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  #1  
Old 04-24-2021, 02:42 AM
Piper J3's Avatar
Piper J3 Piper J3 is offline
 
Join Date: Nov 2014
Location: Hinckley, Ohio
Posts: 2,465
Default What I don’t understand…

Shutting off electric fuel pump. This is being discussed in several threads again, so let’s just have the debate right here and now.

Rotax Installation Manual, and yesterday, the Vice President - Chief Engineer at Van’s Aircraft, are adamant about running electric fuel pump 100% for purpose of preventing vapor lock.

Can someone explain why they have elected to shut off electric fuel pump? Please explain in technical terms and not feels-good-to-do language. Please be specific and technical.

It is very hard for me to understand this behavior. It parallels what is happening now in this country with COVID vaccine reluctance. When something is proven effective, has scientific basis, explained well to the end user, with imminent danger if not followed – people are sticking their fingers in light sockets.

I experienced vapor lock several weeks ago and never want to have it happen again. I started a specific thread to discuss mitigation and now I read how happy people are to flaunt manufacturer’s advice on a safety related issue.

-----------

Please read once again Van’s Aircraft – Rian Johnson, Vice President Chief Engineer:

To put an end to all of this discussion the main reason that there is a fuel pump in the RV-12 is to prevent vapor lock. Although some may not have an issue with the pump turned off, they may not be operating at a fuel type or density altitude that will cause an issue. Others may follow your lead and have an engine failure. There are multiple reports (that I know of) of pilots turning off the pump after reaching pattern altitude and experiencing partial power loss. The pump has been placed close to the tank to provide pressure all the way to the engine thus reducing the chance of vapor lock as the fuel passes through valves and gascolators (which may be points of cavitation/pressure drops where vapor can form) or heated fuel lines on its way to the engine.

A Rotax is not a Lycoming therefore do not add a switch to operate the aircraft in a similar manner. The pump needs to run all the time.

Next about checking the engine-driven pump. When you turn on the aircraft the fuel pressure will rise to a steady-state level. When the engine comes on the fuel pressure will rise to a higher level letting you know that the engine-driven pump is working.

What amazes me is why anyone would not want the electric pump running all the time? The pump is designed to be running all the time. These pumps will last for years and years and are only $40. Are people really risking their lives to save $40 over a period of 15 years (approx how long mine lasted on my RV-7) ... that is $2.67 per year. Not even a gallon of gas or a gallon of milk these days.

My main mission at Van's is to ensure that each and every one of you is safe. Let's do the right thing here and please just leave it running.

Rian Johnson
Van's Aircraft
Vice President Chief Engineer
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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 685

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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  #2  
Old 04-24-2021, 03:32 AM
Avanza Avanza is offline
 
Join Date: Jul 2020
Location: Vastervik Sweden
Posts: 57
Default Electric fuel pump.

To begin with, people have different knowledge and experiences.
We see the same things but interpretes it differently.
On a certified aircraft there is a requirement to have two fuel pumps with
separate power supply. Often there is a mecanical and an electric pump.
Recomendations from manufacturers are allmost allways made to protect them from liability. So some people read them in that context.
Both Vans and Rotax recomends an electric fulpump in addition to the mecanical. Vans recomends it to be usead at all times, Rotax does not say
when to use it. Building your own aircraft, you are the manufacturer and
the construction may be different from other aircraft.
You may be a piano teacher or an engineer by profession and have 10 hours or 2000 hours of experience. This results in different pilot decitions.
If the engine lose power and this is because of fuel starvation this can lead to
an accident if not corrected. If having no experience of switching fuel tanks
hearing the engine stumble, this may seem frightening for some people.
For others its buisiness as usual.
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  #3  
Old 04-24-2021, 06:17 AM
DaleB's Avatar
DaleB DaleB is offline
 
Join Date: Sep 2012
Location: Omaha, NE (KMLE)
Posts: 2,320
Default

I know a lot of stuff about a lot of things. I don't know everything about everything. I don't feel compelled to make my RV-12 more like some other airplane "just because" that's what was done on a different airplane, with a different engine and a different fuel system. I figure I'll give the designers of the airplane credit for having some clue what they were doing.

The guy who built my plane put a push-pull breaker in line with the fuel pump wiring, right next to the fuel valve. I removed it and spliced the wires. never did see a point to it, and it was just one more potential point of failure. The thing runs just fine with the electric pump on, thanks.
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  #4  
Old 04-24-2021, 09:21 AM
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Tony_T Tony_T is offline
 
Join Date: Dec 2008
Location: Lacey, WA
Posts: 1,413
Default

When Rian resurrected the 10 yr old boost pump switch thread yesterday, I recalled that I had several posts therein. I have to say that I have vacillated both for and against a separate fuel pump switch ever since then. At that time I decided not to install the switch for the reasons that Van’s states, but it still rankles me that I have to pull the pump fuse to do a database update or other maintenance on avionics. Data base updates come once a month if you care to do them, that relates to a lot of fuse pulls.

To me, a Master Switch controls power to all the system switches. But in the -12 it also is activates the fuel pump system. Overall, I am Ok with that and have been just been pulling that darn fuse when I need to do something on the avionics like put in some user frequencies on the GTR 200 or change a setting on the SV. More than once I have started the airplane to go flying with the fuse removed.

