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Old Nov 12, 2012, 09:53 PM
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HP/Fuel Consumption Tests: FA180, FA180 CDI, FA180HC CDI BBC

I finally got an ideal day for testing the power output differences for my Standard compression Saito FA180 on glow ignition, the standard compression FA180 W/CDI & the High Compression FA180HCCDI BBC (FA220 Big Bore Carburetor) All testing W/the same 15% Cool Power glow fuel.

For some insight into the FA180HC CDI engine check out this thread. http://www.rcgroups.com/forums/showthread.php?t=1754616

Since the FA180HC BBC was on the test stand I double checked the ignition timing. The timing was set @ 34* BTDC. That will give 34* BTDC @ WOT when running @ high RPM. I'm not sure what the advance curve is, but the 24* retard @ start would give 10* BTD ignition timing @ start & idle.

The 220 Big Bore carburetor has the same bolt pattern as the 150/180 carburetors, it is 12mm bore (the 180 carb is 11mm. the 150 10mm) I bored the updraft portion of the FA150 manifold I had on hand out to 12mm. The horizontal runner where the manifold interfaces W/the intake port was bored out to the standard FA180 ID to match the 180 intake port.

Interesting note: The aluminum intake gaskets that come W/the FA180 are smaller in I D than either the intake manifold or the port on the cylinder head. It appears to be the same ID as the 150 port/manifold. Since I have not had any issues eliminating these gaskets on any of my 150/180 engines, I chose to eliminate it for a smoother transition from the manifold to the intake port.

After fiddling W/the HSN, the FA180HCCDI BBC spun the Dynathrust 18x8 prop @ a solid 8400 RPM flashing 8500, idle was steady 1100 RPM. @ 8450 RPM that generated 3.44HP W/20.44# Thrust.

The standard compression FA 180CDI had the timing checked & set @ the same 34* BTDC.

After tweaking the HSN, the FA180CDI spun the same 18x8 prop @ 8000 RPM flashing to 8100, idle was a steady 1200 RPM. @ 8050 RPM that generated 2.98HP W/18.55# Thrust

The CDI was unhooked, the sparkplug replaced W/a glow plug. The needle setting were opened up to OEM start up specs & the engine started on glow ignition.

After setting the HSN & LSN, the FA180 on glow ignition spun the 18X8 prop @ a steady 7900 RPM, the idle was a rough 1400 RPM but it was reliable. @ 7900 RPM that generated 2.81HP W/17.86# Thrust.


CDI ignition gave an additional 150 RPM, .17HP & .69# of thrust over glow ignition & reliable idle was was 200 RPM lower.

The compressionn ratio increase to 12.77:1 from the stock 9.56:1 coupled W/the 12mm FA220 Carb really brought on the power.

The increase for the standard compression F180CDI version was an additional 400 RPM, HP increased by .46HP (15% HP gain) W/1.89# additional thrust (10% thrust gain) & another 100 RPM lower idle speed.

Comparing the gains from the standard glow ignition FA180, to the FA180HCCDI BBC, HP went from 2.81 to 3.44, .63HP gain, (22% HP gain) thrust increased from 17.86# to 20.44#, a 2.58# gain (14% thrust gain) W/300 RPM slower dependable idle speed.

This puts the FA180HCCDI BBC squarely in the power output range of the FA220 W/much better fuel economy & less weight in a more compact engine package. I am very pleased W/the results.
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Old Nov 13, 2012, 07:01 PM
I HATE GLOW PLUGS!
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I picked up a quart of O'Donnell Speed Blend racing Fuel today. 30% Nitro, 8% oil.

WOW! 8850 RPM, corrected for the 47*F ambient temperature, the 18x8 prop @ 8850 RPM generates 23.21# of thrust. The engine is making 3.95HP W/the 30% nitro!

I even saw some 9K+ flashes on the optical tach, but 8800 was the base flashing back & forth to 8900.

