Era of the Starfighter

Jan. 1, 1987

We’re on the threshold of something marvelous in aviation. The era of the starfighter is upon us. I’m not talking about tech­nologies of the year 2100. I’m talk­ing about technologies that are with us right now.”

Lt. Gen. William E. Thurman, Commander of Air Force Systems Command’s Aeronautical Systems Division at Wright-Patterson AFB, Ohio, made that statement not long ago in reference to AFSC’s role in developing the hypersonic National Aerospace Plane (NASP), a joint undertaking of the Defense Depart­ment and the National Aeronautics and Space Administration in which ASD has much of the action.

General Thurman’s context was much broader, though, in the sense that the work on the aerospace plane does not stand in splendid iso­lation from all else that ASD is doing or has ever done in developing mod­em, high-performance combat air­craft for the Air Force.

The NASP promises to be a breathtakingly unprecedented fly­ing machine, at home in air or space, streaking through the upper atmo­sphere at twenty-five times the speed of sound or thereabouts, its airframe, engines, and avionics in­tegrated into a coherent system of thoroughly interdependent ele­ments.

For all its potentially peerless attributes, the NASP will not emerge t as a technological creature wholly alien to the aeronautical world as we know it today. Its technologies will have filial connections to those of the fighters of this generation and 4 the next.

The F-15, more than a decade in service and still the best air-superi­ority fighter in the world, heads the family. Its latest variant, the F-15E dual-role fighter newly in produc­tion, will do both the air-to-ground and air-to-air missions behind en­emy lines better than any US fighter ever.

The F-16, singularly adept at ground attack and no slouch in the air-to-air regime, either, has demonstrated that “smaller” is no longer synonymous with “lesser” in terms of fighters’ combat ranges.

Late last October, USAF decided to modernize its air defense fighter force with modified F-16As already in service in tactical squadrons.

Their combat-range capability was an important consideration in their selection over the competing F-20, Air Force officials said.

The F-16As destined for conver­sion to the air defense mission will be replaced in ground-attack squad­rons by the newer, more capable, and more versatile F-16Cs. They and the F-15Es will eventually be equipped with the Low-Altitude Navigation and Targeting Infrared for Night (LANTIRN) system that ASD has escorted through some technological thickets to the point of full-scale production. (See also “Fighting Around the Clock” on p. 52 of this issue.)

Next comes the Advanced Tac­tical Fighter (ATF), the apple of ASD’s eye and legatee of just about everything ASD and its contractors have learned in creating and im­proving the F-15 and the F-16.

Northrop (teamed with McDon­nell Douglas) and Lockheed (team­ed with General Dynamics and Boe­ing) were chosen last October by USAF to build two ATF prototype aircraft each. Prototypes will be fly­ing two years from now.

All these fighters are the NASP’s progenitors. The NASP’s technolo­gies of fuels, engines, structural ma­terials, aerodynamic shapes, avi­onics, and—perhaps most impor­tantly—systems integration will have had their origins, however brightly or dimly, in ASD’s work on the technologies of the F-15, the F-16, and the ATF.

Among innumerable examples of this are the research programs of ASD and its contractors on high-strength, heat-resistant alloys and cooling techniques for advanced fighter engines, on nonmetallic ma­terials for engines and airframes, on the integration of aircraft avionics, on the use and integration of experimental aerodynamics and avionics as in the Advanced Fighter Technol­ogy Integration (AFTI)/F-16 and X-29 forward-swept-wing aircraft programs, and on variable-camber wings as in the AFTI/F-111 pro­gram.

AFTI/F-111 officials at ASD claim that the F-111s on the Libya raid of last April could have been back home an hour earlier, or could have forgone two of their aerial re­fuelings, had they been equipped with the mission-adaptive wings (MAWs) now being successfully tested in the ASD program.

Among other ASD projects ger­mane to the development of the ATF and probably to the NASP as well are those on very-high-speed integrated circuits (VHSIC) as part of the rapid advances in microchip technology, on software that is so important to the automation of air­craft, on cockpit technologies that enable pilots to take full advantage of such automation, and on artificial intelligence (AI)—a technology that General Thurman says “is becom­ing synonymous with advanced aeronautics” and that ASD is just now beginning to get in hand.

