737 Scale Model Uses Selective Laser Sintering to Fly
Created by aerospace engineering company Area-I in Georgia, PTERA is the unmanned Prototype-Technology Evaluation and Research Aircraft yielding inexpensive flight research for commercial aircraft and NASA, and it’s using 3D Printing in a few instrumental ways.
PTERA serves as a “bridge between wind tunnel and manned flight testing by enabling the low-cost, low-risk flight-based evaluation of a wide array of high risk technologies,” says Area-I’s CEO Dr. Nicholas Alley. This unmanned aircraft serves as a laboratory in which new aerodynamic technologies can be flown and tested for a “fraction of the cost of a manned flight test program,” says Alley. “It’s a testbed with a large payload capacity that facilitates risk-mitigating, flight-based evaluations of sensors, payloads, guidance and control systems, and advance aerodynamic treatments and aircraft configurations before they transition to manned programs.” More simply put: PTERA’s flight tests inexpensively mimic real situations for larger aircraft to reveal airflow dynamics and circulation experiments on a small scale with implications and results relevant to larger aircraft.
“Full-scale, manned flight test is replete with safety, schedule, and performance risks that dominate flight test costs. A technology gap exists between well-controlled wind tunnel tests and full-scale flight testing where most of the system integration issues surface,” says Alley. “PTERA exists to help identify these issues and allows researchers to learn as much as possible about a technology before the investment is made in carrying out full-scale flights.”
PTERA’s ailerons, fuel tank, control surfaces and flaps benefited from Selective Laser Sintering (SLS) 3D Printing to answer to some challenging geometries within the structure of the unmanned vehicle. “Additive manufacturing has completely changed the way we design aircraft,” says Alley. “We used to shy away from certain complex designs, opting for more basic structures. Additive manufacturing has allowed us to design and build mechanisms and structures we wouldn’t be able to make with any other manufacturing method.” Using SLS NyTek 1200 CF (carbon filled Nylon 12) to 3D Print integral features of PTERA resulted in extremely lightweight parts with special structures grown directly into the geometry to reduce weight without compromising part strength; rather, these parts are stronger with increased stiffness thanks to 3D Printing, and the geometries could not have been incorporated via any method other than additive manufacturing. “Originally, we would hand-build ailerons, and it would take about 24 man hours each,” says Alley. “When we had them grown in LS through Stratasys Direct Manufacturing, we had the ailerons designed, built and assembled on the UAV in three days. SLS is easy to work with, installs quickly, is efficient and, from an aesthetic standpoint, produces parts that are gorgeous.”
SLS is a layer additive manufacturing process which sinters nylon material together via a heated build chamber and CO2 laser. The laser melts the powder in computer determined patterns. As each layer is sintered, the build platform moves down until the final product is completed. The nature of layer additive manufacturing with SLS allows complicated inner features to be built without compromising tolerances or part integrity. PTERA’s fuel tank was built via this method, which resulted in inner anti-slosh baffling that helps to steady PTERA in flight without losing any fuel space. The fuel tank was additionally required to conform to ducting which flows beneath the tank. Completing the tank via machining wasn’t viable, but SLS was able to conform to the ducting seamlessly. “We’re firm believers in additive manufacturing,” says Alley.
PTERA’s research into circulation-control wings has benefited from its 3D Printed components. “PTERA was designed to be modular such that it can accommodate a wide array of aircraft configurations and aerodynamic treatments; such as circulation-control wings or wings with active twist and camber,” says Alley. Perhaps most importantly is that PTERA is a direct miniaturization of a 737 aircraft, and the results from PTERA’s flight tests are answers for future aircraft.
“The physical configuration is representative of most commercial/transport aircraft, therefore test data is more applicable to those aircraft,” says Alley. “PTERA’s structure is solid, well designed and stable therefore the test data will be free of unwanted variables that may contaminate the data and the airframe was designed from the bottom up to be modular and general purpose which will meet the ‘common benefit’ need that a lab asset must generally satisfy.”
Using 3D Printing helped the team at Area-I to create components quickly and accurately that mimic their larger commercial counterparts without complicated and expensive machining.