So much for the myth of no power boost from increased nitro W/CDI.

From the 15% Cool Power setting, I had to open the HSN a bit less than 1/4 turn, the LSN was opened 1/2 turn to get a good idle/transition.

I am definately going to reduce the deck height on the standard compresssion FA180 to get to 12.77:1 CR

I won't need the 220 BB carb & 30% fuel for the CAP 232, the standard 180 carb & 15% Cool Power should be ample power for a plane < 10#.

23.21# of thrust in my 16# Dynaflite PT-19 ought to make for crazy vertical!
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Old Nov 15, 2012, 04:12 PM
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Very interesting, thanks for sharing your experiments. When you are correcting for temperature, you are just correcting the calculated power numbers right? RPM would be about the same, because the power used by a fixed pitch prop and the power developed by a naturally aspirated engine are fairly proportional to air density, correct? For example I tried an engine combination at 8000 feet elevation and got about the same RPM as near sea level.
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Old Nov 15, 2012, 04:30 PM
I HATE GLOW PLUGS!
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Originally Posted by flyrod View Post
Very interesting, thanks for sharing your experiments. When you are correcting for temperature, you are just correcting the calculated power numbers right? RPM would be about the same, because the power used by a fixed pitch prop and the power developed by a naturally aspirated engine are fairly proportional to air density, correct? For example I tried an engine combination at 8000 feet elevation and got about the same RPM as near sea level.
Thrust will change W/temperature while RPM/HP remains fairly consistant.

Where density altiutude really comes ito play is the reduced lift/thrust from lower barometric pressure/high temperatures..
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Old Nov 16, 2012, 09:26 AM
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Fuel Consumption Tests

Yesterday we had another decent day to do some more testing. It was a bit chilly, but but there was no wind & the temperature remained stable long enough to get several test runs accomplished.

I added my FA150/CDI engine to the fray for a baseline. It was a bit overpropped W/the 18X8 DT prop, but it still allowed for a comparison W/approximately 12oz of fuel @ 7600 RPM. The FA150/CDI was within 100 RPM of WOT maximum power. All engines were using C&H Synchrospark CDI set @ 34* BTDC.

I will start W/the poorest fuel economy results 1st. Some of the results were fairly close as far as the time it took to drain the fuel tank. These results are not difinative, but they do show a trend, & the most effiecient combo might surprize some of you.

The fuel tank was filled to a point where the "air bubble" @ the top was observed in relation to a mark. The tank was tilted down @ the raer so the mark resulted in fairly cosistant fill volume.

The engine were started @ a high idle speed, the stop watch was started, & @ 30 seconds, the throttle was advanced to attain 7500-7600 RPM. When air bubbles were observed in the fuel line and/or the engine started to surge. The stop watch was tripped.

Again, the FA150/CDI engine was very near to WOT @ 7500-7600 RPM.

Here are the results starting W/the worst fuel consumption results.

The 1st test was W/the FA180HC/CDI/BBC engine running on O'donnell Speed Blend 30% nitro, 8% lube. This is the 12.77:1 CR engine (HC) W/CDI & the 220 big bore carburetor. (BBC)

FA180HC/CDI/BBC, 30% nitro: Run time W/12oz fuel @ 7500-7600 RPM = 8 minutes

All of the following tests were done W/15% Cool Power glow fuel. While there was a significant inprovement in fuel consumption W/the lower nitro content, over the 30% notro fuel, the differences in run times W/15% nitro in the various configurations were not all that significant. They did, however tend to show a trend toward better fuel economy.

