Testors had a line of trainers, TC3 or something like that. Three sizes, 049, 19 and 29. These morphed into the Freshman series. The Brodak Flite Streak Trainer is good. I have seen one fly with a McCoy 19. I had three of the Guillow's trainers, two #2s and a #3. These were picked up at antique shops and refurbished. My favorite was a #2 with a worn out McCoy 19, White plastic 9 x 4 prop. It flew on 63 ft lines and would start off doing 7 second laps, then work down to 6 sec laps as the tank ran down (no uniflow). It would fly 28 laps on a full tank. The engine had no compression, but with a head prime and choke it almost always did a one flip start and ran steadily and reliably. That airplane had several hundred flights on it. I gave all three trainers to CL flying buddies, as I am no longer able to fly CL. It amazed me that such a small, slow, heavy airplane generated enough lift to fly quite nicely going round in circles.