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  1. #141
    Captain MadamBreakneck's Avatar
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    Quote Originally Posted by BobH View Post
    ...other little matters, such as the ASI that I'd fitted. It's a nice big 3" one, but it's in Kts, not MPH, and when I flew with it, it would only go up to around 35kts. To get it to go up to 40kts I had to dive the plane very steeply, so not really practical for my use...
    55mph is about 47kt, so your knot ASI was reading wrongly anyway (assuming your current mph one is correct).

    Good to read you've been airborne though.



    Back to just bimbling in the TST.

    No longer instructing - just pontificating..


  2. #142
    Co-Pilot BobH's Avatar
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    Joan,

    It was pretty obvious from the off that the Kts ASI wasn't working properly. If I blew in it the needle shot round to the upper limit, but trying to just gently breathe into it nothing happened. So I tried it out in the air, but it was unworkable watching it sitting at 35Kts all the time, till I went into a steep dive, then it crept up to 40Kts. The MPH one does work, and I think it's pretty accurate as well because at one point I was flying in virtually nil wind, and the Pilot 3 and the MPH ASI showed the same speed, i.e. airspeed = groundspeed.
    XL's forever! Well, one of them anyway. It's all I can afford, not to mention the Raven and the Mini-Max. Oh, and I almost forgot the Spectrum as well


  3. #143
    Trainee Pilot Mike Calvert's Avatar
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    Quote Originally Posted by BobH View Post
    If I blew in it the needle shot round to the upper limit, but trying to just gently breathe into it nothing happened.
    Quote Originally Posted by Brian Cosgrove 8th edition page 65
    One final point : never, ever, blow into a pitot tube to check that an ASI is working - after doing so it probably won't!
    He doesn't explain why that's a bad idea though....


  4. #144
    Co-Pilot BobH's Avatar
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    Probably due to water vapour in the breath, along with germs and other stuff we all breathe out (Covid??)
    XL's forever! Well, one of them anyway. It's all I can afford, not to mention the Raven and the Mini-Max. Oh, and I almost forgot the Spectrum as well


  5. #145
    Captain MadamBreakneck's Avatar
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    Quote Originally Posted by Mike Calvert View Post
    He doesn't explain why that's a bad idea though....
    Blowing into pitot tubes - bad idea because... see other thread

    As you'll see from the table helpfully provided by Antoni, the OP of that thread, to provide a 100kt reading in a working ASI you need enough pressure to lift water in a tube by only 6 inches (15mm to our young friends). I haven't bothered to try it, but intuition tells me that that's a very gentle blow. Much more than that (very gentle) and you stand a decent chance of overloading the mechanics inside.

    In the case of Bob's knot ASI, my guess is that it's gunged up inside. An old-fashioned clock repair shop might be able to clean it as long as the diaphragm isn't leaking.



    Back to just bimbling in the TST.

    No longer instructing - just pontificating..

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  7. #146
    Trainee Pilot Mike Calvert's Avatar
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    That'll be 15cm, or 150mm then

    Yeah, I did think it would be something like overwhelming the mechanism and breaking it - moisture presumably gets in anyway unless there is ever a day with 0% humidity...

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  9. #147
    Training Captain Gentreau's Avatar
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    Quote Originally Posted by MadamBreakneck View Post
    .......only 6 inches (15mm to our young friends). .........
    Oh dear, Joan, please don't perpetuate the myths ......
    The three most useless things in aviation:
    • The air above you.
    • The runway behind you.
    • The fuel in the bowser.


    Rule #1: Always tie-down your aircraft to the largest heaviest object available. The planet Earth meets these requirements and is readily available in all locations.
    Rule #2: The great thing about twin engined aircraft is, if one engine fails, the other engine always has just enough power to get you to the scene of the crash.
    Rule #3: You can never have too much fuel in an aircraft. Unless it's on fire.

    Semper specto in clara parte vitae.

    .

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  11. #148
    Co-Pilot BobH's Avatar
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    All,

    I blew into it because after my first flight, with it registering nothing at all I guessed it wasn't working. So I gently blew into a tube I attached to the back of the unit. Still nothing, so I blew harder, and eventually the needle shot round, as though it had been stuck. After that I flew the plane again, and this time the needle did move, but only up to 35kts, and seemed to stick there whatever speed I was doing, so I dived the plane and it crept up to 40kts. After that I landed and disconnected the thing, as it may look good, but it's useless.

    I'll take it off and put it in the airing cupboard for a week or two to see if that helps at all, but I don't hold out much hope for it. Assuming it's no better after a good airing, I'll put it up on either Ebay or AFORS as spares or repair, and someone else can lavish it with love and care. I'll just stick to my MPH ASI instead.
    XL's forever! Well, one of them anyway. It's all I can afford, not to mention the Raven and the Mini-Max. Oh, and I almost forgot the Spectrum as well

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    MadamBreakneck (20-09-20)


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