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  #1  
Old 01-19-2021, 10:32 AM
Richard RG Richard RG is offline
 
Join Date: Jan 2021
Location: British Columbia, Canada
Posts: 23
Default New to the forum, long intro, fuel system question

Greetings all,
Little did I know the resources available to a new RV owner. Amazing! I've searched high and low in the various forums and not able to find a definitive answer to my question. Please bare with me while I give a little back ground leading up to my question (s).
Late in the summer of 2020 I became the proud owner of an especially well built RV3b, ident C-GBGF and completed in 2009. I purchased the RV3 from the widow of the craftsman that built it, her husband and builder having died in his C-172. He was flying off the west coast of Vancouver Island, British Columbia, gathering weather information data for NOAA.
The RV3 was his third RV build. His lovely widow knew nothing of the RV3, but after a 5 hour inspection by both myself and a very competent Aircraft Maintenance Engineer (AME) determined the aircraft to be exceptionally well put together and seemingly, strictly built to Vans construction plans.
Having zero tail wheel time when I bought the RV3, discovered its not so easy to get transition training. Fast forward 5 months... I finally got 1.1 hours in an RV6, with a most excellent instructor. I think we spent a bit more of that time doing aerobatics, rather than figuring out how to taxi and land.
During the taxi training phase of my 1.1 hours, discovered the RV6 was a lot more manageable than the RV3, which I had taxied around a number of times. Upon return to home base from my first tail wheel adventure, quickly determined that the tail wheel assembly was pretty much worn out on the RV3. More weeks passed, waiting for the new tail wheel assembly to arrive and install.
Once the RV3 was good to go, intended to resume training in the RV6 but then discovered the left starting mag was dying in my C-150 aerobat, not to mention the transponder started giving me grief as well. The transponder is mandatory in order to fly to the RV6.
Yet more weeks pass and I'm itching to fly the RV, but paranoid about breaking it. Lucky for me, some airport friends took pity and volunteered I could use a Piper Tri-Pacer converted to tail dragger, to carry on learning how to manage a tail dragger.
A very brave and competent fellow jumped into the converted Tri-pacer with me and even more bravely, gave me the left seat with no brakes on his side. After 3 hours of flying around and doing a bunch of landings/takeoffs he announced that I should go fly the RV. I didn't necessarily agree with him, but threw caution to the wind and strapped into the little hotrod, lined up on the runway and with knees shaking, did the most horrendous takeoff I've ever done. I've got 900 hours total, 450 of that in a Mooney M20e and the rest in 150's.
That first takeoff was quite an eye opener! That little sucker has some serious get up and go and will not be nice to you if you pick the tail up real fast. I picked the tail up real fast and it was immediately doing a hard left... I ended up doing a bit of the wild thing down the runway using an awful lot of the 75' width and yep, I had a wee bit of an audience, of course.
Luckily, the RV3 gets in the air very quickly, so managed to get away quickly from my bad takeoff roll and the prying eyes of the seasoned pilots watching my performance. Happily, they didn't have their score cards handy that day. Scoring visiting pilots is a bit of a pass time at our 2400' runway. The Ukrainian judges as they call themselves have score cards that only go to 7, so don't feel bad if you get a 5 or 6.
After an hour of slow flight, some stalls and feeling the plane out, it was time to land. During my hour of feeling the plane out, I switched tanks after about a half hour. Same as the Mooney, always put the boost pump on during the switch and watch the fuel pressure. Boost pump off, watch the pressure.
My first approaches were intentional overshoots, several times. It certainly doesn't take much to execute an overshoot in a little airplane that weighs 821 Lbs, with a 160hp.
Satisfied with the overshoots ,was time to land. Sitting on the ground, I can see pretty much nothing looking forward. So, having memorized this sight picture before takeoff, knew that if my butt was almost dragging on the ground and I could see virtually nothing looking forward, I should be touching down very gently soon. Things worked out a little differently than I hoped. It seems that spring gear can be pretty springy, unless you set those springs down very gently. Apparently I wasn't gentle enough... after the second bounce that was about the same altitude as the first, thought things weren't going to get any better, so powered up and went around. That little RV does a go around really well!
Though I still bounce somewhat, after a grand total of twelve hours of flying the RV3, find that the airplane manages itself just fine if the stick is held full back and you keep it pointed straight. I've actually surprised myself with several greasers, but attribute that more to luck than skill.
Of course, after each flight I very carefully check and calculate fuel consumption because I have never trusted fuel gauges. Early in the process of monitoring the fuel burn, I was shocked a couple of times to discover that the Port tank had come up in level, rather than going down the expected amount. Further, the Starboard tank would be very much lower than expected. In my books, this is very odd and potentially hazardous to ones health and longevity.
Shortly after taking ownership of the RV I discovered that the lever attached to the fuel selector shaft was slightly loose. I applied locktite to the screw that attaches the fuel lever selector to the fuel selector shaft but still felt a small amount of play in this assembly. Looking closer, I could see a small amount of wear between the fuel lever selector socket face and the corresponding profile on the end of the fuel selector shaft. The aircraft has 840 hours on the airframe and likely the same hours on the fuel selector. It appears to be the selector that came with the kit, so have ordered a replacement from ACS and not nearly as expensive as the Andair unit.
When I discovered the unusual tank levels in the RV, suspected that the fuel valve was the culprit and some how cross feeding. It didn't make sense that the the Port (left) tank was always gaining level over the Starboard tank. Right from the first flight in the RV, my habit was to always begin flight with full tanks and always start up and run on the right tank, switching later in flight.
After my most recent flight, filled both tanks full and taxied back to the hanger. When I shut down, I had a pretty big puddle of fuel under the left tank vent. I opened the left tank cap and fuel overflowed from the tank. It finally became clear that something seriously strange was going on with the fuel system.
A close inspection of the fuel system revealed a return fuel line tied in off the main fuel supply line, immediately prior to the carburetor, . The previous owner had installed what appears to be a recirculation line off the fuel supply to the carburetor and is returned to the left tank only.
I am assuming such a line is installed to minimize the chance of vapor lock and also, helps to ensure cool fuel is being delivered to the engine.
My understanding is the previous owner may have used mogas/car gas. In the accident investigation related to his crash in the C-172 it was noted that there was a mix of avgas and mogas in his aircraft and carb ice may have been a contributing factor to the accident.
This recirculation line complicates managing fuel and at this time, I am trying calculate the recirculation rate. So far, I believe there is no restriction orifice in the recirculation line, as even after 40 minutes of drawing down the full left tank in flight and then switching to the right tank for 30 minutes, discover on the ground that the left tank is again full to the max.
At this time, I don't have plans to burn mogas after having had a fright in the Aerobat when using mogas. Very hot day in the Aerobat, climbing out over very inhospitable terrain and the engine starts dying, seriously no fun.
Fortunately, the Aerobat has a 150hp lycoming and requires a boost pump for this STC. The boost pump saved my bacon that day and have shied away from mogas ever since.
Am I on the right track assuming this return line is for vapor lock control? Can I install an isolation valve on this return line to the left tank and open only as required? Will shutting off this return line cause issues with the mechanical double diaphragm fuel pump attached to the back side of the Lycoming E2D?
Would I be better off to install a restriction orifice in the return line (if there isn't one) which should then allow a metered and easily measured amount of fuel recirculation?
Apologies for such a long post, just thought I'd give some back ground before putting my question out there. Any insights to managing my fuel in the safest manner possible, much appreciated!
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  #2  
Old 01-19-2021, 11:28 AM
Mike S's Avatar
Mike S Mike S is offline
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Join Date: Sep 2005
Location: Dayton Airpark, NV A34
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Default Welcome to VAF