All that being said, I don’t see much harm at all in having a switch as long as it is a “proper” switch. Kind of like the British building a “proper” bridge in the Alec Guinness movie.

If employed, the switch should be in plain sight and have a visual indication that it is ON, like all the other switches on the -12 panel. There should be a line item for it “ON” in the pre-start checklist.

So, I don’t have a switch for the fuel pump, except the one sitting on my workbench and never installed. I have been flying factory original for 11 years and loving it but hating having to pull that fuse for minor avionics ground work!
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E-LSA RV-12 ULS
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Last edited by Tony_T : 04-24-2021 at 09:29 AM.
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  #5  
Old 04-24-2021, 10:12 AM
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rcarsey rcarsey is offline
 
Join Date: Jul 2012
Location: North Brunswick, NJ
Posts: 245
Default

I don't mean to be non-technical here. I think the issue stems from initial private pilot training. In most (all?) of the low-wing planes that people are taught in, the electric fuel pump is only used in critical phases of flight. Perhaps that carries over into other planes people end up flying ?

That said, the RV-12iS (more specifically the Rotax 912iS engine) has two electric pumps (no mechanical) and they both have switches. Are there any iS pilots who don't use both, always?
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RV-12iS (N713) / Completed 12/2020
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  #6  
Old 04-24-2021, 10:24 AM
John-G John-G is offline
 
Join Date: Jan 2012
Location: Northeast Ohio
Posts: 757
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Quote:
Originally Posted by Tony_T View Post

All that being said, I don’t see much harm at all in having a switch as long as it is a “proper” switch. Kind of like the British building a “proper” bridge in the Alec Guinness movie.

If employed, the switch should be in plain sight and have a visual indication that it is ON, like all the other switches on the -12 panel. There should be a line item for it “ON” in the pre-start checklist.
I agree ... and although I do have a panel mounted fuel pump switch, I NEVER fly with it switched off. It is a line item in the pre-start checklist. I only turn it off while performing SkyView updates, sifting through SkyView menus or while programming frequencies in the GTR200.

For those of us running auto fuel subject to winter RVP changes, I feel it is especially important during the spring and fall to make sure the fuel pump is running during the entire flight as clearly stated by Van's Aircraft. Flying with high RVP fuel during warm days is NOT a good mix ... so keep that fuel circulating (and spike it with 100LL if it is a really warm day).
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http://www.dogaviation.com/

RV-12 Wings, Empennage, Fuselage, Finishing, Avionics and Powerplant kits all completed
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Donation paid until September 2021

Last edited by John-G : 04-24-2021 at 10:27 AM.
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  #7  
Old 04-24-2021, 10:45 AM
seagull seagull is offline
 
Join Date: Dec 2019
Location: San Bernardino
Posts: 341
Default

Quote:
Originally Posted by Piper J3 View Post
It is very hard for me to understand this behavior. When something is proven effective, has scientific basis, explained well to the end user, with imminent danger if not followed – people are sticking their fingers in light sockets.
....says the guy who wants to put privy vents in his cowl and is insulating the fuel lines.

......you knew that was coming.............
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  #8  
Old 04-24-2021, 11:07 AM
sailvi767 sailvi767 is offline
 
Join Date: Sep 2010
Location: Charlotte NC
Posts: 1,323
Default

It’s kind of like Convective activity. People ducking underneath dodging rainshafts or using data link to dodge buildups always state they have done it hundreds of times without a issues. Those that do end up having a issue often are not around to write about it.
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  #9  
Old 04-24-2021, 11:14 AM
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jrtens jrtens is offline
 
Join Date: Apr 2018
Location: Utah
Posts: 185
Default

Quote:
Originally Posted by rcarsey View Post

That said, the RV-12iS (more specifically the Rotax 912iS engine) has two electric pumps (no mechanical) and they both have switches. Are there any iS pilots who don't use both, always?
The 12iS pumps are switched for two reasons. First, you have to be able to check each one individually before flight. Second, only one pump is used for starting to reduce the electrical load.

Vans warns to never operate in flight with only one pump on for the obvious reason that if the sole operating pump fails the engine will quit.

I'm sure there are pilots who think shutting one down during cruise will save pump life. However, since the one operating pump has to carry the entire load, it is working harder than it would with both pumps running - most likely shortening pump life.
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  #10  
Old 04-24-2021, 01:14 PM
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flytoday flytoday is offline
 
Join Date: Jun 2011
Location: Houston, TX
Posts: 441
Default

Quote:
Originally Posted by Piper J3 View Post
It is very hard for me to understand this behavior. It parallels what is happening now in this country with COVID vaccine reluctance. When something is proven effective, has scientific basis, explained well to the end user, with imminent danger if not followed – people are sticking their fingers in light sockets.
RV12 info and debate is interesting. Is this opinion paragraph about medicine VAF appropriate?

I fly an -A model, some pilots choose tailwheel planes. Riskier? Some choose to decline flights in experimental planes like RVs and some refuse experimental medicine. Maybe we all touch light sockets when we get out of bed? Freedom!

Carl
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RV7A - purchased flying 05/2020
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