28R 180 — —
Diagram: This cutaway of the original PA- 28 shows its imple structure. The Cherokee used just 1,200 parts, compared to 1,600 for the Tri-Pacer it was intended to replace.
Inset below: Cherokee design engineer Karl Bergey
made extensive use of beading to add stiffness to
many of the skin surfaces.
THE INITIAL SPECIFICATIONS FOR the Cherokee were developed
during the winter of 1956-1957 by Fred Weick, famed designer
of the ERCO Ercoupe who had recently been hired by Piper, and
Howard “Pug” Piper, the youngest of founder Bill Piper’s three
sons. They had a simple goal: build an uncomplicated, low-cost,
four-seat metal airplane that could compete with the Cessna 172.
The idea of a metal aircraft was a radical departure from
Piper’s historic sport-trainer designs, but the Cessna 172 had
become such a sales sensation since its introduction in late
1955 that it couldn’t be ignored. The closest thing offered by
Piper did not compare well in the marketplace—the awkward
tube-and-fabric Tri-Pacer, dubbed “the milk stool” for its distinctive tricycle gear.
The initial specs called for the PA- 28 to be powered by a
150-hp Lycoming O-320-E2A with a fixed-pitch propeller. A tricycle gear with a steerable nose wheel and long wheelbase was
chosen for good ground handling. The wide-spread gear, low
wing, and resulting low center of gravity would also make the
aircraft easy to land, particularly in strong crosswinds.
With Weick still in the process of relocating his family to
Vero Beach in early 1957, the famously impatient Pug Piper
tasked John Thorp of California to do a preliminary design
study based on these specifications. Thorp’s finished report was
delivered in the spring of 1957 and consisted of a three-view
drawing and a weight-and-balance tabulation; no structural
details or analysis was included.
version was significantly different from John Thorp’s original design, from its overall
configuration to such details as wing area and airfoil and flap selection.”
In all his design work, Bergey sought simplicity: “My guidance has always been Antoine
de Saint Exupéry’s ‘Perfection is achieved not when there is nothing more to add, but when
there is nothing left to take away.’ [Wind, Sand and Stars, 1939]”
KARL H. BERGEY
TOTALLY ABSORBED WITH THE development of the PA- 25
Pawnee, Weick allowed Thorp’s report to lay dormant for several months. The Cherokee project finally kicked into high
gear when Karl H. Bergey was hired as Weick’s assistant in
September 1957 and immediately put to work on the PA- 28.
He was an expert in aerodynamics and structures who had performed research at the Massachusetts Institute of Technology
under Professor Otto Koppen, designer of the Helio line of
short takeoff and landing (STOL) aircraft.
Bergey described the intense initial phase in the Cherokee’s
development thus: “Over the next five months, I worked exclusively—and alone—on the PA- 28 design, including the final
configuration, the aerodynamic loads, the structural load paths,
and the basic performance and structural analysis. The final
KEY DESIGN ELEMENTS
ALL THE EARLY CHEROKEES featured a “Hershey bar” wing, the name given for its rectangular planform. It used the same airfoil from the root to the tip, meaning all of its
hydro-formed aluminum ribs could be identical. To further reduce production costs, the
design allowed for wing surfaces to be single sheets of aluminum wrapped around the leading edge and riveted at the trailing edge.
A natural tendency to stall at the root imbued the wing with good low-speed behavior
and resistance to spinning. Despite Piper’s switch to a semi-tapered wing with the PA-28-
151 Warrior in 1974, the rectangular wing remains, a very efficient design; thousands of
RVs and Sonexes and countless other aircraft with Hershey bar wings are proof of this.
The NACA 652-415 airfoil chosen for the Cherokee had efficient aerodynamic char-
acteristics, but its chief attribute was allowing the use of a single main spar, an extrusion
provided by Alcoa, to create a stron-
ger, lighter wing. Bergey devised a
strong box structure “carry-through”
that passed under the rear seat and
thus kept the entire cabin floor clear
of obstructions. His design also
had an eye toward the future, leav-
ing enough room for a wheel to
be retracted. Onto the spars were
attached the two main landing gears
as well as twin 25-gallon fuel tanks
that formed an integral part of the