SAWE Report - Cal Poly San Luis Obispo

Mass Flow Performance
Inlet Area Ratio
1.3
1.2
1.1
1
0.9
0.8
0.7
Design Point
0.6
0.5
0.4
0.3
0.2
0.1
0
0 0.5 1 1.5 2 2.5 3
Mach Number
Figure 6.9 - Off Design Area Required for Engine Mass Flow
The inlet capture area was found by first estimating the mass flow rate required by the engine at
the design point. The mass flow of the engine could be estimated using the following equation.
Mass Flow Estimation:
m
e
= 26( FrontFaceDiameter)
2
The front face diameter of 4 ft (122 cm) was used; this yielded a mass flow rate of approximately
405 slugs/sec (5910 kg/sec). Now using the mass flow equation shown below, the area of the
inlet could be found for the design mission.
Mass Flow Equation:
m
= ρ AV
Once this was done the mass flow equation was used to calculate the area at different altitudes
based on conservation of energy. For the desired design point of 1.6 Mach and an altitude of
50,000 ft (15,240 m) this was found to be slightly larger than 5 ft 2 (4645 cm 2 ); however at
55,000 ft (16,764 m)t it was found to be about 6 ft 2 (5.6 m 2 ). Since different parts of the mission
take place at several different altitudes above 50,000 ft (15,240 m), the inlet area was sized to 6.5
ft 2 (6 m 2 ). By sizing the engine to 6 ft 2 (5574 cm 2 ) air could be bypassed from the inlet to cool
the fuel.
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