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06-22-2017, 03:14 PM
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Join Date: Jul 2009
Location: Mojave
Posts: 4,652
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Quote:
Originally Posted by JonJay
Silly me . I thought this thread was about fuel selectors.
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It is. But even the plans sometimes violate established standards. No harm in questioning things - even Van the man.
Here's the deviation from the FAR often seen on Rockets (and maybe the -4?):
?23.995 Fuel valves and controls.
(g) Fuel tank selector valves must?
(1) Require a separate and distinct action to place the selector in the ?OFF? position; and
(2) Have the tank selector positions located in such a manner that it is impossible for the selector to pass through the ?OFF? position when changing from one tank to another.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Michael Robinson
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Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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06-22-2017, 03:23 PM
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Join Date: Oct 2006
Location: Foley, Al
Posts: 563
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I have to side with the OP. Couple of reasons.... 1) He's certainly an expert by most anyone's standards, certainly mine. 2) Why not "build out" any ANY potential gotchas and like he said they'll usually show their ugly head at the worst possible time.
The thought process of know your fuel system is of course important but at the same time, it's not a guarantee. Think of this... during one of the Saturn 5 rocket launches that took us to the moon, one of the main rocket engines shut down. Why, because despite all the checks built in by NASA and the rocket manufacturer they simply had two wires crossed! Their fix was to modify the wires so they would fit only one way thus building out any possible failure modes.
Because I know me, I built my plane as idiot proof as possible! :-)
__________________
Paul Gray
Foley, Alabama
N729PG..... 450+ hrs
RV 7A, Lycoming 0 320 D1A, Sensenich FP propeller
pilotforfun2001@yahoo.com
VAF supporter $$$
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06-22-2017, 03:29 PM
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Join Date: Sep 2007
Location: BC
Posts: 1,674
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Where is the "like" key? I wanted to use it for 1/2 of the posts in this thread.
Bevan
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RV7A Flying since 2015
O-360-A1F6 (parallel valve) 180HP
Dual P-mags
Precision F.I. with AP purge valve
Vinyl Wrapped Exterior
Grand Rapids EFIS
Located in western Canada
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06-22-2017, 03:53 PM
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Join Date: Dec 2015
Location: Lewes, DE
Posts: 364
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One issue with the "both" position that hasn't been brought up yet as far as I can tell is that, particularly with the analog fuel guages shown in the photo, it would be really hard to tell how much fuel really was in each tank. With the traditional setup, it's pretty easy to calculate fuel burn and subtract from a known quantity at the beginning of each flight so that at any given time, one should know exactly how much fuel remains in each tank without reference to the gauges. I'm not an authority, but i'd be surprised if the fuel flowed perfectly evenly from each tank with the selector set at "both" meaning that if one tank should run out, you could never be 100% sure how much fuel was in the remaining tank, only that it was "somewhere between 5 and 10 gallons" on the analog gauge. Digital instrumentation would certainly help, and it's definitely possible to forget to switch tanks on a L-off-R setup which would have the same result. In the end, I don't think it's way more dangerous to have the "both" setting in a low wing plane, but I don't see a single advantage of it either.
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Rebuilt RV-6A N94CR
RV-8 N803DR completed, flying.
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06-22-2017, 04:07 PM
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Join Date: Oct 2008
Location: Carson City, NV
Posts: 493
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So when you are flying along with the selector set to both and the engine coughs from fuel mis management. Which tank are you going to switch it to. Oh wait, let me look at the gauges. I would like to think I will never be the one that runs out of fuel, but I bet no one has ever taken off on a flight and said this is the day I run the tanks dry.
We are all free to build the plane we want, but some of our fellow aviators have paid the price with blood. Mistakes happen, but we can learn from others and hopefully not ever repeat a mistake.
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Joel
N626JA
RV-7A at CXP
Flying!
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06-22-2017, 04:38 PM
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Super Moderator
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Join Date: May 2005
Location: Locust Grove, GA
Posts: 2,626
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Lots of good comments, and I want to be the last one to stifle creativity EXCEPT with fuel systems. A good friend of mine just lost his plane because the engine quit at 12,500' and they rode it all the way to the ground and totaled it without ever switching tanks. The EFIS data clearly shows the tank ran dry.
So how is that relevant here you ask? Well, there were a few posts about how a BOTH system can work in a low wing with extra care and precaution. Ever hear of tunnel vision that some pilots get when faced with an emergency? In this case, they were focused on the turbocharger becasue it had a prior failure a few years back, and the engine just happened to quit as he was adding some boost. Purely coincidental, and lots of failure points after that that we can all armchair quarterback
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But don't judge until you have been faced with the emergency. For me, I'd rather have a fuel system that DOESN'T require some extra precaution at the worst possible time.
