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601XL Fuel System Questions

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crvsecretary

Joined: 18 Mar 2007
Posts: 38
Location: Naugatuck, CT

Posted: Wed Mar 11, 2009 1:05 pm Post subject: 601XL Fuel System Questions

Hello Listers:

 

 I have a question to ask the more experienced builders of the group regarding the fuel tanks & plumbing of the fuel syatem on my 601XL.  I am working on the right wing so i have lots of opportunity to make changes - since everything I am questioning hasn't been built yet !

 

 I am considering using a return line to the tanks and a restrictive orifice (a 'controlled leak') at the carb to maintain fuel flow PAST the carb to reduce and possibly eliminate the chance of vapor lock in my plane.  With regard to changes to the original Zenith design, I see this would require:

 

 a T-fitting and orifice at the carb, return lines to the fuel selector valve, a new fuel selector valve (VERY EXPENSIVE) with a return segment, return plumbing to each tank, and tank modifications to accept a fuel line.  I'm not a welder so I would need to find one to modify the tank, as well as getting a proper fitting to weld into the tank.

 

 My questions are many: is all this worth it?  As I see it, yes.....ALL modern automotive designs incorporate a return line to the tank (yes, I know they are fuel injected, but that's a whole other issue).  There has been some discussion regarding fuel selector valves: in that they represent a single point of failure potential.  Would on-off ball valved be a better solution?  Please...I'd like opinions on this.  

 

 My thoughts are to use rigid tube in the fuselage...does anyone have a primer or a good website on the proper way to bend rigid tube and the best way to anchor it?

 

 Speaking of primers - this time engine primers:  I recently purchased an engine peimer that is tapped to accept 1/8 NPT pipe fittings.  I am looking for 2 fittings:

 

 1/8 male NPT to 1/4" barb, and 1/8 male NPT to that I believe is 1/16" copper tube compression which goes to the primer nozzles in the intake manifold.  Where do I get these tiny fittings ?

 ACS had very little to offer.

 

 Thank you in advance for your help.  I have been at a standstill for a long time about this and I welcome all thoughts and opinions.

 

 Regards,

 

 Tracy Smith

 Zenith Zodiac 601XL N458XL (reserved)

  

  [quote][b]

_________________
Zenith 601XL N458XL (reserved)
Naugatuck, CT
Tail Complete; working on wings

jaybannist(at)cs.com
Guest

Posted: Wed Mar 11, 2009 1:59 pm Post subject: 601XL Fuel System Questions

Tracy,

 

 In my not-so humble opinion, you are WAY overthinking this.  The 601XL is a very simple airplane, comparatively.  It is not a super blow-down high speed pressurized twin with fuel injection, constant speed props and many fuel tanks.  The system ZAC envisioned for the airplane is entirely adequate.    All of the things you are contemplating just add complication and more points of failure; making building more difficult and time-consuming; and adding unnecessary inspection and maintenance chores. 

 

 My 601XL has the ZAC supplied rubber hose from the tanks to the dual stick bulkheads and braided 6AN line from there to the selector valve, fuel pumps and carburetor.  I have a Corvair engine with a MA3-SPA carb, thus no primer is needed - very simple.

 

 My advice: KISS and keep building. 

 

 Jay Bannister

 

   

 

   

 

 --

bryanmmartin

Joined: 10 Jan 2006
Posts: 1018

Posted: Wed Mar 11, 2009 5:52 pm Post subject: 601XL Fuel System Questions

Modern auto designs have return lines to the tanks BECAUSE they are  

fuel injected, and for no other reason. The the fuel pump is in the  

tank and pumps high pressure fuel to the engine. A fuel pressure  

regulator maintains a constant pressure for the injectors, a certain  

amount of fuel must bypass the regulator for this to occur. This low  

pressure bypass fuel is returned to the tank. If you don't have a fuel  

injected engine, installing return lines to the tanks is going to make  

your system way more complicated than necessary.



