Schiff Evaluates PL-12U Airtruk

by Captain Barry Schiff (Circa 2012) Submitted by Mike Feeney www.barryschiff.com

There was nothing unusual about my approach to Nyngan Airport in Australia’s Outback. But my airplane looked so unusual that the local press came to investigate the curious craft that had slipped from the sky to visit their remote community.

What they saw evoked quizzical expressions, poorly disguised chuckles, and a deluge of questioning. There is no disputing it. The Transavia PL-12U Airtruk is a strange-looking airplane. Like a Boeing 747, it has two passenger decks. The pilot and one passenger sit on top in tandem, but the passenger faces aft. Three additional passengers share the lower deck, and they too face rearward. The Airtruk appears ungainly, resembling a Volkswagen that has been modified to look like a Cessna Skymaster with one engine. But instead of having a single horizontal stabilizer, the empennage consists of 2 independent T-tails, each supported by its own slim boom. A pair of stub wings adds to the curiosity.

Gil Forrester, Transavia’s general manager, welcomed me to Sydney. He is amicable, quiet, and polite to the point of formality, not what you would expect of a transplanted New Yorker. He was committed to the Airtruk and defended the homely-looking airplane against any insult, implied or direct. Forrester volunteered that the Airtruk was conceived as an agricultural aircraft, which explains some of its unorthodox features. The designer, Luigi Pellarini, was concerned with function, not aesthetics.

RIght: Captain Barry Schiff prepares to depart from the Nyngan Airport in Australia’s Outback.

In the agricultural configuration, the podshaped fuselage contains a cavernous 220-gallon hopper that carries up to a ton of agricultural material. The unique tail assemblies are 11 feet apart, allowing a loading truck to approach safely from the rear and eliminate the need for the pilot to shut down the engine. The stub wings contribute 20 percent of the lift and preclude the need for the main wings to have greater span.

Swinging the McCauley 88-inch, constantspeed propeller is a Continental IO-520-D, 300-hp engine. Although the Airtruk is not eye-pleasing, agricultural pilots rave about its performance, maneuverability, and safety features. The PL-12 also produces an efficient, 90-foot-wide swath pattern and has comparably low operating costs.

The Airtruk was remodeled and certificated as a passenger aircraft, marking what might have been the first time that an ag-plane went through such an evolutionary change.

A port side view of the Transavia twin tail vertical stabilizer, rudder and elevator.

As we approached the PL-12U, I could hardly believe my eyes. The aircraft is more provocative in person than in photographs I had seen. No question, the Airtruk is a unique breed of airplane. Because the Airtruk has only one set of flight controls, Mitchell suggested that I sit behind him in the upper passenger deck while he flew the airplane to nearby Hoxton Park Airport where there was a runway more suitable for my first solo. The factory strip is little more than a 1,000-foot clearing surrounded by towers, cranes, and tall industrial machinery. I felt somewhat apprehensive as we taxied out. There was no way for me to get to the single-place cockpit should the pilot become incapacitated. Adding to my anxiety was the helpless feeling of being unable to see out the front window.

Before I had a chance to think about opting out, Mitchell had the Airtruk barreling along the dirt runway. After a ground run of only a few hundred feet, the nose pitched up rapidly, and I found myself staring back and down at the retreating ground at an uncomfortably steep angle. Seconds later, a large tower passed beneath and behind. Maybe this sitting backwards isn’t so bad, I mused. By the time you see a hazard, it’s gone. Also, the human anatomy can better endure the deceleration of a crash landing when sitting backward than when facing forward!

Mitchell’s dramatic takeoff and climb emphasized that the Airtruk is a STOL airplane. The wings (all four) have the same airfoil (NACA 23012) as the Helio Courier. Stall fences keep the Frise ailerons effective during stalls. At light weights, takeoff roll is only 255 feet but increases to 600 feet at maximum weight. During cruise, I twisted in my seat and tried talking to Mitchell, but I could not overcome the din. The noise level reminded me of the B-25 Mitchell bomber. In the Airtruk, communication is via written note, even though pilot and upper-deck passenger are seated back to back.

Feeling lonely and slightly claustrophobic, I clambered down into the lower passenger deck and spent the rest of the short flight enjoying the roominess of this compartment. I soon felt the power ease and watched with concern as the flaps extended. When the left flap comes down, it blocks the lower cabin door, making it impossible to open. Not wishing to be a prisoner in an Airtruk, I scampered back to my lonely perch on the upper deck where there is a door through which I could evacuate.

Traveling companion (circa 1974), Carol Gaskell who accompanied Captain Schiff on many of his aviation adventures exits from the upper deckpassenger compartment and also tries her hand at the pilot controls!

