As the season starts for these hornets/wasps blocking usually ASI (pitot) is on again and yes I have 3 instruments back and two are probably damaged due to the use of compressed air. TOTAL NO NO
My suggestion it needs 2 people and usually it is blocked pitot in about 10cm.in disconnect all Pitot lines from ASIs and air switch etc and double check that all is disconnected by the second person watching instruments. Try and dislodge the blockage with piece of lock wire etc and gently apply not sealed off air to the cockpit end and have the other person check if anything comes out. If this fails then I suggest a 1/4 cup of water in your mouth and let this water go in at pitot and just go back and forward a few times and bingo it will be freed up. You may have to run air through pitot to dry up the minimum water you have. Mouth is easily washed out with water!! The cost of replacing innards damaged in ASI will be about $200 and it is a totally unnecessary repair While going Please be careful using an manometer on the ASI as now and then people let water into ASI and again it needs repair at large expense. My experience is most ASIs remain accurate (in GA tests are only done each 3 years if at all depends on LAME) and and our GFA checking each year is overservicing BUT problems do exist with old tubing in gliders and this is the source of many more ASI errors. The worst one is a partly blocked pitot which can easily be missed. This can be picked up by ASI not immediately returning to zero (needs a second person to watch) OR as you go up on winch or aerotow ASI will overread by say 20kts but at landing time (decending) ASi will read 30kts when you really have 50kts. It is a great reason all should learn to fly on attitude but put this one in the back of your mind and I insist people doing DI course understand ASI issues and if in doubt ask for help. . A few years ago a young fellow flying tug was using ASI instead of attitude so we called for more speed at 200ft (not a niece experience). Finally he lowered the nose which caused the rope to break (an old rope with a splice in middle to my horror and I believe should be banned). We had a very interesting turn back at 200ft and all the tug pilot could tell me later was "I had 78hts" I told him you MUST use attitude. Unfortunately he has departed this world in an overseas aviation accident. Personally I believe all tug pilots when trained should be aware of the condition of a part blocked Pitot and its effect on ASI OR LEARN ATTITUDE FLYING (we do it in gliding but I never had it when doing power flying checks but could be done with in GFA when doing tow pilot checks). While going DO NOT seal an ASI with SILASTIC - IT REALLY IS A NO NO and DO NOT glue the needle to shaft with epoxy. If your ASI leaks ask me for new O ring.for FREE Finally if your Winter mini Altimeter has mb out then ASK ME it is easy to fix. So in short *2 PEOPLE, NO COMPRESSED AIR, and TAKE YOUR TIME to think first and ask for assistance* That's all I hope for the next 12 months meanwhile Achim Winter has a few more ASIs to service. Achim tells me we in AUS have a bad record world wide with ASI repairs!!! Ian McPhee PS 1 I now have no loaner ASIs for say 4 weeks PS 2 if you are not worried by drag in a 2 seater get one of those auto pitot cover from Aircraft Spruce for think <$10
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