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Hydromatic Propeller Systems . By Doug Rozendaal. The Plan. •Some History Nomenclature How it Works The Parts The Sparks How it Breaks What you can do about it. Normal Operations The AD… . Hydromatic Propeller History. 1937 First in flight Feathering Propellor
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Hydromatic Propeller Systems By Doug Rozendaal
The Plan • •Some History • Nomenclature • How it Works • The Parts • The Sparks • How it Breaks • What you can do about it. • Normal Operations • The AD…
Hydromatic Propeller History 1937 First in flight Feathering Propellor Developed from the Counterwieghted props Quick Feathering Oil on both sides of the piston Made Reverse Possible 1990 ASME Historic Landmark established
Nomenclature Hub 23E-50 2 = Major Modification (Hydromatic) 3 = # of Blades E = Blade Shank Size 50 = SAE Spline Size Blade x-6547-yT x = Letter designation of shank fairing 6547 = Blade design y = Number of inches diameter reduction T = Telescoping diameter, S = Square
Four Forces Decreases Pitch Increases Pitch Centrifugal Force Aerodynamic Force Engine Oil Pressure Governor Oil Pressure
On Speed Governor • Pilot Valve and flyweights • Pump and Pressure relief • Speeder Spring • Transfer valve
Unfeathering Unfeathering Schematic
Distributor Valve Positions Feathering. Valve does not move till pressure exceeds 400 psi When pressure here exceeds 400 psi valve begins to shift As pressure reaches 600 psi, valve has shifted far enough to reverse direction of oil flow to outside of piston. As pressure reaches 600 psi, valve has shifted far enough to reverse direction of oil flow to outside of piston.
Distributor Valve • Only used in the Unfeathering operation • Begins shift at 400 psi • Starts Unfeather operation at 500 psi • Fully open at 600 psi
Dome Relief Valve • Opens at 300 psi differential between inboard and outboard cylinder ends • Protects Dome from excess pressure when prop reaches low pitch stops during unfeather
Feathering Schematic – Feathering components • Buttons and hold down relays / CB’s • cutout switch • feathering pump solenoid switch Start Schematic review
Feathering Button Pushed Pilot Pushes in button completing circuit to holding coil.
Holding Circuit Takes Over Feathering Solenoid is Energized What happens if CB popped / inop or pressure switch not making contact?
Feathering Motor Starts Current is now supplied to the feathering pump motor What happens if Solenoid Switch contacts are bad / or motor has failed?
Oil Pressure Feathers Prop • Oil Pressure opens the transfer valve in the Governor, bypassing the pilot valve.
Pressure Buildup Opens Cutout When the piston can no longer move forward, the pressure behind it rapidly builds. The cutout switch opens at 400 psi., before the distributor valve shifts. What happens if the cutout switch does not open?
Feathering Solenoid Released With the ground for the feathering button’s hold down coil now open, the button pops out, removing power from and releasing the feathering solenoid. What happens if the solenoid contacts have “welded” together?
Feathering Pump Stops With power removed, the pump stops.
Prop Remains Feathered The propeller remains feathered because the blades are at the High Pitch stop of 88 degrees
Unfeathering Schematic • Feather Button hold down circuit will momentarily work till pressure builds past 400 psi • Pressure is now routed to the inside of the piston, moving the piston forward and turning the prop to the feathered position.
Prop Unfeathers • Pressure builds up past 600 psi, shifting the distributor valve, forcing piston aft, turning blades towards flat pitch. • Prop starts to turn
Prop Unfeathers • Button must be held in to keep pump running while cutout switch is open • Release button passing 800 rpm. • Transfer valve closes • Prop Governor takes over control of rpm.
What can happen when Feather Button is Pushed • Normal Operation • Feather Button Fails to stay in • Feather Button Fails to pop out • Solenoid Contacts weld • Prop Fails to stay feathered
Propeller Malfunctions • Full Low Pitch, Over Speed/Runaway – Possible stuck Pilot Valve – Control with Feather Button • Control cable breakage – Balance spring sets 2200 RPM (?) • Speeder Spring breakage – Senses as Over Speed, Full High Pitch (~57) – Prop Feathers itself due failure of pressure regulator in governor pump
Runaways • •Cycle Prop control may pass an airlock in Governor. • Props windmill as a function of TAS not IAS. • Feathering pump can be used as a Governor video
Typical Runup • Done from memory and checked subsequently to save time, heating, rock & sand wear. • Wind ahead of Prop arc. • Throttles to 1700 rpms, 2-3 reductions, 1 full back to 1200 +/- 50 typical. Checks low pitch governing. • Feather check. PF button down, PNF “Load”, PF “Drop” Button up, PNF “Unload” • Cycle Prop to confirm transfer valve has reset • Throttles to Barometric, 2200+/- 50 typical
Field Barometric Check • •With the airplane facing into the wind, and the propeller on the low pitch stops, Field Baro will yield a consistent Static RPM except for the effect of the winds. • 100 rpm below normal is typically 1 dead cylinder in a two row engine. • The reduction air density reduces the propeller drag yielding a consistent number.
Feather Testing • •Regular (1st flight of the day) testing prevents sludge in the bottom of the oil hopper. • Prop domes are centrifugal oil filters and can become sludged up preventing feathering. • Inflight feathering will confirm blade alignment, and it a great training tool…
AD 83-13-06 • •18 month blade shank corrosion inspection. • If 18 month inspection is clean interval extends to 36 months. • If 36 month inspection is clean interval extends to 60 months. • Outside storage + no flying = trouble.
