23/08/2023
One year of experience with the A6M5 Zero replica and Verner Scarlett 9s. We all know that airplanes are made through close cooperation between the airframe and the engine. Given that new airframe designs and new engine installations are often the worst case scenario, I have to say that after one year of flying, the Mitsubishi Zero replica has succeeded!
There are some minor points to improve on the next airframe, but in general, the airplane is flying well. The stability and controllability in flight are perfect for the whole range of speeds. The landing and taxi characteristics are amazing! There is nothing to change regarding the flight controls or cockpit ergonomics. Take-offs and landings with an open canopy are simply captivating. Four pilots have flown the prototype so far, and all four had smiles on their faces after landing.
Engine. We have to honestly say, we were not 100% satisfied with the engine performance the first few hours. But everything was just to keep the engine run in and learn how to work with the electric in-flight manually adjustable propeller. Today she can cruise more than 125 kt with manifold pressure 25 in and 2000 rpm. The show flying and low passes are at 140 kt or higher. The engine has approximately 85 hours in total, and we enjoy the power and sound!
Last year, the air outlet jalousies were fully open and the CHT rose up to 390°F (200°C) on hot days. This year, with the jalousies almost closed, the maximum CHT is 345°F (175°C) on hot days. More typically, CHT is around 230°F (110°C), although I would sometimes like to see it a bit higher. The NACA cowling is working really well without any baffles or deflectors!
Optimizing the oil temperature was more difficult. For various reasons related to the engine oil system design, we did not use the original Mitsubishi system and oil cooler position. Instead, we placed the oil cooler in front of the cylinders. However, even with the high Rotax oil cooler, the oil temperature would rise above 212°F (100°C) on hot days. We tested many positions in the cowling in front of the cylinders, but the direct impact of the air mass on the cooler surface prevented it from working properly. This situation changed after we added a short diffuser in front of the cooler. The oil temperature is now up to 195°F (90°C) on hot days and averages 167°F (75°C) during cruise. The oil temperature is very dependent on the external temperature; if we fly in temperatures below 70°F (21°C), the oil does not warm up more than 120°F (50°C)! We decided to install a custom-made thermostat with an opening temperature of 173°F (78°C), which should keep the oil temperature optimal. We will report back after testing. The oil We use is Phillips 25W-60 with a BOSCH oil filter. Problems with oil spilling from the oil tank breather during dynamic show flying were solved by an additional oil separator and oil catch tank.
The second airframe is under construction and we are seriously thinking about preparing kits.
