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05-24-2009, 04:02 PM
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Join Date: Oct 2006
Location: Glendale, AZ
Posts: 256
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Here is a good chart...
The guys at APS have put together a chart that very much describes what your saying about efficiency. I got this at the APS class, probably the best money I have ever spent on a class before. I knew engines pretty well when I went, but it just brought it all together. They go into the physics of whats happening, including engine pressures at degrees of rotation of the engine. They call it Theta PP (crank angle at peak cylinder pressure). Without a long drawn out description, you get peak pressure later after TDC which is less pressure on Con rods, cylinders, valves, etc...
The gist of it is pretty straight forward and matches what you posted. There is a new term on there called ICP (Internal Cylinder Pressure). They have a cool pressure transducer they designed that can monitor the engine internal pressures to get that. The best measure of efficiency is BSFC, which basically is power produced per unit of fuel. You can see the most efficient setting (as measured by BSFC) for the engine is about 25 degrees LOP and drops only slightly out to 50 degrees LOP. After that the engine will start to lose power pretty quickly. I run LOP not because it saves fuel, but because I believe that heat and pressure is the enemy of my engine and these settings are better for the engine. Provided of course your Air Fuel mixtures are tight enough to do it, typically only on FI engines.
Quote:
Originally Posted by Kevin Horton
The best efficiency is with a fuel flow that is about 0.6 to 0.7 GPH lean of peak EGT. If you go leaner than that, the hp per fuel flow starts to drop. At this condition, the power is about 9% less than peak power, but the fuel flow has dropped about 22% from the fuel flow for peak power. The efficiency, in terms of fuel required to produce one hp, is about 13% better than at mixture for best power.
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__________________
Roger Whittier
RV7A Quick Build, Tip Up
N1MY Reserved - Canopy finished - Wings mated, Engine hung, electrical 95%
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05-24-2009, 06:34 PM
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Join Date: Jul 2005
Location: Detroit, MI
Posts: 1,587
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Question about the APS chart
On the chart, what do the numbers 1.66 and 2.63 mean? I don't think they are BSFC or HP. They could be the inverse of BSFC for charting purposes. (1/2.63=.38) Is the chart copyright or may it be freely distributed? Thanks.
Quote:
Originally Posted by rwhittier
The guys at APS have put together a chart that very much describes what your saying about efficiency. I got this at the APS class, probably the best money I have ever spent on a class before. I knew engines pretty well when I went, but it just brought it all together. They go into the physics of whats happening, including engine pressures at degrees of rotation of the engine. They call it Theta PP (crank angle at peak cylinder pressure). Without a long drawn out description, you get peak pressure later after TDC which is less pressure on Con rods, cylinders, valves, etc...
The gist of it is pretty straight forward and matches what you posted. There is a new term on there called ICP (Internal Cylinder Pressure). They have a cool pressure transducer they designed that can monitor the engine internal pressures to get that. The best measure of efficiency is BSFC, which basically is power produced per unit of fuel. You can see the most efficient setting (as measured by BSFC) for the engine is about 25 degrees LOP and drops only slightly out to 50 degrees LOP. After that the engine will start to lose power pretty quickly. I run LOP not because it saves fuel, but because I believe that heat and pressure is the enemy of my engine and these settings are better for the engine. Provided of course your Air Fuel mixtures are tight enough to do it, typically only on FI engines.
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__________________
H. Evan's RV-7A N17HH 240+ hours
"We can lift ourselves out of ignorance, we can find ourselves as creatures of excellence and intelligence and skill. We can be free! We can learn to fly!" -J.L. Seagull
Paid $25.00 "dues" net of PayPal cost for 2015, 2016, 2017 and 2018 (December).
This airplane is for sale: see website. my website
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05-24-2009, 08:11 PM
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Join Date: Oct 2006
Location: Glendale, AZ
Posts: 256
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I don't remember at the moment
But I think you are correct about the inverse for charting.
