F-117

The F-117A Stealth fighter is the world's first operational aircraft designed to exploit low-observable stealth technology. Air refuelable, it supports worldwide commitments and adds to the deterrent strength of the U.S. military forces. It was used extensively in the 2003 air attacks against Iraq.

The F-117A can employ a variety of weapons and is equipped with sophisticated navigation and attack systems integrated into a state-of-the-art digital avionics suite that increases mission effectiveness and reduces pilot workload. Detailed planning for missions into highly defended target areas is accomplished by an automated mission planning system developed, specifically, to take advantage of the unique capabilities of the F-117A.

Weapons:

The GBU-10 Paveway II laser-guided bomb consists of a special nose and tail section attached to a standard 2000-pound Mk 84 high-explosive bomb. The tail section of the bomb consists of a set of folding aerodynamic surfaces for stable flight. The nose section includes a laser light seeker, guidance electronics, and control fins. The GBU-24 Paveway III is a more advanced version of the Paveway II with a larger tail surface and a more efficient guidance system which permits it to be used at lower altitudes and at greater distances from the target.

The BLU-109 deep-penetration bomb has a forged casing of hardened steel which permits it to pierce more than six feet of reinforced concrete before exploding. When dropped on softer targets, the BLU-109 can bury itself deep into the ground before exploding, destroying its target by sending earthquake-like shock waves rippling through the ground.

The F-117A can also carry up to two Mark 61 nuclear weapons. For long-range ferry flights, fuel tanks can be installed in the weapons bays in the place of bombs. The F-117A has no air-to-air capability, or at least none that has been announced to the general public. It has no radar, it does not carry an internal cannon, and is not equipped to carry or launch air-to-air missiles.

Detailed Specs:

The F-117A is constructed mainly of aluminum with titanium parts in the engine and exhaust system. The outer shell is built around a complex skeletal frame and is spray coated with RAM.The F-117's main power stems from twin non-afterburning General Electric F404-GE-F1D2 turbofans. Engine design was based on the McDonnell Douglas' F/A-18 afterburning F404-GE-400. They are fed via air ducts on either side of the fuselage and are covered by large gratings. The gratings prevent radar waves from reflecting off engine rotors. With grid spacing of the grate smaller than radar wavelengths and a full coating of RAM, the intake coverings themselves will not reflect radar. Because these gratings restrict airflow to the engines, blow-in doors are fitted above the engine nacelle to allow adequate airflow during taxiing, takeoffs and low-speed flight. Electric heating systems were fitted to prevent ice buld up on the gratings.

The exhaust system is designed to minimize the plane's rear heat signature and prevent radar illumination from behind. The exhaust ducts are round at the rear of the turbofans, but are flattened out by the time that they reach the front of the narrow slotted exhaust outlets at the rear of the fuselage. At the end of each of the narrow slotted exhaust ducts, there are twelve grated openings, each being about six inches square. These grated openings help to reduce unwanted radar reflection from the rear. The exhaust gratings are shielded from the rear and from the bottom by the F-117's platypus-bill-shaped rear fuselage section. The extreme rear edge of the aircraft behind the exhaust slot is covered with heat-reflecting ceramic tiles. These tiles reflect the infrared radiation from the exhaust, keeping the rear portions cool. Bypass air from the engine is used to help cool down the entire metal structure of the rear of the aircraft.

Unlike the Have Blue test aircraft, the tails are mounted in a V formation. They have no pitch control function. Leading wing sweep was reduced from 72.5° to 67.5° in order to improve performance. The wings are fitted with four elevons that provide pitch control.The fly-by-wire system is a modified F-16 system, and is quadruple redundant. Since the aircraft cannot use any sort of radar navigation system, the fly-by-wire system relies on information about airspeed and angle of attack from four individual static pitot probes of diamond section with pyramid-like tips mounted in the extreme nose. Each of the four-sided pitot heads have tiny holes on each facet, and differential readings from each hole provide airspeed, pitch and yaw information to the flight control system. A set of retractable communications antenna are fitted to the upper fuselage just behind the pilot. These are deployed during day flights, but are retracted for stealth missions at night. Detachable radar reflectors can be mounted on the fuselage sides so that local air traffic control can track the aircraft when it is not in stealth mode.

A parachute braking system is provided, since the lack of flaps makes the landing speed quite high (160 knots, or 185 mph). The braking parachute is housed behind split doors atop the rear fuselage and deployed as soon as the nosewheel makes contact with the runway.The landing gear is of the standard tricycle type, with single wheels and tires that retract forward. The landing gear doors have serrated edges that help to reduce the radar cross section.

The F-117 replaced the centerbow windshield on the Have Blue with a flat panel to accommodate the HUD and to improve downward visibility. The canopy has serrated edges and specially treated transparent sections to reduce radar reflectivity. The windshield is coated with a special gold film to prevent radar from reflecting off the pilot's helmet. The pilot is seated in a McDonnell Douglas ACES II ejector seat.

Guidance:

The F-117A cannot rely on radar for navigation, weapons aiming, or weapons delivery since radar emmissions would make the plane detectable. The F-117 aircraft is equipped with forward-looking infrared (FLIR) and downward-looking infrared (DLIR) systems. The FLIR is mounted just ahead of the cockpit front windshield in a steerable turret. The DLIR sensor system is mounted underneath the forward fuselage and to the right of the nose landing gear. The DLIR is equipped with a bore-sighted laser for illuminating the target for attack by laser-guided weapons. Together, these systems form the infrared acquisition and designation system (IRADS). Both the FLIR and the DLIR recesses are covered by a RAM mesh screen to prevent unwanted radar reflections from the active elements, and the edges of the recesses are serrated, with the fasteners being covered with RAM.

Inertial Navigation Systems (INS) backs up the sensors using an electrostatically-suspended gyro as the primary means of guidance. The INS guides the aircraft to the target area and points the FLIR's wide angle field of view toward the general location of the target. As the aircraft approaches the target, the pilot tracks the FLIR image on the HUD screen. When the target is identified, the pilot switches to the narrow view on the FLIR and locks the screen of the display onto the target. As the target disappears underneath the aircraft, control is handed over to the the DLIR, which acquires the target and continues to track it. The pilot then releases the laser-guided bomb. Approximately 7-10 seconds before bomb impact, the DLIR's laser is turned on, illuminating the target and guiding the bomb to impact.

Sources:

National Museum of the USAF

The Encyclopedia of 20th Century Air Warfare, edited by Chris Bishop, 2001, Aerospace Publishing