Older versions of Mi-35 Hind helicopters had wheel boxes so that they could retract their wheels while flying.
Why don't the newest versions of Mi-35Ms have wheel boxes?
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Quick answer: because Russian engineers don't like fancy stuff ;)
Fixed landing gears are common on helicopters even very recent ones, just look at French helicopter Tigre, Italian mangusta or American black hawk. It offers a very lightweight and robust solution for landing while allowing easy ground maneuvers and also offers crash absorption.