Dream Aircraft

by Schiff, Barry

  Schrade keeps his airplane at the North Las Vegas Airport, which is where I was checked out in the S-38 by his friend and instructor, Waldo Anderson. Anderson retired as chief pilot for the University of Minnesota in 1997. There he ran the flight school and transported State personnel in a Beech King Air and a Baron. He met Schrade in 1975, instructed him for most of his ratings (including a flight instructor certificate that Schrade uses as a hobby). At 68, Anderson spends much of his time with Schrade flying the Sikorsky amphibian to air shows all over the country.

  You enter the cockpit by stepping on a tire and climbing through the side and overhead windows. Passengers gain access by climbing through a hatch on the aft left side of the cabin. Agility is required in either case. Unfortunately, you cannot go back and forth between the cabin and the cockpit.

  Starting the engines is unremarkable except for the wonderful sound of radial engines that always takes me back to a bygone era. Taxiing without a steerable tailwheel is not difficult using differential power and brakes.

  Rotation is not needed for takeoff. When allowed, the airplane simply levitates in 3-point attitude at 45 knots. Lower the nose a wee bit to 65 knots, pull the go knobs back to 30 inches and 2,000 rpm, and climb rates settle at 500-800 fpm, depending on load.

  The original S-38 required manually pumping up the landing gear one leg one at a time. Schrade’s airplane has an electric hydraulic pump that results in a quaint ritual involving selector handles, locking valves, and pump switches. Although this requires less physical effort, the legs still come up very slowly and one at a time.

  Raising the landing gear does not reduce drag. It simply raises the wheels and places them flush with the bottoms of the lower wings to get them out of the way for water operations. For land operations only, performance does not suffer if the wheels are left down, but the purist raises them anyway because he knows that the airplane looks better that way.

  Schrade thankfully provides pilots with Telex noise-canceling headsets. Otherwise, the noise and vibration of the Amphibion would be fatiguing. I cannot begin to imagine how Martin and Osa Johnson endured such lengthy journeys in an S-38 without hearing protection. One can only wonder how the Johnsons avoided becoming stone deaf, like the rabbits that dwell between the runways at Los Angeles International Airport.

  At 27 inches and 1,900 rpm at 6,000 feet, the S-38 cruises at 90 knots while consuming 46 gallons per hour. Total fuel capacity of the four tanks (all in the upper wing) is 340 gallons. Maximum-allowable gross weight is 10,480 pounds.

  The airplane is heavily damped in roll, has poor roll response, requires effort to maneuver, and is a handful in turbulence. It also has neutral lateral stability, which means that you cannot pick up a wing with rudder. One can only imagine the physical effort required to fly an S-38 through and near the intertropical convergence zone of central Africa. The airplane is undoubtedly challenging during takeoffs and landings in gusty crosswinds.

  Conversely, pitch forces are relatively light. The nose hunts noticeably about the yaw axis even during mild turbulence, a characteristic probably caused by the long bow.Coping with an engine failure is a no-brainer because the engines are so close to the aircraft centerline. Very little rudder is required to keep the Sikorsky on an even keel even during low-speed climbs with the “good” engine developing maximum power. Engine-out climb performance at heavy weights, however, is virtually nil, even with a feathered propeller.

  The S-38 has benign stall characteristics even during a power-on stall with an engine shut down. Although there is very little stall warning—only a mild buffet a few knots before the break—it does not seem to matter because the airplane is so well mannered.

  An advantage of the North Las Vegas Airport is its proximity to sprawling Lake Mead, a paradise for boating and seaplane enthusiasts.

  Touchdown attitude for a water landing is about the same as when making a 3-point landing on a runway. The S-38 seemingly has no bad habits in the water and makes consistently smooth landings without a noticeable tendency to porpoise. The airplane has limited elevator authority with a forward center of gravity, however, so power is helpful in establishing the nose-high touchdown attitude.

  Like other multi-engine seaplanes, the S-38 does not have a water rudder, but it turns easily using differential power. If necessary, you can lower one landing gear leg to add water drag that helps to turn more sharply in that direction.

