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scottwilko
21-Feb-10, 11:59 PM
Hello everyone, my name is Scott wilkinson I'm from Australia, and I'm about to start building a stainless steel hovercraft, I've never seen a real hovercraft in person but I've seen photos and videos of them, and they look like awesome fun and I've just got to have one, I've started a build page on facebook to document everything I'm doing, I thought this might interest some of you, so here is the link http://www.facebook.com/pages/scott-wilkos-Hovercraft-build-page/324069606879?ref=mf

feel free to leave comments and offer me any guidance you can, I'll will accept all criticism and take everything on board,

I'll be keeping the page updated every few days with what I'm doing

yamah
22-Feb-10, 02:22 AM
Hey Scott,

that's an ambitious project for a newbie, Hovercraft are very tricky beasts and quite a balancing act to get right. There is more than 50 years of development so far and you have given yourself some challenging parameters to work around and an interesting material to use in construction.

These things are low flying self supporting wingless aircraft, there are some that are metal framed and very successful, although usually not of the light sport variety, a lot of care will need to be taken to achieve light weight whatever you build.

The possibilities are there to make something excellent, or you could get part way and be very disappointed by an oversight.

I sincerely hope you use that 50 years of knowledge to work those parameters into the thing you want to be as successful as what you have already seen AND go find your local hovercrafters group.

Start with a detailed expression of what purpose you want it to achieve as a flying object, and then look at using a recent existing design that can accommodate your parameters. I doubt you can improve on their flying abilities, your local hovercraft group will stress that to you, so too will everyone else.

Alan.

hector46
22-Feb-10, 12:15 PM
Hello Scott,

Sounds like an interesting project. Have your 'buidling an aircraft' head on when you start. Try not to think that your building a boat or you may end up with a heavier craft than you wanted. Keep it light. There are lots of knowledgable people on here that can help.

Good luck

Steve

scottwilko
22-Feb-10, 10:29 PM
Hey guys thanks for the responses, I've worked out the weight of the craft, from the material mass guide that was give to me by the people that I get my stainless off, I've over estimated the quantity of steel I'll be using and have come up the weight of 280kgs if I skin the hull in 2mm or 347kgs if I use 3mm, that is the weight of the finished craft including motor, it will have room for 2people

unfortunatly there are no hovercraft in the area where I'm from, the nearest is 2 hours away
and I have no idea where the owner lives, so it's a bit hard to get a look at one, but I'll have a good look around this forum and learn as much as I can before I make a start to the frame

Ross Floyd
23-Feb-10, 08:37 AM
A word of caution - 2 mm skin in stainless - that's massive!!!!

I work with the stuff and its like tool steel,very strong. I doubt you would need 2 mm on an SRN4. Also weights, - my feeling is that there is something very wrong with your calculations. Most stainless is roughly the weight of mild steel ( within 30 % anyway ) so this seems much too light, particularly with that thickness of steel.

I may have misunderstood, but at first glance my alarm bells started ringing!

Sorry if I'm being stupid!! :-)

Ross

hector46
23-Feb-10, 12:29 PM
I agree with Ross something is not quite right with your calcs or it's a very small craft you intend to build. There are aluminium craft out there but even they are not that light. Can you supply your craft footprint, lift and thrust detailsc etc You should build with as large a footprint as you can reasonably cope with.

Steve

John Robertson
23-Feb-10, 12:56 PM
Hi Scott

I've just had a look at your Facebook stuff and it looks like the hover frame is in the background of this pic?
4401
I'm afraid that this size of hull combined with the engine you have has virtually no chance of working (sorry :blush:). If, as you say, the hull weighs in at 280Kgs with engine installed, the drive gear will add at least another 25Kg, plus pilot (75Kg) and fuel, etc making a total of around 380Kg. On what looks like a 10ft x 4ft hull, the cushion pressure will be 22lbs/ft2. I'm not sure you would be able to get a axial fan to produce that kind of pressure - you would probably need a dedicated centrifugal lift fan (adding even more weight!).

Unless I've got it completely wrong and the frame in the picture is just a model or an experiment?

Most small craft (regardless of size) have a cushion pressure of around 10-14lbs/ft2 (there are very good reasons for keeping the cushion pressure as low as possible). A hull of this size should weight around 40-50Kg maximum. For reasonable performance, the finished craft (less pilot) should come in around 110-140Kgs.

