HP-24 Project

Update 4 August 2004: Getting horizontal and vertical

Brigitta and I spent most of the weekend of 24/25 July 2004 in Yosemite, doing a hike from the valley floor to the top of Half Dome and then back again. We've done this once as a two-day, once as a three-day, and now twice as a one-day walk. It's only about 16 miles round-trip, but the elevation gain of about 4500 feet is killer. The last time we did it as a one-day, my left knee went out while descending the stairs below the cables and I had to limp about seven miles back to the valley floor. This time neither of us suffered but the expected muscle aches.

Last weekend, Brigitta and I made two runs up to the shop on Sunday, and brought the remaining five HP-18 and RS-15 forward fuselages down to the house. We stood them on their aft ends and leaned them up against the North wall of the house, where we secured them with a bit of yellow rope. From what you can see over the fence, they look a bit like a salvo of ballistic missiles. Saturday we'd spent rock climbing at nearby Table Mountain, where I frolicked (with abandon) up a lead climb on Sidesaddle, and also did one each crack climb and stemming climb on a hexagonal basalt column like a miniature of what you'd find on Devil's Tower in Wyoming. Brigitta and Alia also made forays at Sidesaddle, with Alia gaining the toprope anchor with a little help from the belay.

Anyhow, with the pods out of the shop, I can use the overhead racks where they used to be to place one or both of the wing plugs while I'm working on either them or the horizontal tailplane.

Speaking of the tailplane, I'd like to thank the senders of the four messages I received recommending the Glasflugel/Schempp-Hirth system of both securing the tailplane and driving the elevator. I've considered it before, but never seriously. I think it might be more complicated than it is worth to do it that way.

The basis of the Glasflugel/Schempp-Hirth system is that the entire horizontal tailplane and elevator are supported by the pins that drive the elevator. Most of the tailplane loading goes through the inboard elevator hinges, so those hinges must be very stiff, and attached very well to both the upper and lower shells of the stabilizer. And further, for the system to work properly, the elevator hinge axis must be very precisely aligned so that it is coaxial with the pivot cluster on the vertical fin when the two are assembled.

In the full-on factory environment, it is relatively easy to jig all this stuff together right. However, in order to make it easier to meet the "Major Portion" rule for amateur-built experimentals, I'd like to have the builder join the top and bottom horizontal tailplane shells. I'd also like to give the builder a comfortable working margin of error to account for the vagaries of the home workshop environment. I think it will be easier to accommodate that environment with a mechanically and topologically simpler system, like that found on the LS-6.

Nonetheless, I have arranged to borrow a Schempp-Hirth tailplane attach cluster so that I can get a good look at its insides. I maintain that indecision is still the key to flexibility!

Next weekend, I figure to put more cradles in the racks vacated by the fuselage pods so I can store the wing plugs. If things go well, I'll make a third attempt to skin the elevators with fiberglass. I'd like to get the tailplane molds done before too long so I can do some test pieces of my proposed internal structure for the tailplane and elevator.

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page updated 4 August 2004 all text and graphics copyright (c) 2004 HP Aircraft, LLC