Question...

I measure the thrust of my engines while it is mounted to the airplane. I use a digital fish scale. I just hook it up and give her the throttle and read the the thrust in lbs.

My question is: "Does the weight of the plane affect the thrust readings?" For instance: "Would a DA50 on a 15lbs plane measure the same (everything else being equal, day, humidity, temp, prop, etc) thrust as it would on a 12lbs plane?" Are there any other variables that might affect the thrust rating? Having the plane on asphalt or grass?

I've also wondered about pulling the plane backwards while taking the thrust ratings? I always get higher ratings when I do this but I've always posted just static numbers without pulling the airplane.

Just wondering.

Thanks
Barry