United States of America
From Leadership Profile: Vertiflite November/December 2017
Dr. Colin Theodore, Associate Project Manager, NASA Revolutionary Vertical Lift Technology
In parallel with NASA’s ongoing Revolutionary Vertical Lift Technology (RVLT) project, Colin Theodore led about 20 investigators looking at new vehicles for new markets including air taxi and package delivery services. DELIVER — the Design Environment for Novel Vertical Lift Vehicles — harnessed the NASA Ames, Glenn and Langley Research Centers for their expertise in design and analysis, high-fidelity computational fluid dynamics, acoustics, propulsion, autonomy, and wind tunnel and flight testing. The Principal Investigator based at California’s NASA Ames explained, “We have tools that have been validated for larger vehicles — traditional helicopters and tilt rotors and the like — for decades. For some of these package delivery drones or urban air mobility-type vehicles that look very different from traditional rotorcraft and rely on electric propulsion, we don’t know how well our tools work.”
NASA’s in-house effort was aimed at helping non-traditional aerospace companies size their innovative platforms. Theodore summarized, “The goal of DELIVER was to demonstrate the applicability of our tools for these new concepts and new vehicles. What do these companies really need in terms of data, and how do they use it as part of their analysis process?” DELIVER formulated a flight test program for NASA’s GL-10 Greased Lightning unmanned aerial vehicle (UAV), and it teamed with San Diego-based Straight Up Imaging to test high-end quadcopters. “We definitely put an emphasis on going out there and testing,” said Theodore.
Researchers used test data to validate the common NDARC (NASA Design and Analysis for RotorCraft) sizing tool and ANOPP2 (Aircraft Noise Prediction Program 2) on unconventional configurations. NPSS — the Numerical Propulsion System Simulation code — is meanwhile being updated for electric motors and propulsion concepts. According to Theodore, “Electric propulsion is really a key enabler to a lot of these new vehicles, particularly as you get to multiple propellers in very different configurations. You can’t really do them with a gas turbine or internal combustion engine and shafts running to each of the props. Electric propulsion really opens up the design space. We need to make sure we’re accurately accounting for the performance, weight, and various aspects of various propulsion systems in our design tools,” He added, “This is also probably the first time that the FAA is looking to certify a vehicle with electric propulsion, so this is a new area. The failure modes, all the redundancies you need, and how the FAA would go about certifying these is kind of an unknown.”
DELIVER concluded at the end of fiscal 2017, one of the accelerated Convergent Aeronautics Solutions (CAS) activities under the NASA Aeronautics Research Mission Directorate. Theodore said, “Most of the work, or at least a significant part of it, will be transitioning to RVLT, taking what we’ve learned from DELIVER and rolling it into more of a research project in RVLT.”
Down Under to Out West
Colin Theodore grew up in Sunbury, Australia, about an hour from Melbourne, in a family without formal aerospace or engineering ties. He recalled, “My father, Barry Theodore, was a keen model airplane enthusiast in Australia and belonged to a local club. I was young but remember being fascinated by the aircraft that they were building and flying, and the passion that they put into it. I always wanted to figure out how the aircraft worked and what made them fly.” The DELIVER Principal Investigator observed, “I always knew that aviation was where I needed to be. I think for me, aviation seemed like one of those really challenging areas that would give me an opportunity to make a contribution to something that just seemed really difficult.”
A bachelor’s degree in aeronautical engineering from the Royal Melbourne Institute of Technology (RMIT) provided the foundation. “I spent a year or so looking for an aerospace-related job, but there were not a lot of those types of jobs in Australia. I ended up getting a job at the Defense Science and Technology Organization [DSTO, now called the Defense Science and Technology (DST) Group], working on fatigue analysis and testing of the F/A-18. That had the goal of extending the life of the fleet.”
The RMIT curriculum had little rotary-wing content, but Theodore remembered, “There was one professor who had an interest in helicopters, Lincoln Wood, who taught what could be called an Introduction to Helicopters. Based on his class, I joined the American Helicopter Society in the late ‘80s. When I was looking for schools to apply to in the United States, he was the one who recommended the University of Maryland. From an early age, I had always wanted to visit the US, probably because of all of the US TV shows that we got in Australia, plus all of the amazing airplanes that were made here.”
Theodore recalled, “It wasn’t until I actually got to the University of Maryland that I learned that my assistantship was in the area of helicopter flight dynamics and controls with Professor Roberto Celi as my advisor. My research focused on flight mechanics simulation and incorporating high-fidelity aerodynamics modeling using a free-wake. That’s been something simulation codes kind of get wrong — off-axis response most of the time is predicted in the opposite direction. I was able to show that if you use a free-wake model for the rotor wake, you’re able to get the off-axis response in the correct direction.”
