Nearing the end of my Phase 1 testing of my RV-9A, I recently began flight tests at increased weight and varying CG locations within the envelope. The plane was loaded with full fuel, one 50-lb sandbag in a duffel strapped down in the passenger seat, and one 50-lb sandbag in a duffel strapped in the baggage compartment. The weight and CG were calculated to be well under max gross and nowhere near aft limits.
I climbed to 5k (4k AGL), and determined the aircraft to have positive stability in all axes as normal. I then performed two power off stalls (one clean, one full flaps), both of which went exactly like all previous power off stalls: mild buffet followed quickly by a slight nose drop, release back pressure and the plane resumes flying. I set up to do one more clean power off stall in order to capture a data point for my Skyview AOA indicator.
This time, however, as airspeed decreased and I increased back pressure on the stick, and with eyes fixed firmly on the centered ball, instead of the usual buffet I was instantly and abruptly rotated nose down, wings level, to what I found out later from recorded EFIS data was a 64-degree nose-down pitch. My cell phone, which was sitting on the seat next to me along with the sandbag, hit the canopy. It seemed like forever before the airplane had built enough speed to recover, but thankfully it did so without any ill effects. Analyzing the data, it turns out that I lost about 600 feet altitude in recovering from this stall. The whole event lasted about 7 seconds.
What went wrong? Well, I can't say for sure but I really hope it's me and not the airplane. But to say that this event got my attention is a huge understatement - I fully expected to have pinched a hole in my seat. I'm quite apprehensive about conducting any further stall testing now, at least until I receive some additional upset training with an acro instructor in a different aircraft.
I feel that I need to continue learning how this airplane stalls at all weights and CGs for safety, but if my aircraft has some unique aerodynamic characteristic that makes it just fall out of the sky, well, I just can't accept that. I'm half tempted to enlist a professional test pilot to perform a complete stall workup.
Have others experienced such abrupt stall breaks in their RV-9's? What could I have done that caused this? Better yet, what can I do to prevent it from happening again (besides not stalling)?
All thoughts welcome. I've got thick skin, and I really hope it's pilot error.
I climbed to 5k (4k AGL), and determined the aircraft to have positive stability in all axes as normal. I then performed two power off stalls (one clean, one full flaps), both of which went exactly like all previous power off stalls: mild buffet followed quickly by a slight nose drop, release back pressure and the plane resumes flying. I set up to do one more clean power off stall in order to capture a data point for my Skyview AOA indicator.
This time, however, as airspeed decreased and I increased back pressure on the stick, and with eyes fixed firmly on the centered ball, instead of the usual buffet I was instantly and abruptly rotated nose down, wings level, to what I found out later from recorded EFIS data was a 64-degree nose-down pitch. My cell phone, which was sitting on the seat next to me along with the sandbag, hit the canopy. It seemed like forever before the airplane had built enough speed to recover, but thankfully it did so without any ill effects. Analyzing the data, it turns out that I lost about 600 feet altitude in recovering from this stall. The whole event lasted about 7 seconds.
What went wrong? Well, I can't say for sure but I really hope it's me and not the airplane. But to say that this event got my attention is a huge understatement - I fully expected to have pinched a hole in my seat. I'm quite apprehensive about conducting any further stall testing now, at least until I receive some additional upset training with an acro instructor in a different aircraft.
I feel that I need to continue learning how this airplane stalls at all weights and CGs for safety, but if my aircraft has some unique aerodynamic characteristic that makes it just fall out of the sky, well, I just can't accept that. I'm half tempted to enlist a professional test pilot to perform a complete stall workup.
Have others experienced such abrupt stall breaks in their RV-9's? What could I have done that caused this? Better yet, what can I do to prevent it from happening again (besides not stalling)?
All thoughts welcome. I've got thick skin, and I really hope it's pilot error.
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