Vapor lock is a phenomenon that occurs at the fuel pump, not the  

carburetor. It occurs when the fuel at the inlet of the pump is  

vaporized. The fuel pump is designed to pump liquid, not vapor, so the  

fuel stops flowing. Putting an orifice at the carburetor won't help  

this situation. Vapor at the carburetor is not a problem as long as  

fuel is still flowing up behind it to push it on through. The way to  

prevent vapor lock is to make sure that the fuel pump always gets  

supplied with liquid fuel. Two things can vaporize fuel: suction and  

high temperature (or a combination of the two). Sucking fuel uphill  

from the tanks in a low wing airplane with a fuel pump mounted on a  

hot engine block in a hot engine compartment is one good way to end up  

with vapor lock. Especially if you are using auto gas. Avgas is more  

resistant vaporization. The most likely scenario for vapor lock is  

fuel in low wing tanks, pump mounted on the engine, hot day, full  

throttle and nose high attitude. In other words, right after takeoff.



Your fuel pump should be located near the low point of the system so  

it always gets gravity feed from the tanks. Just ahead of the  

gascolator is good. Some people have put the fuel pumps right at the  

outlet of the tanks. this also works well but puts pressurized fuel  

through all the lines in the cabin. You should avoid having anything  

upstream from the pump that can cause a significant restriction to  

flow, this will cause a pressure drop and increase the risk of  

vaporization. If you have an engine mounted mechanical pump, you  

should have an electric boost pump mounted ahead of it and use it for  

take off to make sure the engine mounted pump always gets liquid fuel.



I have two ball valves in my system, one for each tank, mounted on the  

floor ahead of the spar on either side of the rudder cable tunnel.  

That was the way the system was originally designed. It's simple,  

effective and inexpensive. I never saw any reason to put a fancy,  

expensive selector valve in there. The valves feed fuel into a tee  

fitting at the gascolator and I have two fuel pumps in parallel on the  

floor just ahead of that. The fuel lines slope downhill all the way  

from the tanks to the gascolator and the pumps are at the same level  

as the outlet of that. Then the fuel line slopes uphill to the  

carburetors. I've never had any hint of a problem with vapor lock with  

this setup.



I used 3/8" O.D. 3003 aluminum tube from the tanks to the valves.  

Mainly because hoses will eventually have to be replaced and I didn't  

want to have to dig into the wing root area to replace fuel lines. I  

used hoses everywhere else. I was planning to use aluminum, but the  

hose was easier to install and it will be easily accessible when it  

comes time to replace it.



For your fittings, you have to remember, hose fittings are sized by  

the I.D. of the hose and tube fittings are sized by the O.D of the  

tube. So if you are looking for a fitting for a 1/16" I.D. tube, it  

will be listed under 1/8" O.D. fittings. Here's your hose fitting:  

AN840 HOSE NIPPLE, PIPE THREAD



http://www.aircraftspruce.com/catalog/hapages/an840.php



There is an error in the above web page, the column that reads Tube  

O.D. should read Hose I.D.



For your tube fitting, maybe this is what you are looking for:  primer  

fitting AN780-2, AN800, AN805



http://www.aircraftspruce.com/catalog/hapages/primerfittings.php



Although I think this is a flare fitting, not a compression fitting.

On Mar 11, 2009, at 5:03 PM, crvsecretary(at)aol.com wrote:



 	  Quote: 	
		   I am considering using a return line to the tanks and a restrictive  

 orifice (a 'controlled leak') at the carb to maintain fuel flow PAST  

 the carb to reduce and possibly eliminate the chance of vapor lock  

 in my plane.  With regard to changes to the original Zenith design,  

 I see this would require:



 a T-fitting and orifice at the carb, return lines to the fuel  

 selector valve, a new fuel selector valve (VERY EXPENSIVE) with a  

 return segment, return plumbing to each tank, and tank modifications  

 to accept a fuel line.  I'm not a welder so I would need to find one  

 to modify the tank, as well as getting a proper fitting to weld into  

 the tank.



 My questions are many: is all this worth it?  As I see it,  

 yes.....ALL modern automotive designs incorporate a return line to  

 the tank (yes, I know they are fuel injected, but that's a whole  

 other issue).  There has been some discussion regarding fuel  

 selector valves: in that they represent a single point of failure  

 potential.  Would on-off ball valved be a better solution?   

