PA28: Difference in constant speed prop vs fixed pitch

Nathan Young wrote:

Can you better explain this? My understanding is that a fixed pitch
prop is typically a compromise in both takeoff pitch, and cruise
pitch. Using the typical car driving analogy - a prop that is stuck
in 3rd or 4th gear in a 5 speed transmission. So I would think a CS
prop would net gains at both cruise and takeoff/climb.

They usually do, for the reasons you stated. If you adjust the controls such that the
engine is producing 75% power in level flight and the CS prop settles into a coarser
pitch than the fixed pitch prop had, you'll see a faster cruise speed. If the fixed
pitch prop was pitched to produce the best cruise speed, the CS prop won't do any
better there, but will improve your ROC.

George Patterson
If a man gets into a fight 3,000 miles away from home, he *had* to have
been looking for it.

G.R. Patterson III wrote:

Nathan Young wrote:

Can you better explain this? My understanding is that a fixed pitch
prop is typically a compromise in both takeoff pitch, and cruise
pitch. Using the typical car driving analogy - a prop that is stuck
in 3rd or 4th gear in a 5 speed transmission. So I would think a CS
prop would net gains at both cruise and takeoff/climb.


They usually do, for the reasons you stated. If you adjust the controls such that the
engine is producing 75% power in level flight and the CS prop settles into a coarser
pitch than the fixed pitch prop had, you'll see a faster cruise speed. If the fixed
pitch prop was pitched to produce the best cruise speed, the CS prop won't do any
better there, but will improve your ROC.

In the performance charts for my 182 a given percent power always
produces the same speed at a given altitude.

Newps wrote:

G.R. Patterson III wrote:

Nathan Young wrote:

Can you better explain this? My understanding is that a fixed pitch
prop is typically a compromise in both takeoff pitch, and cruise
pitch. Using the typical car driving analogy - a prop that is stuck
in 3rd or 4th gear in a 5 speed transmission. So I would think a CS
prop would net gains at both cruise and takeoff/climb.


They usually do, for the reasons you stated. If you adjust the controls such that the
engine is producing 75% power in level flight and the CS prop settles into a coarser
pitch than the fixed pitch prop had, you'll see a faster cruise speed. If the fixed
pitch prop was pitched to produce the best cruise speed, the CS prop won't do any
better there, but will improve your ROC.

In the performance charts for my 182 a given percent power always
produces the same speed at a given altitude.

I'm sure it does, but you would not see that speed if you replaced your CS prop with
a fixed pitch prop that has the compromise pitch that is commonly used on aircraft
with fixed pitch props. Most aircraft with fixed pitch props have a prop that has too
fine a pitch to get the best cruise speed at 75% power. Replacing that prop with a CS
prop will result in higher cruise speeds.

George Patterson
If a man gets into a fight 3,000 miles away from home, he *had* to have
been looking for it.