Yesterday, I had an ingenious idea, "Why not use my Xavien timer on a water rocket?" I was thinking it fairly light and can use a small battery such as an A23. To initiate ejection, I was thinking of using a Nichrome bridge wire to burn though a piece of monofilament fishing line. Then I remembered that the timer needs one half second of acceleration to enable the countdown. When I got home, I found an on-line simulator. To my dismay, the powered thrust phase will be too short to enable the timer. D'oh!
[Title quote courtesy of Richard "Dick" Milhous Dastardly.]