Flaps Controller

I prefer controls that provide visual cues of their current setting. I have a minor in Human Factors from my undergraduate days, and one of my professors was quite passionate about aircraft. As a result, I really don’t like using up/down toggles that are so commonly used on experimental instrument panels, especially for a flaps switch.

Therefore, I created a switch assembly that has a handle that looks like a flap, moves in the same orientation as the actual flaps, has distinct detents, and LED indicators to confirm the current position vs. the commanded position. The LEDs get their information from the position sensor that is built into the flaps motor, so they show the actual position, and the lights will flash while the flaps are in transit. I don’t have a lot of space on my panel, so I designed this assembly to be fairly compact, occupying a 50mm x 60mm cutout on the instrument panel. The legends are also backlit for viewing at night.

Front view
Back side of the controller. It uses a standard 9-pin d-sub connector to interface with my other avionics
Here’s what the flaps controller will look like on the instrument panel

I placed the controller near other controls that are commonly used in the landing workflow. It is next to the prop controller, which is adjusted to the “climb” setting (high RPM) for landing. It’s also just above the throttle, since power changes are also usually needed when adding or removing flaps.

I had the basic idea for this flaps controller quite some time ago, but I spent the last week going through the detailed electrical and hardware design. This switch uses a non-contacting position sensor along with a redundant optical sensor to continuously calibrate itself. Both of these components are rated for millions of hours of operation, so it will be far more reliable than more common metal contact switches, which are typically rated for 104 – 105 operations.

I printed a prototype so that I could evaluate the haptic characteristics of the switch. I am very pleased with the feel, it has a crisp detent action between each setting. The overall range of motion is 45 degrees, so 15 degrees between each detent. This corresponds quite closely with the actual wing flaps, which rotate up to 40 degrees down. The next picture provides some insight to the detent mechanism, which uses a ball bearing and spring.

Detail of the detent mechanism
Prototype to verify the mechanics
View of the inside mechanism

There are some electronics to interface with the position encoder and to drive the LED indicators, which are housed on a compact circuit board along with a small microprocessor. I developed the board in EAGLE and sent the design to a fab house called OSH Park. I should have the boards back next week, at which point I’ll have to “stuff” the boards (populate the components).

Render of the flaps controller board
Controller board installed onto the fascia


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