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johnelling

Joined: 23 Feb 2013
Posts: 18

Posted: Wed Apr 03, 2013 12:18 pm Post subject: Fuel return line

Folks, I've followed the fuel return line thread and I can see that the 

912 ULS installation manual calls for a fuel manifold with a return line 

to the tank.  My 912 ULS on my Titan Tornado does not have one.  There 

is simply a T in the fuel line out from the mechanical pump to each 

carb.  I've recently added an electric backup/boost pump to the fuel 

system which I use on startup and on takeoff and landing (when I 

remember to turn it on).  The electrical boost makes it much easier to 

start the engine.



The engine and airframe had about 650 hours with the original 

mechanical-pump-only configuration and now there are another 30 hours 

with the mechanical+electrical fuel system and I have not had any 

problems running the engine.



What is going on in the fuel system in the absence of the manifold and 

with the electric pump on and off?  Is excess fuel going overboard from 

the carb bowl drains?  Is there some flow regulation that is 

compensating for (what I assume is) the variable fuel pressure?



Is it worth rebuilding the fuel system to add the manifold?



On a side note, none of the other Rotax 912-equipped Titan Tornadoes I 

have seen have had a fuel manifold either.  So leaving it out of 

home-build installations seems common.



Thanks for any advice, John

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Thu Apr 04, 2013 10:43 am Post subject: Re: Fuel return line

Hi John,



Here's the issues. 

Many of the planes from yesteryear wasn't a problem. They were open air engines so hot fuel lines weren't an issue and the old style fuel pump didn't have enough excess pressure to be an issue. Come up to date with many of the newer LSA and Experimental aircraft with nice tight cowls and then throw in on top of that too many owners fail to install the fuel and oil lines in fire sleeve then heat inside the cowl makes a night a day difference. Vapor lock. I see it alot now days with tight cowls. Fire sleeve not only protects from fire, but helps with excessive heat too. Now comes along the new Rotax fuel pump that puts out more pressure and then add on top of that someone who likes to run an electric pump all the time which adds

 .5 -1.0 psi more and the fuel then can't be controlled by the float needle valve and it pukes out the vents all over a hot engine, on hot exhaust manifolds because some didn't bother to install carb drip trays and now we have an issue. Now add that owners haven't rebuilt or replaced an older float needle valve and now we definitely puke fuel and the engine runs rough.

Just a side note* Exposed fuel lines outside of fire sleeve tend to deteriorate faster than fire sleeved fuel lines.

So the bottom line is application is everything and sooner or later your old pump will die and the new pump is all that is available. It's so easy to add the re-circulation line and never have to look back. On any flight the float needle valve can start leaking then you have the issue too. The re-circulation line only cost a couple of dollars to put in, cheap and easy.



As a 30 year firefighter I never went to rescue where someone said, " that has happened 10 tens before". Everyone said, "Well that has never happened before". Always the first time. Do it long enough and odds may not stay in your favor.



Pro-active verses Re-active.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

uuccio(at)gmail.com
Guest

Posted: Sat Apr 06, 2013 10:37 am Post subject: Fuel return line

Hi Roger

I can see why hot  fuel would exacerbate vapor lock problems and this

conversation has convinced me to firesleeve my fuel lines.  But why does a

return line improve the situation.  And I would have thought higher fuel

pressure would lower the incidence of vapor lock (as it increases the temp

at which fuel vaporizes).  Can you shed more light on why higher fuel

pressure is bad?

Regards,

Sacha



--

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Sat Apr 06, 2013 2:19 pm Post subject: Re: Fuel return line

Hi Sacha,



Higher fuel pressure may lead to flooding of the carbs because we tend to use low pressure to start with. Using a recirculation line keeps cooler fuel moving through the system to help prevent the vapor lock. It keeps cooler fuel within the lines while flying. If your sitting still on the ground with the engine off and it was just shut down then the fuel just sits there and cooks. A re-circulation line moves cooler fuel back up to the carbs much faster after a restart. The re-circulation line also helps keep vapors out of the fuel pump just because the system moves more fuel and it is coming from a cooler point within the system.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

uuccio(at)gmail.com
Guest

Posted: Sun Apr 07, 2013 8:32 am Post subject: Fuel return line

Roger,

Thanks! Makes sense...

Regards,

Sacha

BARRY CHECK 6

Joined: 15 Mar 2011
Posts: 738

Posted: Sun Apr 07, 2013 10:09 am Post subject: Fuel return line

Sacha:



You have some great thought provoking questions.  I hope some are provoked.

Fire sleeves or One piece Molded Teflon fuel lines are the way to go.

You always want to do all you can to keep extra heat from fuel and oil lines.

 BUT!  Where did this Old Wives Tail of Vapor Lock come from?  It is a BUNCH OF BUNK!

The "T" fitting does NOTHING for Vapor Lock... High Pressure does NOTHING to prevent Vapor Lock.  Well, almost nothing - It corrects Pilot/Builder error.

 Vapor Lock happens ON THE GROUND and is experienced usually at start up and sometimes in the air, immediately during or after rotation.

Vapor Lock can occur with MoGAs or AvGas.

It is more of a POOR PILOT SHUTDOWN PROCEDURE that anything else.

 And since we are talking Home Built Planes and Self Proclaimed Engineers - - Builder error.

So, what does the "T" fitting do?  Well, the history goes way back to the 1960's...  Electric home made Fuel Pumps were being used on Carbureted engines. And the engines were FLOODING like crazy.  Flooding, Fires, Poor Starts (if at all),  Dying when the throttle was floored and Low HP.  All because of TOO MUCH Fuel Pressure Pushing the Carburetor's intake valve off the seat and flooding the carb. 

 So, how do you get more fuel to the carb so it does not go LEAN?  You do a whole lot of pressure testing and engineering  - BUT!  These were HOME MADE FUEL PUMPS - And Manufacturer made Carbs.  Transducers were not around then.  It was too costly to try to figure out how many GPH and How much Fuel Pressure would work,and what size spring to use...  Too many variables.

 The QUICK and EASY and VERY Effective solution...  Put a "T" fitting in the line and the excess pressure and excess fuel is returned to the fuel tank.

