---------------------------------------------------------- Commander-List Digest Archive --- Total Messages Posted Sat 04/14/07: 1 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 04:09 AM - Re: Re: Servo Failure (Steven) ________________________________ Message 1 _____________________________________ Time: 04:09:55 AM PST US From: "Steven" Subject: Re: Commander-List: Re: Servo Failure John, I've got a pretty good article on the Bendix servo. Monday I can scan the thing and post it to our company's website. If the fuel boost pump pressure and the engine fuel pump pressure were about the same, I can't see that the servo should care which one is feeding it. (For the single speed IO-540 pumps). >From what I understand (and it's limited) the servo is set up on the bench for normal aircraft fuel pressure. All things being equal, if you change the ship's fuel pressure, you change the fuel flow. For example at W.O.T, setting the engine driven fuel pump pressure up and down will have a direct relationship to the fuel flow. The last 'rebuild' on our servo came back twice with a wide open throttle fuel flow lower than what we hoped to see. The second time was better, but we compensated somewhat by running slightly higher fuel pressure on the right side. With this last rebuild it's finally right, but with us running the right engine fuel pressure toward the high end of the green arc, the WOT fuel flow was now too high, and the ship's fuel pressure was dropped back to the middle of standard. On the IO-540's the 'fuel flow' isn't really a measure of flow, but another measure of pressure, this time at the fuel distribution spider. Plug an injector and it would appear you've got more flow, when all you've got is really more pressure. Also keep in mind with these servos that with differential pressures being used, some of the failure modes are fuel crossing to places it shouldn't ought to be. I think everything I said is true. Steve Also Robert, keep in mind that you're flying a Continental-powered Commander, so you have low & high boost pump settings. Us Lyc-powered guys only have "on" and "off" :-). And Steve, the theories sound good. I wonder what effect the failure of an engine-driven pump would have on the fuel pressure? Is the servo self-regulating or is the EDP always the first link in the fuel pressure management process? Being just the guy who pushes the levers around in the cockpit, I'm probably light on the more esoteric points of the IO-540's systems. Perhaps it's time to rectify that. I'm going to dig around and see if I can find any articles or other documentation on boost-pump-related engine floodings on approach. I've seen ONE story along those lines related to Commanders, but I don't remember which model the author was flying. I want to assume a 500A or 685 because of all the Bonanza-specific issues I've heard about with the hi/lo boost pump settings & engine floodings, but I don't know that the Lycs are immune to similar occurence. /J ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message commander-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/Commander-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/commander-list Browse Digests http://www.matronics.com/digest/commander-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.