After parking at the ramp, Mitchell motioned for me to climb into the cockpit. He squatted on the right wing and briefed me on systems, procedures, and what to expect during my first flight as pilot. This reminded me of being checked out in singleplace airplanes. You must listen attentively during such instruction because your first use of the controls will be while alone.

The cockpit is laid out like a military fighter. The throttle, propeller, and mixture controls are clustered on the left sidewall. Also on the left between the seat and the sidewall are the trim wheel, flap handle, ignition switch, and fuel controls. In flight, the left hand can get a little busy, but the right hand is always free to fly. Cockpit visibility is wonderful, like being in a control tower. Sitting above the pistons instead of behind them allows the pilot to look down and ahead at a steep angle to see potholes and other ground hazards only a few feet ahead. It also is nice not to be sandwiched behind the engine, a factor that increases crash survivability. A disadvantage is that you cannot easily relate the position of the nose to the horizon. Attitude is best maintained visually by glancing at the wings.

Mitchell advised me to hold the stick forward during takeoff to keep the nosewheel firmly on the ground. “The rudders,” he cautioned, “are out of the propwash and unusable for ground steering until you’ve gathered airspeed. If the nosewheel isn’t held down, directional control is initially marginal.” Taxiing for takeoff, I noticed that the Airtruk porpoises slightly because of the landing gear’s relatively short wheel base. Increasing taxi speed dampens this effect.

A brisk crosswind swept across the taxiway, and I noticed it had almost no effect on ground handling. The stubby fuselage offers little keel surface to the wind. Similarly, the Airtruk exhibits almost no weathervaning tendency during a crosswind takeoff.

The preflight check and runup were conventional. I taxied onto the runway, reviewed Mitchell’s instructions, and pushed the throttle home. By the time I remembered his caution about holding down the nosewheel, the Airtruk had pushed the ground away and clawed skyward at what first appeared to be a dangerous climb angle but later proved to be a normal Airtruk climb. You do not need to rotate for liftoff; the nose rises positively and without assistance.

At altitude, I retarded the throttle and noticed something strange. Reducing power does not cause the nose to drop the way it does in other airplanes. Conversely, adding power does not cause the nose to rise. I then realized that the elevators, too, are out of the propwash. Power changes have little effect on pitch. If a pilot wants the nose to move, he must move it.

I coerced the Airtruk into a few stalls, poweron and power-off. The airplane does not stall in the conventional sense; it simply mushes along in a nose-high attitude with little tendency to buck or roll. With power off and the stick held fully aft, the Airtruk sinks about 1,000 fpm, depending on weight.

Maximum-allowable gross weight of the passenger model is 3,800 pounds. The agricultural model is approved for 290 pounds more because it has a jettison system enabling the pilot to dump a 2,000-pound payload in 3 seconds in case he cannot clear an impending obstacle.

I extended the flaps fully (30 degrees) on final approach and recalled that, in addition to their normal function, they create a venturi effect between the main and stub wings, thereby increasing the lift of all wings simultaneously.

Landings are easy. After the mains touch, though, it is difficult to hold off the nosewheel. Becoming familiar with any airplane requires a few days of leisurely flying away from the watchful eyes of an instructor. The Airtruk is no hot rod and cruises at only 130 mph. What it lacks in speed it makes up for in load-carrying ability. The Airtruk has an empty weight of 1,849 pounds and a useful load of 1,951 pounds. It is one of only a few aircraft that can carry a load greater than its own weight. Range without reserve is 870 miles.

As airspeed increases, up-elevator and nose-up trim must be applied to maintain altitude, a clue that the aircraft is mildly unstable longitudinally. The aircraft does not do well in turbulence and requires constant pitch and roll corrections. Left to its own devices in turbulence, the PL-12 behaves like a drunk trying to pirouette on a volleyball. The Airtruk wants to pitch and roll every which way and exhibits little tendency to return to its trimmed attitude. I was informed later that extending the flaps to the first notch—7 degrees is allowed at any airspeed—shifts the center of lift and increases stability. Also, the Airtruk has a spring-loaded trim augmenter that could have been used because of the relatively aft location of the center of gravity during my flight.

The Airtruk was the only light plane manufactured in Australia at that time, and although it lacks creature comfort and speed, this flying truck satisfied a variety of utilitarian roles. In addition to reportedly being a good crop duster, the PL-12U would serve well as a firefighter. When the aircraft carries freight, the lower deck can be filled with 80 cubic feet of outsized cargo or a pair of medical patients on 6-foot stretchers. Ample room remains for the pilot and a passenger on the upper deck. This workhorse is also rugged, designed to operate on terrain that would tear away the landing gear from lesser aircraft.