I tried some slow speed climbing in the yak last week and found that it fell off to the right as soon as speed dropped below 110 mph. I tried to keep the climb around 4000 fpm while doing this,after reading your post, but was unable to hold the nose up once speed was in the 100 mph range.
The auto-climb (auto-speed in practice) will not hold it below 100-110 mph. Flying it manually and with lots of rudder input I can hold it at 80mph. At this point it still rockets upwards at ~3500 fpm and no where near stalling speed. The limiting factor is the torque and under 80 mph it will slowly roll over to the right even with full rudder, aileron and trim deflections. This is no where near its stalling speed - this is its minimum controlling speed.
Since its specific excess power at 80 mph is ridiculous, I supposed it is possible to fly it slower by reducing throttle enough to decrease the torque but still leave plenty of power to keep it airborne and climbing. This requires some testing.
Another, more fundamental test to do is to put the engine to idle and lower RPM to the minimum (minimize prop drag). Then put the plane in auto-speed with enough alt to stabilize and mark the rate of decent when crossing some altitude. Then climb and do this again at a different speed, mapping the range from minimum sustained speed to say 180 or 200 mph. The things to look for is the curve of rate-of-decent vs. speed. A particularly interesting point is the minimum speed at which a steady decent can be maintained and the rate of decent at that point.
Then do it for another plane or two for comparison, preferably with a similar wing loading.
Prop drag may be a nuisance in interpreting the results though.