The Carb takes what it needs - Has a steady supply of fuel and does NOT go lean no matter how fast you hit the throttle.

 No Smoke and Mirrors, No ridiculous Vapor Lock theories.  But, hell, this is aviation so everybody just re-invents the wheel with their own ideas.  

In simple terms:  It is better and easier to KNOW you have too much fuel than to take the chance of going lean and destroying an engine or not enough power to clear the trees.

 



What are the 4 most useless things to a pilot?  We all know the first 3:

1 - The Gas left on the ground.

2 - The runway behind you.

3 - Are airspace above you .

 The fourth - 

4 - The Gas you can't get out of your tanks.

Barry



 

On Sat, Apr 6, 2013 at 2:36 PM, Sacha <uuccio(at)gmail.com (uuccio(at)gmail.com)> wrote:

[quote] --> RotaxEngines-List message posted by: "Sacha" <uuccio(at)gmail.com (uuccio(at)gmail.com)>

 

 Hi Roger

 I can see why hot  fuel would exacerbate vapor lock problems and this

 conversation has convinced me to firesleeve my fuel lines.  But why does a

 return line improve the situation.  And I would have thought higher fuel

 pressure would lower the incidence of vapor lock (as it increases the temp

 at which fuel vaporizes).  Can you shed more light on why higher fuel

 pressure is bad?

 Regards,

 Sacha

 

 --

grahamsingleton(at)btinte
Guest

Posted: Sun Apr 07, 2013 1:26 pm Post subject: Fuel return line

Vapour lock certainly does occur. I know of several instances, one of which resulted in a written off aircraft. It happens when the 

engine driven fuel pump gets heated by the engine oil and then heats the fuel. Low fuel flow rate such as  when taxiing or waiting for air traffic on the ground

can vaporize the fuel, especially Mogas. The fuel return  Rotax recommend keeps more fuel flowing through the system which helps cool the pump and ensures cold fuel when you need it for high power. 

Most carburetor installations in cars have a fuel return line for the same reasons.

Graham

        From: FLYaDIVE <flyadive(at)gmail.com>

 To: rotaxengines-list(at)matronics.com 

 Sent: Sunday, 7 April 2013, 19:08

 Subject: Re: RotaxEngines-List: Re: Fuel return  line

  

 

Sacha:



You have some great thought provoking questions.  I hope some are provoked.

Fire sleeves or One piece Molded Teflon fuel lines are the way to go.

You always want to do all you can to keep extra heat from fuel and oil lines.

 BUT!  Where did this Old Wives Tail of Vapor Lock come from?  It is a BUNCH OF BUNK!

The "T" fitting does NOTHING for Vapor Lock... High Pressure does NOTHING to prevent Vapor Lock.  Well, almost nothing - It corrects Pilot/Builder error.

 Vapor Lock happens ON THE GROUND and is experienced usually at start up and sometimes in the air, immediately during or after rotation.

Vapor Lock can occur with MoGAs or AvGas.

It is more of a POOR PILOT SHUTDOWN PROCEDURE that anything else.

 And since we are talking Home Built Planes and Self Proclaimed Engineers - - Builder error.

So, what does the "T" fitting do?  Well, the history goes way back to the 1960's...  Electric home made Fuel Pumps were being used on Carbureted engines. And the engines were FLOODING like crazy.  Flooding, Fires, Poor Starts (if at all),  Dying when the throttle was floored and Low HP.  All because of TOO MUCH Fuel Pressure Pushing the Carburetor's intake valve off the seat and flooding the carb. 

 So, how do you get more fuel to the carb so it does not go LEAN?  You do a whole lot of pressure testing and engineering  - BUT!  These were HOME MADE FUEL PUMPS - And Manufacturer made Carbs.  Transducers were not around then.  It was too costly to try to figure out how many GPH and How much Fuel Pressure would work,and what size spring to use..  Too many variables.

 The QUICK and EASY and VERY Effective solution...  Put a "T" fitting in the line and the excess pressure and excess fuel is returned to the fuel tank.

The Carb takes what it needs - Has a steady supply of fuel and does NOT go lean no matter how fast you hit the throttle.

 No Smoke and Mirrors, No ridiculous Vapor Lock theories.  But, hell, this is aviation so everybody just re-invents the wheel with their own ideas.  

I



 

 

  

 [quote][b]

Alan Carter

Joined: 02 Jul 2012
Posts: 378
Location: Kent, England.

Posted: Sun Apr 07, 2013 1:55 pm Post subject: Re: Fuel return line

Hi All.

My 914 has two fuel pumps, one pump has to run all the time as i think the 914 has no engine drive pump, Why?

These pumps are mounted well away from the engine in the belly of the fuselage, so cooling of the pumps is good,

Has there been any problems with vapor lock on the 914, using Mogas.

Alan

ptag.dev(at)tiscali.co.uk
Guest

Posted: Sun Apr 07, 2013 2:02 pm Post subject: Fuel return line

Thanks Graham .........I was beginning to think I was having a bad dream !  Me too over the M1  from Halfpenny Green back to Wickenby, mind you it was Jabiru originated but no one will convince me anything else and nothing else found after exhaustive checks and re-checks.

As far as I’m concerned there was no BS involved. To say there’s no such thing is misleading in the extreme. The return line must go back into the Europa Tank via the reserve supply side  ensuring only the coolest fuel goes forward.

Best regards

Bob Harrison. (Survived 1000 hours but would never boast about that before a flight ! Also only about half of that was with the Jabiru.)

 

From: owner-rotaxengines-list-server(at)matronics.com [mailto:owner-rotaxengines-list-server(at)matronics.com] On Behalf Of GRAHAM SINGLETON

Sent: 07 April 2013 22:25

To: rotaxengines-list(at)matronics.com

Subject: Re: Re: Fuel return line

 

Vapour lock certainly does occur. I know of several instances, one of which resulted in a written off aircraft. It happens when the 



engine driven fuel pump gets heated by the engine oil and then heats the fuel. Low fuel flow rate such as  when taxiing or waiting for air traffic on the ground



can vaporize the fuel, especially Mogas. The fuel return  Rotax recommend keeps more fuel flowing through the system which helps cool the pump and ensures cold fuel when you need it for high power. 



