John T,
I should point out that the 4-step recovery procedure I stated was written for an audience of students flying Cessna trainers. The stalls I was talking about were level, 1G stalls that may or may not produce a wing drop. It does apply, in general, to other airplanes but there are other factors - that you've mentioned - that would need to be considered.
it might be preferable to emphasise unloading to reduce alpha with the aim of unstalling .. the recovery, say, to straight and level flight occurs post unstall.
Yes, "unloading" would be a more correct term for all airplanes.
that's a little in the way of innovative thought. If one is looking at body axes, I would have expected the elevator to produce pitching moment only ?
The flight controls always control the airplane relative to its axes but bear with me as I try to explain what I was meaning.
In most planes (except model airplanes and very high-powered aerobatic airplanes) the engine power is insufficient to 'pull' a plane out of a stall. I've seen model airplanes stall, with power at idle, at around 30-50 degrees nose up and as soon as the airplane stalls and the nose starts dropping, the operator slams full throttle and the engine literally pulls the airplane out of the stall and puts it into a vertical climb! Now that's a good power-to-weight ratio! Since virtually all airplanes don't have that capability, there needs to be another way to accelerate the airplane back to normal flying speed - this is assuming a 1G stall condition where the airplane is slightly below stall speed by the time the pilot starts recovery.
The answer is: gravity! The nose must go down
because the airplane is going down. If the airplane stalls and starts descending from level flight, the airplane will go deeper into the stall if the attitude is not lowered.
Since the airplane is descending, movement of the nose away from the ground is not conducive to stall recovery. The aircraft's bank is really not a factor in this.
You're 100% correct that rudder only ever yaws the airplane and elevator only ever pitches the airplane - I could probably write that paragraph better. However, considering a 45 degree bank to the left, applying right rudder would yaw the airplane to the right, which in this case, would
raise the nose of the airplane away from the ground. If you were to use elevator instead - you will point the nose towards the ground, and since the airplane is traveling towards the ground, that will automatically decrease the angle of attack. There really isn't much 'load' on the wings at all at this point - gravity is pulling the airplane down and the aerodynamic forces aren't enough to oppose it. If you're at the critical angle of attack, you can unload the wing by either reducing angle of attack or increasing angle of attack - the former is usually more preferable!
AND decrease the directional deviation (yawing moment) from its heading.
can you walk us through just how this occurs ? Sometimes I'm a tad slow picking up the details ...
When the airplane is at the stall and there is a wing drop, the longitudinal axis usually gets tilted off the heading in the direction of the roll. This is due to the airplane not only rolling but 'falling' towards that side due to the sudden decrease in required lift on that side. So when the airplane has 'wing-dropped' to a 45 degree angle of bank, the longitudinal axis would be pointing 10-15 degrees (maybe more, maybe less) off the heading that the stall was initiated on. By pitching down, while at 45 degrees of bank, you will move the longitudinal axis back towards the initial heading.
Increasing thrust significantly while stalled (ie high alpha) may result in significant and undesirable nose up pitching moments, especially for larger engines. Pitching motion potentially may give rise to undesired yawing moments.
You do bring up a good point! Every airplane will be different and I think the specifics of each should be addressed when training to fly that specific airplane.
As to target speed, that would depend on circumstances and priorities on the occasion.
Definitely.
Straight and level flight should be established with full coordinated use of the controls
one presumes that we are referring to post unstall ?
Yes.
In earlier days, it was expected that pilots would be highly attuned to prestall warnings and would be able to recover post warning prior to entry into the stall environment. For many aircraft this was quite feasible with little or no height loss .. indeed, for some of the larger turboprops at low to mid weights, the exercise involved power up and climbing out of the prestall situation ..
I know that there are lots of airplanes that can not only not lose altitude, but can start a climb in a few seconds after power is applied. I don't think a lot of these people realize that the conditions in which you're getting a pilot to recover with zero altitude loss is completely different from what that pilot would encounter in an operational environment. If a pilot has gotten so slow that he hears a stall warning I think it'd be safe to say that he/she has less than the required situational awareness for that phase of flight. In pretty much every case, the pilot wasn't expecting the stall warning to come on - if they had expected it, they would have taken action to fix the low speed situation.
So in one case (training flight) you have a pilot who's purposefully slowing to the stall warning with the express purpose of applying maximum power at the instant the stall warning goes off and then carefully flying the airplane to maintain altitude - that's a precision flying maneuver. In the other case, you've got a pilot who's lost situational awareness, is startled/surprised when the stall warning does come on, and by the time they initiate a recovery action the airplane could very well be well into the stall. Adding power at that point would not be ideal because if there is any sort of differential thrust created you risk flipping over. Looking at the height at which the airplane stalled in the majority of stall-accidents you should be able to see that zero altitude loss isn't/should be a priority!
The line pilot is far more interested in the real world operational imperatives of
(a) not hitting the hard bits
(b) getting back to where the aeroplane was intended to be
I agree with that. But it's becoming apparent these days that pilots don't have the skills and/or training to achieve their operational goals of not destroying an airplane!
At least, in recent times, we have been seeing a pronounced move away from the minimum height loss philosophy.
I'm glad to see that but it seems it's going to take awhile for everyone to get the memo.