 Please...I'd like opinions on this.



 My thoughts are to use rigid tube in the fuselage...does anyone have  

 a primer or a good website on the proper way to bend rigid tube and  

 the best way to anchor it?



 Speaking of primers - this time engine primers:  I recently  

 purchased an engine peimer that is tapped to accept 1/8 NPT pipe  

 fittings.  I am looking for 2 fittings:



 1/8 male NPT to 1/4" barb, and 1/8 male NPT to that I believe is  

 1/16" copper tube compression which goes to the primer nozzles in  

 the intake manifold.  Where do I get these tiny fittings ?

 ACS had very little to offer.



 Thank you in advance for your help.  I have been at a standstill for  

 a long time about this and I welcome all thoughts and opinions.




	




-- 

Bryan Martin

N61BM, CH 601 XL,

RAM Subaru, Stratus redrive.

_________________
--
Bryan Martin
N61BM, CH 601 XL, Stratus Subaru.
do not archive.

trainnut01(at)aol.com
Guest

Posted: Wed Mar 11, 2009 6:32 pm Post subject: 601XL Fuel System Questions

Many carburerated cars from the 60's and 70's were equipped with fuel  

return lines to prevent vapor lock. They used an inline fuel filter  

between the pump and carburetor. The filter had a third fitting  

(undersized) that returned fuel to the tank, The filter that GM used  

is still available from NAPA.

Carroll Jernigan

On Mar 11, 2009, at 9:51 PM, Bryan Martin wrote:

 	  Quote: 	

 >

 Modern auto designs have return lines to the tanks BECAUSE they are  

 fuel injected, and for no other reason. The the fuel pump is in the  

 tank and pumps high pressure fuel to the engine. A fuel pressure  

 regulator maintains a constant pressure for the injectors, a certain  

 amount of fuel must bypass the regulator for this to occur. This low  

 pressure bypass fuel is returned to the tank. If you don't have a  

 fuel injected engine, installing return lines to the tanks is going  

 to make your system way more complicated than necessary.

 Vapor lock is a phenomenon that occurs at the fuel pump, not the  

 carburetor. It occurs when the fuel at the inlet of the pump is  

 vaporized. The fuel pump is designed to pump liquid, not vapor, so  

 the fuel stops flowing. Putting an orifice at the carburetor won't  

 help this situation. Vapor at the carburetor is not a problem as  

 long as fuel is still flowing up behind it to push it on through.  

 The way to prevent vapor lock is to make sure that the fuel pump  

 always gets supplied with liquid fuel. Two things can vaporize fuel:  

 suction and high temperature (or a combination of the two). Sucking  

 fuel uphill from the tanks in a low wing airplane with a fuel pump  

 mounted on a hot engine block in a hot engine compartment is one  

 good way to end up with vapor lock. Especially if you are using auto  

 gas. Avgas is more resistant vaporization. The most likely scenario  

 for vapor lock is fuel in low wing tanks, pump mounted on the  

 engine, hot day, full throttle and nose high attitude. In other  

 words, right after takeoff.

 Your fuel pump should be located near the low point of the system so  

 it always gets gravity feed from the tanks. Just ahead of the  

 gascolator is good. Some people have put the fuel pumps right at the  

 outlet of the tanks. this also works well but puts pressurized fuel  

 through all the lines in the cabin. You should avoid having anything  

 upstream from the pump that can cause a significant restriction to  

 flow, this will cause a pressure drop and increase the risk of  

 vaporization. If you have an engine mounted mechanical pump, you  

 should have an electric boost pump mounted ahead of it and use it  

 for take off to make sure the engine mounted pump always gets liquid  

 fuel.

