HP-18 Center Stick Project

Udate 19 December 2000:

I'm still working on it!

The last few weekends have been spent on more prototypes of the -701 and -702 parts. The -702 pitch carriage went together just fine the first time, and I'm satisfied with it.

The -701 platform, however, has been somewhat vexatious. I had one that fit well, and that had mounting plates that fit well against the fuselage. However, on that one, the roll bellcrank didn't align well with transverse pushrod nor the main longitudinal pushrod. I ended up making another dowel-and-epoxy prototype, and sending it off to the local welder to have a jig made from it.

This new prototype also has provisions for more mounting screws where it meets the fuselage shell on the right side. That will be necessary because I'm putting the control stops there. When the pilot forces the stick against the stops, much of that force is transferred into the fuselage shell as a torsion couple between the two mounting plates. I need two more screws to secure the stop plate to the platform assembly, and I want more screws there to give me more margin against tear-through of the screws on the phenolic mounting pad. I want good, solid, "Basic Glider Criteria" control stops, not wimpy things like they put on the Pegasus.

Well, today at lunch I finally got the jig to the _other_ welder, the one who is good at thin-wall 4130 steel. I'll be picking up the first article this friday morning, so I can fiddle with it in the shop over the Christmas holiday. If it goes well, and my radiant heater gets here from Harbor Fright, I might try glassing the phenolic mounting pads into the fuselage.

I've also started the jigs for the prototype of the -703 control stick. Unlike the other parts, I expect to have changes in this part right up to the end of the program. So the jig is a pretty cheesy affair of aluminum angle and fiberboard. Once I've got a stick that is demonstrably comfortable to a wide range of pilot sizes, I'll send the proto off for an official jig.

Once I've got the steel prototypes of the -701 platform, the -702 pitch carriage, and the -703 control stick, I will be able to do a test installation of the cockpit components in my test pod and accomplish the half of Program step 8 that deals with input forces against the control stops.

page updated 04/02/01 all text and graphics copyright (c) 2001 HP Aircraft, LLC