FA180HC/CDI/BBC, 15% nitro 7500-7600 RPM = 10 min 22 sec

FA150/CDI, 15% nitro 7500-7600 RPM = 11 minutes

FA180HC/CDI (OEM 180 carb) 7500-7600 RPM = 11 min 44 sec

FA180/CDI (standard 9.56:1 CR, OEM carb) 7500-7600 RPM = 12 min 10 sec

The stock FA180/CDI showed significant fuel economy improvement over the FA150/CDI. This is probably due to the fact that while the FA150/CDI was operating @ near WOT, the FA180/CDI only needed a bit over 1/2 throttle to achieve the same power output.
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Old Nov 16, 2012, 11:20 AM
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If you'll be doing this on a regular basis you'll want to get yourself a graduated burette. Watching an engine run for an hour to take four data points is like watching grass grow. Interesting results none the less.

Greg
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Old Nov 16, 2012, 11:39 AM
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Interesting! I would've guessed that the high compression would improve efficiency. Maybe that efficiency only shows up at high manifold pressure (WOT).

Have you done any back-to-back tests on just the BBC? I wonder how the carb bore factors in.
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Old Nov 16, 2012, 11:52 AM
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I've found needle setting contributes most to the consumption figures. It's not easy to detect the leanest setting and the leanest setting might not make the most power. From a hobbyist point of view the test is fine and represents what could be achieved by the average person in the field.

Greg
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Old Nov 16, 2012, 02:48 PM
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The high compression engine seems to have some slight surging issues that will normalize after a few minutes run time. this happens whether I am running the BB carb of the OEM 180 carb.

The HC engine is utilizing inlet/oulet checks to pull lubricating oil through the rear bearing/cam housing. While my previous tests did not show any detrimental effects on WOT performance, I think it may be affecting the mixture.

When I bought the 220 BB carb, it came W/a pair of crankcase pump pressure check valve, & more improtantly, the bleed off regulator for positive, controlled fuel pressure. I think that having the full pump set-up W/the pressure regulator maty stabilize the mixture.

I have adjusted this type of system on my FA300TTDP & once you understand the way it functions, it is yields very stable running from idle through midrange all the way to top end.

Here is a clip of my FA300TTDP running & after warming up, idling reliably @ 800 RPM. It has the same fuel pressure system as I plan to implement on the FA180HC/CDI/BBC.

Saito 300 Twin With C&H Ignition, 800 RPM Idle (8 min 9 sec)


One of the things that makes me think that then HC engine will benefit from fuel pressure is the fact that the slight surge is not present W/the 30% nitro fuel. Perhaps the richer needle setting help eliminate that. The leaner needle setting for the 15% nitro fuel might atomize better under pressure from the crankcase..
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Old Nov 16, 2012, 04:34 PM
I HATE GLOW PLUGS!
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Originally Posted by flyrod View Post
Interesting! I would've guessed that the high compression would improve efficiency. Maybe that efficiency only shows up at high manifold pressure (WOT).

Have you done any back-to-back tests on just the BBC? I wonder how the carb bore factors in.
These were very crude tests. As I stated, they weren't definitive.

About the only significant difference was the marked increase of fuel consumption W/the 30% nitro fuel. That was expected.

I also expected the 180 to get better fuel economy @ the RPM level that was very near WOT for the 150, but just above 1/2 throttle for the 180s..

It would take a lot more testing @ adjustments to the LSN to maximize fuel economy @ part throttle settings. Adjusting the throttle for 7500-7600 RPM is not an exacting proceedure & leaves a lot of variables in play including inexact fuel volumes, start up proceedure & throttle setting @ the high idle before bringing the RPM to 7500-7600 RPM.

What I was trying to get a feeling for was how the various engine configurations would perform @ a given level of flight performance.

I did do back to back test runs W/the BB carb & OEM carb on the HC 180. The BB carb was on the engine for the 1st pull. I then swapped in the OEM carb for the next test run. I have all of the throttle arms oriented the same to simplify changing out carbs/engines.

My conclusions:

The HC & stock 180 were similar enough in fuel consumption to make the increased performance of the HC 180 cost effective. As you surmised, the HC 180 may well be as efficient or even more efficient than the stock CR version once proper fuel delivery adjustments are made.

