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05-04-2016, 09:23 AM
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Join Date: Oct 2012
Posts: 421
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Fuel Pressure Slowly Decreasing in High Alt Cruise
Flew from KIWA to AZ82 yesterday and flight was normal.
On the way back, noticed fuel pressure in cruise after 10-15 minutes level off starting to decline...got as low as 2.2...got a couple of warnings...seemed to stabilize at 2.6-2.7 at 4900 RPM at 10500. Would decline if I increased RPM. Engine never missed a beat - all other indications were green.
Newer fuel pump, aux pump not on switch and was running when I shut down.
Winter premium gas - I departed up north with about 14 gals at 8100' DA - the run up and takeoff all had the usual 5.5 PSI showing. It was pretty warm yesterday.
By the time I landed in the valley, it was showing a more normal 3-4 PSI
I'm thinking the winter gas and higher altitudes maybe caused some vapor issues and filled it up with 100LL.
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05-04-2016, 10:06 AM
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Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,035
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Quote:
Originally Posted by cactuspilot
Flew from KIWA to AZ82 yesterday and flight was normal.
On the way back, noticed fuel pressure in cruise after 10-15 minutes level off starting to decline...got as low as 2.2...got a couple of warnings...seemed to stabilize at 2.6-2.7 at 4900 RPM at 10500. Would decline if I increased RPM. Engine never missed a beat - all other indications were green.
Newer fuel pump, aux pump not on switch and was running when I shut down.
Winter premium gas - I departed up north with about 14 gals at 8100' DA - the run up and takeoff all had the usual 5.5 PSI showing. It was pretty warm yesterday.
By the time I landed in the valley, it was showing a more normal 3-4 PSI
I'm thinking the winter gas and higher altitudes maybe caused some vapor issues and filled it up with 100LL.
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I'm thinking, your thinking is a good possibility.
__________________
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.
Scott McDaniels
Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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05-04-2016, 10:44 AM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,516
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Quote:
Originally Posted by rvbuilder2002
I'm thinking, your thinking is a good possibility.
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Yeah, I'm thinking what you are thinking, too.
So, who is buried in Grants Tomb anyway.
__________________
Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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05-04-2016, 10:56 AM
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Join Date: Dec 2011
Location: Hackettstown, NJ
Posts: 459
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Similar observations...
I seem to see this same fuel pressure behavior in both the spring and in the fall. On this past weekend when descending from altitude (8,500 over NYC) the pressure began to fall in the yellow range. Never into the red this time but last fall it did once or twice. No issues over the winter or during summer flying if I recall. Assume with the warmer weather and with local premium gas still mixed with winter blends, that is causing these temporary low readings this time of year. Usually clears up after several "long" minutes. Engine etc... all operate normally. Just really don't like anything on my engine monitoring page to show up yellow.
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05-05-2016, 01:55 AM
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Join Date: May 2013
Location: Westerville, OH
Posts: 155
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trick question
Quote:
Originally Posted by BillL
Yeah, I'm thinking what you are thinking, too.
So, who is buried in Grants Tomb anyway.
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IIRC, it's a trick question because the answer is not completely obvious: Mr & Mrs. Ulysses S. Grant. 
__________________
David B. Hill
N76012
RV-12 #0760
Dues paid through 6-2021
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05-05-2016, 06:01 AM
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Join Date: Sep 2011
Location: Paraburdoo Western Australia
Posts: 52
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Fuel and fuel pressure problems
Hi Guys,
During the early 25 hour phase of flight time (Early summer so 35-40Deg ambient temps) i also experienced low fuel pressure alarms at higher altitudes but mainly with the electric pump off, (Yes i have a fuel pump switch and glad i have) so I turned the electric pump back on and accepted it would most possibly be vapour lock caused by high temps and altitude.
After a PM exchange with wingedfrog he suggested it may be a good idea to share my experiences on the forum also.
I raised the following questions with him.
I am not concluding my experience and remedy below will necessarily address other peoples issues, just sharing my findings and experiences for other to consider.
- Are you sure the mechanical pump failed?
- How did you confirm it had failed?
- What fuel brand and Octane rating are you using?
- Have you tried to run the engine again with the same fuel pump in a lower ambient temperature?
- Have you drained and refilled the fuel tank with fresh fuel?
The reason for my list of questions is i have experienced the same symptoms as your self, only i was off the ground in climb out off a short strip without enough room to land again on the remaining strip or suitable landing options or sufficient height to turn back both times, before i identified and remedied the problem!
The remedy was to add a minimum of 30% avgas to the fuel tank in hot weather.