I got a hard copy at the APS class (that particular soft copy I got from another board I participate in). They openly encouraged us to go out and talk up LOP with our fellow pilots and to use that chart/data to convince them that LOP was actually better for the engine - properly done. They are on a mission to turn around the ROP/LOP debate. So I think its ok to use but certainly you should credit APS. After all, they are the ones trying to bring LOP back into aviation after a 50 year hiatus.
Quote:
Originally Posted by hevansrv7a
On the chart, what do the numbers 1.66 and 2.63 mean? I don't think they are BSFC or HP. They could be the inverse of BSFC for charting purposes. (1/2.63=.38) Is the chart copyright or may it be freely distributed? Thanks.
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__________________
Roger Whittier
RV7A Quick Build, Tip Up
N1MY Reserved - Canopy finished - Wings mated, Engine hung, electrical 95%
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05-24-2009, 08:19 PM
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Join Date: Oct 2007
Location: Jackson, MS
Posts: 1,262
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Best Power??
I'm not sure I understand the chart completely. It was my understanding that the rich side of peak produces more HP.
When I was measuring IAS during fuel flow testing, it was greatest at 75F ROP. It also dropped off slightly just as I reached peak. According to the chart, most HP is developed on the LOP side of peak. According to my airspeed indicator, it doesn't agree with the chart.
What am I missing here?
Quote:
Originally Posted by rwhittier
The guys at APS have put together a chart that very much describes what your saying about efficiency. I got this at the APS class, probably the best money I have ever spent on a class before. I knew engines pretty well when I went, but it just brought it all together. They go into the physics of whats happening, including engine pressures at degrees of rotation of the engine. They call it Theta PP (crank angle at peak cylinder pressure). Without a long drawn out description, you get peak pressure later after TDC which is less pressure on Con rods, cylinders, valves, etc...
The gist of it is pretty straight forward and matches what you posted. There is a new term on there called ICP (Internal Cylinder Pressure). They have a cool pressure transducer they designed that can monitor the engine internal pressures to get that. The best measure of efficiency is BSFC, which basically is power produced per unit of fuel. You can see the most efficient setting (as measured by BSFC) for the engine is about 25 degrees LOP and drops only slightly out to 50 degrees LOP. After that the engine will start to lose power pretty quickly. I run LOP not because it saves fuel, but because I believe that heat and pressure is the enemy of my engine and these settings are better for the engine. Provided of course your Air Fuel mixtures are tight enough to do it, typically only on FI engines.
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__________________
Webb Willmott
Jackson, MS
N32WW
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05-24-2009, 08:34 PM
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Join Date: Oct 2006
Location: Glendale, AZ
Posts: 256
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Perhaps your reading the labels incorrectly
The way I read the HP curve it peaks just about 75 degree ROP (the black line). The brown colored (bottom line) is an efficiency measure (BSFC) which basically says you reduce FF more quickly than you reduce power production when LOP. I think you might be seeing the labeling, which is a bit weird. The BSFC label applies to the bottom line and is on the left side of the graph. Its easy to see the black HP label and apply it to BSFC.
Quote:
Originally Posted by Webb
I'm not sure I understand the chart completely. It was my understanding that the rich side of peak produces more HP.
When I was measuring IAS during fuel flow testing, it was greatest at 75F ROP. It also dropped off slightly just as I reached peak. According to the chart, most HP is developed on the LOP side of peak. According to my airspeed indicator, it doesn't agree with the chart.
What am I missing here?
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__________________
Roger Whittier
RV7A Quick Build, Tip Up
N1MY Reserved - Canopy finished - Wings mated, Engine hung, electrical 95%
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05-24-2009, 09:00 PM
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Join Date: Oct 2007
Location: Jackson, MS
Posts: 1,262
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Your right, it's the labeling. When I look at the "correct" curve, it is dead on.
Quote:
Originally Posted by rwhittier
The way I read the HP curve it peaks just about 75 degree ROP (the black line). The brown colored (bottom line) is an efficiency measure (BSFC) which basically says you reduce FF more quickly than you reduce power production when LOP. I think you might be seeing the labeling, which is a bit weird. The BSFC label applies to the bottom line and is on the left side of the graph. Its easy to see the black HP label and apply it to BSFC.
