Myron Beaumont Posted October 12, 2011 Share Posted October 12, 2011 Tried an experiment to try a straight piece of 5mm piano wire about 5" long against a similar length of wire mounted in my vice with a coil (3 coils actually) Neither showed any remarkeable difference from the other .All to do with using a straight piece (supplied in my kit for a fixed u/c I could cut to length) as against a coiled version costing quite a bit.to fix to my HK retracts when they arrive. Quote Link to comment Share on other sites More sharing options...
Richard Sharman Posted October 12, 2011 Share Posted October 12, 2011 I agree - the beautiful coil sprung legs on my new electric retracts seem to be so solid they might as well not exist. You can't bend them by hand, and when the model lands it bounces no matter how softly you put it down. Is it something to do with the wire being work hardened as its bent ?How do you get nice soft, springy legs that absorb the shock of landing without having the complexity of oleos, etc ? Quote Link to comment Share on other sites More sharing options...
Myron Beaumont Posted October 12, 2011 Author Share Posted October 12, 2011 Richard Glad you agree (Are we the only ones that have thought about it?) I reckon some sort of hard rubber on the leg would do the job .A bit like exhaust or engine mounts on a car .Yeah! there are problems to do with size etc but so what ? Just my first thought .I shall use straight wire for my Spit U/C Myron Quote Link to comment Share on other sites More sharing options...
Vecchio Austriaco Posted October 12, 2011 Share Posted October 12, 2011 I think without a shock absorber you will always have the spring effect. so no way to pass the oleo or to make something similar yourself. May be you find some parts in the model car corner of a model shop (all kind of shock absorbers) Cheers VA Quote Link to comment Share on other sites More sharing options...
Myron Beaumont Posted October 12, 2011 Author Share Posted October 12, 2011 Vecchio /VA Thanks I shall research that . Never thought of it .Hmmm PS I wonder about the weight of a model car on landing etc ? MyronEdited By Myron Beaumont on 12/10/2011 18:30:10 Quote Link to comment Share on other sites More sharing options...
Alan Cantwell Posted October 12, 2011 Share Posted October 12, 2011 Try compressing a car shock absorber, and see how hard it is, yet they go up and down relentlessly, its all to do with inertia, i very much doubt the wing structure standing up to a hard knock, with no springing, the model weighs what? 8-9lb? treble that with a hard landing, then there are side loads to enter the equation, deffo dodgy ground, 2 coils would be enough though Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted October 12, 2011 Share Posted October 12, 2011 I have used these long shocks. They really work well. The model never bounces. However don't forget that on models most of the loads are backwards rather than up and down. These units are fully oil damped. Mine are 170mm long but shorter ones are available. Price about £12 a pair. Look on EBay. Quote Link to comment Share on other sites More sharing options...
Lazygit Posted October 12, 2011 Share Posted October 12, 2011 Bet they add a fair bit of air resistance (drag). Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted October 12, 2011 Share Posted October 12, 2011 Yes, but then, the model is not designed for speed. It even has barn door flaps and can be hovered in a 10 mph wind. Quote Link to comment Share on other sites More sharing options...
Pete B Posted October 12, 2011 Share Posted October 12, 2011 How about a set of reasonably-priced oleos to go with those nice HK retracts, Myron? Those 5mm shafts will fit and there's plenty of choice on the site if you want to pay a little more. I've just received a tricycle set for a Tucano and they seem fine. Look a bit more scale-like, as well.........Pete Quote Link to comment Share on other sites More sharing options...
GONZO Posted October 12, 2011 Share Posted October 12, 2011 IIRC several decades back this was discussed in one of the mags. It was determined that a coil in the nose leg would be better if it faced foward, not back, and the loads tended to open the coil. It just doesn't look right. Quote Link to comment Share on other sites More sharing options...
Vecchio Austriaco Posted October 12, 2011 Share Posted October 12, 2011 @ Alan 4: The car shock absorbers normally are coming with several different hole plates - the size of the hole changes the damping characteristics. VA - still 3 model cars to get rid off.... Quote Link to comment Share on other sites More sharing options...
James40 Posted October 12, 2011 Share Posted October 12, 2011 A spring without a damper is just that, a spring! For it to work correctly there is quite a lot of science involved, the spring rate should be calculated for the mass of the vehicle it is supporting, there is also the unsprung weight to take into account, but it really needs a damper to control the spring or it will keep on moving at whatever the frequency result of the spring rate and mass create. What you get on an rc aircraft is a very basic spring with no science involved and possibly the reason for many a boucy landing. An oleo is the way to go but comes with all that weight involved, the oleos that are sold for rc aircraft aren't really true oleos but just a contained spring and the use of friction as a damper but for the weights we are talking about they seem to work ok. Quote Link to comment Share on other sites More sharing options...
Craig Spence Posted October 12, 2011 Share Posted October 12, 2011 I think the trick is to fly the plane in smooth and under power.I am by no means an expert but from what I have seen alot of people cut right back on throttle for landings which is fine for fun flys with little weight and good lift but not so good for scale aircraft.I have a wire undercarriage with springs crossed between then and they work great.If the aircraft bounces on landing it comes down to many factors, one of which would be transfers of energy.If a spring compresses on landing it will have to release that energy which is what causes the plane to bounce back up.The dampeners slow this reaction down so it has less kick in both directions, the dampeners on my retracts are rubber and a hollow chamber with an air intake/ outlet.When the inner leg comes down it meets a resistance in air flow as it try's to expell the air through the tiny hole.When it goes up it creates suction reducing the release of the springs energy, in turn minimising the bounce.The rubber just creates the seal so air can't escape from the top of the chamber.So I would go for a set of oleos I think if you wish to preserve the plane. I was never keen on them either but there worth the money because as we all know we don't land perfectly all the time.Hope it works out for you.Craig. Quote Link to comment Share on other sites More sharing options...
