F-4X Super Phantom

During the first half of the 1970s, General Dynamics would attempt to modify the F-4 Phantom - the most used US combat aircraft at the time - into something even more powerful. With foreign interest as well, the idea was floated for a ‘Super Phantom’, and so the F-4X program was born.

In the early 1970s, the Soviet MiG-25s were proving a serious threat to Israel. Flown out of Egypt, these were the fastest interceptors in the air, and were practically untouchable. Operating newly received F-4 Phantoms, the Israeli Airforce were beginning to think they needed an even faster jet.

At the same time, the Israelis were struggling with reconnaissance of the movement of Egyptian missile sites. Without proper recon aircraft, they began flying F-4s extremely low, executing 600-knot passes across areas they wanted to observe. On one occasion in 1971, an RF-4 took a direct hit from an SA-7. This low-level approach proved far too dangerous to continue as reconnaissance.

Israel wanted an aircraft that could be an equal challenge to their neighbour’s MiGs, while also providing LOROP, or Long-Range Oblique Photography recon capabilities. The most advanced designs - namely the U2 and SR-71 - were strictly forbidden for foreign purchase. For a brief window of time, another option was on the table - the RB-57F - a heavily modified Canberra bomber optimised for recon. However, the US soon decided against this, noting that such an aircraft would give a significant advantage to Israel in the region, potentially harming US relations with Israel’s neighbours.

The US had used the G-139 recce pod under the phantom in Vietnam. But these pods weighed 4000 pounds and proved very bulky under the aircraft. The Israelis were interested specifically in the HIAC-1 LOROP system inside the pod. This camera could resolve 25 centimetre objects at a range of over 20 nautical miles. This would enable the IAF to perform recon along their border, without having to send aircraft into neighbouring airspace. The US, however, were only selling the camera as part of the bulky G-139 pod, limiting the aircrafts altitude to 50,000 feet and Mach 1.5. This put the aircraft within striking altitude of other aircraft or SAM sites. More altitude and speed were desirable for safety and better reconnaissance.

So, how can a recon Phantom be made to go higher and faster? In 1959 Operation Skyburner had attempted to do just that - use the Phantom as a high-altitude recon aircraft. The result was an F4H-1 which reached 1600mph, a world record at the time. However, to achieve this the rear seat had been removed to accommodate a large fuel tank to provide a water-methanol injection mix.

Inspired by these early experiments, General Dynamics in collaboration with the Air Force - began work on their own massively upgraded F-4. At the same time, General Dynamics were contacted by the IAF to assist with their reconnaissance dilemma, and a smaller separate research program was begun, codenamed Operation Peace Jack.

UPGRADES

Working with the US Air Force, concepts of this new Phantom were sketched out and mocked-up with paper mache. General Dynamics started developing the concept by installing 300-gallon conformal water tanks above the fuselage engine fairings. Using demineralised water, the goal was to provide pre-compressor cooling. By injecting a mist of water in an early stage of the engine, air would be cooled before entering the compressors. This would increase the density and mass flow, which would help especially at high altitudes, and increase oxidiser to the afterburner.

Such a method had already been tested some time earlier. At Arnold Engineering Development Center, designers tested a similar method of pre-compressor cooling on a J75 engine. The result was not only an increase in power, but researchers managed to keep the engine alive in afterburner for a continual 40 hours. The research suggested that this method would increase the output of the Phantoms two J79 engines by 50 percent.

To manage this increased performance, a new polycarbonate cockpit was built, new flight controls were installed, and the tail area was increased. To accommodate the increased airflow, larger engine intakes were installed, along with a new internal system of bleeds and plates. Controllable intake ramps and vortex generators would enable far better performance.

With all these modifications the aircraft was expected to have a supercruise speed of Mach 2.4, and a maximum speed of around Mach 3.2 and a ceiling of around 78000 feet. This incredible performance meant it could easily rival the MiG-25.

At this point of development, the aircraft was designated F-4X, essentially a blanket upgrade to the standard F-4E flown by Israel. As the performance specifications came into focus, General Dynamics forwarded the project to the US Air Force. Highlighting the expected performance, they suggested that the Air Force should consider developing their own specialised recon variant. This would be referred to as the RF-4X.

The key difference between the two would be loadout. The F-4X may or may not have integrated the HIAC-1 camera, however it would have a radar. It would also have a slightly higher cruise speed of Mach 2.7. The RF-4X would feature the camera but drop the radar to reduce weight. For self-defence, it would use a similar setup to the standard RF-4s in Israeli use; AIM-9 Sidewinders on twin pylons.

The RF-4X didn’t have to carry the large G-139 pod, rather, in 1973, a new miniaturised version of the HIAC-1 camera was installed in the nose, a far more aerodynamic and practical option than the previous underbelly pod. On the bottom of the nose were two windows and the camera could be rotated to shoot through either window. A cooling system was also incorporated to manage the temperature for optimal camera operation.

