Ian Jones Posted February 2, 2009 Share Posted February 2, 2009 On the odd occassion we get any snow I would like to try out taking off & landing on snow with skis but this can't be a permanant adaption. I imagine there has to be some movement in the main skis to allow the aeroplane to rotate & take-off but at the same time they can't be just waving about freely - can they? Quote Link to comment Share on other sites More sharing options...
David Perry Posted February 2, 2009 Share Posted February 2, 2009 http://www.stenulson.net/rcflight/skikits.htm d Quote Link to comment Share on other sites More sharing options...
John Bunting Posted February 2, 2009 Share Posted February 2, 2009 Some skis I made many years ago were 16g alloy sheet, rounded and bent up at the front, with lugs about half-way along that fitted on the axles in place of the wheels. Cords from the rear of the skis to the fuselage were long enough for the skis to be nose-up in flight, and elastic bands from the front to the fuselage kept them in that attitude, but allowed them to lay flat on the snow during take-off and landing. The area of the skis needs to be large enough to prevent them sinking into the snow by more than a few millimetres. You can probably guesstimate this by tests with a bit of sheet metal and a few weights. Hope this helps. Quote Link to comment Share on other sites More sharing options...
Dave S. Posted February 2, 2009 Share Posted February 2, 2009 I have a set of skis for my Wot 4 up in the woodshed, I might be able to get a pic of them tomorrow. Not bothered with them for a few years. If the snow is soft, they need to be bigger than you'd expect to stop them digging in, and if it has a decent icy crust, be prepared for VERY long landing runs! Dave in Finland, where snow is not news! Quote Link to comment Share on other sites More sharing options...
Ian Jones Posted February 3, 2009 Author Share Posted February 3, 2009 Wow! Quality replies these. Dave S, a photo would be extremely helpful, thanks. John Bunting, alloy sheets eh? Sounds quite robust, what did you fit them too? David Perry, thanks very much for your brief but extremely useful & informative link. The torque rods seem like the way to go to me. Anyone even just the slightest bit interested in this topic would find the linked web pages a good read. Quote Link to comment Share on other sites More sharing options...
Dave S. Posted February 3, 2009 Share Posted February 3, 2009 Ian, pictures as promised. These are wooden skis, each made from 2 laminations of 1/16 ply, heavily varnished. The fittings are a bit agricultural, but they do work. The skis are approx 15"x 1 3/4", they are mounted on a standard GRP Wot 4 undercarriage. I included a 12" ruler in the shots to give some scale. Note that they are mounted a little nose-up at rest, to avoid the front touching down first and digging in. Learnt that one via a couple of broken props! Quote Link to comment Share on other sites More sharing options...
Chris C Posted February 3, 2009 Share Posted February 3, 2009 not small then are they heavy?? Quote Link to comment Share on other sites More sharing options...
Dave S. Posted February 3, 2009 Share Posted February 3, 2009 To be honest, I haven't weighed them, but they don't feel much heavier than the standard gear, especially my 'autumn specials' with 4" balloon wheels on! None of it makes the slightest difference to the way the Wot 4 flies, of course. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted February 3, 2009 Share Posted February 3, 2009 As I used on a fun fly a few years ago. OK on hard snow but a little small for soft snow. Kept the tails longer than the noses for aerodynamic stability and they worked fine without any return springs etc. Half hour job to knock them up...might make some bigger ones if the snow persists! Quote Link to comment Share on other sites More sharing options...
Phil Winks Posted February 3, 2009 Share Posted February 3, 2009 some nice ideas here. as I have some past experience on langlauf skis I thought I'd exercise the grey cells and have a stab at working out the ideal ski size/aircraft weight. working from memory my ski's used to be approx 2000mm X 150mm (correct me if I've got that wrong) and given that I weighed at the time app 70kg this makes my load on those skis in the region of 70,000g / 300,000 mm2 or .23g per mm2 now my memory is that these skis would penetrate all but the hardest snow so if we half that figure and use it as a max g/mm2 we should have a starting point for working out ski size for any given aircraft weight.so if our aircraft is say 1.5kg we need to divide 1500g by .115 (half of .23g/mm2) this gives us (I hope) the area of the skis in mm2 a healthy 13043.5 mm2. now I thought that in most cases a 25mm wide ski would look OK so this would make our skis 522 mm in total so divide by 2 and we have skis that are 261 x 25 mm which on an aircraft of 900mm ish wing span prob looks about right. to simplify design we can express this as mm per 100g of aircraft at a std width so if your going with the 25mm wide ski it means you need 35mm of ski for every 100g obviously there will be a min length of ski (I'd suggest about 75% avg wing chord ) and with aircraft above about 2kg it might be prudent to use a fatter ski. if any of you have enough snow for long enough to try this out let me know how badly it fails eh oh and don't forget if you've got tricycle under carriage the nose wheel ski will be able to come out of that figure and it would be a good idea to put a ski on the tail wheel of taildraggers. of course when flying of snow it must be a good idea to pack down a runway this will ease the ski's work load and the soft area around it will act as an overrun preventer when landing. addendum The thought has occurred to me that if the ski's were fitted with the wheel protruding through the ski they could be left on for grass landings and with stays and springs they might help prevent nose overs on taildraggers. Quote Link to comment Share on other sites More sharing options...