Most carburetor installations in cars have a fuel return line for the same reasons.



Graham

From: FLYaDIVE <flyadive(at)gmail.com (flyadive(at)gmail.com)>

To: rotaxengines-list(at)matronics.com (rotaxengines-list(at)matronics.com) 

Sent: Sunday, 7 April 2013, 19:08

Subject: Re: Re: Fuel return line



 

Sacha:

 



You have some great thought provoking questions.  I hope some are provoked.



Fire sleeves or One piece Molded Teflon fuel lines are the way to go.



You always want to do all you can to keep extra heat from fuel and oil lines.



BUT!  Where did this Old Wives Tail of Vapor Lock come from?  It is a BUNCH OF BUNK!



The "T" fitting does NOTHING for Vapor Lock... High Pressure does NOTHING to prevent Vapor Lock.  Well, almost nothing - It corrects Pilot/Builder error.



Vapor Lock happens ON THE GROUND and is experienced usually at start up and sometimes in the air, immediately during or after rotation.



Vapor Lock can occur with MoGAs or AvGas.



It is more of a POOR PILOT SHUTDOWN PROCEDURE that anything else.



And since we are talking Home Built Planes and Self Proclaimed Engineers - - Builder error.



So, what does the "T" fitting do?  Well, the history goes way back to the 1960's...  Electric home made Fuel Pumps were being used on Carbureted engines. And the engines were FLOODING like crazy.  Flooding, Fires, Poor Starts (if at all),  Dying when the throttle was floored and Low HP.  All because of TOO MUCH Fuel Pressure Pushing the Carburetor's intake valve off the seat and flooding the carb. 



So, how do you get more fuel to the carb so it does not go LEAN?  You do a whole lot of pressure testing and engineering  - BUT!  These were HOME MADE FUEL PUMPS - And Manufacturer made Carbs.  Transducers were not around then.  It was too costly to try to figure out how many GPH and How much Fuel Pressure would work,and what size spring to use...  Too many variables.



The QUICK and EASY and VERY Effective solution...  Put a "T" fitting in the line and the excess pressure and excess fuel is returned to the fuel tank.



The Carb takes what it needs - Has a steady supply of fuel and does NOT go lean no matter how fast you hit the throttle.



No Smoke and Mirrors, No ridiculous Vapor Lock theories.  But, hell, this is aviation so everybody just re-invents the wheel with their own ideas.  



 



I





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uuccio(at)gmail.com
Guest

Posted: Sun Apr 07, 2013 2:39 pm Post subject: Fuel return line

Barry/Graham/Roger,

I’m no expert, but I’m going to try and summarize the arguments here.  There is no question that Vapour Lock does occur and that it can be a serious problem.  I plan to fly in a hot climate with mountainous terrain (i.e. at altitude), hence my concern.

To summarize what I’m hearing:

<![if !supportLists]>-         <![endif]>High fuel temp is bad because is causes fuel to vaporize easily (so don’t shut down your engine suddenly and then try to restart it without cooling it as the fuel lines will likely be heat soaked)

<![if !supportLists]>-         <![endif]>High fuel pressure is good to the extent that 

<![if !supportLists]>o  <![endif]>a) it increases the temp at which fuel vaporizes (though IMO this effect would be marginal as the Vaporization Temp varies as 1/log Pressure) and 

<![if !supportLists]>o  <![endif]>b) if a fuel return line is fitted, the fuel pump mixes the warmer fuel in the lines under the cowling with cooler fuel from the fuel tanks/gascolator (unless you left your plane out in the sun and your wings are painted in a dark colour in which case fuel in your  tanks might be quite warm?).

<![if !supportLists]>-         <![endif]>Very high fuel pressure is bad because it can cause the carbs to flood, hence the advisability of fitting a fuel return line

 

If one encounters vapour lock during flight, what is the best way of dealing with it, assuming one has sufficient altitude? Reduce throttle and descent at a decent airspeed to cool the engine?

Sacha

 

 

 

 

From: owner-rotaxengines-list-server(at)matronics.com [mailto:owner-rotaxengines-list-server(at)matronics.com] On Behalf Of GRAHAM SINGLETON

Sent: Sunday, 07 April, 2013 22:25

To: rotaxengines-list(at)matronics.com

Subject: Re: Re: Fuel return line

 

Vapour lock certainly does occur. I know of several instances, one of which resulted in a written off aircraft. It happens when the 



engine driven fuel pump gets heated by the engine oil and then heats the fuel. Low fuel flow rate such as  when taxiing or waiting for air traffic on the ground



can vaporize the fuel, especially Mogas. The fuel return  Rotax recommend keeps more fuel flowing through the system which helps cool the pump and ensures cold fuel when you need it for high power. 



Most carburetor installations in cars have a fuel return line for the same reasons.



Graham

From: FLYaDIVE <flyadive(at)gmail.com (flyadive(at)gmail.com)>

To: rotaxengines-list(at)matronics.com (rotaxengines-list(at)matronics.com) 

Sent: Sunday, 7 April 2013, 19:08

Subject: Re: Re: Fuel return line



 

Sacha:

 



You have some great thought provoking questions.  I hope some are provoked.



Fire sleeves or One piece Molded Teflon fuel lines are the way to go.



You always want to do all you can to keep extra heat from fuel and oil lines.



BUT!  Where did this Old Wives Tail of Vapor Lock come from?  It is a BUNCH OF BUNK!



The "T" fitting does NOTHING for Vapor Lock... High Pressure does NOTHING to prevent Vapor Lock.  Well, almost nothing - It corrects Pilot/Builder error.



Vapor Lock happens ON THE GROUND and is experienced usually at start up and sometimes in the air, immediately during or after rotation.



Vapor Lock can occur with MoGAs or AvGas.



It is more of a POOR PILOT SHUTDOWN PROCEDURE that anything else.



And since we are talking Home Built Planes and Self Proclaimed Engineers - - Builder error.



