By Tommy H. Thomason

Thursday, January 27, 2011

The F-111B versus the F-14A, One More Time


I recently had the incentive to revisit this diatribe in the process of responding to a request from another author about the F-111B program. As before, this assessment was made using the respective Standard Aircraft Characteristics charts, the F-111B’s dated 1 July 1967 and the F-14A’s, dated April 1977. While the argument can be made that the F-111B SAC did not reflect its final weight, I believe that the same argument can be made concerning the one used for the F-14A, so it’s at least a pretty close apples-to-apples comparison. Note: In the following discussion, the F-14A is penalized with the weight of an internal gun and ammunition whereas the F-111B is penalized with the weight of the original Airborne Missile Control System (AMCS) design, roughly the same.

Much has been made of how terribly overweight the F-111B turned out. And it was, compared to a totally unrealistic specification. Many think that the F-14A was far lighter than the F-111B, primarily because most comparisons neglect to do so using the F-111B’s design mission for both aircraft. The F-14A is still lighter, of course, because the Navy changed its requirements so that it would be. Deleted were the escape capsule, bomb bay, and swiveling wing pylon stations among other things. The Hughes Airborne Missile Control System, given a few more years of development, was lighter. The structure was designed for 6.5 gs at 49,548 lbs, about 10,000 pounds less than the F-111B’s design gross weight at that g level. In effect, the six Phoenixes and 3,800 lbs of fuel were treated as an overload for the design of the F-14A structure. At combat weight (13,800 lbs fuel and six Phoenix missiles) the F-111B therefore had a load limit of 5.8 g and the F-14A (12,000 lbs of fuel and six Phoenix missiles), a lower (but not particularly constraining) 5.2 g. The result, however, is a somewhat lower structural weight for the F-14A.

According to the F-111B SAC, when it was loaded with full internal fuel and six Phoenixes, it weighed 77,566 lbs and required 11 knots wind-over-deck on a tropical day for launch; the F-14A, not surprisingly, weighed almost 7,000 lbs less but, surprisingly, required 16 knots wind-over-deck, five knots more than the F-111B. Moreover, at its takeoff gross weight the F-111B was carrying 3,000 lbs more fuel than the F-14, making the difference in takeoff gross weight for the same amount of fuel and weapons carried only 3,866 lbs, or 5%, not exactly the amount or percentage difference that most would have guessed given all the negative publicity garnered by the “Sea Pig.” With that additional fuel, the F-111B could loiter on station for 1.5 hours with the combat fuel allowance assuming an acceleration to 1.5 Mach; the F-14A with the two external tanks of overload fuel, and with the same combat Mach number (one has to read the SACs very closely), could only loiter for 1.1 hours.

As for landing, they were both heavy. In fact, the maximum arrested-landing weight limit of the F-14A precluded it from landing back aboard with all six Phoenixes, whereas the F-111B had a 5,000 lb margin, all fuel, between its maximum landing weight and the landing weight with the standard landing fuel load of 2,417 lbs of fuel and six Phoenix (56,980 lbs). One does not need to be a Naval Aviator to appreciate being able to land with three times the required fuel. On a tropical day at the standard weight, the F-111B needed 15 knots wind-over-deck for landing; the F-14AA could only land with five Phoenix, and even then needed 17 knots wind-over-deck at its maximum landing weight of 51,830 lbs. The F-111B was also less of an handful following an engine failure since its engines were not as widely separated as the F-14A’s.

For a little more on the F-111B at-sea trials often used to condemn the F-111B's carrier compatibility, see http://thanlont.blogspot.com/2009/03/f-111b-carrier-trials.html

This is not to say that the Navy didn’t do the right thing in getting the F-111B program cancelled and replacing it with the more versatile F-14, particularly since the Hughes AMCS wasn’t ready for prime time (the Navy's Phoenix program was about two years behind schedule and production F-111Bs were about to be delivered). However, with respect to its Fleet Air Defense design mission, it got an airplane that could not loiter as long or land with its full complement of missiles, had a higher stall speed, required more wind-over-deck for takeoffs and landings, and was more difficult to bring aboard with two engines running, not to mention with one inoperative.

So which is the real "Sea Pig" then?

My answer is neither of the above. The F-111B could do, pretty much, the Phoenix-based Fleet Air Defense (FAD) mission that it was intended to do while weighted down with Air Force low-level supersonic mission and other requirements. The F-14 could not do the FAD mission quite as well—but well enough if needs be—and it could also accomplish the carrier Navy’s other, equally important, fighter missions.

