Piper Pressurized Navajo

inches of manifold pressure and sucks 90 gph through the engines. Even high cruise exacts 58 gph from the geared Lycomings. Oil capacity is 18 quarts per side, 4.5 gallons of oil in each mill. With a wingspan of nearly 41 feet and a tail that stands more than 13 feet high (both dimensions beyond the province of most tee-hangars), a P-Navajo must normally be housed in either a community hangar or a very large individual one. This airplane is a heavy invest- ment in both dollars and weight, and that’s evident the moment you try to leave the chocks. At rest on the ramp, the king-size Piper manifests the typical big-aircraft characteris- tic of an immovable object. It takes a sizeable burst of irresistible force (better known as breakaway thrust) to get all that mass moving, after which powerful brakes are required to stop it. The machine steers like a Peterbilt on the ground, with all the best and worst that implies. Surpris- ingly, there’s no hydraulic or electri- cal assist on the nosewheel, so asym- metric thrust definitely helps move it around the tarmac. If mounting a pair of 425-hp en- gines on the wings seems an exercise in excess, one result of this power is truly impressive climb performance. Letting 850 hp pull 7800 pounds of airplane through the sky nets a power loading of just more than 9.1 pounds per horsepower, and that means book figure for Vy climb is 1740 fpm, bet- ter than any piston twin I can think of except perhaps the 56 Baron. Best rate of climb speed is 110 knots, slow enough that the aircraft elevates its nose well above the horizon, block- ing any straight-ahead view of what you’re about to hit. Most pilots use a 150-knot-cruise climb and settle for a slightly more lei- surely 1400 fpm ascent in exchange for a lower deck angle. That still allows you to reach a cruise height in the high teens or low 20s well under the requi- site minute per 1000 feet, convenient for flight planning purposes. The Navajo’s pressurization system was designed for tall flight and, for that reason, Piper inflated the cabin to a stout 5.5 psi (the same differential used a dozen years later on the Mal- ibu). This allows a cabin altitude of 5000 feet at an actual 20,000 feet and a 10,000-foot cabin at 28,000 feet. The system is fairly simple and works just fine in the auto mode, providing a cabin rate of climb equal to about one-third of the airplane’s actual as- cent. Yet, if you feel you absolutely must exercise command and control, you can manually run the cabin rate of climb at any setting between 100 and 1000 fpm. Environmental systems become ex- ponentially more important in any air- craft designed to operate at potentially hostile altitudes, and the P-Navajo’s heater is critical to flight safety above 10,000 feet. Since most of the type are rarely flown at cruise below 15,000 feet, the heater has to work well on practically every flight. Williams favors the flight levels whenever possible, and everything on his Piper works all the time. The heater is a 35,000 BTU Janitrol gas unit that keeps even a large cabin warm and comfortable. When an airplane’s level of sophistication reaches that of the P-Navajo, keeping everything running at the same time can become a problem, but JA Air is apparently up to the challenge. For those pilots trained to avoid grossly oversquare settings, the Pres- surized Navajo’s cruise power combi- nations are a little startling. How com- fortable does 36 inches and 1700 rpm sound? That’s Williams’ favorite set- ting at about 70 percent power, burn- ing around 50 gph. These are geared, turbocharged engines, however, and you’re looking at prop rpm, not en- gine rpm. Add half the tach read- ing to the indicated rpm and you’ll be close to engine rpm. That means 1700 rpm translates to 2550 engine rpm, a much more agreeable number. At 1700 revolutions up at 17,000 to 18,000 feet, those huge, 93-inch-di- ameter, three-blade props develop tip speeds of nearly Mach 0.7. Driving the blades much faster would cause them to lose efficiency. The P-Navajo seems to do its best work in the lower 20 flight levels, and Williams usually files for an altitude between 20,000 and 25,000 feet, though he’s had the aircraft as high as 28,000 feet. “I can usually count on a cruise speed of about 220 knots 36 PIPERS FEBRUARY 2015 SPECIFICATIONS & PERFORMANCE SPECIFICATIONS: Used Price: $155,000 Engine make/model: Lyc TOGO-541-E1A Horsepower@altitude: 425 @ 20,000 Horsepower on takeoff: 425 TBO - hours: 1200 Fuel type: 100LL Propeller: 3 blg CS Landing gear type: Tri/Retr Gross weight (lbs): 7800 Std empty weight (lbs): 5044 Useful load – std (lbs): 2756 Usable fuel – std (gal/lbs): 236/1416 Payload – full std fuel (lbs): 1340 Wingspan: 40’ 7” Overall length: 34’ 5” Height: 14’ 3” Wing area (sq ft): 228.7 Wing loading (lbs/sq ft): 34.1 Power loading (lbs/hp): 9.2 Wheel size: 6.00 x 6 Seating capacity: 7 Cabin doors: 1 Cabin width (in): 50 Cabin height (in): 50 PERFORMANCE: Cruise speed (kts): 75% 220 Fuel Consumption (gph): 75% 58 Best rate of climb, SL (fpm): 1740 S/E rate of climb, SL (fpm): 240 Maximum Operating Altitude (ft): 28,000 S/E Service Ceiling (ft): 12,100 Stall – Vso (kts): 73 TO ground roll (ft): 1440 TO over 50 ft (ft): 2200 Ldg ground roll (ft): 1370 Ldg over 50 ft (ft): 2700 1976 Piper Pressurized Navajo All specs and performance numbers are drawn from official sources, often the aircraft flight manual or the manufactur- er’s web site. On used aircraft, common sources of informa- tion are Jane’s All-The-World’s Aircraft or Penton’s Aircraft Bluebook Price Digest. at 23,000 with the Victor engines, which is at least 10 knots quicker than I used to cruise before the overhaul,” he explains. “My typical block speeds for two- or three- hour trips now run consistently over 200 knots, usually 205 to 210. Victor claims the major advantage of the resin coating on the Black Edition engines is better cooling, and I believe it. So far, I haven’t had any heating problems.” Another plus of the new mills, according to Williams, is the phenomenal smoothness. “I carry many passen- gers who are used to the low noise level and smooth ride of business jets, and they automatically expect a prop airplane to be loud with plenty of vibration,” he says. “They’re nearly always surprised at how quiet and smooth the P-Navajo is.” As with many other older cabin-class twins, the total expense of owning a P-Navajo isn’t reflected in the price of admission. Even the very last 1977-model Pressurized Navajos are listed in Aircraft Bluebook at about $155,000 used. A totally unscientific check of Trade-A-Plane revealed a half-dozen of the machines for sale, none more than $100,000. Maintenance cost and operating expenses are the real keys to the bottom-line price. “If you’re going to own an aircraft like this, you have to stay ahead of the potential problems,” Williams suggests. “Preventive maintenance is a must if you hope to minimize downtime.” High-maintenance or not, Guy Williams is sold on his Pressurized Navajo. There may be better piston twins available for the corporate mission, but don’t ask Williams to name one.