 I have two ball valves in my system, one for each tank, mounted on  

 the floor ahead of the spar on either side of the rudder cable  

 tunnel. That was the way the system was originally designed. It's  

 simple, effective and inexpensive. I never saw any reason to put a  

 fancy, expensive selector valve in there. The valves feed fuel into  

 a tee fitting at the gascolator and I have two fuel pumps in  

 parallel on the floor just ahead of that. The fuel lines slope  

 downhill all the way from the tanks to the gascolator and the pumps  

 are at the same level as the outlet of that. Then the fuel line  

 slopes uphill to the carburetors. I've never had any hint of a  

 problem with vapor lock with this setup.

 I used 3/8" O.D. 3003 aluminum tube from the tanks to the valves.  

 Mainly because hoses will eventually have to be replaced and I  

 didn't want to have to dig into the wing root area to replace fuel  

 lines. I used hoses everywhere else. I was planning to use aluminum,  

 but the hose was easier to install and it will be easily accessible  

 when it comes time to replace it.

 For your fittings, you have to remember, hose fittings are sized by  

 the I.D. of the hose and tube fittings are sized by the O.D of the  

 tube. So if you are looking for a fitting for a 1/16" I.D. tube, it  

 will be listed under 1/8" O.D. fittings. Here's your hose fitting:  

 AN840 HOSE NIPPLE, PIPE THREAD

 http://www.aircraftspruce.com/catalog/hapages/an840.php

 There is an error in the above web page, the column that reads Tube  

 O.D. should read Hose I.D.

 For your tube fitting, maybe this is what you are looking for:   

 primer fitting AN780-2, AN800, AN805

 http://www.aircraftspruce.com/catalog/hapages/primerfittings.php

 Although I think this is a flare fitting, not a compression fitting.

 On Mar 11, 2009, at 5:03 PM, crvsecretary(at)aol.com wrote:

> I am considering using a return line to the tanks and a restrictive  

> orifice (a 'controlled leak') at the carb to maintain fuel flow  

> PAST the carb to reduce and possibly eliminate the chance of vapor  

> lock in my plane.  With regard to changes to the original Zenith  

> design, I see this would require:

>

> a T-fitting and orifice at the carb, return lines to the fuel  

> selector valve, a new fuel selector valve (VERY EXPENSIVE) with a  

> return segment, return plumbing to each tank, and tank  

> modifications to accept a fuel line.  I'm not a welder so I would  

> need to find one to modify the tank, as well as getting a proper  

> fitting to weld into the tank.

>

> My questions are many: is all this worth it?  As I see it,  

> yes.....ALL modern automotive designs incorporate a return line to  

> the tank (yes, I know they are fuel injected, but that's a whole  

> other issue).  There has been some discussion regarding fuel  

> selector valves: in that they represent a single point of failure  

> potential.  Would on-off ball valved be a better solution?   

> Please...I'd like opinions on this.

>

> My thoughts are to use rigid tube in the fuselage...does anyone  

> have a primer or a good website on the proper way to bend rigid  

> tube and the best way to anchor it?

>

> Speaking of primers - this time engine primers:  I recently  

> purchased an engine peimer that is tapped to accept 1/8 NPT pipe  

> fittings.  I am looking for 2 fittings:

>

> 1/8 male NPT to 1/4" barb, and 1/8 male NPT to that I believe is  

> 1/16" copper tube compression which goes to the primer nozzles in  

> the intake manifold.  Where do I get these tiny fittings ?

> ACS had very little to offer.

>

> Thank you in advance for your help.  I have been at a standstill  

> for a long time about this and I welcome all thoughts and opinions.

>

 -- 

 Bryan Martin

 N61BM, CH 601 XL,

 RAM Subaru, Stratus redrive.

bryanmmartin

Joined: 10 Jan 2006
Posts: 1018

Posted: Wed Mar 11, 2009 9:25 pm Post subject: 601XL Fuel System Questions

And they generally had a mechanical fuel pump mounted on the side of  

the engine. The bypass line probably helped keep the pump and fuel  

cooler by bleeding off some of the fuel heated by its trip through the  

engine compartment. Some airplanes have bypass lines for a similar  

reason, they also generally have mechanical fuel pumps on the engine.



