HP-18 Center Stick Project

Update 7 May 2001:

This weekend I pretty much finished up the installation of the center stick and its related systems. Now the project revolves around other cleanup items with the testbed aircraft.

The big thing I did was to lay out and make the folded aluminum cover for the push-pull tubes. I made the template by riveting together a bunch of separate parts that I'd cut and folded to fit. Then I used that assembly to trace a scribe template that shows the outlines and the bend lines. Then I used that template to scribe and bend the final part.

In the end, I'm not too happy with the aluminum cover. It'll do for now, but I think that it takes up more of the cockpit than it needs to. I think that when the dust settles, I'm going to go back and make a molded composite part that more closely follows the contours of the P-P tubes. I'll probably just pack the area with Play-Doh (or its homemade equivalent), and pull a fiberglass splash off of that. I can also lower the profile of the P-P tube guides by changing the hardware around a little. I can cut the height there down by about 3/8" just by replacing the AN365 nuts with commercial T-nuts and lock-tite.

I also installed an implementation of what I've come to call the "swaybar trim" system. It's so called because it's based on a torque rod like those used on almost all automotive anti-sway systems. Except that the torque rod in this case is only about 1/8" thick.

What I installed in this ship differs a bit from what I'll be recommending in the installation instructions. The differences comes from where I cut the knee hump for the access cover. I think that I cut the hump of this ship about 1.5" aft of where I could have, resulting in a bigger opening than I needed to install the system. The down side is that that cut line was right were I wanted to run the transverse torque rod for the trim system. I sort of kluged the rod into place using Monel pop rivets and some piano hinge sections. Not pretty, but functional enough.

For the final system, I'll recommend that the installer embed the torque rod in a transverse slot cut in the knee hump just above the height of the seat belt anchor angles. The torque rod will be sheathed in a 3/16" nylon tube, and secured in the slot with two layers of glass tape above and below the tube. The ends of the rod will be bent up. The left end will end in a knob that engages any of several notches in a sector plate. The right end will end in a hook that engages the frangible link that connects it to the pitch P-P tube. Going forward, I'll need to work out the logistics of developing and validating this variation of the trim system.

I've also started fitting the canopy frames to the ship, and started adding the various small attachment and latch parts. I'll be using a bone-stock system, with a two-piece canopy on stock aluminum frames. The frames are from inventory, and are supplemented with little bits that I got with a fuselage I bought from Bruce Patton many years ago. It's going to take a handful of carving and filling to make the contours come out right, but I'm pretty sure it will work out OK with a minimum of work.

This ship originally had one-piece canopy with a carved oak frame, and that's one of the reasons it came into my hands. Over the winter before last, the expansion and contraction of the frame split the one-piece canopy from rail to rail in several places.

Last weekend, I also did some work on a set of 18-576 landing gear yokes that I'm having fabbed. These yokes are a response to the demand for spare parts, and also demand for Matco (or Cleveland) disk brake mounting provisions. Those will get welded up after next weekend.

Next weekend, I'm in for more canopy fitting, and more work on the instrument pedestal. I'll also do a little work on the battery box, and start figuring out where to put an antenna. At worst, I think I'll just use a 23" piece of music wire for an external whip over the aft fuselage. I don't know what else I'll do with the six or eight sizes of music wire I've tried and rejected for the trim spring.

The weekend after that, no HP work of any kind. I'm going to Disneyland with my family!

page updated 05/07/01 all text and graphics copyright (c) 2001 HP Aircraft, LLC