|PROP PITCH - IVO MAGNUM|
|Flts Ending at Hr 65.2
I was assigned a 5 hour test period in an area I choose over the Los Angeles harbor. I had a very helpful inspector that allowed me to do this test out of Compton airport, fly over an industrial corridor and test under the Class B airspace over the harbor. This gave me an area from sea level to 7000 ft and enough distance to make about 10 min legs along the coast. At most points at altitudes above 3000 ft I was gliding distance to either Long Beach or Torrance. I just finished the 5 hours with a short interruption since I picked up some FOD after the second flight. I wanted to check this out very carefully to be sure it really was FOD and not a structural problem with the prop. The damage looked exactly as if a hose clamp had hit the leading edge of blade B at about 18" from the center. I pulled that blade and had IVO inspect it. They said there was nothing internal at that location that could cause a delamination there and they were sure it was FOD. They repaired it like new for $27. I flew at first in the "In Flight Adjustable" mode. In this mode the blade stays at what ever fixed pitch the pilot commands. I put it at full fine pitch from takeoff and got 4500 engine RPM (2432 prop). I don't know why I can't get higher. It would be nice to get 5400 but I sure don't need it. As it is I can barely hard it with the brakes. It accelerates to the 74 kias rotation speed very quickly in about 1000 ft at 1750 lbs. It climbs out at well over 1000 FPM at 90 kias. After checking out the system in Manual or Flight Adjustable mode, I switched over to Governor mode. This took a little doing. The electronic box which controls the pitch in Governor mode has a magnetic pick up to sense RPM. It also relies on measuring both current and voltage to sense when the motor hits a physical limit. The voltage drop across the motor is such that the lead wires (both from the battery to the box and from the box to the prop) are very significant in the sensing circuit. The factory supplies 12' wires on both sides and they can not be shortened. I thought the instruction only applied to the wires from the prop to the Box so I left those 12' (in fact I had to lengthen those a couple feet). However, I cut 7' off each wire from the Power panel. I could not get the system to shut off at the stop this way. So I added 14' to one of the lead wires and voila, it works like the manual says. For the same reason (what ever that is) that I don't get more than 4500 static RPM, I also don't get higher RPM at speeds less than 125 kias. So contrary to rumors I heard from Subaru people with RV's and Eggenfellners engines, this prop has absolutely no trouble absorbing 230 hp. I can put full throttle on at 160 kias and still slow the RPM down to what ever I want (of course the speed will vary). So this is still very much a cruise prop but the takeoff and climb are so much better than the POH for an IO-360 (fixed pitch) that no one would complain. The data is shown in the Performance spread sheet linked here but in summary I got 189 KTAS at 5500 ft and WOT. This was with the governor mis-rigged so I was only at 5080 RPM. At 10,500 ft I got 178 KTAS at 5170 RPM. I did rate of climb tests starting at 2000 ft and ending at 8000. I started at 80 kias and at each 1000 ft increment I measure the time and increased the speed 10 kts. This technique introduces some error since the first 20 seconds includes the acceleration from the last speed to the new speed. Be that as it may I got a linear change in ROC with 2060 at 80 kias and 713 at 130 kias. This technique also penalizes the high speed end because those points are at higher altitude. Man, 2060 FPM at 80 kias is very impressive! That's about double the rate of the fixed pitch props I've tried. It's 10 times greater than the fixed pitch props before I found the timing problem. A world of difference! I think I will repeat the ROC tests with a more scientific technique since this way it indicates that Vx and maybe even Vy are less than or equal to 80 kias. Honestly, I was not comfortable flying full power at less than 80 kias since the nose was so high.
The other issue I'm following very closely is cooling. As I mentioned before, Phils prop improved the cooling significantly. The IVO is almost as good but has some differences. This data is shown in the Performance sheet too but I summarize here. The coolant temps are quite good. The hottest were the full throttle points. Converting to hot day conditions (46 deg F above std =105 deg @ S.L.) the max coolant was 218 deg. The oil was 258 deg. The highest temps were WOT at 5500 ft. Full power climbs present high oil temps too. This area still needs more work. I put on a P-51 style scoop for the oil but it didn't help much. Based on the fact that the prop effects the temps, I think I need to work on the exit pressure. Perhaps a dedicated oil exit reverse scoop. I also want to separate the engine induction to it's own scoop and dedicate the NACA to cooling.