Whoa, not so fast!
Wow! I guess I just learned a lesson.
Seeing Rick's installation, it looked to me that the hole in the stick wasn't all that significant, so I charged ahead and did the same.
Problem is, as I'm not experienced with this type of engineering, I consider my own opinion on this stuff worthless. I knew enough to question drilling such a hole, but quickly accepted another's solution.
While I think the question of "how much stick force" is actually required coupled with a simple test of sticking the thing in a vice and seeing just how much stress it will take seems valid, one word from an engineer at Van's sends my judgement and decision into a tail spin!
I hope to see more logical ideas about this, but for now, I'm thinking I'll be ordering a new front stick and starting over.
Whoa, not so fast guys.
If Vans engineering staff is like everybody else, they are very busy, and don't have time to analyze every potential modification that every builder might make to their kits. Oftentimes, engineering departments will simply issue a CYA statement that they don't recommend changes rather than actually consider the physics involved. This is fine, it covers their butts, and limits their liability. We can all understand that...
However, this has nothing whatsoever to do with whether your stick retains sufficient strength if you drill a hole in it. I'm not saying that builders should modify their control systems willy-nilly, without considering the implications because they are significant. But on the flipside, don't assume that you aren't capable of thinking this problem through, just because you aren't an engineer, and don't just take somebody's sweeping generalization that your plane will fail if you don't build it exactly per plans!
Your logic of determining the worst case stick forces, applying a healthy safety factor to that, and testing the stick to that value and determining that no damage results is perfectly logical and acceptable. I would do that before replacing your sticks or going to extremes building or buying electronics to send all of those signals via RS-232. YOU are the builder of YOUR aircraft and YOU have the ultimate authority and responsibility to build an airworthy aircraft. Just because you aren't capable of performing a stress analysis of your stick doesn't matter. Ten analyses are worth one test, and you can easily test the strength of your stick.
Vans aircraft are not required to be built or certified to FAR Part 23, but this is a good guide to help you think this through. Here are a couple of hints:
FAR PART 23?AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES Subpart C?Structure. Control Surface and System Loads. ? 23.395 Control system loads. (a) Each flight control system and its supporting structure must be designed for loads corresponding to at least 125 percent of the computed hinge moments of the movable control surface in the conditions prescribed in ??23.391 through 23.459. In addition, the following apply:
(1) The system limit loads need not exceed the higher of the loads that can be produced by the pilot and automatic devices operating the controls. However, autopilot forces need not be added to pilot forces. The system must be designed for the maximum effort of the pilot or autopilot, whichever is higher. In addition, if the pilot and the autopilot act in opposition, the part of the system between them may be designed for the maximum effort of the one that imposes the lesser load. Pilot forces used for design need not exceed the maximum forces prescribed in ?23.397(b).
(2) The design must, in any case, provide a rugged system for service use, considering jamming, ground gusts, taxiing downwind, control inertia, and friction. Compliance with this subparagraph may be shown by designing for loads resulting from application of the minimum forces prescribed in ?23.397(b).
(b) A 125 percent factor on computed hinge moments must be used to design elevator, aileron, and rudder systems. However, a factor as low as 1.0 may be used if hinge moments are based on accurate flight test data, the exact reduction depending upon the accuracy and reliability of the data.
(c) Pilot forces used for design are assumed to act at the appropriate control grips or pads as they would in flight, and to react at the attachments of the control system to the control surface horns.
Noah Forden, BSME
Mechanical / Aeronautical Engineer
US Navy