November 2002 Issue of Private Pilot
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In our ongoing coverage of the latest developments at Aerocomp, Inc., the Merritt Island, Florida, supplier of composite kit airplanes, we went along on a fun expedition down the Intracoastal Waterway that laces between Florida’s mainland and barrier islands. This playground attracts boaters, fishermen and seaplane lovers like a magnet because the opportunities are plentiful for fun and exploring.
What makes Aerocomp’s products so well suited to this lifestyle is the company’s long association with water flying. It has offered its SuperFloat line of Kevlar-reinforced composite floats for many years, in both straight and amphibious styles. There are no less than 16 flotation sizes available, and they can be purchased either as you-build-it kit or fully assembled. With a full line of seven distinct airframes, Aerocomp can supply kit aircraft seating from 2 to 11 to fit on the SuperFloats.
The showy yellow Comp Air 8 test airplane belonged to Robin Squires, an engineering consultant in the fields of marine, housing and aviation. Squires and Aerocomp President Ron Lueck loaded us up with fishing gear as we headed out to see what a Comp Air 8 airframe could do with a Walter 60m 657-eshp turboprop engine. Arguably the ultimate personal floatplane, the Comp Air 8 is the next-to-biggest air-_ plane in the Aerocomp line, seating six in cavernous comfort. Only the huge twin tail Comp Air 10 carries a bigger load.
The Comp Air line includes a three-seat Comp Air 3, the four-place Comp Monster and an up-to-six-seat ‘Comp Air 6, all originally designed for piston engines. The Wide-body Comp Air 7 can take piston engines from 250 to 385 horsepower, as well as the Walter turboprop. A Comp Air 7SL incorporates a 12-inch fuselage stretch and uses the turboprop engine, followed by the even-bigger Comp Air 8 and twin-tail Comp Air 10, both marketed for turbine power. The latter can seat up _to 11 in a 13- x, 5 foot cabin. Options for the line include conventional or tricycle gear, a belly cargo pod and a tapered wing for faster cruise speeds.
The Walter turboprops are showing up in many experimental aircraft installations these days because the rugged Czech powerplants are now available in as-removed condition from Eastern-bloc airplanes, following the end of the Cold War. Refurbished by the capable technicians at Diemech Turbines, Inc., in DeLand, Florida, these engines offer an economical half-price alternative to western turboprops. The Walter's squared-out exhaust stacks distinguish it from a Pratt & Whitney PT-6A, to which it bears a physical resemblance.
Diemech's refurbished engines incorporate an autostart function that greatly simplifies the light-up; we simply brought the twin lead-acid batteries on line, actuated fuel pumps and engaged the starter. Igniters started snapping as the compressor wound up to 12% rpm, where we introduced fuel. Ignition and acceleration followed in predictable sequence. Normal ITT limit is 690 degrees C for the cooler-operating Walter, and Lueck's start registered only 650 C. The power quadrant holds only a throttle ("power lever") and fuel/condition lever, because the Avia three-blade propeller runs at a constant 1980 rpm, except when being governed at low power settings by the main power lever. To negate the considerable thrust during surface operations at the 60% idle speed, a beta mode can be reached by lifting the throttle over the stop, starting the propeller blades toward neutral pitch and, with farther aft movement, employing increasing amounts of reverse thrust.
The quadracycle gear of the Comp Air 8 amphibian gave us a stable taxi platform; the twin 5.00 x 5 tires retract into low-drag wells behind the float's step, and the 4.10/3.50-5 nosegear tire moves up into a bumper location on the float's nose. Differential brakes are relied upon for ground steering, and the swiveling nosewheels threaded our way around Merritt Island's taxiways with ease. Swing-up doors that latch to the underside of the wing must be securely closed after engine start to avoid exhaust fumes, so Aerocomp's $11,000, 42-pound air-conditioner option, driven from an unused hydraulic pump pad on the Walter, is defInitely worthwhile. Because turbine engines need no warmup or extensive preflight preparations once the fire is lit, there are few power plant-related checklist procedures to be done at the end of the runway. An overspeed governor is tested at least daily, and the fuel pumps and ignition are armed to come on automatically if needed. Avionics and instruments are set, the electric trim switch on the top of the control stick is used to set takeoff trim and flaps are lowered to a takeoff position.
Lueck launched us down the runway and into the air under the scared-cat acceleration of 657 shaft horsepower, the 5200pound gross Comp Air 8 hardly pausing as it picked itself and two amphibious SuperFloats off the runway at 55 knots in about 1400 feet. Selecting gear-up to gain 10 knots of cruise speed, we climbed out at 85 knots. Leveled into cruise for the short run to the water, we saw 140 knots IAS with 98% rpm and the torquemeter reading about 85%. Fuel bum at cruise is a healthy 45 to 50 gph down low, but when operated in a normal cruise profile above 10,000 feet, the consumption drops to 35 gph. Squires' airplane carries 180 gallons of Jet A instead of the standard 150-galIon setup, so it's limited to four people with full fuel.
As Lueck circled over the landing zone to check the water depth and condition, power was reduced to 75%, and the airplane slowed to an 80-knot approach speed. The gear position was double-checked because I didn't want to practice emergency underwater egress procedures-I'm sure all on board felt the same way. Lueck skimmed onto the perfect water surface, dappled only by 6-inch chop, and brought up 70% power for the step taxi to our island fishing spot. Once we could see the wavelets breaking over the shoals ahead, Lueck moved the power lever to the idle stop to settle into displacement, unlatching the water rudders for tight control even when turning out of the wind.
The beauty of turboprop powerplants on floatplanes, particularly free turbines, is their ability to feather the propeller by entering beta mode, eliminating unwanted forward movement and allowing safer docking with a stopped propeller but with the power section still running. Reverse thrust is rarely needed, except when backing off a beach. Bear in mind that water rudders work only when underway, so be prepared for weathervaning when you heave to.
The fishing gear was unlimbered immediately. The aquatically challenged cast lures from the broad, flat decks of the amphibious SuperFloats, while those who didn't mind getting wet waded into the knee-deep shallows for more casting room. Strikes were rare, but the idea of fishing is to have fun and enjoy the challenge of matching wits with the piscatorial denizens. Taking home a prize is an added bonus
When we had to leave, our friends in the cabin cruiser grounded nearby gave us a push off. We moved aft on the floats to make it an easy shove. They rotated us toward deeper water, and Lueck flipped on battery and start switches to reach 12% N1 and open the fuel cock for ignition. Twin-shaft engines like the Walter require less battery power to spin the compressor section for a start than do single-shaft engines, a comforting thought when attempting a light-up far out in the boonies. We saw the rise in m and N1 as predicted, and Lueck turned the starter into a generator to complete the start.
Takeoff began with a long taxi to reach the open channel away from boat traffic. Then Lueck brought us out of the hole with flaps set to takeoff, stick back, water rudders latched up and the power lever brought up to reach the propeller's governing range. We moved rapidly through a spraying charge onto the step, then dragged our heels until we found the sweet spot for liftoff, a half-mile or so down the channel. Once free of water drag, the Comp Air 8 accelerated like a shot, and Lueck cleaned up the flaps for the short rim back to our land base. Having amphibious landing gear certainly simplifies refueling when the Jet-A runs low, although the Walter can be operated on ordinary diesel fuel in an emergency.
The world of water flying is well suited to turbine power simply because high power-to-weight ratios are advantageous for overcoming the wall of drag we often encounter in float operations. You can never have enough power when the load is heavy and the water is sticky, and a Walter 60lD on the front of a Comp Air floatplane is about the nearest thing to enough power we've found. And the fishing trips are just part of the enjoyment!