Why do some airliners have windshield wipers and others do not?

Keeping airliner windshields clear today is a far cry from the early piston era when pans of alcohol mounted above the instrument panel were lit on fire to prevent windshield icing. Windshield wipers, still in use even on the Boeing 747, are highly effective at sweeping rain and snow away from aircraft windshields, but with the higher speeds of jets, other innovative methods were employed to maintain good pilot visibility during approaches and departures in bad weather. The biggest single advance was using heated high-pressure bleed air ducted from the aircraft’s engines to cover the windshield with a protective layer of hot air to prevent ice from building-up on the glass. Other methods for maintaining pilot visibility in bad weather include electrically-heated wires imbedded in the windshield, thin sheets of alcohol dispersed externally on the windshield, or a combination of trusty windshield wipers augmented by a rain-dispersing agent. Another factor in anti-icing and rain dispersal is the design of the windshield itself. The current Boeing 737 windshield, in use since 1954, has six perfectly flat panes of glass. Newer wide-body airliners have compound-curved windshields with entirely different airflow characteristics for mitigating ice accumulation and rain.