The F-16 is a revolutionary aircraft. It represents a major change in fighter design. Its fine blend of high technology and common sense requirements emphasizes flight performance-range, persistence, and maneuverability – right in the heart of the flight envelope where air combat takes place. The aircraft’s "user-friendly" cockpit and integrated avionic system allow a single pilot to fight and win in aerial combat. The design also emphasizes low cost in procurement, in operation and support, and in provisions for growth. The F-16 introduced many successful technologies. Fly-by-wire and relaxed static stability gave the F-16 a quantum leap in air combat capability over other fighters when it was introduced and this technology still makes the aircraft an unmatched competitor today. The F-16 disproved the adages that bigger was better, that a lot of capability had to be expensive, and that sophisticated systems rarely worked.
Harry Hillaker deserves much of the credit for this revolutionary approach to fighter design. You might say that the F-16 began as a spare-time project for this veteran designer. Back in the mid-1960s, Hillaker spent his off hours designing the plane of his dreams – a lightweight, high-performance jet that could fly circles around all other fighters. His spare-time project turned into an obsession. The obsession became a reality. Today it is a standard – a plane by which others are measured.
Though Hillaker retired in 1985, after forty-four years of design work, he remains active as a consultant to the US Air Force and industry. In 1990, he was inducted into the prestigious US National Academy of Engineering for his achievements. He spent two terms as chairman of the Aerospace Vehicles Panel of the Air Force’s Scientific Advisory Board. Hillaker, who lives about ten minutes away from the F-16 production line in Fort Worth, is always pleased to talk about the F-16 and his part in its development.
In the late 1960s, you found yourself involved in what was called the "fighter mafia." Where did that name come from?
That was the title given to the small group of people responsible for the conceptual design of the lightweight fighter, what became the F-16. The group had three core members: John Boyd, Pierre Sprey, and me. We were given the "mafia" title by people in the Air Force back in the mid-60s. We were viewed as an underground group that was challenging the establishment. We were a threat of sorts.
What made the fighter mafia threatening?
We wanted a change. While most of the Air Force was interested in going north, we wanted to go south. More specifically, they were concerned that we were trying to introduce a new fighter that would jeopardize the F-15.
You see, the F-15 was the first air-superiority fighter that the Air Force had put under contract in twenty-five years. They were committed to the F-15. They felt strongly that our airplane was just a hotdog airplane that was good only for air shows on sunny Sundays at the state fair. This view was strengthened to a degree by their experience with the Lockheed F-104. The F-104 was a really hot airplane that people loved to fly, but it didn’t have much capability and not much range. The Air Force bought only 300 of them.
We were threatening for another reason. We were perceived as being anti-technology. Our slogan was "make it simple." The slogan itself may have been an oversimplification. We didn’t articulate ourselves well early on.
Does technology discourage simple approaches in aircraft design?
There have been debates through the years about just how much technology should be incorporated in any design. The real issue isn’t technology versus no technology. It is how to apply technology. For example, the F-15 represents a brute-force approach to technology. If you want higher speeds, add bigger engines. If you want longer range, make the airplane bigger to increase the fuel capacity. The result is a big airplane. The F-15 was viewed as highly sophisticated because it is so big and expensive. In my mind, the F-15 wasn’t as technically advanced as the F-4.
The F-16 is much more of an application of high technology than the F-15. We used the technology available to drive the given end, that is, or was, to keep things as simple and small as we could. Our design was a finesse approach. If we wanted to fly faster, we made the drag lower by reducing size and adjusting the configuration itself. If we wanted greater range, we made the plane more efficient, more compact.
What are the advantages of simple and small?
In general terms, it translates into lower weight, less drag, and therefore higher performance. Also, a fundamental indicator of an airplane’s cost is its weight.
We were well aware that the avionics folks would be putting a bunch of gadgets in the airplane, which would increase weight and decrease performance. We stacked the deck. We made the airplane so dense that there wasn’t room for all that stuff.
As it turned out, our high-density design was one of the things that looked as though it might hinder the advancement of the airplane. It was later graded on the amount of unusable space. We had 4.8 cubic feet. The F-15 had almost ten times that.
Another reason, besides weight, favors small size. Smaller aircraft have less drag. People always talk in terms of drag coefficients. But drag coefficients really don’t tell you that much. For example, the drag coefficient of an F-16 is about the same as that of an F-4. However, the F-16 has about one-third the drag of an F-4 in level flight. At angle of attack, it is about one-fifteenth. The airplane’s exceptional maneuverability is a consequence of that lower drag and a higher thrust-to-weight ratio.
