that must be converted to the operating condition at any altitude and atmospheric temperature are shown in the right-hand graph. The given engine condition must be known to obtain the HP at the ambient condition. In the example, the task is to find the HP that the engine is producing at 2,100 rpm, at a 23.75-inch Hg manifold pressure operating at a 2,100-ft altitude with an ambient temperature of 19◦F (the ISA day is 511.2 R). The stepwise approach is as follows:

1.In the left-hand graph, locate the point corresponding to 2,100 rpm and at 23.75-inch Hg manifold pressure. Next, the HP at the Y-axis is found to be 114.

2.Transfer the 114-HP point to the Y-axis of the right-hand graph. Then, join that point to the point corresponding to 2,100 rpm and at 23.75-inch Hg manifold pressure in the same graph.

3.From the 2,100-ft altitude at the X-axis, draw a vertical line to the line drawn in

5. For a nonstandard day, use the expression [BHPact/BHPstd] = √(Tstd/ Tact ).

6.Figure 10.42 provides information about fuel flow and has two settings – one for best power and one for best economy – which are adjusted by a mixture-ratio lever. For higher power and rpm, the mixture setting is at best power; for cruise, it is at best economy. It is evident that 2,100 rpm results in best economy. For the worked-out example, it is 50 lbs per hour at a power rating of approximately 68%.

10.11.2 Turboprop Engine (Up to 100 Passengers Class)

Engine performance characteristics vary from type to type. It is cautioned that real engine data are not easy to obtain. The graphs in this section are generic in nature, representing typical current turboprop engines in the class. The graphs include the small amount of jet thrust available at a 70% rating and higher. The jet power is converted to SHP and the total ESHP is labeled only “SHP” in the graph. Therefore, in the absence of industry data, readers can continue working with these graphs. In industry, engine manufacturers supply performance data incorporating exact installation losses for accurate computation.

The sizing exercise provides the required thrust at the specified aircraftperformance requirements. Using the propeller performance given in Section 10.10.5, the SHP at the sea-level static condition can be worked. From this information, engine performance at other ratings can be established for the full flight envelope. Takeoff rating maintains constant power but the thrust changes with speed. Figures 10.43 and 10.44 give the typical turboprop thrust and fuel flow (in terms of psfc) at maximum climb and maximum cruise ratings in a nondimensional form.

Typically, the higher the SHP, the lesser is the specific SHP (SHP/m˙ a-SHP/lb/s). There is a similar trend for the specific dry-engine weight (SHPSLS/dry engine weight–lb/lb). Table 10.6 may be used for these computations.

Takeoff Rating

Section 10.10.5 worked out for Tucano class trainer aircraft the uninstalled SHPSLS = 1,075 to obtain 4,000 lb installed thrust. Once the SHP at sea-level static condition is established from the sizing exercise, the thrust requirement of an installed four-bladed propeller can be computed.