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captainglen

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  1. captainglen

    Fuel Leak

    By captainglen,

    To a lot of Mooney owners a fuel leak can seem quite intimidating especially to those owners who do not hold an A&P rating. I must admit that I was intimidated at first. A small amount of leak (a seep) is permitted per the Mooney service manual as long as it is not into an unvented area so top of wing or gear bay is permissable but cabin, outboard wing area or leading edge are not.
    My seep was into the leading edge and over 4 months drained the left tank dry; not enough to leave a stain on the ground but enouch to stain the stain the bottom of the wing adjacent to the leading edge drain hole. This meant the leak had to be at the bottom inboard corner and the blue fuel dye stains confirmed. As it turned out the hardest part of the job was getting the tank inspection cover open without damaging the wing. Scraping the old sealant was a bit tedious but really only took a couple of hours.
    Using a A-2 gave a lot of work time on a cool day and working with a brush which I had trimmed the bristles to 1/2". I sealed way beyond the leak area to make sure that no fuel could work it's way under the repair.of course I cleaned the area and roughed the surface of the factory sealant.
    To close the tank I used an B-2 wich is not what I would reccomend because it is way to slow, a B-1/2 would be much better. There is an A/D to inspect the stringer and rib drains to make sure you have not clogged them before you close the tank. I allowed a whole week to cure before filling the tank for a leak check and another week before checking for leakage. I am absolutely 100% leak free for $80 worth of supplies.
    For those among you who are not certified mechanics there are mechanics who are willing to work with owner assistance. I know of one on my home field who supervised a non mechanic owner in replacing an entire cylinder set (top overhaul). There isn't much room inside the tank for two pairs of hands but most mechanics would gladly defer the prep work to someone else.
  2. captainglen
    The Davtron indicator had to be removed due to indication incorrect pressure altitude. A continuity check of the harness found no errors in the wiring so the problem had to be elsewhere. Checking altitude encoder grey codes found that the B4 had to be high when it should have been low so there must have been a short. The only nearby high was the C1 so the short had to be here. An inspection of the connector under magnification revealed a tiny bead of solder between the pins of B4 and C1 which I pried out with a sewing needle.
    The indicator now reads accurately and is ready for reinstall in the aircraft. It is essential that this unit function correctly not only because of it's importance in calculating takeoff performance but any inaccuracy will be shared by the transponder. ATC will rely on the altitude reported be the transponder for traffic seperation so the utmost care must be taken to insure that the Davtron indicator to insure that the Davtron indicator does not interfere with the function of the transponder.
    The temprature probe location on the bottom of the aircraft near centerline 16" behind the baggage compartment bulkhead is not ideal but is a reasonable comprimise to the reccomended location. On top is out of the question becaude it will sense skin tempreture heated by the sun. In flight the probe should have little or no effect from the engine exhaust stream or engine heat trail from the cowl flaps. The readings should provide more accurate TAS calculations than could be obtained from the old fashion Aerotherm gague.
  3. captainglen
    First a note of explanation: a manifold pressure gague is an absolute pressure gague. What this means is that it is an uncorrected barometer connected to your intake manifold so with the engine not running it indicates uncorrected field pressure.
    Those among us living at or near sea level can look at the gague and expect it to read the same as the Kolsman window when the altimeter is set to field elevation. Those of us living at significant altitudes above sea level look at the gague and ponder if what we are seeing is right. My field is at 2,400' and my gague reads 27.4" with the local altimeter (corrected barometer) at 29.85", Perhaps a flight to a sea level field might resolve any insecurity but there is another way.
    The website http://www.csgnetwork.com/barcorrecthcalc.html has a handy calculator. You just enter your field elevation and current altimeter setting in the top column and read the uncorrected mercury column and correction factor at the bottom. For my field elevation the correction turned out to be 2.5" which corresponds to 29.8" within .05" of where it should be. Now I have confidence in the instrument without having to go to sea level to check it.
    This same calculator can give you the maximum theoretical full throttle manifold pressure for any cruise altitude and within 1/4" the power you would achieve. A bit helpful when trying to calculate crise performance for altitudes that fall between the charts in the POH.
    As an Airframe/Powerplant mechanic with extensive experience in both large jet transport and general aviation aircraft as well as avionics I will be writing other blogs trying to take some of the mystery out of small aircraft systems. If anyone has questions on or suguestions for articles, please comment.
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