Interesting info...Thanks guys.

But for comparisons (although not perfectly accurate) It wouldn't matter if the plane was heavier. Is that right? I also hadn't thought about the surface being a factor but I'm sure it is. Grass would reduce the thrust a bit because the wheels would have to overcome that friction as well, true? I do lift the tail and hold on trying to keep the fuse level.

What I'm trying to do is compare engines and props to establish which is the best for me at my elevation. Right now I'm comparing the DA50 to my EVO45GX. They are on planes that weigh about 2.5lbs difference I think. I was just wondering if I have to take the weight of the plane into the theory. Sounds like I don't.

Thrust readings are fun. When I take my scale to the flying field everybody there wants to see what thrust they are makeing. Also a good tuning tool and helpful for prop selection. Most interesting to me is on my mighty 110s (I have 5 of them) the 16x6 prop gives me 1 full pound extra thrust than the 17x4W. I would have never guessed that. Yet, the 17x4W is easier to hover with. Go figure.

Anyways, thanks for the info. If any others want to offer an opinion, I'm listening.

thanks
Barry