Combat Aircraft Engine Installation
Combat aircraft have engines that are integral to the fuselage, mostly buried inside; however, in cases with two engines, they can bulge out to the sides. Therefore, pods are not featured unless having more than two engines on a large aircraft is required.
Figure 10.21. Typical flight parameters for a fuselage-mounted turboprop installation
Figure 10.22. Engine installed in a combat aircraft
Figure 10.22 shows a turbofan installed on a supersonic combat aircraft. In this case, it is buried inside the fuselage with a long intake duct. The external contour of the engine housing is integral to the fuselage mould lines. The internal contours of the intake and exit nozzle are the responsibility of aircraft designers in consultation with engine manufacturers.
Early designs had the intake at the front of the aircraft: the pitot type for subson- ics fighters (e. g., the Sabrejet F86) and with a movable center body (i. e., bullet translates forward and backward) for supersonic fighters (e. g., the MIG 21). The long intake duct snaking inside the fuselage below the pilot’s seat incurs high losses. The side-intake superceded the nose-intake designs. Possible choices for side intakes are described in Section 4.19 – primarily, they are either side-mounted or chin-mounted. The intake is placed on a plate above the fuselage boundary layer. A center body is required for aircraft-speed capability above Mach 1.8; otherwise, it can be a pitot intake, and boundary layer plates can act as the center body.
Web Figure 10.25 shows the various flow regimes associated with supersonic intake. To install and integrate an engine in a military aircraft, designers are faced with the same considerations as for a civil aircraft design, but the technology is more complex. Designers must make justifiable choices based on the following:
• Design the engine intake and its internal contour and compute the intake losses plus those from supersonic shock waves. Multiengines are side by side.
• Design the engine exit nozzle and its internal contour and compute the nozzle losses. Military aircraft nozzle design is complex and addressed in Section 10.10.4.
• Suppression of exhaust temperature for a stealth aircraft incurs additional losses at the intake and the nozzle.
• Compute the compressor air-bleed for the ECS (i. e., cabin air-conditioning and pressurization, de-icing and anti-icing, and other purposes). The extent of the air-bleed is less than in a civil aircraft because there is no large cabin environment to control.
• Compute the power off-takes from the engine shaft to drive the electric generator and accessories (e. g., pumps).
• Substantiate to the certifying agencies that the thrust available from the engine – after deducting the off-take losses – is sufficient for the full flight envelope.
Military aircraft have excess thrust (with or without AB) to accommodate hot and high-altitude conditions and to operate from short airfields; they can climb at a steeper angle than civil aircraft.
Figure 10.23. Airflow demand at various conditions (civil and military aircraft intakes)