How were these relationships used in the development of the lightweight fighter?
My first dealings with John Boyd and Pierre Sprey did not involve any airplane designs per se. Our early work was purely and simply an analysis of the relationships of wing loading and thrust loading and fuel fraction (the ratio of fuel capacity to the weight of the airplane). We wanted to understand the relationship between these variables. We knew that we wanted low wing loading and high thrust loading. But we also knew that low wing loading means more weight and more drag. High thrust loading means high fuel consumption.
Airplanes with high thrust-to-weight ratios are normally equated with short range. That’s why we started looking at fuel fractions. We wanted to tie all these things together to get a better feel for the boundaries involved.
Had anyone looked at the problem this way before?
I would say that people had thought about it, but no one had applied it systematically to get a complete picture.
We were trying to determine the trends. We didn’t spend a lot of time looking for exact values. It is one thing to agree that something is better. But how much better is another question. The answer involves finding a trend and asking more questions. Is the design being improved by these actions? How fast is it improving for a given amount of change? The person most responsible for this approach was John Boyd.
What were some of the conventions the fighter mafia challenged?
Range was associated with fuel capacity. High speed was associated with bigger engines. Technology was associated with complexity. Twin-engine designs were considered safer. Size and cost were associated with capability. These were the reigning over-simplifications of the day.
Why were they accepted as truth?
People tend to focus on one part of a given parameter. You can, for example, get a higher thrust-to-weight ratio by increasing the thrust. You can also get a higher thrust-to-weight ratio by leaving the thrust alone and reducing the weight, which is what we did on the lightweight fighter.
We had to take this approach because we had to use a given engine, the F100, which had been developed for the F-15. John Boyd had played a part in defining that engine, and he felt comfortable with it. So the engine was fixed. That meant that the thrust was fixed. If we wanted a high thrust-to-weight ratio, we had no choice but to reduce weight.
The range equation can be treated like the thrust-to-weight ratio. The typical approach to increase range is to simply increase fuel capacity. But increasing fuel capacity increases volume, which means more weight and more drag. People think that big is better. It’s not. With the lightweight fighter, we wanted to achieve our ends through different means. We increased range by reducing size.
Did those involved in the early days of the lightweight fighter program take such a historical perspective?
Boyd and Sprey did two things in this respect. Sprey collected all the data he could get his hands on concerning fighter aircraft reliability and effectiveness. They also collected cost data. They were the first people I know of who took Air Force cost data and plotted it against time.
They started with the P-51 Mustang. The minimum increases in cost in jumping from one airplane to another was a factor of 1.9. The increases were as high as 3.1 in same-year dollars. The data showed the increment involved in going to jet engines, to swept wings, to supersonic, missiles, and big radars. It showed the difference between this airplane and that airplane and the effect of these differences on cost.
The cost per pound of succeeding airplanes went up at the same rate as the overall cost. This is true even for the F-16. That is, if I plot a curve of cost per pound for succeeding aircraft, the F-16 is right on the curve. Its increment of cost per pound has gone up the same as any other airplane. However, if I plot a curve of unit flyaway cost, the F-16 falls off that curve. It reversed the upward trend in unit flyaway cost. It was the only aircraft to do this. So the way we got the cost down was by getting the size down. That was another motivation for reducing size.
How was this design approach different from the norm?
We usually rush into form before we really understand what the function is. That gets us in trouble. The lightweight fighter brought a new perspective to maximum speed and acceleration. Everyone wanted airplanes to go Mach 2 to 2.5. No one asked why.
I had the opportunity one time when we were working on the supersonic transport to track all the supersonic flight time on the B-58.
We had over one hundred B-58s flying, and the most supersonic flight time on any one airplane was seven hours. Seven hours. This was less than five percent of the total flight time. The entire fleet had a total of only 200 hours supersonic.
A lot of people equate flying top speed with acceleration. Big engines, for those setting the requirements, meant high speed and high acceleration. This is not a true relationship. With the F-16, we addressed function first. We asked, what value is derived from a given capability?
What was the riskiest portion of your lightweight fighter design?
The fly-by-wire system. If the fly by wire didn’t work, our relaxed static stability wasn’t going to work. And then the airplane would have had higher drag and would have been less responsive, less maneuverable.
