F-5: Little Plane With a Big Future

Dec. 1, 1964

Airplanes that set new trends and leave a big mark on aviation often have stormy and uncertain births, but few of them can match the gestation record of the Northrop F-5.

The basic F-5 design (company designation N-156) survived more than seven years of no sales before the first production order. Northrop made its original pre­sentations to the United States government in 1955. The company has been selling hard ever since then, but the airplane did not start getting official acceptance until the fall of 1962, and it is not clue to enter wide service until 1966.

The bright spot in the design’s early history was its selection, in slightly modified form, as the USAF’s supersonic trainer, the T-38. This 1958 sale was a large one, and it kept the fighter design alive. More than 460 T-38s have been delivered, another 174 have been funded, and still another 126 have been programmed but are not yet covered by a contract, bringing the total to more than 760 aircraft.

In spite of this success as a trainer, however, many aviation people, as little as two years ago, considered the F-5 in its fighter-bomber configuration a dead project. At that time it was argued strongly that the F-5 would never he considered for first-line missions by either the US or NATO air forces, primarily be­cause of a relatively low top speed and maximum alti­tude. The F-5 is a Mach 1.4, 50,000-foot-altitude air- plane, and most of the USAF Century-series fighters are at least 300 mph faster and can operate above 55,000 feet. Most important, the N-156 lost out in key competitions during 1958 and 1959, which ended with the Lockheed F-104 being selected as the new standard fighter for the Netherlands, Norway, Japan, Canada, and West Germany.

Today, the picture has changed remarkably. Since the DoD’s 1962 evaluation of the F-5 as a possible fighter-bomber to be supplied to allied nations under the Military Assistance Program (MAP), more than 250 of the aircraft have been ordered for Korea, the Philippines, Taiwan, Iran, Turkey, Greece, and Nor­way. The F-5 even has begun to eat into the F-104 market. In response to a Norwegian request, the US is allowing that nation to return one of the F-104G squad­rons it was to have received and “exchange” it as par­tial payment for sixty-four F-5s. Norway is paying the balance of that purchase.

Prospects are good for further F-5 orders. Several nations still are evaluating the aircraft, as is the USAF’s Tactical Air Command, and there is general enthusiasm over the airplane.

At first glance, the reasons for this latter-day enthu­siasm are not apparent. Certainly, the F-5 does not fit the classic description of a pacesetting airplane with great portent for the future. In the past, its ten­-year-old design and far from record-contending speed and altitude performance would have made it an also-ran in the eyes of most military officers for most types of interceptor, air superiority, ground-support, or re­connaissance duty.

But selecting aircraft today is not as simple as it was in the past. Speed, maneuverability, and load-carrying capacity are more important for many mis­sions than high performance at high altitude. The ability to get combat tasks done depends on missile and ground environment as well as on aircraft perfor­mance. Costs are being brought into the weapon se­lection process as never before.

Every new aircraft from the counterinsurgency COIN through the TFX to the new strategic bomber proposals has suffered from disagreements over selec­tion criteria.

The arguments are not going to be settled easily. But there can be little doubt that the F-5 and some of its basic design ideas are going to exert considerable influence on future combat aircraft—bomber as well as fighter. There are sound reasons why the F-5 now is acceptable as a first-line aircraft even though it was passed over a few years ago. There are equally good reasons to expect that the F-5, despite its ten-year-old design, will have unusually long life as a first-line aircraft. And there are also good reasons for believing that the general F-5 design philosophy will become more prevalent.

Basically, the F-5’s appeal rests on the fact that it is the most successful “small” airplane yet developed. It has taken the “lightweight” philosophy to new limits. None of the designers who have expounded the “light­weight” theory in recent years has done as well as Northrop with the F-5. There are two prime “light­weight” examples. The first is the Douglas A-413, which was designed by Ed Heinemann, weighs about 16,000 pounds, and first flew in 1954; the other is Great Britain’s Folland Gnat, weighing in at less than 10,000 pounds.

The main objective with small aircraft has been to reduce production costs, fuel consumption, and oper­ating costs, all of which normally take a big downturn as airframe weight and engine power are lowered. Some sacrifice in maximum speed, altitude, and pay­load-range performance usually has been necessary to get size and costs down to a minimum, but the cost/ effectiveness of “lightweight” aircraft generally has been rated high for many fighter missions.

The F-5’s superiority as a “lightweight” comes mainly from its superior powerplants. From the beginning of the design in 1954 Northrop contended that only two engines in development, or even being considered for development, would be light enough to give a small aircraft truly outstanding performance. These were mis­sile engines, the Fairchild J83 (scheduled for the long-canceled Goose) and the General Electric J85 (under development for the Green Quail). Only the J85 reached production, and the Northrop design activity was in­strumental in expanding the program to include devel­opment of a long-life, afterburner version suitable for supersonic manned aircraft.

The resulting engine is impressive. Each J85—GE-13 in the F-5 produces 4,080 pounds of thrust yet weighs only 585 pounds. Its thrust-to-weight ratio of 7 to 1 is by far the highest of any operational gas turbine today. By comparison, the Orpheus engine in the Gnat has a 4.8 to 1 thrust-to-weight ratio, and the US-built Sap­phire in the A-4D is even lower, at 3.5 to 1.

