Dr MARK JABBAL, Lecturer in Aerospace Engineering, Brunel University, describes how he and his students helped out with the aerodynamics behind the scenes at James May’s Toy Stories channel glider attempt for a BBC TV special. This is a full article published in Aerospace International: March 2013 [caption id="attachment_7832" align="alignnone" width="375"] Top Gear presenter, private pilot and aeronautical enthusiast James May with the students and glider. (via author)[/caption] In March 2012, I received a request from Plum Pictures for a group of student engineers to take part in the latest instalment of BBC’s James May’s Toy Stories – ‘Flight Club’ TV documentary. The challenge? To design and build an unmanned, scale model glider in an attempt to fly it across all 22 miles of the English Channel, representing a first in model aviation. An insight is given into the technical challenges of building the glider, with which the Brunel team were heavily involved, and the practical issues of working on a TV documentary. The glider that was built for the programme was a 1:5 scale model of the Slingsby T45 Swallow; originally designed as a club sailplane and also used as a RAF trainer. James May chose the Slingsby Swallow, as it was reminiscent of the Keil-Kraft type of gliders he built as a kid. It also has a fairly fat fuselage which, although quite ‘draggy’, would be useful for accommodating the cameras and batteries (three Flycam HD; two wing mounted and one rear fuselage mounted) and tracking kit (GPS and Ardu autopilot).
Improving the glide ratio[caption id="attachment_7833" align="alignnone" width="376"] The RJ Mitchell Wind Tunnel at University of Southampton was used to test the design. (via author).[/caption] To verify the glide ratio, wind-tunnel tests of a scale model of the glider were carried out in the RJ Mitchell Wind Tunnel at the University of Southampton. Tests were conducted at a range of free-stream velocities (around the best glide speed) and angles-of-attack (–5 to 5 degrees). The tests revealed that the glider had a maximum glide ratio of 14:1, which would ultimately be insufficient for it to complete its mission. A minimum glide ratio of approximately 20:1 was deemed necessary based on the 22-mile Channel distance and a ceiling for launch of approximately 6,500ft, as permitted by the CAA. The onus on the Brunel team therefore was to improve the aerodynamic efficiency of the glider. No changes were permitted to the fuselage due to the space requirements for equipment (although the original glider undercarriage, a skid, was omitted from the underside of the model fuselage). Furthermore, for filming purposes it was the intention to maintain many of the most prominent wing features true to the original which meant geometric properties such as aspect ratio, taper and twist couldn’t be altered. The original airbrakes were to be omitted with the main focus subsequently drawn to changing the less visible aerofoil section. The original wing has a NACA 633618 aerofoil at the root which extends to 80% of the wing span before transitioning to a NACA 4412 aerofoil at the tip. The laminar flow encouraged by the NACA 6 series aerofoil, however, could be severely affected by rain droplets, dirt or crushed insects on the leading edge. Incorporating ‘bug-wipers’ would be too complex given the time constraints of the project, not to mentioned that there was no dedicated onboard power for such devices. It was thus decided to change the root aerofoil to the NACA 4412 which, although a more ‘turbulent’ wing, has predictable performance that is less receptive to surface roughness as well as having a more slender profile compared to the laminar aerofoil (a maximum thickness-to-chord ratio of 12%, as opposed to 18%). The tip aerofoil was changed to a NACA 6412, which would offer increased camber and CL compared to the 4412; particularly useful for preventing the onset of early wing tip stall. Transition between the two wing sections was kept in the same place as the original. The modified wing design was verified using ‘XFLR5’, an analysis program for aircraft operating at low Reynolds numbers. An improved glide ratio of almost 30:1 was obtained which would be closer to 20:1 after factoring in the fuselage, yet still sufficient to meet the requirements for the mission. The time constraints of working on a TV documentary meant that the new wing couldn’t be verified experimentally in a wind tunnel. In fact, there were only a few days to come up with a new wing design, such that all the modified wing parts could be laser cut by Traplet Publications (suppliers of model aircraft kits) and delivered in time for the filmed glider build. The entire glider was made up of more than 1,000 pieces of balsa wood.
