A new microturbine venture called Sierra Turbines is seeking to revolutionize UAV engines with 3D printing. Using the metal additive manufacturing (AM) technology from manufacturer VELO3D, Sierra Turbines reduced part count in a critical component from 61 to 1 and saw a variety of important performance gains as well.

Sierra Turbines has published a case study on its work with VELO3D. Sierra Turbines CEO Roger Smith also took some time to speak with AUVSI about the case study and the benefits of its microturbine, Aurelius Mk1.

Can you start off by providing our audience with some background information on Sierra Turbines and what you all are seeking to achieve within the UAV industry?

Sierra Turbines was founded in 2017 in San Jose, CA. We are focused on tackling compact, power-dense power generation applications in auxiliary power units (APUs), backup generators and other standby electrical-generation needs.  Another market ripe for innovation is that of propulsion systems for unmanned aerial vehicles (UAVs), both for jet propulsion and hybrid-electric drivetrains.

We had pretty straightforward design objectives from the start, but they are actually very ambitious when compared with existing microturbines: A 40X increase in time-between-overhaul (TBO, which is typically only 25-50 hours for most small turbine engines), significantly increased power-to-weight ratio, and decreased unit cost to machines of comparable power output.

The founding team has gathered multiple decades worth of experience in aerospace, motorsports, and software; with the CEO Roger Smith spending 19 years at Apple before launching Sierra Turbines.

One of the unique things that you all plan to do is additively manufacture (AM) 95 percent or more of your microturbines even when you reach large-scale production, which according to the case study goes against industry belief that AM is limited to prototyping and low-volume work, so how did you come to the conclusion that this method was the best way to go?

Our team has extensive experience with additive manufacturing in the aerospace industry, where the technology has been used extensively for over a decade. For example, each CFM LEAP engine powering the 737 has 19 fuel nozzles that are additively manufactured. By tailoring our designs for additive manufacturing, we can simplify manufacturing, reduce weight and meet our cost target. We believe that embracing AM technology right now with it maturing at its current rate, we will have a steep competitive advantage and that we will reach the economies of scale for our business model very soon.

One of the key pillars of the technology that you all are developing is the metal additive manufacturing system from manufacturer VELO3D; how did your relationship with VELO3D start, and how has that relationship informed your work thus far?

We met VELO3D in 2018 right after the commercial launch of their digital manufacturing solution. Since they are also located in Silicon Valley California, it was easy to visit their headquarters and we were impressed with their team and technology. VELO3D’s applications team has rich knowledge in aerospace like jet engine design; their team brought metal AM to life for Sierra Turbines, and helped us achieve critical design features for our microturbine, while maximizing the benefits of AM. For the gas turbine core, some of the benefits include:

•            Reduced part count. The Aurelius Mk1 core design replaces 61 separate components with one part.
•            Closer tolerances, due to part consolidation, elimination of interfaces, and increased dimensional accuracy.
•            Reduced assembly work and post-processing.
•            Freedom to design complex geometries.

This high level of integration simply wouldn’t have been possible using most currently available AM machines. We approached several of the leading equipment manufacturers and found that none of them could produce the thin-walled, high-aspect-ratio combustor in our Aurelius design. VELO3D certainly has unique capabilities when it comes to manufacturing complex geometries.

The time between overhaul (TBO) for most small turbine engines averages 40 to 50 hours, but you intend to raise that value to 1000+ hours, which is on par with commercial aircraft; what are the benefits of such a large increase, and what will it take to achieve this?

One of our goals is to provide the best solution to power the Federal Aviation Administration (FAA) Part 107 guidelines, which focus on small unmanned aircraft (UAS) operations for drones weighing less than 55 lbs. Here UAVs have hit limits on power density due to lithium batteries storage of just 200 Watt-hours per kilogram. We are offering a 10X increase in power density to 2000 Wh/kg, which enables orders of magnitude of increased flight time and lifting capability. To accomplish this, we needed to address the service interval, and this was in fact what a handful of launch customers are most interested in.

The first part we can talk about today to achieving those lofty goals is the 3D printed engine core in HASTELLOY® X on VELO3D’s Sapphire system. This is the same material that is used in commercial aviation engines from General Electric, Rolls-Royce and Pratt & Whitney. The remaining aspect pertains to turbomachinery and rotating parts, which we cannot disclose details about for now. What we can say is that additive manufacturing allows us to incorporate intricate design features to unlock thermal efficiency and longer servicing intervals previously unseen in this product category.

Where are you all in the development process of your microturbine, Aurelius Mk1?

There is some development remaining as it pertains to the manufacturing and post-processing of the turbomachinery. Our aim is to have a handful of engines running towards the end of 2020.

Once Aurelius Mk1 is complete, how will you all go about commercializing it?

We are in active discussions and have signed agreements with several UAV manufacturers who, pending test data, will be launch customers. Additionally, we intend to work with AUVSI make full use of their expansive network.

How do you all envision your microturbine overhauling the UAV industry?

We see our solution as an enabler to design new UAVs with enhanced capabilities, as well as providing the energy source for UAVs to match and exceed mission profiles of human-operated aircraft. Take, for example, in California where we are located: our utility company uses manned helicopters with LIDAR sensors to inspect 25,000 miles of its infrastructure while flying extremely low at 400 feet. With our powerplant, UAVs can accomplish this mission in a much safer, more expedient manner, more frequently and economically. Our mission is to shift the paradigm in micro-energy solutions.

Photo below: Sierra Turbines CEO Roger Smith (right) with VELO3D’s Director of Aviation and Power Turbine Solutions, Will Hasting, and several 3D printed engine cores designed by Sierra Turbines and printed with a VELO3D AM machine. The front core is cut open to show the intricate internal structure, in which 61 components were combined into one. Photo courtesy of Sierra Turbines