In the Begining
The history of our present day gyroplanes can be traced back to Juan de la Cierva who build the first successful autogyro in 1923. The success of the autogyro lies in the rotor head and the way in which differential lift is managed in flight. It is important to understand that virtually none of the concepts around fixed wing aircraft could be patented, but the specific way in which Cierva solved the differential lift issue with his rotor head design could however, and was, Patented. Cierva was thus very much in control of the autogiro (this is the way Cierva spelt it on his early Patent applications) development in the early years.
One of our proof of concept autogyros eventually earned the nickname “Springkaan” (Locust in Afrikaans) because it was designed to operate in the open field and all the test flights were carried out over fields. The “Springkaan” would then eat a path out through the grass and the whole gyro, inside and outside would be covered with bits and pieces of grass after the flight. The Springkaan was also used to evaluate what happens when you go overboard with horsepower, rotor diameter and low disk loading. The “Springkaan” evolved from a tame 160 hp machine to its current (decommissioned) status of a 300+ hp beast.
What followed was a model named “Kriek”. This is Afrikaans for Cricket, or in French, Le Cri-Cri.
Today the Kriek is in pre-production phase and development is ongoing with a two seat tandem Vlooi and a three seat model LDG.
Sprinkaan - Proof of Concept
Philip Nell is an EAA member currently working at Denel as a consulting Professional Engineer performing airworthiness certification for SAAF Military Helicopters. He is one of the founding members and directors of Wagtail Aviation Pty Ltd. The following overview was compiled by him.
A Brief Overview (2013)
During the past seven years, I have been deeply involved with the development of a number of proudly South African Gyroplanes. This article provides a short overview of the progress to date and plans for the future. While investigating the possible usage of gyroplanes for Military applications, I met Johan von Ludwig, a Chemical Engineer by profession, but a true gyroplane aviator by heart. Two weeks later my amazing journey started with a simple handshake. The deal was that I would assist Johan with the development and airworthiness qualification of a new gyroplane.
By that time Johan had designed, constructed and flown his own tail-dragger gyroplane called the ‘Springkaan’ with a 300 hp Toyota Supra engine and locally developed 33’ composite rotor blades. This was a pure ‘technology demonstrator’ to prove the various concepts. The initial plan was to industrialise the design and then market it as a ‘flying one ton pick-up’. This prompted the need for CAD and Production specialists resulting in Christie Kuys and Jan Rossouw, both Mechanical Engineers, joining the development effort.
The rotor head was the first area of focus, and a unique mechanism was added to the cheek plate’s design to finely adjust the pitch of both blades for accurate tracking and thus low vibrations. To date, the rotor head has undergone a total of seven updates, with more than a 5500 flying hours without a single failure. It, together with the blades, has also been structurally tested to 20 tons in the horizontal and 10 tons in the vertical axis. This is also the area where the most optimization for a specific airframe can be done, as there exists a fine balance between the coning angle, under sling and blade pitch for increased efficiency and reduced vibration levels.
Another lengthy, but in the end very worthwhile development was the hydraulic prerotator system. A modified hydraulic pump is driven from the propeller hub with a toothed belt and electro-magnetic clutch. This in turn drives a rotor head-mounted motor driving a sprocket gear via a one-way bearing. This eliminates the requirement for a Bendix gear and ensures a smooth start, reducing the torque impulse on the rotor mast. In addition, the rotor can be tilted fully back during the spin-up process to decrease the take off distance.
To reduce the developmental risks, all the new systems were extensively tested on ELA 08 and Magni Gyroplanes, and proved to be the correct approach.
Early on in the design of the updated Springkaan, calculations indicated that the 33’ rotor system was not long enough to provide adequate lift for the planned > 1 ton MAUW. The design was therefore re-directed to use a modified Bush Baby frame and fit the proven rotor system to it, hence the birth of the Kriek MK1 which first flew during October of 2005. Excessive vibrations ruined any further flight tests, and it took many months to figure out what the root cause was. It turned out that the rotor mast stiffness and natural resonance frequencies are critical for any Gyroplane design. This resulted in the complete re-design of the frame and mast, using my 6’4” stature as maximum percentile for the cockpit anthropometric dimensions.
Airworthiness Certification basis will be as per PART 28, specifically generated by us as no suitable standard is available for Type Certified Gyroplanes in the world. This will set the standard for future Gyroplane designs and we are in process of getting the standard approved by the South African Civil Aviation Authority which will include on condition based maintenance in place of the standard flight hours and calendar based practices.
The new Kriek MK11A first flew successfully during February of 2009 in a tail-dragged configuration, which was chosen for improved take off performance. Numerous flight tests however confirmed that it had a tendency to yaw at the point of take off and when landing with the tail wheel first. A unanimous decision was thus taken to convert the Kriek to a conventional tricycle configuration with steer able nose wheel. This MKIIB configuration flew successfully on the 20th of May 2009 and confirmed the exceptional stability of the tractor configuration.
The Kriek has also been fitted with a magnetometer on a boom to obtain Geo surveying data that looks very promising as the stable, slow and low flight path and low operating cost is set to revolutionize this industry.
The gyroplane development continued with the major focus on using the Subaru car engine with custom reduction drive and engine management.
In the mean time Jan Loedolff joined the team as a senior technician and AP. Here he is shown with the engine test stand or Bokwa (Its nickname; translation for “goat wagon” as its wheels were taken from one.)
Market forces then directed the design and development effort in the direction of a high performance and nimble gyroplane and the Vlooi (Trojan) was born. This was done in a very short time as extensive use was made of all the existing subsystems.
The Vlooi MkI is shown below boasting a 120l tank and a turbocharged 2 liter Subaru engine.
This was followed by a 2 seater Vlooi trainer which is capable of carrying two 120 kg persons with ease.
In parallel with all the above developments, the first 250 mm cord, locally extruded aluminium rotor blades are ready to be test flown. This should provide up to a 37’ rotor system, suitable for the Springkaan and other larger Gyroplanes. The engine-of-choice for the 680 kg MAUW of the Kriek is the Subaru 2.5 L, and development of dual-redundant ignition and fuel injection systems have been completed.
The latest development is that of the 3-seater LDG, and is set to shake the Gyroplane world with its large rotor and 2.5L Subaru Turbo engine with intercooler producing close to 250 hp.
LDG uses most of the existing subsystems of the Kriek and Vlooi gyroplanes.