Thursday, March 8, 2007

TFX/F111 Page 2

As you can see right from the beginning these two requirements would be hard to do with a single airplane configuration.

In addition the AF airplane basic weapon system required a missile or bomb to be carried in an internal bomb bay. The Navy weapon system was the Phoenix system that required six external missile launch positions. There was no way to carry the Phoenix missiles in the limited space of the internal bay.

Ok, the above requirements are not totally impossible for a single design to handle, but there is still a lot more to consider.

The most difficult thing is the basic size of the aircraft. For the AF if the airplane grows a little, no problem we need a little longer runway. If it gets a little heavy, we increase tire size etc.

However the Navy airplane must operate off an aircraft carrier. Now the Navy said it must not exceed 55,000 pounds gross weight, and 56feet in length with a span shorter than x feet with the wings folded or in this case retracted.

I don’t mean to overlook the tremendous effort made by GD and Grumman in proposing an airplane that can fly at mach 1.2 on the deck for almost 200 miles, and still be able to loiter for a few hours at 30000 feet while protecting the fleet with phoenix missiles, but the Navy version (F111B) was simply too heavy.

When the fourth proposal was about to be submitted the fall of 1962 a huge argument developed at Fort Worth. Grumman weights engineers came up with a gross weight estimate for the B version of approximately 65,000 pounds.

As I recall General Dynamics weights reviewed the data that night and announced in the morning that their estimate was close to 60,000 pounds.

Grumman management backed the Grumman engineers and said Grumman could not support the proposal submittal, and sent every body on the Grumman team home. (Grumman had a team of bout 20 engineers working there in Fort Worth as part of the proposal effort)

Now I don’t want to suggest GD was fudging the numbers, but let us remember the final gross weight of the actual F111b was about 78,000 pounds.

I wasn’t back at Bethpage (the Grumman facility) for more than one day when I was called by the chief engineers secretary and told to get back to Fort Worth immediately. What happened was Grumman management agreed to keeping our name on the proposal , but words were added showing our reservation as regards the B model gross weight.

The Proposal Effort

There were many interesting events during the proposal efforts worth discussing that provide insight of how this airplane evolved.

First, there were two separate groups of engineers: the Texans and the Yankees ( actually the NY Yankees) One group dedicated to the Air Force and the other to the Navy.

However that was never a problem as we worked together very well.

The real problem was getting an overall configuration to contain all the equipment able to do the job and still fit on an aircraft carrier.

Let me explain. The most critical requirement was imposed by the AF need for the Mach1.2 200 mile dash on the deck. As I recall there were no airplanes or very few flying that had ever exceeded Mach 1.0 at sea level. The TFX would do it at Mach 1.2 and for 200 miles!

So it was obvious this design had to have minimum frontal area. However the AF also required the airplane to be able to land on relatively soft terrain. I believe it had to be as soft as a UCI (Unit Construction Index)of around 5. Now don’t ask me why the AF needed to operate on such soft ground.

The Navy on the other hand was dealing with a steel carrier deck and could use extremely high tire pressure.

So the AF airplane gets huge tires and that kind of establishes just how big the body is going to be. Oh, I forgot the airplane is also a variable sweep wing design. The landing gear has to be stowed in the body. Add to the above the need for weapons storage, room for the large Phoenix system radar, and a side by side seated crew system, and you begin to see the design challenges.

(By the way, the only non-experimental variable sweep wing design ever built prior to the TFX was the Grumman F10F-1 Jaguar.( First flight May 19,1953) Unfortunately the 10F was ,to say the least, not a very good airplane. But the mechanics of the sweeping wings and the body mounted landing gear were excellent. That was the first airplane I worked on when I started at Grumman in 1950)

F10F-1 taking off at Muroc CA in 1953 . Click on image fo a larger view

The TFX story page 1

THE TFX STORY- the F111a and f111b

The Request for Proposals begin

In the last few months of the Eisenhower administration the Air Force began to argue that it needed a successor for its F-105 tactical fighter. This became known as the TFX/F-111 project. However Robert McNamara (then Secretary of Defense) changed the TFX from an Air Force program to a joint Air force/Navy under-taking.

On October 21, 1961 the two services sent the aircraft industry the request for proposals for the TFX with instructions to submit the bids by 1st December 1961.

Six bids were received from Lockheed, North American, Boeing, Republic/Vought.\, General Dynamics/Grumman, and McDonnell/Douglas.

Thus began the larges most expensive airplane program in our history. Before the final award was made to General Dynamics/Grumman in November 1962 there were 3 additional rounds of proposal submittals.

This story is told from the point of view of the US Navy and Grumman. General Dynamics realizing it had no real experience with Navy fighter aircraft decided to team with Grumman for this bi-service effort. I was on the team sent by Grumman to Fort Worth to work with the General Dynamics team. Our main interest was to insure the final product would meet all of the Navy requirements without compromise imposed by the dominant Air Force mission.

Of the six original proposals Boeings design was clearly the best, although the General Dynamics /Grumman proposal was considered acceptable. The others were rejected for various reasons.

Without trying to describe the complex politics involved the decision was made by the evaluators to have Boeing and General Dynamics/Grumman both submit revised proposals addressing some unresolved question. That and two more proposals were submitted until the last proposal was received in September 1962.

The Basic Requirements-What made the TFX so difficult to develop

When McNamara combined the Air Force and Navy requirements in to one common vehicle it almost guaranteed a bad outcome. Boeing met these requirements by proposing two not really common designs, where as GD/Grumman maximized the commonality as much as possible.

First, let me explain the critical requirements for both .What designed the AF airplane was a mission for the aircraft to fly a long distance at altitude then descend to sea level and dash 200 miles to the target at a speed of mach1.2.

For the Navy the airplane was designed for carrier task force defense.

This meant it would have to cruise a several hundred mile distance from the fleet and then loiter at altitude to establish a defensive position to destroy any enemy aircraft before it could threaten the fleet.