Originally Posted by
JohnDixson
Thanks, Shy, but it seems I totally misunderstood the use of “ jackstall” in connection with several events involving Gazelles. I thought it signified a condition wherein the maneuver control loads exceeded the force capability of the servos, hence the cyclic became stalled or immovable. What did it in fact mean?
John, Your understanding of the occurrence is correct. Once the feedback forces overcome the maximum available hydraulic pressure, one or more of the jacks obviously do "stall". The PRV in the hydraulic system can only have been there to prevent something in the hydraulic system bursting, possibly the pump drive shearing, or something powered by it breaking, when this occurred. However, you asked if the aircraft was ever modified to overcome the phenomenon. To do so would certainly have required a lot of components to be beefed up, probably including the airframe itself, which is why I gave the answer I did. Seems logical to me that the design philosophy is to protect the airframe at all costs, even at the expense of temporary loss of control if the aircraft was flown beyond its normal limits (and one had to be more than a little ham-fisted to jackstall a Gazelle).