Assembling the glider[caption id="attachment_7834" align="alignnone" width="393"] Constructing the wings (via author).[/caption] The student engineers set about assembling the wings, as well as the tail and fin, over a five-day period in an aircraft hangar at Wycombe Air Centre. James and his assistant engineer constructed the fuselage, also in the hangar during the same period. Meeting James May on the first day, one might have been forgiven for thinking that the students might be overawed by the opportunity to work alongside a well-known presenter. But this was quickly dispelled, due in no small part to James’ enthusiasm for aviation, approachability and very hands-on involvement with the glider build. Different aspects of the glider build were intermittently filmed over the five-day period meaning that, for the most part, the students were working without the constant glare of the cameras. The challenge was ensuring that this air of ‘normality’ was maintained when the glider build, and therefore the students were being filmed. But, again, the students quickly adjusted to this environment due in part to the relatively short time available for building. The fact that many of them had already worked together in group projects at Brunel also helped. A mix of aerospace and aviation students of both undergraduate and postgraduate level were drawn together, among which smaller groups had previously built a model aircraft for the annual BMFA Heavy Lift Challenge (in which, coincidentally, Brunel gained first place among UK universities and second place overall in 2012); an electrical glider, a solar glider and a model aircraft with morphing wings. The most challenging aspect of the glider build was in ensuring that the new wing designed and built by the students would fit well with the fuselage built by James, especially given the modifications to the root aerofoil section and preservation of the original fuselage design. This required some improvising at the wing-fuselage junction through a combination of bespoke cut parts and duct tape, the latter of which was used to act as an aerodynamic seal along any gaps. Applying the skin to the glider in the form of heat shrink wrap is also a skilled art, as many aero modellers will attest to!
What the students learnt[caption id="attachment_7835" align="alignnone" width="375"] Working on the TV project was an opportunity to apply technical and interpersonal skills. (via author).[/caption] It’s fair to say that the students thoroughly enjoyed their time working on this unique project. For those students who had previously secured graduate employment this project provided the opportunity to apply technical and interpersonal skills that will be utilised in the aerospace industry, whileothers have been inspired to continue their aerospace career goals. George Schofield (MEng (Hons) Aerospace Engineering), who led the wing redesign using XFLR5 and is now a Graduate Engineer at BAE Systems, said: “As part of my third year project looking at the effects of ice accretion on aircraft, I learnt to use the XFLR5 computer program. This tool can be used for quick aerodynamic analysis of aircraft. These skills were utilised when the ‘James May Glider project’ team asked for help with the redesign of the glider wing and aerodynamic analysis. It was really good to see my degree used successfully in a real life application.” Adam Todd (BEng (Hons) Aviation Engineering), who was heavily involved with the wind-tunnel test and glider build and is now a graduate engineer at MBDA, said: “After learning how to apply the theory of flight to wind-tunnel testing during my final year project, the opportunity to help out on James May’s Toy Stories was perfectly timed. Bringing that experience into the real world to help analyse an aircraft was invaluable in transitioning from academia into applied engineering, whilst building the model aircraft to engineering drawings is a transferable skill in every area of the industry.” Finally, Tom Small (BEng (Hons) Aviation Engineering with Pilot Studies), a former Air Cadet, who as ‘glider spotter’ was at the helm of the glider RC should manual override of the control surfaces be required during the flight attempt, said: “Piloting the glider for James May’s Toy Stories was not only a fantastic experience but also a privilege. Everything I had learnt while studying Aviation Engineering at Brunel, such as weight and balance and dynamic effects was critical and this knowledge was put to the test during flight testing. The theory I had learnt allowed me to better my piloting skills and predict what the glider may do the first time it was flown. I’m proud to say I was a part of a successful project along with Brunel.”
Summary[caption id="attachment_7836" align="alignnone" width="403"] Working together the students were able to help James May realise his Toy Stories dream of a giant balsa wood glider. (via author).[/caption] If the students and indeed myself can take anything away from this experience, it’s the importance of working together as a team to achieve a common goal under tight deadlines and to expect the unexpected! [The final successful flight was the 22 nautical miles from Ilfracombe to Lundy Island, after the English Channel was prohibited by bureaucracy and the Bristol Channel attempt to South Wales was hampered by the weather]. All these will be important lessons as they embark on what will hopefully be long and fruitful careers in the aerospace and aviation industry. Of course, being associated with a new British record for longest flight by an unmanned model glider and a part of model aviation history in the making is a nice bonus too! Via aerial filming company Flying TV, check out a clip from the TV show here
This is a full article published in Aerospace International: March 2013. As a member, you receive two new Royal Aeronautical Society publications each month - find out more about membership.
Aerospace International Contents - March 2013News Roundup - p 4 News focus- p 11 The 787's woes - lessons from the past? Chinese airpower in the 21st century - part II p 12 China's defence capability and aerospace industry base Inside TV's 'Flight Club' - p 16 Glider aerodynamics with 'Top Gear' star Red Shift - p 18 Russia's air power modernisation Eurocopter sales take-off - p 22 European rotorcraft maker goes from strength to strength Plane speaking - p 26 On the record with British ESA astronaut Tim Peake Smart research - p 30 Finding accurate aerospace research data on the Internet The great runway debate - p 32 Conference report on pros and cons of new SE England runways or airports The last word - p 34 Keith Hayward on the economic implications if Britain left the EU.