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grahamsingleton(at)btinte
Guest

Posted: Mon Apr 08, 2013 12:52 pm Post subject: Fuel return line

"Vapour lock" not a good name perhaps occurs when the fuel boils and vapour flows into the carburetor.

Then the mixture is all wrong and the engine won't give power.

It tends to occur when fuel flow is very low so the fuel doesn't cool the Rotax pump. Taxying with a hot engine on a hot day

then trying to take off.

Bit of thinking required imho

Graham





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

 To: rotaxengines-list(at)matronics.com 

 Sent: Monday, 8 April 2013, 19:36

 Subject: Re: Re: 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:



 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



 



 

  

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[b]

Roger Lee

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

Posted: Mon Apr 08, 2013 4:13 pm Post subject: Re: Fuel return line

Hi Barry,



I think you are only partially right and missed several qualifiers and exacerbating contributory issues.



They talk about vapor lock in flight, but I have not personally seen it happen, but there are a thousand different planes designs out there and Rotax didn't just pull this out of a hat. It probably happened somewhere.



Here are some of the problems. It isn't just fuel flow, it must have a sufficient quantity flowing so the heat doesn't have time to heat the fuel up to vaporize. Having exposed fuel lines without fire sleeve not only leaves the fire danger on the table, but allows for more heat to the fuel. The Rotax or a small size engine may not flow enough fuel and if the engine is encased in a cowl and has a lack of or poor air flow and the fuel flow gets reduced and the fuel sets long enough in the fuel line vapor can happen and the fuel will be flowing.

Vapor lock can happen when an engine is running with fuel flow. My Dad's old Packard used to get vapor lock especially going up into the mountains at a slow pace and getting hotter than normal or an engine with a reduced cooling air flow. It isn't just whether fuel is flowing it depends on the quantity that flows. If the quantity is very small, but still flowing and in an excessively hot area it can absolutely vapor lock, just like the old cars. Fuel flow quantity is the key and the enclosed environment plus heat becomes the next problem. I usually don't see vapor lock while flying and most never will, but I absolutely see it all the time after a plane has landed and sat for 30+ minutes. Then on start up the fuel pressure is 1-1.5 psi until the cooler fuel flows into the upper fuel lines. In a tightly cowed engine the heat is higher with no fuel flow right after shut down. That said I haven't seen an engine cough because of it yet. Putting just a Tee in is really not a re-circulation line. It must have a restrictor in place otherwise you wouldn't have any fuel pressure. Vapor lock seems to happen more on the ground and things aren't cooling as well and there is less fuel flow. A "U" shape fitting won't guarantee or eliminate vapor lock. As the fuel sits in the hot environment more vapor can form and as it expands it will over come the "U" fitting area and expand into the hoses. It all depends on the heat amount, the fuel line surface area, insulating factors( i.e. fire sleeve), air flow for cooling and fuel flow quantity.



After sitting on the ground and starting up with vapor in the lines, then usually a taxi out to a runway will take care of the issue.

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

Alan Carter

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

Posted: Tue Apr 09, 2013 12:39 am Post subject: Re: Fuel return line

Hi Roger.

OK, so vapor lock is possible with flowing fuel, but slow moving fuel.

To me if this happens it pretty serious as it will bring the aircraft down.

So why has nothing been do about it, What about something simple like a 

cooling units clipped round a fuel line powered by the battery, 20 minutes to

 fit , so cooler fuel and problem fixed, There must be some simple fix for this.



Alan

BARRY CHECK 6

Joined: 15 Mar 2011
Posts: 738

Posted: Tue Apr 09, 2013 12:52 am Post subject: Fuel return line

Roger:



It appears that you misread my post.  Almost everything you are saying I said in my post.  The only thing that is truly misread is your statement on "U shape fitting".  I did not say it will cure the problem.  I said it causes the problem.  what is required for a Vapor Lock Failure, is a point for the vapor to be trapped.  A U shape, either Up or Down or a Pig Tail will supply that failure point.  The vapor has to have a place to expand and NOT move to form a vapor lock.

 



Now, I can't comment on Packard's...  They very well and probably did have vapor lock issues.  After all, they are only two steps beyond the invention of the wheel.  Back in those days my Dad was pushing pedals on a bicycle as a Butcher's Boy doing deliveries and hitch-hiking rides on the back of a horse drawn cart.  We advanced a LITTLE since then.

 



Did you know: That back in the late 1800's early 1900's it took one hour to go from one end of Manhattan Island to the other by Horse Drawn Cart.  Today with a 400 Horse Power Car it now takes 4 hours!  Some advancement!

 



Barry





 



On Mon, Apr 8, 2013 at 8:13 PM, Roger Lee <ssadiver1(at)yahoo.com (ssadiver1(at)yahoo.com)> wrote:

 [quote]--> RotaxEngines-List message posted by: "Roger Lee" <ssadiver1(at)yahoo.com (ssadiver1(at)yahoo.com)>

  

 Hi Barry,

 

 I think you are only partially right and missed several qualifiers and exacerbating contributory issues.

 

 They talk about vapor lock in flight, but I have not personally seen it happen, but there are a thousand different planes designs out there and Rotax didn't just pull this out of a hat. It probably happened somewhere.

  

 Here are some of the problems. It isn't just fuel flow, it must have a sufficient quantity flowing so the heat doesn't have time to heat the fuel up to vaporize. Having exposed fuel lines without fire sleeve not only leaves the fire danger on the table, but allows for more heat to the fuel. The Rotax or a small size engine may not flow enough fuel and if the engine is encased in a cowl and has a lack of or poor air flow and the fuel flow gets reduced and the fuel sets long enough in the fuel line vapor can happen and the fuel will be flowing.

