Tim Cheal Posted December 2, 2014 Share Posted December 2, 2014 We are watching Danny!! Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted December 2, 2014 Author Share Posted December 2, 2014 Posted by Tony Bennett on 02/12/2014 19:36:42: does he have a beard as all the best people have one. as per your advice i have purchased some rc modellers glue for me next bash at rivets. He might indeed have a beard You will be pleased to know Tony mine has remained after the end of Movember, somebody said it made me look intelligent Top and bottom of one wing covered in Natural Solartex Cheers Danny Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted December 2, 2014 Author Share Posted December 2, 2014 Managed to get all the fabric bits of the wing Solartexed this evening Really pleased with the sharp trailing edges. I didn't show it but the wing trailing edges were treated to the G10 rebated edges the same as I showed on the ailerons and flaps. Still wont know if the rebated surround is going to work so hold fire if you are thinking of copying? Cheers Danny Quote Link to comment Share on other sites More sharing options...
Tony Bennett Posted December 2, 2014 Share Posted December 2, 2014 now that is looking good. my covering always looks pants. Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted December 2, 2014 Share Posted December 2, 2014 It looks very tidy Danny, I bet the wings rock solid now (not that I have any doubts about it ) John Quote Link to comment Share on other sites More sharing options...
AlexJ Posted December 2, 2014 Share Posted December 2, 2014 Hi Danny, The wing looks superb, are you still going to glass cloth the front of the wing? I have a big piece of the very thin Proskin, I thought I might see if it would wrap around ok, it could be fitted in pieces that represent the panels. Mick Reeves suggests, in his "tips" page I think, that the weight is very similar to glass cloth and resin. What do you think, too much bother? Alex Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted December 2, 2014 Author Share Posted December 2, 2014 Hi Tony, I think covering is an art that you have to practice, Solartex is the nicest of the iron on films in my oppinion, though I haven't tried MonoKote. Hi John, these iron on films add very little strength, not like tissue/nylon/silk and dope would, it does feel like the wing has suddenly put on weight too. I managed to cover one of the flaps this evening before calling it quits. Hi Alex, I like Proskin, but I am not sure its right for smaller lightweight models such as these. The material isn't too heavy its the glue that would worry me. Mick suggests a PU glue I believe? I will stick to my tried and tested 25gsm glass cloth and resin Cheers Danny Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted December 3, 2014 Share Posted December 3, 2014 Oh - interesting question on the shear webs/struts! A wing has to have three main structural properties - it has to be stiff in bending, it should be stiff in torsion (ie twist) and it should be light. It also helps if it can generate lift! The need to be both stiff and light is what calls for some clever design. The simplest arrangement would of course be a top and bottom spar with the ribs notched to receive them. Contrary to what might be thought the ribs really have no role in the stiffness of the wing - they are almost solely about creating an aerodynamic lift-generating shape. So in this arrangement all the strength is really coming from the two spars. Well I'm sure you have flexed a bit of hard balsa, or even a length of spruce, in your hands. Its OK as a beam, but on its own its not that stiff. The situation is much improved when we add the leading edge sheeting. As per full size this stiffens things up markedly and the skin is effectively stressed - taking load in its own plane, a direction in which it is very strong. Can this arrangement be made even stiffer? The answer is "yes", by adding shear-webs between the upper and lower spar. How does this work? Well in bending these webs will be compressed "in plane" (like the skin) and so will add considerable strength. In torsion they effectively couple the upper and lower spar into a single unit (remember the ribs are not structural - you may think that the spars are already connected by the ribs but structurally they are not!). Coupled like this the spars acquire a torsional strength that is more than double their single value - a case of the whole being better than the sum of its parts! So, whats the best direction for the grain on these webs? This is quite difficult to answer. Take a small piece of sheet -balsa, hold it in your hands with the grain going up and down, bend it - it bends very easily, indeed it splits or cracks very easily. Now turn it through 90 degrees so the grain is running from one hand to the other, and bend it. Its a lot stiffer, right? So, if we want to increase the wing's bending strength it would make sense to put the grain horizontally - that way the grain resists wing bending best. However, if we want to increase the wing's torsional strength we should put the grain vertically - this way it most effectively, and stiffly, couples the spars under twisting loads. Well the grain can't go vertically and horizontally - can it? Well in sense yes it can. The ideal would indeed be as Danny's full size example shows - for the grain to be diagonal in both directions - like a cross. You can do this of course using a plywood sandwich cut with the outer facing grains on the opposite diagonals front and back. This is the ideal arrangement - maximum bracing, the best "D" section, for the minimum weight. But actually, on a model that would be very difficult to do. So do are most model wings more in need of extra bending strength or extra torsional strength? The answer is usually the latter. So its usually better to put the grain vertical. This means the web couples the spars most effectively to support torsion. Two diagonal grains would be better, but this is still very good. So now the question is do Danny's diagonals perform like the diagonally cross-grained webs and so are they better than vertical grain webs? TBH its very difficult, without doing a full analysis to be sure,.....but I suspect not. They will certainly significantly stiffen things up in both bending and torsion. And that is valuable. While they will not make as much contribution to torsional stiffness as a conventional vertical grain shear web would do, they would make more contribution to bending stiffness. So with Danny's arrangement you get a bit of both - but not so much of either individually from the webs! The conventional web (in conjunction with the spars) effectively forms a full depth I-section beam - which is a shape with a very high moment of area I (and high polar moment of area, J). When I goes up - bending stress goes down. When J goes up torsion stress goes down. In the case of full depth webs both I and J are large. This is not so much the case with the diagonal struts. Of course this is just "theory". Is the wing stronger with these diagonal struts in than without them? Yes most definitely. Would it be stronger still with full depth webs? Probably, perhaps particularly so in torsion. Is this likely to make a difference? No I don't believe so. My own feeling is that the diagonal struts are a good idea in this case. As Danny says the wing is already quite stiff without them - so they add a bit more strength which is a useful safety margin for very little extra weight. Full depth webs would have added even more strength in torsion, yes; but also more weight and the wing doesn't appear to need that degree of bracing. So I'd say they are reasonable compromise in this case. BEB Quote Link to comment Share on other sites More sharing options...
