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Mark,
I think I may be trying to determine “SAE
Kentucky Windage HP”! :>)
To do this test I would have to estimate
the exact weight of the plane at the time of the test, estimate the density
altitude and all the things that go into figuring it out, estimate what the
climb rate really was, estimate what the descent rate really was, estimate prop
efficiency, estimate the PSRU losses, etc…the only “known”
number I would be working with in the calculation is the number 33000.
I have been telling myself, “Self! I
don’t think my engine is really hairy chested like I wanted it to be!”
I plan to get an estimated descent rate
and climb rate, run it thru this calculation and see if I still feel this
way. :>)
If it turns out to be accurate, I plan to
stay away from dark clouds due to fear of being struck by lightening! :>)
Bill B
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Mark Steitle
Sent: Monday, October 07, 2013
8:24 PM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: Prop and
PSRU efficiency
Bill,
I was getting at a defined standard so that your numbers could be
compared to a certified a/c engine. Wikipedia defines SAE hp, depending
on the configuration of the engine being tested, as follows:
SAE gross power[edit]
Prior to the 1972 model
year, American automakers rated and advertised their engines in brake
horsepower (bhp), frequently referred to as SAE gross horsepower, because it
was measured in accord with the protocols defined in SAEstandards J245
and J1995. As with other brake horsepower test protocols, SAE gross hp was
measured using a stock test engine, generally running with few belt-driven
accessories and sometimes fitted with long tube test headers in
lieu of the OEM exhaust
manifolds. The atmospheric correction standards for barometric pressure,
humidity and temperature for testing were relatively idealistic.
SAE net power[edit]
In the United States,
the term bhp fell into
disuse in 1971-72, as automakers began to quote power in terms of SAE net
horsepower in accord with SAE standard J1349. Like SAE gross and other brake
horsepower protocols, SAE Net hp is measured at the engine's crankshaft, and so
does not account for transmission losses. However, the SAE net power testing
protocol calls for standard production-type belt-driven accessories, air
cleaner, emission controls, exhaust system, and other power-consuming
accessories. This produces ratings in closer alignment with the power produced
by the engine as it is actually configured and sold.
SAE certified power[edit]
In 2005, the SAE introduced
"SAE Certified Power" with SAE J2723.[20] This
test is voluntary and is in itself not a separate engine test code but a
certification of either J1349 or J1995 after which the manufacturer is allowed
to advertise "Certified to SAE J1349" or "Certified to SAE
J1995" depending on which test standard have been followed. To attain
certification the test must follow the SAE standard in question, take place in
an ISO9000/9002 certified facility and be witnessed by an SAE approved third
party.
So, if I understand you
correctly, you are looking to determine "SAE Net HP", which is
measured at the flywheel, and includes air filter, accessories, stock exhaust,
etc. Without these "additions", you would be talking "SAE
Gross HP".
Mark
On Mon, Oct 7, 2013 at 4:42 PM, Bill
Bradburry <bbradburry@bellsouth.net> wrote:
Based on the below statement, where would Tracy’s planet gear system fall?
PSRUs
have losses inherent in their gearsets or belts. Lay people have often
speculated that these losses are up to 40 hp in the case of a 200 hp class
drive. This is absurd as it would represent about 30,000 watts being dissipated
as heat. If this was in fact true, the case or belts would melt in just a few
minutes. Typical losses for single mesh spur and helical gears is around
2-2.5%. HTD belts run at 3-4%. Twin mesh helical gearsets would then have
perhaps a 6% loss as worst case including bearing losses.
The statement came from:
http://www.sdsefi.com/air51.htm
B2
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net]
On Behalf Of Bill Bradburry
Sent: Monday, October 07, 2013
3:42 PM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: Prop and
PSRU efficiency
Mark,
They would be included if the engine was tested on a dyno, so I
consider them to be part of the engine. But not so the PSRU if measuring
from the flywheel.
Ernest,
I don’t know what you mean by .98 to .99?? Certainly
you don’t think it would only be a loss of 1 or 2%!?? It would have
to be in the range of 10 to 20 HP or even greater. That is 5 to 10% in
our HP range. Just the loss due to prop efficiency is in the range of 30
HP!
Bill
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net]
On Behalf Of Mark Steitle
Sent: Monday, October 07, 2013
1:26 PM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: Prop and
PSRU efficiency
While you're at it
don't forget to account for the water pump and alternator(s).
On Mon, Oct 7,
2013 at 12:18 PM, Bill Bradburry <bbradburry@bellsouth.net>
wrote:
I have asked this
question a couple of times and no one has hazarded a
guess.
How much HP is lost from our engines due to the PSRU? I have been
interested in determining what the HP output of my engine is and that info
would be needed for that estimation.
They tell me that most props are about 80-85% efficient, so to calculate the
hp, you take the difference between your climb rate and your glide descent
rate at the same airspeed, multiplied by the weight, and then divided by
33000.
Wt * V / 33000 = HP
This would be the prop HP, so to get the prop flange HP, you would divide by
the prop efficiency, between .8 and .85.
To get the engine flywheel HP, you would have to add something for the loss
of the PSRU.
Is anyone willing to take a shot at that number?? Third or forth chance!
:>)
Bill B
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