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Jeff, Wish I knew something about props, but it seems more
black art than cooling ducts {:>). Having 4 blades with a 74" dia and
spinning 6100 rpm even with 58" pitch would appear to me to indicate a strong
engine. But, you are right, its really hard to compare apples and
oranges.
We clearly saw a significant difference in performance
between Sam's prop and mine - on his engine. Sam was clearly delighted to
be producing over 6000 - it would be nice to have a "Community Prop" that could
be used as a relative calibration point. I know if this prop swap had
happened 3 months earlier, Sam would have been even happier {:>)
One thing that can give you a reality check is your fuel
flow rate at 6100 rpm - to be producing 196 HP, your fuel flow rate should be
around 19-20 GPH. So unless your fuel flow rate is in that vicinity, its
unlikely you are producing 196 HP - although, I would hazard a SWAG that that
you may be close to 180 HP.
A fuel burn rate for the rotary (rule of thumb) is that it
take around 10 GPH flow rate to produce 100 HP. So if your flow rate is
say 15-16 GPH you are probably in the vicinity of 150-160 HP. However, the
rotary has shown the ability to flow more fuel than it can use to produce
useful power. So a higher flow rate does not necessarily all translate
into power, but lacking a portable dyno it’s a place to start.
Ed
Sent: Friday, October 08, 2010 8:41 PM
Subject: [FlyRotary] Another prop performance
calculator
Ed, with my prop
numbers (74"x 58", 4 blades, 59F, 6100 engine rpm or 2140 prop rpm) entered into
this calculator it says I'm making 196 hp static ... seems hard to
believe.
I've always wondered what the difference
is between 4 blades Vs 2 ... the same numbers with 2 blades gives 117
hp..
Also, my prop is a Warp Drive and the
pitch is measured at the tip ... don't most prop manufacturers specify pitch at
75-80% of diameter?
Wish I had been in Paducah to bolt your
prop on and see what happened ...
Jeff
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Here is a link to a STATIC performance calculator
that seems to at least give reasonable results
I could turn 5800 rpm static when my prop was 76x88
which this calculator indicates the engine was producing 168.1 HP to turn
the prop 2035 rpm
When I trimmed the prop back to 74x88 I picked up
200 static engine rpm which this calculator then indicated the
engine was producing167.2 HP to turn the prop 2105 rpm
So between 165 and 170 HP seems
reasonable.
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