Muttley Posted February 12, 2014 Share Posted February 12, 2014 Hi all Decided to get a new model ready for when the sun .. um.. well, for when it stops raining. So, Carbon, stiffer and stronger in flight but is it any more or less resistant to rough landings and hangar dings. Obviously I'm asking on behalf of a friend, my landings are like the softest brush of a maidens cheek, mostly. Quote Link to comment Share on other sites More sharing options...
Dave Miller Posted February 12, 2014 Share Posted February 12, 2014 It seems to me that carbon, whilst very strong is also quite brittle, so for (your friend's) model I would use glassfibre. Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted February 12, 2014 Share Posted February 12, 2014 Muttley has your friend considered a Dural u/c very strong and forgiving, not that you'd need one Quote Link to comment Share on other sites More sharing options...
RGPuk Posted February 12, 2014 Share Posted February 12, 2014 PCM produce premium gliderly machines of carbon, with excellent reputations and plenty of fans, on the premise that they more easily shrug off the inevitable slope rash. Crash 'em properly though, and needless to say they still break. **LINK** Ro. Quote Link to comment Share on other sites More sharing options...
Muttley Posted February 12, 2014 Author Share Posted February 12, 2014 mmmm Erwin, Batmans slope toy and high up on my list. The top candidate at the moment though is to go all aerobaty with a Dorado, and that skinny, snappy looking fuse is the reason for my wondering if carbon would be worth the extra. Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted February 12, 2014 Share Posted February 12, 2014 Carbon has a higher tensile strength so basically its stronger. But glassfibre is more ductile and so more impact proof. It may not look so cool, but I suspect glass works better as a U/C. BEB Quote Link to comment Share on other sites More sharing options...
Stefan Hafner Posted February 12, 2014 Share Posted February 12, 2014 Stiffness is only one part of the story, carbon is much lighter, so impact will have a less momentum behind them. As RGP says, either will break in a proper crash. Remember, carbon is a superb RF shield so 35mhz needs the aerial outside the airframe. Not a problem with 2.4 though Personally I'd go for carbon, even if it is more expensive, just looks so cool too Quote Link to comment Share on other sites More sharing options...
Muttley Posted February 12, 2014 Author Share Posted February 12, 2014 So what if it does break, can it be repaired the same as glass or is it a different art altogether. Quote Link to comment Share on other sites More sharing options...
Stefan Hafner Posted February 12, 2014 Share Posted February 12, 2014 Repairs are much the same, you can use glass or carbon cloth exactly the same way so easy enough to do. Quote Link to comment Share on other sites More sharing options...
Erfolg Posted February 12, 2014 Share Posted February 12, 2014 I think most people consider that Carbon is in many respects better than glassfibre. It has superior tensile strength on a weight for weight basis. I think what you are asking about is about a property referd to as toughness, in broad terms the ability to absorb impacts. On that basis many reach for Kevlar, being better than either than glass or carbon. Others will look at a Kevlar and carbon woven roving, If you are looking at a cost performance criteria, things are not as clear. The cost of raw materials are a fraction of the production cost, obvious really. Then it becomes a question of how much is being charged for the other aspects. Underlying all this iffing and butting is the assumption that ultimate strength of the item is identical, all that is changing is the mass of the material used. I personally take the view if ultimate strength for minimum weight is wanted then it is Kevlar or Carbon dependant on what is being sought. If cost per duty is the requirement irrespective of the slight increase in weight, then glass should be OK. Then I start with my ifs and buts again, if prepreg is used, then the ultimate properties are obtained, if hand lay up has been used then the resulting properties will not be optimised, at best the item will be heavier than necessary, as there will be to much resin. Then again............................ it all comes down to what you are prepared to pay and you have some knowledge of the manufacturing capabilities of the supplier to even form an opinion. Quote Link to comment Share on other sites More sharing options...
Muttley Posted February 12, 2014 Author Share Posted February 12, 2014 Then again............................ it all comes down to what you are prepared to pay and you have some knowledge of the manufacturing capabilities of the supplier to even form an opinion. Hmm I did mention I'm looking at a dorado didn't I. I'm tending to think glass would be best for me, although if I swing for the Erwin it would just have to be carbon, for that one I don't care about the science, just look at it. Quote Link to comment Share on other sites More sharing options...
Erfolg Posted February 12, 2014 Share Posted February 12, 2014 Gives eus a clue muttley, is a Dorado an orange, go on, give eus a clue, no, no, its a, its a, nacho, init! Quote Link to comment Share on other sites More sharing options...
Muttley Posted February 12, 2014 Author Share Posted February 12, 2014 Pug ugly fish actually, but rcrcm thought it was a good name for a glider. Hopefully because it flies like its gliding through tropical waters not coz it stinks like a week old mackerel. Quote Link to comment Share on other sites More sharing options...
