autotrim, stall warning, stable stall, et al...
Hard to keep up, and I am a very fast reader.
- Zorin asked about the autotrim, and others have tried to figure it out. From what I see of the tech manuals and inputs from other contributors, it looks like a basic way of providing the elevator the most authority and reducing the drag of an elevator that is "x" degrees deflected to maintain the current gee or AoA command.
Bear in mind that my primitive FBW system did not have an elevator at the rear of a horizontal stabilizer ( HS). The whole HS moved for pitch commands.
As with the 'bus, HAL "auto trimmed" to our gee command trim setting. Unlike the 'bus, we could trim for a gee, and not be limited to a one gee command.
- Gerard asked a great question, and it is one of mine.
What was the "stall warning" all about after the pilot pushed over a bit?
- Chris brought up the relatively benign deep stall characteristics. It's what got me joining this august grope of "experts", wannabe's and actual 'bus drivers. And others.
All who have flown a delta wing raise your hands! Concorde counts. Mirage variants count. The one I flew as a yute was so deceptive that it was scary - F102. Very slight "buzz", but no real buffet or burble. Great directional stability and lateral stability. But the altimeter was pegged at 10,000 feet per minute going down.
The modern commercial heavies have really great aero characteristics that can make a stall insidious. And the stall is not like the Airbus manuals depict on the lift versus AoA curve. There is no sharp break in the curve at "x" AoA. It's a very gentle curve and one can fly at fairly extreme AoA's without the sharp pitch excursion we all saw when checking out in a Chipmunk or Cessna or T-28 or......
The problem occurs when the jet reaches a certain AoA and c.g. and speed combination that prevents normal pitch down commands from being effective. It's that pitch moment graph I posted years ago ( heh heh).
The test pilot maneuver resulting in a deep stall that I posted was not the classic entry to a deep stall in the Viper. The classic entry was a fairly steep pitch, low gee, rapidly slowing speed, and running outta air molecules for that HS or THS to use to get the nose back down. Does that sound relevant here?
I gotta admit, that from this old fossil's FBW experience and perspective, that there are too many autopilot functions embedded in all the 'laws". The jet seems perfectly capable of flying to the basic limits that all the heavies, if any, can match. And my problem is the "basic" limits seem to take short shrift behind roll angles, autotrim, mach warnings, etc. etc. ad nauseum. Then I read here that one reversion law commands the motors!! BEAM ME UP!! If not in some autopilot mode, let the plane fly. Sheesh.
I thank all here for allowing a "lite" pilot with some FBW experience back when the Earth was still cooling to participate. I am now SLF, and I wanna feel comfortable about the jets I ride in.