Both times ambient temperature was over 35deg C airfield elevation 1,460' (electric pump on)
First sign of a problem was a strong fuel odour immediately followed by partial loss of power and low fuel press alarm. My reaction was to first turn off electric fuel pump,(Because of the strong fuel odour and fear of fire) the engine regained power then started to loose power again along with low fuel pressure warning, so it was electric fuel pump on and off to keep the engine running without flooding to level off get some increased airflow to cool engine bay and get some landing options. Next morning and days following in the cooler temperatures, i could not get the problem to reoccur. Another hot day weeks later a repeat of the same problems occurred. (during the flight prior, i noticed fuel pressure fluctuations with the electric pump off and to a much lesser degree with the electric pump on)
i had landed for a short break with engine shut down, then restarted and departed for the home field when the partial power loss occurred.
My local and only service station in the town was having difficulty with their 95 Octane fuel pump, we could only get fuel early in the morning when the temperatures were cooler. (I only realised the significance of this after the problems occurred)
I suspect they were still selling winter fuel, now in the summer due to low fuel volume sales turnover.
After the first power loss i dismantle the Carburettors looking for problems as to why i got the fuel smell, bowles were clean, floats weighed in correctly. Fuel pressures rechecked, fuel flow re-checked, fuel pump was only 30 hrs old and no sign of fuel from the pump telltale drain pipe.
After the second time and lots of research about fuel and the effect of variations in the Reid vapour pressure due to fuel blending for summer and winter fuels, i drained the fuel tank and refilled with 100% avgas 100. I picked a day over 40deg (plenty of those during the summer here) with delayed takeoff until temperatures were in the Yellow caution area, there was no issue. (My home strip is 2 km long, i had a plan and options)
After landing and allowing the plane to sit and heat soak for 15 mins with very high under cowl temps, the exercise was repeated with no problems, with the electric pump on or off the fuel pressure remained stable. I then experimented with different % Avgas/ULP mix down to 30% Avgas with no further problems in the hot weather. I now run with an Avgas/Ulp mix in the hotter weather with no further issues.
Cheers, Andrew.
__________________
Andrew
RV 120573
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05-06-2016, 09:22 AM
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Join Date: Apr 2010
Location: Ridgeland, SC
Posts: 2,589
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Fuel Pressure Issues
For all the RV12 Rotax members that may be having some fuel pressure issues, we'd like to talk to you. You can email me at tsflightlines@gmail.com or steve@aircraft specialty.com.
Tom
__________________
Tom Swearengen, TS Flightlines LLC, AS Flightlines
Joint Venture with Aircraft Specialty
Teflon Hose Assemblies for Experimentals
Proud Vendor for RV1, Donator to VAF
RV7 Tail Kit Completed, Fuse started-Pay as I go Plan
Ridgeland, SC
www.tsflightlines.com, www.asflightlines.com
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05-06-2016, 09:38 AM
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Join Date: Oct 2012
Posts: 421
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[quote=AJSWA;1076394....After landing and allowing the plane to sit and heat soak for 15 mins with very high under cowl temps, the exercise was repeated with no problems, with the electric pump on or off the fuel pressure remained stable. I then experimented with different % Avgas/ULP mix down to 30% Avgas with no further problems in the hot weather. I now run with an Avgas/Ulp mix in the hotter weather with no further issues.
Cheers, Andrew.[/QUOTE]
Thanks Andrew (and all) - I think that might be it, the heat soaked part perhaps with the weaker winter gas. Certainly the pressure doesn't drop to zero, but seeing it struggle in the low 2's raises some concerns. 100LL is cheaper these days (i think I filled up at 3.73/gal), so it might be worth just using that during these transition to heat times.
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05-06-2016, 10:24 AM
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Join Date: Nov 2014
Location: Hinckley, Ohio
Posts: 2,065
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I don't know if Arizona has winter gas because not much seasonal temp change. Auto fuel gets reformulated twice a year when temps change in the spring and fall. The winter formulation allows better vaporization at lower temps which makes for easier engine starting in cold weather. Vapor lock would be more prevalent using winter gas in warmer temps.
__________________
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Jim Stricker
EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 622 
LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father & CFI) - USAAF 1st Lt. Captain B-17H
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05-06-2016, 03:35 PM
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Join Date: Feb 2010
Location: Perth, Western Australia
Posts: 1,647
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Maybe worth noting that Australia uses RON octane ratings not AKI, so our 95 RON is 90-91 AKI. 91 RON is 87 AKI. Many service stations also have 98 RON or 93-94 AKI, but it's generally less available in country areas.
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rgmwa
RV-12LR 912ULS
120346
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