Dave Hopkin Posted December 3, 2014 Share Posted December 3, 2014 Thanks BEB (an answer worthy of the diplomatic core ) I've had to read it a couple of times to get my head round I and J going up to the polar regions though!!! But an interesting (and educational) post.... So in theory if one was after massive strength then 4 ply fitted with the grains running diagonaly would be the dogs? Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted December 3, 2014 Share Posted December 3, 2014 As usual, BEB has got it. The wing in the bending mode is functioning like a girder and in normal flight the loads in the spars are being translated into tensile in the bottom one and compressive in the top one. Upside down it reverses. The problem is with the compressive load because there's a risk of buckling inwards under compression. If that happens the spar will fracture and the sharp increase in the resulting upward bend will then cause the bottom spar to fracture too and the wing wil break upwards sharply. It's what happened to the DH110 at Farnborough when John Derry and his colleague were killed along with many spectators. In that case the wing was designed to deal with the bending loads through the D-shaped leading edge. Unfortunately it was inadequately reinforced internally and buckled in this way, leading to a catastrophic failure. They altered the design as a result, Bill Gunston made the comment that DH had a habit of building planes that fell apart, largely because they tended to take weight saving too far. The primary purpose of shear webs is to retain the spacing between the top and bottom members and prevent buckling. An I-section steel beam used in construction has all of the toughness and strength described in the steel specification expressed in the flanges, not in the web and particularly not in the "K" area where the two meet. Again, the primary purpose of the web is to retain the vertical distance between the flanges. The disaster report on the Twin Towers in New York describes this characteristic on a much larger scale. It was a welded steel structure (in the UK we normally use bolts) and comprised an inner vertical box structure in which the lifts etc. ran and an outer box to which the cladding was attached. The two were connected by the floor beams. The reason the towers collapsed catastrophically vertically top down was because the prolonged fire caused by aviation fuel and 1000 degree temperatures broke the floor connections. When the first floor to fail went down and effectively doubled the weight on the next one, the same thing happened again more quickly and then again. Because the connection between outer and inner was broken, the vertical beam structure buckled and lost its' compressive strength. At that point the process accelerated and the lot came down. This was the reason why you can see the cladding popping off as the steel buckled. Therefore with a single ply of wood the best grain direction is indeed vertical. With multiple veneers as in plywood where the grains are alternately at 90 degrees, the outer plies should be set at 45 degrees as the best compromise. If they are vertical, half of the plies (you can't see) will be horizontal. With a single ply of typically 3mm balsa, vertical is best. What Danny has done is structurally sound enough, translating bending loads into diagonal compression Warren truss style. It's best to put shear webs between all the ribs or none of them. What John has done has the problem that the potential bending load in the alternate spaces without webs will be doubled. However, I wouldn't worry because I don't think that it will be a problem anyway. The bending loads are in effect being absorbed by compression in the upper leading edge sheeting and as long as it is attached to all of the ribs, it's curvature means that it won't bend. Therefore I'm not bothering with shear webs or diagonal bracing. It is "belt and bracings" and technically elegant, but elegant I'm not and I'm mostly concerned with making sure that all of the glue joints are sound so that everything is connected. However, that's also to do with me being slow and idle as well, but I think it's ok. Edited By Colin Leighfield on 03/12/2014 06:42:41 Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted December 3, 2014 Author Share Posted December 3, 2014 Thanks BEB thats put my mind at rest a really clear post as usual, thank you Thanks also to Colin for his thoughts re-enforcing BEBs Cheers Danny Quote Link to comment Share on other sites More sharing options...