The NASP’s developers will bor­row from ASD’s books on all these projects. Moreover, it is likely that the NASP program itself will con­tribute technological insights to other ASD programs, most notably to the ATF program somewhere along its way into the twenty-first century.

There are those who say that the advent of the presumably world-beating NASP will mean the end of fighters as we know them today and that the ATF will be the last of their long, evolutionary line.

Rearranging the Molecules

ASD is taking nothing for granted in this regard. Its laboratories are nurturing technologies applicable to both the NASP and the ATF pro­grams, but they are also continuing to pursue technologies that may someday apply to flying machines not yet envisioned.

For example, ASD’s Aero Propul­sion Laboratory and Materials Lab­oratory are looking beyond the ATF in their research on highly advanced turbine engines and on exotic mate­rials, respectively, for superswift jet aircraft that would not necessarily transcend the atmosphere in the manner—or with the hybrid rocket/ scramjet air-breathing engines—now planned for the NASP.

Both laboratories are in the busi­ness of rearranging the molecules of Mother Nature’s chemical ele­ments. Their goals are endothermic “designer” fuels that will absorb heat rather than give it off and mate­rials of enormous strength, of mal­leable ductility, and of mighty resis­tance to heat.

Such materials and fuels would be an unbeatable combination in the powerplants of high-performance aircraft, and the materials could be made into aircraft skins virtually impervious to heat and stress.

In one portentous project, the two laboratories are working to­gether, as an Aero Propulsion Lab paper puts it, “to demonstrate a rev­olutionary advancement in turbine engine technology through the 1990s.”

Their goal is to devise fighter en­gines capable of doubling the thrust-to-weight ratios of the engines now being developed by General Elec­tric and Pratt & Whitney, also in prototype-construction competi­tion, for the ATF.

Those ATF engines will greatly surpass the engines of the F-15 and the F-16 in terms of their thrust-to-­weight ratios measured at supersonic speed and high altitude. They will enable the ATF to cruise super­sonically over long distances with­out using fuel-gulping afterburners, an impossibility with existing fight­er engines.

All such advances in the propul­sion world will lead to dramatic im­provements of USAF’s warfighting prowess.

“We’re not going to be range-lim­ited any more,” General Thurman asserts. “We’ll be able to pack much more energy into fuels. This has tre­mendous implications for aircraft designs.”

Among other things, it means that “our younger officers, in their Ca­reer lifetimes, will probably see air­planes the size of F-15s going in and out of space,” the ASD Commander asserts.

ASD itself is on afterburners in preparing for this and for more in the aeronautical arena.

“We’ve never had a better re­search program in our labs, and we’re focusing our lab efforts on applied research,” General Thurman .5′ explains. “There’s a new excite­ment, a vibrancy, at Wright Field, I because our people are working di­rectly on the technologies that we’ll need in the airplanes we’re going to field in the coming decade and in the early years of the 2000s.”

The principal draws upon those technologies are the NASP program, the ATF program, and the Strategic Defense Initiative (SDI) program, in which USAF is a fea­tured player.

General Thurman calls these programs “huge technological kickers” and includes among them, as well, the VHSIC program and the Air Defense Initiative (ADI) program that USAF sees as a necessary comple­ment to SDI.

Serving as clearly delineated aim-points for ASD’s scientists and engi­neers, all such programs “give us focus for what in the past we always saw through a glass darkly,” General Thurman declares.

ATF Avionics Integration

A prime example of how ASD’s major systems development pro­grams are now enfolding technolo­gies once confined to its laborato­ries is that of avionics integration in the ATF.

ASD’s Avionics Laboratory has worked for several years on the Pave Pillar program, in which its contractors defined a generic archi­tecture for the automation and inte­gration of aircraft avionics subsystems—combining, for example, fire controls and flight controls, along with navigation systems, elec­tronic warfare systems, propulsion controls, radars, and cockpit con­trols and displays.

