Complex sentence: At first the ailerons, elevators and rudder were fabric-covered, but combat experience showed that fabric-covered ailerons were impossible to use at high speeds, a light alloy replaced the fabric, enhancing control throughout the speed range.
Split into simpler sentences: At first the ailerons, elevators and rudder were fabric-covered. When combat experience showed that fabric-covered ailerons were impossible to use at high speeds, a light alloy replaced the fabric, enhancing control throughout the speed range.