Little and Large Extra Duo: Chris Burkett flying the Extra 300S – G-Force Aerobatics With Mike Williams Flying the 40% Scale Model

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.

“What do you get when you put Chris’ full size Extra together with Mike’s large scale model Extra? ANSWER: The most amazing display team I have ever seen” [UK Airshow Forums]

Voted a Top Ten Airshow Moment of 2013 by UK Airshow Review:

“Step forward Chris Burkett and Mike Williams, the former flying his Extra 300, the latter remotely piloting his 41% scale model of the Extra 300. This was a display like no-other I’ve ever seen, as both ‘little and large’ flew an aerobatic pairs routine with a precision you simply would not think possible whilst one of the pilots remained on terra firma. Stunningly flown and highly original – exactly what our top ten listing is all about!” [UK Airshow Review]

The display sequence is of course subject to weather – these notes give information on a typical full sequence when the cloudbase allows (c. 2000 feet).

Display Sequence – Manoeuvres

Wherever the runway configuration allows, Chris and Mike take off together; Chris rolling first and further before Mike joins him, offset nearer to the crowdline. Note that in general Mike is flying two and a half times closer to the crowd than Chris. This give the illusion that the two are more evenly matched for size and performance, and it also ensures a separation for safety.

After take-off both aircraft build speed and pull up together for a coordinated stall turn, before commencing a series of ‘formation’ manoeuvres in front of the crowd. The following is subject to change but may consist of: - Stall turn; - Slow roll; - Stall turn; - Loop; - Upward tumble; full left rudder and full forward stick; - 4 point hesitation roll; - Half-cuban; - Loop; - Push humpty bump with vertical hesitation roll; - Torque roll

The model now positions close to the crowd for some low speed high angle of attack flying and ‘prop hanging’ – using its thrust to weight of greater than one to hang vertically in the air using prop thrust alone. Chris positions to perform a couple of passes behind the model.

They then position for a ‘formation’ pass with Chris flying a slow maximum sideslip pass behind Mike. After this, they set up for the formation pairs ‘break’. This is a run towards and break in opposite directions.

Now Mike performs a couple of minutes of close-in solo model flying, showing off his skills and the incredible performance of the model. Meanwhile Chris climbs for height.

Now Chris dives in for some full-size solo figures, with the model off the display axis, typically very low, slow and close-in. His figures include the ‘Mulleroid’ – invented by and named after the Swiss aerobatic champion Eric Muller. 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. Other figures are both left and right foot tumbles, on vertical and 45 degree lines. During these manoeuvres the aircraft flies sideways whilst tumbling end over end, due to the combination of full rudder and full power causing a gyroscopic effect from the propeller (called precession).

After this the display ends, if time allows with a further model plus full-size flyby.

Extra 300S Full-Size 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, is flown by the current World Aerobatic Champion, Francois Le Vot .

What’s It Like to Fly?

When the controls are kept near the centre of their travel it’s an easy (if responsive) aeroplane to fly and, more or less, vice free. Once your brain has adjusted to the pace, take-offs and landings are straightforward. Operating the aeroplane ‘gently’ is entirely possible but this would be a terrible waste.

The Extra is such a willing performer that it begs to be pushed (and pulled) hard and, at the limits, is more than capable of inflicting pain. Despite feather-light control forces during normal operation, in a display sequence Chris is sometimes having to use both hands on the stick to accurately position the controls under very high loads. In negative flicks and some tumbles it feels like your head is being ripped off your body. Yet even whilst doing so the aeroplane remains highly predictable once you have learnt its ways.

Unlike the model Extra, thrust to weight ratios don't quite reach the 'magic' 1:1 level, in fact at roughly 0.75:1 it is a good deal less. So prop-hanging vertical hovers aren’t possible in the full-size machine. Vertical climbs of more than 2500ft, complete with multiple vertical rolls, are the norm, but from a high- speed entry, not a hover!

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!').

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!

The model is also equipped with its own smoke system, operating on similar principles.

