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

 

Bill,

 

While you're at it don't forget to account for the water pump and alternator(s).

 

Mark 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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