Mad (Flt) Scientist, John_T, AirRabbit,
I read loud and clear where you’re coming from, I entirely agree that unless the simulator has been programmed for, and validated by flight testing for a particular flight regime, it is indeed negative value to provide training in such an area. I agree, too, with
AirRabbit that the Roll / Pitch response available from the simulator may not extend to the degree required to accurately accommodate a particular aircraft’s response/s at and beyond the stall.
My (work induced) late response to reactions to my proposal that pilot training in the simulator should be extended to the fully developed stall is fortuitious in that
AirRabbit has reduced my typing load in providing the key to what I was trying to say, i.e.
It would be quite an expansion of the simulator flight model development to allow other than generic training for the stall and post-stall regime
Generic training was the point that I was trying to make. Pitch / Roll rates etc. need not be accurately representative of that which might be encountered in an actual stall, as an example, it matters little if a ‘wing drop’ is at 90°/sec or 180°/sec, provided that the response was appropriate, i.e. a wing drop is precipitated by certain action (or inaction).
My concern is that fully developed stalls do occur, they carry a very high fatality rate, and pilots have no training in the disciplines to be used in recovery from the fully developed stall. To refer to my earlier quote -
Control and recovery procedures differ considerably from their earlier full stall training on prop aircraft, and the application of the intuitive responses learned at this phase could be disastrous
In comparing a pilot’s intuitive response learned on straight wing propeller aircraft, there are some VERY significant differences –
(1) Approach to stall – On the prop aircraft, it’s control wing drop with rudder, don’t even breathe on the roll control. Fatal for the swept wing jet, where it’s RAPIDLY correct wing drop with roll control, don’t even breathe on the rudder. During deliberate stall tests on jets, it’s a case of feet OFF the rudders, engine synch ON, Yaw Damper OFF – all to avoid any yaw moment.
(2) Stall encounter – For the prop aircraft, elevator effectiveness is usually not a problem. It may be for some T-tailed types, but power application is usually sufficient to restore airflow over the tail surfaces. For the T-tailed jet the elevator can become almost useless, particularly if it is a control tab system such as the DC9 (You get one guaranteed shot from the accumulator
Ignition Override, no-one was brave enough to see if a second one was available). Any forces applied causing further pitch up (e.g. tip stall, thrust application from underslung engines) may not be manageable with elevator control alone. Here, the correct use of stabilizer trim is essential, as the much larger stabilizer can be one’s worst enemy or best friend. It’s essential to cease trimming during deceleration at about Vref, such that positive back elevator is required to induce the stall. A stabilizer trimmed ‘to the stall’ will not be ‘lift producing’ if the elevators are relaxed, whereas if trimmed to Vref, it is immediately lift producing upon elevator relaxation, and a good degree of ‘self recovery’ from the stall is possible merely by just ‘letting go’. In the unfortunate event of going beyond the full stall to the deep stall, running stabilizer trim forward may be your only saviour.
(3) Stall Recovery – On the prop aircraft, it’s simultaneously apply maximum Power and forward elevator. A smooth pitch up can be commenced almost immediately due to the slipstream effect of instantly recovering a large portion of the wing from the stall. On the jet aircraft, it’s a case of apply forward elevator, and only when the aircraft has responded with a pitch down, apply full Thrust. The delay between the two actions is essential for several reasons, one importantly being that asymmetric spool-up right at the stall is disastrous. For the rear engined aircraft, compressor stall is highly likely until the wing is first unstalled, aside from engine damage, the ensuing thrust asymmetry is unacceptable. For the wing mounted underslung engined aircraft, a thrust induced pitch-up at the stall is asking for very big trouble, and again thrust must be delayed until the wing is unstalled and a reasonably normal elevator authority is returned. Pitch up after the initial stall recovery must be MUCH slower than for the prop aircraft. Even at full thrust, there is no significant increase in air flow over the wing, and it’s necessary to wait until the speed has increased before gently pitching up. The intuitive ‘prop aircraft’ pitch up inevitably leads to a secondary stall, something I’ve observed with countless trainees during recovery from THE STALL WARNING, without ever venturing to the fully stalled condition in the first place.
All of the above is why I’m a strong advocate of teaching fully developed stall training in the simulator. I have done full stall evaluation on 3 aircraft types, all of them T-tailed, and for the reason that the regulatory authority required to be fully satisfied that ‘deep stall’ provision had been adequately made. This was particularly so for 2 of these types where wind tunnel evaluation indicated a significant ‘deep stall’ potential in their original configuration, and the effectiveness of preventative systems (in these cases, strakes) proven. Deep stalls were repeatedly attempted, but in all cases the prevention / recovery systems were fully effective. The simulator was being developed in parallel with the flight testing, and much of the stall responses immediately passed on to the simulator engineers who reproduced it quite well. Much of it was subjective, but with particular emphasis on the yaw/roll relationship approaching the stall, well incorporated. The latter merely required crossover response data with appropriate ‘break point’ insertion into the code. The generic responses are programmable, and, in my view, important to demonstrate in these areas –
(1) The danger of any yaw input approaching the stall,
(2) The effectiveness and ESSENTIAL use of roll control down to the stall,
(3) The ineffectiveness of the elevator at the stall,
(4) The essential need to NOT trim the stabilizer to the stall, and it’s effectiveness for deep stall recovery if used appropriately,
(5) Thrust must not be increased until initial stall recovery is accomplished (Compresser stall, pitch up etc.)
(6) The need to exercise much slower pitch up following stall recovery to prevent secondary stall.
I consider these criteria essential to incorporate due to the significant differences to that which the pilot was taught during earlier ‘prop’ training. Again, I say that most of the very occasional catastrophies following a full stall on Transport aircraft are preventable
WITH TRAINING. The techniques taught on propeller aircraft, and for recovery from the stick shaker on transport aircraft are inappropriate if the full stall is encountered.
I have deliberately NOT mentioned the aircraft types involved here, lest someone might try it, and it should be stressed that individual aircraft types will vary considerably, as does the same aircraft in different circumstances. Even the generic comments which I’ve made here are for T-tailed aircraft, I’ve not done any of this work on conventional aircraft. When I was press-ganged into doing this work, it was not until after hundreds of hours of observation of wind tunnel test results, and many flights with test pilots that I went ‘solo’ in any of this work. I will add my name to the list of those giving caution here, until you have been exposed to a lengthy preparation process, and accompanied by a test pilot for training purposes, and you are in a very controlled environment, and you are flight testing in an already proven corner of the envelope,
DON’T_EVEN_THINK_ABOUT_IT!
Fly Safe, fly in the KNOWN area,
Old Smokey