Wondering about numbers again

[Dave Stroud]

While waiting for some bandsaw parts to arrive I took the opportunity to compare some ribs I've built to Leonard's and Scott's ( in Iowa ) plans and discovered a fair difference. I've built ribs to date using Scott's supplementary plans while waiting for Leonard's to arrive. Scott's wing rib numbers and drawings are smaller in most respects and larger in one area that I see. For instance, the top to bottom measurement of the aft end of the nose rib is 7" with Leonard and 6 3/4" with Scott. Measuring the overall outside depth of the rib is different too. The second vertical rib stick will make the rib 7 15/16" tall on Leonard's drawings and only 7 11/16" on Scott's. The overall depth of the rib in the location of the third rib stick ( reading left to right ) it is 7 5/8" on Leonard's and only 7 5/ 16" on Scott's. Comparing Scott's drawing to that of Leonard's patched together, the spar positions are pretty close...maybe an 1/8" difference but Scott's nose rib is about 3/4" longer and Leonard's plans make up for that difference back over in the aileron area. Overall, they are both close in length. I've got Leonard's patched together at 55 1/4" and yet Scott's plan says 55.2" but measures right at 55 1/2". Just wondering what others have done. Has anyone compared the two and what have you done in your build ? Should I continue using Scott's numbers or start the ribs again using Leonard's numbers? Scott's numbers will result in front spar depth being reduced about 1/4" and in the big scheme of things this is about 3%. Thanks.

[CHARLES DEBOER]

Which ever one you chose the critical dimensions are where the front and rear spar attach to the ribs.  We are building a slow airplane.  Photo copied sketches vary from copy machine to copy machine.   Leonard's photo copies are not calibrated to three decimal places and he tried to answer all of your questions by offering a full sized drawing.  Since you bought Scott's drawings use them.  Just make sure they are all built to the same dimensions.  The nose ribs are covered with .8 mm ply. so the front spar should be about 1.6 mm smaller in hight than the front of the wing rib so ply doesn't protrude above the wing rib when glued to the front spar.  

The nose rib should be same hight as the front spar.  The wing rib should be [.8 mm top & .8 mm bottom = 1.6mm] taller than the front spar to allow for the ply.

[scottiniowa]

Which ever one you chose the critical dimensions are where the front and rear spar attach to the ribs.  We are building a slow airplane.  Photo copied sketches vary from copy machine to copy machine.   Leonard's photo copies are not calibrated to three decimal places and he tried to answer all of your questions by offering a full sized drawing.  Since you bought Scott's drawings use them.  Just make sure they are all built to the same dimensions.  The nose ribs are covered with .8 mm ply. so the front spar should be about 1.6 mm smaller in hight than the front of the wing rib so ply doesn't protrude above the wing rib when glued to the front spar.  

The nose rib should be same hight as the front spar.  The wing rib should be [.8 mm top & .8 mm bottom = 1.6mm] taller than the front spar to allow for the ply.

Hello XL builders- some thoughts on this. (general ones with somewhat precise reasons)
   I agree whole heartedly with Charles D. in that, one simply has to choose one or the other and stick to them...
I also agree with what many found, that is simply, the full length rib varied from the 8.5" x 11" sheets  Again- one or the other needed to be used.
The last line of Charles is very good...that .8mm top and bottom is required to make the smooth transition from nose ply to balance of wing. That is SO TRUE no matter which of the three you use.  

So, while I have this stated in other areas, the reason I did what I did is simple.  I created a set of Supplemental drawings to speed up the process of building the wing greatly.  NO guessing what needs to fit this or that... Just the clear drawn parts. All parts drawn full scale and precisely.  Again to save time, not to recreate anything better or different.   Both will work.  The possibility that one or the other is going to fly better/faster/farther is so unrealistic to think you will be able to measure this, well it could go the way of the chicken or egg thing... at 50-60 mph,  the changes simply would have a hard time to vary 1 mph up or down...certainly not enough to measure.

On the drawings, I show the slight difference in CG (possible) changed location.  Off of memory, I think between .625 and .750"  Your body weight distribution vs the next person is going to vary this more than anything else.

So simply- why the slight difference?    I used computer generated spline line, from published numbers..  So that if 10 different CAD folks created this line, all would get the same results.  I am a lot more comfortable with measurements that have a known background or formula   Again, not better, not worse, simply a solid method to get to where I got.

Hope this clears up the water a bit.  

Oh yes, the driving force was to help 10 high school kids build vs calculate "how to build" --   1/2 dozen different ways to do almost anything on a bird like this.

cheers
Scott