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The Petrel on the ground. The bubble canopy provides good forwards vision. (Bob Grimstead)
Airtest – Petrel Amphibious Ultralight
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The Petrel
Floatplanes provide the most fun of all flying, but they can also be so expensive.
Water just eats steel and aluminium, and salt water seems as corrosive as acid. But now there is an inexpensive alternative, the Petrel. A kitplane (also available in fully completed form) of fibreglass, anodized aluminium, stainless steel and fabric, this two seat biplane amphibian is comparatively simple to build, flies nicely, can be dismantled quickly and should resist the sea’s attack. Splashing about on the sea in one, I just knew this aircraft was a winner. A French design, built by SMAN of Brittany and with over 50 finished aircraft flying (including a couple with the French Army), the type operates all over the French speaking world. Two patrol around Kourou, French Guyana, to warn of impending Ariane rocket launches, and others are used by coastguards, customs and air-sea-rescue units in France and French protectorates, as well as by sport fliers. Distribution in the English speaking world is handled by Amphibians UK Ltd, of Salcombe, England, who has translated the detailed and comprehensive construction manuals. Their demonstrator was completed in a mere six weeks (with a little help and advice, but without English instructions) by a team of four first time builders. Man hours were logged at around 900. At $21,000 the full kit costs less than a set of ‘straight’ (non amphibious) floats for a conventional aircraft, and yet a Petrel will fly from tarmac, concrete, grass, river, lake or sea. Kit production will soon be moved to Lithuania to minimise costs.
It seems to me that a Petrel could be the recipe for a summer of inexpensive fun and excitement!
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The kit comes in three parts:
The first has the carbon fibre tail boom, wood and fabric tail surfaces and controls.
The second contains the four wings, ailerons and their dacron fabric and paint.
The third is the pre-moulded fibreglass/epoxy/foam sandwich fuselage, complete with engine pylon, requiring only fitting out and instruments.
The engine and French ULX wooden propeller are purchased separately. The original two stroke Rotax 582 is still available, but SMAN now recommends the more reliable and powerful four stroke Rotax 912 with its efficient silencer and carb heat system.
The pretty little Petrel’s unequal span wings can be removed by two men in half an hour for transportation or storage, and the tail boom attaches to the hull with a pin and a single bolt. The upper wings use strong but expensive Zicral 5 aluminium alloy spars and have ailerons. The lower ones use fibreglass covered wood spars with GRP outrigger floats on their tips. All four have foam ribs for their NACA 2412 aerofoil. A stern mounted water rudder is permanently connected to the rudder cables. This is held up by a bungee, and lowered by rope and toggle for marine manoeuvring.
The simple oleo main gear legs are operated by ropes and quadrants. When retracted, the L-shaped legs fit into the fuselage side, with the wheels partly recessed into the wings. The nose leg’s suspension is a rubber block in compression. When raised, the nose wheel becomes a fender, its wheel well covered by a curved glass fibre lid.
A pair of lead ballast weights in its nose stop the aircraft tipping backwards when empty. They are removed for flight (although one might be used for a light solo pilot). An open cockpit and small windscreen are standard, but the demonstrator I flew had the optional tinted forward hinging canopy, jettisonable by pulling two small red rings on the lower instrument panel. With no lock, air loads keep it closed in flight. A small hatch in the bow encloses an anchor and rope stowage which is difficult to reach from the cockpit.
The cockpit is comfortable, with a straight legged seating position and four point harnesses. The thin cushions were fine for a couple of hours. More annoyingly, the canopy forced me to tilt my head inboard a little, and my shoulders rubbed on the ply front spar carry through because of the low seat backs. Dual controls are standard, with neat, short sticks and floor hinged rudder pedals. Only the left seater has brakes, and the elevator trim tab uses a slow moving electric motor switched by a rocker on the panel.
The demonstrator has VFR instrumentation and comprehensive engine gauges, VHF radio and transponder. (The ASI is calibrated in kilometres per hour so, for knots, see the specifications box). The few electrical services are switched by push buttons dotted around the panel, and two red lights provide stall warning. A simple compass, a marine radio and its microphone atop the coaming intrude into the view ahead, but otherwise visibility on the ground is excellent. While stationary, the cockpit was quite warm in bright sunshine but the lid can be held ajar while taxying and, once airborne, the temperature became comfortable.