Wednesday, January 19, 2011

Updates to Prior Posts

11 January 2011: Expanded discussion of nuclear weapon delivery technique, "Not Doing It Right", posted 5 June 2008.

The Gift That Keeps On Giving - Final Chapter

The Supreme Court has heard arguments on the dispute over who owes who how much in the settlement of the 1988 contract between the Navy and its contractors, General Dynamics and McDonnell Douglas (now Boeing), to develop the A-12 Avenger. See Here for the New York Times report. The decision is expected this summer.

For my prior blogs on this long running, multimillion-dollar gift to the legal profession over a multibillion-dollar claim and counterclaim, see here, here, here, and here.

Catapult Development

The basic concept of the aircraft carrier catapult hasn't changed much over the years. The airplane is fitted with something to hook it to the catapult and something to hold it back under full throttle until the catapult is activated. The hold back is designed to break (or nowadays release) when the airplane is being pulled forward at a force somewhat greater than that provided by full power and the catapult shuttle being pulled forward to tighten the hookup. However, the details have changed significantly.

Before World War II, although carriers were fitted with catapults, takeoffs were usually accomplished by a deck run rather a catapult launch. It was quicker and to a small extent safer since catapult failures were not unknown. However, as airplanes got heavier, requiring more distance to take off, and more of them were crowded on deck, resulting in less distance for a takeoff run, the catapult launch became more the rule than the exception.

The catapult bridle (two attach points on the aircraft) or pendant (one attach point) was considered disposable. It simply dropped from the aircraft and fell into the sea off the bow after the launch. It's not clear whether there was an alternative hookup during the war which retained the bridle/pendant on deck.
However, at some point the bridle/pendant was retained on deck by means of a heavy elastic strap that was attached to both the bridle/pendant and the catapult shuttle. After a certain number of launches or visible damage, the bridle/pendants were disposed of, either by a launch without a retainer when it was one launch short of the limit or being dropped over the side if damaged. This is an S2F which used a pendant.
It appears that there was little commonality among aircraft with respect to launch gear, including hold backs, particularly the strength of the "weak links" that broke when the catapult fired.
My guess is that pendants were more desirable than bridles from the deck crew's standpoint because they were lighter but bridles may have been necessary on some airplanes to accommodate a slightly off-center lineup.

Still later, somewhat after the introduction of the angled deck and the steam catapult, "bridle catchers" were added ahead of the catapult on some carriers. It appears that on those carriers without bridle catchers, the previous practice of using elastic straps to retain the bridle/pendant on deck was no longer used and it was disposed of with each launch.
The bridle arrester lanyards were attached to the bridle and a track on the deck parallel to the catapult track.
The bridle rig wound up on the bridle catcher following launch and were retrieved with the shuttle.
The bridle/pendant hookup process was somewhat labor-intensive, time-consuming, and dangerous. It also relied on the skill of the catapult crew for a proper hookup. In this case, the sailors who are going to hook up the hold back are lying on the deck. The bridle is lying on the deck already looped around the shuttle.

The solution was the integration of the launch and hold back hardware on the nose landing gear. Beginning with the Grumman E-2 Hawkeye, all new carrier-based airplanes were to be designed with this capability. The first at-sea E-2 launch was accomplished on 19 December 1962 from Enterprise, the first carrier equipped with the nose tow capability. (An adapter allowed the catapult to be used to launch airplanes that still required the bridle/pendant.)

The holdback is now reusable, although a specific one is required for each aircraft and are color coded accordingly.
Note that only one sailer is required in close proximity to the aircraft using the nose tow concept.

Sunday, January 2, 2011

The Truculent(?) Turtle

An acquaintance recently asked me why the Lockheed P2V-1 Neptune that set a distance record in late 1946 was called the Truculent Turtle when the name on its nose was just "The Turtle". Moreover, the cartoon character on the nose, a turtle smoking a pipe and pedaling the propeller-driven equivalent of a unicycle, was anything but truculent.

In many places (copies of the Wikipedia entry), the interweb incorrectly states that "With time, the aircraft has come to be called 'Truculent Turtle'..." In fact, in press releases before the flight, the Navy was already referring to it as The Truculent Turtle as evidenced by a New York Times article dated the day that the flight began.

The name The Turtle and the cartoon character doubtless originated with the Navy/Lockheed plan, "Operation Turtle," to counter the publicity being garnered by the Army Air Force with long-range B-29 StratoFortress flights, one setting the long-distance record in November 1945. The Navy was concerned that the President and Congress might well overvalue the Army's ability to deliver the newly demonstrated atomic bomb and underfund the Navy's ship and airplane programs. "Turtle" was probably used by the engineers in recognition of the fact that the maximum-range cruise speed of a propeller-driven airplane, even high performance fighters, is slower than most people would think, only about 150 knots or 170 mph. They can cruise at higher speeds, of course, but not go as far.

