By Wade Sullivan, Cherokee Pilots of the West Coast
Throughout the 1950s, Piper had great success in the low-end airplane market with its PA-20 Pacer and PA-22 Tri-Pacer. Although old-school tube-and-fabric designs, Piper was able to produce them cheaply, and they performed very well compared to their competition.
As early as 1952, however, the need for a more-modern, all-metal airplane to compete with Cessna’s Model 170 had been acknowledged. It was then that Piper officials tried to purchase a four-place Mooney design (that eventually became the Mooney Mark 20), but designer Al Mooney refused to sell.
After considering other designs available at the time, Piper decided to design its own modern airplane. In 1953, aeronautical engineer Fred Weick (NACA cowling, Ercoupe) did a cost study for Piper to find if building an all-aluminum airplane was economically feasible. Weick determined that Piper was spending 8% more to produce the Tri Pacer than Cessna was spending to produce the 170.
Weick had developed a friendship with Pug Piper, son of company president William Piper. Together, in 1956 and early 1957, Weick and Pug Piper established the overall design of a next-generation Piper airplane. It was to be a low-wing all-metal design, with tricycle landing gear, 150-hp Lycoming engine, and a cabin width of 42 inches, roomier than the Tri Pacer, but not as wide as the more-expensive PA-24 Comanche that was just entering production.
In early 1957, Piper contracted with airplane designer John Thorp (T-18, Sky Scooter) to do a preliminary design study of the PA-28. By April, Weick had joined Piper as the director and chief engineer of the Piper development center and had hired aeronautical engineer Karl Bergey to be the chief developer of the PA-28. Bergey, with input from Weick and Pug Piper, began the final design of the PA-28 starting from Thorp’s preliminary design.
The final result was dubbed the “Cherokee,” an airplane that was simple to build, simple to maintain, and simple to fly.
Many thoughtful and innovative features were incorporated into the design:
- Low wing, giving the airplane an overall low center of gravity, so that the airplane will handle well in strong winds, including crosswinds.
- Cabin width of 42 inches ~ greater than the Tri-Pacer (which the Cherokee replaced) by 7 inches for more comfort. Weick actually wanted to make the cabin 44 inches wide, but Piper chose 42 inches so as not to compete with the higher-cost Comanche, which had a cabin width of 44 inches.
- Single cockpit entry door on the right side, similar to the contemporary Beechcraft Bonanza.
- Extremely simple construction, with very few complex curves in any aluminum panels. The Cherokee has less than half the number of parts as the contemporary Comanche. The Cherokee also has less than half the number of rivets as the Comanche: 1,785 compared to 3,714.
- All-Flying stabilator (which John Thorp held a patent on) similar to many other Thorp designs, saves weight and reduced wetted area of the tail. The tail that Thorp designed was simplified by Bergey for use on the Cherokee.
- Beaded skins on the tail and control surfaces with no internal ribs or stiffeners, which provide stiffness without increasing the parts count. The ailerons, for example, have 10 parts, compared to 36 parts in the Comanche aileron.
- Simple manually-operated flaps save weight and give the pilot direct control of the movement of the flaps.
- Fuel tanks of similar design to the Ercoupe (designed by Fred Weick), which form the leading edge airfoil and structure of the wing, saving weight, reducing parts count, and simplifying fuel tank maintenance.
- Fiberglass used for non-structural complex shapes such places as cowlings, wingtips, and stabilizer tips for ease of manufacture, lightness, and durability.
- Tricycle landing gear with 10-foot tread for ease of handling, with simple oleo-strut landing gear. The main gears are attached directly to the wing spar, and the nose gear is the same as was used in the PA-22 Tri Pacer.
- 6.00 x 6 tires on all three landing gears, including the nose, for good soft-field operations. Having a nose wheel the same size as the main wheels came from research done by Weick on the Ercoupe, which shows that under some conditions, such as takeoff power, the nose wheel is the highest-loaded wheel. Therefore, on soft fields, a wheel that is at least the same size as the mains is needed.
- NACA 65-415 airfoil for the wing, with the maximum thickness near the mid-chord, allowing a deep and strong single wing spar. By having the spar located near the mid-chord (further aft than other airfoil sections would permit), it was possible to locate the rear seat over the spar, making for a clear and open cabin floor. This airfoil is also a laminar-flow section, improving performance of the airplane.
- Wing spars that are spliced at the sides of the fuselage (rather than in the middle, as on the Comanche), which simplified assembly and also made it easier to ship the airplane using a shorter crate when the wings are removed. he spar carry-through is a box-beam, while the spars outboard of the splices are I-beams. The I-beams are slipped inside the box beam and bolted in place at the sides of the fuselage. The splices were tested for static strength and fatigue durability. In all, some 480,000 fatigue test cycles were applied with no degradation of the joints.