This program encompasses the Avionics Lab’s development of the Integrated Communications, Navi­gation, and Identification Avionics (ICNIA) system, a project aimed at combining into a single, highly reli­able radio all of the variegated communications that modern combat aircraft must rely on and manage.

The Avionics Laboratory com­pleted the design specifications for the Pave Pillar system and has now handed it over to the ATF program office for development and incorpo­ration into the fighter.

The eventual extent of such incor­poration will be determined in the competition between the two ATF contractor teams. Each has been as­signed by the Air Force to build and test ATF avionics-suite prototypes along with—and apart from—their aircraft prototypes.

“It may take longer to bring on the avionics prototypes than it will to bring on the airframe and engine prototypes,” General Thurman says. “Avionics may turn out to be the long pole in the [ATF] tent.”

ASD’s experience with the B-IB bomber taught it not to take for granted that a new aircraft’s avi­onics will need less time in develop­ment, solid advances in microchip technology notwithstanding, than will its airframe and engines.

In the B-IB, says General Thur­man, “we packed all the offensive avionics in the front of the airplane and all the defensive avionics in the back and expected it all to work to­gether when we turned on the switches.”

Instead, it turned out, for exam­ple, that some of the bomber’s trans­missions were picked up by its re­ceivers. This entailed rearrange­ments and better integration of its avionics systems.

Regarding the transition of tech­nologies into systems, some Air Force officials are concerned that the major, blue-ribbon systems pro­grams at ASD are preempting al­together too many of the laborato­ries’ advanced development proj­ects, perhaps prematurely. Some also fear that the Air Force, in its increasing emphasis on applied re­search amid a budget crunch, is drifting away from basic research.

Both trends threaten the labs and, in consequence, their development of the technologies that USAF will need for far-future systems distinct from those now soaking up technol­ogies and resources, such critics claim.

General Thurman doesn’t buy it. “We’re spending more money on basic research at ASD than we ever have,” he declares.

The General also notes that ASD is responsible for working up nearly three-fourths of the seventy ad­vanced technologies and advanced systems concepts that AFSC’s Proj­ect Forecast II study selected as having the potential to “revolution­ize the way the Air Force carries out its mission in the twenty-first cen­tury, guaranteeing continued tech­nological supremacy over any po­tential adversary.”

Thanks to Forecast II

Keith Collier, ASD’s deputy for development planning, tips his hat to the Forecast II study for having “provided us with a very rich set of identified technology potentials.” His shop is mating Forecast II’s technologies and systems concepts with what it perceives to be USAF’s future requirements for them in terms of missions and is reshaping its studies accordingly.

Among the topics of such studies are cruise missile defense, non­nuclear strategic forces, unmanned systems, and “mission/flight sys­tems integration, which anticipates that the next-generation avionics in­tegration will be an order of com­plexity out beyond that of the ATF,” Mr. Collier says.

Forecast II lends leverage to all this. AFSC’s commitment to solid support and funding of the develop­ment of Forecast II technologies and systems bodes well for USAF’s research community and should not be taken lightly, General Thurman claims.

“We’re in the glory days of ASD right now,” the General asserts. “On just the white [unclassified] side, we have more aircraft programs than we’ve ever had—the NASP, the ATF, the F-15E, the F-16C and D, the air defense fighter, the C-17, and the T-46 [trainer] or some variant of it, depending on how the Air Force decides to go.”

The F-15E is now virtually a bird in hand. The first dual-role fighter, its engines and cockpit displays somewhat at variance with those of the production-line F-15Es that will follow, was scheduled to roll out last month at the McDonnell Douglas plant in St. Louis, Mo.

Production of the F-l5Es will pro­ceed at a measured pace, centering on five test-bed models, through most of 1987, and will start hitting its stride about a year from now.

The Air Force plans to buy 392 F-15Es for four operational wings and one training wing well into the 1990s. Destined for the demanding deep-interdiction mission, they are expected to be superior in many ways to the F- ills that they will replace over the next four to six years—most especially, perhaps, in their ability to fight their way out of trouble in air-to-air combat.

