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  1. #1
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    Default new aluminium hovercraft

    Hello to everbody!!!

    Im a newbie and need help !

    Im in the process of designing my first build and could do with a lot of tips and suggestions on ways to go ie (ducted fan vs unducted prop )hull height from floor to top of skirt (planing surface angle)if this is paramount in a design, power to weight ratio s, whats the best floatation medium expanding foam vs solid substance , etc etc a quick insight into my build plans are as follows .

    Im using aluminium as the hull medium it will be built with some aircraft design in mind ie skeletel trusses etc for rigidity and i had thought of injecting the foam medium into the cavity so as i can finish the welding and fabrication without causing undo heat to the foam ! this also gives a good level of density to the craft when the foam medium drys, whats the best skirt/ material? ! the engines i have for lift and thrust are as follows ,

    lift= a MZ 34 313CC 27HP AT 6250 RPM 2 STROKE

    thrust= BMW R1OO WITH ROTAX DESIGN GEARBOX COMISSIONED BY SCRIMINGER ENGINES i think the engine is approx 90 hp

    i did get a prop with this engine its a 3 bladed carbon fibre approx 2 metres dia .

    im ok on the welding and fabrication side but could do with some help with wheres the best to mount lift fans , thrust aspects should i go with pulleys or hydrolics who is going to rip me off and who knows what there talking about(shops)etc

    any help from those who know what there talking about would be a great help!!

    thanks andy

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    Default Re: new aluminium hovercraft

    Hi Andy,



    Welcome to the board.



    Are you planning on racing or cruising with the craft?



    If it's cruising then:



    I see you have a 2-stroke paramotor engine for lift and a 4-stroke for thrust. The 2-stroke will be incredibly noisy for lift as you will be running it flat out nearly all the time. You would also have to have two fuel tanks in the craft and if you are going for a long journey you would have to take a spare jerry can of each type of fuel. Bit of a pain in the ass but if you have the room in the craft then fine. I would seriously contemplate changing the lift engine for a 4-stroke. It would make the build easier as you can have one fuel tank for both engines, it would also make the craft a lot quieter which is something that we as a club are actively trying to encourage. Quieter craft means less grief from nimby's.



    I would also strongly recommend building to a known set of plans. Hovercraft are quite critical in many areas of the design, if you get it only slightly wrong it can be the difference between it working and it just sitting there in a ball of spray or dust!



    I would say that a ducted fan would be the best option but spinning quite slowly in order to keep the noise down. Ian Brooks has done a lot of work with this and will probably be along to offer some words of advice now he's back in Blighty!



    I have only ever built from kits and then fettled from there to varying degrees of success, so my knowledge of craft design is quite limited. Have a look on the links to the craft manufacturers and give them an email, Vortex, Bill Baker Vehicles and K & M Products offer parts off the shelf as well as machining services if needed.



    If you need belts or bearings then give me a PM with the sizes and specs and I can get a mahoosive discount from a well know bearing supplier.



    HTH.

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    Default Re: new aluminium hovercraft

    Hi john and thanks for the info !!!!!!

    im very lucky to live in leigh on sea (essex )and have an entire estuary to go at so the nimby problem is not that much of an issue , the vast quants of morons in very loud and high performing boats with zero experiance is more concerning but they tend to only turn up when its 75 degs and wearing ~~uck all ! my end aim is a WIG vehicle / hover/ground effect ! i can see a woried face lol dont worry im a fully educated engineer and ( apart from my spelling LOL) have 18 years craft expo under my belt alu , tit ,stst materials no prob , your right about the 2 stroke but its out of my paramotor and at hand so it will have to do for the moment , im not on a budget but would like to keep the outgoings to a minimum but wont be scrimping as the project i want to last for a about a year .

    I managed to lay my hands on a hunter hawker canopy and attachments for the cockpit as well as some flight controls out of a cessna all beg borrowed and stole lol so ill uttilzes these in the craft obviosly keeping the weight to a minimum threw out the project, ive read different books on craft design (HOVERCRAFT THE CONSTRUCTORS GUIDEBY HCGB )COUPLE OF OTHERS

    but there all conflicting in parts so any first hand information and experiance would be fantastic ive sent an email to kand m hovercrafts about purchasing the parts i need from them selves but i only want to make the journey a couple of times due to the 175 mile distance .




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    Default Re: new aluminium hovercraft

    Hi Andy,



    The most important aspect of your craft IMHO will be the skirt design. For a WIG to actually lift off you would need to be doing at least 55-60mph (based on Universal Hovers figures for their WIGcraft). In order to get to that speed you will need a very good skirt design that will not plough-in.



    Plough-in, if you are not aware, is when the front skirt section collapses causing the craft to stop very very quickly.



    What weight do you envisage the craft to be?

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    Default Re: new aluminium hovercraft

    Jon i bought a set of universal plans from a very nice gentleman in scotland who s in the process of building a composite craft from plans, i had a good look at them in detail and there very confused and vague and the aero dynamics are rubbish its funny watching square boxs fly ! and yes speed is the key 53 mph rings a bell, over all weight im still calculating approx but when all material are in ill have more idea ill be doing a web blog prob anyway for my freind who lives abroad to follow so other peeps can see too!!

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    Default Re: new aluminium hovercraft

    Cool, keep us posted and of course any more questions, just ask.

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    Default Re: new aluminium hovercraft

    Hello and welcome!



    First - We're here to encourage & help! Sometimes, though, that means we have to be a little discouraging to begin with. Designing a hovercraft is hard - very hard. Which seems like an odd statement because it is patently very easy to get a few planks & a leafblower to hover, But a hovercraft that you will entrust with your life... now that's a different matter!



    Having said that, designing a new hovercraft is within the grasp of an experienced Engineer who is comfortable with technical calculations, so here's a little help to get you going! The first thing you need to do is read up a bit - I recommend "Theory and Design of Air Cushion Craft" by Yun and Bliault (ISBN 0-340-67650-7).The other two references you'll need are "Homebuilt Hovercraft" by Williams, and "Practical Design Guide for Airboats and Air Cushion Vehicles" By Barry Palmer, both old but very relevant. The last one of these is perhaps the starting point. If you PM me an email address I can send copies.



    If you prefer to just get on with the job, then I would recommend building to plans. This has a huge advantage - you know that it will work after you have spent hundreds of hours and several thousand pounds on it.



    From your posting, I see that you want to build a cruiser and would caution that the 2 stroke is just not suitable as a lift motor for a cruiser, it'll be killed by the salt environment and leave you stranded. It would be a shame to compromise the design for a few hundred pounds worth of Briggs engine - about 12-14 HP for a mid-size cruiser. The R100, on the other hand, will be very suitable.



    Here's some links you might want to review:



    Wouter, designed and built an excellent cruiser in his ATTIC!!!!, here's how he did it:



    http://www.xs4all.nl/~wcasten/hoverholic/



    John, has built several excellent cruisers:



    http://www.hovercruiser.org.uk/



    Anyway, I hope that helps!



    Ian




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