Mick Duckt N7XR

9-2-99

I've flown 4 times now, around 2 hours of time in the air. Oil temp is still high, around 220. This improvement was made by increasing the exit area of the oil cooler ducting. Next mod is to increase the inlet area to the oil cooler. I've also started construction of a new 3-blade carbon fiber prop that should have a static RPM of 5000. This should increase my climb and cruise performance. The higher RPM may exacerbate my oil temp problem, but I have room to add a second oil cooler, which hopefully would take care of that.

Flew for the 5^th time on 9-3-99, but haven't flown since L . Had opened the oil cooler intake area slightly, and saw only 210° F in the climb. I was getting some vibration that seemed to be rather strong at my climb RPM of 4500. Cruise at 4000 RPM it was minimized. Decided to wait to have the new prop completed before doing anymore flying. The prop is now complete, and some initial testing has been done. It looks like it should perform, I've been to 4200 RPM and 60 knots (on the ground), all at less than full throttle. I'm getting some vibration even though the prop was statically balanced, that is keeping me from going to full throttle. A guy is coming out today to see what the possibilities are to dynamically balance it. I have a concern the thin carbon fiber blades may not be stiff enough, even though I do have a very thin wood core (0.2 inches thick at the root tapering to 0 at the tip), the purpose of which was to generate the forward surface camber and give a sandwich structure.

Had both 3-blade props dynamically balanced on Tuesday afternoon, 10-26-99. The props I am referring to are my second prop (wood), which to this date was the only one that flew, and the third prop (carbon-fiber), recently completed. It turns out there is a small imbalance in my engine/flywheel/prop adapter/prop extension since both props required similar extra weights on the same two mounting bolts. The reduction in vibration is remarkable. Bad weather kept me from flying until today. Made three high-speed runs down the runway with the new carbon fiber prop, and it looked very promising, 4700 rpm at 90 knots. However this is much lower than I was expecting, around 5000 static. So instead of a 700 RPM increase (4200 static to 5000 static) I saw only about a 200 RPM increase, 4500 in the climb to 4700 (didn't check what the new static rpm was). When I did take off, performance in the climb was actually about the same or less than before, about 400-500 fpm. It's difficult to get a 37 inch propeller to turn 5000 RPM on 120 HP! I haven't succeeded in that task yet. Over the weekend I'm going to put the previous prop back on and fly it with that again starting next week. For the first time, my prop analysis program has failed to match reality.

The good news is my oil temp problem seems to be cured, at least at cool ambient temperatures (50° F). I'm now getting 200° F in the climb, achieved with larger inlet and exit areas to the oil cooler ducting.

The venturi effect of my propeller duct actually accelerates the air to the fan plane, by a factor of about 33%. So if my cruise airspeed is 110 knots, the airspeed through the fan plane is 147 knots. If I went ductless, that would be my theoretical free-stream speed. It would be interesting to put a pitot tube in the duct just aft of the propeller. I can now see where a variable geometry duct would be beneficial, although perhaps a duct with less accelerating effect would be better in cruise without harming the low speed benefits, a more high-speed duct in other words. My next duct may have less acceleration factor, maybe 15%. It looks like I will be building many more props and ducts to get the optimum configuration. I haven't even started to vary the pitch of my props yet! All three props had the same pitch, just varying numbers of blades, blade thicknesses, and blade chords.

Some may ask why I continue to fly it ducted. This is because the low speed performance unducted is terrible, not sure it would get off the ground, or would use more runway than I'm comfortable with. Also, my engine water cooling is marginal unducted, but is not a problem with the propeller duct in place. In fact it will idle all day and barely budges the needle on the coolant temp gauge. I'm concerned about getting in the air and having an immediate overtemp problem. Perhaps it's just a problem during taxi and would be ok in the air, but I'm not ready to find out.

I could always do what everyone else does, and put a reduction drive on. But I like my direct-drive rotary! It's also not my goal here to go out and win races. My goal is reliable transportation, in my mind fewer moving parts means higher reliability.

Eleven flights and 7.6 hours in the air so far. I would be flying much more, but now the damn winter weather pattern has set in, and I'm lucky to find one good day a week to fly. All I can say at this point is: The rotary is a wonderful aircraft engine!

I'm designing a new engine mount and intake system. Yesterday I removed the airfilter, and wow! The manifold pressure went from 27 to 30 inches, and static RPM went from 4200 to 5000! So most of my problems were due to a too-restrictive air filter. Need to do some more testing before flying it, but this should improve performance significantly. 14 flights and 9.5 hours in the air to date.

Reinstalled the carbon-fiber prop, because it has lighter blades, better able to handle the higher RPM I'm expecting now. Took off, wow, this plane is finally acting the way it was intended. Now that the engine can breathe properly, the takeoff roll is considerably shortened, and it climbs at 1000 fpm or better at 90 knots. Max. speed seems to be around 125 knots, still on the slow side, at 5150 RPM. But that will probably be remedied in the future with a new propeller duct and some streamlining of the cowling when the new engine mount and intake system are complete. 16 flights and 10.3 hours.

Glorious weather we've been having lately! And it's expected to hold out all week. I was able to put 3.6 hours on the plane in the last three days. Saturday, 12-18, flew for 1.4 hours, to 7000 ft. Sunday, 12-19, flew for 1.8 hours around 5000 ft. Monday morning, flew for 0.4 hours before work. Getting more confidence in the plane with the improved takeoff performance - did my first touch and go. 19 flights and 13.9 hours.

I don't remember such a string of sunshine days in Oregon in the middle of winter. A high pressure area is parked over us, and we've had about 2 weeks of sunshine. I've been flying nearly everyday. Unfortunately, a new cooling problem has developed. I never had problems with the water cooling before, so something has changed. It is still flyable, but when taking off with a cold engine, I can only get to about 3500 ft (3.5 minutes into the flight) before I have to throttle back. Then I have to hold a power setting that doesn't really allow much climbing. This is unrelated to my increased power, since I was able to climb to 7000 ft. a little over a week ago with no cooling problems. So far I have been unsuccessful in locating the problem, but my theory now is that perhaps one of the two radiators is plugged. If this does not prove out, then it may be that a coolant seal has become blown inside the engine. 26 flights and 18.7 hours to date.

My cooling problem is resolved, it was apparently just some air in the system that I was able to purge. However I am pushing the limits of my 16 PSI radiator pressure cap. A 24 PSI cap is on order, as well as a 0-35 PSI water pressure gauge. Flew to 8000 ft. on the last flight. I notice no effect on engine operation at high altitude, except that the manifold pressure decreases normally. I am relying on the atmospheric pressure sensor to the engine controller to set the mixture (no manual mixture control). Soon will go to 10,000 feet when the weather permits. 30 flights and 21.0 hours to date.

The weather was forecast to be excellent this morning, so I took the morning off from work, because more bad stuff is surely on the way. Unfortunately there was ice on the roads, and the runway too I'm sure. And the ground fog didn't clear until 9:30. But got off at 10:00 to a beautiful 2 hour flight. Only high cirrus. Here is how the clouds looked when I took off:

Climbed to 10,000 feet throttled back to 4400 RPM, which was 19" of manifold pressure at 10,000 feet. At that throttle setting it seemed to not want to climb anymore, of course it would have if I had increased the throttle setting, but didn't want to since I don't have the higher pressure radiator cap yet. Flew over to Aurora (KUAO) at altitude, then back to KMMV. 3600 RPM and 15" of manifold pressure (at 10,000 feet) put me in a leisurely 500 fpm descent. 34 flights and 24.2 hours to date.