MT-Propeller hydraulic constant speed propellers

Presently most of our blades are built in natural composite design, by using high compressed thin layered laminated beech wood, which has a similar tensile strength as steel, in the root section and selected lightweight laminated spruce wood in the remaining part of the blade.
The wooden core is reinforced by layers of epoxy fiberglass, Kevlar® or carbon fiber and sealed by several coatings of acrylic-polyurethane paint. An aluminum blade ferrule is attached to the blade root by using special design patented lag screws.
The critical section of the blade's leading edge is protected by a bonded on stainless steel erosion sheath. The inboard section of the leading edge is protected by a self-adhesive PU-strip. All of the above makes the blade all weather operable.

Propellers for aerobatic aircrafts or propellers built with feathering capability are equipped with counterweights, that are installed on the blade ferrule. The pitch change pin is in a different position and the blades are identified by a "C" in front of the numbers, i.e. C200-15. Blades for feathering propellers are identified by a "CF".

The spinner dome is a single piece part made from fiber reinforced composite (Kevlar®), which replaces the spinformed aluminum alloy used in the earlier days and is extremely crack resistant as well as very light.
The bulkheads are made from spinformed or die forged aluminum alloy. The front bulkhead is seen as a part of the hub assembly and also used as attachment point for static balancing weights. Filler plates increase the stiffness of the dome around the cutouts for the blades. The dome is attached to the bulkhead with stainless steel spinner screws.

The servo pressure necessary for changing pitch is generated by a gear pump located inside the propeller governor, which increases the oil pressure supplied by the engine by factor 6 or higher. Flyweights and a speeder spring move a pilot valve, allowing servo oil flow to and from the piston in the propeller. In an on speed condition there is no oil flow. A speed (RPM) adjusting lever actuated from the cockpit changes the preload of the speeder spring. This results in an engine RPM change by changing propeller pitch. The propeller system is single acting and without oil pressure the natural twisting moment of the blades will always turn them into low pitch position (non-counterweighted propellers). The governor produces usually oil pressure to increase pitch. However, blades having counterweights installed i.e. for aerobatic aircraft or twin engine aircraft always turn into high pitch position without oil pressure and therefore use oil pressure to decrease pitch. The relief valve pressure should be set somewhere between 270 and 340 psi.

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