Floatplane

Overview

The Floatplane is a four-seat single-engine aircraft set on a pair of Float pontoons in place of wheels, so it operates from any sheltered stretch of water long enough to take off and land. It is the workhorse of regions where lakes and rivers outnumber runways: bush operators in the far north, island services, fishing and survey charters, and float training. The conversion from a landplane is not just a matter of bolting on floats. The pontoons add weight and drag, raise the aircraft well off the ground, and shift the side area, so the airframe is reworked with a larger fin and a Ventral Fin to keep directional stability, and the engine is usually a higher-power rating to recover the takeoff performance the floats cost.

The aircraft is built around an aluminium Airframe, a strut-braced high Wing, and a piston Piston Engine driving a constant-speed Propeller. The high wing matters on floats: it keeps the wing and flaps clear of spray, gives a clean view down to the water surface, and leaves the underside open for the Float System rigging. Everything below the cabin floor is given over to water operation.

Float System

The Float System is what makes the aircraft amphibious in function and it is the most distinctive part of the design. Each Float is a riveted aluminium pontoon roughly the length of the fuselage, built around an extruded Float Keel with a V-section Float Bottom Skin that planes on the water and a Float Deck Skin closing the top. The bottom is not a smooth boat hull. It carries a transverse Planing Step partway aft, a deliberate break in the planing surface. At rest and at low speed the whole bottom is wetted and the float behaves like a displacement hull, but as speed builds the step lets air break the suction between the after body and the water, so the float unsticks and rides on the forward planing area alone. Without the step the float would stay glued to the water and the aircraft could not accelerate to flying speed. A pair of Spray Chine rails along each side throws spray down and out, away from the Propeller and the airframe, since ingested spray erodes blades and salt water corrodes structure.

Each float is split by five Float Bulkhead walls into watertight compartments. This is a safety design point: a float that strikes a deadhead or a dock and holes one compartment still floats on the rest, because each section is sealed from the others and each carries an Inspection Cover for checking and pumping. The floats are sized for large reserve buoyancy, around 90 percent more displacement than the aircraft weight needs, so a flooded compartment does not put the deck under water. Three Mooring Cleat fittings per float let the crew dock and tie the aircraft down.

The floats attach to the fuselage through the Float Rigging: front and rear Spreader Bar cross tubes set the track between the two floats and react side loads, Float Strut members carry the aircraft weight down to the floats, and Bracing Wire runs triangulate the whole structure against fore-and-aft and side loads from rough water. The rigging is set with a slight nose-up attitude so the floats sit on their forward planing area for takeoff.

Steering on the water is done by a Water Rudder hinged at the stern of each float. Below flying speed the air rudder has no airflow over it and cannot turn the aircraft, so the Water Rudder Blade drops into the water and steers like a boat rudder, driven from the same Rudder Pedal Set set through a Water Rudder Cable. For takeoff and landing the Water Rudder Retract mechanism lifts the blades clear so they neither drag nor catch a wave. A Bilge Pump in each float clears water that works past the seals into a compartment over time, and an optional Beaching Gear set of small wheels lets the crew roll the floats up a ramp to dry land.

Powerplant and Propeller

The Piston Engine is an air-cooled horizontally opposed six-cylinder piston engine. Air and fuel are mixed in the Carburettor, burned in six Cylinder Assembly units driving Piston assemblies, and the motion is turned into rotation by the Crankshaft. Ignition comes from two independent Magneto units, each firing its own plugs, so the engine keeps running if one fails and needs no battery to make spark. The Oil System both lubricates and carries heat away to the Oil Cooler. The float rating is usually higher than the same airframe on wheels, because water takeoff is a long high-drag run and the aircraft needs the extra power to climb over the step and accelerate.

The Propeller is a two-blade constant-speed unit. A Propeller Governor senses speed with a Governor Flyweight pair and sets blade pitch through the Propeller Hub so the engine holds the rpm the pilot selects. Constant speed earns its keep on takeoff: a fine pitch lets the engine reach full rated rpm and power against the heavy water drag, where a fixed-pitch propeller would bog down.

Airframe and Controls

The Fuselage is a semi-monocoque shell of Fuselage Frame rings, Stringer stiffeners, and riveted Skin Panel sheet, closed at the engine by a stainless Firewall. The wing is a two-spar structure braced to the lower fuselage by a Lift Strut on each side, which lets the spar be lighter than a cantilever wing of the same span. A slotted Flap pulls the stall speed down so the aircraft can touch the water slowly. The Flight Controls are simple cable and pushrod runs from the Control Yoke and rudder pedals to the surfaces, with a Trim Tab on the elevator. The whole control system is corrosion-protected and the cables are stainless, because float aircraft live in a wet, often salt-laden environment.

Systems

The Fuel System gravity-feeds from a Fuel Tank in each wing through a Fuel Selector, with an electric Boost Pump backing up the feed for takeoff and a Gascolator trapping water at the low point. The Avionics are a modern panel: a Flight Display pair, a GPS Navigator navigator, a VHF Comm Radio, and a Transponder. The Electrical System system runs on a belt-driven Alternator and a Battery. Inside, the Cabin Interior carries four Seat units with four-point Seatbelt harnesses and a Cabin Heater drawing warmth off the exhaust.