Gallery: NASA's Frankenstein F-18 Flight-Test Workhorse
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EDWARDS AIR FORCE BASE, Calif. -- The sky over the Mojave has for 60 years been home to some of the world's most innovative and advanced flight-test programs. The United States' first jet flew here during World War II. Chuck Yeager became the first pilot to exceed the speed of sound here, way back in 1947. The incomparable X-15, the fastest airplane ever, first flew here. Even the space shuttle made its inaugural flight over this Southern California desert. Tucked away in a corner of the sprawling air base here is NASA's Dryden Flight Research Center. Some of the coolest things in the world are tested here, and the centerpiece of every flight-test program are the workhorses that serve as flying laboratories. NASA has over the years relied upon various airplanes to test new tricks and technology. These days the F-18 is the mainstay of the NASA Dryden test fleet. Whenever an engineer comes up with a new idea, it is tested on an F-18. Once installed, these modifications are rarely removed. The bits and pieces read like a history of flight-test research. Among the most heavily modified F-18s is a plane known as No. 853. It has been the testbed for several projects, including flying with a bending wing and being tweaked to fly like a plane missing a wing. NASA let us into the hangar to have a look at No. 853 and learn a little more about some of the unusual feats it has accomplished. __Above__: No. 853, high above the Mojave in 2004 during one of its more interesting projects, the Active Aeroelastic Wing project. The goal was to explore twisting, or warping, the wing to provide roll control at transonic and supersonic speeds. *Photo: NASA*
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Technicians tend to No. 853 inside one of the sprawling hangars at NASA Dryden. The plane, shown here getting routine maintenance, carries evidence of past research projects. Some of the instruments and devices are left in place because they may be used again. Others are there simply because leaving them on the plane is easier than removing them. Anything left behind doesn't adversely impact the performance of the airplane. NASA Dryden maintains a diverse fleet of aircraft. In addition to supersonic fighter jets, Dryden pilots also fly everything from Gulfstream business jets converted into research platforms along with a Douglas DC-8 airliner and a former U-2 spy planes now known as ER-2s. Many of these aircraft are used as science platforms for work not necessarily related to flight testing. In addition to #853, the F-18 pictured here, Dryden also operates three other F-18s that are used as "chase aircraft." These airplanes provide an observational/safety aircraft that works with the airplanes doing the actual flight testing as well as being flown for pilot proficiency. The test pilots also currently fly an F-15 fighter as a test platform. NASA Dryden recently acquired a few more F-15s that are currently being converted for use by the flight test group, one can be seen in the back of the hangar behind the ladder on the right side of the picture. *Photo: Jason Paur/Wired.com*
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No. 853's nose is home to an array of navigation and guidance gear, along with research equipment like the Airborne Research Test System. ARTS — it's all about the acronyms at NASA — is a computer that allows engineers to quickly and easily test new software and equipment without installing a dedicated computer for each project. That gray box at the bottom of the nose is an ARTS. To keep all of the wiring from getting mixed up, flight test systems are wired in orange while everything else is wired in other colors. *Photo: Jason Paur/Wired.com*
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No. 853's left wing details the longest history of the plane's role as a test mule. It bears little resemblance, aside from its shape, to the sleek, smooth wing the plane had when it left the factory. The wing is dotted with sensors, equipment and remnants of the epoxy-like material engineers use to hold everything in place. The plane still wears some of the sensors and equipment used during the Active Aeroelastic Wing project that started in the late 1990s. Engineers explored twisting or warping the wing to provide roll control at transonic and hypersonic speeds instead of using the differential rolling horizontal tail, or [stabilator](http://en.wikipedia.org/wiki/Stabilator) traditionally used by F-18s at those speeds. The wing warping on No. 853 was achieved using aerodynamic forces. The thin skin covering the wing was replaced with an even thinner version allowing the wing to flex up to five degrees. Additional actuators were placed in the wing that allowed differential control of the slats on the leading edge of the wing as well as the traditional ailerons on the trailing edge of the wing to induce the wing flex. Here, a technician works on No. 853's wing during routine maintenance. Beyond keeping the aircraft in tip-top condition, the technicians inspect and install strain gauges and other instruments for the next research project. *Photo: Jason Paur/Wired.com*
