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This General Dynamics’ artists concept shows the final RF-4X configuration.

F-4X: The Fastest Phantom

By Emil Petrinic
1/19/2017 • Aviation History Magazine

A joint American-Israeli program sought to modify the F-4 for Mach 3 reconnaissance missions.

On November 6, 1971, a MiG-25R “Foxbat” reconnaissance plane from the Soviet Union’s 63rd Independent Air Detachment rolled out of its hardened shelter at an air base near Cairo. In the cockpit was one of a group of men designated as “farm workers” by the Soviet Union and sent to Egypt in response to an urgent request by President Anwar Sadat. In reality, these were highly trained pilots, led by Hero of the Soviet Union Colonel Alexander Bezhevets.

The Soviet MiGs wore Egyptian Air Force markings, and the men flying them observed strict radio discipline, but their Israeli opponents were not fooled. As the Foxbat sped over the Sinai at 75,000 feet on a mission to photograph Israeli positions near the Mitla Pass that November, it did not go unnoticed. Since March the Israeli Air Force had been frustrated time and again by its inability to intercept the brazen intruders with ground-to-air missiles or fighter aircraft.

This time the Israelis were ready. A pair of McDonnell Douglas F-4E Phantoms, specially modified to be as light as possible and armed with AIM-7E Sparrow missiles, waited on standby. The Phantoms climbed to 44,000 feet and launched their missiles,which rose to the Foxbat’s altitude and detonated, but by then the MiG had long since passed their position. The Sparrows’ proximity detonators couldn’t deal with the closing speed of the encounter.

Back to the drawing board. Israel’s Knesset discussed the reconnaissance overflights twice in emergency sessions, also sending in commandos disguised as Bedouins to have a closer look at the base where the MiGs were stationed. They offered the pilots a million dollars and a villa on the coast to defect. None of it worked. Though the Soviet overflights stopped with the end of the 1973 Yom Kippur War, the MiGs left a powerful impression.

The G-139 pod, shown on an RF-4C, allowed just four inches’ clearance from the runway. (Courtesy Jay Miller)
The G-139 pod, shown on an RF-4C, allowed just four inches’ clearance from the runway. (Courtesy Jay Miller)

The Israelis had already been looking for their own effective reconnaissance platform.They thought they found it in the HIAC-1 advanced high-altitude reconnaissance camera, built by General Dynamics. But the camera was so large it had to be carried in an RB-57F, a recon version of the British Canberra bomber license-built by Martin and General Dynamics, which had not been approved for export by the United States.

By 1971, the attitude in America toward such exports had changed. The U.S. Air Force had developed a pod, designated the G-139, that could house the camera and be mounted under the fuselage of an F-4 Phantom. Even then, however, the camera was so large that the pod was more than 22 feet long and weighed over 4,000 pounds. The camera/pod combo was flown on many reconnaissance flights (designated Bench Box) near the North Korean border, attached under RF-4C Phantoms.

The Israelis were interested in the camera-carrying Phantoms, which led to the birth of Project Peace Jack. A major concern was the adverse impact of the enormous camera pod on aircraft performance. General Dynamics’ engineers decided the best way to address the problem was to increase the F-4’s performance rather than trying to design a lighter camera system. The company sought to boost the thrust of the Phantom’s engines using water injection,an idea for which there was a precedent.

On December 9, 1959, Operation Skyburner had commenced as an attempt to secure high-altitude flight records using the Phantom. But the Skyburner program also had the absolute speed record in its sights. For that attempt, McDonnell engineers added water-methanol injection to an F4H-1. A large tank was installed in the rear cockpit, in the space normally occupied by the weapon systems officer. In addition, the windscreen had to be reinforced,since it would be in danger of breaking due to friction heat at the higher speeds.On November 22, 1961, U.S. Marine Corps Lt. Col. Bob Robinson flew the modified Phantom to an absolute world record speed of 1,606.342 mph.

