christopher small Posted November 20, 2016 Share Posted November 20, 2016 I`m building a 1/4 scale Sig Piper cub,and have some 1/4 square spruce spars to glue in to the wings is there a right way of doing it they seem stronger one way than the other as you turn them over,normally with balsa I just place them on the plan and glue them in .does the wood grain matter. Chris Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted November 20, 2016 Share Posted November 20, 2016 I've no idea what the expert view is but I always use them in the strongest direction to oppose bending loads i.e. up and down. Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted November 20, 2016 Share Posted November 20, 2016 The most important thing is to check for staight grain. Vawyr rarely you can get one where the grain goes across the strip and an angle for a sshort distance. Quote Link to comment Share on other sites More sharing options...
kc Posted November 20, 2016 Share Posted November 20, 2016 If in doubt about the quality of the spruce replace with a decent bit of wood! Especially on 1/4 scale Quote Link to comment Share on other sites More sharing options...
christopher small Posted November 20, 2016 Author Share Posted November 20, 2016 I think its time to go and have a real good look at my spruce strips,normally I don`t bother just eye them up for straightness and glue them in.I have a lot to glue in especially balsa strips. Quote Link to comment Share on other sites More sharing options...
Jon H Posted November 20, 2016 Share Posted November 20, 2016 Once they are shear webbed and glued to the ribs it wont matter at all. Peter is right, as long as its pretty straight you are ok A 1/4 scale cub is neither big nor heavily loaded, and SIG usually over engineer their kits anyway so you will be just fine. Quote Link to comment Share on other sites More sharing options...
christopher small Posted November 20, 2016 Author Share Posted November 20, 2016 Thanks Jon,it does look a strong well made kit so far.I want to have the wings made up by Christmas. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted November 20, 2016 Share Posted November 20, 2016 I've just been having a quick google around and it seems that there is "discussion" on this subject in full size circles - it's a given that the grain runs along the spar but opinions vary about the grain (end on) variation between vertical and horizontal. The vertical grain exponents say it's stronger in resisting bending and the horizontal advocates say it's more likely to fail due to grain splitting from any excessive torsional loads... Bottom line is that, as several posters have suggested, good quality spruce should be more than adequate whichever way it's fitted. Just don't do what the builder of a part built/covered 1/4 scale Cub I bought did and drill them for the lift strut fittings! Yes - I did redesign the fittings when I rebuilt the model! Edited By Martin Harris on 20/11/2016 12:59:27 Quote Link to comment Share on other sites More sharing options...
Former Member Posted November 20, 2016 Share Posted November 20, 2016 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Jon H Posted November 20, 2016 Share Posted November 20, 2016 I wouldn't have a problem drilling through the spar but it would need some sort of doubler plate either side of the spar. 1/16 ply would be sufficient I would have thought. On the sig kit, are the wings cantilever or are the struts load bearing? Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted November 20, 2016 Share Posted November 20, 2016 Oh dear...! Strangely, the previous owner was a quite experienced (although sadly departed) and well respected modeller. The model was being built in partnership with another deceased and very experienced member (although I'm told they fell out over some radio installation and colour issues) so I don't know who was actually responsible for that aspect. Perhaps I should have been wary when I found the engine (which was going to be an OS160 twin, the outline of its backplate was imprinted into the firewall - I used an ASP clone) which had been taken back after the disagreement by the other member, had been mounted an inch or more below the correct thrust line! It's not all bad news though as it's been one of my favourite models for a number of years, since rebuilding the result of the in-flight spar failure on an early flight and covering it in the "proper" colour scheme. It rolled uncontrollably but I somehow managed to delay the "touchdown" until it was the right way up and disappearing behind the clubhouse! Although it's hard to believe, the pilot was unharmed and after being extracted still flies it to this day! Edited By Martin Harris on 20/11/2016 14:49:15 Quote Link to comment Share on other sites More sharing options...
Former Member Posted November 20, 2016 Share Posted November 20, 2016 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted November 20, 2016 Share Posted November 20, 2016 Posted by Jon Harper - Laser Engines on 20/11/2016 14:24:04: I wouldn't have a problem drilling through the spar but it would need some sort of doubler plate either side of the spar. 1/16 ply would be sufficient I would have thought. On the sig kit, are the wings cantilever or are the struts load bearing? I don't know about the SIG but my struts (Premier Models kit) are most definitely load bearing. Funnily enough, your suggestion is pretty much the method I adopted to reinforce the existing and repaired sections with the mounting holes on the neutral axis midway between the top and bottom spars. Quote Link to comment Share on other sites More sharing options...
christopher small Posted November 22, 2016 Author Share Posted November 22, 2016 Hi Martin,nice looking Cub in your second pic.How do I know if my struts are load bearing? Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted November 22, 2016 Share Posted November 22, 2016 Thanks. I don't have any experience of the SIG version but a little googling suggests they are. It was very obvious with mine as the wings slot on to relatively thin piano wire stubs which are obviously insufficient to prevent bending - and the struts retain the wings as well. Which means that negative G manouevres are as per full size - verboten! Edited By Martin Harris on 22/11/2016 19:07:48 Quote Link to comment Share on other sites More sharing options...
Former Member Posted November 22, 2016 Share Posted November 22, 2016 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
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