The addition of Truculent was probably belated recognition that The Turtle did not convey the impression of long-range weapon delivery capability that the Navy wished to make with this record-setting flight even though this was not its stated purpose.

It was, no question, a publicity stunt. Few if any airplanes were as modified for speed records as The Turtle was for the distance record. Lockheed removed as much equipment as possible to minimize the empty weight and parasite drag and then added as many fuel tanks as there was space available until the aircraft gross weight was almost 50% greater than the maximum allowed operationally. In addition to new tip tanks, there were additional tanks in the outboard wing panels, the forward fuselage, and the aft fuselage. The standard internal fuel capacity of the P2V-1, not counting auxiliary tanks in the bomb bay, was 2,350 gallons. The Turtle's fuel capacity, including bomb bay tanks, was 8,541 gallons, well over than three times more.

Hal Andrews collection via Jim Sullivan (The lower radome was removed prior to the record flight and the tip tanks were  dropped when empty.)

In order to accommodate an engine failure shortly after takeoff, a fuel jettison capability was developed to reduce the airplane's weight as quickly as possible in that event. The tip tanks were simply dropped. The fuselage tanks were ganged to a dump station manned by one of the relief pilots during the takeoff. In theory, once the P2V had climbed to 1,000 feet above the ground, he could empty those tanks while maintaining the center of gravity within an acceptable range and thereby reduce the gross weight to that permitting a climb before they lost more than 800 feet.

Even a new, well-broken-in piston engine burns oil. The engine oil capacity was therefore increased by 64 gallons. The oil in the tank added in the nose wheel well was pumped manually as required to one or the other of the standard 78-gallon tanks located in each engine nacelle.

Four JATO bottles were added for the takeoff. These minimized both the length of the takeoff roll and the time it would take to reach the minimum single-engine control speed. Another change was the substitution of heavier duty main landing gear tires because of the higher takeoff speed required at the higher gross weight. The resulting takeoff roll was 4,700 feet on a 6,000-foot long runway. (The normal takeoff distance was less than half that.)

JATO Takeoff Test at Lockheed Burbank

The takeoff from Perth, on the west coast of Australia, was made at dusk local time. One reason given was the desire to begin at night to allow celestial navigation. However, as plane commander CDR Thomas D. Davies admitted to the press before takeoff, a far more important consideration was minimization of the level of turbulence likely to be encountered. At its design gross weight of 54,000 pounds, the P2V was designed for a limit load factor of 2.6. At a takeoff weight of 85,500 pounds, the structure was theoretically capable of being loaded to only 1.64 gs before being damaged. Of course, catastrophic failure of the structure was not supposed to occur before a 50% higher load was encountered, with the likelihood that it would sustain even more than that, but it was best to avoid turbulent conditions until some fuel had been burned off.

An excellent color video of the Turtle at Perth and the JATO takeoff is here: https://www.youtube.com/watch?v=8cyQklgmfzE

It would take almost 60 hours to burn this much fuel at the maximum range cruise speed. To reduce weight, the crew therefore consisted of only four pilots instead of the regular crew of eight, with two resting and two flying at any given time. The flight was not uneventful. The crew had to deal with bad weather crossing the equator northeast of Australia, turbulence and icing in the western US, and unexpected headwinds. The stated destination prior to takeoff was Seattle, Washington*, which would have set the record, but it seems clear that they intended to fly as far as they could, preferably all the way to Washington, D.C. However, after reviewing their fuel status and approaching Columbus, Ohio they prudently decided to land there after 55 hours in the air rather than pressing on to Anacostia where officials and family were waiting. That would set the record at 11,236 statue miles, almost halfway around the world.
New York Times

The flight had the hoped-for impact and specific comparison with the Army Air Force B-29 flights. On 2 October 1946, a New York Times editorial stated "The 7,916-mile record that it shattered was that made by the Army's Boeing Super-Fortress Dreamboat. A plane like the P2V can carry an atomic warhead from any point on the earth's surface to a point half-way round the globe."

Of course, the Times neglected to note that delivering a bomb to a target 12,000 miles away would be a one-way trip for a P2V, it couldn't be a very big bomb (the crew debated the last-minute addition of a 37-pound kangaroo), and the enemy would have a couple of days to get ready to greet it...

*Seattle, Washington was on the great circle route to Washington, D.C. as shown here.
The great circle route is the shortest distance between two points on the globe, which does not appear as a straight line here because it is the depiction of the globe with a Mercator projection. However, winds aloft might (and did) dictate a deviation from this line, which on a long flight is established by a concept called pressure pattern flying (feel free to Google that). Moreover, the reported weather in Seattle dictated a mid-flight deviation to the south as shown on the map of the actual route of flight.