As a college engineering/ design team with a small budget, we worried about the cost of 3D printing the components we needed. We were encouraged by our advisors from Raytheon to work with additive manufacturing company Stratasys Direct Manufacturing. Stratasys Direct Manufacturing showed us that the costs associated with the components we wanted to 3D print were far less than we originally expected. Our Stratasys Direct Manufacturing partnership enabled us to create something never before done in this field and helped our project win the best overall design award at the University of Arizona design showcase.
As is the case with all design projects, time was critical. The parts we designed and had 3D printed by Stratasys Direct Manufacturing saved us countless hours in construction. The fin structure alone, which was created via Fused Deposition Modeling (FDM) with high temperature ULTEM™ 9085 resin material, would have taken seven individual pieces and three days to assemble had we constructed it manually. Due to the cavities inside and the very thin fins in our design, 3D printing was the only way to create the structure as one piece. We wrapped all 3D printed components in carbon fiber for extra strength, slid the pieces into the aft end of the rocket and were ready to go a day after receiving the pieces, just in time to launch on our targeted date.
Rocket Components 3D Printed with FDM ULTEM™ Resin
The sustainer aft body system is comprised of a motor mount, tailcone and 3 fins with NACA 0003 airfoil cross sections. The motor mount and number of fins are a necessity to the design whereas the tailcone is a supplementary feature. Having these components exist as a single piece is not common; they are usually separate and assembled individually. It would have been impossible to manufacture this system as a single piece without additive manufacturing; we would not have been able to produce the rocket fins with airfoil cross sections.
The design we produced via 3D printing reduced drag and increased efficiency by 85% compared to a rounded flat plate. The reduced thickness in the fins incorporated intricate curvature, features very difficult to ensure in a physical product as deformed regions would jeopardize function. In addition, constructing the fins with the motor mount guaranteed equal radial spacing of 120° between fins which is essential for stable flight trajectory. Consolidation of the motor mount and fins immensely improved structural stability and mitigated fin flutter – a dynamic instability between aerodynamic and structural properties often leading to destruction. The mounting structures extended beneath the motor mount to a concentric tube, further increasing the structural integrity. The tailcone, the rearmost component of the design, served to reduce base drag by 40%. Construction techniques considered – which included CNC lathe, male and female mold composite layups or purchased parts – were not capable of completing this component as a single piece. The design which was realized with 3D printing reduced drag and assisted altitude targeting, achieving the goal of our project.
The 3D printed fin structure was placed in the aft of the sustainer stage, which is the top stage of the two stage rocket. The motor in the sustainer is ignited inflight and exhausts directly into the blast plate installed in the top of the bottom stage. The conical structure in the top of the previous picture is exposed to all of the exhaust from the ignition of the motor in a confined space. Exhaust temperatures of the motors used can reach more than 1500°F and is deflected directly towards the cone. The FDM piece made using ULTEM™ resin material behaved phenomenally and was only blackened with no detrimental loss of structural integrity.
To ensure our rocket and rocket flight computers had a safe return it was critical the rocket’s parachutes deploy at certain points during flight/ descent. On one of our first launches, it became apparent accessing the flight computers within the rocket to fix parachute deployment problems was incredibly difficult. The electronics were mounted to a sled deep within the rocket, which meant we had to disassemble the rocket to access the computers. I had previous experience creating circuit cards due to my internship, and suggested we 3D print circuit mounts for the project. We came up with the idea of mounting the electronics to a slide which we could easily pull in and out of the side of the rocket, allowing for short repair times if the electronics were malfunctioning. Once the rocket was properly positioned in the launch tower, we simply slid the 3D printed board into the rocket where it snapped in place; an exposed activation switch arms the controls.
The 3D printed tailcone for the booster stage also incorporated a 3D printed electronics sled for the sustainer stage. These two components are traditionally built using aluminum and plywood respectively. The use of 3D printing allowed us to custom tailor the components to our specifications and requirements.
From the time gained by 3D printing complex assemblies as single pieces, to the ease of use created by novel electronic mounting methods, our innovative ideas came to reality because of 3D printing.
About the Author
Matthew Dusard completed his undergraduate degree from the University of Arizona in May. Dusard’s senior project involved advanced construction of high power rocketry. He turned to 3D printing to achieve challenging design and construction goals to improve upon current structures and create an award-winning rocket.
Area-I provides flight research for commercial aviation and NASA by mimicking real situations for larger aircraft to reveal airflow dynamics and circulation experiments on a small scale with implications and results relevant to larger aircraft. Their unmanned Prototype-Technology Evaluation and Research Aircraft (PTERA) serves 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. The agency exists to help identify issues between wind tunnel and full-scale flight testing and allows researchers to learn as much as possible about a technology before the investment is made in carrying out full-scale flights.
The vehicles for accomplishing this mid-range testing are specific, customizable UAV’s. Area-I engineers had previously shied away from complex designs, limiting the parameters they could accomplish for mimicking full-scale air flight. With the freedoms of design from 3D printing, they were able to build mechanisms and structures they couldn’t previously manufacture. 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.
Recommending Selective Laser Sintering (SLS) technology and Nylon 12 CF, a carbon-filled nylon material, we helped produce a complex fuel tank, ailerons, flaps and a control surface for PTERA. SLS builds with a powerful laser that melts powdered nylons layer by layer. The parts remain encased in powder during the build, removing the need for support structures and allowing for complex geometries. These design benefits make SLS a perfect fit for aerospace production applications.
The ailerons that originally took 24 man hours to hand-build, were designed, built with SLS technology and assembled onto the UAV in only three days. The freedom of design allowed the Area-I engineers to add an inner anti-slosh baffling to steady PETRA in flight without losing fuel space and consolidate a duct component that had previously flown under the tank.
Advanced Ceramics Research designed a small UAV, The Silver Fox, for low-cost aerial surveillance imaging and to carry sensor payload packages. They wanted to develop a more reliable and larger fuel tank for the UAV while not occupying additional fuselage space.
We recommended SLS to produce the complex geometry with interior features from Nylon 11 PA material. The re-designed fuel tank provided greater structural integrity from the integrated piece and incorporated wire-way clearance passages for electrical wiring and cable routing. The part’s new shape increased fuel volume by 25% and included bulkheads to add additional strength and reduce fuel movement, resulting in a longer but more stable flight.
We were able to deliver, adjust and build three prototypes and 12 production fuel tanks in less than 5 weeks for Advanced Ceramics Research.
The advancements of 3D printing technology help create integral components for these advancing aircraft quickly, accurately and at a reduced cost. The benefits are lending in the advancement of UAVs for future applications. The projected commercial expansion of UAVs, including drones and other similar recreational aircraft, is widening the marketplace for this technology. In the coming years, 3D printing will likely continue to contribute to this marketplace and the unique world of unmanned flight.