So, what does the "T" fitting do?  Well, the history goes way back to the 1960's...  Electric home made Fuel Pumps were being used on Carbureted engines. And the engines were FLOODING like crazy.  Flooding, Fires, Poor Starts (if at all),  Dying when the throttle was floored and Low HP.  All because of TOO MUCH Fuel Pressure Pushing the Carburetor's intake valve off the seat and flooding the carb. 



So, how do you get more fuel to the carb so it does not go LEAN?  You do a whole lot of pressure testing and engineering  - BUT!  These were HOME MADE FUEL PUMPS - And Manufacturer made Carbs.  Transducers were not around then.  It was too costly to try to figure out how many GPH and How much Fuel Pressure would work,and what size spring to use...  Too many variables.



The QUICK and EASY and VERY Effective solution...  Put a "T" fitting in the line and the excess pressure and excess fuel is returned to the fuel tank.



The Carb takes what it needs - Has a steady supply of fuel and does NOT go lean no matter how fast you hit the throttle.



No Smoke and Mirrors, No ridiculous Vapor Lock theories.  But, hell, this is aviation so everybody just re-invents the wheel with their own ideas.  



 



I





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uuccio(at)gmail.com
Guest

Posted: Sun Apr 07, 2013 2:46 pm Post subject: Fuel return line

My fuel return line only goes back to the gascolator… but I’m hoping it’s enough as it is at the bottom of the cowling and should get decent cooling from the airflow.

 

I read Transport Canada’s piece on using Mogas in aviation and they say that vapor lock problems can occur more easily if you use winter fuel (which has a lower vaporization temp) in the warmer months.   Not sure if there are different grades of fuel in winter/summer in the UK  - certainly doesn’t seem like there is any need for “summer” fuel this year so far… 

 

From: owner-rotaxengines-list-server(at)matronics.com [mailto:owner-rotaxengines-list-server(at)matronics.com] On Behalf Of Bob Harrison

Sent: Sunday, 07 April, 2013 23:01

To: rotaxengines-list(at)matronics.com

Subject: RE: Re: Fuel return line

 

Thanks Graham .........I was beginning to think I was having a bad dream !  Me too over the M1  from Halfpenny Green back to Wickenby, mind you it was Jabiru originated but no one will convince me anything else and nothing else found after exhaustive checks and re-checks.

As far as I’m concerned there was no BS involved. To say there’s no such thing is misleading in the extreme. The return line must go back into the Europa Tank via the reserve supply side  ensuring only the coolest fuel goes forward.

Best regards

Bob Harrison. (Survived 1000 hours but would never boast about that before a flight ! Also only about half of that was with the Jabiru.)

 

From: owner-rotaxengines-list-server(at)matronics.com (owner-rotaxengines-list-server(at)matronics.com) [mailto:owner-rotaxengines-list-server(at)matronics.com (owner-rotaxengines-list-server(at)matronics.com)] On Behalf Of GRAHAM SINGLETON

Sent: 07 April 2013 22:25

To: rotaxengines-list(at)matronics.com (rotaxengines-list(at)matronics.com)

Subject: Re: Re: Fuel return line

 

Vapour lock certainly does occur. I know of several instances, one of which resulted in a written off aircraft. It happens when the 



engine driven fuel pump gets heated by the engine oil and then heats the fuel. Low fuel flow rate such as  when taxiing or waiting for air traffic on the ground



can vaporize the fuel, especially Mogas. The fuel return  Rotax recommend keeps more fuel flowing through the system which helps cool the pump and ensures cold fuel when you need it for high power. 



Most carburetor installations in cars have a fuel return line for the same reasons.



Graham

From: FLYaDIVE <flyadive(at)gmail.com (flyadive(at)gmail.com)>

To: rotaxengines-list(at)matronics.com (rotaxengines-list(at)matronics.com) 

Sent: Sunday, 7 April 2013, 19:08

Subject: Re: Re: Fuel return line



 

Sacha:

 



You have some great thought provoking questions.  I hope some are provoked.



Fire sleeves or One piece Molded Teflon fuel lines are the way to go.



You always want to do all you can to keep extra heat from fuel and oil lines.



BUT!  Where did this Old Wives Tail of Vapor Lock come from?  It is a BUNCH OF BUNK!



The "T" fitting does NOTHING for Vapor Lock... High Pressure does NOTHING to prevent Vapor Lock.  Well, almost nothing - It corrects Pilot/Builder error.



Vapor Lock happens ON THE GROUND and is experienced usually at start up and sometimes in the air, immediately during or after rotation.



Vapor Lock can occur with MoGAs or AvGas.



It is more of a POOR PILOT SHUTDOWN PROCEDURE that anything else.



And since we are talking Home Built Planes and Self Proclaimed Engineers - - Builder error.



So, what does the "T" fitting do?  Well, the history goes way back to the 1960's...  Electric home made Fuel Pumps were being used on Carbureted engines. And the engines were FLOODING like crazy.  Flooding, Fires, Poor Starts (if at all),  Dying when the throttle was floored and Low HP.  All because of TOO MUCH Fuel Pressure Pushing the Carburetor's intake valve off the seat and flooding the carb. 



So, how do you get more fuel to the carb so it does not go LEAN?  You do a whole lot of pressure testing and engineering  - BUT!  These were HOME MADE FUEL PUMPS - And Manufacturer made Carbs.  Transducers were not around then.  It was too costly to try to figure out how many GPH and How much Fuel Pressure would work,and what size spring to use...  Too many variables.



The QUICK and EASY and VERY Effective solution...  Put a "T" fitting in the line and the excess pressure and excess fuel is returned to the fuel tank.



The Carb takes what it needs - Has a steady supply of fuel and does NOT go lean no matter how fast you hit the throttle.



No Smoke and Mirrors, No ridiculous Vapor Lock theories.  But, hell, this is aviation so everybody just re-invents the wheel with their own ideas.  



 



I





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  [quote][b]

raymondj(at)frontiernet.n
Guest

Posted: Sun Apr 07, 2013 3:21 pm Post subject: Fuel return line

I don't know if this         applies to Rotax engines.

