JOHT 12: Starfighter

[stickmaker]

The Joy of High Tech

by

Rodford Edmiston

Being the occasionally interesting ramblings of a major-league technophile.

Please note that while I am an engineer (BSCE) and do my research, I am not a professional in this field. Do not take anything here as gospel; check the facts I give. And if you find a mistake, please let me know about it.



Credit Where it is Due

Part 2: Starfighter

Y'know, sometimes we humans manage to do something right. Many of the examples come from aviation. That's partly because in aviation, if you get something wrong the results tend to be fatal. Finally getting a plane right can often take time, but it can be done. Some of the most remarkable aircraft of all time were members of what came to be known as the Century Series. For the most part these were huge aircraft, but there was one which stood apart. One which served in one major air force or another as a front-line fighter for half a century. A plane still flown in airshows, where the pilots have trouble keeping it from exceeding the speed and altitude limits. A plane which one aviation writer stated can "still show its heels to most front-line fighters." There are certain advantages to specialization...

In the early Fifties jet fighters were rapidly growing larger and heavier. Many rivaled WWII light and even medium bombers in weight and carrying capacity. There were many reasons for this, some technical, some tactical, some strategic... and some psychological. For instance, the Fifties was the era of the "bigger is better" mindset. As mentioned above, though, there were legitimate technical reasons for the size increases. For instance, jet engines work better in a certain size range, and fighter jets are so expensive that in order to get the taxpayer's money's worth the bean counters decided that in addition to fighting other aircraft they should also perform additional duties. Of course, the extra equipment needed for these duties made the fighters even larger and more expensive. Then there was the concept of the fighter as missile platform. 

Technical optimists felt that (then-)modern missile technology had made the gun-equipped fighter obsolete, and that bullets could be omitted from consideration in air-to-air combat. Actual experience proved this to be very untrue. Even today this goal has not been reached, though modern missiles are much more reliable and capable than those of the Fifties and Sixties. During this period it was felt that fighter aircraft should no longer have guns. Make them big missile platforms. 

Some companies bucked the trend. One of them was Lockheed. Company personnel - including Clarence "Kelly" Johnson - talked with fighter pilots (many of them veterans of Korea, where the US had been surprised by the MiG-15) and asked them what they wanted. To the surprise of on-one except the Air Force brass, these men stated that they wanted something fast, agile and equipped with a good punch. Adding to the motivation at Lockheed for moving away from the "bigger is better" approach favored by the Pentagon was the sour taste left by the failure of the company's huge XF-90, designed to fit the official requirements. So while other design teams were planning such monsters as the F-105 Thunderchief (as heavy as a light bomber and actually intended to serve as one, delivering a single nuclear weapon dropped from an internal bomb bay) Johnson and his team sat down and started with a clean sheet of paper, seeking to solve a different requirement than the official one. Though this was before the famous "Skunk Works" officially formed, the project involved many of the same people who would later be involved with that group, and much of the same methodology.

In November of 1952 Lockheed submitted an unsolicited proposal for a new, lightweight fighter. Jet aircraft technology was advancing quickly, and the US wanted to stay not just up to date, but ahead. Although the Air Force had no official requirement for such a plane they had enough faith in Lockheed and Johnson to issue a General Operational Requirement to eventually replace the then still new F-100 Super Sabre. Johnson and his crew set eagerly to work. 

Johnson's team studied many options and variations. Finally, they picked a concept - the minimum airframe to hold the engine, pilot, weapons and avionics, plus enough fuel to get the job done. Then they decided on the upcoming J79 for the engine. And what an engine that was (and still is)! The team wanted plenty of excess thrust, in case the J79 didn't live up to expectations and for the inevitable growth in aircraft weight. Keeping the plane within their guidelines with that monster inside meant pretty much designing the plane around the engine. As the later A-10 was wrapped around its Great Honking Gun, the new plane was wrapped around a Great Honking Engine. Everything else about the plane was small, especially the wings. After some final adjustments, they realized they had a winner. On paper, at least.

