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Building Tips and technical articles. => Building techniques => Topic started by: John Hammonds on May 04, 2011, 06:19:22 PM
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OK, Been back in this modelling lark for a year or so but still not sure exactly what a "D Box" leading edge actually is. ??? I've started in a model which requires a 1.25" LE and thought of replacing it with a moulded version (I had decided to soak some 1/8" balsa and wrap it around a preformed LE section). Then place Webbing between the ribs. Is this effectively a "D Box" or something different? (Like a recipe for disaster possibly). Should I cut the ribs to include the LE section and slot it over the front and insert the webbing between the ribs or build it as a separate unit?
I don't have any plans which show this method but I'm sure I have seen it on others models at some time or another and I've been told as far as weight verses strength it's a lot stronger than simply using some pre shaped LE stock.
Like I said I know this is a really basic question but I just want to try to understand what I am considering attempting and is it an accepted practice or just a stupid idea.
Thanks in advance
TTFN
John.
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OK, Been back in this modeling lark for a year or so but still not sure exactly what a "D Box" leading edge actually is. ??? I've started in a model which requires a 1.25" LE and thought of replacing it with a moulded version (I had decided to soak some 1/8" balsa and wrap it around a preformed LE section). Then place Webbing between the ribs. Is this effectively a "D Box" or something different? (Like a recipe for disaster possibly). Should I cut the ribs to include the LE section and slot it over the front and insert the webbing between the ribs or build it as a separate unit?
Yes, that's a 'D' tube section. Terminology varies -- usually a 'D-tube wing' or 'D-tube spar' refers to a structure where it's sheet back to the first spar, with shear webs. But a 'D-tube leading edge' certainly sounds right for what you're doing.
You could either make the D-tube ahead of time then put it on flat-faced ribs, or you could make round-faced ribs, put the molded leading edge on, then put in shear webs. I think that getting the alignment good would be easier with the latter method, but I'm not in your workshop so I can't say what'll work best for you.
I don't have any plans which show this method but I'm sure I have seen it on others models at some time or another and I've been told as far as weight verses strength it's a lot stronger than simply using some pre shaped LE stock.
Like I said I know this is a really basic question but I just want to try to understand what I am considering attempting and is it an accepted practice or just a stupid idea.
As far as stiffness and strength in twisting and bending, it's really the outer skin of the part that does the work. You can hollow it out without losing much of that strength. As far as being able to stand up to smacking into your flight box because you weren't paying attention when you launched, a hollow section leading edge will shatter a lot easier, and will be more difficult to fix. Pick your poison.
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Hi Tim,
Thanks, appreciate the reply. I'll go with attaching the LE around the formed ribs simply because as you say it should aid alignment. It will be my 1st tentative steps at any form of molding so I thought I'd start with something really easy and symmetrical.
I'll probably have some left over so I'll save it for the inevitable repairs to come. HB~>
TTFN
John.
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Go read Bob Hunt's post on molded leading edge sheeting. I have done it on several planes illeminating that peice of 1/4 or 3/8 that goes on the leading edge of a rib. If you look at a set of Nobler plans you will see a type of D-Tube wing. H^^
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I've been making smaller molded leading edges by laminating two pieces of 1/32 balsa, rather than one piece of 1/16. I run the rounded end of the ribs in and then do vertical sheet to make the D. I made a larger leading edge the same way, but put three strips of carbon fiber down between the two pieces of 1/32.
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"C" Tube, A wing with sheeted leading edges from the top and bottom spars to the leading edge. This normally also uses cap strips from the leading edge sheeting back to the trailing edge or ribs with a step at the spar to meet the sheeting.
"D" Tube, same as a "C" tube except there are webs of sheet balsa between the top and bottom spar to close out the "C". This makes for a wing that is very rigid when you try to twist the tip.
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ok, I think I finally got it.....
A wing with just a top and bottom spar like 1/4 square and sheeted is a "c" tube...
If the wing has the area between the spars filled like using a 1/8 or 3/33 slotted spar or just shear webs to enclose it then it is a "d" tube ?
Is that correct ?
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You don't sheet I-Beamers. S?P