|Piper Super Stinson|
|Written by Bill Cox|
Those who are familiar with the homebuilt aircraft movement probably remember the name Ken Brock. Brock dealt in kit parts for Rutans, Thorps and a variety of other homebuilt airplanes for nearly 20 years. Brock Manufacturing, in Stanton, California, specialized in dies, tooling and metal stamping. The company also built a reputation for producing high-quality metal products for aviation and other applications.
Brock was well known on the air show circuit for his amazing demonstrations in a variety of gyrocopters of his own design. Ken performed throughout the United States and Canada in hundreds of air shows. I don’t have enough years left to ever stop missing Ken, but his airplanes have survived him.
With such a heritage, it wasn’t surprising that Brock’s personal airplanes reflected his penchant for near perfection. Brock owned a total of nine flying machines, but not all were homebuilts. Shortly before he died in an accident at his ranch strip in the Mojave Desert, he completed a total restoration of a Stinson 108-3 Station Wagon that probably qualified as one of the best of its kind.
Basically a scaled-up version of the earlier, three-seat Stinson 10A, the 108-3 was the final product of Consolidated Vultee’s Stinson Division before the company was sold to Piper Aircraft. Rights to the airplane, along with an unsold inventory of 500 Stinson Voyagers/Station Wagons, were sold to Piper in late 1948. By 1949 Stinson was a part of aviation history.
The late Ken Brock’s Piper Stinson held special significance for him, because it was his first flying machine other than his beloved gyrocopters. The airplane is technically a 1948 Flying Station Wagon, which is only different from the Voyager because the baggage/aft cabin floor is beefed-up to support 600 pounds. The Station Wagon was designed as a semi-utility airplane with ranchers and bush operators in mind. It also featured quick-change/sling-style rear seats for additional loading flexibility.
Brock owned a Cessna 210, a Thorp T-18, a Brantly helicopter and a half-dozen other aircraft, but the Stinson was always his favorite among fixed-wing aircraft. The pilot’s love affair with his big-tailed Stinson began when he bought it in 1960. During his tenure with the Stinson, the airplane went through three separate renovations, the last of which was the most significant. During the final renovation the stock 165-hp Franklin 6A4-165-B3 engine was replaced with a 230-hp Continental O-470R—essentially the same engine used on the pre-1975 Cessna Skylanes.
This is a fairly standard conversion and one that’s been around for a long time. The STC is owned by Seaplanes Inc. of Tacoma, Washington, and it’s a popular modification for Stinsons converted for bush work in the Pacific Northwest, regardless of whether the airplane will ever be mounted on floats or not. Because of their big cabin and excellent load-carrying capability, Stinsons do make excellent candidates for conversion to skis or floats, and the additional power helps them lift the big floats and operate more confidently in the challenging outback.
The late Ken Brock acquired his big Continental O-470 engine from a wrecked Alabama Skylane, and it was one that tried to burn water rather than avgas. Although the airplane was totaled, the engine and cowling were surprisingly left undamaged. The installation and most of the accompanying modifications to Brock’s airplane were handled by Dave Lewis of Flite Craft at Chino Airport in California.
As it happened, the conversion from Franklin to Continental power was a lot easier said than done. The Continental is quite a bit heavier than the Franklin and the metal Hartzell prop weighs considerably more than the original Micarta Aeromatic. As a result, the engine mounts had to be shortened by 3.5 inches and the battery moved back from the firewall to beneath the baggage floor to preserve the CG.
To complement the new engine and prop, Brock found that a Thorp T-18 Tiger spinner fit the airplane perfectly and provided improved aesthetics. In fact, the spinner fits so tightly around the blades that most pilots assume the prop is a fixed-pitch. It’s actually a standard Cessna 182 constant speed and is quite a bit larger than the original Aeromatic.
Because a larger diameter prop meant less ground clearance out front, larger tires (8.00 x 6) and three-inch plugs in the oleos were added to make the Super Stinson perch higher on its main gear. Although this virtually eliminated any forward view during taxiing, it also imparted better short field performance because of the higher natural angle of attack.
An improvement to visibility is the single-piece windshield in place of the original two-piece windshield. New Plexiglas was installed all around and the side windows were modified to accommodate Bonanza-style storm windows.
In addition, the final restoration included a teardown to the bare frame, a sand blast and full zinc chromate in addition to a complete recovering job. The pieces were painted before assembly, and the airplane was finished in brilliant shades of red and burgundy. The paint job is one of those works of art that must be seen to be believed.
Inside the cockpit Brock elected to switch to center stack radios, which is quite a trick in a Stinson because it requires modifying the control system. The original Stinson’s dual controls utilized a single shaft that T’d behind the panel, leaving no room for radios down the center. In order to adapt the airplane to a center stack the central control shaft had to be reshaped to form a “y” shape at the bottom.
