Chapter 17 Trim
I chose NOT to install the plans manual lever trim systems because the prevailing guidance from the community of Cozy fliers was that they preferred electronic trim systems, and in fact many were advocating autopilot installations as well if you like to fly for long distances, which the Cozy is great for. The impression I got from the builder's electronic forum was that most if not all new builders were implementing electronic trim systems. so I decided not to build the mechanical systems to save time and weight.
Note from final assembly time in hangar: I've had the chance to visit with many more Cozy builder/fliers, and I'm impressed with the utility of the manual trim systems. Not many of the flyers who have the manual systems complain about them. They are simple, light weight, reliable and inexpensive. If you are a builder: think through this choice and talk to some folks with manual trim before making your final decision.
I initially built the Vance Atkinson electric pitch trip actuator when going through this chapter in sequence. However, I decided a couple of years later when finalizing the plane for flight to remove it and install a Davenport spring based pitch trim system. This wasn't an easy decision since I had no real desire to negate the work and expense I'd insured with the first system but here are the main reasons for the shift:
1) I'd fabricated the system, mounted it and run the actuator while working on Ch 17, but hadn't fully installed it with the canard and elevators. I'd assumed that the anchor bracket on F-22 near the pilot side anchor pad for the canard bolt would work well and had bonded it in place. In final assembly I realized that I had a 0.25 interference between the actuator and the inboard elevator counterweight. I could cut the anchor point out and move it a little and re-glass to fix this problem.
2. The recommended actuator I'd bought was not build very well, it's a custom built unit from Motion Systems and had been stored for a couple of years in a safe place in my garage and not exposed directly to elements but the RTV seals were pealing off and it no longer sounded super smooth when it was powered. I had lost confidence in this actuator at this later stage of assembly. I'm a lot more educated on linear actuators at the conclusion of the Cozy build, and I would NOT recommend this actuator based on the workmanship and cost, though Vance's specs for it were fine.
3. Getting the clearance throughout the full range of motion for the spring tube would require even more trimming open of the IP hole that it shares with the elevator link tube from the joystick. Remember that this whole thing needs to be clear, regardless of the joystick roll and pitch position.
4. There had been discussion on the Cozy forum about a potential problem with a runaway actuator movement, and the ability to achieve full elevator deflection.
I really liked the simplicity of the Davenport spring, which I'd learned more about while progressing after Ch 17, and I thought that this was my opportunity to step back, and re-do the Pitch trim before first flight. Rick Hall had finished his Cozy MKIV about 18 months previously and had done a lot of work making the Davenport system work for himself, and I had the chance to visit him and see/talk about his implementation. He was very helpful with installation tips and ultimately made a spring blank for me and loaned me his spring fabrication jigs (which are not hard to make by the way). If you are interested in going this route, I recommend contacting him off-list. The rest of this section is devoted to my implementation of the Davenport spring/actuator and I've removed the old pictures of the Vance system. Contact Vance for the details of his system if interested in it, and remember, it's not a bad system, I just chose a different system for the reasons indicated above for MY Cozy.
My mounting bracket for original Atkinson pitch trim actuator flexed and bolted to pilot side of F-22. Note that I later determined that it should have been 0.25" more inboard to avoid an interference with the inboard elevator counterweight... This pitch trim system and bracket ended up NOT getting used (see text)
Davenport Spring Based Pitch Trim Pics
These pics and description are given in a later section of the web sight associated with the final assembly of the Cozy in the hanger. Here's a link to page where you can scroll down to the pitch trim section.
I've also built the spring for the roll trim system following the design of Write-Hanka shown shown below. This spring/actuator mounts behind the firewall out on one side where the aileron pushrod runs out to the wing. I laid up a width sufficient for 2 springs simultaneously using the recommended schedule of 10 plies BID over a 4" PVC pipe section as shown in the figure, and used two little finger sized clay bars to bend one end over. This will the the the one that gets clamped down on the pushrod. The other end is flat and will be mounted with washers and nut directly on the threaded rod end of the actuator (slightly different from the original design). I'll have more pictures of this, and any changes, when I actually do the install and testing of this trim system.
Much later in final assembly in the hangar: short description and a picture of the roll trim system in it's form for inspection is shown in this linked page (scroll down to Pitch Trim section).