The General Dynamics team applied those same lessons to what was now designated the F-4X. The new aircraft would have large 300-gallon conformal water tanks mounted above the fuselage engine fairings. Demineralized water would be used for pre-compressor cooling (PCC) of the General Electric J79 engines, serving three purposes: cooling the air entering the compressor, increasing the total mass flow through the engine (thereby increasing thrust) and adding more oxidizer to the afterburner. GE had tested the engines, and passed along that data to General Dynamics,simplifying the job for the F-4X project engineers. PCC was calculated to increase the J79 engine thrust by 50 percent—more than satisfactory.

The RF-4X mock-up contrasts a stock intake (right) with the enlarged version for the PCC. (Courtesy Jay Miller)
The RF-4X mock-up contrasts a stock intake (right) with the enlarged version for the PCC. (Courtesy Jay Miller)

To allow for much faster air speeds, larger engine air intakes were designed, complete with a sophisticated system of internal plates and bleeds. A new polycarbonate cockpit enclosure would deal with the friction heat.The flight controls were also modified, and the tail area was increased.

In 1973 a smaller, updated version of the HIAC-1 camera was installed in the jet’s nose. With the reduction in drag from the pod’s elimination, the Phantom’s performance was now calculated to increase to a cruising speed of Mach 2.4 and dash speed of Mach 3.2.

But this brought the export of the F-4X into doubt. No country other than the United States and the Soviet Union had aircraft with Mach 3+ performance. In his book Spyplane: The U-2 History Declassified, Norman Polmar cited an example of why that might be a concern. Starting in August1970, two U.S. Air Force U-2R reconnaissance planes were stationed at the RAF base in Akrotiri, Cyprus, during the Suez Crisis. After the first day of U-2 overflights, Israeli Defense Minister Moshe Dayan called the deputy chief of mission at the U.S. embassy in Tel Aviv into his office and complained that the U-2s had deviated from the narrow5-kilometer-wide corridor the Israelis had assigned them. Dayan then threatened to shoot them down using F-4Es.

It’s understandable that the State Department would be worried that another nation—even an ally—might acquire interceptors that could threaten U.S. reconnaissance aircraft. However, the F-4X was not equipped with radar and so was unlikely to be used as an interceptor. The program was thus allowed to continue. In November1974, an Israeli F-4E was flown to General Dynamics’ Fort Worth facility to serve as a mock up for the new aircraft. Engineers worked on the jet well into 1975, by which time the program had run into problems. After extensive testing, General Dynamics concluded that PCC would cause the turbine compressor blades to expand and hit the engine case, causing catastrophic failure.

Meanwhile, the McDonnell Douglas F-15Eagle was finishing its test program and about to become operational. Because theF-4X might offer superior performance in some ways at a lower cost, Air Force officials feared Congress would cut back on F-15 funding. The State Department was also still concerned the IAF would use the F-4X as an interceptor, and that a successful shoot-down of a Soviet reconnaissance plane would create an international incident. This signaled the death knell for the F-4X.

The program wasn’t a complete bust, however, as Israel still wanted the nose-mounted HIAC-1s. Two additional IAF Phantoms joined the F-4E used for mockup work, with all three converted into the new RF-4E(S) variant. Because of the F-4X program’s early termination and budget limits, the converted aircraft still used conventional unmodified J79 engines.

The three RF-4E(S) reconnaissance planes were finally delivered to the IAF in 1976 and 1977. With characteristic irony, the Israelis nicknamed them Tsalam Shablul, or Photographer Snail. Because the Shabluls flew their missions at altitudes approaching 70,000 feet, the pilot and systems officer wore full pressure suits, the same David Clark Company A/P22S-6 suits used by American reconnaissance pilots.

The Shabluls were retired in May 2004 after a long and busy career. Two were placed into storage at Ovda, and the third can still be seen at the Israeli Air Force Museum at Hatzerim Air Base.

 

Originally published in the March 2015 issue of Aviation History. To subscribe, click here.

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