fly boy3 Posted October 2, 2009 Share Posted October 2, 2009 Hi all,I am building a bi plane that requires a leading edge of 25mm by 15mm.I cannot source these exact measurmentc in any mail order firm. Do I use a 25mm/25mm block,and reduce to size and if so, is it done before glueing to rib front,or after glueing. Also has the final section of leading edge have to follow the profile 100%. The model is a sports type. Thanks flyboy3 Quote Link to comment Share on other sites More sharing options...
ken anderson. Posted October 2, 2009 Share Posted October 2, 2009 fly boy3-what is the name of the model?....... ken anderson. Quote Link to comment Share on other sites More sharing options...
andy watson Posted October 2, 2009 Share Posted October 2, 2009 Shave down a bigger strip, as you suggest. Glue the whole strip to the ribs, then shave it to the rough profile. From there a sanding block should get the job done quickly. Quote Link to comment Share on other sites More sharing options...
fly boy3 Posted October 2, 2009 Author Share Posted October 2, 2009 Hi Ken, the model is from an old RCME plan.It is called Josefin (Josephine) designed by a man called Bo Gardstat. Top wing is 54inches,bottom wing is 40 inches,with ailerons only on lower wing,and a 46/2stroke up front.I believe it is a sport airobatic model.. It looks a basic type build with the u/c and lower wing secured by rubber bands. It also has the rear u/c wire strut held on with the same bands as the lower wing,quite unusual. For Andy ,I ll take your advice and do as you suggest . Thanks flyboy3 PS. there is also a design for floats on the plan.Edited By fly boy3 on 02/10/2009 21:32:24 Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted October 2, 2009 Share Posted October 2, 2009 15mm is near enough 5/8, personally I'd go for laminating 1/2" and 1/8" to make up the thickness, if for no other reason than it would probably work out cheaper than 1" square, and would save throwing half of the wood in the bin as shavings.I've also had problems in the past with heavily thinned wood warping, as the internal stresses are released on one side only as you plane it down. If you decide to plane down the bigger section, as Andy says. do it after gluing to the wing as the rest of the structure will help it stay straight. Quote Link to comment Share on other sites More sharing options...
andy watson Posted October 2, 2009 Share Posted October 2, 2009 Bob makes a good point about putting a 1/2*1/4 strip with a 1/2*1/8 for the leading edge- it will be cheaper. Personally I would pay the extra for the 1/2 square- if for no other reason than the glue is harder than the balsa, which can make sanding more awkward to get it smooth and avoid a ridge along the glue line. Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted October 3, 2009 Share Posted October 3, 2009 Andy - flyboy is talking about a piece 25 mm by 15 mm that's 1" * 5/8" - and planing it down from 1" square, not 1/2". That's 1" * 3/8" to plane off before even starting to round off to the L/E shape, a lot of wood going in the bin. With such a big section, I'd probably go for a soft 1" * 1/2" at the back, with a firmer 1/8" at the front to resist dings. it's still a heck of a lot of wood for a leading edge on a 54/40" wingspan. It shouldn't be any harder to sand to a smooth contour than a normal small section L/E with sheet D box. Keep the glue to a minimum and don't use anything rubbery like Resin W, stick to cyano or aliphatic. then use a hard backed sanding block, rather than a sheet of sandpaper held with fingers - that will dig into the softer balsa faster. Quote Link to comment Share on other sites More sharing options...
fly boy3 Posted October 3, 2009 Author Share Posted October 3, 2009 Hi all, thanks for the very usefull info on leading edge. I think that lamination,used with aliphatic( for its sanding properties) is the way to go. The drawing is of the type where a lot of info is left to the builder to provide ,hence my problems. Before I start a build ,I like to have all the problems as such sorted. Just one more query, the wings require 3mm by 7mm spars,should these be a hard wood or should I ask supplier for hard balsa. Thanks again flyboy3 Quote Link to comment Share on other sites More sharing options...
Erfolg Posted October 3, 2009 Share Posted October 3, 2009 As an idea. The leading edge could be redesigned, to reduce size? An lot of design designs are arbataryor sometimes just driven by "oh, look this peice of wood in my materials stock will do, I cannot think of any other use for it" For really rounded leding edges, I have seen people use a variety of wrapped sheet, to achieve there needs. Erfolg Quote Link to comment Share on other sites More sharing options...