The F-15E’s dual-role versatility has been put to the test in the fight­er’s simulator at McDonnell Doug­las.

Col. Roy B. Marshall III, chief of the projects division of ASD’s F-15 program office, recalled that it was “impressive how quickly we could go from air-to-air to air-to-ground” in that simulator.

“As we were going into the target, the simulator operators brought up a MiG-23,” Colonel Marshall said. “We got radar contact, negated the M1G-23, went back down in the weeds, and continued our bombing attack. We were satisfied.”

Optimally, each F-15E would car­ry four radar-guided, launch-and­-leave AIM-120A Advanced Medi­um-Range Air-to-Air Missiles (AMRAAMs) and four infrared-homing AIM-9L Sidewinder mis­siles.

Colonel Marshall and Lt. Col. Edward J. Atkins, the F-15E pro­gram manager at ASD, acknowl­edge that some work needs yet to be done on making the fighter’s avi­onics gear compatible and on inte­grating its software in a timely man­ner.

The F-15E will be “software-in­tensive,” loaded with digital, pro­grammable avionics, including the Joint Tactical Information Distribu­tion System (JTIDS) and the Tac­tical Electronic Warfare System (TEWS).

The integration of all such sys­tems is by no means easy, but “we don’t see any real show-stoppers ahead,” Colonel Marshall says.

Prospects for the F-15E

Powered either by P&W F100-220 engines or GE F110 engines, the F-15Es will be built for the carriage of conformal fuel tanks to give them the range they will need for their far- ranging interdiction forays beyond enemy lines.

The 81,000-pound (fully loaded) F-15E’s range and advanced avi­onics will enable it to do something that the 68,000-pound F-15C was not built to do in the air-to-air re­gime, namely, to escort ground-at­tack fighters beyond the Forward Edge of the Battle Area (FEBA).

The ATF was designed from scratch—in its propulsion system, aerodynamics, and avionics—to do just that, without conformal fuel tanks, and to do it far better.

Cockpit technologies are at their contemporary zenith in the “mis­sionized” forward and aft crew sta­tions of the F-15E.

The front cockpit has two mono­chromatic displays, one color dis­play, and one wide-field-of-view, holographic head-up display (HUD). The rear cockpit has two color displays and two monochro­matic displays. All displays in both cockpits can show the fighter’s atti­tude, altitude, and airspeed, plus in­formation pertaining to its arma­ment, forward-looking infrared (FLIR) navigation, radar altimeter, terrain-following radar, fire-control radar, and communications sys­tems. A voice warning system will alert the crew to danger when the fighter dips down too low.

By mid-1988, the F-15E will be the only variant in production. Pro­duction of the F-15Cs and Ds, now entering its final phase, will have ended.

All USAF attack aircraft will ben­efit from ASD’s AFTI/F-16 pro­gram. F-16Cs are being equipped with flight controls that the program has successfully tested, and the F-15Es will draw from its avionics innovations to some extent.

Such improvements, with more to come in the operational Air Force, will make it easier for F- 16C pilots to handle LANTIRN, for ex­ample. Moreover, it is no stretch of the imagination to assume that AFTI/F-16-induced advances in digital, fly-by-wire flight controls, in aircraft maneuverability, and in a host of cockpit technologies, such as voice controls and voice warning systems, will find their way into the ATF and even—in forms much far­ther advanced—in the starfighters of General Thurman’s foreseeable future.

Easing the Tough Tasks

In its current phase, the AFTII F-16 program is concentrating on trying out the Automated Maneu­vering and Attack System (AMAS) to ease the tough tasks of low-flying attack pilots.

Among the integrated technolo­gies involved in AMAS are an IR sensor/tracker that provides precise target information with respect to the aircraft’s position, a digital weapons interface called “standard avionics integrated fuzing” because it enables the fire-control system to fuze weapons automatically just pri­or to their release, and cockpit dis­plays of terrain maps that are pro­jected both on film and by means of digital electronics.

