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  • Polini, Briggs and 447

    Just got a mail from John at Ace Aviation:-

    http://www.polini.com/en/page_719.html[/u]

    John

    *This is the unit that Paul's been playing with on the Dragonfly, so looks like the two stroke is far from dead, although direct-in-head EFI would be the icing on the cake.

    I used to read from Jeremy Harris that a two stroke specific fuel consumption is much higher than a four stroke's, has this changed? I'm getting 7.75 litres per hour from a fairly amateurishly tuned Briggs pushing a trike that needs 33-35hp to fly properly, certainly less than the 11-12 litres per hour from a 447 in the identical prop and trike setup.

    Cheers

    Kev
    G-KEVA
    BMAA 5696

    "If anybody ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me: it's all balls."

    R.J. Mitchell :- Designer of the Supermarine Spitfire

  • #2
    Polini, Briggs and 447

    Hi Kev,
    the twin carb 503 on my Phantom runs at about 10l/hr for a two-stroke trike compatible cruise speed of 55mph or so. It's well throttled back at that, very relaxed cruising. So two-stroke consumption on tradiational microlights doesn't have to be too bad, so long as you don't try flying fast.
    Cheers,
    Paul.

    Comment


    • #3
      Polini, Briggs and 447

      ASI is out on my trike, about 5mph low, but reading 56mph gave that figure so 60 actual.

      You're right of course, I flew to Spamfield 252 miles with about 10-20% slower trim on, 55mph true airspeed, and it was remarkable how a mere 5mph reduction knocks the stress off on draggy aircraft.

      With the Briggs I'm being deliberately hard on it, bashing it up to 5400' at continuous full throttle to test for overheating issues, and cruising at fastest trim to get the 7.75 litres/hour figure.

      Too many bull_____rs on engine stuff, I can pick up my Briggs engine and redrive, the 447 is lighter but add in the exhaust and the difference starts to erode. Would love to have the spare Wonga to build and try a direct drive version on a soaring trike spinning a high speed prop (2500-3200) and dump the flywheel, like the Luciole does. No tuning needed at all and featherweight too

      Kev
      G-KEVA
      BMAA 5696

      "If anybody ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me: it's all balls."

      R.J. Mitchell :- Designer of the Supermarine Spitfire

      Comment


      • #4
        Polini, Briggs and 447

        The ultimate 2 stroke anybody has ever had was the pony in both of my Chevvrons, the only 4 cylinder radial available I believe! Konig 340, 4 125cc jobbies strapped together.

        Wherever I flew 2 up, we always came out at 10l per hour take off to landing and virtually always 50 knots. Planning was a doddle and sometimes full power for an hour just to get 4k so as to cross to the IOM relatively safely. Mind you, you had to be 10 minutes ahead of your self to get her down first time or you were forever doing circuits just to lose height.

        H

        Comment


        • #5
          Polini, Briggs and 447

          I have to agree with Hugh the Konig was a beaut of an engine, light in weight, smooth, quiet and thrifty, relieable as well a lovely piece of kit built like a swiss watch.

          Paramotoring friends of mine have spoken highly of the older Polini engines with a lot of praise for the super smoothness of the unit, something that you don't hear often for any single cylinder engine. I was told that the only problem was with the carb fitted, a Tillitson or similar I believe, it seems that that may have been addressed. I look forward with interest to Pauls results.

          It is dead right that careful use of the throttle hand make a huge differance to a two stroke, my TST, hardly the slickest thing in aerodynamics, one up has always returned 10-11 LPH. Not the last word in low consuption but not bad either.

          Ginge

          Comment


          • #6
            Polini, Briggs and 447

            I saw one of these recently and I have to say that it is a big jump into the next level of technology. Balancer shaft, so it should have minimal vibration, integral reduction gear drive, watercooled for thermal stability and twin spark. Very powerful and not heavy either (also not cheap). Don't know what the SFC is but it should be good.

            Comment


            • #7
              Polini, Briggs and 447

              I have the polini 200 in a dragon trike and it is very smooth and powerful. Polini have had a few issues with carburettor settings and compression that need to be sorted before it can be highly recommend. The water cooled 250 does sound an improvement though. I spend my time flying mine with one eye on temperature gauges which doesn't allow total confidence. Jk

              Comment


              • #8
                Polini, Briggs and 447

                Yeah-but .. downwind of a 2-stroke is not a place to be (unless you're into glue-sniffing, perhaps). Or have the recent designs fixed that?

                Mike

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                • #9
                  Polini, Briggs and 447

                  A lot less than we subject our children to getting on and off the school bus. And of course at 2000' there is rarely a group of children following a few feet behind.

                  Paul

                  Comment


                  • #10
                    Polini, Briggs and 447

                    Never put my child on a school bus, so cannot comment on that. But have many times been walking along a country lane when a 2-stroke motorbike went by and had a mouthful (and presumably lungful) of oil. Not sure how it's better if that motor is flying above me rather than alongside me. But yes, that is one reason I have always favoured pusher aircraft! Every tractor aircraft I've flown in has been smelly.

                    Comment


                    • #11
                      Polini, Briggs and 447

                      And to me the scent of a 2 stroke is such a nice thing...each to there own I suppose.
                      "When once you have tasted flight...you will forever walk with your eyes turned skywards..."

                      https://www.youtube.com/user/nickjaxe/videos.

                      Comment


                      • #12
                        Polini, Briggs and 447

                        I'm thinking of the polini for the Dragonfly. Cruising at 37mph it presumably won't be an awful lot worse than the Bailey which is 3 litres per hour but working at 75% throttle to manintain height. The polini should allow a very short take-off run, and should take just a couple of minutes to get up through a hole in clouds
                        Mike

                        Comment


                        • #13
                          Polini, Briggs and 447

                          Nick, indeed, I've assumed there must be people that like the smell of petrol and oil. Clearly an acquired taste!

                          And not what I think of when I read "When once you have tasted flight..." :-)

                          Mike

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                          • #14
                            Polini, Briggs and 447

                            peter.finlay@nov.com[/U]

                            [3]Cheers,[/3]

                            [3]Pete[/3]

                            Comment


                            • #15
                              Polini, Briggs and 447

                              That sounds encouraging, it seems that with the latest model they are trying to address the carb problem, friends in the paramotoring world seem to rate the Polini. Is the new carb adaptable to your engine?

                              The combination of lightness, smoothness and power could make it ideal for SSDR use

                              Ginge

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