Superb primer by Wg. Cmdr. Vikram Singh, in plain English. I am glad that the LCA team is openly publishing the characteristic, challenges and testring strategies etc. I am not sure if this is unique to LCA or if other countries publish so openly as well.
It appears that the testing philosophy is "Departure prevention" rather than actual "spin recovery", while being prepared for an actual spin recovery in the event of a departure.
I am quoting some pieces here because it is extremely interesting for me personally and I am assuming it will be for some of you as well.On some of the challenges:
The correction factors are initially estimated from CFD studies andwind tunnel measurements and therefore can have significant errors especially attransonic Mach Nos. Thus in any new combat aircraft programme a significant part ofthe flight test programme consists of experiments which are directed towards aero datavalidation and air data calibration. Based on the flight test results and the closeness ofmatch with the corresponding wind tunnel data the envelope is systematically expandedin stages to ultimately cover the boundaries including the nonlinear high angle of attack regimesOn testing Philosophy:
However, a full investigation of HAoA characteristics of a highperformance ac including spinning is a very high risk, high cost and time consumingproposition. Considering the large number of external stores configurations and theneed to clear a two seater version, the test campaign could well take a few years ofwork up, flight test, analysis, re design and certification.On recovery techniques
it was decided that the ac would not be intentionally spun.Departure prevention, rather than spin recovery, will form the basis of test philosophywith full preparation for an OOCF event and its recovery.
(a) Recovery With Control Surfaces
(i) Deflect full OUT-SPIN rudder simultaneously with IN-SPIN aileronsfollowed by down elevator after 2 sec delay. Recovers within 2 turns.
(ii) Some other configurations (stores, zero slats etc.) showed moredifficult recovery.
(iii) Some configurations required 18.5 deg In-Spin Aileron(e.g. Zero Slat, A/B etc.)
(iv) Some configurations required 25 deg In-Spin Aileron(e.g. Ext. Store configs.)
(v) Recovery from Inverted Spins easier (Neutral Aileron sufficient)
(b) Recovery With Spin Parachute
Restore rudder and aileron to NETURAL.After a delay of about 2 secs, deploy parachute and restore elevator to neutral.Recovery within 2 turns.