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No. 853 was known officially as the X-53 for the Active Aeroelastic Wing project. To accurately measure and monitor the wings during the project, sensors along the wing measured air pressure as well as strain on the wing structure. The line of circles shows the location of small holes where the difference in air pressure could be measured during flight testing. The black diamonds mark the location of mirrors used to measure the strain on the wing as it is flexed and twisted. *Photo: Jason Paur/Wired.com*
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Small reflectors are placed along the wing. Light emitted from a transmitter along the spine of the airplane is bounced off the reflector back to the box, allowing engineers to precisely measure wing strain in three dimensions. Engineers placed more than 350 strain gauges on the wings of No. 853. Two of the "previously owned" F-15s being converted for use by NASA Dryden can be seen in the background on the left. *Photo: Jason Paur/Wired.com*
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The blue box houses the transmitter and receiver that work in conjunction with the reflectors to measure wing strain. All of those sensors and other equipment require miles of wire, and No. 853 is packed with them. By using wing warping to control roll, No. 853 was something of a retro-plane. The Wright Brothers used wing warping on their early airplanes to control roll, including on the airplane used for the [first powered flight](http://stag-komodo.wired.com/thisdayintech/2009/12/1217wright-brothers-flight-kitty-hawk/) on December 17, 1903. *Photo: Jason Paur/Wired.com*
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These tubes protruding from the wing spars of No. 853 once were connected to the static pressure sensors on the wing. The sensors measure air pressure over the top of the wing to help determine the airflow during various maneuvers. The lift generated by the wing is dependent on the flow of air around the wing. Engineers can better understand the effects of various tests such as the wing warping if they have a precise way to measure the air pressure over the wing Many of the sensors, parts and other instruments of past projects are left on the plane when the experiment is done. They provide a tangible history of past research, and often are used in later projects. *Photo: Jason Paur/Wired.com*
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NASA researchers found wing warping could produce adequate roll rates at transonic and supersonic speeds. The software control laws that manage warping to control roll offer several advantages over traditional roll control, including reduced drag and improved maneuverability. And perhaps counter intuitively, a lighter structure can be used because aerodynamic forces on the wing can be more closely controlled, reducing strain. NASA Dryden's #853 F-18 is an early "A" model former Navy aircraft and among the oldest still in service. Their advanced age means they require more maintenance, but given how much is invested in the electronics and instrumentation, NASA keeps them in the fleet. Some of the other F-18s NASA Dryden uses as chase aircraft are actually pre-production "Y-ish" F-18s. These early models were part of the flight testing program used by McDonnell Douglas when the company was developing the F-18. In recent decades, many of the pre-production fighters were given a "Y" rather than the more familiar "X" in front of their designated number such as the YF-16, YF-22 or the YF-17 which led to the F-18. *Photo: Jason Paur/Wired.com*
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This is the office of a NASA Dryden test pilot. It's not the biggest, or most comfortable workspace, but it's got a window and you can't beat the view. Most Dryden pilots who have flown in the flight test programs over the years are former military pilots who have graduated from either the Air Force or Navy test pilot schools. The cockpit of No. 853 has been upgraded from the original with glass avionics and other improvements in the decades since she rolled off the assembly line decades ago. *Photo: Jason Paur/Wired.com*
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You'll find all kinds of interesting airplanes parked outside the maintenance hangars at NASA Dryden, further evidence of projects past. That's a highly modified F-15B in the front formally known as the NF-15B to signify its research status; the canard wings near the nose are actually tail surfaces from an F-18. The airplane participated in many research projects with both the Air Force and NASA, spanning more than 30 years. Among them was short take off research, thrust vectoring experiments and advanced fly-by-wire research. No. 851 is another F-18 used by NASA. Behind it is No. 848, a highly modified F-16 modified with asymmetric delta wings. *Photo: Jason Paur/Wired.com*
