In order to study the self-start characteristics of 2-D hypersonic inlet

a mixed compression 2-D inlet with swept side wall was tested in a wind tunnel at free stream Mach number 4 and 3.5. The start

unstart and self-start phenomenona were obtained with back pressure simulation system. Results showed that the inlet alllowed for self-start at Mach number 4 and 3.5

rather than at Mach number 3.5 with 2 degree angle of attack. With the inlet unstart by high back pressure

separated bubble and separated shock appeared on top wall near the bottom of side wall

and spillage was induced. After analysis of the phenomena and data from test

it indicated the inlet's unstart behavior was soft

and different from classic self-start theory. But the test data showed that the self-start Mach number was lower than the value from classic self-start thoery slightly. When the Mach number of internal compression part was below 2.5

its self-start Mach number could be approximately estimated by classic self-start theory.