Hovercraft!

calumwm

calumwm

calumwm

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Joined
24 Dec 2008
Posts
58
helloo, i thought i'd stick this on here just to see what response i get :D

i'm going into upper 6th in september, and one of my subjects is product design. i'm known around school for making the biggest and most unusual projects - and as it's my last chance i thought i'd go out with a bang :D
hopefully not literally though...

so i've decided to build a HOVERCRAFT! it'll be 8x4ft, and powered by a 250cc yamaha bike engine. the project will start rolling properly in september, but so far i've got a sheet of 1.2m x 2.4m x 2.54cm marine plywood.
the skirt will be made from 2 tractor tyre inner tubes (ext diameter 1.2m, tube width 22cm), with a third chopped from each, and sealed back together in a figure of 8 sort of shape.

i've looked into propellers, and i think a paramotor one is what i'm after - although i'd like one around a metre diameter, but i can't find any :/

at the moment the body will be fibreglass, but i'm considering carbon fibre - it will all depend on my budget - after a bit of research i've been quoted £125 p/m^2 of finished surface.

because of this i'm also after funding for it, so i've sent letters to the likes of boeing, BAe, top gear, urenco, sellafield, and VT aerospace. if anyone has any useful contacts i'd be more than happy to get in touch with them :D
at this stage i think it could cost anywhere between £500-1000, and i've had £100 sent so far...



on another note, an interesting thing i've found is the 'Hovercraft Act 1968' - in section 4 (3), it says:
Except as otherwise provided by or under this Act or an enactment passed before the date of the passing of this Act, a hovercraft shall not be treated as being a ship, aircraft or motor vehicle for the purposes of any such enactment or any instrument having effect by virtue of any such enactment.
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SOURCE

does this mean it will be allowed on roads or not? if it's not treated as a 'motor vehicle' is it governed by other law requirements such as having lights, brakes, ability to steer - all the MOT stuff?



anyhow, i'll be updating this with pictures etc throughout - enjoy! i know i will :D

Calum :D
 
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a 250cc engine probably won't have enough horsepower to lift and drive an 8x4 foot hovercraft unless you make it out of polystyrene and balsa wood
 
i might be able to get hold of a 450, but a local college is donating it to me - theyre after collaboration between our school and themselves, so i might be able to sort it...

are there any formulae for working that sort of stuff out? so far i've found the skirt pressure needs to be about 0.1psi using force=pressureXarea, so i'm after something that will let me work out the power required.. any suggestions?

i also didnt mention before that just one engine will provide thrust and lift - i'm looking at making a box behind the propeller - half of the air will be used as thrust, and the other half will be channelled into the skirt to lift the craft.
 
Road? NO!

Have you ever piloted a hovercraft? If you had you would not welcome them on the road!

Good luck with your project. Probably worth looking at what engines are specced in the commercially available hovercrafts used by adventure sports / stag type facilities as they are of a similar physical size to the one you are planning.

If anyone is interested I went hovercrafting on a stag do recently and totally pwned everyone walking away with a 1st prize trophy!:rolleyes: Very similar to quad biking which I am handy at.
 
Laser402 said:
Sounds a lot less reliable, practical than just 2 engines
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Entry level hovercraft kits would seem to agree with me after a bit of research...

Driving the craft is easy as it has only two controls; steering and throttle. Slowly advancing the throttle will bring the craft up on cushion. Adding a little more power accelerates the craft. Speed is easily controlled by increasing or decreasing engine rpm. First time pilots can learn to operate the craft in a very short period of time.
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Fair enough, after watching the posted scrap heap video, it does seem like a cheaper way of doing things, just as long at you keep the revs up enough to keep the skirt inflated, else your flying off it.
 
nope, i havent flown/driven one, so it makes it more exciting when it's finished :p lol

i have got an RNLI station nearby with a hovercraft, so i'll have a look at that when we get back to school, and ask very nicely for a go :D

and more engines = more weight, but more power obviously.. grr compromise :/ :p plus space issues, and weight distribution - it'll probably limit it to one man.
i'll have to ask the college in september, and have a big discussion about it.

