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  #1  
Old 09-29-2005, 01:03 PM
rv6ejguy's Avatar
rv6ejguy rv6ejguy is offline
 
Join Date: Mar 2005
Location: Calgary, Canada
Posts: 6,448
Default H6 Sube Fuel Flows

Eggenfellner has just finished testing fuel flows with modified fuel pressure on his H6 engine and showed some tangible performance gains:

Old:

4830 engine rpm
FF 10.1
TAS 148 knots

New:

4830 engine rpm
FF 8.4
TAS 160 knots

Leaning the overly rich OE ECU settings has reduced fuel flow and increased power. Good news for Egg owners and kudos to Jan for testing and improving his products.
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  #2  
Old 09-29-2005, 01:37 PM
cobra cobra is offline
 
Join Date: May 2005
Location: Utah
Posts: 274
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Full power or cruise?
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  #3  
Old 09-29-2005, 01:49 PM
DGlaeser DGlaeser is offline
 
Join Date: May 2005
Location: Rochester Hills, MI
Posts: 927
Default H6 fuel flow

That is full power (2650 prop rpm -> 1.82 PSRU).
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  #4  
Old 09-29-2005, 04:28 PM
cobra cobra is offline
 
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Location: Utah
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Great economy for full power!
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  #5  
Old 10-01-2005, 03:16 PM
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Jconard Jconard is offline
 
Join Date: Apr 2005
Location: Twin Cities
Posts: 438
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8.4 gph at 160kts is approximately one gallon per hour more than an O-320 with a Hartzel, on an RV7a.

I know one builder who can fly at 7.5 gph all day long at 161kts, in an rv7-a that is a little heavy (full interior, paint, IFR panel). It is a carbureted engine and he runs at 50-100 degrees rich of peak.

Of course an O-320/ Hartzell FWF could easily be completed for less than 25K and with half the parts count.

Do people intend to fly these things in cruise at 4800 rpm?
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  #6  
Old 10-01-2005, 03:50 PM
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rv6ejguy rv6ejguy is offline
 
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Location: Calgary, Canada
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Merely relaying the progress being made on this front with the Sube, 1.7 gal./hr. less and 12 knots more is significant. Yes, standard cruise rpm on most Sube conversions is between 4200 and 4800 rpm. About the same piston speed as an O-360 at 2600 rpm. Many thousands of hours at these rpms have successfully been flown now. Nothing much to be concerned about.
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  #7  
Old 10-01-2005, 09:22 PM
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mgomez mgomez is offline
 
Join Date: Mar 2005
Location: Northern California, USA
Posts: 537
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Quote:
Originally Posted by rv6ejguy
Eggenfellner has just finished testing fuel flows with modified fuel pressure on his H6 engine and showed some tangible performance gains:

Old:

4830 engine rpm
FF 10.1
TAS 148 knots

New:

4830 engine rpm
FF 8.4
TAS 160 knots

Leaning the overly rich OE ECU settings has reduced fuel flow and increased power. Good news for Egg owners and kudos to Jan for testing and improving his products.
Increasing speed from 148 to 160 kts, all else being equal, is a ~25% increase in power. Reducing fuel flow from 10.1 to 8.4 gph is a ~20% reduction in fuel flow. Combined, that means the SFC went down by a third...pretty good improvement! (It must've been pretty bad before, though)

So I guess he's using fuel pressure to adjust mixture, since he can't fiddle with the Subaru ECU's settings? I wonder why the ECU runs rich? Must be the software designers assuming that "If the driver has hit foot down and the RPMs up, he must care about power more than fuel economy...fatten up the mixture!"
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Martin Gomez
Redwood City, CA
"My RV-7 is a composite airplane: it's made of aluminum, blood, sweat, and money"
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  #8  
Old 10-02-2005, 02:00 AM
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rv8ch rv8ch is offline
 
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Location: LSGY
Posts: 5,109
Default Subaru ECU mapping

Quote:
So I guess he's using fuel pressure to adjust mixture, since he can't fiddle with the Subaru ECU's settings? I wonder why the ECU runs rich?
I believe this is the case. I think Ross (rv6ejguy) needs to get his sales guys to get on the phone to Eggenfellner to sell his unit. I personally would be much happier with a simple system to control the fuel and the fire.
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  #9  
Old 10-02-2005, 08:54 AM
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Jconard Jconard is offline
 
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I know that alot of people focus on piston speed. However, the problem with High RPM is not piston speed, it is acceleration and inertia loads on the rod, crank, pin, etc...

A piston must stop and accelerate twice per stroke, from a dead stop to full speed. Thats four times per revolution. The load is greatest, on the reciprocating assembly, at these times.

4800 X 4 = 19,200 acceleration cycles per minute

2600 x 4 = 10,400 acceleration cycles per minute.

In addition, even if the stroke were as short as half the lyc stroke, and it is longer, piston speed is still higher in order to travel the route twice as many times in a given time frame.

3.875, lycoming O-320 stroke.
x 4 = 15.5 inches travelled per revolution.
x 2600rpm = 40,300 inches travelled per minute
672 inches per second

3.15, Subaru H6 stroke in the Outback.
x 4 = 12.6 inches per revolution.
x 4800rpm = 60,400 inches travelled per minute
1008 inches per second.

O-360 stroke 4.375 inches.
piston speed 759 inches per second at 2600 rpm.

Just some math to illustrate my point, but an H6 at 4800 rpm must start and stop a piston alot more times every minute and it must accelerate to a higher speed each time than does either an O-320 or O-360.


But, as demostrated, the piston speed is NOT "about the same" as the lyc at 2600 rpm.

Last edited by Jconard : 10-02-2005 at 08:57 AM.
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  #10  
Old 10-02-2005, 11:41 AM
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rv6ejguy rv6ejguy is offline
 
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Yes, high fuel flows on the Egg conversions was a problem due to the very rich near WOT default open loop programming of the OE ECUs. These were setting AFRs richer than 11.5 in some cases causing a loss of power and high fuel flows.

The lower fuel pressures have been easier to implement than reprogramming the ECUs at this stage. Eggenfellner is working on other ECU solutions and new redrive ratios in a further effort to reduce fuel flows.

Piston speeds in the engine design/development area are usually denoted in ft./min. 1750-2000 is commonly thought to be a very safe limit with modern forged, ferrous connecting rod materials and construction as used in the Subaru engines for instance. My EJ22 in cruise at 4600 rpm would have a piston speed of 1130, a Lyc. O-360 would be 948 at 2600. So yes, my Sube has a higher piston speed but it is far, far below any critical fatigue range.

The short stroke design of the Sube permits much greater crankpin overlap than on a long stroke design. The EJ22 has .750 overlap.This coupled with 5 main bearings instead of 3 as on a Lycoming makes for a far stiffer and well supported crank assembly. In addition, the parts are far lighter, reducing tensile and compressive loads. The pistons are under 600 grams, the crank is only 13.5 inches long and weighs 20 lbs.

I'll reiterate this for about the 3rd time. I can find no documented cases of crankshaft or rod failures on EJ, EJ or EZ engines used in aircraft. They have accumulated well over 100,000 flight hours to date. The STI EJ engines have demonstrated power outputs in excess of 950hp using the stock block and crankshaft for short periods. This would equate to an O-360 producing 2242+hp. IMHO the Lyc would be shrapnel before it got to half that output in less than 1 second. You decide which is the stronger engine.

Fact, piston speed on a Sube IS higher than a Lyc at typical cruise power settings.

Fact, this is a non-issue as the stress levels are far below the point of critical fatigue life. This is born out both by analytical and real world flight experience.

Nuff said.
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