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04-22-2016, 09:21 AM
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Join Date: Apr 2008
Location: Great Falls, Montana
Posts: 84
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Quote:
Originally Posted by Tony_T
I can't believe how many people change the design of the RV-12 fuel system by installing a switch and then don't use a checklist to be sure it is ON for takeoff. This would not look good on an NTSB report.
Is there any question why Van's did not include this switch in the design of the RV-12?
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I agree that Van's should not install a fuel pump switch in their design. Their Job is to make the design as idiot proof as possible. That being said, I have a fuel pump switch. My reasons are that when working on the plane with the master switch on, the fuel pump is always on. If I pull the fuse, it also cuts off the avionics cooling fans, which I do not want. In the advent of an alternator failure, I like to be able to shed every thing except my comm radio. If the facet fuel pump fails, I want to be able to shut it off. Yes, and I do have a checkist
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04-22-2016, 09:28 AM
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Join Date: Sep 2012
Location: Omaha, NE (KMLE)
Posts: 2,247
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Quote:
Originally Posted by Tony_T
Is there any question why Van's did not include this switch in the design of the RV-12?
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Well... they did, actually. In the design, but not in the finished product. If you look at the wiring diagram for the older D180 setup, there is a switch position for the fuel pump. At some point before production the switch was deleted, and the pump run directly to the fuse. I verified that there is an empty switch position on my PCB for the pump. It's set up for the same lighted switch used for the ignitions. All you'd need to do, I believe, is cut the hole in the face plate, solder in the switch and move the fuel pump wire from one connector pin to another. In fact that's what I had planned to do.
So why am I not doing it? I suspect for the same reason Van's deleted the switch in the first place. I can't think of a compelling reason to do have it there. I see no problem leaving the pump running in flight, since Van's decided to make it that way and hundreds of RV-12s are flying just fine that way. I do want to be able to shut the thing off while doing maintenance on the ground with the master on -- there's a fuse, and the builder also installed a breaker next to the fuel valve.
It's a cheap automotive fuel pump, not a $900 Weldon certified part. If it quits I'll replace it. It's one less checklist item to worry about. I don't really mind the extra breaker being there -- it would be pretty much impossible to accidentally turn it off -- but it's just not worth the hassle of installing the switch for no real advantage that I can see.
And from what I have seen and read, I trust that mechanical fuel pump about as far as I can throw the whole plane.
__________________
Dale
Omaha, NE
RV-12 # 222 N980KM "Screamin' Canary" (bought flying)
Fisher Celebrity (under construction)
Previous RV-7 project (sold)
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04-22-2016, 09:30 AM
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Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,035
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Quote:
Originally Posted by WingedFrog
This is a good point and I would expect these steps to be part of the official Checklist by VANs.
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It is.
First step on the engine start page of the check list says
"Fuel Pressure - NORMAL"
__________________
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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04-22-2016, 10:45 AM
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Join Date: Mar 2010
Location: Raleigh, NC
Posts: 863
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Quote:
Originally Posted by rvbuilder2002
It is.
First step on the engine start page of the check list says
"Fuel Pressure - NORMAL"
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In my case, the fuel pressure was NORMAL when starting first (after a 1:30 flight and a 3 hours stop) and during taxiing. It was normal during run-up and until about 10 sec. after I went full throttle (I was not looking at the fuel gauge during takeoff run until I got the audio alarm so it might have started going down a bit earlier). Taxiing back to the ramp it went back to normal. After stopping the engine and restarting it to make further troubleshooting fuel pressure was normal even with the electric pump off. In the fake run-up at 4000 rpm pressure looked normal for about 5 seconds then started going down, 2 to 3 seconds later the audio message came and after another 2 to 3 seconds the engine gave the first sign of fuel starvation. All these figures are from memory and might be off a bit but not much. Of course, with the electric fuel pump on fuel pressure would have looked even more normal...
One question, Scott, about the decision Vans made to not provide a switch: are there other LSA manufacturers who made the same choice?
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04-22-2016, 10:53 AM
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Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,035
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Quote:
Originally Posted by WingedFrog
In my case, the fuel pressure was NORMAL when starting first (after a 1:30 flight and a 3 hours stop) and during taxiing. It was normal during run-up and until about 10 sec. after I went full throttle (I was not looking at the fuel gauge during takeoff run until I got the audio alarm so it might have started going down a bit earlier). Taxiing back to the ramp it went back to normal. After stopping the engine and restarting it to make further troubleshooting fuel pressure was normal even with the electric pump off. In the fake run-up at 4000 rpm pressure looked normal for about 5 seconds then started going down, 2 to 3 seconds later the audio message came and after another 2 to 3 seconds the engine gave the first sign of fuel starvation. All these figures are from memory and might be off a bit but not much. Of course, with the electric fuel pump on fuel pressure would have looked even more normal...
One question, Scott, about the decision Vans made to not provide a switch: are there other LSA manufacturers who made the same choice?
