MIT Lincoln Laboratory has a new test asset. The aircraft is 6.5 feet long, has a wing span of 10 feet, is made of nonreflective, nonmetallic composites, weighs 48 pounds and can carry a 5-pound payload, and is powered by a two-stroke, two-cylinder
6-horsepower engine. Flight tests showed that the aircraft has the potential to reach a flight ceiling of 15 kft above mean sea level, to achieve a maximum of 80 knots true airspeed, and to fly for three hours without refueling. The tests also confirmed the communications system worked well and the aircraft can successfully hand over to an onboard autopilot. This unmanned aerial vehicle is the second iteration of a prototype designed and built during the 2009–2010 academic year by 40 students in the MIT Department of Aeronautics and Astronautics. The aircraft will be used to carry an MIT Lincoln Laboratory payload for measurement of ground-based antenna patterns.
In this collaboration with MIT campus, Lincoln Laboratory researchers from the Tactical Defense Systems Group not only provided design guidance and antenna-test-range support but also acted as the “customer” for the aircraft, providing the students with the experience of managing a real-world project. The students, who were enrolled in either the upper-level undergraduate Flight Vehicle Engineering course or the graduate Aircraft Systems Engineering course, learned the actual stages of project development—reviews of systems requirements, concept design, preliminary design, and critical design; procurement and prototyping; risk assessment; building; and flight testing.
The Tactical Defense Systems Group, which has a long history of developing and employing high-fidelity airborne measurement capabilities to characterize an array of advanced radio-frequency (RF) and infrared systems, operates two business-class jets for this purpose. In partnering with campus, the group saw an opportunity to develop innovative approaches for this type of testing through the use of low-cost unmanned aerial vehicles (UAV). The partnership combined the Laboratory’s understanding of the measurement mission with campus’s expertise in small-vehicle design.
“Early discussions of the concept with Prof. John Hansman of the MIT Department of Aeronautics and Astronautics led to the conclusion that what was needed was a specialized vehicle designed wholly around the Laboratory’s testing needs,” says Lincoln Laboratory’s Marc Viera, now associate leader of the Advanced Capabilities and Systems Group. The UAV would require high-altitude autonomous operation and specialized materials to minimize interference with the payload’s RF operation.
Josiah VanderMey, a research assistant working with the students, says the authenticity of the project gave it a dimension not usually available in classroom-based assignments. “Most classes look at a single specific aspect of design and development. Although they may reference other disciplines, the true comprehensive nature of design and development is often missed. This class provided the students with a holistic view of the process and gave them an appreciation for the significance of system-level design and interfacing between disciplines.”
Jerry Richard, a senior majoring in aerospace engineering, compared the project to work in a start-up or small company instead of a class in which professors create a workplace scenario. “The external agents were real. If there was an ambiguity in the requirements, we had to contact Lincoln Laboratory for clarification, and the answer wasn’t prescripted by professors.”
From initial system requirement review to the final flight test in early May at Camp Edwards on Cape Cod, the project took two semesters. This time frame included the requirements discussion with Lincoln Laboratory, design development, various design reviews, construction of a first prototype, two separate flight tests at a small airfield in Shirley, Mass., modifications based on lessons learned from the Shirley flights, construction of the final aircraft, and the third flight test at Camp Edwards.
The development process was as much a part of the course as the actual engineering. “This was practical design,” says Adam Mohamed, who took Aircraft Systems Engineering during his senior year. “We took what we saw and actually built it. It’s one thing to see the pretty CAD [computer-aided design] drawings and another to actually get your hands into the epoxy.”
“Having this type of ‘real-world’ project is extremely motivating to the students when they know that they will have to deliver the aircraft,” says Prof. Hansman. “Lincoln staff played an important role as the customer, helping the students define the system requirements and both guiding and pushing the students.”
A particularly challenging part of the process was the level of communication required to complete the aircraft. “The complexity of this project necessitated that the students break into subteams to specialize in the different components of the vehicle. This specialization required a great deal of communication to ensure that the interfaces between systems were consistent,” says VanderMey. “Aside from the six hours a week of scheduled class time, there were only select groups of individuals in the lab at any given time. This increased the difficulty of coordinating work and sharing information.”
The students used a variety of methods to manage the necessary communication: a lab log, a shared Google calendar, document sharing via Google docs, out-of-class meetings, email, and a server to provide a secure repository of drawings, simulation codes, and other files. In addition, since Lincoln Laboratory did the design work for the payload antenna, the wiring, and the electronics box, the subteams had to interface with Laboratory engineers to ensure that systems worked together seamlessly.
Because the vehicle will be used in real measurements, students knew that vehicle safety was critical. The team did a thorough hazard analysis to determine factors that could be of risk to the vehicle. In addition, Lincoln Laboratory and the Camp Edwards test facility imposed safety requirements for using vehicles on closed ranges that influenced system design. The team included two independent means to bring the aircraft down in the event of some type of distress or failure. A termination sequence was programmed into the system to automatically bring down the aircraft should the engine fail or the aircraft veer uncontrolled into an area not within the geographical boundaries preprogrammed for the flight. The aircraft’s autopilot feature can be manually overridden in case the vehicle malfunctions or appears headed for trouble.
The flight tests, which are critical to the development of a final aircraft that works, added another real-world dimension to the project. “Having real flight tests forced them [students] to think through all the different scenarios that could occur. These considerations were used to inform the vehicle design,” says VanderMey.
During one class session, James Dunn of the Tactical Defense Systems Group shared with the students lessons learned in his 30 years of experience in flight testing. “It was most important to stress that they should spend a large amount of time considering the test objectives,” says Dunn. Prof. Hansman hopes to have Dunn repeat this lecture on flight test planning and execution during another collaborative class project with the Laboratory.
Results from the first two flight tests at the Shirley field led to modifications to the design: larger fuselage to accommodate components, widened tail booth, redesigned landing gear, conduits added to the wings, and a strengthened floor to support added components. Early flights tests on an uneven and stone-covered field revealed the necessity of having a launcher since takeoff on a bumpy surface was problematic.
The students honed project management skills and learned that keeping to deadlines was crucial since scheduled flight tests could not be rearranged. VanderMey says that it often took longer than planned to accomplish tasks, resulting in late-night sessions. Yet, the project was completed on schedule, met its specifications, and came in under budget—a success for any industry project.
Lincoln Laboratory staff worked with the students and faculty throughout the project, participating in design reviews and working groups on campus, supporting RF testing in the Laboratory’s anechoic chambers in the RF System Test Facility, and assisting with final flight testing at Camp Edwards to demonstrate operation of the Laboratory’s payload in flight. “In all of these efforts, we found it a pleasure and exciting to work with highly motivated students dedicated to making sure their vehicle met customer needs,” says Viera.
Damon Henry, another senior in the Department of Aeronautics and Astronautics, offered the consensus on the experience. “It was frustrating at times. We tried five sets of wings before we got it right. But it was rewarding.”
During the summer, Henry and others stayed on a short time at MIT to make a few adjustments before transitioning the aircraft to Lincoln Laboratory. The Laboratory plans to complete final vehicle development and payload integration to demonstrate an initial operational capability for measurement of ground-based antenna patterns in spring 2011.