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View Full Version : Advice and suggestions sought



Ashwin Murali
12-Jan-10, 01:18 AM
Friends, i'm at a very crucial juncture of my project - the Hovercraft. I've my first review in 10

days time. I'm in the process of material selection now. Despite going through numerous

articles and essays on Hovercraft, doubts still persists. Your advice and valuable suggestions are sought for the following questions:

1. I've decided to use a 12mm ply coupled with a 5mm foam for my hull. Is it ok or shall i go with ply (of 19mm) alone?

2. Skirt design baffles me completely. I'm yet to find a suitable website / article / thread in a forum that would help me with it. Though i've selected a material of nylon for it and decided to go for bag skirt, am unable to understand as to what dimensions the skirt should be cut and what calculations it involves. Please help me with this.

3. Which type of blower is suitable? An axial one or a centrifugal one? I've seen some centrifugal blowers and am inclined to go for it. Should i proceed or should i reconsider?

Your valuable advice and suggestions are sought. Please help. I took upon this project only after i found out that i can bank on the people in this forum who would help me with any doubts that may creep into my mind in the course of this project.

broad5186
12-Jan-10, 01:33 PM
1 - 12mm or 19mm ply is very heavy for a hovercraft - small craft use as little as 4-5mm ply - foam is only useful if it is sandwiched between plywood layers

2 - can't help you with bag skirts - i can if you coose segmented

3 - Axial fans dominate for thrust and lift for small hovercraft - larger craft use centrifugal - manufacturers such as multi-wing and hascon wing are our main source of fans

hope that helps

tony

KipMac
12-Jan-10, 04:41 PM
Ashwin,
As previousl advised why don't you go to the HCGB Homepage and look at the "Downloads " that are available.

You do not appear to have decided on anything at all and yet you are asking for help.
Without some input from you as to where you think you are going it would take a weeks of questions and answers.
Most of the info you require is available on this website.

You can even get plans.

Kip

John Robertson
12-Jan-10, 04:43 PM
1. Impossible to answer without some idea of the hull structure and shape. As Tony says, 12mm ply is too heavy for any design. Using 5mm foam is pointless - it's too thin to provide any composite strength (if you are using it that way) and too small a volume to give much useful flotation.

2. There are plenty of sources on skirt design on the web - check http://www.4wings.com for example.

3. Once more its impossible to provide an answer without more detail (craft weight, payload, cushion area, operational limits, etc).

I don't want to put you off but hovercraft look simple in theory but it's notoriously difficult to design one that works properly (the difference between a working and non-working craft can be something very small - there is no such thing as an almost-working hovercraft :))

There are designs out there for simple hover craft - from the vacuum blower "disc" (http://amasci.com/amateur/hovercft.html) to the UH entry level craft (http://www.hovercraft.com/content/index.php?cPath=39&main_page=index) and others.

Ken_A
12-Jan-10, 05:33 PM
Ashwin,
Reducing the overall weight of a hovercraft should be a primary design consideration.
The strength of a craft is not acheived by using strong heavy materials but by using construction techniques that allow the use of lightweight materials. Techniques such as folds and curves are examples of this.
An old but very succesful design can be seen here:-
Caliban (http://www.flightglobal.com/airspace/media/galleries/images/13928/500x400/kent-caliban-3-cutaway.jpg)

curtis5420
12-Jan-10, 06:39 PM
i have a sneaking suspicion, this hovercraft he wants to build is a plywood disk with a leaf blower??

Ashwin Murali
13-Jan-10, 04:34 PM
Friends, Thanks a lot for responding promptly.

Mine is a single seater craft of dimensions 4ft X 7ft (may extend a little say 4ft X 8ft).

I planned it for a payload of 150kg but am ready to relax this limit a bit say 200 kg including the driver.

Am planning to use 2 stroke petrol engines for the lift as well as thrust.

@ Tony: Will a 4-5mm ply be good enough to withstand the weight of the engines?

