Page 22 - Volume 15 Number 4

ASK THE EXPERT
Reversing Propellers ... and When
They Won’t
by Tom Clements
Reversing propellers made their appearance on the King Air A90 that ushered in the 1966 model year. The Straight 90 model of 1964 and 1965 utilized non-reversing propellers similar to those that were installed on the Lycoming-powered Queen Airs being concurrently produced. As one would expect, reversing propellers were a big hit and although they were an optional piece of equipment I don’t think there was ever an A90 that was not built with this option. It has continued as standard equipment on all models that came after it, right up to and including the 260 and 360 models of today.
the competent King Air pilot must have understanding.
To begin, we must understand what makes a “Constant Speed Propeller.” Two independent variables determine the speed at which a particular propeller will rotate. The variables are (1) the factors that make the propeller want to rotate; and (2) how much the propeller resists that rotation.
Power and airspeed are the factors causing rotation. From our very first flying lesson, it became immediately obvious that pushing the throttle forward – increasing engine power – made the engine/ propeller combination increase its rotational speed. This lesson was almost always conducted in a simple, single-engine airplane with a fixed-pitch propeller. In this simple
All pilots who have undergone initial King Air training have been taught about the propeller system in detail. It is one of the more difficult systems to learn and to understand in-depth. The intent of this article is to discuss the method that allows the propeller to reverse but to
explain it in a very nonscientific, nonmechanical, non-engineering manner. Other important pro- peller-related systems – e.g., the Overspeed and Fuel Topping Governors – will not be reviewed in any depth, although they, too, are important systems for which
20 • KING AIR MAGAZINE
APRIL 2021