Sorry to be the bearer of bad tidings but it's better to find out now rather than once you spent all the time and money building it :o

I would suggest that you buy a set of plans from one of the suppliers listed HERE (http://www.hovercraft.org.uk/showthread.php?t=18860) for a craft of similar size and use them as a guide to the sort of weight and performance you can expect to get. Take a look at examples of these craft operating in the real world (YouTube is a good place to start) and then decide what you want.

scottwilko
23-Feb-10, 10:07 PM
Hey guys, the frame in the background was something I was working on 2 years ago, it was to be a small one person hovercraft powered by a 6.5hp engine, it was to be a proof of concept, the frame in the photo is all stainless and weights in at 16.7kg, but there was too much electrolosis in the frame and so it defeated the purpose of it being made from stainless so I've scrapped that frame. My plan for the size of the new one is 2900mm long x1800mm wide

hector46
23-Feb-10, 10:36 PM
Hi Scott,

As John will tell you I love stainless steel. I work with it every day (very high pressure equipment) but wouldn't really use it as the basis for a hovercraft hull. I can see where your coming from but ideally GRP or even ply would be better. Use the stainless for all the brackets and the like.

Keep going but maybe think of using an alternative material, even buy some ASV plans they are on your continent:).

Steve

yamah
24-Feb-10, 02:44 AM
Hi Scott,
your footprint at 2.9 x 1.8 still seems too small for the SS and Kombi parameters.

re ASV plans and the kombi motor, they >can< be scaled up to get the cushion pressure right.

A very well documented build of a 235 superwedge (same thing), is on Lazza's Superwedge page, http://www.hovercraft.geek.nz/ ...ended up being half a metre longer and 300mm wider than the plans to get the cushion pressure calcs back to okay before he started building.

Final size was 4.05 x 2.1 overall. Total finished hull 140kg minus the Subaru EA81 engine and occupants and that was a plywood build that worked out pretty well as a cruiser.

Also http://www.speedjunky.net/ which is same size as Lazza's and even higher performance after sorting a few misconceptions and miscalculations.

Alan

scottwilko
24-Feb-10, 06:57 AM
Thanks alot for all the great advice, I guess using ss as a skin most Likely won't be successfull, because as I'm starting to work out the weights on a larger footprint they are really starting to get out of hand, so at this stage the chassis will still be stainless, I can keep the weight low( I don't have a material weight for the square tube yet, so I'll have to weight the lengths when they arrive) and I'll maybe look at using fiberglass( which i have no experience with) or maybe alloy,

my replys are abit short and dodgy because I'm doing all this from my mobile while I try to fix my computer, as soon as I've got my comp up and running I'll give you all a detailed explaination of my plan,

Paul Fitz
24-Feb-10, 10:17 PM
Scott, If you build a frame from tube and clad it, you will end up with a heavy craft. Craft weight is critical on a hovercraft. I assume you are competent using sheet material (as you suggest St.St) so consider building the craft from a thin material using the structure to form stiff elements.

I would advise that you purchase some thin card and build your design at 1/10 scale bonding the sheets together using paper glue and strips of typing paper. You will be suprised at just how stiff it can be made.

With the right design, a hull could be constructed from much thinner material than the 2mm you propose.

curtis5420
25-Feb-10, 07:52 PM
Hey guys thanks for the responses, I've worked out the weight of the craft, from the material mass guide that was give to me by the people that I get my stainless off, I've over estimated the quantity of steel I'll be using and have come up the weight of 280kgs if I skin the hull in 2mm or 347kgs if I use 3mm, that is the weight of the finished craft including motor, it will have room for 2people


2 or 3mm stainless is extremly overboard, your not building the titanic, which is likely to go the titanic route if you skin in this material.

have alook at the attached pics, i built this several years ago, its made from 1.5mm aluminium with a 3mm ally floor.

the strenght is in the shape of the hull, and the ribbing inside. i actually ending up putting lots more cross bars in the front of the craft.

with that monster of a vw engine (what power is that by the way) perhaps you should consider aluminium, with maybe a SS internal frame. but the strength of the hull is not in the frame its a combination of the shape of the hull and the internal ribbing. bit like an aircraft wing.

yamah
27-Feb-10, 02:04 AM
Hi Scott,

good luck with the welding, be prepared to cut it into quarters and add at least 1.25m length and 400 width later on if it is still the 2.9x1.8 you mentioned previously. It will probably still be heavy and perform marginally. Size does matter, large helps lower the cushion pressure, gives it some chance of getting off the ground.

What IS the calculated cushion pressure ? ? Ring Ring..

Here is an Australian made hovercraft ~2.9x1.8 that goes really well 30-60hp

composite monocoque skin construction, total weight around 140 kg RTF.


http://www.hovercraft.org.uk/attachment.php?attachmentid=1767&d=0

and here is one ~100hp that has a square hollow thin wall steel tubular frame and mostly foam and alum skin.

http://www.hoveraid.co.uk/images/hover.jpg
and another although may not have much of a frame

http://www.hoveraid.co.uk/images/gifford_reduced.jpg

Alan