|
This article appeared in the October 2000 issue of Code One Magazine.
Print friendly version of this article (text only)
 Spectacular and functional may best describe the first flight of the Lockheed Martin X-35, the demonstrator aircraft for the Joint Strike Fighter. Spectacular because the first flight of any new aircraft, especially a fighter, is a display of raw power and high-technology wrapped into a single moment. Functional because this maiden journey takes the aircraft only a few miles from its present location to its new home. The aircraft, more accurately labeled X-35A, takes off from a runway at Lockheed Martin in Palmdale, California, accompanied by two chase F-16s, flies northeast a few miles over the Mojave Desert where it completes some circuits high above the lakebeds, lands at nearby Edwards AFB, and taxis to its new home at the Air Force Flight Test Center.
“The purpose of the first flight is to get some air under the wheels and get a feel for the airplane,” explains Tom Morgenfeld, designated test pilot for the premiere flight and chief test pilot for the JSF X-35 program for Lockheed Martin. “I’ll perform some aileron rolls and cycle the landing gear. But, overall, the flight plan is somewhat conservative.” Morgenfeld takes the X-35A to a maximum speed of about 270 knots and an altitude of 10,000 feet in the first flight, which lasts about thirty minutes. In subsequent flights, the envelope expands in relative short order to 1.5 Mach and to more than 40,000 feet.
 |
| Tom Morgenfeld is the designated test pilot for the premiere flight and chief test pilot for the Lockheed Martin JSF X-35 program. |
Flight Test Team
About 150 government and industry personnel will follow the X-35 from Palmdale to Edwards. The flight test pilot team—three industry and four government pilots—is led by Morgenfeld on the industry side. He is joined by Lockheed Martin test pilot Joe Sweeney and BAE Systems test pilot Simon Hargreaves. The government pilot team is led by Lt. Col. Paul Smith (USAF). He is joined by Maj. Art Tomassetti (US Marines), Lt. Cdr. Brian Goszkowicz (US Navy), and Sqd. Ldr. Justin Paines (UK Royal Air Force).
“We add credibility to the contractor and to the data produced on the program,” says Smith. “Having a pilot from each service involved on the program helps ensure the respective services that the airplane is worth the investment. We communicate between the competing programs at a higher level to ensure the entire program is being run safely, fairly, and efficiently. We are also showing the Defense Department that the three services can work as a team — that we can take representatives from different services and safely execute a flight test program. That experience will become more important in the next phase of the program. In the meantime, we have set precedents for creating a more interoperable service.”
 |
| Lt. Col. Paul Smith (USAF) leads the government pilot team. |
While test pilots account for a more visible and a more acclaimed portion of a flight test team, a host of talented mechanics, technicians, and engineers from a variety of disciplines perform the work that keeps the airplanes in the air. Dick Burton, a veteran of Lockheed Martin flight testing, leads the team of engineering representatives from Lockheed Martin, Northrop Grumman, BAE Systems, and even the government. His impressive resume includes the U-2, the SR-71, the F-117, and Have Blue (the F-117 prototype). But this is his first X-plane. “Have Blue was like an experimental aircraft,” he explains, “but it was a classified program—so its official status never came up.”
Experimental Designations
The X designation for the JSF concept demonstrators can be traced to funding. When the program was called the Joint Advanced Strike Technology, the official congressional language said that JAST was purely a technology demonstration program. Accordingly, the concept demonstration aircraft were given X designations to abide with the original funding definitions for the program. So, officially, the aircraft are not prototypes; they are technology demonstrators. Consequently, they received X numbers from NASA’s nomenclature. The design chosen for production (based on either the X-32 or X-35) will become the F-24, not the F-32 or the F-35, since the numbering sequences for production aircraft and experimental aircraft are completely separate.
 |
| Dick Burton leads the flight test engineering team. |
X-35 A-B-C’s
Keeping track of X-35s is as simple as X-35 A-B-C. The first to fly is the conventional takeoff and landing X-35A (also known as CTOL). The second to fly is the carrier-suitable X-35C (also known as CV). The third to fly is the X-35A, again, once it’s converted into the short takeoff vertical landing X-35B (also known as STOVL). “The X-35A is basically an up-and-away airplane,” Burton explains. “We use it to establish most of the flight envelope. We use the second X-35, the X-35C, to demonstrate carrier operations—handling and flying qualities in the low-speed region of the flight envelope. We use the X-35B to demonstrate our vertical lift concept in short takeoffs, vertical landings, hovering, and transitions between jetborne and wingborne flight. All three versions will test up-and-away performance to show that they provide similar levels of high performance.”
 |
| George Law is chief engineer for the JSF demonstrators. |
Burton expects the X-35C to accumulate the most flight hours because it flies shortly after the X-35A and then racks up additional flights while mechanics and technicians spend ten to twelve weeks converting the conventional X-35A into the STOVL X-35B. The X-35 aircraft are designed for operational-like conditions of 8 g’s and Mach 1.8.