  During the plowing phase of a water takeoff, forward visibility all but disappears behind the heavy spray across the windshield, but this clears away rapidly as the airplane comes over the hump and onto the step. After that, it is a simple matter of establishing and holding the right attitude (finding the “sweet spot”) and allowing the Sikorsky to accelerate and fly itself off the water.

  Overall, the Sikorsky S-38 is an advanced, well-behaved airplane considering that it was designed only a year after Lindbergh’s historic flight and 25 years after the Wright Brothers’ first successful effort.

  Those interested in the adventurous exploits of Martin and Osa Johnson are encouraged to visit the Martin and Osa Johnson Safari Museum’s web site: www.safarimuseum.com

  You are also invited to visit the museum in Chanute, Kansas. The city was named after aviation pioneer Octave Chanute and is the birthplace of Osa Johnson. Not coincidentally, Chanute is served by the Martin Johnson Airport.

  My son and I were soaking up heritage at an aviation museum. Brian studied each archaic device with awe, wondering how pilots of bygone days had the courage to fly such ill-equipped and seemingly fragile-machines.

  Soon we reached an area displaying engines of the past. The center of attention was an engine that triggered fond memories.

  “Dad,” he asked, “Did you really use these weird-looking engines?”

  I nodded and realized just how far we had come since aviation’s dawn at Kitty Hawk.

  “But Dad,” he continued, now more bewildered than before, “How did this thing work?”

  “Well,” I began, “There’s a half-dozen coffee-can-shaped thingamabobs moving back and forth in holes inside that big iron block.” I continued with verbal diagrams of valves, spark plugs, cam shafts, and other complicated aspects of the obsolete, reciprocating, piston engine.

  This reverie describes what I really thought it would be like to someday take my son to an aviation museum. After my first exposure to a turboprop engine in a small, single-engine airplane, I had thought that the future of the reciprocating engine was doomed. But it was not to be so. The piston engine thrives and survives. Despite the advantages of turbine engines, the cost of manufacturing, maintaining, and operating them will have to improve dramatically if they are to displace piston engines in small, general aviation airplanes.

  My first experience with a turboprop-powered single was in 1968. This is when I was invited by the Garrett/AiResearch Corporation to fly their experimental Piper Comanche 600, a Comanche 400 modified with their TPE-331 turboprop engine.

  AiResearch told me that the unmodified Comanche fuselage was chosen as an early test bed for its turboprop engine because of the Comanche’s relatively high redline airspeed of 250 mph. This choice had nothing to do with the Piper Aircraft Company and did not mean that Piper intended to produce a turbine-powered Comanche.

  The one-of-a-kind aircraft, N8401P, and its veteran test pilot, Jack Womack, achieved public recognition on May 15, 1968 when they established a new world altitude record of 41,320 feet for that class of turboprop aircraft. The previous record of 34,173 feet had been held by Pierre Bonneau of France in a SIPA (French) aircraft.

  The TPE-331 is a lightweight, single-shaft, production engine available in power ratings of 575 to 715 shp (shaft horsepower). The one in the Comanche had 575 shp but could put out 605 eshp (effective shp) during flight.

  Even though AiResearch’s Turbine Comanche 600 and the stock Comanche 400
had identical fuselages, it would be unfair to compare their performance. The engines were worlds apart, eliminating the significance of any visual similarity between the two airplanes. The 8-cylinder, 400-hp Lycoming engine weighed 597 pounds (dry) while the TPE-331 turbine weighed a little more than 300 pounds and produced 50 percent more power. In other words, the Lycoming engine produced only 0.67 horsepower per pound of engine weight while the turboprop engine enjoyed a 2.0 hp/lb ratio. Pound for pound, therefore, the turbine was almost 3 times as powerful as the 8-cylinder engine.

  Although the turboprop engine does amazing things to an otherwise fine aircraft, AiResearch insisted that the Comanche fuselage was not designed or modified to accommodate a turbine engine. If an aircraft of the Comanche class were designed from the get-go to utilize turboprop power, the performance would compare to the Comanche 600 as a tiger does to an anemic house cat.

