Just because his readings seem unbelievably high, doesn't mean they are impossible.

I own an ASP .40 which throws a Master Airscrew 10X6 up to 22,500 RPM in sunlight. The same tach measured my friend's Webra .91 at 17000, and SuperTiger .61 at 16,500. All props were 2 blade, with the tach set to 2 blade. Another tach has since confirmed my readings.

Numerous calibration tests with an AC lightbulb have always read 3600 "RPM" (proper reading).

Thrust HP claims this would require 4.88 HP. I have often heard that ThrustHP doesn't match real-world results. At higher RPM's, the prop blades are traveling through the turbulent air created by the previous blade(s). This results in lower resistance to the blade than non-turbulent air. Perhaps ThrustHP doesn't take this into consideration... I am no aerodynamic engineer, so I can't explain it further.

I am at a loss to explain WHY my engine (and apapa's) reach such high RPM's. I only know that my ASP .40 has considerably more power than my Magnum XL .40 with the same prop.