At this writing, AMAS features have been tested in nearly 200 flights of the AFTI/F-16. One of those features, a ground collision-avoidance system, has been vali­dated while turning at five Gs at 200 feet, a bomb-run maneuver that the AFTI/F-16’s qualities of aerody­namics and avionics can handle with hardly any sweat.

The AFTI/F- 16’s combination of terrain-avoidance and digital ter­rain-mapping systems may well turn out to be the biggest boon ever for such hill-hugging attack aircraft as the F-16Cs and the F-15Es.

The Marines and the Army—and the British, too—are interested in the AFTI/F- 16 digital terrain man­agement and display system’s po­tential for improving their night-at­tack capability.

“The great thing about the system is that its data doesn’t become ob­solete,” says Lt. Col. Donald H. Ross, ASD’s AFTI/F-16 program manager. “They’re not going to blow away the hills that we have on our digital maps.”

Despite its successes, the AFTI/F-16 program, at this writing, is fac­ing a severe drawdown and maybe even the termination of its funding at the hands of the Air Force.

This is also true of the AFTI/F-l11 program for testing the mis­sion-adaptive wing.

That program has demonstrated that variable camber wings have the potential to make a major difference in flight efficiency and maneu­verability and that such wings have a place in the Air Force’s opera­tional future. However, the program has not progressed to the point where the wings on the test-bed F-111 are controlled in the fully au­tomatic mode.

Such testing is scheduled to begin in a few months. It may be curtailed for lack of funding, however, to the regret of program officials. “We’re really just scratching the surface of what we can do with the MAW sys­tem,” says Ron DeCamp, ASD’s AFTI/F-111 program manager.

It is possible that both AFTI test programs have already contributed just about all that they need to con­tribute, for now, to USAF’s under­standing of the technologies they have explored. Now it may be time for USAF to concentrate on those technologies in a more pragmatic manner, namely, in the ATF pro­gram, some officials believe.

The AFTI/F-16’s spin-off for the ATF seems clear and substantial. Less clear is the spin-off to be ex­pected from the AFTI/F-111 pro­gram.

Applying the Lessons Learned

USAF wants the ATF to be capa­ble of relatively short takeoffs and landings, given the wartime pros­pect of damaged runways in opera­tional theaters. Consequently, the ATF designers will probably draw from lessons learned in yet another blue-ribbon ASD program, one that will demonstrate “STOL and ma­neuver technology” in a test-bed F-15 that is moving closer to pro­duction.

The ATF’s engines are expected to be capable of reversing and vec­toring their thrust in order to en­hance the aircraft’s maneuverability as well as to give it STOL capability. The key to this will be engine noz­zles of the type to be tested on the F-15 STOL demonstrator aircraft.

Pratt & Whitney, one of the two competing ATF engine contractors, will supply two of its F100-220 en­gines for the modified F-15 and is now building the nozzles to go with those engines, with ground-testing of the whole system scheduled to begin later this year.

P&W expects that its nozzles will be capable of vectoring thrust as much as twenty degrees up or down.

GE, too, is involved in the STOL test-bed aircraft program. Its work has to do with coupling the controls of the thrust-vectoring nozzles and the canards with the conventional flight controls of the F-15, thereby making it possible for the pilot to handle the whole affair as a package of controls, not as controls in isola­tion from one another.

Among other technologies to be tested aboard the aircraft will be a STOL “mode guidance” system (featuring cockpit displays that will show the pilot the best pathway for landing on a bomb-damaged runway), a low-visibility, precision-touchdown system, and a landing gear system that couples nosewheel steering and braking controls with flight controls and thrust-reversing controls.

The demonstrator aircraft is ex­pected to be capable of taking off from a 1,500-foot runway with full internal fuel and a 6,000-pound pay­load and of landing in that distance or less in the rain, under a 200-foot ceiling and crosswinds of up to thir­ty knots, with half-mile visibility and no landing aids.

Its radar and inertial navigation system will enable it to make such landings in daylight. For night land­ings, it will be equipped with a LANTIRN navigation pod and HUD.

