Abstract:
The performance of a turbo-jet engine has been measured, and alternative methods of determining gross thrust and air mass flow calibrated in a ground level static test bed and an altitude test bed simulating flight conditions. The agreement between the two test beds is very good. It is shown that if it is necessary to extrapolate calibrations to flight conditions, this may be made most accurately in terms of 'effective areas'. The preferred method of measuring gross thrust in flight is that based on the final nozzle static pressure measurements. The measurements of air mass flow required to convert gross thrust to net thrust are subject to quite large random errors, but the method based on the measurements from the transition section between the turbine and jet pipe is easiest to apply, and it should be possible to improve its accuracy. Using these methods, random errors of the order ± 4 per cent for net thrust determination can be expected. Comparison of 'non-dimensional' performance measured in flight, and in the test beds, was good for non-reheat conditions, but significant differences were noted for the reheat results. It is believed that these differences were due to the effects of the intake on the reheat fuel control unit in flight. The accuracy of net thrust in flight determined by the 'non-dimensional' method is of the same order as that based on the detailed calibrations for the non-reheat conditions, but would have a systematic error of 10 per cent for reheat conditions.
