|Flight 35 1779lbs 101.9" 15 Jan 05 0.6 hrs
Ok the 40 hours are flown and the proper entry made in the log book. So, it's time to venture out of the box. Since the last flight I took the bird over to Advantage Aviation to work on both the Narco 12D and the Terra Nav/Com. The Terra had to be sent to Free Flight in Texas but the Narco was up and working better than ever. It had been a couple weeks since I flew so I started off with a thorough preflight. That went well, no water in the tanks even after all the rain we got. It was indoors the whole time but that condensation can add up anyway. All runup checks were normal. This includes a check of the left and right fuel pumps and the emergency power system. It was pretty warm so the climb out showed the expected temps on the high side. I shut off the cooling fans at pattern alt. but I did not do my cruise check list which turns off the aux battery and the left fuel pump. I usually leave the aux battery on for 15 minutes to fully charge it after starting (especially after sitting 2 weeks). I started off with a flight over the old test area to be sure the temps and all else was ok then I planned to fly over to Compton and buzz my home field. I flew to the test area and back and had about a 1/2 hour of flight time and thought of my cruise check list. I turned off the aux battery, fine. I turned off the left fuel pump and the zzzzzz started slowing down. I immediately put the left pump back on and the engine sped back up. At this point I was at 6500ft about 5 miles from Chino (home away from home). I didn't want to do any testing at that point. Why risk stopping a working engine? So I decided to land and chcek it out. All was normal on the landing and taxi. At my hangar, before shutdown, I turned the left pump off again, with the same result and turned it back on. OK there must be a problem with the right pump. So I shut off all the normal systems. This should not stop the engine since the emergency system still powers the computer and the right pump. However, the engine began to shut down but started right back up. At that point the left pump was off. The right pump must have started pumping again working on the emergency power. I had been thinking it was an electrical problem but no popped breakers, besides the emergency system would by pass that. Now since it started working again it must be either intermittent electrical, clogged pump, or vapor lock in that pump. It's pretty strange since both pumps pull from the same source downstream of the gas collator. You would think if one got an air lock the other would too. If one got contamination and clogged so would the other. Well, it's time to pull the cowl and do some tests.
Flight 36 1749 lbs 101.8" 19 Jan 05 1.0 hrs
I mentioned my fuel pressure loss to Phil Johnson and he offered a theory that with both pumps on the fuel flow is double since they are positive displacement pumps. This could make the inlet pressure low enough to cause cavitation in one pump. If I then turned the other pump off, there would be no fuel pressure until the cavitation was cleared. That fits the symptoms perfectly, except I did not wait with the pump off to see if the pressure would recover. So I decided to test it. I cleaned the gas collator just to be sure there was no problem there. It was fairly clean, just 2-3 small bits of fiberglass and some grey greasy specs. I then did a ground test at full power. I started with both pumps on then turn the left off. No loss of pressure. Then both on and right off. Again no loss. Well that matches the last 40 hours of flying. So I decided to try it in flight. I took off with both pumps since that is the way I've done it for 40 hours. I climbed to 5500' and then turned the left pump off. No loss of pressure or engine power loss. I repeated both on and right off (emergency power off too since this powers the right pump also). Again no loss of pressure or power. My conclusion is that on rare occaisions a cavitation can occur in one pump. It is better in my opinion to operate only on one pump and use the other as an emergency backup. I will modify my check list as such. I decided while testing the fuel system that sooner or later I will accidentally drain the right tank dry, since it transfers fuel fairly rapidly to the left tank when the right is selected. So I positioned the airplane over Chino at 6500' and let the right tank go dry. I expected the engine to quit immediately but it didn't. As the tank ran dry the pressure slowly dropped over 5-10 sec and the engine RPM slowly dropped in proportion. That seems like a very docile failure mode and plenty of time to notice and switch tanks. So I switched tanks and the RPM and pressure rose at about the same rate it went down. So the airplane is off probation and ready for the new prop. It arrived today (1/20). I'll put it on Sat. and see what RPM rise I get. The current prop is a 70x89. The new is 70x86. My current prop has a track error of .188" on the plane. I checked the new prop on a surface table. It has a track error of only .061". I'll see if this holds when installed on the plane. I can't wait to see how much the acceleration and rate of climb improve!
Flight 37 1701 lbs. 101.8" 22 Jan 05 0.8 hrs
I did a static run up with the old prop, Sensenich 70x89, just to be sure I had a one to one comparison. It surprised me a little. It ran up to about 3400rpm then slowly increased to the normal 3600. However it continued climbing to 3720 and stabilized. I've seen numbers like that before but I always thought it was due to the start of my takeoff roll. I let it stabilize at WOT for 60 sec. I then installed the new Sensenich 70x86. I taxied out and did my static run as a preflight run up. This shocked me. I also left it to stabilize for 60 sec and it rose to the exact same RPM 3720. Well, that was disappointing. I expected at least 4000 based on the info Sensenich provided. I had actually hoped for 4150 based on the theory that the torque curve increase assoicated with the RPM increase would amplifiy the effect. So, I decided I should go ahead and see what it did in flight. The takeoff roll was about usual. I got a distance measurement but haven't retrieve it yet from the GPS. The climb out was pretty good but I chose a different speed than usual 110 kias. I climbed to 6500 ft and took climb data at speeds from 80 to 130 kias. I also did a speed/power run at speeds from 100 to 160kias. The high speed point was the same speed as tested with the old prop and the RPM was 4860. That's 49 prop RPM less than before. So the new prop behaives as if it were the same or maybe even a tad higher pitch than the old one. In my dissappointment I forgot the data out at the airport and haven't felt like going out to get it. I sent the 70x89 prop back to Sensenich. They don't understand it either. They will check the pitch and dimensions of the prop and then recarve it. I asked that they make it 4" less pitch than what ever it is.That's the only thing to do at this time. Keep widdling the prop down until the static comes up to at least 4250 (2300 prop). Then see what the top end does. While I was up I checked the VOR against the GPS. It was within one degree at all radials from 90 thru 240 deg. I also did a practice ILS and the loc/GS worked perfectly.
Flight 38 1765 lbs 101.8" 29 Jan 05 1.0 hrs
This was primarily just a ferry flight back to CPM. I put in the Terra NAV/COM that just came back from repair to check them out. The Com went fine and checked out in flight too. The Nav would not seat in the tray properly and did not even light up. I'll try again during the next week and perhaps take it back to Advantage in Chino to help. The flight was completely normal. I did a touch and go at CPM and climbed out to see obsticle clearence. It was adequate. So I landed and went back for a takeoff from a stop. It took a lot of the runway, I guess 2400'. That left 900 remaining. and climb out was adequate but I would not want to takeoff there much heavier until I get a prop with better static RPM. There were several EAAers there to greet me. It is great to be home!
I just heard from Sensenich. They did measurements on the first prop and confirmed it was a 70x89. They did say that it was 3/8 to 1/4 deg high in a couple of spots. They have re-pitched it to a 70x85 which reduced the chord about 1/4" also. It will ship tomorrow. I'll probably get it Monday.