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  #11  
Old 12-26-2018, 09:28 AM
John C's Avatar
John C John C is offline
 
Join Date: Mar 2005
Location: Moundridge, KS
Posts: 149
Default Two Facet Pumps?

Scott, I am comfortable with the one electric pump.

It appears that the cavitating pump is still pushing sufficient fuel, even though the fuel pressure is low. The Bing carbs can likely work with very low pressure as long as the fuel flow is 2.5 gph.

While playing with the pressure issue, I inadvertently made a series of 3-4 takeoffs with the c/b pulled. The fuel pressure did not dive. Go figure. I don't remember having a pressure drop with the c/b pulled. Also, others have added a switch for the Facet pump. I suspect others have either left the c/b pulled or left the switch off for takeoff. Wonder what they saw.

The 4th graph shows the fuel flow as very good even though the pressure was in the 2s. I never saw a lessening of fuel flow. If the fuel flow was taking a hit, I would be worried.

Also,the pressure recovers very quickly by simply leveling off a bit and pulling the throttle a bit. For example lower the nose 5 degrees from the climb angle and pull back to 4000 rpm for a second or two.

Jim, on your other post, you experienced vapor lock. Was that on initial start up and taxi or on takeoff. I can see where pumping 1.5 gph cool fuel through the system before start would cool the entire fuel circuit. But once up and running, the system is pumping 4-5 gph keeping the system cool. ((1.5 gph for the restrictor and whatever the engine is using at idle, 3 gph perhaps))
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John Clark
Moundridge, KS
RV-9A 90512 N6699 Sold
RV-12 120323 N6699Z 410 hours
dues paid 2018

Last edited by John C : 12-26-2018 at 09:31 AM. Reason: fix names
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  #12  
Old 12-26-2018, 09:44 AM
RFSchaller RFSchaller is offline
 
Join Date: Oct 2010
Location: Phoenix, AZ
Posts: 2,459
Default

I have a switch. The lowest Iíve seen without cavitation on just the mechanical pump is just above 3 psi. With cavitation in hot Phoenix summers fuel pressure has taken a nosedive, but recovered to >3 psi when I turned on the pump.
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  #13  
Old 12-26-2018, 09:45 AM
RFSchaller RFSchaller is offline
 
Join Date: Oct 2010
Location: Phoenix, AZ
Posts: 2,459
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I have a switch. The lowest Iíve seen without cavitation on just the mechanical pump is just above 3 psi. With cavitation in hot Phoenix summers fuel pressure has taken a nosedive, but recovered to >3 psi when I turned on the pump.
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  #14  
Old 12-26-2018, 01:54 PM
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Piper J3 Piper J3 is offline
 
Join Date: Nov 2014
Location: Hinckley, Ohio
Posts: 1,384
Default

Quote:
Originally Posted by John C View Post
Jim, on your other post, you experienced vapor lock. Was that on initial start up and taxi or on takeoff. I can see where pumping 1.5 gph cool fuel through the system before start would cool the entire fuel circuit. But once up and running, the system is pumping 4-5 gph keeping the system cool. ((1.5 gph for the restrictor and whatever the engine is using at idle, 3 gph perhaps))
John

Vapor lock happened on the ground after restarting hot engine that sat for about 15 minutes. There are many threads in this forum discussing the merits of the electric fuel pump. Vanís recommends running the electric pump all the time - itís very good adviceÖ
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Jim Stricker
Hinckley, Ohio (1OA2)
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
RV-12 E-LSA #120058 AWC July 2012 N633CM
RV-12 Bought Flying Oct 2015 with 48TT - Hobbs now 441

LSRM-A Certificate 2016
Special Thanks... EJ Trucks - Crew Chief A-4 Skyhawk
and MJ Stricker (CFI) - 1st Lt. Captain B-17H
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  #15  
Old 12-26-2018, 02:14 PM
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scottmillhouse scottmillhouse is offline
 
Join Date: Apr 2007
Location: Madison, AL
Posts: 278
Default My experience

I also had low pressure issues on take off but only with full fuel. I had just the tank vent. Added the vent in gas cap with the idea that with full fuel take off angle may have fuel blocking the vent. Never had a problem since I drilled the hole in the fuel cap in over 250 hours. Coincidence or solution?
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New RV-7A N579RV is inspected and now an airplane- first flight soon
RV-12 N319RV 1st flight 12/2015, now over 300 hours.
Purchased RV-12 sold, RV-9A- 536 hours sold, RV-7 sold, Kitfox sold
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  #16  
Old 12-26-2018, 02:19 PM
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John C John C is offline
 
