HP-24 Project

Not much to report lately, but I thought I'd put up something to let everybody know that I haven't forgotten about the HP-24. During the Christmas holiday, while my company was shut down for almost two weeks straight:

• I made a detailed set of measurements of the HP-24 wing spars that we made last summer. I need this set of measurements to validate that the spars are in the neighborhood of what I intended. I also need them in order to design the profile of the wing plugs so that the spars will fit inside the finished wing skins. It would be a real bummer to try to seal up the upper and lower skins and find that they wouldn't close as intended. A real bummer. Our wing profiles are pretty much locked down, but we will scale them in thickness by a few hundredths of a percent as required to fit the spars snugly.

• I got out my various and sundry implements of destruction and tore down the wooden plugs for the wing spar molds. That plug has done its job, and I need the architectural joists from the spar plug table to make a wing sanding table. But while sawing the spar plug to pieces, I saved a bunch of souvenier sections. Anybody who wants one of these priceless mementos of the HP-24 development project can have one for the asking (plus a dollar for the padded envelope).

• I got quotes for CNC hotwiring of the foam cores for the wing plugs. After talking to a few more R/C airplane builders, I got the notion that getting good foam cores is another of those learn-once technologies where I'd be better off just sending money to those who've already learned the hard-knocks lessons.

• I bought a set of 608ZZ and 608-2RS inline skate wheel bearings to see if I could figure out why they have such ridiculously low load ratings. The answer is simple: They just don't have the balls for the job. The 608s I opened had only 6 balls in the whole bearing, while the KP-3 and K-3 airframe bearings I cut open have 12 balls. And the 11-164 and RE3M6-2N rod end bearings have 20 balls each. I did find a Chinese outfit that can make me KP-series airframe bearings at very low prices; but I'd have to order hundreds of them to mee the minimum quantity. I'd have to get a bunch of folks signed up for $4 KP bearings to make that work.

• I designed the steel spindle that will stiffen the wing plugs enough so that we can handle them. This is just a 2.5" steel tube that steps down to a 1.75" steel tube out near the tip. The CNC hotwired foam cores will have a tunnel hotwired into them for the spindle. I decided to use steel tube spindles instead of the real flight article wing spars because the real spars are expensive, and because that would require a lot more finish work where the cores are cut away at the point of maximum thickness. With the steel tube spindle, the only surface disruption is the .020" wide slot where the wire dips into the core to cut the spindle tunnel.

• I rented a Cessna 150 and spent the better part of an hour puttering around the Calaveras County countryside.

• I played around with various designs of wing root fillets, and sketched a bunch of ways to achieve them.

• I turned forty.

• I made a pair of aluminum birdhouses with my daugher Alia. This was sort of an introduction to sheet metal for her. We covered the basics of bend radii, setbacks, and fixture alignment. She wants to paint them blue.

• (Added 9 January, because I had previously forgotten about it) I changed the head gasket on the family's Volvo 1990 740 wagon with Bosch LH-Jetronic EFI. This was my first-ever major surgery on a car with all the electronic bells and whistles. I pretty much wrestled it to a draw, since it runs about the same after as before. But now at least it won't be blowing combustion gas into the coolant. This engine has been toasted into the red twice now, once because of coolant loss through a knackered water pump seal, and again when the thermostat broke. So I'm hardly surprised that the head gasket gave in. What I'm surprised about is that there are no other signs of distress; 170000 miles and everything is shiny and happy and there are still honing marks from the factory.