           

           There is another way a carbureted                     engine can vapor lock.  Back in the 50s and 60s some automotive                                   engines had the carb bolted directly                                       to the intake manifold, without                                           an insulating                                             spacer.  The                                               heat from the engine block                                               could be conducted to the                                               carb and                                                 cause                                                   the combination of                                                   fuel draw through the                                                   venturi and the fuel evaporation                                                   out of the bowl to                                                   exceed what the needle valve                                                       could let it in.        The fuel bowl would get low and the engine would stop.  Then the       heat soaking of the stationary fuel in the lines in the engine       compartment would start.  Some times it took 20-30 min or more       with the hood open to be able to start the engine again. 

        	  Quote: 	
		  Raymond Julian

Kettle River, MN.



"And you know that I could have me a million more friends,

and all I'd have to lose is my point of view." - John Prine 	
       On 04/07/2013 04:25 PM, GRAHAM SINGLETON wrote:

     

     [quote]                Vapour lock certainly does occur. I             know of several instances, one of which resulted in a             written off aircraft. It happens when the 

         engine driven             fuel pump gets heated by the engine oil and then heats the             fuel. Low fuel flow rate such as  when taxiing or waiting             for air traffic on the ground

         can vaporize the fuel, especially             Mogas. The             fuel return  Rotax recommend keeps more fuel flowing through             the system which helps cool the pump and ensures cold fuel when you             need it for high power. 

         Most carburetor installations             in cars have a fuel return line for the same reasons.

         Graham

                                                    From:                 FLYaDIVE <flyadive(at)gmail.com> (flyadive(at)gmail.com)

                 To:                 rotaxengines-list(at)matronics.com (rotaxengines-list(at)matronics.com) 

                 Sent:                 Sunday, 7 April 2013, 19:08

                 Subject:                 Re: Re: Fuel return line

                

             

             Sacha:               

               

               You have some great thought provoking questions.  I                 hope some are provoked.

               Fire sleeves or One piece Molded Teflon fuel lines                 are the way to go.

               You always want to do all you can to keep extra heat                 from fuel and oil lines.

               BUT!  Where did this Old Wives Tail of Vapor Lock                 come from?  It is a BUNCH OF BUNK!

               The "T" fitting does NOTHING for Vapor Lock... High                 Pressure does NOTHING to prevent Vapor Lock.  Well,                 almost nothing - It corrects Pilot/Builder error.

               Vapor Lock happens ON THE GROUND and is experienced                 usually at start up and sometimes in the                 air, immediately during or after rotation.

               Vapor Lock can occur with MoGAs or AvGas.

               It is more of a POOR PILOT SHUTDOWN PROCEDURE that                 anything else.

               And since we are talking Home Built Planes and Self                 Proclaimed Engineers - - Builder error.

               So, what does the "T" fitting do?  Well, the history                 goes way back to the 1960's...  Electric home made Fuel                 Pumps were being used on Carbureted engines. And the                 engines were FLOODING like crazy.  Flooding, Fires,                 Poor Starts (if at all),  Dying when the throttle was                 floored and Low HP.  All because of TOO MUCH Fuel                 Pressure Pushing the Carburetor's intake valve off the                 seat and flooding the carb. 

               So, how do you get more fuel to the carb so it does                 not go LEAN?  You do a whole lot of pressure testing and                 engineering  - BUT!  These were HOME MADE FUEL PUMPS -                 And Manufacturer made Carbs.  Transducers were not                 around then.  It was too costly to try to figure out how                 many GPH and How much Fuel Pressure would work,and what                 size spring to use...  Too many variables.

               The QUICK and EASY and VERY Effective solution...                  Put a "T" fitting in the line and the excess pressure                 and excess fuel is returned to the fuel tank.

               The Carb takes what it needs - Has a steady supply of                 fuel and does NOT go lean no matter how fast you hit the                 throttle.

               No Smoke and Mirrors, No ridiculous Vapor                 Lock theories.  But, hell, this is aviation so everybody                 just re-invents the wheel with their own ideas.  

               

               

               I

             

           

         

       

        	  Quote: 	
		  

	
     [b]

ptag.dev(at)tiscali.co.uk
Guest

Posted: Sun Apr 07, 2013 10:33 pm Post subject: Fuel return line

Hi! Alan/all

The Jabiru incident to which I refer was with their engine mounted fuel pump

plus another electrical pick up pump.

But of course in my ultimate bad dream, actually a nightmare! The Jabiru

3300 I had fitted was never without overheating problems ...... then take it

up on Mogas in a stinking hot summer day to about 5,000ft and it lets you

know the limits of using Mogas. With the 914 Rotax I would never fly hot and

high with Mogas, I think the recommended limits are about 2,000ft and 20deg

C Ambient but having said that someone more clever than me will likely

correct me !

But the 914 on 100ll and two electrical pumps took me safely to 17,500ft

over Mont Blanc with Ivor Phillips as a "two ship" last August. Outside

ambient at that height was approx 4deg C  but at -2deg\C per 1000ft the

ambient at ground was very hot.  (as an aside had the Jabiru been the

"donkey" it used to struggle at less than 50ft per minute climb at 13,000ft

like "watching paint dry" even without vaporisation !)  Sorry about that

chaps I couldn't refrain any longer ! 

Bob Harrison. G-PTAG



--

davidjoyce(at)doctors.org
Guest

Posted: Mon Apr 08, 2013 12:17 am Post subject: Fuel return line

Bob, I strongly suspect that altitude is of no great 

consequence, certainly compared with fuel temperature 

issues. With my 914 I have flown round the upper regions 

of the Alps on Mogas with no problem , and it is striking 

that all Austrian Rotax planes seem to use the Mogas which 

is available on virtually every Austrian airfield, (and I 

think I have been told that their CAA does not impose a 

height limit). The few instances of what I have diagnosed 

as vapour lock, that I have experienced have all been at 

low level in hot weather shortly after take off after 

stopping for lunch, when the plane has been sitting out in 

the sun, and under cowl temps have been very high.

Regards, David Joyce, G-XSDJ



On Mon, 8 Apr 2013 07:31:53 +0100

  "Bob Harrison" <ptag.dev(at)tiscali.co.uk> wrote:

[quote] 

<ptag.dev(at)tiscali.co.uk>

 

 Hi! Alan/all

 The Jabiru incident to which I refer was with their 

engine mounted fuel pump

 plus another electrical pick up pump.

