Dream Aircraft

by Schiff, Barry

  Maintenance also is simplified because nothing is buried beneath floorboards or side panels. Everything, including control cables, brake cables and fuel lines, is fully exposed and easily accessible. These features might blemish the aesthetics, but this is, after all, a utility aircraft.

  The wing spar is Sitka spruce. When I questioned Diehl about using a wood spar, he grinned, indicating that I must not know much about bush flying, something I candidly admit.

  “Suppose,” he said, “that you screw up a landing in the boondocks and slam a wing into a tree. If you bend a metal spar, it stays bent. But a resourceful pilot can field-splice a wooden spar and return to civilization.”

  Such is Alaskan spirit and resourcefulness. “And,” he continued, “if you can’t repair the wing and have to spend the night, you can sleep in the Interstate’s 6-foot-long baggage compartment.”

  I peered and ultimately crawled into this cavernous compartment. It runs almost the entire length of the fuselage aft of the rear seat. Diehl was right. I am tall and had no difficulty stretching my frame on the plywood floor. With such a voluminous compartment, it would be easy to overload the S-1B2 and exceed the maximum-allowable aft center of gravity. The FAA insisted that a red line be painted across the floor designating the point aft of which no load may be carried in flight. I doubt, however, if the FAA would fuss if you allowed a few fishing poles to cross the red line and extend into the restricted zone.

  Maximum-allowable gross weight of the aircraft is 1,900 pounds. Deducting 1,100 pounds of empty weight leaves a respectable 800-pound useful load.

  Other exterior features offer further evidence that the Arctic Tern is intended for unimproved strips. The horizontal stabilizer and propeller have unusually high ground clearance for a taildragger and the large, high-flotation tires allow the airplane to be landed safely on unexplored beaches or riverbeds.

  Cockpit entry requires hauling yourself in; there is nothing graceful about it, but once inside, the accommodations are comfortable. The door is a seaplane type that drops flush against the fuselage, needed by the pilot wanting to equip the Arctic Tern with floats. A conventional door is undesirable on a seaplane. It would get in the way when trying to hand-prop the engine from behind in case of a dead battery.

  I would soon be flying the airplane over some of Alaska’s spectacular wilderness, and Diehl handed me a bag of survival gear. In addition to other useful amenities, it contained 2 large bottles of mosquito repellent, enough to kill a caribou. If stranded in the bush without repellent, a swarm of mosquitoes could drive a man insane to the point of death.

  I climbed into the front seat with a set of sectionals and an anticipation of excitement. What more could I want? I had an aerobatic bush plane without a Hobbs meter, full fuel tanks, and all of Alaska to explore.

  Taxiing toward Anchorage International’s Runway 31, I scanned the spartan instrument panel. Everything needed is there but there are no extras except for an electric auxiliary fuel pump. This, according to Diehl, is needed only when gravity fails, an FAA certification requirement.

  Cockpit visibility is outstanding. The greenhouse design of the original L-6 liaison aircraft has been retained, resulting in large windows and a skylight that spans almost the entire cockpit roof. The rear-seat passenger does not feel as though he is sitting in a hole as he does in so many other taildraggers with tandem seats. The wide, rear bench-type seat accommodates 2 small passengers behind the pilot, but they will be cozy. At such times, the rear control stick can be easily removed to increase legroom and prevent possible control interference.

  After a normal engine runup, I extended the semi-slotted Fowler flaps to the first notch by pulling on the Johnson bar located next to the left sidewall some distance forward of my knee. Some torso bending is required for this, and is no problem on the ground. In the air, however, there is a tendency to unwittingly move the control stick forward as a pilot reaches for the flap handle.

  With the throttle wide open, the 82-inch propeller snarled, and by the time I thought about raising the tail, the Interstate was off the ground. Ground roll was approximately 150 feet.

  Landing distances are about the same as those needed for takeoff under similar conditions, which is comforting to know when operating in and out of critically short fields. This means that a proficient pilot can get out of almost any field on which he can land. This is not true when flying most other aircraft because they typically need more distance for takeoff than for landing.

