Martian Posted March 20, 2020 Share Posted March 20, 2020 KC started an isolation build thread I suggested a Hovercraft and 1 or 2 would like me to share a build blog so here it is. about 40 years ago I built from a plan an SRN1 it was ok and like the prototype had no skirt (must have been cold ) lift was produced by a large centrally mounted lift duct and bled air to 2 parallel thrust ducts air was fed fore and aft to help with control it had a plenum chamber which was a balsa fence to try to contain the air performance was useless so after a bit of research I settled on drawing my own plans of a roughly to scale Britten Norman CC7 . I realized it wasn't enough to just push air into a plenum chamber in order to provide decent lift it had to have a skirt which increased the air volume trapped under the craft it was 6ft long and about 30inches wide with a 4-inch high segmented skirt held on with Velcro, powered by two IC glow engines lift provided by a veco 60 I think it was a 12 inch prop and I think a 35 os (not sure) lift was impressive but not enough thrust dangerous to start both engines starting the lift engine first would require a lot of downward pressure to counteract the powerful lift or risk losing your hand never mind fingers equally the thrust engine was within a closed thrust chamber to replicate the real craft so again a bit risky. Never the less it was impressive and made the local rag claiming it chased all the cats. So that's my introduction about my hovercraft knowledge more tomorrow. Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted March 20, 2020 Share Posted March 20, 2020 ... keep this up, Martian. I don't know anything about IC - not much more about leccy motors - but I would suggest to keep it rotor/stator choice. Are you going for single or dual power unit(s)? Looking forward to seeing you progression. Cheers Chris Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted March 20, 2020 Share Posted March 20, 2020 And so it begins... Thanks Martian Quote Link to comment Share on other sites More sharing options...
Richard Harris Posted March 20, 2020 Share Posted March 20, 2020 Martian, Good to see something different!, will be watching with interest Rich Quote Link to comment Share on other sites More sharing options...
Mark Stevens 1 Posted March 21, 2020 Share Posted March 21, 2020 I remember that original SRN1 plan - I have it but not got around to building one yet. It's still available - Link Mark Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted March 21, 2020 Share Posted March 21, 2020 Will be watching with interest as I am sure you will be adding your take on the original design and bring it up to date. Chris Quote Link to comment Share on other sites More sharing options...
Robert Putley 1 Posted March 21, 2020 Share Posted March 21, 2020 I built a model of an SRN1 in 1959 at the young age of twelve years, having seen the original at the Earls Court boat show. I designedit it as I went along. Built out of balsa and powered by the venerable Mills 75 swinging an 8x4 wooden prop. Ran it on the road outside the garden. Gave it a gentle push and it fairly wizzed along over puddles and all. a couple of motorist stopped to take a look. It was very light, which I feel helped a great deal with sprightly performance. The two thrust boxes on top were fairly ineffective Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted March 21, 2020 Share Posted March 21, 2020 Robert That absolutely amazing! I too built a hovercraft in 1960 out of 1/4" and 1/16" balsa also powered by a Mills 75 (the only engine I had!) swinging a 8x4 plastic prop. The tips were trimmed to just clear the duct that had been built around an 8" cake baking tin. Being an inveterate hoarder I still have it 60 years on! It quickly had a clear polythene skirt added to create a deep plenum chamber which worked very well. Of course the vertical component of the engine thrust was probably a significant proportion of its weight. I not unreasonably assumed that by taking air from the front of the duct and directing it to rear would drive it forward but I had completely misjudged the effect of engine torque on such a free running thing. The end result was it did hover, simply rotated about it axis and quickly started to travel down wind at what ever the wind speed was. I did build another but with the Mills driving a 4 blade 6x4 prop facing forward with a duct diverting the air 90 degrees down into the plenum. It sort of worked and it did travel forward but this time the engine torque caused it to 'list' to one side with the result it moved sideways at the same time. Never did cross the channel in an SRN4 or take a 'Bay of Biscay jolly' in Concorde come to that, both of which I never quite got to do. Ah! well. Opportunities missed. Quote Link to comment Share on other sites More sharing options...
Martian Posted March 21, 2020 Author Share Posted March 21, 2020 Welcome Simon your knowledge of air management will be useful as I like your Hovercraft SC1 Quote Link to comment Share on other sites More sharing options...
