![[xhawk_load_tests.mp4]] → [Youtube Video Link](https://youtu.be/UPvK5xR43sY) On April 9th and 10th, 2025, the Bearhawk "XHawk" Patrol underwent a series of non-destructive structural load tests to verify airworthiness. These tests were performed to satisfy local CAA requirements for obtaining a Special Airworthiness Certificate under Annex I regulations. Not all CAAs require this for the Bearhawk series of airplanes. Due to Bearhawk's minimal exposure in EASA-land, my CAA insisted on these tests. This verification process added approximately 150 hours to my build time. However, I coped with it by embracing the deeper understanding that came from creating and executing a test program. In the end, I enjoyed observing the Bearhawk's performance under load. The XHawk proved robust during testing, handling the applied forces effortlessly and strongly hinting at capability well beyond the test parameters. ## The Test Program We conducted five targeted tests on the aircraft's critical structural components. The test program selectively applied requirements from EASA CS-VLA/CS-23 (very similar to FAA Part 23). We focused specifically on primary load-bearing elements: wings, tail surfaces, engine mount, and landing gear. This approach verified structural integrity under Normal Category loading conditions on these components. It provided the necessary technical validation without subjecting the airframe to the destructive ultimate load testing that would be required in a full certification process. ### Horizontal Tail Test ![[Critical Load Testing-20250412185050194.webp|240]] The horizontal stabilizer was subjected to a 200kg (1962N) downward load, representing the critical tail force expected during a full elevator up maneuver at Va. This represented the highest calculated load (others being balancing, maneuvering and gust loads). The structure showed expected deflection during loading and returned to its original position afterward. ![[Critical Load Testing-20250412203208323.webp]] ### Vertical Tail Test ![[Critical Load Testing-20250412190432394.webp|240]] We applied a 58kg (569N) side load at the tip of the vertical stabilizer, simulating the forces generated during a 15° sideslip. The tip load was calculated to match the moment load of the aerodynamic force on the entire vertical stab. In the calculations, sideslip loads were the highest, dominating over gust and max deflection loads. We conducted the test on both left and right sides, with the structure performing as expected in both directions. ![[Critical Load Testing-20250412191641399.webp]] ### Engine Mount Test The engine mount was tested with 425kg (4169N) of asymmetric loading resulting in 950Nm of torque. This represents the combined effect of engine torque and flight loads at max-allowed pitch-up maneuvers. A custom loading beam was used to apply these forces precisely. No permanent deformation was observed. ![[Critical Load Testing-20250412203621086.webp]] ### Mainplane Test ![[Critical Load Testing-20250412204041828.webp]] We loaded the wing with 94 sandbags (25kg each) totaling 2.35 tons (23054N). This load was distributed in an elliptical pattern to simulate the aerodynamic force at 3.8g. The wings were positioned at a 9° cant angle to simulate the actual load vector. The wings exhibited the expected deflection curve during loading and returned to position after load removal. ![[Critical Load Testing-20250412205352070.webp]] The cant angle calculations are based on the following input data: ![[Critical Load Testing-20250412210855255.webp]] ![[Critical Load Testing-20250412210828080.webp]] ### Drop Test We conducted a drop test from 38cm height to verify landing gear strength. The test was performed without wings installed. The drop height was increased to compensate for the reduced weight. The landing gear compressed as designed and returned to position with almost no bounce. ![[Critical Load Testing-20250412203732180.webp]] ![[Critical Load Testing-20250412205622664.webp]] ## Results and Implications All components successfully withstood the applied loads without showing signs of permanent deformation or structural damage. The tests verified that the aircraft meets the structural requirements necessary. While these tests confirmed compliance with Normal Category requirements, they did not approach the actual design limits of the Bearhawk structure. Generally speaking, the structure deformed surprisingly little and seemed to take the loads with ease.