ashfordeOU Engine Flight Test (flight-test-operations/performance/engine-flight-test)
Use when the task is engine flight testing for a flight test program: installed thrust determination from the climb or the level acceleration, fuel flow and specific fuel consumption checks, exhaust gas temperature margin against the limit, altitude performance verification, and acceleration and deceleration transient timing.
Domain quick reference
- Units: forces and weight in N, speeds in m/s, rate of climb in m/s, fuel flow in kg/s, thrust specific fuel consumption in kg/(N*s), temperatures in deg C, ambient temperature in K, densities in kg/m^3.
- thrust_from_rate_of_climb: T = D + W * ROC / V, the small-angle form of the steady climb balance T = D + W * sin(gamma).
- thrust_from_acceleration: T = D + (W / g) * a, the level flight balance from Newton's second law.
- fuel_flow_from_tsfc: Wf = TSFC * T, the fuel flow burned at the determined thrust.
- tsfc_from_flight: TSFC = Wf / T, the achieved specific fuel consumption from the measured fuel flow.
- egt_margin: margin = T_limit - T_egt in deg C; a negative margin means the exhaust gas temperature exceeds the limit.
- egt_corrected_to_isa: T_corr = (T_egt + 273.15) * 288.15 / T_amb - 273.15, the absolute temperature ratio correction to the ISA day.
- thrust_at_altitude: T_alt = T_sl * rho_alt / rho_sl, the density ratio scaling of the sea-level thrust at constant Mach number.
- accel_time_between_speeds: t = (W / g) * (V2 - V1) / (T - D), the time to accelerate between the test speeds at the excess thrust.
- decel_time_between_speeds: t = (W / g) * (V1 - V2) / (D - T_idle), the time to decelerate at the idle thrust drag force.
- thrust_verification_error: e = (T_ach - T_pred) / T_pred * 100 in percent; negative means a thrust shortfall against the prediction.
- Test condition: engines stabilized at the test thrust setting, the airplane trimmed in level flight or a steady climb at the test configuration, no configuration changes during the transient.
Workflow
- Stabilize the airplane at the test configuration and the thrust setting; record weight, altitude, airspeed, fuel flow, and exhaust gas temperature at the stabilized condition.
- Determine the installed thrust with thrust_from_rate_of_climb from the rate of climb, or with thrust_from_acceleration from a level acceleration, using the measured drag.
- Compute the fuel flow with fuel_flow_from_tsfc from the thrust specific fuel consumption, or reduce the measured fuel flow to the achieved consumption with tsfc_from_flight.
- Check the exhaust gas temperature margin with egt_margin against the engine limit, and correct the measurement to the ISA day with egt_corrected_to_isa when the ambient temperature differs.
- Verify the altitude performance with thrust_at_altitude, and compare the achieved thrust with thrust_verification_error against the predicted installed value.
- Time the acceleration and deceleration transients between the test speeds with accel_time_between_speeds and decel_time_between_speeds from the excess thrust and the idle thrust drag force.
- Report the determined thrust, the fuel flow, the EGT margin, the altitude verification error, and the transient times for the engine flight test assessment.
Pitfalls
- Mixing unit systems: the mass comes from W / g, so weight, forces, and g must share one consistent unit system (N, kg, m, s).
- Treating the drag as zero: the determined thrust is the drag plus the climb or acceleration term; neglecting drag overstates the thrust.
- Reading the rate of climb term as exact at steep angles: W * ROC / V is the small-angle form of W * sin(gamma); use the exact energy balance when the climb angle is large.
- Confusing fuel flow with specific fuel consumption: Wf is kg/s and TSFC is kg/(N*s); the ratio TSFC = Wf / T only holds in consistent units.
- Taking the measured EGT at face value on a non-ISA day: apply the absolute temperature ratio correction before the margin comparison.
- Scaling the altitude thrust with the pressure ratio alone: the density ratio is the first-order turbojet scale at constant Mach.
- Discarding a negative EGT margin: it is a limit exceedance and a test finding, not a computation error; report it.
- Timing a transient with configuration or thrust changes: the acceleration and deceleration times are only valid for the fixed setting and configuration of the test segment.
- A non-positive excess thrust has no acceleration: the transient time is undefined and must raise.
Behavior contract (gate 3)
The thrust, fuel flow, EGT margin, and transient logic is exercised by
the gate 3 contract test: scripts/test_engine_flight_test.py against
scripts/engine_flight_test_logic.py (stdlib unittest, offline). Run:
python3 scripts/test_engine_flight_test.py
Compliance
- Standards referenced, not reproduced: FAR-25 is US government work (public domain) and CS-25 is a free EASA download; installed thrust determination and engine performance verification in flight is common flight-test methodology in the FAR 25.101 general performance context, summary-only per standards-map.yaml.
- compliance: STANDARDS-REF, gated: false.