at the moment steering will be rudders on the top half of the back of the propeller, and we've been thinking about the one engine doing both tasks - could bevel gears be a feasible way of sorting it? if we can work out the size of the cogs required to provide enough lift, we could work something out so that the prop speed can be changed as you change gears but the lift fan speed would remain constant? i've been warned to stay away from gears, and after typing that i can see why :p


and a few classmates have mentioned the scrapheap challenge thing, watching it now, 8-9 mins in? they lift off a bit higher than i thought :p
 
calumwm said:
at the moment steering will be rudders on the top half of the back of the propeller, and we've been thinking about the one engine doing both tasks - could bevel gears be a feasible way of sorting it? if we can work out the size of the cogs required to provide enough lift, we could work something out so that the prop speed can be changed as you change gears but the lift fan speed would remain constant? i've been warned to stay away from gears, and after typing that i can see why :p
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You essentially just need a scoop at the bottom of the prop exit airflow to take away some of the air to fill the skirt.

You can experiment with the height of the scoop to make sure enough air is being shifted to fill it just before the thrust is enough to start you moving.

Its a fairly standard method on the small racing type craft it seems :)
 
calumwm said:
nope, i havent flown/driven one, so it makes it more exciting when it's finished :p lol

and more engines = more weight, but more power obviously.. grr compromise :/ :p plus space issues, and weight distribution - it'll probably limit it to one man.
i'll have to ask the college in september, and have a big discussion about it.

at the moment steering will be rudders on the top half of the back of the propeller, and we've been thinking about the one engine doing both tasks - could bevel gears be a feasible way of sorting it? if we can work out the size of the cogs required to provide enough lift, we could work something out so that the prop speed can be changed as you change gears but the lift fan speed would remain constant? i've been warned to stay away from gears, and after typing that i can see why :p
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Firstly earlier you said the skirt will be inflated to 0.1psi that seems way too low to me, even 0.1bars seems low. Especialy with the weight you will be holding.

Some other ideas for you, have you thought where the engine will be mounted as if it is at the back you will have to counter weight this from the front? But are you in fact heavier than the engine in which case your nose will be lower. Also if the engine is at the back driving the fan you will have to redirect second airflow back forwards to wards the front underneith the skirt.
This causes more problems.

Another idea instead of rudders why not just have the fan able to swivel? Could be easier than making a full set of rudders.

Im a bit rushed in reply at work but i could help you with your design. Just email me in trust i can also help your calculations.

:D
 
i thought that too about the PSI, but thats what the formula tells me - and an example was similar, so i'm not sure :S

the weight issue is just going to be improvised i think, and the engine(s) will be as central as possible - and does the air have to be channelled once it's on the underside? doesnt the air spread out until the pressure is constant on the whole underside?

we've looked into swivelling the fan, but i think it will make it more difficult as the engine would have to be attached and moved with it, which would make it quite heavy and difficult to steer :/

rudders are simple i think as they have a few ways of controlling them - i think it could be as simple as steel wires (like bike brake cable), but it would look bad and probably be dangerous having them across the body..

i've also been drawing up a few ideas today, and landing gears popped into my head - its going to have to get around school, and wherever else i take it (without engines occasionally) so i'll have to make a trailer, or wheels for it.
to make sure it definitely does hover and isnt just a fancy go kart, theyd have to be retractable, so is it a good idea? comments?

and as it IS a school project, there are strict things about me doing the work, so the majority of it is up to me - including the design, but thanks for the offer!
 
My opinion is I wouldn't bother making it out of cf, just use gf. On a project like that the weight saving will be so small it's not worth bothering about. You're probably going to paint it anyway.

Aod said:
a 250cc engine probably won't have enough horsepower to lift and drive an 8x4 foot hovercraft unless you make it out of polystyrene and balsa wood
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It should be plenty. I made one with two petrol leaf blowers and it still *just* worked with 8 people on it on a smooth surface.
 
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