spleener:
MD-11 LSAS, Longitudinal Stability Augmentation System.
This is copied from the MD-11.org web study guide (great page, by the way)
LSAS provides:
1) Pitch Attitude Hold and Automatic Pitch Trim –With no force
on the control column, and bank angle less than 30 degrees,
LSAS holds the current pitch attitude. LSAS holds this attitude
by deflecting the elevators as much as 5 degrees. The
horizontal stabilizer is automatically adjusted to relieve the
sustained elevator deflection and maintain a full 5 degree
elevator authority.
2) Pitch Attitude Limiting –LSAS maintains pitch attitude to less
than 10 degrees of dive, or less than 30 degrees of climb.
3) Pitch Rate Damping – Increases the apparent static stability to
reduce the chance of over-control in pitch. It is active
throughout the flight envelope. 100% of max damping is
available above 20,000ft, decreasing linearly to 30% below
16,500 ft.
4) Speed Protection – If the autopilot is not engaged and the
autothrottle is not available (or able to maintain a safe speed),
LSAS Speed Limiting will engage to provide overspeed or
stall protection. LSAS overspeed protection is accomplished
by changing pitch. LSAS does not provide flap, slat or gear
overspeed protection.
5) Stall Protection – At 75-85 pct of the angle of attack required
to activate the stick shaker, the LSAS stall protection engages.
LSAS reduces pitch until the AOA is sufficiently reduced.
6) Pitch Attitude Protection and Positive Nose Lowering -During
takeoff rotation, LSAS provides Pitch Attitude Protection
(PAP) to reduce the possibility of a tail strike. During landing,
after spoiler deployment is commanded, LSAS initiates
Positive Nose Lowering (PNL) to assist in transitioning the
nose wheel to the runway after main gear touchdown.
The picture referenced by ManAdaSystem in post 19 showing a KLM MD11 on final approach and the tailplane angle indicates a real problem. I have seen MD11s with this absurd tailplane incidence many times. Does it not show a fundamental misdesign? The wing is evidently too far back- it even looks it. The tailplane is desperately trying to provide enough downforce. Put yourself in a baulked landing with low airspeed and you then have a real problem trying to hold the nose up. If the pilots had full back elevator and the nose still fell like that, then this aeroplane should be withdrawn from service.
I have read a lot of nonsense in pprune. But that has to take the cake