“By the end of this year [1987], all flight units should have been deliv­ered, and we will begin installing them in the airplane on our way to meeting our first flight date in April 1988,” says David Selegan, who is ASD’s deputy manager of the pro­gram.

“We are very fortunate,” Mr. Se­legan continues, “in that everyone involved in the program has put first-class people on it—first-class not only technically, but also so­cially. That’s a big, big factor in this program because it’s an integration program. We have broken ground in the relations between engine and airframe contractors and sub­contractors that’s never been broken before, because our integra­tion of everything—such things as the landing gear with the flight-con­trol system—has never been done before.”

Hallmark of the ATF

Such integration will be the hallmark of the Advanced Tactical Fighter. The prototyping approach to its airframe, engines, and avi­onics as separate entities prior to final assembly of the competitive ATF flying machines should pro­vide clear perspective, from the standpoint of actual hardware, on how to put them all together.

“The prototyping approach has changed the program in several ways,” explains Col. Albert C. Pic­cirillo, the ATF program director. “We’ll have prototype ATF air­frames and engines flying almost two years earlier than originally planned.”

The idea in the beginning, since abandoned, was to have several contractors compete on paper and with isolated hardware and then to choose one of them to build an ATF model for flight demonstration and testing.

As of now, ASD plans to have both the Lockheed-Boeing-General Dynamics YF-22A ATF prototype and the Northrop-McDonnell Douglas YF-23A ATF prototype flying by the end of 1989.

“The flight prototype will be a major part of the program,” Colonel Piccirillo explains. “We need flight testing to demonstrate the proper balance among the critical ATF characteristics of supersonic cruise, high maneuverability, low [radar and IR] signatures, and excellent fighter handling qualities prior to pinning down the design for full-scale development and produc­tion.”

All this will be mighty challeng­ing. General Thurman’s thoughts on it are as follows:

“In the past, the trade-offs were relatively simple. Questions of ma­neuverability, size, range, and speed could all be analyzed in the context of propulsion systems and aerodynamics.

“Now, we have to look at perfor­mance—maneuverability—against low observables. They aren’t mutu­ally supportive. The things you do to increase maneuverability may not be the things you do to lower your observables. The design team can’t just say we’re going to make the fighter highly maneuverable by putting a great big tail on it.

“So the problem of designing a fighter these days is tremendously complicated.”

The saving grace in all this is the computer. “Computer power allows us to analyze those trade-offs and make them work,” General Thurman says. “The exciting thing to me, as an old aerodynamicist, is to go out to an aircraft design shop and watch as they put their designs to­gether on a big screen, with a com­puter.

“They lay down a design, and someone sitting there, maybe from the manufacturing side of the house or the maintenance side, says, ‘Hey, you can’t do that, because the air­plane would be tough to build or to keep in shape.’

“Then they change it, move the lines around on the screen, and they say, ‘There, how about that.’ Some­one says, ‘Well, I want to make this little aerodynamic change right there,’ and someone else says, ‘Hold it, what are the implications of that change on the observabili­ty—the radar cross section or the JR cross section—of the aircraft?’ “

This sort of computer-generated dialogue and teamwork, as it were, “now allows us to get an F- 16C with superb performance and ninety-five percent availability,” General Thur­man adds.

Three Types of ATF Prototypes

The development of all three types of ATF prototypes—airframe, engines, and avionics—will tell the Air Force a great deal about how to make the trade-offs and still come up with a fighter of great speed, ma­neuverability, and range and of low radar and JR cross sections.

The avionics prototypes “will be just as important as the flying pro­totypes,” Colonel Piccirillo declares, adding that they “will be ground-based at first, and they’ll take into consideration the insertion of new technologies, such as VHSIC, using a common-core ar­chitecture and distributed process­ing. Later in the program, both con­tractor teams will be flying their avionics prototypes in large, air­liner-type test-beds.”

Centered on all its prototypes, the ATF program’s design demon­stration/validation phase should take about four more years, and then the fighter will proceed—with the winning contractor team having been selected—into full-scale de­velopment on the way to production and operational service around the mid- 1990s.

