To: Grey Area
“This is not so much a design flaw as a flight limitation, and common on small helicopters with parallel flying controls”.
You’re statement above is basically the same as the cautions placed in the Robinson POH which restricts the pilot from flying out of trim and from sideslipping the helicopter as something bad will happen if the pilot violates the cautionary statements in the POH.
Both the restrictions on the Aerospatiale products and the Robinson are to compensate for a design flaw.
From what I understand the Aerospatiale helicopter in this discussion has a hydraulic system that could be considered low pressure by comparison to the systems used in other helicopters. I would assume that the pump used is a constant displacement pump and I would assume that because of the existence of the jack stall problem it does not have an accumulator and if it does, then it is of low displacement.
What I visualize happening is that under certain maneuvering conditions there is a high demand on the hydraulic supply system. This causes a pressure drop in the system and if the pressure drop is sufficient, the bypass valves in the servos open and the jack is now part of the control linkage and the feedback forces can pass through the jack. Upon the cessation of the demand on the hydraulic system the pressure builds up and the bypass valves close and the jack is now operational.
This is a killer just like having high flapping loads on the Robinson. The protection of the pilot rests on a few words in the respective POHs and not by proper system design.
Regarding the French logic in using words to describe something when I was working in the Service Department at Sikorsky we got a telex from the French Forces in Algeria asking something about the dirty link. This caused some confusion so we asked them to identify the part number under discussion. The number provided was for the sloppy link on the primary servos. It seems that the French did not have a word for sloppy so they figured that sloppy equated to dirty.
[ 05 December 2001: Message edited by: Lu Zuckerman ]