HP-24 Project

Update 19 November 2007: Making skins and getting skinned

This weekend Brigitta and I laid up another horizontal stabilizer skin. Now I can use the two skins together to develop simple squish plugs and then molds for the stabilizer internals. We'll have one large shear web at the chordwise station of the carbon sticks, and probably another shorter shear web forward at the site of the forward attachment angle. There'll probaby be a root rib at the plane of symmetry, but I haven't yet decided whether I'll bother with tip ribs. I probably will, but the skins are so stiff that it seems a bit of overkill.

The process was pretty simple and saved a lot of time for funner things. Saturday morning pretty early, we went up to the shop, organized the workspace and the laminates, mixed and sprayed the gelcoat, and fired up the heater. Then we closed up, went home, and did other stuff for a couple hours. It wasn't really fun stuff - we cleaned out the gutters, put in the gutter screens we made the other week, and strung the Christmas lights. But it was more useful that hanging around the shop watching paint dry, that's for sure.

Then, later in the afternoon we went back and did the layup on the cured gelcoat, bagged it down, and took off again.

This layup complicated by the fact that we needed to include the alignment armature for the elevator hinge gudgeons. This welded steel contraption has a few sharp corners that we needed to tape over. As we discovered fairly late in the game, it also crosses the aft squeeze-out trench in a way that requires the vacuum bag to bridge in a threatening-looking manner. Going forward I need to add a filler piece to the armature to prevent that bridging and its potential for bag rupture.

On Sunday I went rock climbing again in Yosemite with the offwidth crew, it seems that the entirety of the wideness aficianados turned out for some thrashing in the fine crisp fall air. I teamed up with Ed Hartouni and former A-4 pilot Gary Carpenter on Moby Dick Center, which Gary led and I cleaned after belaying Gary. The upper third requires offwidth skills in which I am still very weak, so after the bare minimum of hand stacks and butterflies I mustered my inner sport climber and liebacked through the roof.

After we were all at the top of Moby Center, Gary lowered Ed and I off and then joined our pair of ropes for a toprope session on Ahab. Down low that climb is your typical Yosemite old-school awk-fest, requiring decent stemming and slab skills, a couple of hand jams, but nothing a gym weenie like me couldn't muster after breakfast. Then, maybe forty feet off the deck, the real climbing begins. You insert your body into a squeeze chimney too tight for typical chimneying moves but too loose for offwidth-style foot stacks. And then you do whatever it takes to ascend. Gary, offwidth Jedi that he is, found the perfect combination of hip jamming and chicken winging and grunting and scumming and whatnot and made significant progress up the chimney. Ed got up to the chimney and made maybe three feet of progress. I got up there, stood on the launch ledge at the base of the chimney, and laughed and laughed because I could not imagine any situation better suited to give the illusion of climability without the actual potential thereof. Not for me, at least. I thrashed at if for a while, alternately gaining and losing a couple inches and returning again and again to the hearth. And then I laughed some more and lowered off to the deck.

The meanwhile, Supertopians Scuffy B. and Zander and another Bob were about a hundred feet to our left taking their laps on (I think) Little John right and Little John left. After a while they came over to us and took their throws and throes at Ahab, averaging between what Ed and Gary had accomplished. Then I took a toproped half-lap on what they were climbing, getting to the top of the relatively easy stuff before lowering off.

And that was pretty much it for the climbing. Long about then, the sun went down behind the rim of the valley, but still shone strong on the face of El Capitan half a mile above us. That golden light filtered down through the trees onto us as we were packing up and we were bathed in its glow as we stumbled down the talus to the meadow.

Back at the car we opened a couple beers using the carabiner trick, and encountered yet another Supertopian, Kate, who was heading up for a week or so on Tangerine Trip with her partner Aidan. And then it was time to parcel ourselves out to our cars and carpools and head back to what everyone seems to call reality.

The meanwhile I was rending my anemic hide on the Yosemite granite, Brigitta found some time to get up to the shop and check up on the stabilizer skin. That threatening-looking spot where the bag bridged over the alignment armature had held, and the part looked good. She stripped off the bag, breather, perf, and peel plies, and got some photos. Here they are:

The center section of the part. Bottom center is one of the alignment arms that crosses the squeeze-out trench and forces the green vacuum bag to bridge.

Green like Vulcan blood

Spanwise view, still bagged. This photo shows the three alignment arms and two vacuum taps crossing the trench. Going forward I'll add a filler piece where the alignment arms cross the trench, and use a different arrangement of vacuum tap.

This is how they invented crop circles

Spanwise, debagged and de-breather-perf-peel-plied. A nice, straight, neatly organized part.

Take it all off!

Center, peeled, showing one of the three offending bridge opportunities.

And a rare Whitworth adjustable wrench

Starboard tip (this is the inside of the upper skin..

The Sharpie marks toughen the epoxy. Really. Not.

Spanwise from starboard, showing how the alignment armature orients the four inboard hinge gudgeons. On this skin we'll add the outboard two hinge gudgeons in a secondary operation. Going forward I'll probably just make the outboard hinges just like the inboards, it'll be easier to just use the same parts and techniques at all six stations.

We re-grind the gelcoat overspray and sell it as fake dandruff

Closeup of the starboard tip showing the foam strips that replace the carbon sticks out beyond where full strength is required. Also shown is the clever semi-random pattern of perforations that allow air to escape from between the foam and the outer laminates. Doug makes this pattern much more regularly than I do, especially when I do it at the last minute.

Fractals at work

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

Return to HP-24 page

page updated 19 November 2007 all text and graphics copyright (c) 2007 HP Aircraft, LLC