Bell 533

The U.S. Army began a program to study improvements to current helicopters that could be demonstrated by testing. Analyses by three helicopter companies showed that performance could be greatly improved. Bell Helicopter was one of the participants and investigated improvements to the UH-1B Iroquois. After the study, Bell submitted a proposal for the High Performance Helicopter. On 7 August 1961, the Army's Transportation Research and Engineering Command (TRECOM) awarded a contract to Bell Helicopter for a high-performance helicopter to conduct research. In response, Bell built the Model 533 from a YH-40-BF, one of the six preproduction UH-1s. The dynamic components of the YH-40 were updated with components designed for the UH-1B. The research for the contract was split into two phases; phase one would be to determine the benefits of an overall reduction in drag, phase two would determine the benefits of auxiliary thrust. The Bell 533 was flight tested in three main configurations. The first configuration was the basic YH-40 helicopter with drag reduction changes. The second configuration added a pair of jet engines for additional thrust. The third configuration added swept wings for extra lift. ==Operational history==

Initial testing During the first phase, a general clean-up of the airframe was performed to reduce drag. New aerodynamic fairings were developed using fiberglass honeycomb sandwich for the rear fuselage, a cambered vertical stabilizer was developed which, in cruise flight, aerodynamically unloaded the tail rotor. The skid landing gear also had streamlined fairings applied to it and the rotor mast was replaced by a mast that could be tilted in-flight. The final configuration of the Model 533 for the research contract was with a proprietary, four-bladed, flex-beam rigid rotor developed by Bell. Afterwards, the Model 533 was returned to its original two-bladed configuration and retired. ==Surviving aircraft==

The Model 533 is on display (in highest speed configuration) at the US Army Aviation Applied Technology Directorate, Fort Eustis, Virginia. ==See also==