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F-4X: The Fastest Phantom Fighter That Was Never Built

F-4 Phantom. Image Credit: Creative Commons.

Meet the F-4X: The F-4 Phantom was a legend.

It served the U.S. military well for decades and, in fact, still serves a few nations today.

And yet, there was an idea to make it even better: 

A few months ago, I wrote an article titled, “How An F-4 Phantom Tried To Catch An SR-71 Spy Plane.”

Anyone well versed in aviation technology knows that there was no way the F-4 Phantom II was going to catch the world’s fastest air-breathing aircraft

In response to that article, one of my LinkedIn Connections brought to my attention a January 2017 story penned by Emil Petrinic on HistoryNet titled, “F-4X: THE FASTEST PHANTOM.” I am pleased to now present the story of the F-4X to our readers. 

Original F-4 Phantom Brief History and Specifications

 Okay, this is going to seem repetitious to those of you who read last week’s article, or indeed any of my earlier articles on the Phantom, but for the benefit of new readers, here goes: 

The McDonnell Douglas F-4 Phantom II — the successor to the late-1940s vintage McDonnell FH-1 Phantom — made her maiden flight in 1958. The F-4 ended up becoming the mainstay fighter-bomber of the U.S. Air Force, Navy, and Marine Corps during the Vietnam War. Despite the warbird’s large size, it could attain a top speed of Mach-2.23 (1,711 mph). 

The F-4 had a max takeoff weight of 60,000 pounds, a fuselage length of 63 feet, a wingspan of 37 feet 5 inches, and a height of 16 feet 5 inches. The combination of size and speed inspired Phantom driver Dick Anderegg to joke that the big bird provided “proof that if you put enough thrust behind a brick you can make it fly.”

Israeli Ideas and American Knowhow

Rewind to the year 1971, when MiG-25 Foxbats — the world’s fastest interceptors — with Egyptian Air Force markings were being flown by Soviet pilots at the behest of Egyptian President Anwar Sadat to conduct photographic reconnaissance flights over Israel. The Israeli Air Force’s (IAF’s) own F-4s and surface-to-air missiles could never catch the MiG-25s. As Petrinic put it, “Though the Soviet overflights stopped with the end of the 1973 Yom Kippur War, the MiGs left a powerful impression.”

The Israelis decided they wanted their own ultra-fast photo reconnaissance bird. They already had the camera — namely the General Dynamics HIAC-1 advanced high-altitude reconnaissance camera — but the device was so large that it had to be carried in a Martin RB-57F, an American license-built recon version of the British-designed English Electric Canberra bomber. That particular aircraft hadn’t been approved for export by the U.S. government, and furthermore, at a max airspeed of a mere 570 mph, it fell well short of the IAF’s speed requirements.  Luckily for the IAF, fortuitous developments intervened. To quote Petrinic again:

“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 fine folks at GD came up with the idea of boosting the F-4’s engine thrust via water injection, an idea with precedent in December 1959, when a water-methanol injection was added to an F4H-1. The modified airframe attained a then-absolute world speed record of 1,606.342 miles per hour.

The X-Phactor, er, Phantom

Thus the concept of the F-4X. This plane would have large 300-gallon conformal tanks mounted above the fuselage engine fairings. Demineralized water would be used for pre-compressor cooling (PCC) of the General Electric (G.E.) J79 engines, which, without getting into excessive technical detail, were calculated to increase the engines’ thrust by 50%. 

Meanwhile, in 1973, along came an updated, reduced-size version of the HIAC-1 camera which no longer required a pod and could now be fitted in the Phantom’s nose, thus reducing drag on the airframe. This combination of increased engine thrust and reduced drag resulted, on paper at least, in boosting the F-4’s cruise speed to Mach-2.4, with a max airspeed of Mach-3.2. The latter figure put the plane on a par with the Foxbat. To use a catchphrase from my own USAF days, “High-speed, low drag, baby!”

However, in the immortal words of ESPN College GameDay’s Lee Corso, “Not so fast, my friend!” After extensive further testing, GD’s research and development team concluded in 1975 that the seemingly beneficial PCC procedure would actually cause the turbine compressor blades to expand and hit the engine case, causing catastrophic failure. What’s more, by this time, McDonnell Douglas was putting the finishing touches on the F-15 Eagle’s test program, which took priority. 

Lastly, the U.S. State Department feared that the IAF would use the F-4X to shoot down a Soviet reconnaissance plane and create an international incident. Quoth Petrinic one last time: “Thus signaled the death knell for the F-4X.”

F-4 Phantom. Image Credit: U.S. Air Force.

F-4 Phantom. Image Credit: U.S. Air Force.

Christian D. Orr is a former U.S. Air Force Security Forces officer, Federal law enforcement officer, and private military contractor (with assignments worked in Iraq, the United Arab Emirates, Kosovo, Japan, Germany, and the Pentagon). Chris holds a B.A. in International Relations from the University of Southern California (USC) and an M.A. in Intelligence Studies (concentration in Terrorism Studies) from American Military University (AMU). He has also been published in The Daily Torch and The Journal of Intelligence and Cyber Security. Last but not least, he is a Companion of the Order of the Naval Order of the United States (NOUS)

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Christian D. Orr is a former Air Force officer, Federal law enforcement officer, and private military contractor (with assignments worked in Iraq, the United Arab Emirates, Kosovo, Japan, Germany, and the Pentagon).