|PROP PITCH 3|
In our last episode, I flew the IVO and had great results. Since then Marc reviewed the EG33 torque and HP curve and speculated that there could be a fixed pitch prop that would work. Well, as usual Marc is right on the money! I had some FOD damage on one of the IVO blades so I'm having IVO inspect and repair before I fly it again. In the mean time I decided to put the propeller that Sensenich re-pitched for me back on. This prop originally was a 70x89, it was repitched to a 70x85, then they re did it again to a 68x77. It is also quite a bit smaller in chord now, however I did not measure that dimension yet. This is a drastic change in dimensions. These were based on the data I took before I found the valve timing problem. I was quite sure it would have good static but was equally sure it would over speed in cruise. It did have good static. Almost as good as the IVO. It turned 4450 eng. or 2400 prop RPM. It did not accelerate as good as the IVO but much better than any of the fixed pitch props in the past. I was fairly heavy at 1915 lbs but it still lifted off in about 1300 ft and climbed at about 1200 fpm. It was overcast in the morning so my first data point was in the pattern at 1100 ft. Much to my surprise it did not over speed at full throttle! It hit my limit RPM (5400 RPM eng, 2920 prop) at full throttle and 178 kias. After the clouds burned off I was able to get data at altitude. At 5500' I got a WOT point of 160 kias (181 ktas) at 5300 RPM (2865 prop) and 23.0" MAP. At 10,000' I got WOT at 145 kias (175ktas) and 20.0" MAP. Here the RPM actually dropped to 5170 eng or 2795 on the prop. This actually is about as good of a compromise as I could hope to get. That is pretty good takeoff performance for that weight and the top end is fair too. It may be 8-10 kt slower than the IVO but that's not too bad.
I'm taking the plane on it's first cross country next weekend but after I get back I want to try Phil's prop again and see what that does. That will be the first real one to one comparison of the valve timing change.
I loaded the plane to 2000 lbs for my cross country to Medford, OR. It's about 3.5 hrs from home. Takeoff was noticably longer at about 2200 ft. but it climbed nicely at over 1000 fpm and the temps were near but below limits. I put on a P-51 style scoop for the oil cooler but the oil temps were only down about 10 deg. I have moved a thermocouple to the downstream side of the oil cooler to measure the exiting air but don't have any data yet. I'm wondering if it is poor air flow, poor oil flow or too small of an oil cooler. The cross country didn't get so far. I got about 45 min north and suddenly had a rough engine for about 30 sec. I imediately headed for Lancaster (desert town) since that area was clear of clouds. I was at 10,500 so had about 20 miles of glide distance. The engine continued to run fine except for one more short episode. I landed at Fox Field. There we had lunch and waited for better weather at home. I pulled the cowl and found that one connector to the #1 coil was not plugged in tight and the #6 plug was fouled with lead oxide. I plugged in the connector and made sure it was locked and changed all the plugs to NGK platinum. I then ferried the plane home. After landing and parking I found a fuel leak. One of my steel fuel lines that I noticed vibrating during the rough running had cracked. That needs a new line and better securing.
Phils prop is installed now and will be next after the fuel line is repaired.
PHIL'S 68X90" Flt Hr 59
I flew Phil's prop Friday (6/17) but it was pretty bumpy. Then Sunday (Father's Day) I took my kids and Grandkids for joy rides, so no data then either. Yesterday I took my long time friend (Hedeki Obayashi) and also an ex Flight Tester with me and we got some good data. I'm getting nearly the same static RPM as Phil get's on his EG33 engine, 4250 RPM. That's still way below the peak HP. This is 450+ RPM more than when the timing was off. The takeoff and climb were not measured but qualitatively I guess pretty much like the POH with the IO-360. At the high speed cruise end the prop is still slightly over pitched for me. I got 4940 engine RPM (2670 prop) at 5500 ft, OAT 73 deg, TAS 183. Since peak HP is at 5400, it would be good to hit that. However, since Phil has retractable gear and will cruise at least 10-20 kts faster, it may be about the best one can do with a fixed pitch. I took data at 5500 ft and 10500 ft. I also measured full throttle TAS at various altitudes. These were:
Hp KTAS FF NMPG
5000 182 11.6 15.7
10500 174 9.4 18.5
The performance data has been updated in the linked perfomance sheet . Aside from the propeller data there are 2 other remarkable charateristics with this prop. First the rate of climb data taken at 80-120 kias between 4000 and 5000 ft indicated that Vy is less than 80 kts and Vx is below that. Boy, the nose is way up there at those speeds. The other charateristic I noticed before, but now have documented, is the significantly cooler engine oil and coolant temperatures with this prop. The coolant is a good 20 deg cooler with this prop even after correcting to hot day conditions. The oil was also that much cooler but I did not correct that. My theory is that Phil's prop carries the high pitched aerofoil in close to the root. Much more so than the Sensenich. This high pitched root must creat a low pressure area in the cowl, making a higher delta P for both the oil cooler and the radiator.