If I got a engine that delivered several lbs. less thrust than advertised, I would feel ripped off and the engine would be shipped back ASAP. If it still didn't delivered very close to the advertised thrust @ the advertised rpm (and temps), I would demand my money back!
I'm sure several turbine manufacturers is glad they customers don't do that...
We did a simple installed thrust test one day at the field earlier this year, and the test was very revealing.
The test was done hooking the planes up to a digital fish scale with a rope, and done on a flat and smooth tarmac surface.
Temperature was about 12-14c. Altitude around 150 meters.
I don't claim that the figures are 100% accurate, but they clearly show some big differences between engines in the same (claimed) thrust range.
Originally posted in [link=http://www.rcuniverse.com/forum/fb.asp?m=5065243]this thread[/link]:
18,9 kg / 41.58 lbs - AMT NL Olympus HP, C-ARF Lightning, stock pipe (probably starved for air by the small intakes)
16,5 kg / 36.30 lbs - Merlin MKII, Eurosport, stock single pipe
16,1 kg / 35.42 lbs - Merlin MKII, Eurosport, Tam's bi-pipe
13,8 kg / 30.36 lbs - SimJet Nexus, AW Cougar, stock single pipe
11,5 kg / 25.30 lbs - SimJet 3000, SM F-15, stock bi-pipe
11,2 kg / 24.64 lbs - Behotec JB 130, Yellow F-15, homemade single pipe