  The Comanche 600 was based at AiResearch’s Phoenix Division. It looked like any other Comanche except for its unique nose section. The cowling had been redesigned to house the smaller powerplant. Because the turboprop weighed considerably less than the piston engine, the propeller was extended 9 inches forward to preserve the original center of gravity. A large, stainless-steel exhaust stack was molded to each side of the cowling and directed the spent gases beneath each wing so as not to interfere with normal airflow about the wing roots. If the exhaust were to flow through a single-channel exhaust stack, an additional 30 hp of jet thrust could have been realized. The propeller was an 82-inch, 3-bladed Hartzell and was both reversible and featherable. The longer blades placed the propeller tips closer to the ground, requiring caution while taxiing on gravel.

  After a quick look at this unusual aircraft, I was introduced to Womack who knew most about the project. He had been with AiResearch since 1948 and involved with the development of the turboprop engine since its first flight in a Martin B-26 Marauder test bed in February, 1964. He was the original test pilot of the Comanche 600 beginning with its maiden flight on July 16, 1965.

  I asked Womack, “Because AiResearch is so deeply involved in turboprop development, why is the company equally aggressive in marketing turbochargers? It would seem that turbochargers and turboprop engines compete with one another.”

  Standing under the Arizona sun, Womack folded his tanned arms across his chest and said, “By selling turbochargers, more people will be exposed to the advantages of flying in the middle altitudes—between 12,000 and 20,000 feet—a regime where the turboprop engine is truly master. This will help to create a demand for pressurized aircraft. When these finally become available, we’ll have aircraft properly designed for turboprop engines.”

  Womack showed me how to preflight the engine for internal damage. If the propeller can be rotated effortlessly and freely without binding or unusual noises from the engine, then everything is normal. He suggested also that I look into the air inlet duct while turning the propeller to check the compressor blades for damage. A small sensor located within the duct also was inspected. This probe sent inlet-air temperature and pressure signals to the fuel controller, which metered the proper amount of fuel to the engine, depending on the position of the power lever in the cockpit.

  The tanks were filled with 130 gallons of jet fuel (kerosene). Although the engine holds 8 quarts of turbine oil, it was almost ludicrous to check quantity before every flight. The TPE-331 may require a quart every month or so, but the engine can almost always be flown from oil change to oil change without adding any.

  Satisfied with the preflight, Womack motioned me into the left seat.

  Having many hours in a Comanche, I felt comfortable although some changes had been made to the instrument panel. Instead of the manifold pressure gauge and tachometer were an engine torque meter redlined at 44 psi, a small exhaust-gas temperature gauge, an equally small tachometer that indicated turbine rpm in percent (redlined at 105 percent).

  An engine control pedestal mounted at the center of the instrument panel contained a robust, stainless-steel power lever, one that a pilot could really get a grip on.

  The other, smaller one was a condition lever that controlled propeller pitch.

  Starting the engine was dirt simple: 1) Turn on the master and inverter switches; 2) Turn on the fuel and ignition switch (this armed the circuits for activation later in the start process); and 3) Tap the spring-loaded start switch and release. That is all there was to it. The remainder of the start process was automatic.

  The engine began to whine and within a few seconds, engine rpm reached 10 percent. This activated the circuits that caused the fuel valve to open and the 2 spark plugs to spray high voltage into the engine’s burner section. EGT rose rapidly, peaking at about 700 degrees C with the engine accelerating through 30 percent rpm. The whine became more intense and the propeller, rotating in flat pitch, began to make a neat whooshing sound.

  We watched EGT carefully; if it continued climbing rapidly to 780 degrees or above, a hot start would have occurred (probably due to low battery voltage and weak engine cranking power). We would have had to shut down the engine. Instead, the engine continued to wind up. At 55 percent rpm, the starter disengaged and the ignition turned off automatically. (Once combustion had begun with a steady flow of fuel, ignition was no longer required.) The engine stabilized at 65 percent with the EGT at 350 degrees.

  One hundred percent rpm is equivalent to 41,730 engine rpm and 2,000 propeller rpm. The propeller is geared down 20.9 to 1.