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The NORMAL that step in the check list is checking for is performance of the electric pump prior to cranking the engine for start. Thus evaluating the performance of the electrical pump. After engine start the performance of the engine driven pump is noted by seeing the pressure rise because of both pumps now operating.
I don't know what other low wing LSA's have done (high wing wouldn't typically use a second pump).
__________________
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 ")
Last edited by rvbuilder2002 : 04-22-2016 at 10:57 AM.
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04-22-2016, 10:55 AM
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Join Date: Oct 2012
Posts: 421
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Quote:
Originally Posted by engineerofsorts
Every time I post engine-related problems, I generally get negative points for "excess display of ignorance", but the symptoms sound much like my problems which I attributed to vapor lock problems:
Our plane has the stock fuel pumping scheme--electric pump always on.
After flights with 20-30 minute intervals between flights, (Young Eagle Flights) we experience power failure either on run up or takeoff.
The fuel pressure drops into the low yellow range (would have to confirm exact values).
Engine runs extremely rough--indicating one carb is starved.
Problem is solved by keeping the electric fuel pump running, and cutoff valve opened, oil check door open for air circulation.
Problem occurs during cool months, when high vapor pressure Mogas is used.
No problem during long, multi-hop cross country flight to Oshkosh using summer (low vapor pressure) Mogas.
I'm fixin to instrument a few thermocouples on the carbs/mechanical fuel pump, etc., to further investigate/characterize this.
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I think this is exactly right. The main purpose of that electric pump is to prevent vapor lock.
That RV-12 engine compartment gets pretty dang hot.
In fact I have gotten into the habit to use 100 LL as I approach the summer months solely to help mitigate this problem of crappy winter gas and high outside ambient temps.
If an engine driven fuel pump outright fails, the engine will fail.
I suppose there is some kind of engine driven pump failure that will still allow an electric pump to flow fuel to the engine at some reduced power setting possibly, but unlikely due to how the pump is designed.
And I love how every systems book says gravity feed of fuel is possible! Not.
Ask me how I know.
Last edited by cactusman : 04-22-2016 at 11:05 AM.
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04-22-2016, 11:06 AM
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Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,035
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Quote:
Originally Posted by cactuspilot
If an engine driven fuel pump outright fails, the engine will fail.
I suppose there is some kind of engine driven pump failure that will still allow an electric pump to flow fuel to the engine at some reduced power setting possibly, but unlikely due to how the pump is designed.
And I love how every systems book says gravity feed of fuel is possible! Not.
Ask me how I know.
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There have already been failures of engine driven pumps on 912 powered airplanes where an aux. pump has aided in providing adequate fuel flow to keep the engine running normally.
All of the engine driven pump failures that I am aware of have not been catastrophic failures. They have caused a degradation in pumping performance that generally gives strong signs of something not being right (If the pilot pays attention).
Gravity works fine for fuel delivery in airplanes.... as long as the system is designed correctly.
__________________
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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04-22-2016, 11:20 AM
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Join Date: Oct 2012
Posts: 421
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Quote:
Originally Posted by rvbuilder2002
There have already been failures of engine driven pumps on 912 powered airplanes where an aux. pump has aided in providing adequate fuel flow to keep the engine running normally.
All of the engine driven pump failures that I am aware of have not been catastrophic failures. They have caused a degradation in pumping performance that generally gives strong signs of something not being right (If the pilot pays attention).
Gravity works fine for fuel delivery in airplanes.... as long as the system is designed correctly.
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If the engine driven pump's actual failure condition can keep allowing fuel to continue to flow to the engine, I would agree that is possible.
In my two experiences, the engine driven pumps failed on turbofan engines and all 6 electric pumps were providing fuel pressure, but the fuel wasn't able to get to the engine, this being a different design than the Rotax 912 system, comparisons are hard and one can watch the early 912 fuel pump mx videos that were put out on EAA by Rainbow for more info on that design and the problems that can arise.
http://eaavideo.org/video.aspx?v=4457527542001
In the event of a catastrophic engine driven pump failure on any engine that won't allow the fuel through to the engine, I think you are in big trouble.
Last edited by cactusman : 04-22-2016 at 11:43 AM.
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04-22-2016, 11:34 AM
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Join Date: Oct 2012
Posts: 421
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04-22-2016, 11:44 AM
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Join Date: Nov 2013
Location: Prescott, AZ
Posts: 1,614
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I should have been more specific when I said you were lucky. I meant when the problem presented itself, you were in a good position to abort. I know planning is what we all do. But, failures won't go according to plan. I have crashed with an onboard fire and crashed with an engine failure. I always have a plan... but I still credited part of my survival to good fortune.
Anyway, I am sure you are doing your best to pick operating procedures to insure safe flight. Have a great weekend. nc
__________________
"Kindness is never a bad plan."
exemption option waived. Donation appropriate.
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