Here is something that is only relevant to the -500 model of the Lockheed L-1011. The active control system provides a means of relieving loads caused by the increase in wing span on the -500. Load relief is accomplished by outboard ailerons symmetrical deflections programmed by the Active Control System (ACS). The ACS is dual channel with either channel capable of performing the proper programming of aileron deflections. The system uses a revised outboard aileron servo with 2 ACS series servos (1 and 2) mounted to each outboard aileron servo . Triple accelerometers located in each wing tip and forward cargo compartment ceiling (9 total) provide the acceleration signals, and 3 impact pressure (Q) sensors provide airspeed affect for gain scheduling.
Great write up. I was the principle engineer on the ACS and can answer any questions you have. This was another Lockheed first. It was the first commercial airplane to be be certified for use of electronics to satisfy load design criteria. FAA and CAA realy didn't trust that the ACS would be there when needed. This was also digital which made it very hard to identify failure modes and ensure that there would be no latent failures that would show up during ultimate turbulence and disconnect the system when needed.
ReplyDeleteFor example, one of the problems was hydraulic starvation caused by the huge hydraulic actuators on the horizontal tail sucking down the pressure to the outboard ailerons servos. If the horizontal stabilizer was moving at max rate, there was little left for the ailerons and the servo responses became nonlinear which could cause the servo monitors to disconnect thinking there was a fault. We did some special detection threshold scheduling that sensed the magnitude of the command and opened the thresholds to keep the system operational.
We tested this condidion at Rye Canyon iron bird and nearly broke the lab with these huge surfaces moving at max rate with simulated ultimate turbulence. But the ACS hung in there and the accelerometers didn't fall off.
The airplane was allowed to fly with the ACS inoperable for a while until a convient maintenance depot could repair it. It was only needed when in ultimate turbulence and this was a remote enough condition to expose the airplane to and still maintain the proper level of risk.
Hello VAMFUN. Sorry it took me so long to reply to your posting on my blog here. I would like to stay in touch with you. Could you please contact me? Yes, I would like to learn more about that ACS and especially I would like to learn more about your involvement with the L-1011 development. I think you have an amazing story there! If you could, please contact me at curdzechmeister@gmail.com.
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