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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 aircraft – performance 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/ma -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.
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SHP^£,y/dry engine |
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SHP/m a – SHP/lb/s |
weight-SHP/lb |
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Smaller turboprops < 1,000 SHP |
^ 0.012 (at TO) |
^ 2.2 to 2.75* |
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Larger turboprops > 1,000 SHP |
^ 0.010 (at TO) |
^ 2.5 to 3.00* |
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Notes: * Lower factor for lower SHP. SHP = shaft horsepower TO = takeoff |
The psfc of turboprops at takeoff is from 0.475 to 0.6 lb/hr/shp. For an SHP of less than 1,000, use a psfc of 0.6 lb/hr/shp; for more than 1,000, use a psfc of approximately 0.48 lb/hr/shp.
Therefore, fuel flow at SHP^ is 0.5 x 1,075 = 537.5 lb/hr. FromTable 10.6, the intake airmass flow at SHP^ is 0.011 x 1,075 = 11.83 lb/s. The dry-engine weight = 1,075/2.75 = 390 lb.
