I want to build a Hovercraft, Help!

[ashley needhamParticipant @ashleyneedham69188]

An afternoon session with a "deflector bar" underneath the lift fans and having blocked up more of the holes in the front bulkhead in an effort to get more air to the rear has produced only a very small improvement. Un less the weight is absolutely in the right place it tends to nosedive or the back end is just dragging in the water. Oddly enough it went really well over the wind blown debris in the leeward pockets of the pond….could be important on a Sunday when i answer critical heckling over its hovering capability. As i was about to decamp and put the mucky craft in the boot, I had a whim to try it on the car park, and boy…did it go!!! i was running after it the little wotsit.It didnt have a battery in it as ballast mind you. I recon the real thing will weigh less that half the current 1.6Kg prototype, so in actual fact the skimming weight across the car park may well be the final actual weight as finished (I will only put one coat of undercoat and one topcoat to save weight!)

As to improving the situation I am going back to basics as per Sir Richard Cockerell and the SRN1 (coz the original didnt have a skirt) and will box in the bottom of the fuselage and allow the air to escape around the underside edges via holes….this will even up the air distribution at the expense of a tiny loss of efficiency (possibly) ideally the air would be directed inwards from angled tubes. This would  be easy to adjust at the pondside as I would make lots of holes, and tape them up, untaping them a few at a time to note the effect.. ALSO I wondered about angling the foreward thrust motors downwards by just a few degrees to assist in levitation.

Sorry, have I lost anyone yet?? Len, still interested in a hovercraft?   Ashley

[Len OchiltreeParticipant @lenochiltree67043]

Hi Ashley,

Yes I am still interested,do you mean that you have 4 x props/motors and ducted fan motors for lift?.

I like the idea or using pipe lagging as an ex plumber I have a garage full of different sizes.

Please keep posting your thoughts and photos.

Len.

[ashley needhamParticipant @ashleyneedham69188]

I have 4 motors driving the 4 air props, and two ducted fan units providing lift UNDER the front pylons. I have decided that the current lagging is too small, and I have spotted some approx 60mm in outside diameter moulded in black that will be fantastic if i can find a local(ish supplier)…armaflex is the trade name, or I may have to buy on-line. After some more thought I think the nosediving is due to the small shelf around the perimiter to which the skirt is attached. This catches waves and acts like a scoop, the more the weight of water, the further it dips. I will build a loading ramp like the original at the front and box in the shelf and this should cure the  tendancy to dig in the water. Larger size lagging will also help by giving a larger "bow",  I see that on the full size craft the skirt top was in fact higher at the front than the sides/rear.  Having the air distributed through  the body of the craft will also help in containing a steady flow of air and not dumping it wholesale when a corner of the skirt lifts up. Finding handed 4.5" props is going to be the difficult part. Ashley.

[ashley needhamParticipant @ashleyneedham69188]

I have discovered the big Travis and Perkins builders merchant opposite us at work in Vauxhall has a large range of pipe lagging sizes, the man was very helpful when i told him what I wanted it for. I purchased some for a 45mm pipe which had a wall thickness of 9mm, giving me the 60ish mm overall size I wanted. HOWEVER, on reflection.. they had some stuff approx the same overall size but intended for a much thinner pipe, This means the wall thickness was much greater and thus the pipe would keep its round profile better, giving me a flatter bottom, weight would not be an issue its so light . It was a bit tricky bringing home two 2M lengths of the stuff on me push bike.

I just had another thought.. If the bottom wasnt flat enough, a few laps around the car park would sand it to an even level !!!!   I am going to  make a floating only military style srn6 non-hovering hovercraft for the lad for xmas. This would simply be the original idea of a floater, but air powered. That lagging is really really bouyant, a reasonable size srn6 I am sure would float in probably 1/2" of water no sweat.     Ashley.

[Len OchiltreeParticipant @lenochiltree67043]

Hi Ashley,

Yes Armaflex is the Rolls Royce lagging,and not cheap.

Are you using it with the slit in the top or the side?.

Len.