- External stiffeners under the cabin floor (which is also the outside skin of the airplane) save weight and simplify construction compared to contemporary internal-structure designs from Cessna and Beechcraft. By installing the stiffeners externally, there is more headroom in the cabin without having to make the cabin section of the airplane taller.
An experimental prototype was completed and made its first flight on Jan. 10, 1960, with Piper’s chief test pilot, Thomas Heffner, at the controls. After an accelerated flight testing program, a type certificate was issued Oct. 31, 1960. The airplane was a sales hit from the very beginning, selling 286 in the first year, and ramping up and spawning several variants.
A variety of powerplants were eventually approved for the basic airframe, from a 140-hp Lycoming O-320 to a 235-hp Lycoming O-540. The model numbers denote the engine horsepower. For example, the PA-28-140 has the 140-hp engine, the PA-28-180 has the 180-hp engine, and so on. Cherokee’s direct lineage included various models of the Warrior, Archer, Arrow, Dakota, Pathfinder, and Cadet. The PA-28-181 Warrior III and PA-28R-200 Arrow are still available from Piper Aircraft.
After the introduction of the original Cherokee, the next big advance came in the form of Cherokee Six, which began production in 1965.
The concept for this airplane actually started out as a six-place trimotor airplane, with three 115-hp Lycoming O-235 engines and fixed-pitch propellers. An experimental prototype was built by modifying a PA-28-235 with the following changes:
- The cabin area of the fuselage was literally cut longitudinally along the centerline and a 7-inch plug installed between the two halves, making the cabin 7 inches wider than the basic PA-28. The prototype did not feature a rear door, as later installed on the PA-32 and PA-34 models.
- A 30-inch plug was installed at the aft end of the cabin area, creating room enough for two additional seats, for a total of six.
- The tail cone from the aft end of the cabin aft, was split down the middle, and a triangular section added so that at the front of the tailcone the width matched the new cabin dimensions, and at the rear it was the same as the original Cherokee.
- To maintain balance, an additional plug was added between the front of the cabin and the front (center) engine. This area was used as a baggage compartment.
- The original PA-28-235 wings were used, with tip tanks already installed, with some additional strengthening where needed. For the experimental trimotor airplane, an engine was added to leading edge of each of the wings.
- The PA-28-235 tail was also retained.
After testing the concept, the trimotor did not work out, but Weick recognized the potential of an airplane with the larger cabin, so the wing engines were removed and a single 260-hp Lycoming O-540 installed in the nose.
The new single-engine airplane became the PA-32 Cherokee Six, one of Piper’s best load-hauling airplanes. When equipped with a large rear door on the left side of the aft cabin, the Cherokee Six competed with Cessna’s model 206. In the 1970s, the type was given retractable gear similar to the Arrow and dubbed the PA-32R Saratoga. The type also served as the basis for the twin-engine PA-34 Seneca series airplanes, with the single engine removed and an engine mounted in each of the wings.
After the fixed-gear Cherokees were well-established in the marketplace, development of the retractable-gear PA-28R Arrow began. Production of the Arrow began in 1967. The airplane was nearly identical to the fixed gear PA-28-180 Cherokee 180, with the following changes:
- Obviously, retractable gear, with structural changes to the wings and engine mount to accommodate the gear.
- In order to make room in the engine cowling for the nose gear, the carbureted O-380 engine was replaced with a fuel-injected IO-360 engine.
- Even with the new engine, the nose tire diameter had to be reduced to fit in the cowling, and a 5.00 x 5 tire was used. This does limit the soft-field capability of the airplane somewhat, but is the same as the nosewheel of the contemporary Beechcraft Bonanza.
- The change of engine necessitated changes to the fuel system to accommodate the fuel injection.
- A constant-speed propeller was fitted as standard equipment.
- The Arrow featured an automatic gear extension system that, when it sensed a low airspeed (as used for landing) would automatically lower the gear, even if the pilot forgot.
In 1969, Piper investigated improving the climb capability of the Cherokee by increasing the wingspan. However, increasing the wingspan would impose higher bending loads in the inner portions of the wings, which they did not want to re-design. The solution was to use a tapered wing section outboard of the wing flaps, which increased the wingspan from 30 feet to 35 feet, but reduced the load at the tip. The new semi-tapered wing did not require substantial strengthening or re-design of the inner wing sections. The new wing design was incorporated on the PA-28-150 in 1973, making it the new PA-28-151 Warrior. The new wing gave the airplane better climb and flatter glide. By 1978, all of the Cherokee models still in production were fitted with the new semi-tapered wing.
The most-produced version of the Cherokee through the years has been the PA-28-180/-181 series. Well over 10,000 have been built. The carbureted 180-hp Lycoming O-360 engines installed on these airplanes has proven to be a combination of reliability, economy, and power that attract owners.
For more information: Piper.com