RV Quick Stick

Home shop machinist.

September 4, 2019

Mark Beattie at work in his garage on the RV-6.

I live in a pretty cool neighborhood, which happens to include a couple of locals who are building airplane projects in their garages. In the April 2016 issue of KITPLANES®, I introduced Phil Hooper. The subject of that column was a custom drill guide for Phil’s Velocity RG. This month’s subject is a quick-release system for the copilot’s control stick on Mark Beattie’s RV-6.

While the two airplanes couldn’t be more different—the Velocity is a retractable-gear, canard-wing, composite pusher, and the RV-6 is a fixed-gear, aluminum, low-wing monoplane—both Phil and Mark have the same detail-oriented mindset when it comes to the plans and instructions.

Using a parallel gently pinched between the tube and the drill bit is a quick and accurate way to center a tube for drilling. When the parallel is square to the drill, the tube is centered. (See “Parallels, Stops, and Travel Limiters” [KITPLANES® July 2017] for more information.)

When Phil was ready to set the angle of incidence for the canard, for example, he checked, rechecked, and re-rechecked the procedure for leveling the fuselage. Then, for good measure, he allowed it to settle for a couple days and checked it again before finally setting the canard in place. The old saying, “measure twice, cut once” is his guiding principle. If you’re an airplane builder, you can probably relate to that type of fussiness.

(Left) To assure perfect alignment, the control stick and socket are assembled, aligned, and drilled together. A 17/64-inch drill provides the perfect clearance hole for the 6.5-mm (0.255-inch) spring button. (Right) Deburring is always important, especially when tubes telescope. But always deburr, regardless.

Mark’s particular affliction for detail is he sometimes wakes up at night with “builder thoughts” in his head. Such was the other night when he was fretting about running wires through the wings for strobes. Then he remembered: No problem! When he assembled the wings, he put in nylon cords so he could fish the wires through when the time came.

(Left) Installing the spring button is as simple as lining up the button with the hole and inserting it into the stick. (Center) Note the double bend at the end of the spring. It eliminates exposure to the sharp end and prevents button overtravel. (Right) Red arrows painted where the stick and sleeve align provide visual confirmation that the spring button is properly engaged.

Both Phil and Mark started their projects before CAD, match-drilling, or quickbuild options became the norm. “Vintage” kits, while quite good, often leave many less-than-critical aspects of the assembly up to the builder. That’s part of the fun: It not only gives the builder a chance to learn and be inventive, it helps personalize the project.

Which brings us to the copilot’s control stick on Mark’s RV-6. Unlike the pilot-side stick, which is non-detachable, the copilot’s stick slides into a coupling sleeve at the base of the control mechanism. How to fix the stick to the coupling is up to the builder. Some bolt it together, others use a cotter or a cross pin with a ring grip. Mark wanted a solution that, above all, would be safe and reliable, and, if possible, provide quick release with no loose parts that might get dropped under the floorboard or misplaced.

What we came up with is simple and easy to install: a spring-loaded “button pin” or “spring button.” Spring buttons have been around for decades to engage telescoping mechanisms. Most people are familiar with typical carry-on roller-bags with telescoping handles, which usually have spring buttons made from stamped steel, or the ubiquitous Razor kick scooter, which has solid brass or steel buttons to engage the handlebars. It turns out that scooter handlebars are the same diameter (0.875 inch) as the Van’s control stick, so we repurposed a spring button from a Razor and made it the key component of the quick-release system for the copilot stick.

Spring Button Guard Option

The goal of any quick-release mechanism is that it should never inadvertently release. The solid steel buttons used on scooters, as long as they are engaged correctly, will not inadvertently or accidentally disengage. One of the reasons for this is the head of the button is protected from inadvertent contact by being recessed in a countersunk pocket in the handle. If necessary, this type of protection from inadvertent or accidental contact should be included in the design.

The option to not have a guard depends on the location of the spring button. In the case of Mark’s RV control stick, we pondered the situation and agreed that three things added up to assure a safe installation without a guard. One, because the button was located below the floor, no person could inadvertently bump it. Two, the placement and angle of the button on the stick was such that if some object were to be accidentally left in, or somehow worked its way toward the mechanism, it could never get pinched or jammed into the button, regardless of the position or movement of the stick. Last, in order to prevent access to the release button and the control mechanism in general, a stick-boot cover will be installed.

Using a parallel to find the tube center. A stub-length drill or spotting drill is more accurate than a twist bit, which can flex and distort the accuracy.

(Left) Using a 0.187-inch drill to make a pilot hole in a length of 11/8 x 0.065 tube. (Right) Core out the pilot hole from the tube with a 7/8-inch hole saw.

Taken together, the spring button is effectively “guarded by position.” So while there’s no direct mechanical guard around the button, its remote position and concealed access prevent inadvertent or accidental contact. The guarded-by-position concept is easy to understand, but when considering applicability, it’s important to study every possible scenario, including abuse and potential user error.

This sequence shows how to make a spring button guard to fit a 1-inch x 0.65-inch sleeve for a 7/8-inch diameter telescoping tube with a spring button. The guard was made from a 11/8 x 0.065 tube.

(Left) Deburring is essential to create a flush fit of the guard to the sleeve. Be careful! Small parts are hard to hold and can get hot. (Right) Position the guard over the sleeve and tack weld as shown. Three or four good tacks secure the guard in place.

(Left) With the 7/8-inch telescoping tube lined up inside the 1-inch sleeve, drill through the guard and both tubes. (Right) Use a countersink bit to taper the opening of the guard. Make the depth of the counterbore no more than the thickness of the guard.

(Left) A quick trip to the deburring wheel is all that’s needed to polish the guard to a smooth finish. (Right) With a guard in place, it takes a deliberate effort to disengage the spring button from the sleeve.

RV Quick Stick

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