Folks:

I'm preparing some aluminum to be used for my aileron spar webs (starting small, so the screwups, er, learning, costs less), and am running the numbers to cut the needed material for the blanks. I have found a disagreement with what appears to be standard practice for bending vs. what is included on page seven of "The Bearhawk Book" as well as what appears in Eric Newton's wing build manual.

I am using the Bingelis Sportplane Construction Techniques book to calculate bend allowance, setback, etc. I've included a picture of my calculations for the aileron spar web with the dimensions in the plans (my aileron spars will need to be a bit taller to account for my as-built rib heights, and the fact that I'm not planning to joggle). Basically, the Bingelis method says that the aileron spar webs (per the Model B plan dimensions) need to be made from a blank that is 5.230" tall, whereas the Bearhawk Book method indicates that the aileron spar web blank should be 5.433" tall.

I went to a third source - https://www.flight-mechanic.com/layo...ng-part-three/ - and used the "J-chart" method. That gives me a spar blank height of 5.175", which is admittedly a little error-prone since I'm interpolating from the chart.

Am I missing something? Does anyone know why "The Bearhawk Book" uses its particular approach? I suspect it is for simplicity, and errs on the side of slightly more flange material. (The same is true of the practices for bending the rib flanges - my rib flanges are all slightly larger than called for, but when I calculate the additional weight penalty, we're talking something like a pound or two for all of the ribs, so I'll probably leave them as-is.)

I'm preparing some aluminum to be used for my aileron spar webs (starting small, so the screwups, er, learning, costs less), and am running the numbers to cut the needed material for the blanks. I have found a disagreement with what appears to be standard practice for bending vs. what is included on page seven of "The Bearhawk Book" as well as what appears in Eric Newton's wing build manual.

I am using the Bingelis Sportplane Construction Techniques book to calculate bend allowance, setback, etc. I've included a picture of my calculations for the aileron spar web with the dimensions in the plans (my aileron spars will need to be a bit taller to account for my as-built rib heights, and the fact that I'm not planning to joggle). Basically, the Bingelis method says that the aileron spar webs (per the Model B plan dimensions) need to be made from a blank that is 5.230" tall, whereas the Bearhawk Book method indicates that the aileron spar web blank should be 5.433" tall.

I went to a third source - https://www.flight-mechanic.com/layo...ng-part-three/ - and used the "J-chart" method. That gives me a spar blank height of 5.175", which is admittedly a little error-prone since I'm interpolating from the chart.

Am I missing something? Does anyone know why "The Bearhawk Book" uses its particular approach? I suspect it is for simplicity, and errs on the side of slightly more flange material. (The same is true of the practices for bending the rib flanges - my rib flanges are all slightly larger than called for, but when I calculate the additional weight penalty, we're talking something like a pound or two for all of the ribs, so I'll probably leave them as-is.)

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