Today, in 90 degree weather, I test flew a couple of rockets designed for 1/8A-1 engines. These are the smallest engines available.
Both worked well enough. One rocket, that was three eights of an inch in diameter, stayed up for 15 seconds on a streamer. The other rocket, a quarter of an inch in diameter, seemed to fly better, but I forgot to time it. I'm hoping for a 20 second long flight at NARAM next week.