HP-18 Center Stick Project
Update 2 April 2001:
Lots of progress this weekend, but unfortunately no photos. Here's what I got done:
I also made some progress on a couple of non-center-stick items that I need to do to get the ship into the air:
- Tested the cockpit stick mechanism stops to 100 lbs in pitch and 75 lbs in roll. Nary a complaint; no squeaks, pops, groans or even creaks. Further, it seemed that there was a lot less deflection than I remember from the preliminary tests with the mechanism anchored in a test fixture made from 2x4s. However, that was 140 lbs on a 15" arm, and these later, better-calculated tests were 100 lbs and 75 lbs on a 13" arm.
- Located and installed the nylon push-pull tube guides near the seat back bulkhead - this involved installing two more of those phenolic pads, and four more holes through the fuselage.
- Located and cut the four bulkhead holes that the aft sections of the push-pull tubes go through. I located the holes by eye, and they came out fine, but it could have been better. After I finished the holes, I had an epiphany on how to exactly locate the holes using a tool made out of some scrap wood and a laser pointer. I think I'll do an article on that for Wayne's site some free afternoon.
- Determined the length for the aft section of the pitch push-pull tube.
- Cut the aft pitch push-pull tube to size, and press-fit the ends into it (they'll get welded in on the next wave of TIG welding). Of course, I just had to screw the rod ends into the P-P tube and pin it in place. And when I moved the stick fore and aft, the mixer pivoted in response. Just like magic!
- Made a wooden mockup of the roll bellcrank support tripod. In the process, I discovered that equal parts 5-minute epoxy and flox makes a very handy mixture for prototyping.
Next weekend, I hope to:
- Replaced the 500x5 tire with a lo-pro Lamb tire - for better gear door closure and a slightly lower takeoff attitude.
- Removed the old landing gear counterbalance springs, pulley, and cable - I'll be replacing them with a gas strut. If it works out, I might offer the gas strut in an upgrade kit.
- Make a one-time jig for the aft roll belcrank support tripod
- Fabricate the prototype aft roll bellcrank
- Size the aft section of the roll P-P tube
- Start work on the stick mechanism access cover
- Start work on the P-P tube cover
- Fabricate an anti-torque coupling to prevent the flap/aileron mixer tube from twisting under aileron loads
- Maybe start adapting one of several instrument pods to fit with the center stick
- Start installing the landing gear counterbalance gas strut
page updated 04/02/01 all text and graphics copyright (c) 2001 HP Aircraft, LLC