I just flew my Piper Cherokee 140 with the 0-320, upgraded cylinders (160hp) and PowerFlow exhaust from KWST to KPGD (Westerly RI to Punta Gorda FL). If everything is as claimed, that puts me at between 165-170hp. Now, I'm going from memory here, but the first leg (KWST to KMFV), I held the RPM's at 2400 and was getting about 88-92 knots on the AS indicator. The next leg was KMFV to KISO and was seeing 90-95 knots on the ASI at 2400RPM. Next leg, KISO to KDYB, still kept the power at ~2400 (maybe 2450) and the ASI is now 95-98 (still don't recall seeing it go over 100 knots). At this point I'm beginning to think this airplane may just be really slow!. The next leg was KDYB to 28J and still, ~2400RPM and 95-98 knots. Now, here is where it gets interesting....the final leg, 28J to KPGD, I decided to see what she could do. I pushed the RPM up to 2500-2550 and the ASI stayed in the 105-110 range. I'm going to check the RPM with a laser to make sure the tachometer is accurate (but assuming it is), should 100-125RPM really make that much of difference in airspeed? The fuel burn for the lower RPM legs was about 7-7.2GPH and the last leg was 8.7GPH. I leaned by pulling out of the vernier mixture knob until the engine stumbled, then 1/4-1/2 turn back in until it smoothed out.
The altitude for the ~88-~98kt was either 4500 or 6500MSL. The ~107kt airspeed was seen at 3500MSL.
Any thoughts as to why a 5% increase in RPM would result in a 9-10% increase in airspeed?
I hope I've provided enough information for a good answer!
The altitude for the ~88-~98kt was either 4500 or 6500MSL. The ~107kt airspeed was seen at 3500MSL.
Any thoughts as to why a 5% increase in RPM would result in a 9-10% increase in airspeed?
I hope I've provided enough information for a good answer!