The gear gives a rather firm ride. Steering is by differential braking, making manoeuvrability excellent, with a remarkably tight turning circle. Brakes are hardly needed to keep straight on takeoff, as the rudder is right in the propwash.
With full aft stick the nose wheel lifted at 60km/h (32kt) for a 70km/h (38kt) liftoff after a couple of hundred metres. Winding up the main gear means swapping hands, cranking 15 turns on the left sidewall drum, then jamming the rope in a clam cleat. The nose wheel is retracted by heaving on a toggled cord on the floor and jamming that in its cleat.
With two adult males and full fuel we were at top weight, but a good 700ft/min climb was indicated at 80km/h and 5400rpm. The noise level, although high pitched, was nicely low. Thanks to the small nose, visibility was excellent all around and downwards to about 20 degrees behind us, but rearwards, and particularly upwards, the wings hid much of the sky.
The Petrel has a remarkable 230kg (507lb) empty weight so, even at its 450kg (992lb) maximum, it has little momentum. Yet, like any amphibian, it has plenty of drag, and the pylon mounted Rotax’s high thrust causes a noticeable pitch up with power reduction. So a sudden engine failure in the climb demands prompt action to get the nose well below the horizon before the speed drops dangerously. Practising this, I had to make a zero G push over to contain the speed loss to within 10km/h (5kt).
Levelling at 1500ft, I let the speed build before throttling back to 5000rpm, for 115km/h (62kt) IAS. Our gentle cruise trued out at just 65kt (120km/h); similar to a Cub or Champ, and a lovely sightseeing speed. And you can fly as low as you like in a Petrel, knowing that if the engine stops, you can plonk it on the tiniest field or pond.
Pitch, roll and yaw stability were all surprisingly good for such a short fuselage. The ailerons were heavier than rudder or elevator, but not unpleasantly so, and none of the controls had particularly high forces at cruise speeds. Turning caused some adverse yaw, but with rudder, gave a surprisingly good roll rate. Slowly closing the throttle induced a gentle six or seven degree pitch up, followed by the nose dropping safely to stabilise speed after a power reduction.
The nose wheel is lowered by uncleating its cord and letting it free-fall. The main legs extend by heaving on a toggle between the seat backs, confirmed by checking their operating quadrant is correctly aligned. All undercarriage operations require a little effort.
The approach angle is quite steep at around 90km/h (49kt) with 2000 to 3000rpm, and even steeper with the throttle closed. Reducing speed to 80km/h (43kt) at the threshold gives a very brief hold off before a 60km/h (32kt) touchdown. The rudder is slightly less effective then, but still good enough to push off the drift. The published maximum crosswind is 15kt (giving quite a large drift angle at just 70km/h [38kt]). Lowering the nose gently at 40, we stopped in around 150 metres in a 10kt (19km/h) headwind. The Petrel is quite easy to land, but you sit low, so the flare is pretty near the ground.
That steep approach is useful in crowded harbours, where you can squeeze in between powered craft, buoys, yachts and their masts. Water landings are made directly into wind, with water rudder and wheels retracted and self bailer closed. The hold off is even nearer the surface, and touchdown slightly nose high, with the stick hard back, giving prompt deceleration after the fuselage settles almost alarmingly deep in the water. For one horrible moment I wondered if we might be sinking!
Twenty centimetre waves caused no problems, and the owners’ manual quotes a maximum safe trough of 60cm. Control was good into wind, and improved in other directions using the water rudder.
Water takeoffs are made with the stick fully back initially, carefully opening the throttle until the hull climbs on to the step. Once the aircraft is planing, and going as fast as it will, you pull back to lift off cleanly. The hull seems to stick on the surface in a level attitude, so this low speed liftoff minimises takeoff distance, but naturally requires a few moments of acceleration in ‘water effect’ before climbing away at 80km/h (43kt).
After two days experimenting with planing attitudes and aquatic techniques, I just knew this aircraft was a winner. (Bob Grimstead)
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