Too low velocity for Figure 10.37. It is close to static condition and agrees.

uninstalled power to ≈ 1,043/0.97 = 1,075 SHP to obtain 4,000 lb installed thrust corresponding to installed 1,000 SHP.

Check the diameter with the empirical relation, D = K(P)0.25 = 18 × (1,050)0.25 = 102.5 inch. The empirical relation is close to the cropped 93-inch diameter computed previously. The smaller diameter is retained for better ground clearance.

Case II: Thrust from HP (worked out with 1,000 SHP installed as maximum takeoff rating at sea-level static condition on STD day). Once the installed SHPSLS is known, the thrust for the takeoff rating can be computed. The turboprop fuel control maintains a constant SHP at takeoff rating, keeping it almost invariant. This section computes the thrust available at speeds up to 160 mph to cover liftoff and enter the enroute climb phase. Available thrust is computed at 20, 50, 80, 120, and 160 mph, as shown in Table 10.5.

Compute:

J = V/nD = (1.467 × V)/(40 × 8) = 0.00458 × V, where V is in mph

Power coefficient:

CP = (550 × SHP)/(ρn3D5) = (550 × 1,000)/(0.00238 × 403 × 85) = 0.11

For an integrated design, CLi = 0.5 and CP = 0.11. The propeller ηprop corresponding to J and CP is obtained from Figure 10.37 (4-blade, AF = 180, CL = 0.5), as shown in Table 10.5.

Compute thrust: T = (550 ηprop × 1,000)/ V = 550,000 × ηprop/ V, where V is in mph (see Table 10.5). Use Equation 10.46 for the FPS system.

Figure 10.40 plots thrust versus speed at the takeoff rating (see Section 10.11). In a similar manner, thrust at any speed, altitude, and engine rating can be determined from the relevant graphs (Figures 10.41 through 10.44). Section 13.3.4 works out the installed turboprop thrust.

Refer to Section 10.11.2 to obtain the SHP at various engine ratings. For example, an engine throttles back from the takeoff rating to the maximum climb rating for an enroute climb. Up to about 4,000-ft altitude, it is kept at around 85% of the maximum power and goes down with altitude.

10.11 Engine-Performance Data

This section describes typical engine outputs. The data are presented in nondimensional form. All power plants have prescribed power settings, as discussed herein. Power settings are decided by the engine rpm and/or by the exhaust-pressure ratio