TO: FAA APPROVED PROPELLER REPAIR STATIONS

SUBJECT: IMPROVED PROPELLER BLADE-ANGLE DISTRIBUTION

PROPELLER MODEL AFFECTED: 69CK SERIES

AIRCRAFT MODEL AFFECTED: CESSNA 150 SERIES with SENSENICH PROPELLER

An improved blade-angle distribution. for SENSENICH 69CK series propellers installed on CESSNA 150 serIes aircraft, has been developed. It has been found that incorporating the revised angle distribution makes possible a reduction of 2 inches in propeller pitch, improving takeoff and climb without experiencing a reduction of cruise performance. Test data shows that, with a "50" pitch (52 pitch is standard on CESSNA 150 airplanes) and the revised blade-angle distribution, time to lift-off may be reduced by about 15%; rate-of-climb may be increased by a factor of about 9%; and the airplane upon which the prototype propeller was tested showed an 85 knot cruise at 10 rpm less than was required with the standard propeller. (For those interested in "why" a revised blade-angle distribution and a decrease in the pitch of a propeller at the 3/4 radius blade station could improve takeoff and climb and not affect cruise, more accurate knowledge of the natural flow in front of the aircraft cowling makes it possible to design a propeller to waste less energy)

This revision in blade-angles may be incorporated by FAA approved propeller repair stations when any propeller of the 69CK series is reconditioned (overhauled). Incorporation of the blade-angle distribution (shown on page 13 of SENENICH repair manual SPRM 590), dated 1 August 1988, shall be indicated by addition of a suffix "L" after the propeller pitch identification on the hub face (with steel stamp) and on the identification decal (with ink pen). All new and reconditioned propellers obtained from the SENSENICH facility will incorporate the revised blade-angle distribution and have an "L" suffix included after the pitch identification. An example of the model designation of a propeller which incorporates the revised blade-angle distribution is "69CK-0-50L". This propeller is 69 inches diameter and 50 inches pitch, incorporating the "L" revision to the blade-angle distribution.

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