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__________________
Webb Willmott
Jackson, MS
N32WW
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05-26-2009, 10:52 PM
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Join Date: Oct 2007
Location: Jackson, MS
Posts: 1,262
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Graphed results
Here are the graphed results that Kevin is using some of the other data in another post regarding fuel flow and power. Best IAS was at 9.2 gal/hr when #4 was 75 LOP but the others were approximately at 90 ROP. I'm hoping to see the flow rate drop to around 8.8 when all cylinders will be close to 75 LOP.
I'll post again after replacing the #4 restrictor to verify the change.

__________________
Webb Willmott
Jackson, MS
N32WW
Last edited by Webb : 05-26-2009 at 11:01 PM.
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05-27-2009, 01:06 PM
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Join Date: Feb 2005
Posts: 571
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I apologize as this is not quite over the plate in this conversation, but it's still in the same ballpark, I think.
It appears from the graph provided by Kevin, that useful bSFC's run from approximately .410 to .471 but these only apply at LOP. I will fly my Rocket this summer and was wondering what I should expect to see for fuel flow on takeoff at full rich? I'll be at sea level, turning 2,700 rpm on an IO-540 with AFP fuel injection (FM-200) and 9.5 to 1 pistons. I have been told to expect something on the order of 280 hp. A quick check shows a pretty big range of fuel flows if you plug in bSFC values from say, .40 to .50 of from 18.7 gph to 23.3 gph. It might be nice to know on initial takeoff if I am seriously lean at full power or not.
Any ideas on what I should see, or even more to the point, what the bSFC should be under these conditions? Assuming the bSFC in these conditions is well established, shouldn't I be able to legitimately "back out" my hp at full power from my fuel flow? I imagine many RV-10 guys have this same or a similar engine configuration.
Regards,
Lee...
__________________
Lee Logan
Ridgeland, SC (3J1)
F1 Rocket #160 flying
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05-27-2009, 07:12 PM
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Join Date: May 2006
Location: Pocahontas MS
Posts: 3,884
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IIRC, you should see significantly more than .50 lb/hp/hr. I've seen numbers as high as .55.
The Lyc operator's manual #60297-12 shows a carb, 8.5/1 compression O-360 180 hp engine full throttle Bsfc between .52 & .54 as rpm increases from 2200 to 2700 rpm, power from 160 to 180 hp.
A lower compression -B series engine at 168hp (max) is ~.58.
Charlie
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05-27-2009, 07:37 PM
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Join Date: Jan 2005
Location: Ottawa, Canada
Posts: 2,357
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Quote:
Originally Posted by logansc
I apologize as this is not quite over the plate in this conversation, but it's still in the same ballpark, I think.
It appears from the graph provided by Kevin, that useful bSFC's run from approximately .410 to .471 but these only apply at LOP. I will fly my Rocket this summer and was wondering what I should expect to see for fuel flow on takeoff at full rich? I'll be at sea level, turning 2,700 rpm on an IO-540 with AFP fuel injection (FM-200) and 9.5 to 1 pistons. I have been told to expect something on the order of 280 hp. A quick check shows a pretty big range of fuel flows if you plug in bSFC values from say, .40 to .50 of from 18.7 gph to 23.3 gph. It might be nice to know on initial takeoff if I am seriously lean at full power or not.
Any ideas on what I should see, or even more to the point, what the bSFC should be under these conditions? Assuming the bSFC in these conditions is well established, shouldn't I be able to legitimately "back out" my hp at full power from my fuel flow? I imagine many RV-10 guys have this same or a similar engine configuration.
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This ancient Lycoming power from fuel flow data I have seems to suggest a bSFC for your engine in the range of 0.46 at best power. But at full rich the bSFC should be quite a bit higher than that. I'll venture something on the order of 0.55 as a SWAG. Assuming you really have a 280 hp engine, I think I'd want to see at least 23 gph. I suspect you'll actually see 25 or 26 gph.
But, keep in mind that I have no experience with 540s, and this Lycoming data is a long ways from having been validated. These comments are worth what you paid for them.
Last edited by Kevin Horton : 05-27-2009 at 07:49 PM.
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