Cuban8 Posted March 21, 2020 Share Posted March 21, 2020 Around about 1967 (when I was ten) I remember saving up my pocket money for a small electric model hovercraft kit that was advertised IIRC in the Valiant boys' paper that I used to get weekly. When it eventually came, as was usually the case back then, it didn't resemble the dynamic picture or description in the advert, but was a just a collection of plain vac formed bits and pieces that needed to be cut out and a really pathetic Mabuchi motor that could be found in most small motorised toys. Probably ran on a couple of 1.5V torch batteries, but I forget now. Managed to put it together, but what I do clearly recall is how it just sat on the lino floor of our kitchen just whirring and shaking itself along rather than on a cushion of air! Not surprising really. A long shot, but does anyone remember the model? Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted March 21, 2020 Share Posted March 21, 2020 Hi Martian, A few years back, I wanted to try building a hovercraft and my attention went to Mark Porter's Griffon 2000. Not a small beast with a length of 1 meter and 50cm wide. Then I lost my reason somehow and decided to have a go at Peter's Ballerina and I'm still haunting the corridors if this forum... If you're looking for ideas or some spare parts - even Nylon + PU fabric to make the skirts - here's a UK based company named Palaform LTD. Could be of interest for potential 'Iso-Builders'... Cheers Chris Quote Link to comment Share on other sites More sharing options...
kc Posted March 21, 2020 Share Posted March 21, 2020 The idea of a hovercraft appealed to me until I read the bit about chopping off a fingertip because of an unprotected lift prop. Unless the design includes some sort of mesh grill that prevents contact then it's not for me. Just imagine what would happen if it came into contact with someones slipper, toes or next doors cat! Quote Link to comment Share on other sites More sharing options...
Keith Berriman Posted March 21, 2020 Share Posted March 21, 2020 Back in the early 70`s I had swopped an Electronic Calculator for a 2.46 ED engine and fancied something easy to control so made a home made Hovercraft. First trial test flight found it wanted to spin due to prop revs so added some vertical fins but this not improve things. It was getting out of control and went to grab it and as above but took the skin off my thumb end by 1/4 " . I then stamped on it to stop it and threw the project in the bin ( Not the Engine ) Never fancied one since even with improved engines radio control etc but maybe electric is the safer way to go Quote Link to comment Share on other sites More sharing options...
Martian Posted March 21, 2020 Author Share Posted March 21, 2020 Posted by kc on 21/03/2020 18:22:24: The idea of a hovercraft appealed to me until I read the bit about chopping off a fingertip because of an unprotected lift prop. Unless the design includes some sort of mesh grill that prevents contact then it's not for me. Just imagine what would happen if it came into contact with someones slipper, toes or next doors cat! Hi KC the lift motor is not accessible underneath this will become clear as I lost more details , I was testing balance with lift motor running my own fault for not thinking it through it was at the top of the duct same sort of prop strike from a plane prop. I will be looking to guard the inlet safely. Quote Link to comment Share on other sites More sharing options...
Martian Posted March 21, 2020 Author Share Posted March 21, 2020 Posted by RC Plane Flyer on 21/03/2020 18:34:56: Back in the early 70`s I had swopped an Electronic Calculator for a 2.46 ED engine and fancied something easy to control so made a home made Hovercraft. First trial test flight found it wanted to spin due to prop revs so added some vertical fins but this not improve things. It was getting out of control and went to grab it and as above but took the skin off my thumb end by 1/4 " . I then stamped on it to stop it and threw the project in the bin ( Not the Engine ) Never fancied one since even with improved engines radio control etc but maybe electric is the safer way to go There has to be a balance with weight but without knowing your layout it's hard to guard the problem . I have this picture in my head of you stamping on your Hovercraft with blood dripping everywhere at least you got a decent motor. Quote Link to comment Share on other sites More sharing options...
Martian Posted March 21, 2020 Author Share Posted March 21, 2020 I would personally be loathe to build another ic powered hovercraft because I found them to be inherently dangerous unless you like to give blood 😱 Quote Link to comment Share on other sites More sharing options...
Martian Posted March 21, 2020 Author Share Posted March 21, 2020 I wanted to build this Hovercraft with what I had and that is foam board A1 that is the basis for size bits of Ali and ply and a length of pine spar. I had printed a 3d lab Super sabre but am unable to get the correct oleos for that I bought a FMS 12 bladed 90mm EDF which is supposed to produce 3kg of thrust this will be the thrust motor and for lift a turnigy 3542 1250kv both will run on 4cell 4000mh lipos and at the moment a single servo for thrust vectoring . the easiest way to demonstrate is with pictures so I will do that and be back. thanks for following along Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted March 21, 2020 Share Posted March 21, 2020 Nothing to add, coz out my depth, watching though. Quote Link to comment Share on other sites More sharing options...