  The spunky airplane climbs well, too. At the best rate-of-climb speed of 60 mph, it goes up 1,000 fpm. Best angle-of-climb speed is 48 mph.

  At 2,500 feet, I headed southwest and followed the snow-patched cliffs that plunge precipitously into the icy waters of the Turnagain Arm, so called because when Captain Cook sailed up this dead-end finger of water, he was forced to “turn again.”

  I experimented with various power settings to find a compromise between power and noise. Like other aircraft in its class, the Interstate is not quiet.

  The cabin heater could use some redesigning, too. When you pull the knob, your right shin gets scalded, but the rest of the cockpit remains cold.

  At 75-percent power, the S-1B2 cruises at a true airspeed of 110 mph while burning 9 gph. This results in a no-wind range of about 450 mile plus reserve. By slowing and leaning, range can be stretched to 650 sm.

  The fuel system has a unique safety feature, a reserve tank similar to that of early-model Volkswagens. The reserve tank is actually the bottom 4 gallons of the left wing tank, which holds a total of 20 gallons. The recommended fuel-management procedure is to initially use the left tank. This allows you to burn only 16 of its 20 gallons. When this runs out, switch to the right tank for an additional 20 gallons. When this is gone, you are assured that an additional 4 gallons remain at the bottom of the left tank, but it is useable only by moving the fuel-selector valve to the reserve position. By then, it is time to find a place to land.

  I arrived over the gravel strip at the foot of the Portage Glacier but was in no hurry to land. The glacier is an awesome spectacle. It is a thrill to soar above this glistening blue-white river of ice as it winds and carves its way between snow-capped sentinels of towering majesty.

  Downwind and abeam the approach end of the strip, I chopped power and extended the flaps to the first notch, retrimmed, and then pulled the handle to the second and final notch. At this point, the Arctic Tern seems to halt abruptly in midair, behaving somewhat like a bird trying to use its wings to back up upon discovering that it is about to fly into the cat’s mouth. I added power and allowed the airspeed to settle at 50 mph, safely above the 39 mph, 1-G stall speed. A moment later the well-mannered airplane plunked onto the gravel runway tailwheel first and rolled to a stop next to a small, glacial river.

  The Arctic Tern is an honest, straightforward airplane. It has no adverse flight characteristics, and can be looped and rolled with ease. The controls respond nicely during slow flight, and the aircraft is a joy to fly in all flight regimes, especially when over our 49th state.

  A Goodyear blimp is one of the most recognizable aircraft in the world. Yet when people see one over the Super Bowl or Dodger Stadium, most believe they are looking at the Goodyear blimp, not realizing that there are four. Known technically as a Goodyear Model GZ-20, each is named after a winner of an America’s Cup Yacht Race: America (based in Houston), Enterprise (Pompano Beach, Florida), Columbia (Los Angeles) and Europa (Rome, Italy). As familiar as they may be, only a few pilots really understand them.

  Unlike most aircraft that have fixed or rotary wings to create lift, a blimp is lifted by the buoyancy of helium, which is 86 percent lighter than air. On a standard day at sea level, a cubic foot of this inert gas can raise slightly more than an ounce of weight. Although hydrogen is lighter and can lift more, its flammability makes it impractical.

  When there is exactly enoug
h helium in a GZ-20’s 202,700-cubic-foot envelope to support the aircraft, it is said to be in equilibrium; its net or static weight is zero. The engines can be shut down, and the blimp will float at constant altitude and zero airspeed.

  In lighter-than-air lingo, a blimp is statically heavy when gross weight exceeds the lifting ability of the onboard helium. For each 50 pounds of static weight, a GZ-20 sinks about 100 fpm. One way to maintain altitude when statically heavy is to dispose of ballast (consisting of 25-pound bags of shot). Also, fuel can be dumped, but only from the auxiliary tanks. The preferred way to preserve altitude, however, is to use engine power to build forward airspeed and apply up-elevator to raise the nose. Because the envelope of a GZ-20 is shaped like a symmetrical airfoil, it can develop enough dynamic lift to maintain altitude when the blimp is as much as 800 pounds heavy (maximum allowable static weight). At maximum heaviness and a cruise speed of 32 knots, an 11-degree, nose-up attitude is needed to maintain altitude.