@ Kip: You're right. I've a lot to refer before i post my next thread. Thanks

@John: Thanks a lot. Your links were really helpful. I want my hovercraft to be something like the UH - 6F Trainer.

@ Ken: Thanks a lot :)

@ Curtis: Its not a leaf blower craft. Though my first impression of hovercrafts was formed after watching videos of leaf blower crafts, i intend to build something better. My craft will be better than a simple disc type leaf blower craft but it will not be as complex as the crafts that i come across in this website (those racing crafts).

The craft that i intend to build will be somewhat like these:

http://www.vtualerts.com/wp-content/uploads//2009/11/personal-hovercraft.jpg

http://cheaphovercrafts.tripod.com/imagelib/sitebuilder/misc/show_image.html?linkedwidth=actual&linkpath=http://cheaphovercrafts.tripod.com/sitebuildercontent/sitebuilderpictures/hover_test_drive_4.jpg&target=tlx_new

http://www.hovercraft.com/content/index.php?cPath=39&main_page=index

I intend to build it more like the first link provided than the other two.

I suggest that those wishing to help me by providing advice may take a look at the above links so that they get an idea about my craft and its requirements.

Thanks a lot everyone, once again.

John Robertson
13-Jan-10, 07:13 PM
Ashwin,

To be honest, looking at your budget and plans, you would be far better off just making the disc type craft and fitting a simple leaf blower for lift and some thrust. It will easily carry 150Kg on a smooth surface (I've built one and it does!) and will probably perform as well as any of the craft you have listed (apart from going onto water like the UH6F).

Your choice should be the disc-type craft or a "proper" hovercraft that will have some functionality - none of the craft you show are practical in any way. To build a functional hovercraft your best (and lowest cost) option is to buy plans for a proven design. Spending more money (than the disc-type) building something in-between that has no purpose seems pointless to me.

Winst
13-Jan-10, 07:56 PM
I intend to build it more like the first link provided than the other two.

I suggest that those wishing to help me by providing advice may take a look at the above links so that they get an idea about my craft and its requirements.

Thanks a lot everyone, once again.

If you intend to build it like the first craft please, please, please make sure you have a gaurd on the fan. There is potential for a very nasty accident if not.

curtis5420
13-Jan-10, 08:22 PM
Ashwin,

Your choice should be the disc-type craft or a "proper" hovercraft that will have some functionality - none of the craft you show are practical in any way. To build a functional hovercraft your best (and lowest cost) option is to buy plans for a proven design. Spending more money (than the disc-type) building something in-between that has no purpose seems pointless to me.

i agree, those links point to a big galourified disk leaf blower craft, Not practical as hovercraft in anyway, apart from going around a car park (if that).

if you are going to do a duct and belt reduction drive to a fan, then why not build a proper hull.

if you want to experiment in something like a car park, build a disk with a leaf blower whihc will cost bugger all. but dont try and make it better, as it will disapoint dramatically.

then maybe build something properly, but dont spend lots of money on a flying sheet of ply.

atters
14-Jan-10, 07:01 AM
Building a Challenger like this did not cost all that much when built from ply and with the clubs plans. I had mine together in a week, the hard bits were the drive train and duct. But again quite easy to get right if you just follow the plans.

I say do it proper first time, I messed up my build by not going to the plans and paid big for it.
I got back on track with the help of the club and ended up with a great little craft that me and the family could enjoy.

Ashwin Murali
16-Jan-10, 08:02 AM
@ John: I'll take your suggestion. Thanks :)
@Winst: Sure. Thanks :)

@ Curtis: I get that. In fact, my requirement is just that. Once the craft is built, i need to take it for 2 demo rides - one in water and the other on land say around a car park. After successful demo rides, the craft will be submitted to the college.

@Atters: Thanks. Your pic has boosted my confidence :)

Now i get a good idea of my own requirements and what needs to be done for it. I've started designing a 3d model.

Thanks to everyone. I'll clarify my doubts, if anything were to arise during the course of my project, by posting my queries in this forum.

Thanks again everyone.