 But of course in my ultimate bad dream, actually a 

nightmare! The Jabiru

 3300 I had fitted was never without overheating problems 

...... then take it

 up on Mogas in a stinking hot summer day to about 

5,000ft and it lets you

 know the limits of using Mogas. With the 914 Rotax I 

would never fly hot and

 high with Mogas, I think the recommended limits are 

about 2,000ft and 20deg

 C Ambient but having said that someone more clever than 

me will likely

 correct me !

 But the 914 on 100ll and two electrical pumps took me 

safely to 17,500ft

 over Mont Blanc with Ivor Phillips as a "two ship" last 

August. Outside

 ambient at that height was approx 4deg C  but at -2deg\C 

per 1000ft the

 ambient at ground was very hot.  (as an aside had the 

Jabiru been the

 "donkey" it used to struggle at less than 50ft per 

minute climb at 13,000ft

 like "watching paint dry" even without vaporisation !) 

 Sorry about that

 chaps I couldn't refrain any longer ! 

 Bob Harrison. G-PTAG

 

 --

Alan Carter

Joined: 02 Jul 2012
Posts: 378
Location: Kent, England.

Posted: Mon Apr 08, 2013 12:51 am Post subject: Re: Fuel return line

Hi All.

Wow 17500 ft over mountains, you chaps must have God on your side.

The 914 totally reliant on Electricity, wants a little generator to pop out the side as a back up.

My concern is Ethanol, have posted before on this subject.

But could somebody sent me a private email on what's at the garage for flying in the UK and only at UK temperature. ie private e-mail only.

Alan

grahamsingleton(at)btinte
Guest

Posted: Mon Apr 08, 2013 6:29 am Post subject: Fuel return line

Sacha

all sounds reasonable to me, I would just add that low pressure caused by suction from the pump(s) could cause vaporization too. 

I once had low fuel pressure because there was a minute leak upstream of the electric pump and at low tank contents it

sucked air in.

no end to the variety of gotchas out there is there?

Graham





        From: Sacha <uuccio(at)gmail.com>

 To: rotaxengines-list(at)matronics.com 

 Sent:  Sunday, 7 April 2013, 23:38

 Subject: RE: Re: Fuel return line

  

 

Barry/Graham/Roger,

Iâ€™m no expert, but Iâ€™m going to try and summarize the arguments here.  There is no question that Vapour Lock does occur and that it can be a serious problem.  I plan to fly in a hot climate with mountainous terrain (i.e. at altitude), hence my concern.

To summarize what Iâ€™m hearing:

-         High fuel temp is bad because is causes fuel to vaporize easily (so donâ€™t shut down your engine suddenly and then try to restart it without cooling it as the fuel lines will likely be heat soaked)

-         High fuel pressure is good to the extent that 

o  a) it increases the temp at which fuel vaporizes (though IMO this effect would be marginal as the Vaporization Temp varies as 1/log Pressure) and 

o  b) if a fuel return line is fitted, the fuel pump mixes the warmer fuel in the lines under the cowling with  cooler fuel from the fuel tanks/gascolator (unless you left your plane out in the sun and your wings are painted in a dark colour in which case fuel in your  tanks might be quite warm?).

-         Very high fuel pressure is bad because it can cause the carbs to flood, hence the advisability of fitting a fuel return line

  

If one encounters vapour lock during flight, what is the best way of dealing with it, assuming one has sufficient altitude? Reduce throttle and descent at a decent airspeed to cool the engine?

Sacha

  

  

  

  

From: owner-rotaxengines-list-server(at)matronics.com [mailto:owner-rotaxengines-list-server(at)matronics.com] On Behalf Of GRAHAM SINGLETON

Sent: Sunday, 07 April, 2013 22:25

To: rotaxengines-list(at)matronics.com

Subject: Re: Re: Fuel return line

  

Vapour lock certainly  does occur. I know of several instances, one of which resulted in a written off aircraft. It happens when the 



engine driven fuel pump gets heated by the engine oil and then heats the fuel. Low fuel flow rate such as  when taxiing or waiting for air traffic on the ground



can vaporize the fuel, especially Mogas. The fuel return  Rotax recommend keeps more fuel flowing through the system which helps cool the pump and ensures cold fuel when you need it for high power. 



Most carburetor installations in cars have a fuel return line for the same reasons.



Graham

From: FLYaDIVE <flyadive(at)gmail.com (flyadive(at)gmail.com)>

To: rotaxengines-list(at)matronics.com (rotaxengines-list(at)matronics.com) 

Sent: Sunday, 7 April 2013, 19:08

Subject: Re: Re: Fuel return line



  

Sacha:

  



You have some great thought provoking questions.  I hope some are provoked.



Fire sleeves or One piece Molded Teflon fuel lines are the way to go.



You always want to do all you can to keep extra heat from fuel and oil lines.



BUT!  Where did this Old Wives Tail of Vapor Lock come from?  It is a BUNCH OF BUNK!



The "T" fitting does NOTHING for Vapor Lock... High Pressure does NOTHING to prevent Vapor Lock.  Well, almost nothing - It corrects Pilot/Builder error.



Vapor Lock happens ON THE GROUND  and is experienced usually at start up and sometimes in the air, immediately during or after rotation.



Vapor Lock can occur with MoGAs or AvGas.



It is more of a POOR PILOT SHUTDOWN PROCEDURE that anything else.



And since we are talking Home Built Planes and Self Proclaimed Engineers - - Builder error.



So, what does the "T" fitting do?  Well, the history goes way back to the 1960's...  Electric home made Fuel Pumps were being used on Carbureted engines. And the engines  were FLOODING like crazy.  Flooding, Fires, Poor Starts (if at all),  Dying when the throttle was floored and Low HP.  All because of TOO MUCH Fuel Pressure Pushing the Carburetor's intake valve off the seat and flooding the carb. 



So, how do you get more fuel to the carb so it does not go LEAN?  You do a whole lot of pressure testing and engineering  - BUT!  These were HOME MADE FUEL PUMPS - And Manufacturer made Carbs.  Transducers were not around then.  It was too costly to try to figure out how many GPH and How much Fuel Pressure would work,and what size spring to use...  Too many variables.



