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Thread: Help me find a quiet craft ??

  1. #1
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    Lightbulb Help me find a quiet craft ??

    Hi I am a new member .
    Many years ago I had an Osprey Falcon. it was great, but vary loud !!
    ( 503 Rotax and a 900mm prop )
    So I am looking for a quieter craft .
    May be one with a bigger prop ,moving slower , and a small lift engine?
    Has anyone tried a LE 200 cc velocette engine ?They were silent .
    It must take two people !

    Any help would be great .

    Mekon

  2. #2
    Forum God > 400 posts Club Member
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    Default Re: Help me find a quiet craft ??

    Hi - I originally replied from the Magnolls race meeting near Blackburn Lancs at the weekend but I'm not sure that post uploaded properly so here's a slightly longer version.

    The Velocette Viceroy engine was used on early HoverAir craft in the 60's but it isn't made anymore. It was only 15bhp and you need at least 25bhp and preferably 35bhp for a viable 2 seater to go over hump on water. A long as you use a low revving 4 stroke engine such as the 35bhp Briggs and Stratton engine used in many F35 craft with adequate air intake silencer and exhaust silencer there is little problem with engine noise, the problem is largely fan noise. That will be the same problem with electric power which some are experimenting with. Electric power has its own probs at the moment especially cost.

    As you suggest the key to fan noise is to lower the tip speed from around the 120m/sec commonly used to around 80 m/sec, reduce duct tip clearance to around 5mm with a strong, perfectly round duct, remove all the clutter in front and behind the fan which disturbs the air going through the fan and 'gas flow' any lift splitters etc behind the fan. That approach has been shown to reduce craft noise at 25 metres on full power from around 90dba for your old Osprey Falcon to 75 dba

    Whereabouts in the country are you?
    Keith

  3. #3
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    Lightbulb Re: Help me find a quiet craft ??

    Hi Keith,
    thank you very much for your help .
    i have had a word with Ian of flying fish .it seems my best bet is a small two engined finger skirt craft .if the new craft are actually down to 75 db compared to my old Falcon which you reckon was about 90db that is a big reduction in noise !!if i am right the db scale is a log scale so the noise should be reduced by 1/2 for every 3 units !!! have i got this right ?? I have just called an expert and he reckons that although i am right . But while the ear will hear a considerable reduction but not 30x . apparently it would be like the difference from a loud motor bike and a passing car that was not accelerating . next . do you know of any cruising members in the London area?
    where a bouts are you based??

    Mekon

  4. #4
    Forum God > 400 posts Club Member
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    Default Re: Help me find a quiet craft ??

    I'm near Maidstone - there's an active SE Branch with a lot of Flying Fish craft regularly cruising on the mud of the lower Medway and Swale. The next event is 17/18 May with an overnight stopover on an island in the middle of the Medway - click on the 'search calendar' button for details.
    3db is a mathmatical halving of sound power, the human ear thinks 6db is a halving! Anything under 80 at full power would be an improvement.
    Keith

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