We had a backup that not too many people know about. We designed the fuselage so that if the fly by wire did not work, we could go back to a statically stable design by moving the wing back. We had bulkheads in the fuselage that were designed to carry the load of both placements of the wing.
Were other companies looking at fly-by-wire control systems?
McDonnell Douglas had contracts with the Air Force and with the Flight Dynamics Lab for test programs for fly-by-wire systems, relaxed static stability, and the high-acceleration cockpit for the F-4. The technology was available, but these companies didn’t take advantage of it.
Shortly after we won the full-scale development contract for the F-16, I was invited to give a talk to the St. Louis chapter of the American Institute of Aeronautics and Astronautics. My initial response was, You must be kidding. You want me to go into the lion’s den? McDonnell Douglas did all kinds of advertising and everything else that was anti lightweight fighter. My immediate reply was, thanks but no thanks.
About fifteen minutes later, I got a call from Dave Lewis [then-chairman of General Dynamics Corporation]. He said, Harry, I hear that you’re giving a talk on the F-16 up here to these McAir guys. That’s great. I want you to give them hell, and I’m going to be there to see you do it.
I called the AIAA guy back up and said I had second thoughts. A presentation might be fun. I didn’t really think that. But I’m influenced by politics, too.
A couple of days before the meeting, the program chairman said that the chapter had sold more tickets to that meeting than to any other past meeting, even meetings with astronaut speakers. He said they had over one hundred coming from McDonnell Douglas alone. You can imagine how I felt.
I gave the talk. After about an hour of questions and answers, the program chairman interrupted to let those who wanted to leave, leave. Two hours after that, the hotel manager came in the room and asked us to leave because they had to set up the room for a breakfast the next morning. At 2:30 in the morning, about fifteen McAir guys and I closed the bar. These were the same people who worked on fly by wire, relaxed static stability, and the high-acceleration cockpit, all the test programs the Air Force and its Flight Dynamics Lab had conducted for the F-4, which McDonnell had the contract for.
Now here’s McDonnell building the F-15, the world’s latest-greatest fighter, which did not contain one of these technologies. I had 125 McDonnell guys who were more interested in the F-16 than they were in their own F-15 because they saw the fruits of their labors being incorporated in my airplane.
Why didn’t they incorporate these technologies?
The F-15 was very expensive. It had been twenty-five years since the Air Force had had an air-superiority fighter. It had taken more than five years just to get the program approved. They couldn’t afford to take any risks.
How was it that you could take these risks?
The contract for the lightweight fighter prototype was for a best effort. We did not have to deliver an airplane, legally. Once we spent our $3 million, we could have piled all the parts on a flatbed trailer and said to Mr. Air Force, here’s your airplane.
We could fly the airplane when we were ready to fly it. We pushed for a flyable airplane because we were competing against Northrop. But my point is that we were not working against a difficult, but arbitrary schedule. And most schedules are arbitrary. Furthermore, there was no fixed follow-on. The airplane was simply a technology demonstrator.
Why was Northrop unwilling to take the risks involved with the new technologies in their prototype for a lightweight fighter?
Northrop wanted an airplane to replace their F-5. They were more interested in sales to foreign markets and stayed very rigid and conservative in their design because they wanted to be able to show their foreign markets the airplane at any point in its design.
We were interested in what the US Air Force wanted, and we stayed flexible in the design to respond to their needs. We looked at a number of designs. We waited until the very last to choose the best one. We could afford to put these advanced technologies into the airplane. We were more apt to accept the risk.
A number of companies were caught off guard by our winning the lightweight fighter prototype contract. They were out there promoting their ideas around the Air Force. We weren’t. We were deliberately quiet about what we were doing because we were handicapped with a bad reputation, though quite undeserved, from the F-111 days. We couldn’t brag. Instead, we quietly did our homework and did it thoroughly.
We were ready to fly the lightweight prototype on 1 February 1974. We found out Northrop wasn’t flying until June or July. That really worried us. We first thought that they had one-upped us. Their design is a production design, we thought, not a prototype. In actuality, they were just behind. One of the reasons the Air Force eventually chose our design was that it was closer to a full-scale development than Northrop’s.
Are you comfortable with the title "Father of the F-16"?
I’m flattered by it. As its father, I had the best part, providing the sperm. Now the gestation period and much of what happened later was something else. Other people can take credit for what happened there. My interest in airplanes is the external shape. I’m not that interested in what goes inside, except as how it affects the outside shape.
Interviewed by Eric Hehs, Managing Editor/Code One