Building with Craft Foamboard

[Colin BishopModerator @colinbishop34627]

Ashley,

A year or so ago I visited the Hovercraft Museum by appointment during the week, they just let us wander around everywhere, it was great!

Might be worth a try,

Colin

[ashley needhamParticipant @ashleyneedham69188]

Colin, yes thet is certainly an avenue, however at their open days there are loads of working models and stands etc etc, all very useful to see. Not sure if the srn4`s are open to personal wandering?

Paul, You will only have to stick velcro to the skirt (unless it is sewn on and it may be too late now!!) so save on glue and just use double sided. You are not likely to wear a skirt out ?? (or at least not during the day)

Ashley

[Paul TParticipant @pault84577]

Ashley

Your right about me never wearing my skirts during the day…..my legs are terrible…. and even worse now that my foot is bandaged up.

Paul

[Colin BishopModerator @colinbishop34627]

Ashley,

Yes, we were just left to wander around the SRN4 (both in fact) although I'm not sure we should really have been permitted to as getting to the cockpit involved climbing a rickety aluminium ladder from the car deck in the dark which was crammed with old hovercraft of all shapes and sizes including possibly some lawnmowers….

The pilot's view seemed to be very limited, a bit like trying to steer a multi storey carpark from the roof – terrible sightlines.

Colin

[ashley needhamParticipant @ashleyneedham69188]

On a gloomy day it must have been like sitting on a big cloud, sitting in that little box.

Ashley

[ashley needhamParticipant @ashleyneedham69188]

first one… worth thinking about?? second… garage, or hovercraft?

Ashley

[Colin BishopModerator @colinbishop34627]

Yup, looking for Cap Gris Nez and then seeing the Eiffel Tower come up….

Colin

[ashley needhamParticipant @ashleyneedham69188]

And you probably could in an `N4… is it 12 feet or more, the hovver height?

[Paul TParticipant @pault84577]

I have had no luck in finding a suitably sized computer cooling fan but my good friend Ashley has put me onto a site which sells replacement ducted fan blades. There are some superb and cheap parts on this site but nothing large enough for my needs, however I have sent them an email asking if they can locate a 150mm unit.

Had an xray this morning to check that all the shot had been removed from my foot and all is ok.

Paul

[ashley needhamParticipant @ashleyneedham69188]

Paul. Hope your foot is ok. Do keep the shot, it will make handy ballast.

The largest fan listed is approx 115mm diameter, and looks like the front fan on an rb211 jet. FANtastic. Puts out a whopping 5000g thrust it says.

just possibly you could use this slightly smaller unit, disguising the "looser" fit with vanes or something?? It is after all a purpose designed item, and I feel that almost anything else (from a computer or `fridge etc) will just not be up to the job. Mind you, if they can find a 6 inch unit…put me down for one! They are very cheap considering, although you would have to purchase a suitable fan/motor adaptor seperately as I see it, not expensive either.

Ashley

[Paul TParticipant @pault84577]

Ashley

I'm looking at the 115mm unit with a view to adapting the hovercraft chassis to suit.

My foots alright….it was my own fault for having the wrong cartridges in the gun.

Paul

[Paul TParticipant @pault84577]

The hovercraft is complete and I am please to report that it has survived its initial test runs, although I do need to change the lift fan for a more efficient unit.

As for the results of the initial proposition i.e. the suitability of craft foamboard for this type of model construction, I'm happy to say that the board has passed with flying colours and that coupled with a light timber frame the body of the hovercraft performed in the same way as liteply and resisted light to moderate impacts as well as 4mm ply.

The next stage is to see if there are any problems in decorating the model with traditional paints

Paul

 

Edited By Paul T on 03/05/2013 07:13:38

[ashley needhamParticipant @ashleyneedham69188]

Paul. So glad that your model is a success, but how could it not be??

I think that an all-over coat of Eze-cote would be the thing now and then you could paint it with whatever you wanted.

