The composite engine cowling is one of the key contributors to the look of a Sling aircraft. I love the way Slings look. There are other models available from Sling Aircraft now, but it’s the Sling 2 that started it all. Now my Sling 2 is starting to look like it should.
There are a few pointers in the plans about the cowling, but mostly it’s up to the builder to figure out how to get the cowling to fit – properly and securely. I’ve complicated the process by introducing a custom spinner assembly. The factory-supplied spinner, while likely adequate, has to be built up from parts. The spinner I ordered through the propeller manufacturer – Whirlwind – is beautifully made from carbon fiber, comes finished and ready to paint. It’s a slightly different look, but still very, very Sling-like.
The 9.75″ Whirlwind spinner is notably different from the factory unit. The backing plate flange faces backward instead of forward. This will mean that the cowl will have to fit somewhat farther back on the fuselage than it otherwise would for the standard spinner.
To get the cowl aligned and with the proper setback, I’ve made a fixture that mounts to the prop hub extension. The hub extension is a standard part of the kit. Repeated fitting and trimming will hopefully arrive at a near perfect position and alignment. More to come on that.
It didn’t take long before I realized that I’m in for a battle. The fiberglass wingtips, as supplied with the kit, simply don’t come close to fitting the wing. They’re obviously hand-made parts and are nowhere near identical. Frankly, I expected better. But, they are what they are.
I don’t have much hope that if I push the factory for new parts, I’ll get anything [much] better. I’ll count myself fortunate if I can get satisfactory results with less than the 130 hours another Sling 2 builder has put into his wingtips. Jeez – that’s a lot of time!
Right off the bat – the overall length is far too long to fit into the end of the wing panel. The airfoil shape cross-section is decidedly too flat. The up-sweeping trailing edge scallops are oddly different shapes. The lack of alignment at the point where the tapered wing skin is supposed to accept the trailing edge of the wingtip is unfortunately grotesque. Cutting and reforming will be necessary. Ultimately, the wingtips will be permanently mounted with 3,2mm multi-grip blind rivets. I haven’t settled my mind as to how I will mount the wingtip lights.
I decided to make a simple wing-shaped jig from a 2 x 4 foot section plywood. This jig is much less elaborate than others I’ve seen, but it will hopefully result in a useful tool and a reasonably consistent reference I can use to evaluate and correct the various eccentricities of these fiberglass parts.
I’ve been fortunate to be able to see what other builders have encountered and done with their wingtips, and so, I’ll share my adventures too. For the Sling 2 builders, we all seem to be – more or less – in the same boat.
As far as I can tell, once an experimental aircraft build project gets to a certain point, there’s a right-of-passage that must be embraced — sitting in the thing. Today is the day.
I made a work platform from wood. It fits inside the fuselage on either side. I can sit on it, if and as needed.