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Thread: Fresh water Central Scotland

  1. #17
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    Default Re: Fresh water Central Scotland

    The thing is you don`t need to bolt the air filter to the engine,it could be fitted lower down in the hover in a cleaner air position and linked to the engine air intake with ducting.
    There are loads of after market parts available out there , a lot of them are not designed for our type of environment
    In the real world machines designed to work in dusty or wet environments have good quality filters fitted to prevent down time on the job, I don't think hovercraft's are any different

    Trev

  2. #18
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    Default Re: Fresh water Central Scotland

    From memory it dropped the intake noise significantly but the overall noise only came down a couple of dba (which isn't very significant) because of the fan noise - caused largely by turbulence from obstructions (frames, belts, splitters etc) being too close (within 100mm) of the fan. I was impressed by the low noise from a 50-60bhp rotax 2 stroke in a hovpod recently, due to the excellent air intake box and after muffler. The craft wasn't quiet overall because of fan noise probs but thats another story. It does show that a 2 stroke can be much quieter although I think its still beaten by a low revving (<4500rpm) 4 stroke.

    The airbox is essientially a helmholtz resonator tuned to the engine firing frequency. In electrical terms the box acts as a capacitor supplying air quickly to the engine as it sucks air in on each cycle, whilst the intake to the airbox is a restricted size acting as a resistor to slow the refilling of the capacitor. This tuned circuit means that the pressure fluctuations (ie acoustic noise) reaching the outside world are smoothed (thus quieter). It does mean any old box won't do, it must be designed to fit that engine.

    I would have thought an exposed mesh air filter wasn't a good idea, particularly with salt spray.

    Keith

  3. #19
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    Default Re: Fresh water Central Scotland

    OK, so what you saying is:

    If I buy one of these air boxes, and a after muffler and then enclose the motor like I was going to anyway, and being that is is going on a Sev.

    This should be enough to keep the green peace guys happy.? Right ?
    In the beginning there was the Cube; I know where is came from and it has the power to create Hover life. But with great power comes great Fun.

  4. #20
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    Default Re: Fresh water Central Scotland

    ...and keep any obstructions away from the prop. That'll make that particular design as quiet as you can, and thus more acceptable. But noise acceptance is subjective and without a stated dba limit and objective dba testing to prove you meet that limit you can't say it will be acceptable to everyone. but hey go for it!
    Bye the way my tests show relatively little noise comes from the engine body (except in cases where the engine is about to seize) so enclose it for reliability reasons ok but don't forget its an air cooled engine and could overheat, especially in Africa!
    Keith
    Last edited by Keith Oakley; 4-Jun-09 at 09:03 AM.

  5. #21
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    Default Re: Fresh water Central Scotland

    Yes I have solution to that, a gauze hole in front of the engine cover to let air flow through. If I can I also want to mount the motor just above the lift engine so that it gets as much air as possible but as low as I can for better wight distribution. The last thing I want is a top heavy craft that falls over every time I turn. With the fuel tanks placed on the floor on either end it should keep the craft well balanced.
    In the beginning there was the Cube; I know where is came from and it has the power to create Hover life. But with great power comes great Fun.

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