A substantial reduction in aircraft size has been achieved by Northrop through use of the J85. It is dif­ficult to be exact about this reduction, but it is in the neighborhood of 5,000 to 6,000 pounds according to an old rule of thumb. This is the rule that says that if the F-5 were powered by engines with a thrust-to-weight ratio of 3.5, or half that of the J85, the aircraft’s engine weight would go up immediately by more than 1,000 pounds. This added load would necessitate an increase in structural weight. Fuel weight also would have to go up if the range were not to suffer. This added weight would call for a heavier, more powerful, engine to keep top speed from dropping. Experience has shown that the spiral of engine, structure, and fuel weight increase results in a total aircraft weight of five to six pounds for every pound of dead weight that must be added in any form.

By this rule, the F-5 should fly as fast, climb as rap­idly, and carry as big a load over as great a range as an aircraft that weighed 5,000 to 6,000 pounds more but was powered by engines only half as efficient from the thrust-to-weight standpoint and about equal in the fuel-consumption department. Applying this rule is tricky because excellence of aerodynamic and structural de­sign and the weight of electronic systems and acces­sories also can have a large effect on aircraft weight.

The fact that Northrop has taken commendable ad­vantage of the J85’s potential can be illustrated by comparing the F-5 with the F-100. The first F-100 flew in 1953. Its C model has a powerplant thrust-to-weight ratio of about 3.5. Takeoff weight is around 30.000 pounds for most missions, yet the F-100C is directly comparable to the F-5, which takes off in the clean configuration at 12,000 pounds and has a maximum flight weight of 20,000 pounds.

Maximum ordnance payload is 5,000 pounds for the F-100C and 6,200 pounds for the F-5A. For most attack missions their range-payload performance is compar­able. The F-5A is 0.03 Mach number faster in level flight. It lands twenty knots slower and it has a 28,600 feet-per-minute (fpm) unaccelerated rate of climb at sea level, compared with 19,000 fpm for the F-100C.

The F-5’s small size gives it an extremely powerful cost/effectiveness advantage in lower fuel consumption. It uses about thirty percent less fuel on any given mis­sion than the F-100. Such a logistical savings is difficult to ignore in modern operations. For instance, in a thirty-day emergency operation an eighteen-airplane F-5 squadron would use 2,700,000 pounds of fuel, or 1,380,­000 pounds of fuel less than a similar F-100C squad­ron. This does not include the fuel consumed in de­livering the squadron’s supply.

Northrop pushed hard to expand the F-5’s basic cost advantage. Every effort was made to make maintenance simple and to keep the required mechanics’ skills rela­tively low. Maximum use was made of early Century-series flight experience in developing a configuration which has exceptionally docile handling characteristics at both subsonic and supersonic speeds. Twin-engine design was planned from the first to improve the attri­tion rate as well as to keep the engines small.

The accomplishments of this effort include a T-38 accident rate that is the lowest of any USAF supersonic aircraft. Large-scale T-38 operations have demonst­rated an operational readiness around seventy-four percent, at a utilization rate of sixty hours per month and a maintenance man-hour expenditure of about eleven hours per flight hour.

Maintenance materials costs for the F-5A are about $45 per hour, or about the F-84 and F-86 level compared to more than $100 per hour for the F-100 and nearly $250 for some Century-series fighters. Direct maintenance man-hours per flight hour again is at the F-84, F-86 level and about half that of the F-100.

Personnel strength (less pilots) of an F-5 squadron is forty-two percent less than an F-100 unit—144 men to 210. On an equivalent manning basis it would be possible to operate seven F-5 wings with the personnel of four F-100 wings.

When all costs are considered—fuel, personnel, training, maintenance, attrition, etc.—a unit of 400 F-5s could be operated for seven years for forty-eight percent less than an equal number of F-100s.

Over-all the cost arguments for the F-5 are about as impressive as those ever advanced for any airplane. Certainly, it has ushered in a new era of low-cost supersonic operations and has set some standards that are going to be difficult to top in the future.

Undoubtedly, the sales effort on the F-5 was slowed because the savings claims were so large and because they were the key selling points. Airplane performance data is relatively easy to come by with a prototype or two, but it takes years to gather reliable, verifiable cost data that can stand up under the type of checking and rechecking common today in military evaluations. Without the good services of the T-38 trainer force it probably would not have been possible to bring the F-5 costs down to their present level and to verify them adequately.

The continuous reappraisal of military requirements during the last ten years also has had its effect on the pace of the F-5 program. Today, it has become acceptable to divide military operations into at least three basic types which overlap considerably. They range from Vietnam-type guerrilla actions through large Korean-type operations to general or all-out war.

Each type places unique requirements on airpower. The COIN fighter, recently contracted to North American for development, is the first recent design aimed for guerrilla wars. The F-5A is among the aircraft now being evaluated by the Tactical Air Command as a “super-COIN,” which could control the air effectively and inexpensively in Korean-type operations.

