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Thread: Polini, Briggs and 447

  1. #21
    Senior Member 500 Club
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    Polini, Briggs and 447

    Hi All,
    I have the PKW carb on the 250 Polini ( fitted to a Flylight Dragon) and it is a bit of a pain but Dave and myself are enjoying the messing around to sort it and after all its just a carb if made down to a price.
    Two stroke fuel burn in general is more than a four stroke but you need to factor in the extra weight of the four stroke which with modern two stroke design redresses the difference in fuel burn and oil out the back.
    Will let you know what the consumption is when we fit the fuel computer.
    As an example my Shadow fitted with the 503 Rotax can get 5lts/hour with even me driving it and with Dave in comps the best was 3.5Ltrs.
    At the end of the day if you are interested in performance forget weight at your peril.
    Just saved 1.5Kg off the Polini installation and now await to see if it works.
    This dereg is so much fun. :-)
    Mick

  2. #22
    Diamond geezer 500 Club
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    Polini, Briggs and 447

    Yesterday did some testing with a full tank of gas, as mine has a 35 litre tank the change in performance full to empty is quite noticeable; from rolling start it got to 650 feet in one minute; this was with the GPS equipped camera rolling so isn't wishful and I might stick it on YouTube.

    So not massive performance but gets much better as the fuel empties, however it has got a leaning device on and it is interesting what you can achieve with one:-

    I warm up with the leaning device open as you can see the slight exhaust smoke left over from choke to start disappear as it takes effect; it clears the excess and reduces bore wash from excess fuel, but this also means liberties with jetting precision can be OK too.

    The makers sell a 'high altitude jet kit' to drop the gas at over 5,000 elevation use, I ordered one but then decided to leave the carb alone and just lean as required during the flight, hardly stressful other than remembering to set back to full rich in the circuit.

    Built the leaning device for 10-15 using Hoselock micro watering tube and fittings, plus a 5 needle valve from eBay and a knob pressed onto the knurled top for gloved hands use; details happily given on request

    Looking forward to longer flights in Summer to see what max range and fuel burn is

    On the Polini you maybe could install a leaning device and fail safe back to rich if it starts heating?

    On a two stroke definitely only to be used with EGTs...

    Kev

  3. #23

    Polini, Briggs and 447

    No mention of any kind of torque damper, and it has gears. How are they lasting??
    Dave

  4. #24
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    Polini, Briggs and 447

    Dave,
    If you are talking about the Polini then the jury is still out as far as long term reliability of any parts.
    The engine has a centrifugal clutch so would not need a torque damper and together with a balancer shaft seems to be as smooth as you can get a single cylinder motor.
    Its a bit strange to watch the prop blowing around when on the ground and I have fitted a prop brake so we have that option in the air which must possibly make it a first trike fitted with three brakes.
    So we can stop it and are now working on the fine tuning to the going bit.

  5. #25

    Polini, Briggs and 447

    Thanks Mick.
    Yes, it was the Polini.
    I ask because users of gears have traditionally had problems without a damper.
    I did think that centrifugal clutches locked up in both directions once up to speed, but perhaps there's a freewheel incorporated?
    Or perhaps there's very little torsion reversal once beyond the clutch revs?
    Hours so far?
    Dave

  6. #26
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    Polini, Briggs and 447

    Hi Dave,
    Traditionally you will only get problems at low revs due to the power pulse especially on a single cylinder unless there is a frequency problem in the drive train and as the drive is disengaged at low revs it should remove any problems.
    The clutch will lock up when engaged which happens at about 3000 engine rpm
    We are playing with different set ups at the moment so have not done any meaningful hours though all indications are good so far.
    Information from the factory is a bit slow but I suspect that is down to the supply train as much as anything.
    They have sent the early motors out with less than perfect carburetion and depending on what its fitted to you may need to experiment a bit.
    Paul took the Flylight demonstrator to Slovakia for the Europeans with basically a new motor out the box and it did not show any signs of trouble with no running in and two weeks of comp flying , much of which was flat out.
    Mick

  7. #27

    Polini, Briggs and 447

    Don't forget the Polini 100 and 200 engines use the same gearbox and clutch set up, and have been sold in quite large numbers and been out for a little while now, and I haven't heard of problems in this area yet.

    Also the Germans very keen on centrifugal clutches for some reason and run Rotax 582's with them using C gearboxes with rubber damper removed.

    The BMW R100 conversion in a UK Skyranger uses a c box and centrifugal clutch. If I remember correctly they got better results than with the rubber damper - the clutch proving to be a better smoother of large pulses at the low RPM range.

    Paul

  8. #28
    Senior Member
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    Kaunas, Lietuva (Lithuania)
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    Polini, Briggs and 447

    I have done 20 hours with BB Trya 03, Rotax 447, Hellix propeller (160 cm) this year. It consumes 7 ltr/h at 5500 rpm, ground speed average 75 km/h. (my weight 95 kg).

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