Richard, welcome to VAF
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  #3  
Old 01-19-2021, 11:30 AM
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rv8ch rv8ch is offline
 
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Location: LSGY
Posts: 3,909
Default

Hi Richard, there are lots of different ways the builder may have set up the fuel system. It's great that you are asking for help. My recommendation is to find a good AME or even better another RV builder in the area to check it carefully with you and create a diagram and some operational processes for your fuel system.

There have been a lot of unnecessary tragic incidents due to fuel mismanagement, and the best way to avoid this is to really understand how your fuel system works from the gas caps to the exhaust pipes, and every part in between. Best of luck, and welcome to VAF!
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  #4  
Old 01-19-2021, 12:08 PM
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pierre smith pierre smith is offline
 
Join Date: Jan 2005
Location: Louisville, Ga
Posts: 7,908
Default No return line

Hi...and welcome,
I have flown behind many a Lycoming and only my fuel injected RV-10 had a fuel return line. None of the carb'd engines did. Seems like the builder may have had some so-so advice and added an unneeded return line. I can't see why it can't be eliminated and plugged.

Regards,
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  #5  
Old 01-19-2021, 12:12 PM
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DeeCee 57 DeeCee 57 is offline
 
Join Date: Sep 2018
Location: LSZF
Posts: 686
Default

Hi Richard, interesting story, sounds like a nice RV you got there And thanks for sharing.

Mickey has a good point, drawing a diagram of your fuel system is a good idea.

I will keep my comment to your question re the fuel system since my bird has one probably akin to yours... I'm sure others will jump in re the flying technique

Attached is a diagram of my system. As you mention, the return line was installed as a way of preventing vapour lock. As you can see, an expensive dual Andair fuel selector valve is being used. Which means the tank selected is also the tank were the fuel is returned. 3 fuel pumps, 2 elec and the engine driven one give good redundancy.

I usually keep the left tank on MOGAS, whilst the right is on AVGAS. Take-off and approaches/landing on the AVGAS, switching to MOGAS at safe altitude.

Hope it helps
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  #6  
Old 01-19-2021, 06:00 PM
Bicyclops Bicyclops is offline
 
Join Date: Oct 2012
Location: LA, California
Posts: 373
Default

Quote:
Originally Posted by pierre smith View Post
Hi...and welcome,
I have flown behind many a Lycoming and only my fuel injected RV-10 had a fuel return line. None of the carb'd engines did. Seems like the builder may have had some so-so advice and added an unneeded return line. I can't see why it can't be eliminated and plugged.