Broadening military requirements has broadened the attractiveness of the F-5, which also would be useful in a general war. For instance, in the words of the Norwegian government, the F-54s considered on the basis of “an over-all evaluation of cost and operation more suitable for the tasks of the Norwegian Air Force,” which includes defending against a swiftly striking, nuclear-armed attacker. Northrop reports that the Norwegian flight tests showed that an F-5 was able to handle the faster F-104 consistently by using its superior turning and climbing ability at most altitudes to stay in position to launch its missile armament which compensated for the speed disadvantages.

Certainly there won’t be universal agreement about the validity of the Norwegian tests, but it does illus­trate some truths about airpower and point up some reasons why the F-5 probably will be around for many years. Air warfare today, of the super-COIN and gen­eral war varieties, is much faster than anything of the past. Missiles have not taken it over by any means. Tactical doctrine, imaginative leadership, swift deci­sions, numbers of aircraft, human skill, courage, and perseverance count more than ever. The true criterion of performance is getting the job done. And it does not necessarily follow that the fastest airplane at 40,000 feet will meet this standard.

High theoretical survivability during ground-support operations is another advantage credited to the F-5. The F-5’s small-size, high-speed, twin engines appear to give it a significant and at least an officially un­recognized advantage in this type of operation, which is critical across the complete spectrum of hostile air operations from COIN to general war.

Two new F-5 models now are being offered—one the “Improved F-5” and the other the “STOL F-5.” The first one features about five percent more engine power than the F-5A, a “maneuvering” flap to cut down turn radius, more advanced fire control, and other improve­ments. The STOL version has J85s uprated to provide twenty-two percent more power than the F-5A’s en­gines, increased wing area, and the other features of the “Improved” model. Takeoff distance drops from 2,410 feet to 1,190 feet on the clean STOL configura­tion. Ferry range goes up from a maximum of 1,515 nautical miles for the F-5A to 2,400 for the STOL F-5.

Other improvements undoubtedly will be made in the future to increase the airplane’s utility and service life. However, one fact over which Northrop has no control probably will be the biggest factor in giving the F-5 a long, useful life. This is the sad shape of the US gas-turbine development program. The Air Force and Navy programs have both slowed down drasti­cally since the middle 1950s. The only really advanced work has been done in the Air Force’s lightweight gas-turbine technology program, which has resulted in the construction of “demonstrator” engines by five manufacturers. These engines feature advanced compres­sors, combustion chambers, and turbines. The basic objective in each is to use a level of technology that is at least twice that of any operational engine. While this program is a major step in building technology the “demonstrator” engines are far from operational mode

Extensive and expensive development programs will be required if we are to put any of these advanced ideas to use.

No plans for developing these engines have been approved. It will be many years then before engines are ready which have thrust-to-weight ratios signifi­cantly better than the J85. Until then it will not be possible to build a “lightweight” fighter significantly better than the F-5.

F-5 Family Comparative Performance Summary

F-5A

Improved F-5

STOL F-5

Sea-level Static Thrust

Engine

Pounds

J85-GE-13

4,080

J85-13/J5

4,300

J85-J1A

5,000

Takeoff Gross Weight (Clean)

Pounds

13,000

13,550

16,892

Empty Weight

Pounds

7,733

8,283

10,609

Takeoff Distance

Feet

2,410

2,050

1,190

Sea-level Rate of Climb

Feet Per Minute

28,600

29,500

29,400

Maximum Speed

Mach Number

1.40

1.42

1.50

Touchdown Speed

Knots

130

135

99

Landing Distance

Feet

2,050

2,150

1,500

Ferry Range

Tanks Dropped

Tanks Retained

Nautical Miles

1,515

1,230

1,495

1,215

2,400

1,710

Basic performance figures on the F-5A, the “Im­proved F-5,” and STOL F.5 are listed at left. Performance gains are achieved with more pow­erful engines and a larger, more efficient wing on the STOL F-5. Both new aircraft also would have large “maneuvering” flap to make tighter turns.

Tactical Ordnance for the F-5

A major F-5 requirement is to upgrade allied air forces receiving aircraft under the Military Aid Program (MAP) by providing supersonic interceptor, air superiority, and reconnaissance capability while performing all of the heavy ground-support missions now accomplished by F-84 and F-86 fighters. More than fifteen basic combat ordnance loads and two training loads are now provided for the F-S. The maximum ex­ternal load is 6,200 pounds, and it is exclusive of the two M-39 20-mm. cannon and ammunition totaling 420 pounds. The major loads that can be carried in various combinations include:

• Two GAR-8 Sidewinders.

• Two Shrike antiradar missiles.

• Four GAM-83A Bullpups.

• Three Walleye guided bombs.

• Fourteen 30-gal. napalm containers.

• Five 110-gal, napalm containers.

• Sixteen 250-lb. bombs.

• One 2,000-lb. bomb, two 1,000-1b. bombs, and two 750-lb. bombs.

• Four rocket pods.

• Bomblets-5,500 lb. total.

• Four special stores.