One-engine inoperative testing
All vertical performance test methods remain valid in an OEI situation but particular attention must be paid to the engine rating used. It may be necessary to get dispensation to operate at, for example, a 5-minute power rating for relatively prolonged periods in order to accomplish adequate testing. Under normal circumstances the power required will not change OEI and the engine’s performance will still be obtainable from test bed data. However, some aircraft require a different NR to be used OEI and so extra testing will be required in this case. As a first estimate it may be permissible to use data gathered during ‘all engines operative’ testing and simply apply the OEI limits to get the desired performance information. However, actual OEI testing should be conducted later to confirm the estimates. OEI operation may in fact consume more power because of asymmetric loading of the transmission and adverse engine inlet conditions.
3.5 CLIMB PERFORMANCE TESTING
Despite the majority of helicopter roles requiring flight only at low level there is sometimes a need to climb rapidly and efficiently to altitude. Although the main object of partial climb performance testing is the determination of the optimum climb speed and associated rate of climb, of equal importance is the variation of these parameters with density altitude, rotor speed, power available and aircraft mass. Associated tests are the documentation of pressure errors and the assessment of engine and rotor governing characteristics. The pressure errors may differ markedly from those recorded during level flight tests because of changes in main rotor wake strength and direction.