Terry Walters Posted December 3, 2014 Share Posted December 3, 2014 Well that lot woke me up this morning! It is apparently good to have the 'old grey matter' tested but this early in the morning gGentlemen? Really? . Good job I have just had my first bowl of porridge this Winter (I know it's not really Winter yet but this morning it feels like it!) so the brain cells have some fuel! Thanks for all that chaps much appreciated and mostly understood! Danny - is the Solartex just ironed onto contact as per normal or have you beefed it up with Balsaloc or something similar? It would be great if it works but if it is a straight flat contact I feel uneasy that it will pull away. Are you thinking of sealing the edges further? Terry Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted December 3, 2014 Author Share Posted December 3, 2014 Hi Terry Balsaloc all around the edges should be sufficient. I am going to wick thin CA in the edges too just to be doubly sure Cheers Danny Quote Link to comment Share on other sites More sharing options...
Terry Walters Posted December 3, 2014 Share Posted December 3, 2014 Sounds good to me Danny and will solve the issue really well - thanks. Don't worry - not going to rush off and do it - long way off that yet but it is natural solartex for me too - easiest to work with. It will be interesting to see how you keep the sharp demarcation line between 'metal' and 'tex when you glass fibre and resin the 'metal' surfaces but I guess you have something up your sleeve for that as well? ! Just about to order some hypos! Terry Quote Link to comment Share on other sites More sharing options...
Dave Hopkin Posted December 3, 2014 Share Posted December 3, 2014 Thanks BEB and Colin,,,,, especially for translating complex mechanical engineering theorems into short words for me!!! And thanks Danny for the superb build thats giving me so many new ways at looking at things - keep going Quote Link to comment Share on other sites More sharing options...
Silver Wolf Posted December 3, 2014 Share Posted December 3, 2014 Hi Danny, What's the reason for the solartex tuck away? Do you intend to have the glass cloth overlap the solartex? I am considering using tissue and silk (not used it before), as I may use that method on next model, possibly. Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted December 3, 2014 Share Posted December 3, 2014 Thank you for the kind comments gentlemen. Colin describes the role of the webbing very well indeed and I didn't know that loss of bracing leading to buckling was the cause of the 9/11 building failure - interesting. Yes Dave - full depth webs with diagonal grain mutually at right angles on each outer face is the very best overall compromise - but TBH is probably much more fiddly than is worthwhile for 99.999% of models. Our wings tend to be well over-engineered anyway! BEB Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted December 3, 2014 Share Posted December 3, 2014 Yep very interesting the kind of thing I enjoy reading and learning, two points though Why not tell me the way I had done it compromised it before ? second, the ply brace in the middle is pretty much a shear web, so do's that not double the potential bending load in the next empty bay just the same as alternate shear webs ? John Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted December 3, 2014 Share Posted December 3, 2014 John, I didn't mention it because I didn't think it mattered. Your build quality is a sight better than mine and I can't see you having any structural concerns at all. It's just that different local levels of stiffness along the span will affect the even-ness of the load distribution. The fact that it's never going to be critical anywhere as far as I can see means that it's an observation, but not any risk at all as far as I can see. I'd be more concerned about my codging than your approach to building. Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted December 3, 2014 Share Posted December 3, 2014 O.k. Colin but I like to learn things so feel free to speak up John Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted December 3, 2014 Share Posted December 3, 2014 Sorry John, didn't like to mention it at the time, but you're right. I'm sure you would do the same for me and I appreciate that. Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted December 3, 2014 Author Share Posted December 3, 2014 Sorry John I too should have said something I suppose not that i thought it was wrong, but I should have questioned the solution as i hadnt seen it done that way before. My braces i had seen on an artf so guessed it was legit.cheers Danny Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted December 3, 2014 Author Share Posted December 3, 2014 Posted by Silver Wolf on 03/12/2014 09:33:13: Hi Danny, What's the reason for the solartex tuck away? Do you intend to have the glass cloth overlap the solartex? I am considering using tissue and silk (not used it before), as I may use that method on next model, possibly. Hi SW, I would like to try silk over tissue as well, but not on this model The reason for the solartex tucking down is to give me more contact area around the edges, I have had Solartex pull away from edges before. I could and I know a couple of Chippites that are, just going to overlap the Solartex/covering with glass cloth, this should be fine, I was just trying to come up with a way to simulate the rather unusually join a little better. It might not work of course, but you don't learn unless you try something different every now and then Cheers Danny Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted December 4, 2014 Author Share Posted December 4, 2014 Covered the other flap and the ailerons tonight. Made the ailerons slightly longer towards the root just by adding some 1/8 and sanding it down to fit before covering. Just to close the aileron/flap gap slightly, likewise at the tips Onwards and upwards Cheers Danny Edited By Danny Fenton on 04/12/2014 23:15:06 Quote Link to comment Share on other sites More sharing options...
Tony Bennett Posted December 4, 2014 Share Posted December 4, 2014 looking good, be time for rivets soon. Quote Link to comment Share on other sites More sharing options...
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