It looks like you were able to make it to the back side. It is great to see folks out there exploring the slow end of the envelope. Too many (especially Lancair) pilots are scared to death by it.
Looking at your data and weight shown (didnít change between flights), the lift coefficient at 40 KIAS is a way up there ~2.3. There appears to be a little bit of a contradiction between the glide test and the level test at the extreme low end. In the glide, the left most point had power required going down, whereas in level flight it went up. The high power to maintain level flight may be enabling these lower flight speeds Ė airflow and direct lift (deck angle is probably ~20 deg).
It also struck me that the low end points could only be maintained for a few seconds? It should be a stable condition. In general it is really difficult to determine if one has a steady state level flight condition in just a few seconds. You are juggling power and trying to get altitude and airspeed to remain constant.
I wanted to rewind real quick back to the initial post about drag vs power curves and their differences and relate back to what you are seeing. I also found some additional theoretical curves on-line that show a good side-by-side comparisons of drag vs power.
The drag curve minimum is somewhere in the middle of approach speed region. It is not immediately apparent where this point is in that you would need to plot out sink rate vs forward speed or descent angle to find it. Sink rate doesnít start climbing when passing this point. It is the ratio of D/L that starts climbing.
The power curve is obtained by multiplying the drag curve by velocity. This pulls the left end of the drag curve down dramatically. The minimum of this curve occurs at a much lower speed than minimum drag. The onset of any significant rise in power required in your plot showed how close to stall you had to get.
I think what confuses many is this. Having read about the back-side concern when on approach, they pull the nose up and see the speed decay. The initial thought is that it must be the back-side of the power curve when in fact this is a normal response even on the front side of the power curve. A flatter descent angle requires more power to maintain speed. If power is not added during the angle change, speed decays. The only difference is that it will decay faster on the back-side because you now have an additive effect. What your exercise showed is how close to stall your aircraft has to be before the induced drag portion kicks in as a significant contributor. Normal approach speeds should keep you well clear.