Suggestions to Preston Briggs
This site was last updated on February 15, 2008.
This line-pull shutoff was invented by Roy Glen and is available from Mekzlik.
Here are two versions; the heavier wire is more recent.
It's typically bolted to the engine's mounting lugs.
Here's a live example, showing a variation that includes a mounting bracket for an OS remote needle valve. Notice the homebrew arming device: When the plane takes off, the line tension will pull the arm to the left, unhooking it. Then, if line tension is lost, the spring arm will pinch the fuel line.
As opposed to some of the other line-tension shutoffs, this one works via a separate loop of string (say, fishing line) that runs from one leadout, through the loop on the spring arm, and back to the other leadout.