andy watson Posted October 3, 2009 Share Posted October 3, 2009 Bob, I agree with you, but there are sometimes more than one way to achieve the same end result. Glue does affect the characteristics of the wood- cyano is used to harden balsa/ply, for example where a screw is needed. I sometimes find it is possible to sand a piece of wood that is glued and the area next to glue penetration can be sanded more than the area that the glue has soaked into. I use a lot of aliphatic glue, and it is much harder than balsa, although it doesn't soak in as thin cyano will. Bob is correct that a sanding block makes sanding these areas much easier than holding the paper, also be careful if using coarse grades of sand paper- it is very easy to gouge a big chunk of wood out with 60/80 grade. The price difference between 1"*1" and 1"*1/2" +1"/1/8" is not great. Blackburn sells 1" sq for £1.98, the 2 pieces comes to £1.10 + (£1.10/3)= £1.41. (all 36"- I got the 1/8 price by cutting a sheet down) I was suggesting the route I might take would cost 50p more, but save some messing around and possibilities for mistakes. If I were being really pedantic I could suggest the end result of a single piece would be lighter (I don't think any weight difference would be significant in truth) and if cut carefully, the offcut could become a perfectly useable 1"*3/8" strip for some other project. I certainly know I am tightfisted enough to try save some of that wood rather than reduce all of it to shavings! All spars should be hard balsa- and if your supplier can't/won't grade them like that then there are ones that will- SEC & Blackburn models being 2. Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted October 3, 2009 Share Posted October 3, 2009 "and if cut carefully, the offcut could become a perfectly useable 1"*3/8" strip for some other project."that I can relate toI thought you were thinking in terms of planing it down, sorry! Quote Link to comment Share on other sites More sharing options...
Allan Jordan Posted October 7, 2009 Share Posted October 7, 2009 Hi flyboy, Just a thought have you tried this ? [email protected] They might just have what you are looking for. Quote Link to comment Share on other sites More sharing options...
kc Posted October 9, 2009 Share Posted October 9, 2009 Surely spruce spars would be best unless really hard balsa is avail.The leading edge method advocated by Philip Kent might be useful.This pic shows the method with sheeting going over the first LE and being capped by the front piece.If you laminate from several thicknesses of say 1/8 in decreasing widths you will not only save wood but get some guidance in shaping. Draw the 1/8 or whatever thickness on the end view of the LE and measure the exact width for each layer. Edited By kc on 09/10/2009 17:23:58 Quote Link to comment Share on other sites More sharing options...
fly boy3 Posted October 9, 2009 Author Share Posted October 9, 2009 Hi hc,That looks like good solution to the problem, but I have already started on the wing, but as its a bi-plane I might give it a go on the top wing. Also I am using hard balsa from Slec.with thanks also to Allan Jordon. I would like to thank all who have joined in the thread,and hope to send some pics.of completed model. fly boy3 Quote Link to comment Share on other sites More sharing options...
kc Posted October 10, 2009 Share Posted October 10, 2009 Shaping the LE on the wing can loosen all the glued joints.It is much easier to shape LE and TE on the bench rather than when installed on the wing. Fix the balsa to the bench with small pieces of double sided tape ( not full length or you will not release it! ) and shape with a razor plane & then glasspaper or a Permagrit sanding block.In this case fixing to the edge of a piece of timber 1 inch thick and about 2 or 3 inches wide will enable you to get right around the shape with a razor plane etc. Clamp the timber in a vice or Workmate etc.Mark a centre line for guidance and use a template for exact shape. A similar shape all along is more important than the precise plan shape. Edited By kc on 10/10/2009 12:46:20 Quote Link to comment Share on other sites More sharing options...
andy watson Posted October 10, 2009 Share Posted October 10, 2009 Sorry, but I disagree. If you do it in situ you will shape precisely to the sheeting requiring. If a bit of shaving and sanding loosens it, then you didn't glue it on properly in the first place, and better that it falls off in your hand than in the air. Quote Link to comment Share on other sites More sharing options...
kc Posted October 11, 2009 Share Posted October 11, 2009 Just the last few thous should be sanded off in situ ( in my opinion ) the basic shaping is best done on the bench or by the balsa supplier. In this case we are talking about removing large quatities of wood and you want both wing halves the same. So preparing the basic shape on the bench seems best to me.Depends on the wing construction. The lighter type of non sheeted wing has little to hold except the wing ribs during LE shaping and can parallelagram causing strain on glue joints ( they peel apart ) and the last thing you want is a weak wing. Do whatever seems easiest & best. Quote Link to comment Share on other sites More sharing options...
fly boy3 Posted October 11, 2009 Author Share Posted October 11, 2009 Hi all, thanks for all the info generated on this leading edge theme,It seems there are very many differant ways of doing this job. I am now spoiled for choice,and I am far more knowledgable than when I started.flyboy3 Quote Link to comment Share on other sites More sharing options...
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