African Pilot - May 2004
Slick 360 - Text by Glen Dell and Francois Jordaan. Photos by Athol Franz.
A look down the flight line of any of the 5 Advanced World Aerobatic Championships (AWAC) that have been held, will reveal a gaggle of great ex unlimited aerobatic aircraft.
The AWAC concept was brought about as an alternative to the World Aerobatic Championships (WAC) where competitors were going to absolutely any length (and cost) to achieve the ultimate in aerobatic aircraft performance. While there will always be a place for unlimited aerobatics, no one could deny that, to an extent, pilot skill was being overshadowed by the cost of participation. Hence AWAC. Any aerobatic aeroplane of less than 260 horsepower as well as those planes that were no longer competitive in unlimited (and could thus often be purchased at a reasonable cost) were allowed to participate. The formula worked well with the first Advanced Championships proudly being held in Cape Town.
Since then the sport has grown with numbers of competitors taking part exceeding the numbers in unlimited WAC. One problem however came to the fore – participants were “running out of” suitable mounts. The trusty Zlins, Pitts and Yaks were 30 plus years old. The cost of maintaining these aircraft was becoming exorbitant. Many of these planes have heavy airframes and require a big thirsty engine to allow them to complete the required manoeuvres. A Yak 55 for instance, flying at full power at sea level, uses in excess of 100 litres per hour. In Europe this would equate to a cost of R1500 per hour, fuel only! Some really good planes were being designed and built but had their own problems. The One design, a small plane powered by a 180 horsepower engine, had really good performance. Its drawback however was its size – aerobatic judges complained it was just too small to critique accurately. The Giles 200 and 202 are great planes but do have problems, not least of which is their +/-200 000 US Dollar price tag.
One aeroplane, which was doing particularly well at AWAC, was the Extra 230. This little plane had won two of the five competitions. Its 230 horsepower engine gave it performance equal to that of the 300 to 360 hp Zlins and Yaks. The problem here was that Walter Extra stopped making them 15 years ago because he could no longer obtain the high quality wood needed for the main spar! What (in our summation) the ideal aerobatic steed was therefore, was an aircraft based on the Extra 230 but constructed from the latest materials such as Carbon Fibre and Kevlar.
Thus the concept of the Slick 360 was born. It was built and designed primarily by AeroCam of Wonderboom, Pretoria. Francois Jordaan attended to structural design while Chris Hattingh did most of the shaping, construction and assembly.
The engine came from Canada, the propeller from Germany, undercarriage, instruments and exhaust from the USA and all else was manufactured here in South Africa.
The little plane is a pleasure to fly. Ground handling is a breeze and performance easily matches or exceeds its 300 / 360 horsepower advanced aerobatic cousins. Roll rate at 320 degrees per second is slower than wished for, but new ailerons, designed to increase this to 400 are already in the moulds. Max cruise speed is 210 mph which is quite a bit faster than the never exceed speed of a Zlin. Flick rolls are perhaps the aircrafts forte, which is to be expected baring in mind its Stephens Acro, Laser and Extra lineage.
All in all a delightful little aerobatic thoroughbred on which I look forward to updating you during the course of its further development
Slick 360 - Born to be a Thoroughbred - by Francois Jordaan (designer and Structural Engineer)
In contrast to the smooth and ballet-like aerobatic performances we have become accustomed to at airshows, competition aerobatics is all about lines and crisply executed precision manoeuvres. To excel in this highly competitive sport a pilot needs to develop exceptional skill and have a flying machine with exceptional manoeuvering capabilities.
The challenge faced by the Slick 360 development team was to produce a competition aerobatic aircraft which would afford its pilot the best chance of developing real aerobatic excellence. The combination of pilot and machine needs to have the potential of reaching the top in world championship contests with an affordable price tag attached!
"Affordable" in this sense does not only refer to acquisition cost, but also to operational and maintenance cost. In short, the pilot must be able to maintain his aircraft, and it must really only sip fuel. This points to two requirements - the aircraft must be registered in the NTCA (Non-type certified aircraft) category and it must operate on a not-so-thirsty 4-cylinder engine of sufficient power.
When Glen Dell approached AERO-CAM in June 2003 with the proposal to develop a new competition aerobatic aircraft, we already had the expertise of three staff members who were involved with the development of the Celstar aerobatic glider with which the late Peter Cilliers almost won the 1989 World Glider Aerobatics Championship in Hockenheim, Germany. We grabbed the opportunity with glee!
Glen was also able to find a welded steel fuselage frame and tail surfaces from an abandoned Laser project. Magnaflux testing of the steel truss showed that it was perfectly airworthy, and a project was born. With an all-composite wing, a detailed mass and balance calculation showed that we could place the engine 45mm further aft than in the Laser planes. This was achieved with a redesigned engine mounting frame. The shape of the rudder was changed to proved improved inverted spin recovery capability.
The wings are constructed with moulded fibreglass composite sandwich panels. The aileron aerodynamics were re-designed with a set back hinge line to provide lower pilot input loads, and used a construction similar to the wings. The wing main spar is built with carbon fibre spar caps and was designed for a limit load factor of +10"g", and with a factor of safety of 2.0. This means they should not break before a 20"g" load is applied (unlikely event!). To demonstrate the validity of the design, the wings were subjected to a simulated 11 "g" load in a special test rig before being integrated with the fuselage.
The power plant chosen is a Lycoming IO-360 engine, specially prepared by AeroSport Power in Canada to produce up to 240 horsepower. The propeller is an MTV 9, 3-blade lightweight unit produced by Gerd Muhlbauer in Germany. Some teething problems are still being attended to regarding the inverted oil system and propeller constant speed unit, but after only 10 hours of flight, the performance is awesome!
A lot of effort was put into the fuselage fairing and engine cowl shapes. This really paid off, as we were able to produce a very slick (no pun intended) and good-looking aircraft!
For competition aerobatics three factors are important : high power loading, high speed and high roll rate. The first is achieved by keeping the mass down and pushing the engine power and propeller efficiency up. The prototype Slick 360 weighs 450 kg (just under 1000lb). Together with the excellent engine/propeller performance the Slick has an exceptionally high power to weight ratio compared to other aircraft in its class.
The maximum level speed of the Slick 360 at Pretoria's altitude (5000 ft) is in excess of 200 mph indicated, which equates to at least 215 mph at sea level. The maximum dive speed is 250 mph, which, together with the low aerodynamic drag, is high enough to ensure good vertical penetration. The roll rate of the prototype Slick needs to be increased somewhat. At the time of writing it had not been quantified, but subjectively it is estiimated at around 320 degrees per second. Larger ailerons are planned for the production model, to achieve a roll rate of 400 degrees per second.
Where do we go from here? The production Slick 360 will have all composite (carbon fibre) tail surfaces, larger ailerons, lower weight and a modest price tag. We hope to deliver the first production model to its owner at the end of June, and one per month thereafter.
At some time in the not too distant future we will consider type certification of the Slick 360 as an option to the buyer. This will be a requirement to enter the European market.
If all goes well, Slick 360 will be proudly carrying the South African flag at the Advanced World Aerobatic Championship in Sweden during August of this year! Who knows - we may have given birth to a world champion thoroughbred!