HP-18 Center Stick Project

Update 23 April 2001:

This weekend, it seemed like everything I did was in slow motion.

Saturday, I worked out the mounting provisions for the gas strut that I'm using to counterbalance the weight of the landing gear. The gas spring replaces the springs, pulley, and cable that are used in the stock arrangement. The gas strut is lighter, and a bit more effective at lightening the gear retraction loads. I'm certain that if they'd been common and inexpensive in the 1970s, that's what Dick would have used. Anyhow, I tried two struts before I found one with the right amount of force. But it really is right on, and the gear cycle is way smoother than before.

Sunday, I did the final reassembly of the ruddervator mixer. That was sort of a mess. I found out that the mixer that I had modified had less clearance between the rudder bar and the pitch pivots than the one that came with the ship, and it would bump into the pivot brackets. Instead of making the pitch pivot brackets more slender, I assembled a mixer using some more parts from inventory and the modified pitch carriage. I had to make some aluminum spacers to go with them. They turned out pretty rough, because I don't have a lathe up at the shop. But they'll do just fine.

I also did the almost-final assembly of my double-geared flap crank. I got the sector plate drilled for the locking locations, and also made a gear cover to keep big stuff from getting into the gears and jamming them. It went together about as well as I expect for a prototype. I don't look forward to disassembling it, painting it, and reassembling it. This unit is definitely not the mechanical marvel that Richard Buege's is, but it is light and simple, and I think is a good match with the general complexity of the aircraft.

Another thing I got some work done on is the hydraulic brake. I got the Yamaha master cylinder opened up, and wiped a bunch of slimy brown gunk out of it, and reassembled it. I did the same for the Cleveland caliper; but it was full of sticky red residue instead of brown gunk. I'll be using a silicone brake fluid that is compatible with the seals in both the master cylinder and the caliper. Anyhow, I got the master cylinder installed and connected to the brake handle. I also got the plumbing installed, and also adapted both the master cylinder to the 1/8" Nylo-seal tubing. I was about to hook it up and bleed the air out when I broke one of the brass Poly-flo fittings, and work on the brake ground to a halt.

The next big problem to solve will be a trim system. I've been holding off on that, but it's time to start sorting it out. What I've got in mind is a steel torsion spring made out of 1/16" music wire. The trim spring will run along the underside of the access cover from a handle on the left side to an arm on the right side. The arm will engage a little lug that gets clamped to the pitch push-pull tube. In sum, it sounds hokier than it looks. The important thing is that it is light and simple, and that a failure of it will not impede the primary flight controls. I think that it will meet those criteria.

From the perspective of this weekend, it looks like my center-stick project has spun off into four separate upgrade programs:

If the project goes as planned, I'll probably offer upgrade kits for each of these separately, with a discount for those who buy all at once.

page updated 04/23/01 all text and graphics copyright (c) 2001 HP Aircraft, LLC