Join Date: Mar 2005
Location: Moundridge, KS
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Default

Quote:
Originally Posted by Piper J3 View Post
John

Vapor lock happened on the ground after restarting hot engine that sat for about 15 minutes. There are many threads in this forum discussing the merits of the electric fuel pump. Vanís recommends running the electric pump all the time - itís very good adviceÖ
I agree with you.
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Moundridge, KS
RV-9A 90512 N6699 Sold
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dues paid 2018
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  #17  
Old 12-27-2018, 05:24 PM
ben barron ben barron is offline
 
Join Date: Sep 2013
Location: Fall City, WA
Posts: 118
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Quote:
Originally Posted by scottmillhouse View Post
I also had low pressure issues on take off but only with full fuel. I had just the tank vent. Added the vent in gas cap with the idea that with full fuel take off angle may have fuel blocking the vent. Never had a problem since I drilled the hole in the fuel cap in over 250 hours. Coincidence or solution?
I reciently drilled a slightly larger hole in my gas cap after replacing the mechanical pump and sensor (without solution) and it seems to have solved my problem
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  #18  
Old 12-27-2018, 07:47 PM
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Piper J3 Piper J3 is offline
 
Join Date: Nov 2014
Location: Hinckley, Ohio
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Default

I have just the vent hole in the tank filler cap per Van’s original RV-12 design. My logic is that I run 93E10 exclusively and don’t want the filler neck vent because it would provide too much air exchange in the tank when the airplane is sitting for extended periods.

Unlike Avgas, the octane will degrade in 93E10 if subjected to the atmosphere. Also the alcohol in the fuel is hydroscopic and will suck moisture out of the air.
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Jim Stricker
Hinckley, Ohio (1OA2)
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
RV-12 E-LSA #120058 AWC July 2012 N633CM
RV-12 Bought Flying Oct 2015 with 48TT - Hobbs now 441

LSRM-A Certificate 2016
Special Thanks... EJ Trucks - Crew Chief A-4 Skyhawk
and MJ Stricker (CFI) - 1st Lt. Captain B-17H
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  #19  
Old 01-06-2019, 09:27 PM
Charlie12 Charlie12 is offline
 
Join Date: Oct 2014
Location: Port Orange FL
Posts: 21
Default short surges of low fuel pressure

I installed the later-design fuel tank vent line, so that is not an issue. I also added an on/off switch for the electric fuel pump, at the recommendation of instructor in my Rotax iRMT class. For two years and 175 hours I have routinely used the electric pump only for takeoff and landing and have no recollection of fuel pressures low enough to be any concern. For no apparent reason on a flight a few days ago (81 deg F ambient) I had a couple brief instances of fuel pressure low enough to trigger the audio warning, 2 psi, when the electric pump was off. One instance was at cruise, one was taxiing at the end of a 1.5 hour flight. No apparent change in engine operation. Turning on the electric pump made the pressure immediately jump back to around 5 psi.


Today I carefully did three full stop and taxi back trips around the pattern with the electric pump on and the fuel pressure stayed around 5 psi at all times. This included takeoff climb at 5200-5300 RPM. I need to experiment with this some more, and will study JC's data carefully. But for now my guess is that there is a possibility of inconsistent engine-driven pump operation due to placement of the tank unusually far aft, which would explain why the kit does not provide a switch for the electric pump. I plan on leaving mine on all the time from now on, or at least until I get a clearer understanding of what is happening.
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  #20  
Old 01-07-2019, 03:15 AM
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Piper J3 Piper J3 is offline
 
Join Date: Nov 2014
Location: Hinckley, Ohio
Posts: 1,384
Default

Quote:
Originally Posted by Charlie12 View Post
I also added an on/off switch for the electric fuel pump, at the recommendation of instructor in my Rotax iRMT class.
Did Rotax maintenance instructor say why he recommended shutting off electric fuel pump? Seems to me that he would have a good reason to tell someone to alter a safety feature designed by mfgr. I don't think I would want that liability...
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Jim Stricker
Hinckley, Ohio (1OA2)
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
RV-12 E-LSA #120058 AWC July 2012 N633CM
RV-12 Bought Flying Oct 2015 with 48TT - Hobbs now 441

LSRM-A Certificate 2016
Special Thanks... EJ Trucks - Crew Chief A-4 Skyhawk
and MJ Stricker (CFI) - 1st Lt. Captain B-17H
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