Vance Jaqua wrote:
OK you have my program so adjust the rates of change
of HP with
RPM and prop efficiency with aircraft speed to
reflect what
you feel are the real world results.
For example what kind of efficiency can we expect at
10 MPH
with a constant speed prop?
I will adjust the efficiency from 10 to 50 MPH in a
linear
or other math function and do a separate chart for
the constant
speed prop.
So the engine would only bog to 2100 RPM rather than
1986 RPM
What HP do you guess a 100 HP engine would be
generating
at 2100 RPM. I can fix that.
Paul Lamar
Paul - using several pages of print outs from PRPLRIT'
and other sources this is the table I came up with for
a 160 hp engine (like 320 Lyc) with a prop sizeds for
about 190 mph for a clean RV6 or KIS two place class
of airplane.
fixed pitch 70X78 const spd var gear
mph rpm bhp f lbs eff f lbs eff f lbs eff
0 1940 108 407 0 603 0 525 0
30 1950 109 393 28 530 26 505 25
60 1960 110 353 51 480 50 460 47
90 2080 118 327 66 425 63 420 62
120 2400 130 307 76 366 73 365 73
160 2500 149 283 81 299 80 299 80
190 2720 160 268 83 268 83 268 83
The attached set of curves shows the relationship in
perspective the top curve is 100 percent propulsion
eff the same as if you had a sky hook and a wtless
frictionless infinite transmission, The next one down
represents 160 horsepower delivered without loss into
the air stream of prop dia - perfect 70 in prop,The
next down is a constant speed prop operated at full
160 hp rated rpm max man pressure - best pitch, next
is a variable transmission turning the 70X78 prop at
the right speed to absorb the 160 bhp, and the lower
one is of course the fixed pitch prop with the engine
turning the rpm that it can - direct drive - usual
airplane configuration. Both of the curves spinning
the fixed pitch prop show the result of poor l/d ratio
of the high pitch at low forward speed. Tho I would
not warrant the data to 3 decimal places, I am
cnvinced it is a good representation of real world
operation - Remember that eff is the ratio of thrust
hp to delivered shaft hp that is how you can have more
thrust even tho eff is down - Vance
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