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Building superlight

Part 1: Introduction to the Cricri

Aircraft are built to fly, but the process of assembling, creating, fabricating and finally completing an aircraft can be rewarding in itself. In this, the first of three articles on the process of constructing and flying a Cricri over six years, Wayne Butt (SAA SP1517) describes his experience. he ultimate SAA activity has been and always will be the successful building and flying of aircraft, so my purchasing the first non factory-built Zodiac CH601 didn't quite cut the mustard. Even removing its original VW engine and replacing it with an EA81 Subaru was just not the same as building an aeroplane from scratch -- but it did give me 10 years of fettling and fiddling with a sound example to hone skills for that titan of aircraft projects -- building an aerobatic aeroplane from plans. With the idea incubating for 20 years, the final push was having Nev Hay invite me to a cockpit seating in his newly finished Cricri at Pikes Point in 2003. Within weeks, with wife Gill's ap-

John King

T

proval, garage cleaned out and work cut back to accommodate the immense scale of the project, the plans were ordered from the designer himself and the battle commenced. The Cricri is a very long build for such a small aeroplane. The starting point is a scroll of plans and an excellent construction manual. There is no kitset and only a few of the requisite parts can be purchased -- fuel tank, fibreglass wingtips, main undercarriage and canopy, all made to order from small manufacturers scattered across France. Its phenomenal light weight is the most appealing feature of this diminutive aeroplane. The end goal is to have a completed, painted, instrumented and ready-to-fly aircraft weighing under 75 kg (165 lb). Well, that's the goal. Most builders make their first weigh-in at 85 to 90 kg, which still gets you flying with a full tank as long as the pilot weight is less than 75 kg. I weigh 72 kg and the final empty weight of my Cricri was 89 kg (196 lb), but non-standard engines and titanium expansion chambers probably contribute most to the mildly heavy weigh-in. Building light is the goal for every single component. The Cricri doesn't

skimp on controllability. Even at 85 kg (187 lb) you get brakes, steerable nose wheel with bungee suspension, full flaps and controlled vents for outside air. Thought and shavings go into every fabricated part, from fasteners to brake systems, fuel cocks to wheel hubs, throttle quadrants to instrument panel, and even your selection of headset. For those who are new to the story of the Cricri, around 1970 a very gifted French aviation technical student, Michel Colomban, set himself the task of designing the lightest possible single-seat aircraft. It was to have all the control facilities of a conventional aeroplane and was designed to be aerobatic from the outset. All this transpired well before "microlights" became common parlance in aviation. Michel Colomban is now in his 70s and living on the outskirts of Paris. His first design was the Cricri which marked the start of an exemplary aviation career. My plans and manuals arrived from France on April Fool's Day 2003. Digestion of the plans in every detail was the starting point. So much to learn for a first-time builder. There have been plenty of "what have I done?" moments. Cricri build-

Wayne Butt

Still in the garage, weighing 89.4 kg after six years of building. The engines turn opposite directions which meant finding a source for matching left- and right-hand propellers.

Wayne Butt

One wing set up in the jig, with 34 ribs bonded to the main spar, almost ready for the skin to be vacuumed bagged on for rivet-free surfaces.

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Winter 2010 SPORT FLYING

Wayne Butt

Even the latches for the canopy are fabricated from sheet 2023 aluminium. This three-piece over-centre latch represents five hours of work, tempering the aluminium to achieve tight radius bends.

ing is deÀnitely not for the fainthearted. Even a very basic example might consume 2000 hours of recreational time, but what aircraft builder can resist the temptation to build in "improvements"? Before you know it you can be thinking (as I did) of an upgrade to hydraulic brakes, a taller canopy, an EFIS instrument panel, an inspection hatch for the hard-to-getat area, non-standard twin-cylinder engines and customised tuned expansion pipes. Just small changes, yet they account for hundreds of additional hours -- all just part of the fun. The Cricri is skinned in 2023 aluminium of 0.4 mm and 0.5 mm thickness with solid and blind rivets and extensive use of epoxy adhesive which is the only Àxer of wing skins to the ribs. The T tail is hinged with spherical metal bearings, as is the rudder. The wings are designed for +6 and ­ 3G limit loads, allowing for quite vigorous aerobatics. They plug into a box section within the fuselage, secured with two main pins and four additional PIP pins. The ailerons/Áaperons run the full length of each 2.2 metre wing and are attached within the fuselage to torque tube and pushrod controls by a simple snap-on ball Àtting. The whole aeroplane can be dismantled and installed in its custom trailer in about 10 minutes -- but why rush? Less chance of damage if you take 20 minutes. Monsieur Colomban has mastered lightness. If I had to pick an innovation rarely seen on homebuilt aircraft to achieve this, it would be the structure of the wings. All 64 ribs are identical, fabricated from Klegecell, a dense foam used in the boatbuilding industry. The 6 mm thick ribs are formed in batches of six SPORT FLYING Winter 2010

The network of fuel lines and electrical systems is set up before the top skin goes on. The design doesn't include a hatch to this area, but it is an extra that just seemed logical.

with a rotating sanding drum following a metal template. The wing skins are secured to the bonded ribs with a vacuum bag process using epoxy adhesive. The result is an efÀcient looking laminar Áow aerofoil with no rivets or fasteners except at hard points and trailing edges. Constantly following a theme of lightness, the builder is encouraged to leave out all the washers under fasteners, to cut and Àle all screws and bolts to the correct length and to leave the aircraft unpainted to save weight. If you must paint, he suggests just spray the Ànish coat directly on to the aluminium. Cockpit Àttings are manufactured, not purchased. Even the latches for the large goldÀsh bowl canopy are fabricated using a technique of "amateur tempering" as described by the designer, by quenching the heated part to give 30 minutes of pliability before the alloy returns to its original state of temper. This technique is used to bend and fold numerous small parts with a radius that would normally turn 2023 aluminium into two small parts. With the huge jumble of parts completed, fastened, epoxied and assembled to create one single-seat twinengine microlight aeroplane -- here is what you have:

Wayne Butt

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ZK-CRI

Empty weight Maximum fuel 23 lt Pilot weight MAUW Engines LH (with alt.) 22hp ea RH

lb 198 35 160 420 21 18

kg 90 16 72 190 9.5 8.3

South Pacific Avionics Ltd

De Havilland Lane, Ardmore Airfield

http://www.cricri.zoomshare.com/[email protected]

PHONE 09 298 1373 [email protected] www.avionics.co.nz

17

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