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I gathered some cruise performance data on three flights with the Hartzell prop (the older model, with 7666A blades, not the newer “blended airfoil” prop), before it met its demise, and I was looking forward to getting a comparison with the new MT prop. All the cruise data with the Hartzell prop had been gathered when the EFIS was working, and I recorded EFIS and engine monitor data on my laptop, for later analysis. I used an experimental method to determine engine power, based on fuel flow data. This method was apparently developed by Lycoming, as a means to determine engine power during flight testing. It supposedly allows engine power to be determined, based on fuel flow, fuel flow at peak EGT, rpm, compression ratio and engine displacement. I consider the method as experimental, so I won’t share it with the world yet. If it proves to give credible and consistent engine power, I will document it and provide a spreadsheet that incorporates it.

My first attempts at gathering speed vs power data were on flights 6 and 7, and the results showed a lot of scatter. Close analysis of the data showed that I needed to adjust the fuel flow much more slowly when searching for the fuel flow at peak EGT, and that I needed longer stabilisation times to better determine airspeed at each power setting. On flight 10, I was much more successful, using very slow fuel flow variations to determine fuel flow at peak EGT, and averaging the speed for 10 or more minutes at each power setting. The data from that flight shows a very smooth variation of speed vs power. But, there is usually some small vertical motion in the air mass, which affects aircraft performance. The air in a low pressure system is rising, and the air in a high pressure system is descending. So, it is best to rather performance data from several flights, in different weather systems, and average the results.

I installed the MT prop, model MTV-12-B-C/C183-59b, in February, but the EFIS has not worked properly yet in 2009. Thus I have been unable to record any EFIS data, and the performance testing with the MT prop has relied on hand recorded data from the round dial ASI. Based on the propeller efficiency data claimed by Hartzell and MT, I had hoped that the aircraft would be several knots faster with this new prop. However, the speed vs power data I recorded on flight 18 appears to suggest that the aircraft is no faster than before, and in fact may be slower by a few knots. :( But, the only data I have with the MT prop is not of the best quality, so this conclusion may change when I get more data.


This plot shows all the cruise performance data I have taken, with both Hartzell and MT props, with each test point corrected to sea level standard day and 1800 lb weight. You will note quite a bit of noise in the data. The data for flight 10 with the Hartzell prop is the best quality, and it shows several knots more speed than the other Hartzell points. I’m not sure if the higher speed is truly correct, or whether there was some vertical air motion on that day. The data for the MT prop shows a lot of scatter, due in large part to the fact that it was hand recorded, rather than averaging several minutes of cruise flight as I did on flight 10 with the Hartzell.


This plot is similar to the first, but it does not include the Hartzell data from flight 10. On this plot, the average of the MT data is very close to the average of the Hartzell data.


This plot shows power times speed vs speed to the fourth power. In theory, the points for each prop should approximately fall on a straight line. You can see that the points for flight 10 make a nice straight line. The other points show a fair bit of scatter.

The EFIS was sent to Dynon for service, and returned home a few days ago. Whenever I start to fly again, I will be able to get much better quality data with the MT prop.

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