DBWI: USAF gets the F-111 fighter-bomber

Today (July 27, 2017) is the 49th Anniversary of the delivery of the first four British Aircraft Corporation (now British Aerospace) Eagle Mk. I (known during its development as TSR.2) to the RAF operational unit. One year later, the US-licensed version, the A-8A Marauder II, built by a joint venture of Lockheed and the Martin Company, began deliveries to the USAF. Today, the original TSR.2 design has been substantially updated, what with the newest GE F101 engine, modern radar, an improved intake design and a larger wing (adopted after the first production models) for better low speed and high altitude performance, and is still being built now to replace older Eagle and A-8 airplanes. The current version is the British Aerospace Eagle GSR.7 and the Lockheed Martin A-8F Marauder III.

I sometimes wonder what would have happened had the General Dynamics F-111 not suffered two horrible crashes early in the flight test program. First, the plane was notoriously prone to compressor stalls, what with the poor engine intake design and the Pratt & Whitney TF30 engine also being prone to compressor stalls. As a result, the first YF-111A prototype was lost when the crew tried to restart the engine from a low-altitude compressor stall. Seocnd, the third YF-111A prototype was lost when the right horizontal tailplane broke off during an attempted steep climb from low altitude. Finally, they had really serious problems developing the avionics for the plane. No wonder why the USAF pulled the plug on the F-111 project in August 1966. Like what happened in the early 1950's when the Martin XB-51 failed to live up to expectations and USAF decided to buy the license built version of the English Electric Canberra instead, USAF in 1966 chose again to license a British design--the TSR.2--as its primary interdiction platform, built by the Lockheed/Martin Company joint venture I mentioned above.

The more I think about it, had the F-111 been developed correctly, it would have carried a pretty large bomb load, had a pretty large internal fuel load for long range (though with a reduced bomb load), and variable-geometry wings would allow for operations out of fairly short runways.

The F-111 may have been a failure for General Dynamics, but what they learned from that project proved vital in that company winning the Lightweight Fighter (LWF) project with the F-16 Fighting Falcon. It did help General Dynamics was building a lot of new submarines for the US Navy at its Electric Boat division in the second half of the 1960's, so the financial impact on the company was relatively low. And Grumman Aerospace--who developed the variable geometry wing system for the F-111 (that was the part of the F-111 that actually worked well)--used its experience to eventually build the F-14 Tomcat jet fighter for the US Navy.
 
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That crashes led to US importing its fighter and bomber jets from european countries. Eagle was a start. Eurofighter typhoon was adapted as F-19 instead of that F-20 tigershark.
 
No, the F-111 was a bit too ambitious a design, and it appeared that General Dynamics didn't design the engine intake properly and the use of the P&W TF30 with afterburner proved to be a major problem, too. In fact, while the TF30 worked better on the F-14 Tomcat, that engine was still somewhat prone to compressor stalls at high angles of attack and once the P&W F401 (derived from the F-15 engine) became available in 1975, no wonder why all the initial production F-14's were retrofitted with the F401 and new production planes used the newer engine. In retrospect, the TF30 was originally designed for a subsonic jet. Adapting it for a supersonic jet proved to be its undoing.

The other problem was the horizontal tailplane failures. Like I said earlier, the third YF-111A prototype was lost when the right tailplane fell off in steep cimb from low altitude, and a pre-production F-111A successfully made an emergency landing when the left tailplane fell off in a similar test flight.

The TSR.2 design was not without its faults, either. The original Rolls-Royce Olympus Mk. 320 engines were not paragons of reliability, and that wasn't solved until the Olympus Mk. 505 (which used a lot of the technology from the Olympus Mk. 593 used on the Concorde SST) became available. At Lockheed's insistence, General Electric offered a modified version of the F101 engine that the B-1 bomber used, and the result was the F110-GE-140, rated at 35,000 lb. thrust, which became the standard engine for the BAe built versions and for newer production A-8 models. The other change after the initial production runs was a larger, lighter wing, which improved low speed handling and high-altitude flight, plus allowed for a larger bomb load.
 
That crashes led to US importing its fighter and bomber jets from european countries. Eagle was a start. Eurofighter typhoon was adapted as F-19 instead of that F-20 tigershark.
And then Congress was revealed to have accepted bribes from European manufacturers, and the US went right back to its Not-Invented-Here ways.
 
The problem with the A-8, especially with early versions, is that it was designed as a nuclear bomber. The A-8A had a severely limited bomb load, at about 10,000 lbs. That's about as much as an A-4 Skyhawk in a much larger airframe, and much less than the Navy's A-6 Intruder. That's why the Navy's A-8A squadrons rarely saw more than half their aircraft on a single carrier. The A-8A had some important advantages over the A-4 and A-6, particularly the terrain following radar that made the aircraft useful for low-level penetration missions, but it was very much a niche aircraft. The bomb load problems were partially addressed by new engines and intakes and the wing size increase, but it wasn't until the A-8F that bomb loads began to approach what the F-111 prototype was said to be able to carry. Fortunately for the Navy, the A-8 was able to serve in the tanker and electronic warfare roles, much like the EKA-3 Skywarrior -- which was one of the largest navalized aircraft before the A-8, and with a similar bomb load issue -- that it replaced.

In the Air Force, there was always the problem that the A-8 didn't have the glamor of an F-for-fighter designation. The Air Force had the foresight to demand that the A-8 be able to carry two Sidewinder missiles, giving it some self-defense abilities. Like the Navy, they aggressively pushed for the improvements to engines, intakes and wing area, as well as more hardpoints. The successful F-16 could carry more bombs than the original A-8A. If BAC hadn't made their A-8B and C conversion kits available at low cost, the A-8 might have been canceled early on and supplanted by the F-16 or even -- to this day the Air Force talks about wanting to do it -- a strike version of the F-15.
 
That was the reason why for the new wing and the upgraded engines. A big problem with the original TSR.2 design was it was TOO optimized for the nuclear strike role and could only carry around 11,000 lb. bomb load. But with the new wing and the F110-GE-140 engines, the bomb load went up to nearly 16,000 lb., and they developed an installation for the Pave Tack target laser designator system on the A-8C and D models that fir in what was the center bomb bay (the A-8F today can field-switch between bomb bay or the Pave Tack installation).

By the way, all A-8F's and RAF Eagle GSR.7's will soon switch to a new engine: the General Electric F120-GE-200. Rated at almost 38,000 lb. thrust in full afterburner mode, the F120 engine has the ability to "supercruise" as high as Mach 1.47 on this plane without using reheat, which means a far lower infrared signature and far lower fuel burn at supersonic speeds.

Yes, there was serious work on the F-15 as a two-seat strike fighter, but simulated combat tests showed the A-8E (the version in service at the time McDonnell-Douglas built its YF-15E demonstrator) was faster at low altitude carrying the same bomb load as the F-15E. But even though the F-15E was not picked up for service, it did result in the F-15C/D air superiority fighter with far longer range than before, thanks to the new conformal fuel tanks installed.
 
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