The gun chosen was the then-new Vulcan. This is a 20mm, multiple-barrel rotary weapon, basically a motor-driven Gatling gun firing a small cannon round. With a high rate of fire it could put more rounds on target in the same interval than the multiple .50 caliber machine guns used by US fighters in the Second World War, and those rounds were not only larger but carried an explosive charge.

Another departure from the norm came with those thin, tiny wings. Supersonic wind tunnel data showed that swept wings made supersonic flight easier, and delta wings gave better maneuverability than simple swept wings. Most companies were going with a delta-wing configuration. However, a delta wing has a lot of supersonic drag. The same data also showed that a very thin, straight wing had most of the same advantages, plus some others, such as low supersonic drag. (Remember that the Bel X-1 used thin, straight wings.) Lockheed had plenty of experience with this configuration, having used thin, trapezoidal wings successfully on the X-7 ramjet drone research vehicles. Many long and heated discussions, accompanied by research and testing, went into the exact design of the wings and their fit to the aircraft as a whole. After a rather short and very hectic design and construction period, two XF-104 prototypes flew. Using the data which these produced the design was modified (primarily by being enlarged) and several YF-104A service trial aircraft were produced. Note that the XF-104s were already setting records...

With the afterburning version of the J65 the second XF-104 prototype reached Mach 1.79. In fact, the prototypes set several speed and time-to-climb records, even though they were under-powered with a J65 engine and did not yet have the famous half-cone inlet shock ramps. (Which were so revolutionary that covers were placed over the inlets of early planes with them to hide the shape before photos were allowed.) 

Switching to the present for a moment, there have been many claims made about the F-22 Raptor. Unfortunately, in their enthusiasm the new fighter's supporters have said some things that just aren't true. For instance, it is not the first plane capable of maintaining level supersonic flight without using an afterburner. Many of the Century Series fighters could do this, though most of them just barely. Before the F-22 most supersonic planes were, indeed, designed to exceed the speed of sound for short dashes only. The F-22 is capable of maintaining Mach 1+ for much longer periods, in what is known as supercruise mode. (Flying supersonic without afterburner use.) Though that term came long after the F-104 did it. 

I haven't been able to verify the information, but I believe that late models of the F-104 with the J79-19 engine could maintain Mach 1.4 in level flight in military power (maximum throttle without afterburner). This isn't surprising when you realize that the J79 engine was vastly improved during the long production lifetime of the F-104, with later versions producing nearly as much thrust without afterburner as early models did with.

There was at least one civilian plane which could supercruise. The Concorde got enough range to cross oceans by only using the afterburners of its four huge engines for takeoff, climb and acceleration to cruise conditions. Once at cruise the thirsty afterburners were shut off and the plane supercruised for most of its flight. 

Performance of the production aircraft verified the Lockheed team's faith. An F-104A could take off, climb to 20,000 meters, accelerate to Mach 2 and fly at that speed for fifteen minutes, and still have plenty of reserve for descent and landing. All on internal fuel only. Adding wingtip tanks not only increased the fuel available, but decreased the drag, because they acted as endplates on those stubby wings, recovering some of the wingtip vortex energy. Later models of the J79 engine gave both more thrust and better fuel economy. Later models of the F-104 also had improved internal tankage, so they could cruise supersonic for even longer. 

The top speed of most fighters - even today - is limited by thrust (the F-16 has a much higher thrust-to-weight ratio than the Starfighter, but it also has a delta wing which is optimized for dogfighting, not supersonic flight) or airframe stability. The F-104 was restricted by heat in the compressor section of the engine. Early Starfighters could not exceed Mach 2.2 without damaging the engine; on later models this was increased to Mach 2.3. The canopy limit is Mach 2.6. The airframe on late models is stable out to Mach 2.8.