Gary Binnie Posted October 12, 2011 Share Posted October 12, 2011 I think Myron's original question was does the coil do anything. I have a set of Carelli retracts with lovely coils but the wire is so thick that they won't move a gnat's under any force! The coil on the main legs will also not fit into a typical leg cut out in the wing. With thinner gauge wire they work, especially if the lower part is canted back . It's an aesthetic feature that has probably been copied with no understanding of how it is supposed to work. It works fine in clothes pegs and mouse traps as we know! A weird thing is that '40' trainers often have this sprung coil for the nose leg but the main legs are unsprung. Perhaps it's to keep the C of G forward and increase the wing loading!! GB Quote Link to comment Share on other sites More sharing options...
andy watson Posted October 12, 2011 Share Posted October 12, 2011 The oleos from himodel linked by Pete above are so cheap it's incredible. I needed a set of oleos for the Vulcan, and couldn't work out which set would be best. So I just bought one of each! Quote Link to comment Share on other sites More sharing options...
James40 Posted October 13, 2011 Share Posted October 13, 2011 I think one reason for the coils may be to prevent a fatigue failure of the leg? Take a straight metal bar and flex it a few hundred times, eventually it will snap due to fatigue. Now add in 3 coils to that metal bar and it offers an area for that flex to take place so in theory giving longevity to that flexing metal bar. Quote Link to comment Share on other sites More sharing options...
Craig Spence Posted October 13, 2011 Share Posted October 13, 2011 My mistake, the coil stops the the energy transferring from the legs straight through the wing or fuselage which usually ends in tears or a search party lol.It slows the transfer of energy down and absorbs most of the impact. Quote Link to comment Share on other sites More sharing options...
James40 Posted October 13, 2011 Share Posted October 13, 2011 The spring is the true shock absorber although we always give this name to the damper on most vehicles, the damper is just there to control the ocillations of the spring. On a wire u/c though the coils don't do either. Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted October 13, 2011 Share Posted October 13, 2011 I think one reason behind the spring is that it effectively extends the length of the leg and the wire itself is a spring. It's normally used on noselegs and retracts because the leg is short and rigidly fixed at the top, or at least it's supposed to be rigidly fixed.It's not there to counter vertical shock loads like the suspension on a car, it's to absorb the horizontal load as the wheels 'gently contact' the ground while travelling forward at 20-30 mph. Your vertical speed is supposed to be next to nothing on touchdown so there shouldn't be a vertical component. Quote Link to comment Share on other sites More sharing options...
Myron Beaumont Posted October 13, 2011 Author Share Posted October 13, 2011 James I just can't imagine a fatigue failure on either a straight leg or one with a coil .Not with 5mm dia wire on a model weighing about 9 or 10 lb anyway -no matter how hard the "arrival" .Anyway ,I'm going for a set of legs mentioned by Pete & Andy from Himodel .My "runway" is bumpy grass at the moment 'til I make myself a proper runway , so hopefully I'll be able to get up & down in one piece. Quote Link to comment Share on other sites More sharing options...
Richard Sharman Posted October 13, 2011 Share Posted October 13, 2011 I've tried springs/shocks from a model car, and apart from the fact that they look ugly on a plane, they seem to work on a swinging arm in the car, which of course I don't have on my scale planes.So, I've just bought a set of "oleos" for £10 ! Really light, nicely springy, but requires moderate pressure to compress, so looking good for the legs on the EDF jet. However, the electric retracts are designed such that the 3mm wire of the old leg lies exactly on the unit when retracted, and therefore there's no space to mount the 10mm thick oleo unit -- snookered ! So I can have the oleos and not retract, or not have the oleos and retract -- ughh ! Quote Link to comment Share on other sites More sharing options...
Doug Ireland Posted October 13, 2011 Share Posted October 13, 2011 ...'till I make myself a proper runway...Go on Myron, rub it in! Quote Link to comment Share on other sites More sharing options...
Pete B Posted October 13, 2011 Share Posted October 13, 2011 That's unfortunate, Richard.The 3mm version must have less clearance. Just to reassure Myron (who I hope has bought the 5mm version for up to 4.7kg models!), I've uploaded a video which shows the HobbyKing Digital Servoless Retract, 5mm shaft version matched with the Himodel 60-120 size Landing gear Set. The Himodel oleo body is 11.4mm diameter and closes fully without any problems.The Himodel Aluminium Shock Absorbing Wheel Shaft is 9.7mm diameter, so there's a little more clearance on that one: For those who live in the BBC South area, please excuse Sally Taylor's voice in the background....... Pete Quote Link to comment Share on other sites More sharing options...
James40 Posted October 13, 2011 Share Posted October 13, 2011 Myron, The legs will flex during taxi, take off roll and landing. What I'm saying is, the constant flexing of a straight metal bar will create a fatigue issue eventually. With the coils at the top of the leg it gives an area for that movement to occur. Quote Link to comment Share on other sites More sharing options...
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