I have both. Here's what I believe to be the major contributors to the difference in flying quality. By the way, I agree the DP is much much sweeter to fly.

The construction method on the DP is very very light. Holes everywhere you can think of and just the right amount of wood for strength where it is needed. For example, the fuse section from the wing saddle to the firewall on the H9 is 2x 1/8" ply glued together(1/4") ... the DP is 1/8" ply with a few doublers. H9 is heavier for it's respective size.

Size: visually the DP is much larger...fuse is fatter wings are much wider... just bigger. One of the guys at the field thought it weighed 20+lbs... It's really between 14 +16...

Wing area: Dp=1220 vs H9 1010

I'm telling you the DP flies itself. For me, when it comes to low and slow 3d ... you need a plane that can recover without losing alttitide and that means wing area and low wing loading.

Based on a lot of valuable feedback I received on this board about the tail heavy DP I was able to avoid a lot of frustration. Ended up mounting a Moki 2.10 (heavy but POWER) to off set the tail. Additionally, I mounted a 1800 mah Nicad on the engine box. No lead needed. I will now start moving the battery pack back bit by bit to fit my flying needs.

However, the H9 looks very cool. And i would be willing to sell mine if interested?? Perfect shape...just not sure about shipping?

Mike