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Thread: Quiet Hovercraft Project

  1. #9
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    Default Re: Quiet Hovercraft Project

    I agree the air conditioning industry is a great source of ideas for us - especially as we use their fans. I've been to a couple of international conferences for that industry and gleaned a few ideas which I'm using, but I wouldn't claim in any way to be an expert. It strikes me that half the papers presented at these conferences are by experts using CFD software to analyse airflow virtually in a computer model. Its way beyond my skills and seems to need very powerful computers and expensive software plus theres a problem mapping between the virtual model and whats actually happening in a real craft. If theres any members out there with these skills and willing to join in our project I'd love to hear from them.

    As you say centrifugal fans are a leading contender for twin engine craft lift fans particularly on a cruising craft where there is more space. They were quite common in the early days before multiwing fans kind of took over. One of the quietest craft I've tested is a New Zealand built Air Slider. Tests I did on 2 of those in the US in 2009 gave a very credible average of 78dbA static at 25metres for the 53bhp version. Noisecam tests on it showed prop fan and engine noise and very little noise from its two small centrifugal lift fans. But the problem is sourcing a suitable lightweight centrifugal fan. The NZ folk made their own, as did I back in '67. If anyones aware of a suitable fan again I'd love to hear from them.

    Keith

  2. #10
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    Default Re: Quiet Hovercraft Project

    Quote Originally Posted by Keith Oakley View Post
    I’m proud to announce that after 40 years of noise research I have finally built a hovercraft which is radically quieter than any other of the over 150 craft I have measured worldwide; without compromising the craft’s performance.
    This is EXCELLENT news, Keith. Thank you for your work.
    This could be a major milestone in the development of the hovercraft.

    Quote Originally Posted by Keith Oakley View Post

    The craft is a specifically designed to cruise at low noise/ low speed in sensitive areas.
    Something I am keen on doing what I can with myself, as living in Portsmouth, I am (paradoxically) somewhat limited in where I can go locally.

    Quote Originally Posted by Keith Oakley View Post
    The advent of wider chord fans has now enabled lower tip speeds,
    Would anybody be able to recommend a supplier of wider chord fans/blades?
    This something I am very keen incorporate into my build as soon as possible, mainly because I am yet to make a start on the thrust engine & fan.

    Quote Originally Posted by Keith Oakley View Post
    Although the EEC directive specifically excludes air cushion vehicles I think it would be a powerful lever with harbourmasters and authorities worldwide that we have voluntarily met that stringent test and can prove it.
    Should I get there before any of the rest of you, I am more than willing to be a gunnie-pig with Langstone harbour master.

    Quote Originally Posted by Keith Oakley View Post
    I’m afraid I don’t frequent Facebook because the level of ‘Trollism’ there isn’t helpful.
    Facebook is for poseurs, your best off out of it my friend.
    Regards trolling, I once read in a book about making music and the tribulations of getting it to the masses and although it was written in and for the pre-internet age, I can not help but remember this gem of a line; "The reviewer will have forgotten what they said seconds after their hands finished typing it. You, however, may carry those words around with you in your head for the rest of your life - don't let that be a problem."


    Quote Originally Posted by Keith Oakley View Post

    More info to come as the R&D program cranks on – in the meantime I’m happy to answer your questions on this HCGB Bulletin Board - I’m also starting some posts on the members only HCGB Cruising Talk Forum with more detailed information and I’ll be happy to try to answer some of your questions there.

    Keith Oakley
    Thanks again for your efforts Keith, it is very much appreciated.
    Last edited by Aaron; 14-Apr-15 at 07:14 PM.

  3. #11
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    Default Re: Quiet Hovercraft Project

    H Aaron

    Thanks for your as ever incisive and thought provoking comments. I really appreciate your support.
    I'll send you a pm with some thoughts

    Keith

  4. #12
    More than 30 posts! Club Member pest619's Avatar
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    Default Re: Quiet Hovercraft Project

    Quote Originally Posted by Keith Oakley View Post
    I agree the air conditioning industry is a great source of ideas for us - especially as we use their fans. I've been to a couple of international conferences for that industry and gleaned a few ideas which I'm using, but I wouldn't claim in any way to be an expert. It strikes me that half the papers presented at these conferences are by experts using CFD software to analyse airflow virtually in a computer model. Its way beyond my skills and seems to need very powerful computers and expensive software plus theres a problem mapping between the virtual model and whats actually happening in a real craft. If theres any members out there with these skills and willing to join in our project I'd love to hear from them.

    Keith
    Hi Keith,

    first of all I look forward to seeing Q1 and have a lot of respect for the work you've been doing over the years. I hope some day to get to where you are in my field!

    You might have seen that ive been working on a new fan blade -primarily designed for racing- but hopefully the increased efficiency should translate to reduced noise as well. http://www.camracing.co.uk/fan-fun

    I looked into CFD when i was designing the fan and found that for a rotating fan is much more advanced, difficult and unknown than just running air over a plane or a racing car to work out the drag etc. Also I found that much more basic analytic design methods get you 95% of the way there. CFD has the potential to eek out a few extra percent but only with some very experienced people and a few months, as well as a physical test program.

    I work closely with aerodynamicists using CFD during my day job so will their opinion if i get the chance, but for noise stuff my opinion is that you are already doing the best thing by physical trial and error.

  5. #13
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    Default Re: Quiet Hovercraft Project

    Hi Pete

    Thanks for the feedback. I've been watching your developments with great interest for some time, and I'll be keen to noise test your new fan when its ready. As you say noise and efficiency are closely linked, anytime air doesn't flow smoothly you'll tend to get noise generated.

    I was particularly interested in your experience of CFD. Certainly the limited experience I've had of it is that its difficult, with the limited resources we've got, to map between the CFD virtual model and whats actually happening on a real craft. I'll drop you a pm with some thoughts.

    Keith

  6. #14
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    Default Re: Quiet Hovercraft Project

    Keith,

    I have access to some CFD software and have been using it on and off for many years. Depending on how large the model you are trying to simulate CFD software can be run on a good spec home computer. I have 3D simulated some interior hull designs with some success, but have not valudated them as have limited access to test instrumentation. I have not tried to do the fan, but a stationary 2D or 3D model would be simple enough. Simulating a moving fan is a lot more complicated and maybe beyond the software I have. If you let me know which areas you are looking to expliot with CFD than maybe we can discuss them in more detail.

    If you are looking at redesigning the fan, there is lots of papers on blade design for gas turbine engines that maybe useful for getting a better starting point. I worked at Cranfield University developing blades for Rolls Royce and would be willing to share some of my ideas on how to reduce the effects of noise from tip clearance and the hub.

    The relationship between Rotor and Stator is another important consideration and these should be designed as a pair. Fifteen years ago when I did this type of research a lot of consideration was the distance between the Rotor and Stator.

    Darren

  7. #15
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    Default Re: Quiet Hovercraft Project

    Hi Darren

    Thanks for your offer of help. At the moment I'm using an off the peg fan rather than trying to develop an optimum one so the key areas I'm interested in for CFD are essientially stationary. They may well be within scope of your software. I've sent you a pm with some details.

    Keith

  8. #16
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    Default Re: Quiet Hovercraft Project

    Hi Keith,

    Hope all your preparation work is still ongoing and giving you good results. Last time we talked about fan blade noise and alterations within the air conditioning industry to reduce noise and air drag, I said I would send you a picture of the new blades in production, well this is it.Click image for larger version. 

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    As you can see the shape can give a great weakness at the base of the blade so will be fine for constant speed or slow speed increases but would be no good for the torque put through them in racing craft.

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