It was pretty clear from the weather picture late last week that Friday would probably be the last flyable day for a bit, so I juggled my work schedule so I could take half a day off. I hoped to gather some more airspeed accuracy and cruise performance data, but it turned out to be too bumpy. It snowed on both Saturday and Sunday, so I definitely picked the right day to fly.

I’ve done a bit more thinking about the performance increase I’ve noted recently. The plots of speed vs power I posted last week rely on fuel flow to calculate engine power, using an method that Lycoming developed many years ago. I carefully calibrated the fuel flow indication back in 2008–2009, so it was accurate to ±0.5%, based on fuel used vs fuel added from the pump, over ten flights. It is possible that something has changed to affect the fuel flow calibration, so I’ve started collecting data to check it again. It would have to be under reading by about 10% now to fully explain the latest power vs speed relationship. I’m sure it isn’t anywhere close to that far off, but it could be out by a few percent.