Modern autos with fuel injection have electric fuel pumps submerged in  

the fuel tank, which makes vapor lock impossible. An electric pump  

located in a cool area with good gravity feed will also prevent vapor  

lock. It's also a whole lot simpler than all the extra plumbing. If  

you do have an engine mounted pump, using fire-sleeve on the fuel  

lines also helps.



 	  Quote: 	
		   

 >



 Many carburerated cars from the 60's and 70's were equipped with  

 fuel return lines to prevent vapor lock. They used an inline fuel  

 filter between the pump and carburetor. The filter had a third  

 fitting (undersized) that returned fuel to the tank, The filter that  

 GM used is still available from NAPA.

 Carroll Jernigan




	




-- 

Bryan Martin

N61BM, CH 601 XL,

RAM Subaru, Stratus redrive.

do not archive.

_________________
--
Bryan Martin
N61BM, CH 601 XL, Stratus Subaru.
do not archive.

K Dilks

Joined: 22 Sep 2008
Posts: 108
Location: UK

Posted: Wed Mar 11, 2009 11:01 pm Post subject: Re: 601XL Fuel System Questions

In the UK a vapor return line is required by the gods.

 If you fit a 0.35 mm carb jet in the return fuel line it will relive the vapor pressure but only return a small amount per hour , approx 2 liters . This way you just return straight to your primary tank, left in my case and label the change valve to use left tank first. As you will change tanks to keep trim about every 1/2 hour then there will be no problem over flooding the return tank.

 This also help priming the system when empty as the pumps dont have to force the empty line air through the carb  which may have enough fuel to close its needle valve, important if you forget to change tanks in the air..................done that and have the T shirt! Doh!  



 Cheers 

Kevin

_________________
Back home .................

crvsecretary

Joined: 18 Mar 2007
Posts: 38
Location: Naugatuck, CT

Posted: Thu Mar 12, 2009 3:03 pm Post subject: Re: 601XL Fuel System Questions

Gentlemen:



Thank you very much for the replies - THIS is the fellowship of building !  Since I have the fuel selector, I'll install it...but I really liked the simplicity of ball valves.  I will NOT install a return line - again, keeping with simplicity.  I will, however, put the pumps in the wing roots to keep the entire system under pressure and I'll firesleeve EVERYTHING forward of the firewall.



One last question: I'll be installing a Corvair with a mechanical fuel pump.  Do I abandon it and just go with the electric pumps? or put it in series inline to the carb?  Will this cause an over-pressure condition at the carb?



Thank you again, everyone.



Tracy

_________________
Zenith 601XL N458XL (reserved)
Naugatuck, CT
Tail Complete; working on wings

craig(at)craigandjean.com
Guest

Posted: Thu Mar 12, 2009 7:08 pm Post subject: 601XL Fuel System Questions

In general William Wynne says junk the mechanical Corvair pump. He has seen

plenty of reliability issues. Search his web site.



So with no mechanical pump you will want a back-up electrical pump and a

largish battery. So make sure you choose pumps (primary and backup) which

will pass fuel when not pumping. As to over-pressuring it depends on the

carb. The aerocarb is intended for gravity feed and doesn't like any pump.

The Ellison TBI can take some pump pressure, see the Ellison site.



-- Craig



--

hills(at)sunflower.com
Guest

Posted: Thu Mar 12, 2009 7:54 pm Post subject: 601XL Fuel System Questions

Howdy all;



If you think you might have high fuel pressure problems at the carb, or just

want to maintain a even fuel pressure, install an inline fuel pressure

regulator. I got mine at the auto parts store cheap, it adjust from 1/2 psi

to 5 psi and was intended (I guess) for a motorcycle.   Of course, you will

need a fuel return line off of it back up to your tank.



I set mine to 1 psi and ran a fuel pump to the aerovee carb because my

header tank would give low pressure below 1/2 full and start to lean out the

carb.



Roger



--

hills(at)sunflower.com
Guest

Posted: Thu Mar 12, 2009 8:03 pm Post subject: 601XL Fuel System Questions

As far as vapor lock.



Don't forget your fire sleeve on the fuel lines, they act as insulation for

the fuel against engine heat too, which protect against vapor lock.