[ashley needhamParticipant @ashleyneedham69188]

Len, I am using it with the slit at the top, JUST in case water gets in. It is also a handy line to put at the top of the tube when cutting it on the bandsaw  so each end`s cut is er, square on,,if you know what I mean. I have some of the thick-wall stuff now , £5 for 2M and its nice and circular for the length, so should be better. Although its twice as heavy the extra weight should be neglegible in the grand scheme of things.( its spelt rong,isnt it?)

[Len OchiltreeParticipant @lenochiltree67043]

Whats spelt rong? rong is spelt wrong but wrong is spelt right or is it write or rite ? this could go on and on.Now what was the question?

[ashley needhamParticipant @ashleyneedham69188]

Its no good, the laging duz not wont to b glood by the UHU or Wilkinsons all purpose gloo (properly, it sort of gloos it). I may try Evo stick. I hav now splashed sum  paint on the craft, wite sides,gray top and red pylons/ruders, and it looks much betta. Its funy, the culers do make a diferance to yo` persepshun of perporshun, an i originily thort that the pylons wer to small, but i fink they is about right axshuali. i av boxed the botom in and it looks ded good. if i can be bovvered i might take a pikshur, or then agen , i mite not. depens on `ow i feel. Ashlee.

[Len OchiltreeParticipant @lenochiltree67043]

Hi Ashley,

I seem to remember that I used Evostik if I had to glue Armaflex. I got so used to cutting mitres with a Hacksaw blade that I could guess 45deg ( I cant find the deg symbol on the Keyboard anyone know where it is ? ).

Any more Photos yet ?.

   Len.

[ashley needhamParticipant @ashleyneedham69188]

Len, no pics yet, I am having another bash over the weekend when i have some evo stik. My bandsaw cuts the stuff ok with a fine ish blade and I can set up the angles easy on the sliding guide.The boxed in bottom with its edge holes and guide flaps looks good. it had better work or i shall have to cut it all out !   Ashley

[ashley needhamParticipant @ashleyneedham69188]

O.K, first picture, sticking the 60mm diameter foam skirt together with, phew! Evo-stick, Second picture, the bottom covered with more 3mm MDF, 18mm holes drilled in, both hole size and spacing determined by strict scientific methods…it looked about right to me. Notice the access hatch to get to the lift motors, glued in by hot glue, so it is removable if required without too much trouble. Third picture, The new ramp and side pieces to stop the front getting swamped, hopefully, although i am relying on the larger skirt to do this. Fourth piccy, rear view showing masterful paint job and posh new taller fins. You see now the value of painting it> It does add clarity to the proportions, The pylons look a tad short to me. but the fins are about right. Painting the motors of course would add to the apparent height.

[ashley needhamParticipant @ashleyneedham69188]

What I should be working on of course, never mind I will finish it after the hovercraft, perhaps.

[Paul TParticipant @pault84577]

Wow Ashley

Don’t you think that this hovercraft might be a little over powered.

Paul

[ashley needhamParticipant @ashleyneedham69188]

Paul. There is no such thing as overpowered in my book !!!    Ashley

[ashley needhamParticipant @ashleyneedham69188]

Todays test showed only a very small improvement, althogh was stopped prematurely when a motor fell off…… And this may have been down to the larger skirt alone. It certainly floats much better, and supports 2x batteries no problem now. I may be missing a trick here though…. I am going to tape up the edge holes and make some larger holes around the centre well to let the air out. The new theory is that the air is intruduced into the centre of the craft before seeping out, as I am not sure the deflectors on the edge holes made any material difference. There was STILL a tendancy to nosedive if there wasnt a battery positioned right back in the centre well. It is also not going to be fast enough. I have seen some slim graupner 5×2 props (not very pitchy) that will made a composite 4 blader of a better size, these will need a 400 motor though and I will need to get some long propeller adaptors, possibly made up custom. As this should provide adequate power, the front motors could to advantage be less powerfull to save current consumption , Aesthetically they would need to be around 400 can size–any suggestions?,.. I also need to get some capacious NiMh batteries, as I dont think the SLA`s like dishing out 13+ amps at a time. Whew, hard work on my brain cell this. Ashley

[Len OchiltreeParticipant @lenochiltree67043]

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