Monthly Archives: February 2021

Wingtips – More Rework

After a gallant effort on the original RH wingtip, I ordered and received a replacement RH wingtip. The new part still had too much length and thickness at the trailing edge, but the workmanship of the layup was much improved and it had noticeably better overall shape. It has still taken lots of work to get the new RH tip to fit. But, it’s coming along and it’s going to work out well.

The LH tip is proving to be huge headache. Despite extensive rework, it’s now clear that the LH wingtip isn’t close enough to the proper cross section to fit and it would take extraordinary effort to get it in the ballpark.

Just like the RH wingtip, the length of the LH part at trailing edge is too long and the trailing edge profile (taper) is too thick to fit the trailing edge wing skin. But the kicker is the overall height. It’s just too narrow – top to bottom. It’s almost 2 cm short, at the widest point.

Trying to stretch the height of the LH tip requires too much force. The LH wingtip has no imbedded reinforcement strip on the bottom edge. The top reinforcement is out of position. Without proper stiffness, the tendency for waviness between the rivet holes would be profound.

To continue with the original LH wingtip, I’d have to section the part and almost re-manufacture it. I’ve decided that it’s much too much time and effort, although I have seen one other builder go to such lengths and spent over 130 hours on just trying to get his wingtips to fit. I’m at more than 40 hours on wingtips and I’m going to cut my losses and get a better baseline part.

I went ahead and negotiated a new LH wingtip from the factory, as I did for the RH side. They’ve kindly agreed to send me one. Kudos to Sling Aircraft for standing by their product. Stay tuned.

VS – Trial Fit

One things leads to another. A question about the factory-installed rudder cables got me started down the road of test-fitting the vertical stabilizer. I was very pleased to find that it was easy to do and the fit appears to be excellent.

I hadn’t really expected to do this step just now. But, in order to evaluate much about the rudder cables, the entire control mechanism for the rudder and steerable nose-wheel needs to in place and adjusted. I learned this during a customer support exchange with Sling Aircraft’s Jean d’Assonville. I’d called him because I was concerned that the rudder cables may have been installed improperly during factory the quick-build of my fuselage. Jean assured me that it was very unlikely that the cables were wrong.

I was wondering because the KAI talks about one cable being slightly longer than the other. Somehow they seemed to be the other way around. Jean said that the only way to properly evaluate the setup would be to assemble everything. It only takes 15 minutes, he tells me! LOL. But, he really meant it!

It’s going to take me hours and hours, over days and days, to get the entire rudder control mechanism in place. That’s not only because I’m slow and plodding, but also because I’m not ready to install the nose-wheel yet. It’ll all just have to wait until I get the avionics rack, LRU’s and harness in place while the wheels are off and the fuselage is low and as easily accessible as it can be.

So then. I still don’t know for certain that the rudder cables are installed properly. But, I did get inspired to get the VS out from storage in the house and get it fitted on the fuselage. Technically, that’s progress! The nice fit between the fuselage and vertical stabilizer is satisfying too.

Wingtips – Rework in Progress

The fiberglass composite wingtips are needing a lot of rework. I don’t really believe it was intended be this way. What’s a simple amateur home-builder supposed to think?

The biggest area needing attention seems to be where the inside trailing edge of the wingtip is supposed to fit into the narrow skin at the tip of the wing. Several issues are being dealt with. Overall length is too long – by about 2cm (almost 1/2 inch). And, the fiberglass structure doesn’t match the contour of the wing profile near the TE. The taper of the fiberglass needs to become quite narrow. Plus – it’s all got to look pleasing and with and both wingtips ending up to be nicely matched – both aesthetically and aerodynamically.

I’ve decided that some sort of struts are needed to help the wingtips fit the contour of the wing. The kit instructions indicate that the wingtips are just match drilled and riveted. But, just letting the rivets pull the fiberglass shape seems like it’s going to lead to unwanted waviness from dips between the rivets. I fabricated simple struts to take some of the tension load off of the rivets. We’ll see how that goes.

I’m making progress, little by little – but it’s slow. Rework involves epoxy and with winter temperatures, each cycle needs a full 24 hours or more to cure. There’s plenty of sanding and shaping to do. Check fit. Then repeat.

I expect building an airplane to take some work, so I’m not going to complain too loudly. I fill terrifically privileged to be doing this project.