Erfolg Posted February 13, 2014 Share Posted February 13, 2014 Muttley Given that you are buying a ready built model, the ultimate performance is very dependant on not only the design, but the weight. The robustness of the model is often related to this weight and the materials of construction and what is bunged into it. In general terms a prepreg model will be far stronger than any hand lay up for the same weight. The reason being that the optimum fibre to resin ratio will not be achieved. Hand lay ups always having to much resin, to achieve wetting out. How ever hard you try. It may interest you that matrix strength is obtained by the forces generated in over stresses conditions being dissipated dissipated by crack propagation around and along the fibres. That is why some strength can be regained in a fractured composite of this type by wicking in superglue. Totally bored, oh well. So you are completely unmoved by composites suffering from fatigue from stress and cycles above certain levels, unlike wood which has no threshold value. Quote Link to comment Share on other sites More sharing options...
RGPuk Posted February 13, 2014 Share Posted February 13, 2014 Posted by Muttley on 12/02/2014 20:07:36: mmmm Erwin, Batmans slope toy and high up on my list. The top candidate at the moment though is to go all aerobaty with a Dorado, and that skinny, snappy looking fuse is the reason for my wondering if carbon would be worth the extra. I was fondling one of the latest batch of glass Dorados at T9HobbySport only a couple of days ago - in fact they only have one left now until their next delivery. **LINK** Very nice it is too. Lots of improvements and added reinforcement over earlier versions. Tough and tasty. Ro. Edited By RGPuk on 13/02/2014 13:28:50 Quote Link to comment Share on other sites More sharing options...
Muttley Posted February 13, 2014 Author Share Posted February 13, 2014 Efolg, think I'm gonna regret this but why would wood have no threshold. More on topic is it possible to look at a model and tell what layup has been used. Thinking about your previous post you may be on to something, a carbon fibre nacho may take fast food to a whole new level. Quote Link to comment Share on other sites More sharing options...
Muttley Posted February 13, 2014 Author Share Posted February 13, 2014 Ro. Hope you had gloves on, the way things are going that might have been my new baby you were fondling Quote Link to comment Share on other sites More sharing options...
RGPuk Posted February 13, 2014 Share Posted February 13, 2014 Posted by Muttley on 13/02/2014 20:20:37: Ro. Hope you had gloves on, the way things are going that might have been my new baby you were fondling No worries matey - respectful gentle mode was fully engaged. ..... ..... She really is a beauty - certainly a lot of lovely machine for a damn good price and looks stunning in that colour scheme. A flying buddy of mine got the next to last one of the same batch - he's delighted with it. I was sorely tempted but I'm a couple of mouldy assemblies behind as it is. Rog. Quote Link to comment Share on other sites More sharing options...
Erfolg Posted February 13, 2014 Share Posted February 13, 2014 Ah materials. I am being a little mischievous, for our models fatigue is not likely to be a problem. Being a little more serious, a proper answer is needed from a a metallurgist, no, today, it is a materials scientist. With metallics it is all about slip planes and energy. It is interesting to an engineer though how energy is dissipated in matrix type structures. Which is again about energy and crack propagation. As a hobbyist it all matters not a jot Quote Link to comment Share on other sites More sharing options...
TigerOC Posted February 14, 2014 Share Posted February 14, 2014 Really interesting subject. I have used and worked with fibre glass for some 35 years on hobby projects. My experience with canoes is that fibre glass hulls started to become brittle after 10 years and cracked and punctured more easily indicating that the resin component became harder and less plastic with time. I am in the process of building an old balsa design glider using glass cloth/carbon fibre tow and polyester resin for the fuselage. I am not an engineer but a scientist with a speciality in chemistry. What is clearly obvious is the enhanced plasticity of this combination over natural wood. As an experiment I took the newly formed fuselage and dropped it nose first on to a carpeted floor from a height of a foot and it bounced back about half that height. I would never do this with a balsa fuselage purely because I know the nose would end up dented. From this it is apparent that the combo is able to dissipate shock along its length as opposed to wood that absorbs shock partially by crumple effect and partly by energy absorption (plasticity). This simple test demonstrates features that are highly desired in model aircraft and particularly slope soarers because they do have a hard life. The feature we all seek is the plasticity but the boundary is the point at which we loose form. From initial paragraph my experience is that the plasticizer becomes harder with time and therefore more brittle. Rob Quote Link to comment Share on other sites More sharing options...
Tony4147 Posted February 14, 2014 Share Posted February 14, 2014 Carbon every time, stronger and better resistant to hanger rash. Btw you won't go far wrong with an Erwin, very, very versatile, light to medium winds. Tricky build the Erwin but well worth it, if you want really strong then the D60 is carbon/kevler but you will be limited to when you can fly it, and they do break!!! Edited By Tony4147 on 14/02/2014 19:46:22 Quote Link to comment Share on other sites More sharing options...
Erfolg Posted February 19, 2014 Share Posted February 19, 2014 Tiger It is a me to, I also made canoes (in my case slalom and white water racers), When I made canoes it was in the days of Strand Glass, over 40 years back, One thing I am certain of is that a pre preg composite is stronger weight for weight, when compared to a hand layup of the same constituents The problem I have is that without knowing the mass of the layup, the materials etc., descriptions tell you little. What is more reliable then, is the experience of modellers with the various models. Edited By Erfolg on 19/02/2014 20:12:48 Edited By Erfolg on 19/02/2014 20:14:30 Quote Link to comment Share on other sites More sharing options...
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