I plan the go the much simpler route of reducing the case deck to also bring the stock 180 up to 12.77:1 CR. I will utilize the OEM 180 carb.The mdifification is worth it IF you are planning on running CDI which, IMO, is the 1st modification anyone should do to an FA180. Once CR is increased to that level, the engine is no longer viable W/glow ignition. It has NASTY habits on GI!

The fuel consuption of the BB carb is not that much higher than the OEM 180 carb. There is not a significant boost in top end RPM W/the BB carb, perhaps 50-100 RPM @ best. The significant performance improvement W/the BB carb is throttle response & spool up W/the heavy prop. Those were significantly better W/the BB carb. The difference in fuel consumption (if there is any) is outweighed by the performance boost IF one wants something that will quickly go vertical from low airspeed. I think the BB carb will be overkill in my 73" CAP 232, but might be nice in my heavier 89" PT-19. It would fly around scale-like @ low throttle setting, then do a Dr. Jeckle/MR Hyde act when the throttle is firewalled. The plane had some very nice albeit docile airobatic capabilities even W/the FA150/CDI engine. (that was eventually turned into the FA180HC/CDI) 50% more HP would really wake that airframe up.

Likewise, it would be nice to add some 30% nitro fuel occasionally, open up the HSN a bit & really send that sucker vertical.

The performance of the FA180HC/CDI W/the 30% nitro using the BB carb is a bit startling, bordering on violent.
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Old Nov 16, 2012, 07:35 PM
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I also expected the 180 to get better fuel economy @ the RPM level that was very near WOT for the 150, but just above 1/2 throttle for the 180s..
Quite logic, that it doesn't.... of two otherwise comparable engines of different size, the bigger will always be less efficient when both engines are delivering the same absolute output, unless the smaller engine is running markedly above its normal operating limit.

That is simply caused by the fact that the bigger engine has a partly closed throttle, thus a lower charge pressure, and if looking at the P-V diagram, the intake line drops further below the atmospheric line compared to the smaller engine.
Therefore, the process requires more energy on the intake stroke, that needs to be compensated by a stronger power stroke. The fact that lower charge pressure makes for lower compression end pressure, will reduce the efficiency of the thermodynamic process even further....
Thus, for the same shaft output you need more fuel to overcome the bigger intake resistance.

Brgds, Bert
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Old Nov 16, 2012, 09:22 PM
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Originally Posted by Brutus1967 View Post
Quite logic, that it doesn't.... of two otherwise comparable engines of different size, the bigger will always be less efficient when both engines are delivering the same absolute output, unless the smaller engine is running markedly above its normal operating limit.

That is simply caused by the fact that the bigger engine has a partly closed throttle, thus a lower charge pressure, and if looking at the P-V diagram, the intake line drops further below the atmospheric line compared to the smaller engine.
Therefore, the process requires more energy on the intake stroke, that needs to be compensated by a stronger power stroke. The fact that lower charge pressure makes for lower compression end pressure, will reduce the efficiency of the thermodynamic process even further....
Thus, for the same shaft output you need more fuel to overcome the bigger intake resistance.

Brgds, Bert
Then why do the 5.7 Hemi powered Dodge Ram Pickups get better mileage than the 4.6 powered trucks of similar size/weight?

This was observed even before the MDS was introduced in the 5.7 truck engines.
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Old Nov 17, 2012, 04:09 AM
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To be honest, I am not familiar with the trucks you are talking about, and "MDS" does not even ring a bell....

But that does not do anything for the validity of what I said....
If all other design features are kept equal, the throttle valve (and the "vacuum" in the cylinder caused by it during the intake stroke) are the sole reason for the fact that a bigger engine, delivering the same output at the same RPM, is less efficient.

It all follows from the P-V diagram at part load, where it becomes clear that the intake part of the 4 stroke cycle has a big influence on power output. For me as a marine propulsion engineer, that was stuff from the first semester, and it is for example the reason why diesel engines (no throttle valve, thus better efficiency at part-load) have been the dominant engine principle in marine and power generation applications.