Vic
__________________
 Vic Syracuse
Built RV-4, RV-6, 2-RV-10's, RV-7A, RV-8, Prescott Pusher, Kitfox Model II, Kitfox Speedster, Kitfox 7 Super Sport, Just Superstol, DAR, A&P/IA, EAA Tech Counselor/Flight Advisor, CFII-ASMEL/ASES
Kitplanes "Unairworthy" monthly feature
EAA Sport Aviation "Checkpoints" column
EAA Homebuilt Council Chair/member EAA BOD
Author "Pre-Buy Guide for Amateur-Built Aircraft"
www.Baselegaviation.com
Last edited by vic syracuse : 06-22-2017 at 04:43 PM.
Reason: wording
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06-22-2017, 04:40 PM
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Join Date: Oct 2005
Location: Seattle, WA
Posts: 16
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I have a "both" fuel tank selector option on the 6A that I just bought, and I've found myself using it less and less as I fly my plane more. I was reminded during transition training in my airplane to always have the selector on the fullest tank (not on "both") for takeoff and landing, which is what I've always done. I'd then go to "both" once established in cruise. Most of the time though I'd still eventually see uneven fuel levels in the tanks after a while at cruise, so I'd just revert back to feeding from an individual tank and switching when the GRT Sport interval alarm would go off anyway.
I have much to learn about RVs and airplane ownership in general, so I really appreciate the discussion and various opinions on here. I now feel a bit of confirmation in my thinking pertaining to how I'm using my fuel tank selector, and really see no good reason to utilize "both" in the future!
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06-22-2017, 04:50 PM
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Join Date: Aug 2007
Location: Ontario, Canada
Posts: 2,291
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And now for a slightly different perspective... I'm building a Glasair Sportsman - a high-wing aircraft with fuel in both wings and gravity feed to the engine. A perfect candidate for a "both" fuel selector, right?
Think again!
The default design from the factory has the fuel lines from L and R tanks coming to a Tee, then to a simple On/Off selector. Great! Simple, cheap, easy, light... Except that some aircraft would develop significant fuel imbalances because the fuel tank vents could produce different air pressures in the tank, essentially force-feeding fuel from one tank while the other tank remained pretty much full. Not good!
As a result of the fuel imbalances experienced in the field the standard fit now is a 4-position valve (L-Both-R-OFF) which allows us to even out fuel burn if we need to.
As with many lessons in aviation, the "no Both position on low wing aircraft" rule of thumb was written in blood. While the Both position may work, it might also bite you at a very inopportune time. Better not to have the Both position than to have the risk of it being misused.
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06-22-2017, 04:52 PM
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Super Moderator
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Join Date: May 2005
Location: Locust Grove, GA
Posts: 2,626
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Quote:
Originally Posted by rplittle
I have a "both" fuel tank selector option on the 6A that I just bought, and I've found myself using it less and less as I fly my plane more. I was reminded during transition training in my airplane to always have the selector on the fullest tank (not on "both") for takeoff and landing, which is what I've always done. I'd then go to "both" once established in cruise. Most of the time though I'd still eventually see uneven fuel levels in the tanks after a while at cruise, so I'd just revert back to feeding from an individual tank and switching when the GRT Sport interval alarm would go off anyway.
I have much to learn about RVs and airplane ownership in general, so I really appreciate the discussion and various opinions on here. I now feel a bit of confirmation in my thinking pertaining to how I'm using my fuel tank selector, and really see no good reason to utilize "both" in the future!
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Thank you! I am very proud of you.
Consider putting a placard over the BOTHposition to blank it out.
Vic
__________________
 Vic Syracuse
Built RV-4, RV-6, 2-RV-10's, RV-7A, RV-8, Prescott Pusher, Kitfox Model II, Kitfox Speedster, Kitfox 7 Super Sport, Just Superstol, DAR, A&P/IA, EAA Tech Counselor/Flight Advisor, CFII-ASMEL/ASES
Kitplanes "Unairworthy" monthly feature
EAA Sport Aviation "Checkpoints" column
EAA Homebuilt Council Chair/member EAA BOD
Author "Pre-Buy Guide for Amateur-Built Aircraft"
www.Baselegaviation.com
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06-22-2017, 05:18 PM
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Join Date: Oct 2005
Location: Seattle, WA
Posts: 16
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Quote:
Originally Posted by vic syracuse
[/b]
Thank you! I am very proud of you.
Consider putting a placard over the BOTH position to blank it out.
Vic
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Good idea, Vic.
Some may view taking that step as unnecessary, reactionary, or even over the top, and that's fine. But for me, if I have the option to eliminate a certain risk (not using "both" at all, and placarding it as such), rather than just decrease the risk (by "proper" use of "both"), in this case I would rather get rid of that risk altogether. Why chance a fuel starvation situation by using "both" when it can just be avoided in the first place?
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