg, 0m/s = 340 km/h unstick (320 km/h at +2° UUA) 8500kg 345 km/h unstick, 725m run, 900m rwy req., +10-15% reheat, +20-25% full throttle Actual Full throttle take off is impossible without grossly exceeding safe pitch Nose wheel unstick at 290 km/h lightweight (7500kg), 305 km/h medium weight (9300kg), 308 km/h heavy weight (10400kg) If pitch of 4-5° is used, UUA-1 is 11-13° and base of pitot at point of vane attachment is level with horizon If pitch of 7-8° is used, UUA-1 is >15° and base of pitot support boom at attachment to fuselage is level with horizon 8500kg passing 834m is only going 257km/h in full reheat. The idea of unsticking with full throttle takeoff at 11° UUA-1 within 906m run as predicted is unthinkable. With lightweight (7500kg) config the following are unstick distances and speeds at full reheat for nose wheel, main wheel with 5 degree technique, and 8 degree technique respectively. NWU 992m @ 290 MWU-5 1850m @ 374 MWU-8 2080m @ 378 === Acceleration of airplane during takeoff roll is insufficient to meet documented performance. UUA-1 produces too high of a reading at takeoff attitude or takeoff attitude does not produce a takeoff Takeoff run distances in some configs are approximately 200% of their charted values 4 9
MiG21bisFishbedL Posted December 4, 2021 Posted December 4, 2021 (edited) It's been like this for sometime. Nice to see someone put in the effort and numbers, at least. A track would be nice to have, as well, as a reference at least. Edit: Just flew to confirm. Unstick of nosewheel happens well past 250km/h. Not surprised, that's what I usually see it at, lol. Edited December 4, 2021 by MiG21bisFishbedL Reformers hate him! This one weird trick found by a bush pilot will make gunfighter obsessed old farts angry at your multi-role carrier deck line up!
Hiromachi Posted December 4, 2021 Posted December 4, 2021 Track and reference would be good indeed, but optimally Frederf, you should add this (if you want it to be treated as bug report) into Mantis. 1 AMD Ryzen 5900X @ 4.95 Ghz / Asus Crosshair VII X470 / 32 GB DDR4 3600 Mhz Cl16 / Radeon 6800XT / Samsung 960 EVO M.2 SSD / Creative SoundBlaster AE-9 / HP Reverb G2 / VIRPIL T-50CM / Thrustmaster TPR Pendular Rudder Pedals / Audio Technica ATH-MSR7
Maxthrust Posted December 10, 2021 Posted December 10, 2021 (edited) On 12/4/2021 at 1:53 PM, Frederf said: I attempted to takeoff according to MiG-21bis Pilot Flight Operating Instruction, Day Circuit Flying, Concrete-Runway Takeoff without much success. ISA atmosphere, no wind, no stores, 50% fuel (7500kg) as assumed to day circuit flying training. Expected Engine stabilized at takeoff power setting before brakes release Upon 150-200 km/h control stick back 75%. Upon 250-270 km/h nose wheel unstick. Rotate to takeoff attitude: base of pitot at horizon, UUA-1 11-13°. Upon 340-360 km/h main wheels unstick. Retain liftoff pitch angle without airplane tendency to balloon or stall Retract landing gear at 10-15m height Retraction of flaps below 100m involves a controllable nose down moment No significant difference is expected with ventral tank, and up to two missiles or two UB-16 pods Unstick speed and takeoff length increases with heavier loads Manual Chart 8500kg, 11°, 760mmHg, 0m/s = 340 km/h unstick (320 km/h at +2° UUA) 8500kg 345 km/h unstick, 725m run, 900m rwy req., +10-15% reheat, +20-25% full throttle Actual Full throttle take off is impossible without grossly exceeding safe pitch Nose wheel unstick at 290 km/h lightweight (7500kg), 305 km/h medium weight (9300kg), 308 km/h heavy weight (10400kg) If pitch of 4-5° is used, UUA-1 is 11-13° and base of pitot at point of vane attachment is level with horizon If pitch of 7-8° is used, UUA-1 is >15° and base of pitot support boom at attachment to fuselage is level with horizon 8500kg passing 834m is only going 257km/h in full reheat. The idea of unsticking with full throttle takeoff at 11° UUA-1 within 906m run as predicted is unthinkable. With lightweight (7500kg) config the following are unstick distances and speeds at full reheat for nose wheel, main wheel with 5 degree technique, and 8 degree technique respectively. NWU 992m @ 290 MWU-5 1850m @ 374 MWU-8 2080m @ 378 === Acceleration of airplane during takeoff roll is insufficient to meet documented performance. UUA-1 produces too high of a reading at takeoff attitude or takeoff attitude does not produce a takeoff Takeoff run distances in some configs are approximately 200% of their charted values M3 has not touched up the -21 in a long while. There has been other slow speed AoA/G availability discussion before which received the same runaround from M3, hence the dead forum. Edited December 10, 2021 by Maxthrust
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