Propeller Owner’s Manual
175
INTRODUCTION
61-00-75
Page 1-4
Rev. 1 Jun/11
3.
Airframe or Engine Modifications
A. Propellers are approved vibrationwise on airframe and
engine combinations based on tests or analysis of similar
installations. This data has demonstrated that propeller
stress levels are affected by airframe configuration, airspeed,
weight, power, engine configuration and flight maneuvers.
Aircraft modifications, which can effect propeller stress
include, but are not limited to: aerodynamic changes ahead
of or behind the propeller, realignment of the thrust axis,
increasing or decreasing airspeed limits, increasing or
decreasing weight limits (less significant on piston engines),
and the addition of approved flight maneuvers (utility and
aerobatic).
B. Engine modifications can also affect the propeller. The two
primary categories of engine modifications are those
that
affect structure and those
that
affect power. An example
of a structural engine modification is the alteration of the
crankshaft or damper of a piston engine. Any change
to the weight, stiffness or tuning of rotating components
could result in a potentially dangerous resonant condition
that
is not detectable by the pilot. Most common engine
modifications affect the power during some phase of
operation. Some increase the maximum power output, while
others improve the power available during hot and high
operation (flat rating) or at off-peak conditions. Examples
of such engine modifications include, but are not limited to:
changes to the compressor, power turbine or hot section of
a turboprop engine; and on piston engines, the addition or
alteration of a turbocharger or turbonormalizer, increased
compression ratio, increased RPM, altered ignition timing,
electronic ignition, full authority digital electronic controls
(FADEC), or tuned induction or exhaust.
C. All such modifications must be reviewed and approved by
the propeller manufacturer before obtaining approval on the
aircraft.
OBSOLETE PROPELLER MODELS. SEE COVER PAGE
WARNINGS AND SERVICE BULLETIN HC-SB-61-331