You will read in some references that the F-104 is not very maneuverable. Well, down low and going slow, it isn't. However, high and fast - which was where it was designed to operate - it is just about untouchable. Pilots of other aircraft flying practice dogfights against a Starfighter would get left behind when their opponent went into a climb they couldn't match. While they were trying to spot the tiny plane, it would suddenly dive on them from behind. It wasn't bad at turning, either, especially at high speed and altitude. The plane could drop flaps to takeoff position at an EAS (Equivalent Air Speed) of up to 523 knotts under any conditions. That's supersonic at altitude.

The F-104 was designed for supersonic flight. In fact, the inlets don't even start working right until Mach 1.4, at which point the pilots describe the plane as "going into passing gear." Above Mach 1 those tiny wings work very well, indeed. The plane is so supersonically smooth that pilots have reported passing Mach 1 by accident, and not even realizing it until they looked at their instruments. 

The Starfighter was intended as a point-defense fighter, a plane designed to deal with enemy fighters, bombers and attack planes trying to destroy an important facility. Yes, the plane is hard to fly, but a pilot who works at learning how can fly rings around almost anything else in the sky. So what did the Air Force brass tell Lockheed, after the plane had proved itself to be everything the company claimed? To make it carry bombs. Big ones, including the heavy nuclear weapons of the day. 

Does it seem to you that someone missed the point?

Well, Johnson did it. His team even devised a way for the F-104 to carry a single, large nuclear weapon under the belly. The thing nearly scraped the ground during taxiing, but the plane could deliver it as asked. The US Air Force unenthusiastically ordered a handful of the planes. Fortunately, it was also cleared for export, and Germany was very interested. 

Unfortunately, the German air force promptly crashed a large number of them. Fingers pointed, many of them at the downward ejection seat. Because the F-104 has a high t-tail it was felt that the upward ejection seats of the Fifties would not be able to get the pilot clear in all flight modes. So the unhappy solution of a downward ejection seat was used. This meant that if a pilot had an emergency at low altitude he had to either ride the plane in or try to roll upside down and eject. Neither of these were satisfactory solutions (a wheels-up landing in an F-104 buckles the frame at the cockpit, killing the pilot). Starfighter pilots were an especially tense lot during takeoffs and landings until later models used an improved, upward-firing ejection seat.

As it turned out, the problem with the German Starfighters wasn't the planes but improper pilot training. (Spain, flying the same planes on the same missions in the same weather over the same terrain crashed none during this period.) Once the pilots were given more appropriate instruction the safety record for the F-104 improved to about typical for fighters of the day. However, by this time the US military had already decided that the F-104 was not for it. This attitude would remain until the Lightweight Fighter concept became popular, eventually resulting in the adoption of the F-16. 

The Starfighter was still popular in many other countries - including Japan and Italy - though, and remained in production for several more years. In fact, Italy flew it as a front-line aircraft until 2005. Even then, it was retired not because it couldn't do the job, but because of a political agreement to participate in the Eurofighter program. 

Most countries which flew the F-104 have since declared it surplus. Not because it is inadequate, but because parts are becoming hard to find. Italy made its own parts for its F-104S, but this plane is not completely compatible with the older models, even being slightly larger. However, while enough parts to keep an entire air force's supply of Starfighters running are hard to find, scrounging what is needed for individual aircraft is pretty easy. Especially if the planes are demilitarized. 

For instance, there is a private company which does flight testing for NASA, performing such tasks as evaluating improved spacecraft atmospheric entry thermal tiles. They have an F-104B, the first two-seat version. Without armor, weapons and heavy military avionics, once the plane uses half its fuel it has a thrust-to-weight of better than 1:1. The main pilot loves the reaction he gets when the control tower advises private pilots approaching the airport where the plane is based that there is a Starfighter in the pattern behind them.

Oh, and about the title of this column: The official nickname for the F-104 is Starfighter. However, the favored nickname given to it by the people who fly it is Zipper. Because it... well, you get the idea. 

By the way, don't get the wrong impression about the comparison I made between the F-104 and the F-22. The latter plane is an improvement over the Starfighter in just about every way. Of course, it was designed some 40 years later.