Stabs Trims & Controls

1/28/2009

Having finish painted the rudder pedals, I decided next to tackle a relatively 'biggie', the empennage and controls. Of course, I am cheating a little since I am utilizing some parts from this salvaged plane I have.

The rudder cable turnbuckles were removed, polished, lacquered and refitted. The rudder cables were then fitted, rudder and pedals locked at neutral, and the turnbuckles tensioned accordingly. At this point I discovered some binding with the cables on a tube as they exit to the rudder horn, so I have to add another pair of fairleads. Amazingly, there were no stops on this old fuselage, except for the elevator stops at the reverser.

Fitting the stabilizer was interesting, since the wires had not been labelled upon removal by the previous owner. I eventually worked out through trial and error where which wire went where, some fitted where they shouldn't, so the key was to find a fit that had optimum adjustment left on the threads, since the manufacturing process of these unique streamlined wires means no two wires are of the exact same length or thread length. Fun :0|

Once the horizontal stab' was set and bolted down. I did notice a few things I didn't like:

1. Looking down the stab spar, through the tail to the other stab...I have a taper, like a slight 'sweepback' of the stabs. Although slight, this really annoyed me. I initially thought about upsizing the two front stab connector bolts from 3/16 to 1/4 so I could then move the stabs in at the front, this would bring the stab spar line straight, then I thought I may as well make a new small stab connector tube with the two bushings so i have blank tube ends to drill new holes through. Trouble is, when I dry-set the required position (linear spar line) with clamps, the travel of the stab was binding at the horn. So, having called in my IA/A&P buddy along with luckily finding an FAA designated inspector who was signing off a plane a few doors away, they advised me that although it obviously doesn't look right if you 'reaaaally look' down the spar line, it will not be noticeable whatsoever once covered, and since there is no binding when in the existing position, it isn't an issue.

2. The port elevator is lower than the starboard side :0|. This I will fix. Running a line across, the difference is 1/2". Luckily, when the starboard stab is clamped at neutral, the whole of the port elevator is off. This means there's no funky twist anywhere to fix, I just need to either weld a patch plate on the port elevator horn, or make a new horn, set the port elevator to neutral, then match drill through from the starboard horn.

3. The original elevator travel to the stops at the reverser is 29 deg up and 24.8 down, they should be 25 up and down. Down is ok, but I am going to cut off the stop tube at the reverser and weld on another to achieve the 25 degrees.

4. With the elevator at neutral, the rear control stick in the cockpit is not vertical, so I will be changing out one of the control connector tubes for a new one and adjusting its length to suit.

5. When the rear cockpit stick was vertical, the one in the front cockpit wasn't :0\ it was off 4 degrees, to fix this, I would have had to make a new connector rod going through the torque tube, the easy way out was to simply heat bend the front stick slightly, it looks OK now.

I know this sounds like a bunch of crappy work on the original plane, but there are some good signs in the old build, the welding for example, is beautiful. I am scratching my head as to how one can achieve such a neat stack o dimes look, when for example welding something thin to something much thicker... boggles the mind. There are also signs of crappy post work by someone else: In the trim tab pic below, the steel web thing spanning the tubes is definitely a retro fit sometime later. I will be cutting it off.

I found a vernier trim tab mechanism in a box that came with the project, I found only one hole the thing could fit in in the cockpit [see pic above], and came to the conclusion after 3 million hours of playing with it that it was never on the original plane. There was a mysterious T-tube on the vernier deal which didn't seem to have a purpose, so I went browsing through some old Skybolt newsletters looking for ideas for trim, and there it was, a diagram of a vernier trim tab deal by Mac McKensie. The T-tube was meant to be welded to the side of the seat. Mystery solved.

I also have to modify the elevators for the trim tabs. Whatever hinge mechanism that was there is no longer there, and the hinge gap is way too big.

I was going to mention my attempts at welding, but I think that deserves another post of its own later... :-\