G-Force Aerobatics : Chris Burkett flying the Extra 300S Commentary Notes Please see the website http://www.gforceaerobatics.com for similar/supplementary information. Please mention that we can be booked to fly at private events, and refer to the above website. The display sequence is of course subject to weather – these notes give information on a typical full sequence when the cloudbase allows (at least 2000 feet). Display Sequence – Manoeuvres A diving start, with multiple flick rolls, usually towards the crowd (depending on site). Pull up into a freestyle manoeuvre usually known as a Mulleroid – invented by and named after the Swiss aerobatic champion Eric Muller. His own name for it was the “Zwirbelturm” or “spiralling tower” sometimes referred to as the “helicopter spin” which is also quite descriptive. This is an upward negative flick roll, which is made flatter and flatter until the plane is spinning horizontally at the top with its nose on the horizon, before descending back down in a positive flat spin at full throttle. The next figure is usually an upward tumble with the nose held on the horizon by full rudder plus the effect of torque and precession from the propeller, which keeps the aircraft sideways as it tumbles upwards. At the next pull-up Chris flies a double flick roll at the top of a loop, sometimes known as an avalanche. Instead of continuing the pull he pushes upwards round a full outside loop, quite an uncomfortable manoeuvre with the blood rushing to your head under negative g. At other times Chris’ body will be experiencing 8 positive g and weighing more than half a tonne, hence a regular training programme is important to withstand the extreme forces of unlimited level aerobatics. He continues the push to the vertical, with a stall turn against the engine and into an inverted flat spin. Full power and full control deflections combine with the propeller gyroscopics to keep the inverted spin very flat. A humpty bump with a push over the top is followed by a rolling pass. Then he pulls up into a half loop with one and a half negative flick rolls at the top and then straight into a tumble using full left rudder,full forward stick plus some deft aileron inputs. Now up to 5 negative g as Chris pushes up through a half loop before pulling into the vertical for a stall turn to the left, this time letting the nose swing right through onto the horizon, before pushing full forward stick and entering a downward tumble known as a knife-edge spin – a fun manoeuvre to fly, but at times it can feel as if your head is being ripped off your body! If the exit from this manoeuvre is away from the crowd this will set up for a half loop pull-up to demonstrate a two and a half turn end-over-end forward tumble coming towards you. This manoeuvre is often known by its French name the ruade, which translates as a ‘mule kick’ – you can certainly feel like you are inside a tumble drier if not being kicked by a mule! A rolling quarter clover leaf and pull through positions for a 45 degree knife edge with a single turn ruade from knife to knife, followed by a bridged apex and pull through. After a pass he pulls up for a stall turn with an upward vertical flick – a tricky manoeuvre from the unlimited level competition repertoire. The next crowd centre pull-up is a continuous left roll in the vertical, becoming a torque roll, with propeller torque and slipstream keeping the plane rolling, even when it runs out of speed at the top and starts sliding backwards through its own smoke! Through the display, speeds go from close to the maximum speed of 220 knots down to less than zero in the torque roll. Towards the end there are passes with slow then fast roll rates, and in knife edge or with extreme sideslip. There is also an inside-out positive-negative flick roll on a climbing line. Smoke The Extra has a separate tank which is able to hold up to 35 litres of a special oil, and this is pumped at a rate of about 2 litres per minute into the lower part of the exhaust. The heat from the exhaust vaporises the oil into a white smoke. The mineral oil that Chris uses is akin to baby oil – it is very pure, safe and harmless to the environment. Though when he flies backwards through it, it can sometimes fill the cockpit for a while which is a bit disconcerting! Aircraft The aircraft Chris is flying is the Extra 300S, which is a lighter, higher performance single seat variant of the more common two seater, the Extra 300L. It was designed by Walter Extra, a German aerobatic pilot and engineer. His designs have rewritten what it is possible to do in an aerobatic plane. The carbon fibre wing spar is