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07-02-2012, 01:16 PM
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Join Date: Apr 2009
Location: Propwash Airport (16X), Texas
Posts: 136
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Is it possible the return line in the fuel tank fell down into the tank. Mounted correctly in the filler neck the return line has no back pressure. If it were to come loose from the top of the tank and fall into the tank and get submerged you might get some back pressure that could give you varying flows when the tanks fuel level changed from full tank to half or quarter tank.
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07-02-2012, 01:50 PM
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Join Date: Nov 2007
Location: Jesup, Iowa
Posts: 1,657
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My experience today - -
It was a toastie 33 C at the airport ( about 980' ). I climber to 7500', and it was a nice 18 C ( about 66 degrees F ). I noticed my fuel flow also rose higher than normal. For the RPM I was at, I would normally see about 4.8 GPH. It was reading 5.8 GPH. The DA was at 9750' when I was at 7500' ALT. I stayed at 7500' for about 1/2 hour. Everything else was pretty normal, but fuel flow was higher. Seemed ok once back on the ground.
John Bender
397.8 hours
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07-02-2012, 01:54 PM
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Join Date: Jun 2006
Posts: 316
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I know our carbs are supposed to be altitude compensating[/quote]
Rotax carbs are not altitude compensating. They are sometimes called "constant velocity carburetors"
don
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07-02-2012, 11:08 PM
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Join Date: Dec 2008
Location: Lacey, WA
Posts: 1,365
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Semantics?
"The fuel/air mixture the carburetor provides to the engine varies with air density. Air density fluctuates with ambient temperature and altitude above sea level." Quote from Rotax literature
This may not meet the definition of "altitude compensating" exactly but it must be pretty close
Tony
__________________
Tony
E-LSA RV-12 ULS
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07-03-2012, 05:57 AM
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Join Date: Jun 2006
Posts: 316
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Not Semantics, just facts
"The fuel/air mixture the carburetor provides to the engine varies with air density. Air density fluctuates with ambient temperature and altitude above sea level." Quote from Rotax literature
To me this means that the fuel air ratio that the carburetor delivers to the engine varies with air density. This means that the carburetor is not altitude compensating. If the carburetor was altitude compensating then the fuel air ratio would be constant with altitude or air density. The key word here is fuel air ratio (fuel/air mixture) not fuel flow.
By the design of the Bing carb, it does not have any component that will adjust the fuel flow to keep the fuel air ratio the same, at different air density or altitudes.
Don
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07-03-2012, 10:50 AM
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Join Date: May 2010
Location: Wharton, Texas
Posts: 122
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Strange thing about it, although the fuel flow indicates high 7 GPH/hr at higher altitudes, fill-ups indicate an average of 4.5 - 5.0 GPH. I think something may be goofy with the Dynon at 7000' + at DA.
Gary
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07-05-2012, 11:07 AM
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Join Date: Oct 2008
Location: CAMARILLO, CALIFORNIA
Posts: 119
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Same Problem
I have experienced the same problem.
Constant altitude, RPM, fuel pressure, OAT, and the fuel flow changed from 5.3 to over 7 in less than 40 seconds.
Fuel flow actually went as high a 10 with no other changes.
rpm 5300
altitude 7500 ft
fuel pressure 4.3
OAT 57
All with no change in actual fuel consumption.
Gary
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07-05-2012, 12:54 PM
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Join Date: Jul 2008
Location: kansas
Posts: 330
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That could really pucker ones hiney. Thinking you might have fuel leaking on a hot engine. EYOW!
__________________
Larry Vandegrift
ULPower 260is
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07-06-2012, 09:16 AM
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Join Date: Nov 2008
Location: Gloversville, NY
Posts: 1,587
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Quote:
Originally Posted by BigJohn
.... to Mike just now. Wayne, keep in mind that the fuel system measures flow in between the two pumps, and measures pressure after the two pumps. It is concievable that for some unknown reason the return flow to the tank increases dramatically during this event. Doesn't seem likely, but could explain the high rate of flow.
If you want to see the graph, send me an email at johnpeck@nycap.rr.com.
John
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The email to support@dynon.com just came beack as undeliverable, after 4 days of trying. I re-sent it but don't have any confidence it is going through.
__________________
John Peck, CFII, A&P, EAA Tech Counselor, Flight Advisor.
?Master Pilot? Award, UFO Member.
RV-12 N37JP 120176 Flying since 2012.
One Week Wonder Build Team, OSH 2018.
VAF paid through 10/2019.
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07-06-2012, 09:51 AM
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Join Date: Jun 2009
Location: Dayton, OH
Posts: 838
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Sent your address
directly to Mike at Dynon, John. I'm sure he'd want to see your plots. The only thing I can think of is that the message is too big for their mailbox.
Sure hope you can get the info to him.
Wayne
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