The QUICK and EASY and VERY Effective solution..   Put a "T" fitting in the line and the excess pressure and excess fuel is returned to the fuel tank.



The Carb takes what it needs - Has a steady supply of fuel and does NOT go lean no matter how fast you hit the throttle.



No Smoke and Mirrors, No ridiculous Vapor Lock theories.  But, hell, this is aviation so everybody just re-invents the wheel with their own ideas.  



  



I



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 [quote][b]

klinefelter.kevin(at)gmai
Guest

Posted: Mon Apr 08, 2013 9:36 am Post subject: Fuel return line

I operate the 914/Airmaster powered Europa regularly from high desert and cruise at 17500' over the mountains of the western US burning 91 auto gas ( up to 10% ethanol) with no problems.

Kevin

On Apr 8, 2013, at 1:16 AM, "David Joyce" <davidjoyce(at)doctors.org.uk> wrote:

[quote] 

 Bob, I strongly suspect that altitude is of no great consequence, certainly compared with fuel temperature issues. With my 914 I have flown round the upper regions of the Alps on Mogas with no problem , and it is striking that all Austrian Rotax planes seem to use the Mogas which is available on virtually every Austrian airfield, (and I think I have been told that their CAA does not impose a height limit). The few instances of what I have diagnosed as vapour lock, that I have experienced have all been at low level in hot weather shortly after take off after stopping for lunch, when the plane has been sitting out in the sun, and under cowl temps have been very high.

 Regards, David Joyce, G-XSDJ

 On Mon, 8 Apr 2013 07:31:53 +0100

 "Bob Harrison" <ptag.dev(at)tiscali.co.uk> wrote:

> 

> Hi! Alan/all

> The Jabiru incident to which I refer was with their engine mounted fuel pump

> plus another electrical pick up pump.

> But of course in my ultimate bad dream, actually a nightmare! The Jabiru

> 3300 I had fitted was never without overheating problems ...... then take it

> up on Mogas in a stinking hot summer day to about 5,000ft and it lets you

> know the limits of using Mogas. With the 914 Rotax I would never fly hot and

> high with Mogas, I think the recommended limits are about 2,000ft and 20deg

> C Ambient but having said that someone more clever than me will likely

> correct me !

> But the 914 on 100ll and two electrical pumps took me safely to 17,500ft

> over Mont Blanc with Ivor Phillips as a "two ship" last August. Outside

> ambient at that height was approx 4deg C  but at -2deg\C per 1000ft the

> ambient at ground was very hot.  (as an aside had the Jabiru been the

> "donkey" it used to struggle at less than 50ft per minute climb at 13,000ft

> like "watching paint dry" even without vaporisation !) Sorry about that

> chaps I couldn't refrain any longer ! Bob Harrison. G-PTAG

> --

uuccio(at)gmail.com
Guest

Posted: Mon Apr 08, 2013 10:04 am Post subject: Fuel return line

Graham,

Interesting, I hadnâ€™t thought of that one  Â 

Another question (tell me if this is boring you): has anyone had experience of vapour lock and then been able to successfully restart the engine in flight?Â  What steps were taken?

Sacha

 

 

From: owner-rotaxengines-list-server(at)matronics.com [mailto:owner-rotaxengines-list-server(at)matronics.com] On Behalf Of GRAHAM SINGLETON

Sent: Monday, 08 April, 2013 15:29

To: rotaxengines-list(at)matronics.com

Subject: Re: Re: Fuel return line

 

 Sacha

all sounds reasonable to me, I would just add that low pressure caused by suction from the pump(s) could cause vaporization too. 

I once had low fuel pressure because there was a minute leak upstream of the electric pump and at low tank contents it

sucked air in.

no end to the variety of gotchas out there is there?

Graham

 	  Quote: 	
		   	


  [quote][b]

BARRY CHECK 6

Joined: 15 Mar 2011
Posts: 738

Posted: Mon Apr 08, 2013 10:36 am Post subject: Fuel return line

Graham:



You have identified yourself as a creator of myths and a woman of Old Wife's Tales.  Let's take each of your statements:

" I know of several instances, one of which resulted in a written off aircraft. It happens when the engine driven fuel pump gets heated by the engine oil and then heats the fuel."  I'm sure there was more to it, but... That sure sounds like poor design/construction.  ALL Lycoming and Continental engines have a mechanical fuel pump mounted directly to the engine case; why don't they have this mythical Vapor Lock ever warm day?  YES - ALL engines take the chance of Vapor Lock, but, it is things like aluminum fuel lines, TEFLON fuel lines and Fire Sleeves that prevent it.  And more so proper handling by the pilot/builder.

 I have flown 5 planes on MoGas over a 12 year period and NEVER had Vapor Lock.  Yes, in the summer's of the Mid Atlantic   I also caused Vapor Lock in a C-172 using AvGas, just to prove it can be done.  Of course on the ground and it was done after an improper shutdown and inproper restart.

 

 Vapor Lock - CANNOT be created when there is fuel flow.  As long as the fuel is flowing it is not expanding.  It MUST happen at shut down.  UNLESS - as I said some very poor building practices were followed, which ran a fuel line next to or above a hot point such as an exhaust pipe.  I'm trying to believe that even if the builder made that mistake the DAR would have caught it.  AND isn't this the supposed purpose of installing the "T" fitting.  

  Vapor Lock requires two things:

1 - The fuel to be heated allowing it to expand and

2 - A place for the expanded gas (VAPOR) to be TRAPPED.

  Such a Up or Down U bend or a pig-tail.  

End of your first myth .



  

Second myth: "The fuel return Rotax recommend keeps more fuel flowing through the system which helps cool the pump and ensures cold fuel when you need it for high power."  Where to begin with this one, it is equivalent to cleaning the Augean Stables.

  Part A:  If you have two pumps in series Pump X and Pump Y.  And Pump X comes from the tank and Pump Y feeds into the carb.  And Pump X feeds at 10 PSI and 10 GPH and Pump Y Pushes at 12 PSI and 12 GPH what do you think will happen in the connection between the two pumps?  

