Last Update: 30.01.2021
Vertical Stabilizer (Rudder)
Horizontal Stabilizer (Elevator)
With the horizontal stabilizer, it’s a good idea to test fit the whole assemby in order to clarify a few things.
- The countersunk holes in the stabilizer are to mate with the cone-shaped thread fairings of the mount. The screws to be used here are not countersunk.
- The mount is on the upper side of the stabilizer.
- The control horn goes to the upper side as well.
- The torsion spring goes to the lower side and needs to drive the elevator control surface downwards.
This test also reveals that my kit came with its mount threads clogged with surplus resin. This has to be taken care of with caution, restisting any brute force attempts.
And now for the part that worries me: Installation of the torsion spring. This is not about being awkward or so. There is just not enough room between the carbon skins of the tapering control surface to host the 20 x 0.8 mm anchoring lever of the spring. Any measure to avoid the constriction, clipping or bending the spring, will degrade the lever arm available to the delicate control surface to cope with the loads imposed by the permanently tensioned spring.
I decide not to cut or bend the spring and to accept causing minor flaws on the elevator. Unfortunately, with instant regret. Although the lighting here makes it look worse than it really is, the result is not satisfying. See red bubble.
Steering Linkage Reconsidered
Growing uneasy with the solution selected I decide to have a closer look at the physics of that string and spring thing. With a steel hook and a cardboard box I try to figure out the force needed to operate the rudder or to hold it in its normal position: 400 grams, almost double the flight weight of the whole plane. That is an inherent force of 4 Newton straining the servo permanently, aerodynamic forces of the flight excluded.
With a setup of similar professionalism as the force evaluation above, I try to measure the power consumption of the poor X08 servos under load. My multimeter doesn’t seem to provide stable measurements in the low milliampere range, but the current when working against those 400 grams is about 5 times higher.
That does it! I’m reverting to my proven steel rod linkage. Durability was one of the concepts, remember?
Rudder – Take 2
Elevator – Take 2
As far as the elevator is concerned, you can hardly tell the difference from the outside. A 2 mm piece of polystyrene tubing heated and stretched to an inner diameter of 0.5 mm is used to modify the hook-style elevator horn. This makes a play-free bearing for the rod, but still allows to remove the horizontal stabilizer for transport.