The similarities among the three demonstrators simplify the flight test program. “The wiring, the hydraulic system, the environmental control system, the secondary power, and the cockpit are identical in all the aircraft,” notes George Law, the chief engineer for the demonstrators. Some exceptions involve the flight control actuators. “The horizontal tails are larger on the CV, so that aircraft requires larger actuators. The flaperon actuators are larger in the CV airplane for the same reason. We don’t have ailerons in the CTOL, so no aileron actuators are needed.”
 Winning Looks
If appearance equates to performance, the X-35 should wow test pilots and reviewers alike in the coming months. From a distance, the basic shape, with its side-mounted inlets and tail configuration, gives an illusion of an F-22. Get closer and the similarity fades. First, the single-engine X-35 is more compact than the two-engine Raptor. From the front, a smooth diverterless inlet on the X-35 contrasts with the intimidating forward angles of the inlet lips. Two serpentine intake ducts conceal the engine face. The bubble canopy rises in front of a humped spine to create space for the lift fan. The fan itself is contained in a bay covered top and bottom by louvered doors with serrated edges. From the rear, a single massive engine dominates the view. From every angle on the ground, beefy main landing gear firmly anchor the aircraft to the tarmac.
 “The gear is derived from the A-6,” explains Law. “It is designed for field carrier landing practice with the Navy variant. We use the same gear on all the demonstrators, so it is somewhat over-designed for the conventional and STOVL aircraft.” Roll posts and a lift fan system distinguish the X-35A from the X-35B, which share the same airframe. The X-35C has a larger wing surface thanks to larger outboard sections and control surfaces. The X-35C can also accommodate a vertical lift system if needed.
As with other demonstrator aircraft, the X-35 borrows from existing aircraft to reduce costs and design time. The A-6 main landing gear pair with nose landing gear from the F-15E. The environmental cooling system comes from the F-18E/F. The auxiliary power system comes from the F-22 while the engine-driven hydraulic pumps are vintage YF-23. The airframe-mounted accessory drive comes from the B-2 bomber. The Upco ejection seat is the same one used on the Harrier AV-8B. And the two large color multifunction displays come from the C-130J. The engine is derived from the Pratt & Whitney F119 found in the F-22. Many subsystems and controls come from the F-16.
 |
| Bob Barham is the flight test engineer for the X-35A/B. |
Three Demonstrators From Two
The conversion of the X-35A conventional aircraft to the X-35B STOVL demonstrator takes place back at Lockheed Martin facilities in Palmdale after the X-35A completes its flight test program at Edwards. “The airplane side of the conversion is not the toughest part,” explains Bob Barham, the lead flight test engineer for the X-35A/B. “The mechanical work, installing the shaft-driven lift fan in the fuselage and the roll ducts in the wings, accounts for only a small portion of the conversion span. Checking out these systems requires more time than the installation itself. But most of our effort involves the software, which is completely new.”
Technical Challenges
Software underlies much of the development process for any modern aircraft. The X-35 fits into that category. “We have a totally digital flight control system in the X-35,” Burton notes. “Nothing in the cockpit is attached to anything that moves in the airplane. As airplanes evolved from cables and bell cranks into wires and electronic flight control systems, their capabilities and complexity increased.”
Technical complexity reaches its zenith when X-35B, the STOVL demonstrator, fires up its lift system. “The STOVL flight envelope has some tricky spots,” Barham notes. “We can test wingborne flight. We can test the transition from wingborne to jetborne. And we can test the hover press-ups. But the transition from 100 knots to hover is new ground and tough to approach. Software-based control systems make the handling qualities of the STOVL version worlds better than the mechanical control systems. Once we complete our first conversion between hovering and horizontal flight, we can refine the handling qualities further. We have nice STOVL modes that make the airplane relatively easy to fly—certainly easier to fly in the STOVL environment than the Harrier.”