Did you use the 115 fan unit and if so what motor and voltage please (just interested for no particular reason). The lift fan on a hovercraft has to produce pressure in a "space" (plenum chamber) rather than just a fast stream of air and I believe ordinary propellors are not the best thing for this, a proper fan or a rotary blower (hairdryer style) is much more efficient. Bugbear of this is ordinary props are easily available whereas the other is not.

Same site has a 127mm fan unit designed so it says for 540 sized motors….interesting…. or do they mean the equivalent brushless??

Ashley

[Paul TParticipant @pault84577]

Ashley

I used a 150mm aircraft 4 blade pusher propeller on a 500 motor knowing that it wouldn't provide the performance that I wanted but sufficient to test the theory. I am still on the lookout for a set of 150mm fan rotors to provide the required lift.

I looked at the design specs for the 115 fan unit and concluded that it wouldn't maintain sufficient air volume for my particular model and although I am sure that this unit would easily power a model with a smaller or circular hull plan it is just to small to simultaneously maintain skirt inflation and provide adequate lift for my test model.

Cant comment on the brushless question as I have no idea how the comparison would work. (try Dave M)

Paul

[ashley needhamParticipant @ashleyneedham69188]

Using air props for this sort of thing needs experimentation just like a boat. i think that you would have better results with a normal twin blade low pitch prop.

Low (air) speeds..best thrust on low pitch, high (air) speeds high pitch.

I think that if I were to persue a hovercraft i would make a test rig using the kitchen electronic scales, to get a comparison on thrust/power consumption. How would one measure the ability to build up pressure on the inside of a hovercraft though??

Ashley

[ashley needhamParticipant @ashleyneedham69188]

Box, shoe or otherwise….opening in top to suit motor/prop/fan under test (tunnel etc).

Plastic tube set one end in box (end shielded)…other end on outside, higher end than inner….with water in..like a level.

Turn motor on connected via ammeter….watch external tube water level rise as internal pressure rises…mark. with felt pen….. compare levels with different cominations.More internal pressure, higher the water level rises

Will not give a reading in "BAR" or what have you, but will show differences in pressure build up in the box. Could try with perhaps some holes in the box…as a representation of air escaping from the skirt.

AShley

[Trevor HollowayParticipant @trevorholloway99134]

A home made U-tube Manometer !

Lots of fiddling possible – what made me put my hovercraft in the loft was the skirt kept undoing the velcro underneath loosing all down thrust and the lack of forward thrust as it kept bogging down on the grass, tryied it in a carpark and it just fell down the camber !

[ashley needhamParticipant @ashleyneedham69188]

As I have said, double sided tape I think is the way to do it (no experience , just what I have read).

A manometer indeed.I suppose may be useful.. would give you a yardstick to go on, when you try something and it is not powerful enough, you know what to try next!!

Sunday?? Final runs for projects 1 and 2.

Ashley

[Paul TParticipant @pault84577]

Double sided tape works great for fitting the skirt.

[Paul TParticipant @pault84577]

The craft foamboard on the hovercraft is decorating very well as so far I have used acrylic, cellulose, oil based paints and vinyl all of which have taken well and produced a first class finish.

I will post some photos when the decoration is complete.

[ashley needhamParticipant @ashleyneedham69188]

You can paint anything on paper, just the foamy bits might squirm with cllulose, but if they are covered with card and PVA the werld is yer oysta.

Decoration…..Laura Ashley?? or designer?

Ashley

[Paul TParticipant @pault84577]

Designer…and obviously it has to be Norman Foster

[Paul TParticipant @pault84577]

The hovercraft is almost finished.

I got a little carried away with the yellow paint.

Edited By Paul T on 10/05/2013 15:34:15

[Paul TParticipant @pault84577]

The hovercraft is almost finished.

I got a little carried away with the yellow paint.

Edited By Paul T on 10/05/2013 15:34:15

[Paul TParticipant @pault84577]

The hovercraft is almost finished.

I got a little carried away with the yellow paint.

Edited By Paul T on 10/05/2013 15:34:15

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