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OK, its hot here in SC, so wen;t flying with no doors. The breeze felt good and the plane handled well. the only adverse condition was a little wind noise being picked up by the head set mike. Now for the rest of the story, we, ( Robert my partner) and I were not planning this. It started because we were not happy with the 68" GSC wood prop in use. Although the tracking was spot on there was always a small vibration we did not like. So we ordered a new 71.5 " Kiev prop and installed. After setting the pitch where we thought it should be, we ran the engine for a static test. The run up resulted in a very smooth operation at all rpm, and seemed right for a test flight. Robert took off and was going around the patch, he was checking rpm at WOT and the airspeed was slightly over 100 mph. All of a sudden there was a loud bang, and the pilots door flew open. Other than scarring the H out of him for a few seconds the only other effect was a yaw to the left that the rudder took care of. Robert throttled back and came on in. The door was broken on the rear frame at the lift strut, at the top front frame and a large section of the window in the back was gone, ( I will post pictures ). Now we do not know why this happened, the door latch was checked and properly latched before starting the engine, and I had installed springs(see old pictures) on the door latch when building to prevent the door latch from vibrating open during flight. We do not know if there is enough vacuum on the door to deform it in any way at high speed. I also do not know if we had the latest design from Zenith on the door latch system. I will be speaking with Roger soon. We will take a very close look at the door latch system when installing a new door. I will post a couple of pictures of the door.
We removed the other door and I took off to finish checking the prop and to experience flying the CH 750 with the doors off, very enjoyable reminded me of my old Kolb Firestar. And guess what the prop pitch was dead on, no other adjustment needed.