Regards,
+1 on eliminating the return line.

Even fuel injected Lycomings usually don't have a return line unless it is from a purge valve. This would not be operated in flight. It diverts fuel from before the injectors and will kill the engine. The Bendix style injection doesn't have a continuous return.

Ed Holyoke
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  #7  
Old 01-20-2021, 08:15 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 6,326
Default

I have return lines on both my planes and they are very helpfull after heat soaking (20 minute gas stop for example) in the summer with Mogas. I would not recommend an unrestricted return line. Mine have both a valve to actuate the return function, when needed and also have a .040" restrictor (approx 8-10 GPH @ 25 PSI, much less @ 5 PSI) to insure that the return cannot draw off more flow from the pump than is required to run the engine at full power, if the valve is accidentally left open.

I suggest either putting a valve on it (be sure it can handle 10 PSI) or remove and cap off the return.

Larry
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Last edited by lr172 : 01-20-2021 at 08:19 AM.
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  #8  
Old 01-20-2021, 11:00 AM
Richard RG Richard RG is offline
 
Join Date: Jan 2021
Location: British Columbia, Canada
Posts: 23
Default

Thank you for welcoming me to the forum, reading through my intro bordering on being a short novel and the feed back regarding my discovery of the fuel recirculation line.
As suggested by Pierre, the builder may have had so so advice on the return line, but having met the builder several years ago, struck me as being exceptionally knowledgeable, competent and certainly a very meticulous builder.
I'm not anxious to remove anything he has installed as I'm thinking a lot of thought went into anything he has done on the RV3. It would've been nice if there was a placard warning how to manage the fuel, or a POH that provide such information.
It would be nice to have a fuel system such as the one DeeCee 57 has installed, but would require significant mods to the RV3, add weight and complexity.
Currently, I am waiting for a replacement 4 port 3/8" fuel selector to arrive from ACS. Plan is to replace the fuel selector valve because I do not like the tiny bit of play in the connection of the fuel lever to the fuel selector shaft. Once the fuel tanks are drained, I will be checking for a restriction orifice in the recycle fuel line back to the left tank. I'm assuming if a restriction orifice is installed, will be located at the T connection off the fuel supply line at the carburetor? The normal fuel supply pressure is 3-5 psi so with any luck may find a restriction orifice that is .040" as Ir172 mentioned in his reply.
If there is no orifice, is this something that is DIY, or can be purchased?
I am not keen to do ANY changes to the fuel system, fully aware that fuel management/supply issues are right near the top of the list of things that hurt pilots and wreck airplanes.
With that in mind, I am considering installing an isolation valve in the return line, so if I ever wish to exercise this option, remains available. Though the fuel pressure is very low, any suggestions on a certified isolation valve, or a valve that is light weight and built to the highest standards?
With the fuel system drained and opened up will also be installing fire sleeve on fuel lines FWF.
Thanks so much for responses!
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  #9  
Old 01-20-2021, 12:30 PM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
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Default

Quote:
Originally Posted by Richard RG View Post
If there is no orifice, is this something that is DIY, or can be purchased?
I am not keen to do ANY changes to the fuel system, fully aware that fuel management/supply issues are right near the top of the list of things that hurt pilots and wreck airplanes.
With that in mind, I am considering installing an isolation valve in the return line, so if I ever wish to exercise this option, remains available. Though the fuel pressure is very low, any suggestions on a certified isolation valve, or a valve that is light weight and built to the highest standards?
With the fuel system drained and opened up will also be installing fire sleeve on fuel lines FWF.
Thanks so much for responses!
You definately want some type of restriction to insure that there is enough fuel to feed the engine at all times. Also want to limit the emptying of one tank into another, as you learned. First, clean out the inside of the AN fitting, including scraping off the anodizing. You can use JB weld to fill it in and then dill out to size. There is a risk that it breaks down and causes problems. Safer bet is to use a steel fitting and fill with an acid core solder (don't used your rosin core stuff) or silver solder and then drill out

You can find tools online that will give you a GPM rating based upon the inlet pressure and orifice size.
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  #10  
Old 01-20-2021, 08:22 PM
Richard RG Richard RG is offline
 
Join Date: Jan 2021
Location: British Columbia, Canada
Posts: 23
Default Fuel return line

Ir172,
Thank you for your reply and suggestion, re drilling out an orifice to 0.040 into JB weld applied to the interior of a prepared AN fitting of the fuel recirculation line. Though I've used JB weld, or Permatex metal epoxy in quite a few applications, think that it not wise to use this approach in an aircraft fuel system.
The thought of potential particulate breaking free of the JB weld is not appealing, due to fuel incompatibility or erosion, best case scenario being scoring of piston rings and cylinder walls. Worst case scenario, being blockage of gascolator or plugged jets?
I appreciate the feedback and am waiting (almost 2 months now) for ACS to deliver a new fuel valve. Hoping I might find a restriction orifice in the fuel return line to the left tank when I open up the fuel system. Thanks for taking the time to offer your suggestions.
Richard
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