Sunday, November 20, 2005

Speedbrake position sensor

The GRT EFIS has the ability to display trim & flap positions based on the use of Ray Allen position sensors or trim servos. The Ray Allen is a linear POT that varies resistance with position. I wanted to install one on our speedbrake so that we can see the position of it on the EFIS screen. I am hoping that GRT adds a Speedbrake label to the indicator (I requested the feature) and that they also add extension warnings based on speed/RPM, etc... The above photo shows the Pitch Trim indicator and the Speedbrake indicator (Labeled as flaps). This was the last photo I took after I got it working. The roll trim servo is not yet mounted to the airframe.

I started with the sensor taped up to a mounting block, along with some Dubro linkage. The Dubro linkage is designed for RC aircraft use, is very durable, lightweight and is sold at hobby stores. Some 4-40 allthread is used for the shaft. I ended up mounting the sensor directly to the seat back with two nut plates.

This photo shows the linkage attached to the speedbrake. I created a bracket from some aluminum angle and bolted it under one of the hinge attach bolts. Of course this project ended up taking the entire work day even though I was sure it was only about 2 hours of work. But fabricating the linkage, mounting bracket, installing nut plates, wiring, adjusting, calibrating and testing took longer that I figured. At least I didn't have to mix any epoxy! I'll be back to fiberglass work on Tuesday.

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