|The Boeing Stearman best known bi-plane
in aviation history. Commonly referred to as the Stearman
PT-17, it was manufactured by the Stearman
Aircraft Company in Wichita, Kansas from 1934 through 1945. Boeing publicity
claims a total of 10,346 Stearman “Kaydet” trainers
built, but this figure includes equivalent spare parts.
The actual total of Model 75’s that were completed
from the prototype X-75 to the final E75 built in 1945
In 1938 the Stearman Aircraft Company became the Stearman
Aircraft Division of the Boeing Aircraft Company so in
actuality, the majority of the airplanes manufactured
were designated as Boeings. However, they are still almost
universally known as Stearmans.
Original engines installed on the Stearman airframes
included the Lycoming
R-680 (225 hp); Continental
R-670 (220 hp) and the Jacobs R-755 (225 hp). Post-war modifications
include the Lycoming
R-680 (300 hp); Pratt & Whitney
R-985 (450 hp) and the Jacobs
R-775 (275 hp). The propellers
generally in use on Stearmans were the Sensenich fixed
pitch wooden prop, the ground adjustable McCauley
steel blade prop and the ground adjustable Hamilton Standard
and 2B20 counter weight Hamilton Standard propellers.
Also a rare exception of the ERCO COMPREG blade, installed
in a constant speed counter weight Hamilton
Standard 2B20 hub.
The Lycoming Controllable Propeller while in rotation
enabled the pilot to select the most advantageous blade
angle for maximum airplane performance under all flight
The primary purpose of the Lycoming Controllable
Propeller in all flight conditions; namely, take-off, climb,
and high speed, was to permit the engine to develop full
rated power. Second, the propeller permitted the blades
to operate at the most advantageous blade angle from
the standpoint of aerodynamics, thereby providing greater
thrust than could be obtained with adjustable pitch propellers.
Third, the propeller permitted a readjustment of the
blade angle to the particular power settings and atmospheric
conditions existing at any altitude.
This latter advantage
was particularly important with engines incapable of
operating at full throttle at sea
level and whose rated power was delivered only at high
The Lycoming controllable propeller also played
an important role as a safety factor in aircraft operation.
in aircraft design toward higher speed ranges, heavier
wing loadings and geared engines required large propeller
diameters to absorb high engine power at altitudes and
large blade angles to permit high airplane speed with
low propeller rotational speeds. The result was an airplane
with very poor take-off characteristics. The Lycoming
controllable propeller remedied this condition by affording
a complete range of blade angles for take-off, climb,
cruising and for high-speed airplane performance.
The Aeroproduct propellers were hydraulically
operated, constant-speed propellers. A separate pitch-changing
mechanism was contained in each blade socket. This type
of construction left an unrestricted opening through
the center of the propeller hub, permitting the installation
of an aircraft cannon.
The blades were of hollow steel
construction and had
a longitudinal rib running throughout the length of the
blade, from the blade tip to the shank. The blade was
constructed of two members, which were copper-brazed