The panel on the airplane was all new—a definite improvement on the original fascia that looked like something out of a South American locomotive. The panel combined with the all-new interior provides all the ingredients for an uncommon reconstruction. Though purists may argue that the finished product is far from stock, the changes are fairly logical improvements. The one-piece windshield is definitely an aesthetic as well as a functional success. The engine replacement improves TBO from 700 hours on the original Franklin to 1,500 hours on the Continental. Of course, performance improves dramatically with the additional 65 hp.
Flying the airplane belies the airplane’s age. All other factors being equal, takeoff acceleration is largely a function of one factor: power-to-weight ratio. The more horsepower there is to push each pound, the quicker the airplane will leave town. The Super Stinson employs 230 hp to accelerate only 2,400 pounds of airplane, so the power loading is a low 10.4 pounds/hp.
Translated into laymen’s terms, this means the reinvigorated Stinson really punches you in the back when you drop the hammer. I probably made a dozen takeoffs and landings during the eight hours I flew the airplane, and it was such a thrill to feel the Stinson’s instantaneous response.
Surprisingly, there was never any particular problem with torque or P-factor. The airplane tracked true and consistent with minimum rudder dancing. Part of the reason is that the Flying Station Wagon was granted more rudder than it knew what to do with. The tip of the vertical stabilizer stands nearly 7 ½ feet off the ground, providing an inordinate amount of yaw control.
I tried Maule-style jump takeoffs a few times, releasing brakes at the power peak, pushing over to the wheel attitude, pulling in full flaps and rotating abruptly. I found the Super Stinson easily capable of some definite STOL numbers. Liftoffs occurred in consistently less than 300 feet, followed by excellent climb.
The Maule M7, by the way, uses only five hp more to lift an extra 200 pounds of gross weight, so it shouldn’t be surprising that the Stinson nearly matches the pure-STOL Maule’s numbers. The two airplanes use similar wind spans and the wing areas are similar, but there’s no question the Maule is the more optimized for STOL operation.
I held 75 knots for climb in the Super Stinson and recorded excellent climb, if at the cost of forward visibility. I saw a consistent 1,500 fpm on the VSI, but that’s about all I saw as I looked straight ahead—other than sky. A more practical climb speed would be 90 knots, which allows for a 1,000 fpm climb while still allowing a degree of over-the-nose visibility.
Predictably, cruise performance also improves with the injection of horsepower. The engine swap increased power by 39 percent, which meant I should have expected to see a 13 percent cruise increase. Years ago, Brock had reported a realistic cruise speed of 105 knots with the original Franklin engine, so standard rules might suggest I’d see a 14-knot improvement.
In fact, the cruise was actually closer to 20 knots. The Super Stinson recorded about 125 knots cruise. Because I trust airspeed indicators about as much as I do fuel gauges, I ran the airplane back and forth between two points of known distance and verified the 125-knot cruise speed.
The down side of extra power is higher fuel burn. The O-470 has never been known as an especially thrifty engine. Specific fuel consumption on early general aviation engines rarely runs below .45 pounds/hp/hr, and there’s no way to avoid a proportionately higher fuel burn if you use more horsepower. While the old Franklin allegedly burned 9.7 gph at 75 percent, the larger Continentals chug down 13 gph at the same power setting.
One alternative is simply to throttle back. During a later flight, I used a 55 percent setting that produced 110 knots in exchange for just less than 10 gph. The engine swap either gives a pilot the option of flying faster—as long as he’s willing to pay for it—or flying at the same speed for the same burn.
All things considered, the Super Stinson maintains the rock-solid stability Stinson’s are famous for. Despite being relatively light, the modified Stinson plows thru turbulence with a minimum of fuss. Just keep the roof-mounted elevator trim moving in order to maintain balance and keep elevator forces from becoming uncomfortably heavy.
The Super Stinson is slightly heavier than stock because of the larger engine. Empty weight is 1,350 pounds, which is 50 pounds more than the original. This leaves the 108-3 with a useful load of 1,050 pounds. Top the 46 gallon tanks and you can still load 774 pounds inside the cabin. That’s far better than most modern four-seaters, and it explains why the airplanes are still popular in places where how much you can carry and where you can take it are more important than how quickly you can get there.
The Super Stinson also works well at low speeds in the pattern. Using 70-75 knots for the circuit, the Stinson will walk its Scott tail wheel onto the ground without complaint and will resist a traditional three-point kerplunk-style landing. If you do succeed in three-pointing the airplane, the outboard wing slots assure a docile, forgiving stall, making this one of the world’s easiest-flying taildraggers.
The Stinson Flying Station Wagon represents one of the best of a bygone generation of airplanes. It also continues to offer performance, comfort and payload comparable to airplanes that are 50 years younger.