A presentation based on his dissertation earned Theodore a contract job at the US Army Aero flight dynamics Directorate (AFDD — now part of the Aviation Development Directorate, ADD) at Moffett Field, California. “I didn’t have a much background in flight or wind tunnel testing, and AFDD, particularly Mark Tischler’s group, had a lot of activities where flight testing was key.” Theodore recalled, “I was able to participate in a lot of projects with AFDD including fixed-wing and vertical flight, starting with some of the small ducted fans that DARPA [the Defense Advanced Research Projects Agency] was looking at and including very large aircraft, in particular the Boeing 777.
“I am especially proud of the work that I did in development of flight dynamic and structural models of the Boeing 777 from flight tests. We were demonstrating the simultaneous identification of flight dynamics and aircraft structural modes. This work was also the first and only time that I’ve actually been on the aircraft during system identification flight testing, and also riding in the cockpit during landing is something that I will always remember.”
AFDD also conducted PALACE — the Precision Autonomous Landing Adaptive Control Experiment — to land a Yamaha R-MAX UAV in an obstacle-rich environment without GPS navigation. “This was really my first exposure to technology development for UAVs and UAV operations, and it gave me a really good appreciation for the real-world challenges that are involved.”
Theodore joined NASA in 2007 in the flight dynamics and controls technical area. NASA and AFDD ran joint wind tunnel tests of Individual Blade Control (IBC) on a full-sized UH-60 main rotor in the National Full-Scale Aerodynamics Complex (NFAC). Theodore explained, “One of the things they had problems with is when you change IBC inputs or turn IBC on and off, the rotor trim changes in terms of thrust and propulsive force. Is the benefit because of IBC or because the rotor trim was different? I developed an automatic trim control system, so regardless of what you’re doing with IBC, rotor trim stays exactly the same. You could really make an apples-to-apples comparison between what is the true effect of IBC in terms of performance, power required, things like that.” NASA’s Large Rotor Test Apparatus trim controller was used all through IBC tests in 2009 and UH-60A airloads tests in 2010.
NASA subsequently turned its rotary-wing focus on big civil tiltrotors. “What we did in the flight dynamics and control area was look at what are some of the specific challenges of flying these vehicles from a piloting and handling qualities perspective, and how can we mitigate those.” Theodore worked on piloted simulations in the Ames Vertical Motion Simulator to explore civil tiltrotor control strategies.
DELIVER targeted a new design community with a very non-government culture. “Almost all of the companies working urban air mobility or package delivery are not traditional aerospace companies,” said Theodore. “They have a completely different culture than NASA. They’re not used to working with the government. We have different goals, different timeframes, and completely different ways of doing things.”
New vertical lift concepts also present different challenges. “Autonomy is really going to be a key enabler in a lot of these new markets, whether it be urban air taxi or drone package delivery. You’ve got a lot of components on the vehicle; you’ve got software; you’ve got communications equipment. All of these things that enable you to do your mission weigh something. They take power, and they take volume. You need to take that into account up front. As you get smaller vehicles, all this equipment may have a significant impact on the size and weight of the vehicle.”
Theodore noted, “Noise is probably the biggest barrier to increased use of helicopters and rotorcraft around urban areas. The biggest perception is drones — because they’re small and electric — are going to be quiet. For urban air taxis, the perception is the same. The reality is noise is going to be a big factor in any kind of urban operations. In DELIVER, what we really wanted to do was focus on small delivery vehicles; a lot of them are multicopters. We wanted to understand the characteristics of the noise; how well do our current tools predict noise. We also wanted to understand the level of annoyance, so we did some human-subject testing where we compared noise from multi-copters to noise from ground delivery vehicles like cars and panel trucks.”
Understanding operating costs is also key to new vehicle acceptance. Theodore offered, “Helicopters have traditionally been fairly expensive to operate, so if you want to use one of these new vehicles for urban air taxis, it has to be affordable. Reducing airframe costs and reducing maintenance and operating costs are key. I think that, ultimately, autonomy will be one of the key factors that removes the pilot or operator from the vehicle itself, so that reduces your costs and increases your payload. I don’t think autonomy is really there yet in terms of being used for these vehicles at least in the short term.”
Theodore has joined several aerospace professional associations over the years but noted, “AHS is really the only one that’s stuck. I was destined to be in the helicopter field even before I knew it.” He is currently the AHS Western US Region Vice President on the AHS International board of directors. “We have a San Francisco Specialists’ Meeting coming up in January, and I’m the technical chair,” said Theodore. “What I’m really excited about is that this conference will bring together the traditional aeromechanics and transformational flight technologies communities. I see some real synergy there that will benefit everyone.”