F-117 Nighthawk, U-2 spyplane: how do they achieve radar invisibility

The success of the U-2 Spyplanes led to highly classified research work in the US, known as ’Stealth’, to create a military aircraft that was invisible to radar

U-2, F-117 Nighthawk: how do they achieve radar invisibility

In the late 1950s, the American CIA began sending Lockheed U2 ’spy-planes’ over the Soviet Union to take intelligence photographs. The U-2’s flew at 80,000ft (24,000m) to be out of range of anti-aircraft fire, but it then became clear that radar was not detecting them. These extraordinary planes were little more than jet-powered gliders built of plastic and plywood. On takeoff they jettisoned their small outrigger wheels from the ends of their wings; they landed on their main, retractable wheels in the centre.

It was not until May 1960, after more than four years of overflights, that the Russians shot one down using new radar equipment belonging to SA-2 surface-to-air missiles. And even then the U-2 did not receive a direct hit. A missile exploded close enough to put the fragile aircraft into an uncontrollable dive, and the pilot, Gary Powers, had to eject.\

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The Stealth programme

The success of the U-2s led to highly classified research work in the US, known as ’Stealth’, to create a military aircraft that was invisible to radar. The U-2 had gone undetected for so long because it was made of non-metallic materials which absorbed radar waves rather than reflecting them back to the radar ground station, as normally happens.

The Stealth programme aimed at designing high-performance military aircraft incorporating, among other features, a minimum of metal and with the exterior clad in highly absorbent tiles. The aircraft would be almost invisible to radar and could make most radar-controlled anti-aircraft systems obsolete. After being developed under a blanket of secrecy, the high-tech B-2 Stealth bomber was unveiled at the Northrop Company’s manufacturing plant in Palmdale, California, in November 1988.

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It is pertinent to mention that an audience of invited guests and journalists was kept well away from the plane, which was designed to slip through enemy radar defences without being detected and then drop up to 16 nuclear bombs on key targets. To help achieve radar invisibility, the bomber is coated with radar-absorbent paint on its leading edge.

A similar technology is used underwater to foil sonar detection. Modern submarines are coated in a thick layer of a top-secret resin which is highly absorbent acoustically, and reflects only a minute amount of the energy transmitted by sonar detectors. Another technique used by aircraft to avoid radar is to fly at very low levels where there is a great deal of ’ground clutter’, radar reflections given off by buildings and other objects.

Low-level aircraft can go undetected by most radar systems. But the latest, most sophisticated ground-defence systems are designed to discriminate between ground-clutter and hostile planes. In addition, ground-clutter is partly avoided by using ’look down’ radar systems, which track aircraft from other aircraft flying above.

Events of the Gulf War; F-117 Nighthawk goes undetected

In the Gulf War, we saw on TV, the Baghdad AAA; they were getting bombed, but they did not know by what, they were shooting all over the sky hoping for a hit. The skeleton of the F-117 is made mainly of aluminium. The aircraft’s skin, by contrast, is mostly composite RAM (Radar Absorbent Material). The twin butterfly tail obscures the exhaust plume from infrared sensors aboard pursuing fighters. The Nighthawk’s twin General Electric engines are buried deep in the fuselage. That has shallow “platypus” exhausts, which cool and deflect the exhaust gases upward to minimize heat emissions.

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The edges of the F-177 Nighthawk’s cockpit canopy, like all surfaces, have no right angles (right angles are strong radar reflectors). The Stealth can be refuelled in flight. But rumours about the handling of the F-117, said it was somewhat ’erratic’, especially when refuelling… as a result, one of the first nicknames for the plane was “Wobblin’ Goblin”. Forty F-117’s were deployed to the Gulf. Only 59 production F-117s were built, yet the total cost of the program is over six billion dollars.

F-117 Nighthawk Specs

Type: Single-seat low-observable strike fighter.

Powerplant: Two non-afterburning General Electric F404-GE-F1D2 engines, each delivering 10,800lb thrust.

Max Speed: Mach 1 (estimated)

Combat Radius: 750 mi. Unrefueled, with 5000lb weapon load.

Service Ceiling: Not revealed (perhaps one of you people know?)

Weapons: Up to 5,500lb. Carried internally. Principle weapons are BLU-109 low-level or GBU10/GBU 27 medium-level laser-guided bombs. Provision for two AIM-9L air-to-air missiles.

Weights: Empty 30,000lb; loaded 52,500lb.

Dimensions:

Span: 43ft. 4″.

Length: 65ft. 11″.

Height: 12ft. 5″.

Wing area (estimated): 913 sq. ft.

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F-117 Nighthawk Engagement Profile

The Stealth fighter/bomber detects its targets via the forward-looking infrared turret, called FLIR, embedded in its nose. This provides a good picture of the target from several miles away, on even the darkest of nights. Bombing from medium altitude, the F-117 Nighthawk’s fire-control computer calculates the proper release point for the weapons to reach the general target vicinity. Weapons release will generally be a range of one or two miles. Closer to the target, control is switched to the downward-looking infrared turret, or DLIR. This is equipped with a laser designator. As the weapon approaches the target, the laser designator is fired. Sensors in the nose of the weapon now steer it toward radar reflection, where it detonates with devastating accuracy.

Sibtain Ahmad Dar specializes in Pakistan affairs and geopolitics, specifically the US strategy in the Middle East and South Asia. He can be reached at daar.sibtain@gmail.com. The views expressed in this article are the author’s own and do not necessarily reflect the editorial policy of Global Village Space.

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