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Thread: New starter needs advice!

  1. #1
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    Default New starter needs advice!

    Hi my name is Colin,

    I have been planning to build a racing craft for sometime,

    I have just finished reading the constructors guide and watching Flying without Wings, and would really like some help and information.

    <font size="3">[color = red](THANKYOU IN ADVANCE)[/COLOR][/COLOR]



    I want to build from plans to start with,

    (I may make some small mods along the way)



    I think Ply-wood and GRP will be the way to go for me,



    I think I will end up using a Rotax 503 due to cost of other engines,



    1/ can you suggest some names of craft for me to have a look at before I buy some plans?



    2/ Is it a good Idea to go for a Rotax 503 as a first power plant?



    3,I wanted to design a contra-rotating fan,

    to increase efficancy, reduce fan RPM (noise)and counter act engine Torque.

    A bit like this....

    [img]index.php?t=getfile&id=2167&private=0[/img]

    Any ideas on if its a good idea or is it just madness setting in?



    Thank you all for your help!



    Colin







    Attached Images Attached Images

  2. #2
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    Default Re: New starter needs advice!

    Hi Colin welcome along.



    I see you are in Manchester, there's a good group of racers around there so it would be good to get in touch with the local branch. Contact email for the North West branch can be found here...



    http://www.hovercraft.org.uk/about/b.../branches.html



    I would recommend coming to the first race meeting of the year on the weekend of the 2-4 May near Oswaldtwistle. Come along and have a chat with some of the 503 drivers, they're a friendly bunch really.



    I would personally recommend trying to find a second hand craft, either complete or without engine so that you can get hovering quickly in something that will actually work and give good performance. I would recommend a Moto hull personally although there are many other hull designs that perform well. The Alien is also a good hull as is the BBV hull. The Raptor is the next level up and not many (if any) available second hand yet. These are all fibreglass hulls so they are not available as a plan build.



    What is your budget? You could probably get a complete second hand craft for the same price as building one.



    If you find a good 503 engine that is standard they will be bullet proof. The engine that I used to race was brand new and un-modified and has never missed a beat in 4 years.



    I'm sure some others will be along shortly to completely disagree with me!

  3. #3
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    Default Re: New starter needs advice!

    You would be wasting your efforts building a Contra rotating fan for a racing hovercraft. CR fans improve effeciency in fans which are designed for providing pressure (has potential in a lift system for a large hovercraft). For thrust you require a large volume of air moved at very low pressure. Each stage in the the CR fan would move the *same* volume of air through its disk and both would absorb similar power. ie about twice the power consumption of a single stage fan and the same thrust.




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    Default Re: New starter needs advice!

    Supporting what Paul has said the only contra rotating fan I can recollect is one of Nigel Beales Cyclones which had a second engine and fan unit bolted on the back of the duct. Although it crossed the English Channel the second fan didn't double the thrust and it was pretty noisy, probably because the rear fan was operating in the very turbulent air behind the front fan.

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    Default Re: New starter needs advice!

    Thanks all for your advice,



    My idea behind the contra-fan was to run the 2nd stage behind a flow straightner to reduce noise, and at a higher pitch since the air is allready moving backwards,

    Say 30 degrees on the 1st stage (straightner) and 50 on the 2nd.



    My hope was to move more air through the same or smaller sized duct(lower centre of graverty), since it is a single engine setup I thought the increased pressure would allow me to use less area for the splitter and have more going out for thrust.



    I think from your advice i will leave the contra-fan idea for now...more thinking required...



    I will do my best to get along to the first meet, I really had my heart set on building one and paying for it as I go along rather than getting a second hand craft,

    I will have a look at the Moto, Alien and the Raptor and see if I can be tempted.....



    I recon my budget over all is about 800-900

    My dad flys microlights, and has found me a standard 503 with only 100hrs on it for 500



    Cheers Colin

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    Default Re: New starter needs advice!

    Now you have the engine have a look at the Vortex shop (other manufactures are available) to give you a rough idea of prices for the rest of the project (fan hub, blades, skirt material etc etc).



    With only 3-400 quid left after the engine it could be a bit tight. Having said that if you are going to self-build and have no desperate deadline then you can always save some extra as you go.



    Keep us posted on how your getting on and if you need any advice then just shout!

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    Default Re: New starter needs advice!

    [color = red]Cheers for your help guys![/COLOR]



    Will keep you posted of how things are getting along, Im sure I will be back with more questions...



    Cheers Colin

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    Default Re: New starter needs advice!

    hi colin



    i'm near wigan and work at the university in preston where i keep my craft - you're welcome to come and look at to give you ideas/inspiration/dread



    pm or email me if you're interested



    tony




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