Most of the initial STOVL tests occur over a concrete pit ten feet deep and covered with a thick metal grate. The pit reduces the ground effects produced by the vertical thrust from the engine and lift fan, and it allows engineers to study vertical flight modes while the aircraft is on the ground. For most of these early tests, the X-35B’s landing gear is replaced with a fixed “dummy” gear, essentially bolting the aircraft to the ground. The fixed gear contains strain gauges that measure forces in all dimensions. “We get most of our forces and moments data from the dummy gear,” explains Barham. “The setup verifies that the software and controls work and that the forces and moments are what we expect. We perform ground tests with the actual landing gear as well. Tire deflections can make the airplane wobble, feeding this movement back to the flight controls. We have to make sure that we account for even these small motion in the flight control system.”
 |
| Rita Jones is the instrumentation lead for the X-35A/B. |
Morgenfeld, Burton, Law, Barham, and other members of the X-35 flight test team are confident they will meet these technical challenges during the flight test program. “The technologies we build these aircraft to demonstrate usually work out fine,” Barham notes. “In other words, the revolutionary technology almost always works. Most often the systems that have been around for thirty years create most of our day-to-day challenges—things like hydraulic and mechanical systems, fuel tanks, and generators. We don’t put as much engineering emphasis on them, so they are more likely to cause a few problems.”
Instrumentation
Instrumentation for monitoring aircraft performance and accumulating and transmitting useful data from the aircraft during ground and flight tests plays a key role in this flight test program as it does in any other flight test program.
 |
| Bob Burton heads the BAE X-35 engineering team. |
“Both X-35s are filled with sensors to record and transmit a plethora of measurements from strain gauges, thermocouples, accelerometers, potentiometers, pressure transducers, fuel flow meters, and microphones placed all over the aircraft,” notes Rita Jones, the instrumentation lead for the X-35A/B. “Sensor information as well as bus data on the aircraft are transmitted from the instrumentation system to the ground where flight test engineers monitor them from specialized trailers.” These trailers, resembling mobile homes with small windows and deluxe satellite television reception, accommodate the numerous moves of the X-35s as they travel to and from the various test sites. Part of the cost of changing test sites involves spinning up a new control room with realtime displays of aircraft and engine measurements. These data trailers ease that transition, save a little time, and reduce costs. The last portion of the flight test plan involves ferrying the aircraft to the Navy Test Center at Patuxent River, Maryland, for sea-level performance and flying qualities testing.
STOVL Flight Testing
To make STOVL work, Burton’s team is relying on BAE Systems’ experience on the British Harrier program. “BAE brings a lot of STOVL expertise to the program,” notes Bob Burton, who heads a group of seven BAE engineers working on the X-35. “The biggest differences between the Harrier and the JSF may be the increased speed, payload, and range. But digital flight controls play an enormous part in the flight test program. We also have more control variables to play with in this airplane. The lift fan system allows us to adjust the amount of thrust between the front and the rear of the airplane. We can’t do that with the Harrier.”
STOVL testing presents the biggest challenge for the test program. The conventional takeoff and landing demonstrator presents relatively few demonstration requirements. They include engine/inlet compatibility and high-speed performance. The Navy version has to demonstrate carrier approaches and other handling characteristics related to carrier operations. Most of the flight tests dealing with these carrier operations take place at the Navy Test Center at Patuxent River. Before the X-35C is ferried to the Navy facility, it completes most of its up-and-away testing and envelope expansion at Edwards. This testing includes initial, low-speed, and supersonic envelopes up to Mach 1.5. The aircraft also demonstrates more than 6 g’s and altitudes greater than 40,000 feet, while verifying performance predictions for range and acceleration with an engine and shape nearly identical to the production configuration.
Final Thoughts
The flight test program culminates a demonstration phase evolving the X-35 from lines on a computer-aided design screen to a real aircraft lifting off from the tarmac. “Huge anticipation tends to set in just before taxi testing,” says Barham. “During the previous engine runs, we have tested the airplane as an integrated system, operating the airplane like we intend to fly it. After the following taxi tests, our efforts become a little more routine. So, first flight is somewhat of a relief. But when we land at Edwards, we face a huge set of new challenges that will highlight the capabilities of this outstanding fighter. First flight is only a beginning.”
Eric Hehs is editor of Code One Magazine
|
