University of Southampton – AM Aircraft takes flight
Professors Keane and Scanlan from the Southampton University worked in partnership with 3T to produce ‘the world’s first 3D-printed plane’* – The Southampton University Laser Sintered Aircraft (SULSA) – which has successfully taken flight.
The brief from the Professors included that the aircraft had to be lightweight and strong, as it would be built in just four parts – the main fuselage and rudder fins, the nose cone and two outer wings. They were looking for a process that could integrate multiple design features to make the assembly of the model quick and easy, without the need for time-consuming post-processing. The aircraft fuselage and wings housed a number of internal mechanical components and they required a simple method of fitting them.
The SULSA team took advantage of the benefits offered by plastic Additive Manufacturing (AM) and used the nylon Selective Laser Sintering services of 3T. The four parts of the plane simply clipped together to form an Unmanned Air Vehicle (UAV) with a 1.2 metre wingspan.
The Solidworks design drawings created by the SULSA team were passed to 3T’s team of CAD Engineers who incorporated the snap fittings required to hold the four nylon parts together to form the overall aircraft. They also designed mountings and channels to hold the ten internal components, enabling the motor, battery, avionics and controls to be clipped into place inside the main fuselage, and two servos, one in each wing. The wings had two ailerons moulded in with hinges and there were similar large hinged flaps on the rear control surfaces.
All these features were incorporated into the aircraft’s design and the ability of plastic AM to create hinge features and clips meant that they were built as integral parts to the main components, thereby increasing their functionality and reducing the need for additional parts to be fitted post-build. No screws or other mechanical fasteners were used in the design at all.
Jim Scanlan, Professor of Aerospace Design at University of Southampton, says “The entire structure of the aircraft has been printed including wings, integral control surfaces and access hatches. Thanks to 3T’s CAD Engineers, no fasteners were used and all equipment was attached using ‘snap fit’ techniques such that the entire aircraft can be put together without tools in minutes.”
The flexibility of the laser sintering process allowed the SULSA design team to re-visit historical techniques and ideas that would have been prohibitively expensive using conventional manufacturing. One of these ideas involved the use of a Geodetic structure. This type of structure was initially developed by Barnes Wallace and famously used on the Vickers Wellington bomber which first flew in 1936. This form of structure is very stiff and lightweight, but very complex. If it was manufactured conventionally it would require a large number of individually tailored parts that would have to be bonded or fastened at great expense. Hence, plastic AM offered the ideal solution for this project.
Scanlan adds “Another design idea that laser sintering facilitates is the use of an elliptical wing planform. Aerodynamicists have, for decades, known that elliptical wings offer drag benefits. Heinkel produced the He 70 aircraft in the early 1930’s which exploited such a wing. More famously Mitchell’s, aerodynamicist Beverley Shenstone selected this shape for the Spitfire aircraft of the late 1930’s.
The Spitfire wing was recognised as an extremely efficient design but it was notoriously difficult and expensive to manufacture. A direct contemporary of the spitfire, the German Messerschmitt 109, used a tapered wing that was slightly less aerodynamic but roughly half the manufacturing cost of the Spitfire wing. Again, laser sintering removes the manufacturing constraint associated with shape complexity and in the SULSA aircraft there is no cost penalty in using an elliptical shape.”
Stuart Offer, plastic AM Sales Manager at 3T, concludes “This project took little more than a month to complete with initial design drawings being submitted to us in early May 2011, and the UAV making its first flight on 8th June 2011. With simplified assembly due to the internal design features, plastic AM was the ideal solution as it also offered tremendous strength despite the weight of the plastic parts being less than 2kg. The ability to produce complex yet lightweight components contributed immensely to the success of this project.”
The aircraft was flown by a miniature autopilot developed by Dr Matt Bennett, one of the members of the SULSA team.
The additional design work was carried out by Rob Weighill and Dan France, both plastic AM CAD Engineers at 3T, and between them they spent approx. 7 full days working on the extra features.
The case study featured in the New Scientist in July 2011 – view the article here.
University of Southampton has a section on their website dedicated to the UAV – view it here.