  When a blimp is light, however, it simply rises like a child’s helium-filled balloon, unless forward airspeed and a nose-down attitude are used to create negative dynamic lift.

  Maneuvering a blimp in flight has been compared to handling a submerged submarine; each is controlled only with power, elevators, and rudders. Turning a blimp is remarkably simple but initially disconcerting to airplane pilots accustomed to coordinating ailerons and rudder. A blimp has no ailerons. An airship pilot simply stretches a leg and shoves a rudder pedal to its forward limit. After what seems an eternal delay, rudder deflection takes hold and the ponderous nose sluggishly begins to slue along the horizon. Although maximum turn rate is little more than 3 degrees per second, the turn itself is incredibly tight because of the slow airspeed.

  Because the blimp’s car (or gondola) and its useful load hang beneath the envelope, a blimp has an exceptionally low center of gravity. Consequently, the airship acts like a giant pendulum. During turns, centrifugal force pulls on the car and rolls the blimp into a shallow bank, which is why ailerons are unnecessary.

  During turbulence, pendulum effect keeps the blimp on an even keel. Since the envelope is so long and resilient (there is no internal framework as there is in a dirigible or rigid airship), the blimp pitches very little, even in heavy turbulence. This is why lap belts are neither required nor installed in Goodyear blimps.

  The elevators are contro11ed by what appears to be a mammoth elevator trim wheel next to the pilot’s right leg. Raising the nose requires pulling the top of the wheel rearward and vice versa. The process, though, can be a laborious, two-handed effort. Pitch control, especially in turbulence, requires almost constant hauling and tugging. Shoving the nose down feels as though you are trying to hold a basketball underwater.

  Goodyear pilots usually fly their blimps in a somewhat statically heavy condition, which helps them to descend for landing. Consequently, cruising at 40-percent power and 30 knots requires a 5-degree, nose-high attitude. Raising the nose to 20 degrees without adding power produces a 400 fpm climb; pushing the nose 20 degrees below the horizon results in a 600-fpm descent. Curiously, these gross attitude changes have almost no effect on airspeed. This is because the blimp’s static weight is so light (usually 100 pounds or so) and its drag so great.

  The complexities of handling a blimp become obvious during climb and descent. When the aircraft gains altitude, outside air pressure naturally decreases. Consequently, the helium expands and increases pressure against the 21,600 square feet of the neoprene-coated, 2-ply Dacron envelope. If this internal pressure increase goes unchecked, the material could stretch to intolerable limits, weaken, and possibly tear. (Envelopes are replaced every 10 years, cut into large tarpaulins, and donated to schools to protect their athletic fields from rain or snow.)

  The simplest way to relieve this internal-pressure increase would be to open a valve and allow some of the expanding helium to escape. But considering that a GZ-20 carries tens of thousands of dollars worth of the stuff, this would add unacceptably to the already high operating cost. Venting helium during climb would result in a more serious problem. During descent, the remaining helium would compress because of the increasing outside air pressure and become insufficient to provide needed buoyancy. Also, there might not be enough helium left to maintain the envelope’s shape at lower altitudes resulting in the airship pilot’s ultimate embarrassment: returning to base with a limp blimp.

  To compensate for changes in altitude, temperature, and atmospheric pressure, a large, air-filled balloon, or ballonet, is installed inside and at each end of the sausage-shaped envelope. During climb, the pilot opens a pair of valves that allows air from within the ballonets to escape the envelope at the same rate that the helium expands. This allows pressure within the envelope to remain approximately constant.

  When the helium compresses during descent, the ballonets are replenished with outside air and expand within the envelope to take up the slack. (Air scoops positioned behind the pusher propellers provide the air pressure necessary to keep the ballonets properly inflated.)

  It is natural to presume that considerable internal pressure is required to keep the envelope inflated and shaped, but this is not so. The pressure differential between the inside and outside of the bag is normally only 0.04 to 0.07 pounds per square inch, barely enough to make your ears pop. This pressure difference is so slight that a bullet hole in the envelope would produce such a slow leak that it might not even be noticeable during a normal flight.

