The pilot stated that, before departing the airport in Hopkinsville, Kentucky, in his Bellanca 7ECA, a U.S. Army CH-47 heavy-lift helicopter departed and proceeded upwind.
When the helicopter was established on the downwind leg of the traffic pattern, the pilot initiated his takeoff.
At 40 feet above ground level in the initial climb, the airplane “hit the helicopter’s rotor wash,” which rolled it “about 135° to its right.”
He was able to level the wings before the airplane touched down in low brush to the right of the runway and came to rest near the airport boundary fence.
The airplane sustained substantial damage to the main landing gear support structure.
The pilot, who was not injured, reported there were no mechanical malfunctions or anomalies with the airplane that would have precluded normal operation.
Probable Cause: The pilot’s inadvertent encounter with helicopter wake turbulence during initial climb, which resulted in a loss of airplane control.
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This August 2023 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
He didn’t mention a time interval. The AIM recommends a 3-minute interval when departing behind a super aircraft. I’d consider a CH-47 a super aircraft.