I chose "amateur built" for a number of reasons: I really did build more than 51% of the aircraft (rebuilding the engine and building the radio from scratch helped me reach that mark), at the time I started the project the exhibition sub-categories had a number of restrictive geographical limitations, and most importantly, since I am now officially the manufacturer I get to decide the max gross weight, giving me the ability to choose a figure that is within the requirements for a light sport aircraft. When I get to an age that prevents me from holding a medical certificate, I may still be able to fly the aircraft. An FAA medical is not required to fly light sport.
This is all by way of introducing the fact that when a certificate of airworthiness is issued in an experimental category, some amount of time is assigned for testing during which the aircraft must stay within a designated test area, passengers may not be carried etc. The amount of time one must spend testing is at the discretion of the person issuing the certificate, but is typically 5 hours for an imported, flying aircraft, 20 hours for an amateur built aircraft with a certified engine, and 40 hours if the engine is not certified. - I got 40 hours. This seemed to be rather a long time, but at least the FAA were extremely generous in assigning me a test area of 100 statue miles radius from my base of operation. 25 miles is more typical and that would have been much less satisfactory. You really can't argue with 31,400+ square miles :)
The Sport Aviation Association fly-in, Wynkoop airport, Ohio
Here is what happened during my 40 hours:
Before I even flew for the first time, I had a problem with a puddle of oil on the hangar floor. The result of a leaky strut seal. Taking the strut apart I found that the O-ring had been damaged at installation. There followed two weeks of frustrating work with O-rings of different sizes none of which I could persuade inside the strut cylinder without either sealing insufficiently or being damaged as the gland nut is tightened. It finally dawned on me that I was being an idiot. What it took was an O-ring of a smaller diameter. Installing it in the carrier stretched it slightly which in turn reduced the thickness slightly. After a couple more experiments the right compromise was found and no more leaks.
The first flight followed but with an adrenaline level of 112% I can only tell you that it flew, and there were no surprises. On the second flight, I was more relaxed and found the Jungmann was slightly left-wing heavy. I was able to tweak an aileron trim-tab to resolve this, but then the ailerons were not flying in exact alignment with the wing. That would not do. Worrying that this might be just the start of chasing adjustments I started by slackening the wires on the left wing, turning them by ½ turn and re-checking the tension. What do you know? - On the next flight it flew perfectly straight and level, hands and feet off the controls. Sometimes its good to be lucky. Now it was time to test a little more thoroughly. Trim at maximum speed, minimum speed, erect and inverted were all good. It must have been my really lucky day.
Next on the list was the elevator trim. I knew by now that the CG was about where I wanted it because I could just about get a stall break from a slow deceleration at idle power, and I could just about land with all three wheels touching at the same time, but the trim control was further aft than I would like. I reduced the height of the phenolic spacers under the leading edge of the tailplane by about 1/8" and flew again. It flew the same, but the trim control was now closer to the center of its range in cruise flight. Now though, we need to make one more measurement. With the elevator clamped so that it was exactly aligned with the tail, I cut a length of knotted string and tied it to the back of the front seat in such a way that the knot was precisely lined up with the top of the stick. In flight, I trimmed for level flight at cruise power and was happy to see that my knot still aligned exactly with the stick, thereby proving that the elevators were flying exactly level. Yay!
A couple more hours of flying followed with no particular schedule in mind, but just getting used to the ‘plane and learning how she likes to be flown.
There is another airport within sight of my home base and they had a fly-in the next weekend. Seemed like a good time for N28Bu's public debut. Everything was checked over one more time and I set off for the nearby airport. Everything went well except that after I landed I was horrified to see the whole side of the aircraft covered in oil! The cause of this was not at all obvious. I could see no leaks, the oil level was only slightly down, and I could not seem to reproduce the problem. I flew the 5 minutes back to base watching the engine gauges very closely!
To cut a long story short, the problem was that the return line from the oil scavenge pump to the tank was too close to the tank breather port, and return oil was splashing in the vent. I re-positioned the vent and no more oil streaks.
A few more hours of flying and as spring sprang the oil temperature rose. Argh! Another problem. As reported here earlier, I obtained an inexpensive oil cooler (actually a transmission oil cooler) and installed it under the cowling. It slowed the temperature rise, but not the ultimate temperature. Still too hot on a warm day. Next, learning from Richard Epton's Bestmann experience, I made a bulkhead to separate the oil tank from the warm engine compartment as found on a Jungmeister. Now it took a little more time still to get too hot, but it was still too hot. OK, I give up. Time to do the job properly. A real, proper oil cooler (http://www.jegs.com/i/Earls/361/41008A/10002/-1?parentProductId=1676010) was installed in the lower cowling and an NACA style flush inlet of suitable size was cut. This surely would take care of the problem. Nope. Somewhat cooler, but not cool enough, and yet the oil cooler was large and the inlet generous. What could be wrong? Some mistake I made in overhauling the engine?
Then it hit me. The NACA submerged inlet was invented in 1945, the Jungmann in 1934. No wonder it didn't understand what to do. I made a simple old-fashioned scoop about ½" (1 cm) deep and attached it to the cowl ahead of the oil cooler. The oil temperature dropped by 40F (22C) and remained steady. Too good to be true? That's what I thought, but a thermocouple in the oil tank confirmed it. It really does work that well. So much for technology. I ended up reducing the size of the scoop slightly to get the temperature I wanted.
The "real" oil cooler
With the Jungmann in trim, not leaking, no longer puking oil down the side of the fuselage, and with the temperature just where LOM say it should be, it was time to get flying in earnest. I started going to fly-ins further afield and exploring the limits of my 100 miles radius. As time passed I started getting more and more confortable in the aircraft. Landings were becoming second nature and my aerobatics more accurate. I sent some pictures to the LOM factory in Prague and asked them for advice on a slight hesitation I was experiencing as the throttle is opened on takeoff. As documented here previously, they wrote back right away. They told me that my cooling baffles were out of date, and that my fuel injection system was a very old version and to ship everything back to them for update and calibration. After being updated, bench tested, and dyno tested, I received everything back from the Czech Republic early this summer and soon had it back on the aircraft.
More test flying ensued. Different power settings, different altitudes, different temperatures and much measurement. When it was complete I found that the engine was precisely in agreement with the books. 6.6 gph (25 litres/hr) and smooth at all power settings. I completed the spin testing to the left and to the right, both ways up, and attended a couple more fly-ins. I feel extremely comfortable with the engine and the aircraft now. A couple of friends have flown it and said the right things (its good to have polite friends) and I am thinking about taking people for rides in it.
Here's the interesting thing: Having now reached this point of comfort and seeming stability, guess what the tachometer/Hobbs meter says? - 41 hours! Grumble at them as some might, the FAA knows a thing or two!