  (During preflight inspections, the pilot removes a panel from the car’s ceiling, climbs into a tight, dark compartment, and inspects the envelope’s innards through a viewing lens. Pinholes of light in the envelope are leaks that need patching.)

  Pressure differential must not be allowed to fall below 0.04 psi. Otherwise, the envelope will begin to lose rigidity. Excess pressure, of course, can damage the rubber-coated fabric. To prevent this, an emergency helium relief valve opens automatically at 0.10 psi. Redline envelope pressure is 0.12 psi. Airship pilots spend considerable time monitoring and controlling envelope pressure, a factor as critical to them as airspeed is to airplane pilots.

  In addition to using ballonets to compensate for changes in helium volume, these air-filled compartments (each of which occupies up to 14 percent of the envelope’s total volume) also are used as trim devices. Assume that the airship is slightly heavy and needs to be flown nose high to maintain altitude. The pilot could roll back the elevator wheel, but holding the necessary control pressure for very long would be fatiguing. Instead, the pilot further inflates the aft ballonet. This forces helium inside the envelope to be squeezed forward. As a result, the center of buoyancy moves forward and lifts the nose above the horizon. By reversing the procedure, a blimp can be made to fly nose low.

  There is nothing exciting about a GZ-20’s 30-knot cruise speed (the never-exceed speed is 43 knots), but do not underestimate its climb performance. Since almost all of a blimp’s maximum-allowable gross weight of 12,320 pounds is supported by helium, very little power is devoted to producing lift. Consequently, most of the power produced by the 2 Continental IO-360D, 210-hp engines can be devoted to rocketing the blimp skyward at an impressive 2,400 fpm (maximum allowable). The GZ-20 could climb at 3,400 fpm, but the helium would expand faster than the ballonets can be deflated, risking excessive envelope pressure. Also, a 3,400-fpm climb requires more than the maximum-allowable, 30-degree pitch angle.

  In theory, a blimp can be pointed straight up, but this would impose an unacceptable strain on some of the cables that support the car from the roof of the envelope. Also, the engines are not configured for inverted flight (nor are the seat-beltless passengers).

  One advantage of airship operation is that it is almost impossible to violate center-of-gravity limitations. This is because the blimp is so long and the entire 3,281-pound maximum useful load is concentrated in the car at its middle. (CG range is stated in feet, not i
nches.)

  Flying a blimp at altitude in smooth air is a joy, especially on a warm day with the side windows slid open and your elbow propped on the sill. The cabin is extraordinarily spacious, and the view hither and yon is Cineramic, except when looking up. Then there is an ominous, Dacron overcast everywhere, a constant reminder of the blimp’s mammoth dimensions. (GZ-20s are 192-feet long, but consider that the Hindenburg was four times as long and 30 times as voluminous.)

  Although the GZ-20 is certified and equipped for IFR flight (including radar), it usually is flown only VFR. Flying through a rain shower is often desirable, however, because this is the only way to wash a blimp. (Clinging raindrops add 300 pounds to the static weight.) The U.S. Navy once speculated that the undulating bag of a blimp would not collect structural ice. But the Navy was wrong. Goodyear’s blimp America, flying between Dallas and Houston, once picked up an estimated ton of ice. (A safe but severely overweight landing was made at Houston, even though the blimp came to rest with the nose burrowing into the ground. The ice melted at the warmer ground temperature.)

  Wind poses more frequent but less serious problems. Because a blimp flies so slowly, a 20-knot headwind can be catastrophic, reducing cruise speed from 30 to 10 knots and normal range from 396 to 132 nautical miles. (With the auxiliary tanks full, a GZ-20 carries 294 usable gallons and has a still-air range of 850 nm.) This explains why airship pilots, like glider pilots, usually fly only upwind of an airport during local flights. Otherwise they might not be able to return should the wind pick up. Endurance, of course, is not affected by wind. By shutting down one engine and operating the other at 3 gph, a Goodyear blimp can remain aloft for more than 4 days.

  Although the propellers cannot be feathered, the drag created by windmilling blades at such slow speed is inconsequential. Also, the engines are mounted so close to the aircraft centerline that no yaw results from shutting one down.