XL Spars

[914pete]

I just started building my left front spar and have a question: Page 34 notes the front spar over-all height at 6 7/8". I ordered Leonard's full length rib drawing where the front of the rib noted for the LE and XL is actually 7 1/4" over-all. Why is there a difference of 3/8"? Also, the rear spar is noted on page 34 as 5 1/4" over-all where the rib plans opening for it is 5 5/8"?

[Kamcoman77]

Everything depends on which rib drawing you want to use. Many people have reported a range of rib dimensions from the XL plans, and if using the IronDesign LLC rib drawings, you will get yet another dimension. This is what is important.... You can go one of two ways. #1. Decide on which rib drawing you are going to use. Build your first rib. Then build your spars to fit your rib. Match your nose rib to your front spar after beveling. My front spars had an 8-degree bevel. #2. Build spars according to Page 34 dimensions. Then re-size your rib drawing so the rib height matches your front spar. Then match your nose rib to spar, after beveling. I did not make my spars first, since I believe they should fit my ribs, not the other way around. I used the IronDesigns LLC rib drawing so my ribs will be a little different height than yours, if you use Leonard's full-size rib drawing. Either rib profile will work just fine; pick one and stick with it. The rear spar height does not fill the opening in the rib. On my rib-to-spar joint there is about 1/4" gap at the top of the rear spar. The top of my rear spar does not need a bevel like the front spar.

[kalazzerx]

I second that - build your spars to fit your ribs - whatever that turns out to be.   Also good info on the bevel and taking that into account.

[scottiniowa]

Everything depends on which rib drawing you want to use. Many people have reported a range of rib dimensions from the XL plans,   This is what is important.... You can go one of two ways. #1. Decide on which rib drawing you are going to use. Build your first rib. Then build your spars to fit your rib.
YES  

Match your nose rib to your front spar after beveling. My front spars had an 8-degree bevel. #2. Build spars according to Page 34 dimensions. Then re-size your rib drawing so the rib height matches your front spar. Then match your nose rib to spar, after beveling.
Yes, but but number 1 is easier as no interpolation of the rib drawing is required (resizing)

I did not make my spars first, since I believe they should fit my ribs, not the other way around. I used the IronDesigns LLC rib drawing so my ribs will be a little different height than yours, if you use Leonard's full-size rib drawing. Either rib profile will work just fine; pick one and stick with it.
Yes again, There is no one that is ever going to tell or be able to measure a difference in performance

 The rear spar height does not fill the opening in the rib. On my rib-to-spar joint there is about 1/4" gap at the top of the rear spar. The top of my rear spar does not need a bevel like the front spar. 
This is just me, but knowing how spar strength is calculated, I like to take advantage of everything I can get, so I try to make this as tight as possible.  Sure will work as explained here.

Kamcoman77 pretty much nailed it. !

[914pete]

Thanks for the replies. I have built 14 ribs so far using Leonard's full rib drawing. When comparing to the dimensions in the plans for the spars I thought maybe I did something wrong. So I will build the spars to match my ribs.

Question: I can't seem to find in the plans, should the front spar height be such that the nose ply is flush with the curve of the ribs when in place? So the leading edge of my ribs are 7 1/4", should I make the front spar 7 1/4" high or less the thickness of the nose ply top and bottom so the transition is smooth to the top and bottom of each rib? The nose ply only covers the spar caps, not any part of the rib correct?

[Kamcoman77]

Good progress, 14 ribs. You are correct in your thinking about front spar height. Highest part of front spar (rear edge) should match sanded rib height minus two thicknesses of 0.8 mm ply. When making my front spars, I made a nose-rib/spar/wing-rib mockup to determine the bevel angle on top of the front spar. I calculated 8° for my plane. I cut the 8° bevel on the two upper spar caps before assembling the spar caps and verticals. I used the dimension of 5-5/32" for my verticals since that is what I measured on my mockup. My nose-rib/spar/wing-rib joint needs almost zero sanding to have a smooth junction.

[914pete]

Great! Just wanted to be sure. First time builder. Thanks!

[Kamcoman77]

First time too, on Legal Eagle. Built a KR2 in late 1970's but only RC models since then.