John Bunting Posted February 3, 2009 Share Posted February 3, 2009 My skis, Ian, were on an old APS 'Frankenstein', 50 inch span, weighing about 2 lb, with single-channel radio, They were about an inch wide and 10 or 12 inches long, so 20 to 24 square inches total area. The model took off OK with them, but there was only a light fall of snow at the time, so I'm not sure how they would have performed on deep snow. Quote Link to comment Share on other sites More sharing options...
Ian Jones Posted February 3, 2009 Author Share Posted February 3, 2009 Well this is all very encouraging, there's got to be enough information here to have a bash! I happen to have some light ply knocking about and the other bits must be in my hangar somewhere - so time to get busy before the snow goes. The photos are great to, thanks everyone. Quote Link to comment Share on other sites More sharing options...
Dave S. Posted February 4, 2009 Share Posted February 4, 2009 Before you get too far with the 'lite ply', I should point out that the Wot 4 size skis I posted pics of were made from two laminations of 1/16" Finnish birch ply, not this nasty weak lite stuff which in my opinion is of no use for anything; the stuff doesn't even burn well! I'm also not sure how well 'lite ply' bends, compared to real ply. Quote Link to comment Share on other sites More sharing options...
Ian Jones Posted February 4, 2009 Author Share Posted February 4, 2009 ooh! I'd better find some better material then - thanks. Quote Link to comment Share on other sites More sharing options...
Dave S. Posted February 4, 2009 Share Posted February 4, 2009 Ian, I really think you might live to regret it if you don't, I can't see lite ply having the strength required, the skis can take quite a pounding and need to be able to flex a bit. It's also not easy to keep snow & water from soaking between the laminations of the porous stuff, real ply is in a different league. Quote Link to comment Share on other sites More sharing options...
Phil Winks Posted February 4, 2009 Share Posted February 4, 2009 Dave has a good point there Ian I'm about to make some using 1/32nd ply in 3 laminations. it will bend so easy untill laminated using a 30 min epoxy. Try to find an epoxy that has some flexibility when set. Z-Poxy springs to mind. hopefully I'll get them started this week so might post some pics of the process I use by the weekend. Quote Link to comment Share on other sites More sharing options...
Phil Winks Posted February 6, 2009 Share Posted February 6, 2009 Well it snowed again last night so nothing for it but to get on with some skis. what I've come up with are very much my prototype but they work. prob the 1st and last time you'll see ski's on a chance vought corsair F4U this is the gws bird at 35" span and with the ski's on and its big bty on board weighs in at 800g the skis are 240mm X 35mm and work well. well taxiing they do any way although you need to be so carefull as once it starts moving the lack of drag has it shooting of very quick indeed. they work best on packed snow obviously but not to bad on soft stuff now to see if the roads to flying field are passable Quote Link to comment Share on other sites More sharing options...
Ian Jones Posted February 6, 2009 Author Share Posted February 6, 2009 'eck Phil you don't hang about. Yep, it's strange to see skis on the Corsair. I'm looking forward to hearing how she flies. How did you shape the the front of the skis? I'm thinking about - did you make some of jig to get them both the same? Quote Link to comment Share on other sites More sharing options...
Peter 'Ivanna Crashalot' Savage Posted February 6, 2009 Share Posted February 6, 2009 I might try and make some skis for my .40 vietnamese ARTF! I hope it snows like this every year, not only just to do snow flying, but so we actually get used to having this much snow, so we dont haveaccidents or shut down the bus system every time a flake of snow falls out of the sky Quote Link to comment Share on other sites More sharing options...
Phil Winks Posted February 6, 2009 Share Posted February 6, 2009 Hi Ian below is a photo of one of the ski's in the jig a really simple affair all I did was draw a line in (this case on some old plastic facia board) of the shape I wanted the ski bent too. then put pins (latge nails) alongside the line to keep the ply in place while drying. I used 3 laminations of 1/32nd ply and some 5 min epoxy lots of clamps and flat bars to hold things in place. I laminated oversize blanks then cut to size and shape afterwards Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted February 7, 2009 Share Posted February 7, 2009 Dug my way into the field today and flew my Limbo Dancer on the skis shown in the picture I posted on 03/02...slightly modified by epoxying some thin ply to the bottom of the ali to double the area. This time, instead of allowing free rotation, I locked them up as the axles are bolts rather than the piano wire/collet arrangement illustrated. This worked well as it allowed the tips of the skis to stick up out of the snow. Touch and goes worked very well (most of the time) and great fun was had by me and a few friends that I handed the sticks to... I also found a new take-off method with my foamy electric shock flyer - simply stick the tail feathers in the snow and whack the throttle open for a rocket-style launch! Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted February 7, 2009 Share Posted February 7, 2009 Meant to ask whether anyone else has been having fun today? Quote Link to comment Share on other sites More sharing options...
Peter 'Ivanna Crashalot' Savage Posted February 7, 2009 Share Posted February 7, 2009 nah, just sitting on the sofa, not being able to do anything Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted February 8, 2009 Share Posted February 8, 2009 30 minutes on the Big Rock - wind chill factor made it VERY cold - nice flight though, then came home for warm scones, hot chocolare, and some Blade MCX action around the living room. Quote Link to comment Share on other sites More sharing options...
Peter 'Ivanna Crashalot' Savage Posted February 8, 2009 Share Posted February 8, 2009 thereis something wrong with my dad's MCX, when you release the controls it starts doing a conical motion :s Quote Link to comment Share on other sites More sharing options...
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