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)

The Model

Mike’s Extra 330SC is designed after its full-size counterpart by the Czech company Krill Aircraft. The airframe is fully composite, comprised largely of carbon fibre. The design has been tweeked in order to cope with demanding 3D manoeuvres which are now the norm for model freestyle flying. The wing planform copies the full-size, however the model features much larger ailerons both in chord and span. It also uses a significantly different aerofoil section. The leading edge is much sharper than full-size and this gives a much cleaner break into post-stall manoeuvres like the harrier.

One of the reasons Mike can do manoeuvres like the harrier (a deceleration in level flight into ultra-high angle of attack beyond 45 degrees) is because the model flies with much lower wing loading than full scale, which makes the 41% machine incredibly forgiving and allows Mike to get away with things that Chris can’t. It also results in a very impressive thrust to weight ratio of roughly 2.5:1, which in turn allows the model to prop-hang at between 30% and 50% throttle. Full power results in an impressive acceleration out of the prop-hang and vertical lines can be extended indefinitely or until out of sight.

Power is provided by a 175cc flat twin two-stroke MVVS petrol engine, where each cylinder feeds into its own tuned exhaust canister system. This not only controls engine noise but also provides more linear throttling characteristics. In order to perform extreme 3D manoeuvres the control surfaces have around 60 degrees of available movement and are fully utilised when 3D rates are on.

Freestyle flying isn’t just full-on 3D, it also incorporates smooth aerobatics at which the model also excels. There are, however, some manoeuvres which the full-size can perform that the model can’t replicate – mainly any manoeuvre which requires large amounts of gyroscopic force. With a lightweight carbon-fibre prop and lower inertia, the gyroscopic effect on the model is drastically reduced.

Overall the 41% scale Extra is incredibly forgiving – though like any aeroplane there are limits to its flight envelope which must be respected.

Comparative facts: Model vs Full Scale

41% scale Extra 330 100% Extra 300S 100% Extra 330SC Length (m) 2.9 6.65 6.7 Wingspan (m) 3.1 7.5 7.5 Wing area (m) 1.7 10.4 9.8 Weight (kg) 17.7 750 700 Power (BHP) 20 300 320 Never-Exceed Speed N/A 220 kts 220 kts Max Cruise Speed N/A 170 kts 170 kts Thrust to Weight ratio 2.5:1 0.75:1 0.85:1 Price £6500 IRO £175,000 IRO £300,000

Pilot, Full-size – Chris Burkett

Chris has been an aviation enthusiast all his life, and first flew aerobatics in a de Havilland Chipmunk as an RAF cadet. Later he part owned his own Chipmunk, which 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.

For the last decade his focus has been advanced aerobatics, firstly in a Pitts Special biplane, and since 2008 in an Extra 300S, winning several trophies in aerobatic competitions. 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 focussing mainly on flying air displays under the moniker G-Force Aerobatics. This year has been an exciting one, with displays at major international airshows, firstly in Bahrain and then in China. At the Bahrain airshow he was flying a display for the courier company DHL, which involved flying in formation with one of their Boeing 757’s. In China, Chris was flying as a member of the Global Stars 4-ship display team, helping Skoda to launch a new car onto the Chinese market.

The “Little and Large” display with the radio controlled model that Chris and Mike are performing is quite unique, and at its debut in 2013 was voted a “Top Ten Airshow Moment of the Year” by UK Airshow Review.

Chris is also an aerodynamicist by profession. His company develops aerodynamic software for the design of wings. In fact their technology is most widely used by the Formula One motor racing teams. They need similar capabilities but this time for the generation of downforce to keep the cars glued to the track around high speed corners.

Advanced and unlimited level aerobatics is an intensely demanding activity, mentally and physically. Apart from “pulling g”, Chris enjoys tennis, squash, running, climbing, skiing and ski mountaineering to help stay in shape.

Chris is married with one son and lives in Bedfordshire.

To book a display at your event please contact Chris via his website at gforceaerobatics.com

Pilot – R/C Model: Mike Williams

Mike started flying radio controlled models at the age of nine and by the age of ten was learning aerobatics. Today he is one of the UK’s foremost competition and display model pilots. His achievements include: British Freestyle Champion, Top Gun aerobatics champion (twice) and numerous wins in F3A pattern aerobatics, F3A Advanced Class National Champion and Unlimited Class UK Shoot Out Champion. See http://www.novisiblehorizon.co.uk