Thank you for sharing those videos.
However for LCA, they are not going to have the pilot induced OOCF (our-of-control flight). They will stick to prevention rather than recovery.AN APPROACH TO HIGH AoA TESTING OF THE TEJAS LCA
Overall Test Philosophy.
Modern fighter aircraft are designed to be flown near their maximum performance limits to capitalize on advantages over other aircraft.This can result in departures from controlled flight. A pilot rarely enters out-of-control flight intentionally. When it does occur, it’s usually in a dynamic and disorienting manner. Due to the normally forgiving handling qualities of the Tejas and its contemporary aircraft, OOCF incidents are quite surprising to the pilot and challenging,violent and unexpected motions can be encountered. This testing must therefore be extremely thorough so that hidden traps are not passed on to the user where costs are likely to be high. However, a full investigation of HAoA characteristics of a high performance ac including spinning is a very high risk, high cost and time consuming proposition. Considering the large number of external stores configurations and the need to clear a two seater version, the test campaign could well take a few years of work up, flight test, analysis, re design and certification. Given the Tejas’ flat, fast and oscillatory nature of predicted spin modes, the sharp cliffs in critical stability derivatives and the internationally evolving philosophy of testing departure prevention rather than post departure behaviour, it was decided that the ac would not be intentionally spun.Departure prevention, rather than spin recovery, will form the basis of test philosophy with full preparation for an OOCF event and its recovery. In this regard it may be recalled that in the recent CFH test campaign of the BAe Typhoon II ac not a single departure was encountered and the spin chute was never used, although the ac was subjected to every combination of OOCF causing events. Further, although several spin recovery techniques have been identified in the vertical tunnel experiments, no recourse to a “piloted” recovery will be made and the spin chute will be used immediately on departure to protect hydraulics and provide fastest possible recovery.
They know how to recover the aircraft using just the controls. But, that was predicted to be risky and avoided by going for the spin-chute if departure happens.
What is interesting is that LCA has been cleared for 26 degree AoA (the maximum that they wanted to achieve) without any aircraft being fitted with a spin-chute (or did I miss it)! So did LCA show better authority than predicted?In the JSF, the recovery seems to be left to the flight computer
Clearly, the spin recovery technique is an involved procedure requiring good orientation(knowledge of spin direction) and timing of controls. This is not a satisfactory situation considering the very high rates of rotation and build up of longitudinal acceleration at the pilot’s location. During several similar programmes abroad it was decided that the max negative longitudinal (nx) acceleration permissible at the pilot’s location is –4g. Beyond this value the pilot would not be able to assume the correct posture to eject. As estimated from the vertical tunnel tests, the spin axis would pass through a point between the pilot and the ac cg. This point would move backwards and finally pass through the cg. Thus the ‘eye balls out’ acceleration felt by the pilot would continue to increase. Considering all the above, no attempt to recover the ac through use of controls would be made and spin chute would be deployed immediately the CAS drops under chute operating limits.
. This is very interesting and ideal (IMHO) because the computer is not prone to the limits of the human body. However, it requires excellent sensors and algorithms which can identify when the plane has departed and when not. If they have perfected this, they deserve credit. In case of LCA, CLAW will momentarily relinquish control to the pilot to recover the plane
Peculiarities Of A Fly-By-Wire Configuration And Impact Of Full Authority Flight Control System.
As opposed to conventionally controlled ac, in the case of a full authority closed loop control ac such as the LCA, departure will cause the controls to oppose the ac motion. Since little response will be seen to these inputs, the controls will hard over at up to max actuator rate. Thus oscillatory post departure/spin characteristics will cause full deflection, max rate, and oscillatory deflections of control surfaces, which will result in large hydraulic system demands. If the engine flames out,the emergency hydraulic pump will not be able to cope with this demand and will stall or cavitate. Therefore the emergency hydraulic system must be capable of supporting these control system actuator demands. Further, the control system will apply out spin roll controls, which in the case of the Tejas, post stall AoA, will be pro spin. Therefore to be able to achieve quick and full recovery it is desirable to provide the pilot with full and direct control surface authority. LCA being a highly augmented aircraft, under normal flying conditions, the control laws significantly reduce the pilot’s command authority over the control surfaces. Therefore, in the post stall flight regime the control laws should be inhibited from reducing the pilot authority over the control laws and this is achieved by incorporating an additional pilot selectable spin recovery mode in the control laws which disconnects the feedbacks from the inertial sensors and scales the pilot stick input to give full authority over the control surfaces. However, as the Tejas is unstable and unflyable without the CLAW, the ac will have to be stabilized by a spin parachute before the pilot takes over manually.