Besides, you should not confuse mileage (which includes weight, rolling resistance, aerodynamic shape, tire size, and lots more factors) with engine efficiency, especially when you are using one of the worst type of vehicles as for fuel efficiency, American Pick-ups with typical American V-8 engines, to make such statements.
The difference being, that mileage is determined by the combination of efficiency of the engine AND the power a certain vehicle requires to maintain a given speed, whereas engine efficiency (what I was referring to) is the amount of chemical energy an engine needs to generate a certain amount of power on the shaft.

And (please, I am NOT trying to insult anybody), american automotive engines are not, and never have been, a good example, because due to the traditionally low fuelprices in the US, American engines historically have always been designed with fuel efficiency as least important factor, therefore they have typically always been large displacement, low specific power designs, compared to Japanese and European designs, which were smal(ler) displacement, high(er) output, and solely by that fact, were more fuel efficient.

It is an emotional thing: You would buy a Dodge Ram (or whichever other truck) with an American made 5.7 litre V-8, making 350 HP (for example), but you probably wouldn't buy that same vehicle, if it was equipped with a European or Japanese 2.5 litre 4-in-line, making 400 BHP, just because "it wouldn't be the same".... And I have to admit, I wouldn't too....

The Hemi is a "superior design" amongst American V-8 engines, but it is still an old, inefficient design compared to European and Japanese engine designs. Again, I am not out to insult anybody, it is just the truth, and the reason why American Pick-ups (and american cars in general) are not very popular in the rest of the world, where fuel prices are high (at the moment gas in Europe is around 8,5 U$ per gallon, and there have been times, gas was over 5 times more expensive than in the US).

Getting back to your experiment, I am pretty confident, that when it comes to full power, and you set out fuel consumption against power output, your 180 will be more fuel-efficient compared to the 150.
You will most definitely see an improvement on that 180 compared to that 150, if you would let the 180 do its part-load at lower RPM's
(for example, test the 150 with an output of, say 2 HP at 8000 RPM, and the 180 with that same 2 HP, but at 7000 RPM)
But that is just in line with what I said, which comes down to: "a too big engine for the application (and thus an engine that is running on part-load) is less fuel efficient compared to an engine that is tailored for the job.

Brgds, Bert
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Old Nov 17, 2012, 08:11 AM
I HATE GLOW PLUGS!
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Getting back to your experiment, I am pretty confident, that when it comes to full power, and you set out fuel consumption against power output, your 180 will be more fuel-efficient compared to the 150.
You will most definitely see an improvement on that 180 compared to that 150, if you would let the 180 do its part-load at lower RPM's
(for example, test the 150 with an output of, say 2 HP at 8000 RPM, and the 180 with that same 2 HP, but at 7000 RPM)
But that is just in line with what I said, which comes down to: "a too big engine for the application (and thus an engine that is running on part-load) is less fuel efficient compared to an engine that is tailored for the job.

Brgds, Bert
Go back to my experiment & you will find that I stated that the 150 was "overpropped" & it was operating very very near to WOT. The 150 engine was "operating above it design limit" to some extent.
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Old Nov 17, 2012, 10:13 AM
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How is the 150 operating above it's design limit?

If the 180 was to make 2HP at 7kRPM it would need to make 13% more torque than the 150 with a 20% displacement advantage. It would very likely still be less efficient. Chances are you would not see a consumption advantage until the RPM was low enough that the 180 was running WOT nearer it's peak torque. Then, you would be using very different props for the aircraft and they would have just as much influence on economy. These engines make max torque somewhere near 5000RPM. Usually best brake specific fuel consumption (BSFC) is near the torque peak. IMO, there is no such thing as an over propped engine, unless you're looking for peak power.

Vehicle fuel economy is so much more than displacement.

Greg
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