The initial, demonstration phase of the program will require an Air Force expenditure of about $2.5 billion; the full-scale development phase, about $7 billion; and the production phase, about $35 billion for 750 of the fighters, according to Thomas E. Cooper, Assistant Secretary of the Air Force for Research, Development, and Logistics. All prospective expenditures are quantified in terms of the buying power of the dollar in Fiscal Year 1985.

Dr. Cooper sees the integration of the ATF’s avionics as the program’s biggest challenge, but also regards it as holding the promise of “tremen­dous payoff.”

The engines being developed for the ATF are already well along and are “the pacing items in the pro­totyping program,” Colonel Pic­cirillo says.

ASD anticipated that the ground-demonstration version of the GE YF120 engine for the ATF would be up and running by the first of this year. The Pratt & Whitney YF 119 engine ran for the first time last Oc­tober.

Both powerplants are in large measure the products of technolo­gies developed in the ASD Aero Propulsion Laboratory’s Joint Ad­vanced Fighter Engine (JAFE) pro­gram over the past few years.

That program has been folded into the engine portion of the ATF program itself. But this does not mean that the Aero Propulsion Lab has gone out of the business of de­veloping advanced fighter engine technologies, not by a long shot.

“We’re out to double the thrust-­to-weight [ratio] of the ATF-genera­tion engines—and to maintain the same level of reliability—by the year 2000,” asserts Walker Mitch­ell, deputy director of the Aero Pro­pulsion Lab. “Our technology pro­gram is embedded in Project Fore­cast II—we’re a big player in that—and it is much broader than just looking forward to the next ATF. We’re looking at hypersonic air­planes and missiles, among other things.”

Endothermic fuels are a major consideration in all this. They are being researched in the lab’s avia­tion fuel technology program, and they have enormous implications for air-breathing engines of the fu­ture.

“We call them designer fuels,” Mr. Mitchell explains, “because we’re rearranging molecules to get the characteristics that we want out of them. They absorb heat instead of giving it off.”

In connection with this, high-per­formance aircraft and missiles may one day burn gaseous hydrogen compounds instead of liquid fuel, Mr. Mitchell says.

This is feasible in turbine engines, he says, “because they don’t care what they’re burning.”

The laboratory is involved in a number of technology programs un­der the heading of “high-speed pro­pulsion.” They are aimed at “rapid­ly developing an Air Force capabili­ty for high-speed flight, including turboramjet engines for Mach 5 in­terceptors, hydrogen-fueled en­gines for hypersonic cruise vehicles or space boosters, and new engine options for high-speed missiles.”

One of the lab’s aspirations is a supersonic combustion ramjet (scramjet) engine of the sort slated for the National Aerospace Plane.

Hand in hand with the Aero Pro­pulsion Lab’s endeavors are those of ASD’s Materials Laboratory. The lab is in pursuit of “intermetals,” such as titanium aluminide, and, farther out, of carbon/carbon mate­rials and ceramic composites that would far surpass today’s compos­ites and superalloys in strength and resistance to heat.

“Nickel-based superalloys are the backbone of turbine engine technologies,” explains Larry Hjelm, assistant chief of the Mate­rials Laboratory’s metals and Ce­ramics division. “They date back to the early 1950s. Incremental im­provements in them have allowed us to double the thrust-to-weight ratio of fighter engines, but we can’t take them any further, so we’re looking for alternatives.”

Titanium is one such alternative, but it is much too costly. Fused with aluminum in titanium aluminide in­termetals, it becomes inexpensive enough to buy, in relatively small quantities, for engine components and for airframes.

The intermetals can stand tem­peratures that far exceed the melt­ing points of titanium itself, let alone the melting points of nickel-based alloys.

The Materials Lab is also explor­ing the rapid solidification of alumi­num and of other metals to make their molecules reform in unnatural, stronger patterns.

All such work is being driven by ASD’s “activity in hypersonics,” Mr. Hjelm says. Such activity “will carry our work along well past the aerospace plane,” he adds, “and we expect to get some benefit from the NASP program.”