Douglas Butterworth Posted December 23, 2007 Share Posted December 23, 2007 Hi all i am trying(very)to build from plans did it once thought i would try it again, on the plan i have it has two Datum lines on it quote" Wing Datum at Fus,Side and Datum at Wing Centre",the question i am asking is,what are they and what are they for,what do yuo do with them,(answer that one cleanly please) any help at all will be greatly appreciated,regards Doug. Quote Link to comment Share on other sites More sharing options...
Jonathan Lewzey Posted December 23, 2007 Share Posted December 23, 2007 I would guess these lines show the angle of incidence between the wing and the tailplane. (It should be between 0 and 3 degrees depending on model type.)If it is then this angle is one of the most important in the build and should be reproduced exactly as on the plan.jonathan Quote Link to comment Share on other sites More sharing options...
kdc Posted December 23, 2007 Share Posted December 23, 2007 It's probably due to dihedral. At the wing centre the wing is lower than at fus side. Are the lines parallel? If there is no dihedral than the lines would be the same. The crucial thing is the incidence of wing and tailplane. Often this is shown as O degrees, 1 degree etc. Mark the position on the fus sides and ensure the wing centre line is also marked on TE and Leading edge which should line up with fus side markings. Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted December 24, 2007 Share Posted December 24, 2007 This sounds a really strange set up. Normally the datum is an arbitrary line, often the thrust line or the top of the fuselage side. it is used as a reference line for things like the actual thrust line, i.e. the down thrust or side thrust and the incidence angles.The line of the wing is normally called the chord line.Why anyone would need to show the chord line at the side of the fuselage AND the centre of the fuselage is beyond me. the one on the side of the fuselage should be enough.You don't say what the plan is or where it came from. That could help. Quote Link to comment Share on other sites More sharing options...
Douglas Butterworth Posted December 24, 2007 Author Share Posted December 24, 2007 Hello Peter Miller the plan is a Brian Peckham design from 1989 was ressurected in 2002 by Mike Parry and is Mr Peckhams version of the Percival Mew Gull only he called it Chorus Gull and the plan No is RM356 and i have the original free plan from the March 1989 Radio Modeller and a bigger one from the RCM&E plans service and they both say the same thing so there is no miss print,what do you think?any help will be very much appreciated,regards Doug Butterworth. Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted December 24, 2007 Share Posted December 24, 2007 Sorry, I am not familiar with the plan and I don't understand the two datums. I would say that just build to the shapes shown, after all, if you cut the side to the shape shown on the plan the wing should line up correctley, it isn't as if you were trying to rig struts etc.I am sure that there are some builders of Chorus Gull who will be able to help you in more detail. Quote Link to comment Share on other sites More sharing options...
Mike Rolls Posted December 24, 2007 Share Posted December 24, 2007 I happen to have the plan and have just had a look at it. The 'wing datum lines' are in fact chord lines. Why both are shown is totally beyond me - as Peter says, if you follow the shapes intended the wing will be positioned correctly. There are two chord lines because. as kdc surmised, the differenece in caused by the dihedral causing the chord line at the centre being about 3/32" lower than that at the fuselage side.Looking at - and puzzling over - the plan the only possible suggestion as to a reason that I can make is the position of the wing dowel. This is shown as being centred on the chord line at the fus side, whereas it is located on the centre line of the wing. I suppose if someone were to be foolish enough to drill the dowel location in the leading edge by measuring from the plan using the fus side chord line, then he might find it didn't line up with the hole in F2. But surely nobody would do that? I've never met anyone who does anything other that assemble the fus as far as need be, offer up the wing, and drill through the hole in the former.Mike Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted December 25, 2007 Share Posted December 25, 2007 The only other reason for the chord lines would be one at the root and one at the tip to show washout. This wouod in fact be pointell but could be a reason. It doesn't apply in theis case.Er, Mike I use a different system. I make the hole in the wing for the dowle by making a slot in the centre rib and laminating sold ribs each side of that, true, it is a square hole. I plot and drill the hole in the former fractionally too high and ease it down to a perfect fit afterwards.Works OK for me and no one has complained so far. Quote Link to comment Share on other sites More sharing options...
Mike Rolls Posted December 25, 2007 Share Posted December 25, 2007 PeterEach to their own. Personally, I distrust relying on measuring anything for that critical - I know my limitations!Merry ChristmasMike Quote Link to comment Share on other sites More sharing options...
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