Turning my attention back to the HS-702 spars, I made doubleplussure that I marked the bend line where it was supposed to go before making any cuts. I was determined to take it slow this time around and not make another $70 mistake. When you're building using flight instructor pay, every dollar counts!
The flanges need to be trimmed back and then flattened to match the rest of the spar web, and practicing on my old scrap HS-702s allowed me to find a good method to accomplish this with good results. First, I cut the flange widthwise to halfway along the bend. This gave me a nice large tab, which made it easy to use the hand seamer and some blocks of wood to flatten it and remove any bend from the transition from the spar web to the flange. I then went back to the bandsaw to trim most of that tab off, and finally used the Scotchbrite wheel to grind the remaining material flush with the rest of the web. While it doesn't produce perfect results, I used the plans method of drilling the relief holes with a #30 bit followed by the unibit to form the notch and a round file smooth everything out.
The flanges technically need to have another triangle-shaped section trimmed off before final assembly to make sure the spars don't interfere with the HS-00005 ribs. The only issue with trying to do this right now is that the hole meant to be used as reference for the minimum edge distance to maintain isn't on the spars yet. I'll have to wait until I can cleco on the skin and mark the location of that hole before I can trim this section. In the meantime, I bent the big tabs to 6 degrees and the HS-702s were finally ready to be attached to the rest of the HS assembly for drilling.
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| Ahh, this looks much more like the picture in the plans. |
Joining the front spars using the HS-710 and HS-714 angles started to give me an idea of just how wide this HS was going to be. I'll definitely end up having to move my workbenches closer together to support the part on both work surfaces.
The ends of the angles needed to be trimmed round to fit onto the spar without interfering with the skin when it's attached. I chose to grind each end using a metal grinding disk on the bench grinder, which was honestly a bit scary. It works well, but it's loud, it shoots hot metal shavings everywhere, it quickly heats up the piece, and it takes a long time to grind down this much material. Gloves, safety glasses, earplugs, and a long-sleeve shirt were a must for this operation. In hindsight I may have been able to simply use the bandsaw to trim off the excess material before grinding/polishing with the Scotchbrite wheel, but I still got decent results with the method I used, so eh, whatever.
After forming the ends, the angles needed to be bent to match the 6 degree bends I made in the spars. The plans call for putting the angles in a vise and hitting them with a hammer, but I found that bending them over the edge of my workbench by putting my weight on the tab with a wood block worked far better.
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| Before (R) and after (L). |
