Definition
A turboprop engine design in which the gas generator turbine, the reduction gearbox, and the propeller are all mechanically connected on a single common shaft, so the engine's internal turbines and the propeller always rotate together. Engine RPM is held constant in flight by a governor that adjusts propeller blade angle, and power output is controlled by varying fuel flow rather than by changing RPM.
Plain English
A turboprop layout where the propeller is bolted, through gears, to the same shaft that drives the engine's turbines. Once running, the whole assembly spins at a fixed speed, and the pilot changes power by adding or reducing fuel, not by speeding the engine up or slowing it down.
Context Anchor
Seen in turboprop engine discussions when comparing fixed-shaft engines with free-turbine engines and when learning how turboprop power and propeller rpm are controlled.
Derivation
"Fixed-shaft" means the shaft connection is permanent and direct -- the propeller and turbines cannot turn independently. "Constant-speed" comes from propeller terminology: the propeller governor varies blade pitch to keep RPM steady regardless of power or airspeed. Together, the phrase describes an engine that is mechanically locked together and held at one operating speed.
Why Pilots Care
Pilots must understand how power changes affect propeller operation and aircraft handling in this common turboprop arrangement.
Grounding Statement
When the pilot adds power, propeller rpm may stay nearly steady while the blade angle changes to produce more thrust.
Intuition Check
“Fixed-shaft” does not mean the propeller blades are fixed in one position. “Constant-speed” does not mean the airplane flies at a constant speed; it means the propeller rpm is held nearly constant.
Example Sentence 1
In the fixed-shaft constant-speed type, the pilot advances the power lever to add fuel, and the propeller governor changes blade angle to hold RPM steady.
Example Sentence 2
During the descent the student reduced torque on the fixed-shaft constant-speed type engine and watched the governor coarsen blade pitch to hold the chosen RPM.