When everything had come together it was obvious that the aircraft had greater potential than first anticipated. General Dynamics, and the Air Force, had to reconsider the export implications of such a development. Could Israel continue to be part of the Peace Jack project?

EXPORT PROBLEM

At this time, only the US and Soviet air forces had access to Mach 3+ capable aircraft. Despite being in a cold war, both sides were rather self-constrained with their use of new technology, knowing that any accident or poor decision could lead to global war. The US knew that the Soviets would only use deadly force if western aircraft penetrated Russian airspace, and vice versa.

The same degree of self-constraint could not be assumed about the potential customers of the F-4X. A chief concern for the military was the potential rash employment of such a weapon, or its use against allied forces. One incident was noted by author Norman Polmar when writing about the history of the U-2 spy plane. In August 1970, two U-2s had been operating out of Cyprus during the Suez Crisis to monitor the situation. The Israelis had ordered that the U-2s could only fly along a narrow 5-kilometre corridor dictated by them. On the first day of U-2 recon flights, Israeli Defence Minister Moshe Dayan called the US Embassy, and said that he thought the U-2s had diverted off the narrow corridor. He threatened to shoot them down using his older F-4Es. The U-2s may have been able to escape F-4Es, but a new F-4X could easily intercept and destroy such friendly spyplanes. The US also believed that the Israelis may use the enhanced F-4 to shoot down Soviet aircraft - which they had already been trying to do with older versions of the Phantom.

To mitigate this hypothetical risk of an F-4X as an interceptor fighter upon export, the program stripped the variant of weapons and radar. The RF-4X would be a recon only export, thus bringing Israel back into the Peace Jack program.

PRODUCTION CONTINUES

With the State Department now reassured that the Peace Jack program wasn’t going to turn into a high-performance interceptor, General Dynamics secured permission to test the RF-4X concept on an Israeli Phantom. An Israeli Air Force F-4E was flown to the General Dynamics Fort Worth plant in late 1974, where it underwent months of extensive testing and modifications.

The program did however encounter some problems. After extensive experimentation, it was found that the water-methanol injection method would eventually cause the turbine compressor blades to expand due to increased heat. Upon expansion, they would hit the casing of the engine, tearing it apart internally. To remedy this, designers would need more time to build and install stronger compressor blades.

There was also another problem. By this time, the F-15 program was now in full swing. The new fighter was technologically superior to the F-4X, offering many new benefits right off the production line. Some Air Force officials were concerned that the development of the F-4X may threaten funding of the F-15 program. The new Phantom would be faster and have a higher service ceiling, while also being cheaper – the General Dynamics project was clearly threatening competition to McDonnell Douglas.

Concerns grew in regard to foreign exporting, performance reliability and competition between manufacturers and eventually the US Air Force pulled out of the program. No doubt a decision driven by politics as much as pragmatics.

ISRAEL GETS AIRCRAFT

The Israelis still wanted this high performing recon aircraft but could not afford to fund the necessary compressor fan redesign to handle higher engine operating temperatures and were thus limited to funding the new camera system.

The prototype for the F-4X assembled in 1974 would serve as the first IAF phantom to receive the new camera upgrade, along with another smaller camera system - the KS-87 - mounted aft of the HIAC-1. On the side of the cockpit, sights were placed to ensure camera alignment with a target. It would first fly on December 20th, 1975, and was delivered on July 30, 1976. Two other IAF Phantoms would be sent over to receive similar upgrades.

The final variant was designated as the RF-4E(S), with ‘S’ for special, of which only three would ever exist.

Despite never reaching the full potential of the program, these three Phantoms, unique in their appearance and tasking, would operate at altitudes up to 70,000 feet. Because of this, pilots and systems officers had to wear special pressurised suits. In fact, they would wear the same High Altitude Flying Outfit used by some American pilots - the A/P22S-6.

These RF-4E(S) aircraft would fly for several decades. The Israelis retired them in May 2004, with two being relegated to storage, and a third being put on display at Hatzerim Air Force Base.

CONCLUSION

The F-4X program highlighted the potential capability of the Phantom if further resources were dedicated to it. In its initial conceptual form, the F-4X would have been a Mach 3 interceptor with fighter capabilities. Its incredible cruise speed of Mach 2.4 to 2.7 gave it an edge over other interceptors at the time, allowing it to catch the fastest stealth aircraft, and directly chase down the otherwise untouchable MiG-25.

At the end of the day however, the F-4X potential speed and altitude performance was shadowed by the F-15s more advanced systems and better air-to-air performance. Nevertheless, the Phantom lives on as a legendary aircraft.