Martian Posted March 21, 2020 Author Share Posted March 21, 2020 Right I found my camera and grabbed some pics not carefully posed though. I will try to explain each picture it seemed only right to bring back history with a coffee tin .the thrust vectoring is a portion of a coffee tin wrapped in carbon tape to stiffen you can just make out the pivot point and closed loop connectors this pic is of the underneath with all the relevant parts labeled , I should add at this point the length is 900mm and width is 580mm just over the 2-1 ratio. note the is no direct opening to the lift duct .if anyone want's to know more just ask inside the lift duct complete with blood this is 225 mm across and 100 mm deep made by scoring around the outside and curving to shape inside the bottom is a shallow cone to divert the air in all directions there are also flow diverters inside lift motor plonked in place with a 9x6 prop with the ends clipped I may have to experiment with this or opt for a 4 bladed prop to get air cushion pressure right next two pics are of the EDF with vectoring duct showing the extent of travel it really doesn't need this level of thrust but its what I had ( expensive with the esc ) EDF mounting side of deck this is 80 mm between levels the lift air is directed by the separating support ribs, they only go in a short distance between exch rib is two outlet holes one for the plenum and the other for the skirt which will be the loop type or bag skirt the front view with a sketched out cabin position Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted March 21, 2020 Share Posted March 21, 2020 Martian That's very impressive. I do wonder if you might loose quite a bit of air pressure directing the air through all those channels. It might be better to simply make the inside basically hollow with just the minimum of support structure and let the air find its own way out of the holes in the bottom plate. It will be interesting to see how you get on.. Quote Link to comment Share on other sites More sharing options...
Martian Posted March 22, 2020 Author Share Posted March 22, 2020 Thanks Simon , the majority of the space between the decks is open with no obstructions the short ribs are to support the top deck the aim is to maintain a constant cushion pressure I will expect to experiment maybe cutting larger holes or introducing them in the middle of the plenum . The pressure in the skirt needs to be constant whereas the cushion pressure do not need to be to high or the skirt will blow out. If the skirt pressure is to weak the craft will be unstable . The cg has to be as low down as possible also to improve stability. Quote Link to comment Share on other sites More sharing options...
Nigel R Posted March 30, 2020 Share Posted March 30, 2020 Hi Martian, any update on the hovercraft? I've been watching along Quote Link to comment Share on other sites More sharing options...
Martian Posted March 30, 2020 Author Share Posted March 30, 2020 Hi Nigel a slight hiccup because of my finger but it is now functioning properly 😎 will be back on it today also am going to design a smaller single motor hovercraft about half size of this and it will be easier to build Quote Link to comment Share on other sites More sharing options...
Martian Posted March 31, 2020 Author Share Posted March 31, 2020 Still working on closing the side decking I.ve not tried complex bending of foam board before so I still need to practice the foam board that is available in the UK is the 5mm A1 sheets that are normally available from HobbyCraft sadly closed at the moment. Any way this can be worked into bends by first removing one of the glossy sides either by peeling the top layer after damping then rubbing with your finger to remove the under layer sometimes it comes off in one go. Flite test sell a different type of foam board the has easy peelable outer layers. Then foam can then be dragged over the edge of a table whilst holding down with the other hand open palm it can be work in more than one direction essentially what is happening is the foam is being crushed where needed. Whilst I will be still working on the craft posted here I am going to make a single motor craft. The motor is mounted at the rear as a thrust motor part of the thrust generated is diverted by a splitter plate at around 20% to 25% of the thrust duct area I'm going to 3d print the duct complete with the motor mount. There are some general rules on length to width ratios which are usually width at just over 50% of the length this provides stability fore and aft. Whereas a craft can be made without a skirt it will not have much hover height and only be suitable for a smooth floor. Below are pictures taken from my light hovercraft handbook Fig a is an open-loop air is blown in through an opening in the bag skirt and allowed to bleed into the plenum chamber maintaining a positive pressure the hole size is achieved by experimentation to high a bag pressure make the bag stiff and the obstacle clearance is poor > this is the type of skirt I am using, the skirt material being polyurethane coated nylon the material used for kites. the type b skirt is a finger skirt complex to make requiring a downward feed of air it is not very efficient. Type c is a bag and finger skirt generally regarded as the optimal but not in the way the air is fed in from the top it is really stable and effective when fed through the thrust duct via a splitter plate. very difficult to make unless you are a skilled seamstress and not really suitable for a model . Quote Link to comment Share on other sites More sharing options...
Martian Posted April 3, 2020 Author Share Posted April 3, 2020 Decided to hold fire on the big Hovercraft and build a half size one -- son of hover. this one can be made from 2 sheets a1 foamboard or 1 if scaled down more. this is a single motor craft using a Turnigy 2830 1300kv, I will test various lipos. First up I cut out a piece roughly half a sheet 590x430mm and then marked out on the cutout piece the centre line then marked out 70mm from the front edge and sides and a line 40mm from the back edge. at the rear I made a cutout to accommodate the thrust duct with integral motor mount this was 3d printed at 130mm diameter . The thrust duct set in cutout at about 30% Thrust duct with motor fitted and temporary prop I will use a cut down 5 inch prop to keep the spacing tight at the side of the duct. 40mm high duct cradle 40mm high inner side walls which will have bottom deck glued to Quote Link to comment Share on other sites More sharing options...
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