HP-24 Project

Update 9 July 2007: Constant Radii Challenge

As occasionally happens, the last few weeks have been strong on IBS (itty bitty stuff) and short on VP (visual progress). This last weekend I finally accumulated enough VP to actually get some photos of it.

What I've been doing is shaping the lower hinge radius on the right wing flaperon sections. Unlike the tapering upper hinge radius, for which I built the Radius Maximus machine, the lower hinge has a constant radius. To form the lower radius, I made sanding tools various and sundry, glued in assorted blocks of foam and junk, and proceeded to use the hinge gudgeons as ruling features to sand in the radius. Then I added some epoxy with cabosil to seal the pores of the foam. Then I added bondo. Then I sanded some more. It's going OK, though turning the shop into a dust-laden disaster zone.

When all this junk is done I'm going to make molds off of the upper suface and hinge radii portion of the flaperon plugs, and make appliances that I can put on the lower wing mold to form the lower flaperon skins.

Partway through gluing on the PVC foam blocks for the lower radius. Two segments in the foreground are sanded to near-final shape.

Closeup of the hinge gudgeon I'm using as a sanding guide feature.

The foreground segment at near-final shape, the background one is rough-shaped with the die grinder and ready for sanding to near-final shape.

All segments sanded to near-final shape, then painted with epoxy resin thickened with cabocil.

All segments sanded, the treated with Bondo, then sanded some more.

Closeup of that same gudgeon. Looks a fright at this point. Yes, the plug lower surface is taking a beating. However, I'm only molding to about the pink/white interface, so I don't really care about the rest of the bottom surface.

Sunday afternoon we took a short hike in Big Trees state park. One of the odd things we encountered was this sign that has been seriously and methodically chewed on. I think it was a deer, Brigitta thinks it was a bear. I suppose it could have been the scrawny, hungry bear we saw checking out the cars in the parking lot. Fortunately, the bears in Big Trees don't break into cars the way Yosemite bears do.

We also saw this broken tree with a shattered split of the type sometimes called a "widowmaker." Such a tree develops an internal delamination that causes it to liberate huge jagged spikes when stressed or cut into. For some unlucky loggers, something like this was the last thing they ever sawed.

Here's a couple shots of my lower radius-forming tools. This is just a plate of aluminum, bent at the requisite 56-degree angle, using a brake shoe that gives it an inner bend radius of 1/2", and flush-riveted to a chuunk of 1" square steel tubing that stiffens it and offers a convenient handle.

This is a shorter chunk of the same aluminum with the same bend for eyeballing the radius between the guide features. It's shorter and without the handle.

Homebuilt aviation is not for folks who don't try things at home.

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page updated 9 July 2007 all text and graphics copyright (c) 2007 HP Aircraft, LLC