A.A. Barry Posted May 25, 2015 Share Posted May 25, 2015 I am sure I cannot be the only one who has experienced this fact When the wing shape calls for double taper, from plans, and the sandwich method is used, we end up with with each rib having a taper on each rib width wise. This can be very acute, particularly cord wise, if the wing is going to be sheeted there is hardly any wood to glue onto, plus the fact that the dimensions may not be correct. This is very pronounced if the ribs are 1/8" thick. Do we draw the outline of each one and redo??? What is the secret??? Barry Edited By A.A. Barry on 25/05/2015 21:18:23 Quote Link to comment Share on other sites More sharing options...
jrman Posted May 25, 2015 Share Posted May 25, 2015 When you make up the sandwich put a scrap "spacer" of an undersize rib between each real rib. This reduces the taper, not eliminating it completely but has no detrimental effect on the rib profiles. Quote Link to comment Share on other sites More sharing options...
kc Posted May 26, 2015 Share Posted May 26, 2015 It is usual that you give each rib a light sanding to give a square edge. Quote Link to comment Share on other sites More sharing options...
A.A. Barry Posted May 26, 2015 Author Share Posted May 26, 2015 KC, JRman, here is a pic for a better explaination, it is just a bit of scrap, but ya can get the idea position A is the finished rib profile, if one sands down to make the edge square, the profile then moves to position B (appox). The rib now is either short and/or narrow As mentioned before, if one draws around the finished rib (taper and all), and cut another one, the size would be somewhere near correct Cheers Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted May 26, 2015 Share Posted May 26, 2015 That looks a bit of a dramatic example! There is usually a slope when I've used the sandwich method but very much shallower. I just cut the end profiles marginally oversize and let the overall sanding before sheeting take care of the profiling. Quote Link to comment Share on other sites More sharing options...
A.A. Barry Posted May 27, 2015 Author Share Posted May 27, 2015 Perhaps this is a better example:- the rib drawing is drawn to scale....1/8" thick x 12" root and 6" tip, this could be the platform for a delta, and a pack of 12, only the ft half is shown, as ya can see at least 1/8" is "lost " if the rib is squared off Martin I agree that over sizing the templates would alleviate the problem, but if one cuts the template to the plan shown, using the "sandwich method", the outcome platform will be incorrect , but at least this should be highlighted Barry Edited By A.A. Barry on 27/05/2015 02:05:31 Quote Link to comment Share on other sites More sharing options...
Jim Purcha Posted May 27, 2015 Share Posted May 27, 2015 I cut the ribs for my Hawk model using the sandwich method. I left one rib out to compensate for the using the tip and root ribs to sand the profile too. Something I did not do, but is mentioned in my old Harry Higley's Master Modeling book is to use these tapered ribs as a pattern on another sheet of balsa for the actual ribs. This eliminates the problem of the minimum gluing surface on the rib edge. Jim Quote Link to comment Share on other sites More sharing options...
Simon P Posted May 27, 2015 Share Posted May 27, 2015 Good tip, Jim. Quote Link to comment Share on other sites More sharing options...
Tony K Posted May 27, 2015 Share Posted May 27, 2015 I think I would tackle this as follows:- sandwich eleven blanks (W2 - W12) between the two templates and shape to this red line. Then use the W1 template to cut a separate W1. The separated sandwich ribs can now be squared up, as kc says. You should now have a set of ribs to the correct length ready for a final light sanding after assembly to achieve the correct angle for maximum glueing area. Quote Link to comment Share on other sites More sharing options...
A.A. Barry Posted May 27, 2015 Author Share Posted May 27, 2015 Jims idea is great, some good thoughts from all, I prefer oversizing the templates, but then again W9, 10, 11, and 12, may be better if it was recut ummmmm Barry Quote Link to comment Share on other sites More sharing options...
DH 82A Posted May 27, 2015 Share Posted May 27, 2015 Make all the ribs ( for BOTH wings) in one "block", that will reduce the taper. Then take the two "root ribs" together, sand the edges square, or slightly tapered, then the next pair, sand them, and so on. Quote Link to comment Share on other sites More sharing options...
Jim Purcha Posted May 27, 2015 Share Posted May 27, 2015 Posted by Jim Purcha on 27/05/2015 04:32:42: I cut the ribs for my Hawk model using the sandwich method. I left one rib out to compensate for the using the tip and root ribs to sand the profile too. Something I did not do, but is mentioned in my old Harry Higley's Master Modeling book is to use these tapered ribs as a pattern on another sheet of balsa for the actual ribs. This eliminates the problem of the minimum gluing surface on the rib edge. Jim Actually leave out an extra rib for the tip and the root. So if you need 12 ribs in all counting the tip and root, only 10 should be sandwiched between. Edited By Jim Purcha on 27/05/2015 12:03:03 Quote Link to comment Share on other sites More sharing options...
A.A. Barry Posted May 27, 2015 Author Share Posted May 27, 2015 Dh82, I like your process Quote Link to comment Share on other sites More sharing options...
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