1. Testing of the stream thrust probe was conducted September 27, 2003 at Middle Tennessee State University's Aerospace Maintenance Facility. The J85-GE-5H engine (SN 231664) used in the thrust probe test is a high-thrust, lightweight turbojet engine currently used in the USAF T-38 Talon aircraft. It has an eight-stage, high-lift, axial-flow compressor driven by a two-stage turbine rotor. The engine incorporates a through-flow, annulartype combustion system, controlled compressor interstage bleed air, and an afterburner with a variable area exit nozzle. The basic hot engine is 109.14 in. long and 20.43 in. in diameter. Engine dry weight with afterburner is 584 Ib. The design engine thrust at standard-day, sea-level static conditions is 2680 Ibf at military power and 3849 Ibf at the maximum afterburner condition.5Enginespeed and airflow at these power settings are 16,542 rpm and 44 Ibm/sec, respectively.
2. The exit plane pitot pressure measurements were obtained by a 16-port Scanivalve system with a pressure range from 0 to 150 psig. The probes were spaced at 2 in. on centerline, with a total of 12 pitot probes and one Mach flow angularity probe spanning the nozzle extension exit diameter. The tips of the probes were within 1 in. of the exit plane of the cooling duct. An illustration of the probe and rake setup is shown in Fig. 5. The horizontal location of the rake was recorded by a linear potentiometer attached to the traversing table, and it was calibrated on site. Figure 3. MTSU Test Configuration
3. Figure 8 shows the comparison of the load cell and probe-derived scale forces. The probe-derived scale force [from Eq. (10)] assumes an inlet mass flow of 43.65 Ibm/sec. This is the nominal military power mass flow as given by the engine GE Report.6The value of the probe-derived thrust is 2095 Ibf. This number is in close agreement with the average value indicated by the load cells, which is 2133 Ibf. Therefore, the error between the probe-derived thrust and the measured scale force is -1.8 percent.
4. Determination of thrust from pitot pressure measurements