incredibly stiff and strong, designed to an ultimate failure load of 24g – at these stress levels the weakest point in the system is more likely to be the pilot! The high strength and stiffness make it possible to fit enormous control surfaces – rudder and elevator have large maximum deflections, and the ailerons are almost full span. This gives eyeball popping roll rates of around 400 degrees per second - and even faster than this in 'snap' or 'flick' rolls. Trying to improve upon the highly successful Pitts Special biplanes of the 1970's and early 1980's, Walter Extra soon concluded that the future of aerobatics lay with monoplanes, both because of the intrinsically higher performance available from an aircraft that did not have to carry external struts and bracing wires, and also due to the cleanness of the profile presented to the aerobatic judges during competition. His designs have evolved from the Extra 230 (4 cylinder engine, wooden wing), through the Extra 260 (6 cylinder engine, wooden wing), to the Extra 300 series of aircraft with their 300+hp six cylinder Lycoming engines and carbon fibre wings. The fuselage is of 'conventional' welded steel tube construction (good for 16g) and covered by glass fibre panels, with some fabric covering at the rear. Chris’ aeroplane was built in 2006 and was the last Extra 300S model produced. The Extra 300S has placed highly in World Aerobatic Championships, and has been flown in the Red Bull air races by pilots such as Nigel Lamb, Paul Bonhomme and Peter Besenyei. Its latest evolution, the Extra 330SC, won the World Championships in the hands of Renaud Ecalle when flown at Silverstone UK in 2009. Unlike a model aerobatic plane, thrust to weight ratios don't quite reach the 'magic' 1:1 level, so indefinite 'hovers' are not possible - though full scale machines are getting ever closer to this. However, thrust to weight, propeller torque and gyroscopic precession are all sufficiently high that it has been possible to invent a new class of aerobatic manoeuvres with these aircraft – the gyroscopic “tumbles”, and Chris demonstrates these in his display. The plane can be yawed so that it is travelling completely sideways, whilst tumbling in a tight outside loop end over end. This can be achieved whilst going vertically up, vertically down, from the top of a loop, or even straight towards the crowd! The usual reaction is 'how did he do that?!' (and, often, 'ouch, that must hurt!'). Extra 300S Statistics Engine: Lycoming AEIO-540, 300hp at 2700 rpm Maximum full power fuel consumption: 1.5 litres per minute Propeller: MT 4- bladed, constant speed (3 bladed version also available but noisier!) Empty weight: 630kg Maximum aerobatic take-off weight: 820kg VNE never exceed airspeed: 220 knots Stall speed from steady flight: 55 knots Rate of climb: 3200 feet/minute Fully certificated aerobatic g-limits: +10g to -10g Wing span: 7.5 metres (24.6 feet) Wing area: 10.4 square metres (112 square feet) Pilot – Chris Burkett Chris has been flying aerobatics for the last decade, firstly in a de Havilland Chipmunk. This also led to some early display and formation flying as part of Captain Neville's Flying Circus, involving balloon bursting, flour bombing and flying 'limbo' underneath bunting. Aerobatics however was always the special focus and Chris progressed to flying the Pitts Special, the iconic aerobatic biplane flown by almost all the great competition and display pilots at some stage in their careers. In 2006 Chris entered aerobatic competition in the Pitts. He started the season with a maiden win first time out in both of the first two tiers of aerobatic competition, and ended the season as UK National Aerobatic Champion in the Standard category. Competition aerobatics involves flying Known and Unknown sequences of aerobatic manoeuvres within a designated 'box' of sky, in front of a panel of judges, who award marks for accuracy. In recent years Chris has been flying advanced aerobatics in the Extra 300S. He has held a CAA Display Authorisation for the last six years, and has been a member of the British Aerobatic Association for many years, participating as a competitor and serving as a judge and volunteer. Competition flying experience provides excellent discipline and progression through the aerobatic repertoire to the more advanced freestyle maneuvres. He now also offers training to others - a previous student was coached from aerobatic ab initio to a win in his first aerobatic competition. Chris has had an interest in aviation since childhood, and is an aerodynamicist by profession. His company develops aerodynamic software for the design of wings.