I have a 1973 8KCAB. The aircraft some time in it's life was converted from the CS prop to a fixed pitch. The engine is the 150 HP and the aircraft admittedly is a bit of a dog, well at least compared to the maule I last flew. I am happy with the performance in cool weather and one person operation. It is great for the type of acro I am interested in doing and I like simplicity. Still, I wonder if converting it back to the CS prop would be a good move. Has anyone flown both the 150 fixed and 150 CS decathalon? If so, can you tell me your impression regarding any differerence in climb and cruise performance. The present prop is a 74DM6S8-0-52. I do not know if it is a cruise, climb, or standard. My guess is is a standard. Assuming gages are correct, I can cruise in the present cool weather of New England at 120 MPH with 2500 RPM's. Any comments would be appreciated.
Prop choice, fixed or CS : yes or no
- Thread starter kpin
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djpacro
Member
I have a 150 hp FP Decathlon and have flown one with a CS prop.
My prop is supposedly 58" pitch, same prop as yours but coarser - the 1978/79 POH indicates pitch ranging from a climb prop of 56" to a cruise prop of 60". The POH only gives climb performance for a climb prop and cruise performance for a cruise prop! Making some allowance for the pitch difference I don't have much argument with climb and cruise performance in the POH.
So, straight from the POH at SL standard day:
CLIMB
56" fixed pitch prop is 1000 fpm vs CS prop of 880 fpm.
CRUISE at 75% power
60" fixed pitch prop is 134 mph vs CS prop of 134 mph.
But you can't get both good climb and good cruise with a FP prop. My friend's CS aeroplane was about 10 kts faster cruise and both seemed to climb at about the same rate. Another friend with a FP prop but coarser than mine is also about 10 kts faster in cruise but doesn't climb anywhere near as well.
My prop is supposedly 58" pitch, same prop as yours but coarser - the 1978/79 POH indicates pitch ranging from a climb prop of 56" to a cruise prop of 60". The POH only gives climb performance for a climb prop and cruise performance for a cruise prop! Making some allowance for the pitch difference I don't have much argument with climb and cruise performance in the POH.
So, straight from the POH at SL standard day:
CLIMB
56" fixed pitch prop is 1000 fpm vs CS prop of 880 fpm.
CRUISE at 75% power
60" fixed pitch prop is 134 mph vs CS prop of 134 mph.
But you can't get both good climb and good cruise with a FP prop. My friend's CS aeroplane was about 10 kts faster cruise and both seemed to climb at about the same rate. Another friend with a FP prop but coarser than mine is also about 10 kts faster in cruise but doesn't climb anywhere near as well.