Also, I put a remote temperature monitor on the fuel filter before my carb,

on a hot day it would show fuel temps of 122 degrees, but usually less than

115 on a normal day.



Finally, I don't think vapor occurs while flying, it's something associated

with trying to start the engine after it's been trying to cool off on a hot

day and the fuel has heat soaked enough to go to vapor.  Get the cooling air

flowing again, and the problem goes away. 



Roger



--

malcolmhunt(at)mha1.fsbus
Guest

Posted: Fri Mar 13, 2009 3:48 am Post subject: 601XL Fuel System Questions

Hi Kevin



What was the internal diameter of you return line and how did you connect to 

tank (location)?



Best wishes



Malcolm Hunt

CH 601XL Plans builder in England

---

annken100

Joined: 15 Nov 2007
Posts: 62

Posted: Fri Mar 13, 2009 4:27 am Post subject: Re: 601XL Fuel System Questions

Hi Tracy,



The mechanical fuel pump on corvairs has been used in flight applications, however it is prone to leaks. Considering that the stock mechanical pump is located on top of the engine it certainly poses a fire risk being that it can leak on hot engine components.



You also might want to rethink running pressurized lines through the cabin.  You are probably aware that the majority of corvair powered 601s are running Wynne's dual fuel pump system on the firewall.  I have this setup on my plane and it works perfectly.  I must say that I have yet to fly my plane so I can't speak first-hand about how it works in the air.  I can say that I've spoken to a multitude of people running the dual electric fuel pump system and they report that fuel delivery is more than adequate in all flight regimes.  I've never heard of any cases of vapor lock with this system either.



I agree with the other posts that simplicity is the best policy when it comes to fuel systems.



Good Luck,



Ken Pavlou

_________________
601 XL / Corvair

hills(at)sunflower.com
Guest

Posted: Fri Mar 13, 2009 3:47 pm Post subject: 601XL Fuel System Questions

Speaking of dual electric pumps, if you don't have dual batteries running

them, then you will have a big problem if your alternator shorts and drains

your battery down.  You should have a second isolated battery, charged via a

diode from the main battery, to keep the second fuel pump running in the

event of a total electrical power loss (the same goes for backup ignition

for those of us without a magneto ignition)



Personally, I prefer one mechanical pump and one electric one...Makes me

feel safer in the air (sense of false security????).



Roger



 



--

bryanmmartin

Joined: 10 Jan 2006
Posts: 1018

Posted: Fri Mar 13, 2009 4:47 pm Post subject: 601XL Fuel System Questions

You can put a fuse or fusible link in the output of the alternator so  

it will isolate itself from the battery if it ever shorts out.



On Mar 13, 2009, at 7:45 PM, Roger & Lina Hill wrote:



 	  Quote: 	
		   

 >

 Speaking of dual electric pumps, if you don't have dual batteries  

 running

 them, then you will have a big problem if your alternator shorts and  

 drains

 your battery down.  You should have a second isolated battery,  

 charged via a

 diode from the main battery, to keep the second fuel pump running in  

 the

 event of a total electrical power loss (the same goes for backup  

 ignition

 for those of us without a magneto ignition)



 Personally, I prefer one mechanical pump and one electric  

 one...Makes me

 feel safer in the air (sense of false security????).



 Roger


	


-- 

Bryan Martin

N61BM, CH 601 XL,

RAM Subaru, Stratus redrive.

do not archive.

_________________
--
Bryan Martin
N61BM, CH 601 XL, Stratus Subaru.
do not archive.

hills(at)sunflower.com
Guest

Posted: Fri Mar 13, 2009 6:15 pm Post subject: 601XL Fuel System Questions

Fusible Link, Good idea, but other things can drain your battery too, just

not as fast as the alternator (you leave the landing lights on). All that

ready has to happen is the alternator stop charging the battery for some

reason, if your in the air you might not notice the voltage drop until it's

too late and suddenly the engine stops.  If you have a backup battery, then

you just switch the secondary pump on and keep going (in level flight). Of

course, you still have no power for the radios and such (but I always carry

a handheld radio on board too).



 



--

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