Hey guys,
Maybe we can pull together to find out by how much Thrust Hp is optimistic? that way we can get a deviation percentage or so. (Thought i would never use the % error back in high school) . So lets get some numbers guys. Thanks.

Adam

APC 17 x 8 at 9300 RPMs measured 18.5 lbs thrust static.
Thrust HP : 21.67 lbs thrust static.

One could also change the air pressure, which will change the thrust a little bit. I typed 25.54 and got exactly 18.5 lbs thrust. I am just wondering if we could just change this factor to get more accurate measurements.

Another one:
APC 18 x 8 at 8400 RPMs measured 15.5 lbs thrust static.
Thrust HP : 22.22 lbs thrust static.

It is even worse here, this with the same engine plug etc.

3d Joy, what altitude is quebec at?? Thanks

Sorry, I don't know. Maybe someone else knows? I may suspect we are at a fairly high altitude since the specs above are for a YS 140 DZ, and I seem to only see, on the net, better performing engines than mine.

Well you may want to check the tuning of yours. I live at 6000 Ft and swing a 18x8 APC at over 9000 rpms! Same engine and fuel and plug, etc. I dropped the air density to 21 on thrust hp, and it seems to be more on the ball, but still a little on the optimistic side. I measure around 16lbs and it says like 17, but My thrust measuring technique I think is a little bit off. So it may be pretty close. I will just have to wait to fly my plane.