  Since Pump Y requires/displaces more fuel than Pump X can deliver there will be a LOSS of fuel between the two...  To the untrained eye that may look like a Vapor Lock but it is just Fuel Starvation.  That is why you place the HIGHER supplying pump (Pump X) before the lower supplying pump (Pump Y).  You can always reduce what you have - You can't reduce what you don't have.

  Part B:  If there you have fuel at Zero Deg F and it is not flowing through the pump there is NO cooling taking place.  Sure there is some conduction BUT the mass of the fuel pump Vs the mass of the fuel in the fuel line and the line itself is NOT worth considering.  Ah, but I just did, just in case you use Machiavellian Logic.   What kind of fuel lines are people using?

  Part C:  Let's use some of this ridiculous logic that is being spewed forth...  Let's say you have a really terrible cooling system on your plane and through the use of this Magic "T" fitting the Hot fuel is being returned to the tank.  What about the fuel that is in the line between the electric fuel pump and the mechanical fuel pump of the HOT engine? Why isn't that causing Vapor Lock?  Then again it may?  All dependent on how well the builder did their job.  

 



Questions:  How many are using TYGON fuel lines?  How many are using some-other plastic fuel line?

  



Third myth: "Most carburetor installations in cars have a fuel return line for the same reasons."  Most old carbureted cars NEVER had a fuel return line.  As I stated before, when electric fuel pumps came into play they needed a method of increasing fuel flow without flooding the carb, therefore "T" fittings and fuel return lines.  Fuel return lines came into play NOT because of Vapor Lock but because of:

  a> The EPA - They did not want gas fumes evaporating into the atmosphere.

b> This was first fought by the car manufactures but later was proven to be helpful BECAUSE they were able to brag (advertise) about an INCREASE in gas mileage... Not really true - But just that you had more gas in you tank due to less evaporation.  How much more?  Ask the EPA!

  Today all cars have return lines and pressure gas caps and many have fuel injection.  So if one wants to use Machiavellian Logic here again - - - It was because of Vapor Lock.  NOT!

 



A Vapor Lock is the Void between a myth being trapped in the mind and the truth trying to replace it.

 



Barry

Hey, I'm 7 days late but:  Did you know you have to do a New W&B if you change from AvGas to MoGas because MoGas does not have Lead!

 



 



On Sun, Apr 7, 2013 at 5:25 PM, GRAHAM SINGLETON <grahamsingleton(at)btinternet.com (grahamsingleton(at)btinternet.com)> wrote:

  [quote]  Vapour lock certainly does occur. I know of several instances, one of which resulted in a written off aircraft. It happens when the engine driven fuel pump gets heated by the engine oil and then heats the fuel. Low fuel flow rate such as  when taxiing or waiting for air traffic on the ground can vaporize the fuel, especially Mogas. The fuel return  Rotax recommend keeps more fuel flowing through the system which helps cool the pump and ensures cold fuel when you need it for high power. 

  Most carburetor installations in cars have a fuel return line for the same reasons.

Graham

          From: FLYaDIVE <flyadive(at)gmail.com (flyadive(at)gmail.com)>

   To: rotaxengines-list(at)matronics.com (rotaxengines-list(at)matronics.com) 

 Sent: Sunday, 7 April 2013, 19:08

   Subject: Re: RotaxEngines-List: Re: Fuel return  line

  

 

Sacha:



You have some great thought provoking questions.  I hope some are provoked.

Fire sleeves or One piece Molded Teflon fuel lines are the way to go.

  You always want to do all you can to keep extra heat from fuel and oil lines.

 BUT!  Where did this Old Wives Tail of Vapor Lock come from?  It is a BUNCH OF BUNK!

The "T" fitting does NOTHING for Vapor Lock... High Pressure does NOTHING to prevent Vapor Lock.  Well, almost nothing - It corrects Pilot/Builder error.

   Vapor Lock happens ON THE GROUND and is experienced usually at start up and sometimes in the air, immediately during or after rotation.

Vapor Lock can occur with MoGAs or AvGas.

It is more of a POOR PILOT SHUTDOWN PROCEDURE that anything else.

   And since we are talking Home Built Planes and Self Proclaimed Engineers - - Builder error.

So, what does the "T" fitting do?  Well, the history goes way back to the 1960's...  Electric home made Fuel Pumps were being used on Carbureted engines. And the engines were FLOODING like crazy.  Flooding, Fires, Poor Starts (if at all),  Dying when the throttle was floored and Low HP.  All because of TOO MUCH Fuel Pressure Pushing the Carburetor's intake valve off the seat and flooding the carb. 

   So, how do you get more fuel to the carb so it does not go LEAN?  You do a whole lot of pressure testing and engineering  - BUT!  These were HOME MADE FUEL PUMPS - And Manufacturer made Carbs.  Transducers were not around then.  It was too costly to try to figure out how many GPH and How much Fuel Pressure would work,and what size spring to use...  Too many variables.

   The QUICK and EASY and VERY Effective solution...  Put a "T" fitting in the line and the excess pressure and excess fuel is returned to the fuel tank.

The Carb takes what it needs - Has a steady supply of fuel and does NOT go lean no matter how fast you hit the throttle.

   No Smoke and Mirrors, No ridiculous Vapor Lock theories.  But, hell, this is aviation so everybody just re-invents the wheel with their own ideas.  

I



 



 

  

    	  Quote: 	
		  

	
[b]

Alan Carter

Joined: 02 Jul 2012
Posts: 378
Location: Kent, England.

Posted: Mon Apr 08, 2013 11:47 am Post subject: Re: Fuel return line

Hello All.

I like the idea that a vapor lock will not occur when the fuel is flowing, this make scene to me, but will occur on the ground with a hot engine.

The fuel has got to turn to vapor and expand along the fuel pipe so locking it, 

and i would not think this would happen in a flowing fuel line.

Engines stop in flight from fuel starvation, but this could be for many reasons, 

and if unknown, claimed a vapour lock. But im not convinced,



Kevin, your another high flyer , do you use a oxygen mask up at 17.5



Alan

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