I like flying with small acro trainers.
I used a OS 50 SX for several months on a Soprano (1,55m - 2,6 kg - APC 12 x6 - Cool Power 15 % Nitro) with great satisfaction. Suddenly the engine lost some power. Reason : several balls in the rear ball bearing where damaged, and the particles did ruin the engine. OS (Graupner Germany) accepted no warranty.
I replaced the OS by a Magnum XLS 46. Performed well after runnung in. A few weeks later : sudden power loss and same story as above. Chrome did come apart of the balls of the rear ball bearing.
As far as I heard, this happens very seldom.
Can there be a common reason ?
Thanks for anny comment.