RADIO CONTROLLED HYDROFOIL MODEL ‘CARTON ONDULE’ BY HANS JORGEN HANSEN
The photos in this album show the hydrofoil model named ‘Carton Ondule’ built by International Hydrofoil Society member Hans Jorgen Hansen of Espergaerde near Copenhagen, Denmark.
The model is a semi-scale representation of the Supramar PT 150 Mk III built to a scale of 1:25. This was developed with reference to Jane’s Surface Skimmers. While the hull and superstructure are very much based on the PT 150, the foil arrangement is more akin to a Rodriquez RHS 160 or RHS 200. The hull is around 1520 mm long and 300 mm wide. The model has a mass of 11520 grams when complete with the set of eight NiCad batteries alone weighing some 2400 grams while ballast water in plastic bottles adds a further 3000 grams. This mass would correspond to 180 tonnes at full load, and brings the model to the waterline Hans Jorgen intended it to operate at. This full loaded displacement reported for the PT 150 is 165 tons so it is apparent the model has no problem operating beyond the scaled weight of its full size counterparts. In fact ‘Carton Ondule’ has been ballasted to a total mass as high as 12000 grams, and even with this substantial weight the model still becomes foilborne. To prevent the model from sinking if it becomes flooded, expanded polystyrene foam is also added inside the hull.
The method of fabrication of the hull is quite unusual in that cardboard is used as the basic building material. In fact, the name of the model is based on its use of cardboard (Carton) and the French word for waves (Ondule). Once the cardboard shell of the hull is assembled and stiffened where necessary, the inside of the hull is coated with fibreglass and polyester resin. In the process, the resin soaks into the cardboard leading to a tough waterproof shell. The exterior can then be lightly sanded to smooth the surface before it is painted. The entire superstructure is likewise constructed of cardboard and can be lifted off the hull to give good access to the battery packs, motors and radio control gear.
The bow foil is of a surface piercing ‘W’ configuration with an overall span of 640 mm and chord length which originally varied from 46 mm at the centre to 115 mm at the foil tips. When foilborne, the submerged portion of that foil has a span of about 450 mm. This foil provides the main longitudinal and lateral stability for the model. The stern foil is also of a surface piercing arrangement with a ‘\__/’ geometry so this also contributes to the stability of the model when foilborne. This has an overall span of 430 mm and originally had a constant 50 mm chord length. Both the bow and stern foils are manufactured from 3 mm thick solid aluminium alloy strips filed back to form streamlined hydrofoil profiles. In recent years, Hans Jorgen has experimented with reducing the chord length of both the bow and stern foils with the aim of reducing frictional resistance and hence increasing maximum speed. The bow foil chord has therefore been reduced to 20 mm over its centre portion increasing to 80mm further outboard. Likewise, the stern foil chord has been reduced to 23 mm at its base increasing to 35 mm near the tips. With these modifications, the model can travel at about 15 knots.
The bow foil is attached to the hull via three alloy struts. The outboard struts are rigidly connected to the hull while the centreline strut is simply bracketed to the keel of the hull without being fastened to it. This strut therefore simply helps to support the hull weight while the model is foilborne. The bow foil assembly was originally intended to have an adjustable incidence angle, which could be controlled by a motor driven actuator. This was subsequently found to be an un-necessary complication and so the bow foil incidence angle is maintained by a simple fixed link between a control horn attached to the bow foil and a bracket inside the hull. This arrangement also serves as a weak link that will fail should the model run aground. The stern foil assembly is connected to the hull via an aluminium rectangular hollow section cross beam. The two outboard struts fabricated of polycarbonate are connected to the port and starboard ends of this beam. A single centreline polycarbonate rudder also transmits the hull weight into the aft foil. The chord length of the rudder has also been reduced in recent years in an effort to increase the speed of the model.
Originally, Hans Jorgen had intended to power the model using a chain saw engine. This proved to be somewhat difficult and so he decided instead for it to be powered by a pair of Tamiya RX540VZ Technigold electric motors. Reduction gears with a toothed belt drive are fitted between the motors and the propeller shafts. The reduction ratio was originally 1:2.66 however this was later modified with new gears to become 1:2.90. The gear wheels were manufactured by Hans Jorgen using his own lathe. In more recent years, the motors have been replaced by LRP V10 type which are double wound with 11 turns (article no. 5711). The propeller shafts are 3 mm diameter piano wire which is thinner than the scaled dimension of the shafts of a PT 150. This helps to minimise hydrodynamic drag. The shafts are supported at the gearwheels adjacent to the motors, as they pass through the stern tubes, at an A bracket supporting each shaft and at bossings attached to the trailing edge of the stern foil. The shafts run in Teflon bronze bearings manufactured by Hans Jorgen with the aid of his lathe. In way of those supports, the shaft is built up to 4 mm diameter using stainless steel tubing which has been glued to the shafts. Elsewhere the steel shafts are painted to prevent rust. Each shaft originally drove a two bladed 45 mm diameter Graupner propeller with a high pitch ratio. For the faster model with its modified foils, 42.5 mm diameter Graupner propellers of medium pitch are instead fitted. Four sets of 7.2 Volt Sanyo 1500 mAh NiCad batteries supply power to each of the motors, providing 6 Amps current.
Control of the model is through a two-channel Futaba radio control unit, one channel for speed control the other for steering. This same unit is also used on Hans Jorgen’s smaller ‘El Foil’. The receiver is a Futaba FP-R102JE type, this being powered by the same battery pack as for propulsion using battery elimination circuitry (BEC). To cope with the large current flow, each motor has its own electronic speed controller, these being LRP F1 Pro Reverse Digital types (article no 8336). These controllers each have their own receivers and are fitted with similar crystals. The single servo on board the model controls the rudder through a straightforward pushrod protruding through the transom.
The model was built between 1981 and 1999 though it was largely complete by 1985. It continues to be used from time to time. The model has an endurance of some 45 minutes on the full set of batteries.
This is one of several hydrofoil models that Hans Jorgen Hansen has built or started to work on.
For more details, Hans Jorgen Hansen can be contacted by posting a message on the IHS Bulletin Board (see: www.foils.org)
All photos by Hans Jorgen Hansen.
1 & 2. ‘Carton Ondule’ underway.
3 & 4. ‘Carton Ondule’ on the work bench.
5. The bow foil of ‘Carton Ondule’ showing a ‘W’ layout similar to that on the Rodriquez RHS 160
and RHS 200 series hydrofoils.
6. The stern foil of ‘Carton Ondule’ showing a fairly typical Supramar / Rodriquez layout but unlike that of the PT 150 which had a fully submerged stern foil.
7 & 8. The motors and gearing and toothed belt arrangement used on ‘Carton Ondule’ showing the originally fitted Tamiya RX540VZ Technigold motors. The battery tray can be seen at the extremity of both photos.