  One of many early problems faced by AiResearch was providing 24 volts to the starter while the rest of the aircraft needed 12 volts. The solution was simple. Two 12-volt batteries were installed in the Comanche. When the engine was not running, the batteries were in series producing 24 volts for the starter. But at 55 percent rpm—when the starter disconnected—a relay operated to place the batteries in parallel and produce 12 volts for flight.

  Without further ado, we were ready for takeoff. The propeller (condition) lever was left in the aft or low rpm position for ground operations. Womack pointed out that the condition lever should be kept in the ground-idle position while taxiing. Pulling back on the big T-shaped throttle, the propeller went into reverse pitch, which was used to save wearing out the brakes or to back up, literally.

  Womack had me push the condition lever forward, out of the ground-idle detent and into the flight-idle position. He also cautioned me not to retard the throttle into reverse pitch when airborne because of possible tail buffeting that could result from the use of reverse thrust in the air. He emphasized that the Comanche was not designed to operate in this configuration. The Pilatus Porter, though, was designed to accommodate airborne reversing to enhance its unusual maneuvering requirements.

  As we taxied to Runway 26R, I was shown how an engine fire (outside the engine but under the cowling) activated the fire-warning system and which button to push to spray fire-extinguisher agent into the engine area.

  Propeller feathering was accomplished by a pulling a red vernier-type knob that allows oil to drain from the propeller dome. A flick of the unfeathering switch pumps oil back into the dome should the pilot want to windmill the propeller in preparation for an airborne start.

  There were no engine checks to make at the runup pad. Nor did the turbine engine need to be warmed up.

  The rpm (condition) lever was advanced to the flight idle, high-rpm position.

  As we waited in position on the runway for takeoff clearance, Womack pointed out that the engine was canted 3 degrees right to compensate for left-turning tendencies. This correction was obvious when looking over the Comanche 600’s long nose.

  Although the engine can put out 605 eshp under standard conditions at sea level, power demanded from N8401P’s turbine was limited to less than 450 shp. Womack explained that the aircraft structure was not designed to accept the stress and strain of so much power. The application of full throttle could have cau
sed structural twisting and failure aft of the firewall. “But,” Womack said, “All 450 shp is available up to 18,000 feet. At higher altitudes, available power decreases.”

  The clearance to go crackled through the cabin speaker and by advancing the power lever, I commanded the fuel controller to pump 45 gph into the fiery pits of the engine’s burner section (engine torque was about 44 psi). The large propeller took huge bites out of the desert air and hurled the Comanche forward. Acceleration was incredible. The strong and steady pull of the turboprop engine was smooth, and we used much less runway than I had anticipated.

  I rotated the nose at 80 mph. After raising the gear, I asked Womack about reducing to climb power. “Forget it,” he stated flatly. “The power has already been reduced (from 605 to 450 eshp). Hold the airspeed at 140 mph and let’s see what happens.”

  The climb angle was steep and the vertical-speed indicator showed more than 2,000 fpm on the way up to 5,000 feet. “She’ll climb even better at 120 mph,” Womack said, “but the steep attitude makes some pilots uncomfortable.”

  It was a hot day, and we still climbed to 20,000 feet in only 17 minutes. Thirty thousand feet, I was told, usually requires only 26 minutes. Once at 30,000 feet on a standard day, climb rate is still a respectable 1,000 fpm.

  At 20,000 feet, N8401P cruised at 250 mph while burning 30 gph. At economy cruise, the Comanche 600 flew at 215 mph with a consumption of 21.5 gph. This was less fuel per mile than was possible with the piston engine. The range under these conditions (allowing for taxi, takeoff, climb, descent, and a 10 percent fuel reserve) was an impressive 1,225 sm.

  Cavorting about the Arizona skies in this marvelous machine gave me a privileged feeling, as though I was flying a futuristic airplane, and I suppose that was true. The airplane had a heavy, solid feel, and the sound of the engine was exciting. It exuded strength and capability; it did not scream or vibrate to attract my attention. If the turbine could talk, it might have said, “Watch what I can do in my own quiet way; ignore the bellowing roar of lesser engines.”