  

 

 Vapor lock can happen when an engine is running with fuel flow. My Dad's old Packard used to get vapor lock especially going up into the mountains at a slow pace and getting hotter than normal or an engine with a reduced cooling air flow. It isn't just whether fuel is flowing it depends on the quantity that flows. If the quantity is very small, but still flowing and in an excessively hot area it can absolutely vapor lock, just like the old cars. Fuel flow quantity is the key and the enclosed environment plus heat becomes the next problem. I usually don't see vapor lock while flying and most never will, but I absolutely see it all the time after a plane has landed and sat for 30+ minutes. Then on start up the fuel pressure is 1-1.5 psi until the cooler fuel flows into the upper fuel lines. In a tightly cowed engine the heat is higher with no fuel flow right after shut down. That said I haven't seen an engine cough because of it yet. Putting just a Tee in is really not a re-ci!

   rculation line. It must have a restrictor in place otherwise you wouldn't have any fuel pressure. Vapor lock seems to happen more on the ground and things aren't cooling as well and there is less fuel flow. A "U" shape fitting won't guarantee or eliminate vapor lock. As the fuel sits in the hot environment more vapor can form and as it expands it will over come the "U" fitting area and expand into the hoses. It all depends on the heat amount, the fuel line surface area, insulating factors( i.e. fire sleeve), air flow for cooling and fuel flow quantity.

  

 After sitting on the ground and starting up with vapor in the lines, then usually a taxi out to a runway will take care of the issue.

 

 --------

 Roger Lee

 Tucson, Az.

 Light Sport Repairman - Maintenance Rated

 Rotax Repair Center - Heavy Maint. Rated

 Home [url=tel:520-574-1080]520-574-1080[/url]  TRY HOME FIRST

 Cell [url=tel:520-349-7056]520-349-7056[/url]

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=398196#398196

 

 

 

 

 

 

 

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 -List" target="_blank">http://www.matronics.com/Navigator?RotaxEngines-List

 ===========

 http://forums.matronics.com

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 le, List Admin.

 ="_blank">http://www.matronics.com/contribution

 ===========

 

 

 

 [b]

BARRY CHECK 6

Joined: 15 Mar 2011
Posts: 738

Posted: Tue Apr 09, 2013 1:04 am Post subject: Fuel return line

Allen:



Somethings have been done about it.

Aluminum fuel lines.

TEFLON fuel lines.

Fire sleeves.

Better designed feed systems.

Better designed under the cowl air flow systems. 

 And an instruction book on what and what not to do... AC43-13.

Problem is we refuse to learn from history so you will be doomed to repeat history.  Each generation thinks they know better than the past generation.

 



You want to invent a clip on air conditioner that will install in 20 minutes YET!  Be a SIMPLE FIX!?!   I love your irony.

Barry

On Tue, Apr 9, 2013 at 4:39 AM, Alan Carter <alancarteresq(at)onetel.net (alancarteresq(at)onetel.net)> wrote:

 [quote]--> RotaxEngines-List message posted by: "Alan Carter" <alancarteresq(at)onetel.net (alancarteresq(at)onetel.net)>

  

 Hi Roger.

 OK, so vapor lock is possible with flowing fuel, but slow moving fuel.

 To me if this happens it pretty serious as it will bring the aircraft down.

 So why has nothing been do about it, What about something simple like a

 cooling units clipped round a fuel line powered by the battery, 20 minutes to

  fit , so cooler fuel and problem fixed, There must be some simple fix for this.

 

 Alan

 



[b]

grahamsingleton(at)btinte
Guest

Posted: Tue Apr 09, 2013 2:37 am Post subject: Fuel return line

There is a simple fix:

Fit the fuel return as Rotax recommend and recirculate the fuel.

Graham





        From: Alan Carter <alancarteresq(at)onetel.net>

 To: rotaxengines-list(at)matronics.com 

 Sent: Tuesday, 9 April 2013, 9:39

 Subject: Re: Fuel return line

  

 

--> RotaxEngines-List message posted by: "Alan Carter" <alancarteresq(at)onetel.net (alancarteresq(at)onetel.net)>



Hi Roger.

OK, so vapor lock is possible with flowing fuel, but slow moving fuel.

To me if this happens it pretty serious as it will bring the aircraft down.

So why has nothing been do about it, What about something simple like a 

cooling units clipped round a fuel line powered by the battery, 20 minutes to

 fit , so cooler fuel and problem fixed, There must be some simple fix for this.



Alan





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=398222#398222          - The RotaxEngines-List Email Forum -http://w            http://www.matronics.com/contribution" target="_blank">http://www.matroni====================



 

 

  

 [quote][b]

jim.kulbeth(at)insightbb.
Guest

Posted: Tue Apr 09, 2013 3:31 am Post subject: Fuel return line

Hi Guys,

Just a short comment.  I have read all of the blogs on the vapor locking problem and the only time I have experienced vapor lock was on the ground with certified aircraft and in those instances it was very hot and I stopped for fuel enroute.  I have two aircraft, one with a Jabiru and one Rotax. Both have the fuel return back to the tank.  Neither have ever experienced vapor lock no matter the condition and I depart airports that are from sea level to 8000 ft in up to 110 degrees F.     Maybe the reason is my fuel is cooler since it has farther to recirculate.



By the way what started this particular blog. Did someone experience this or was it a hypothetical question?



Regards

Jimmy



On Apr 7, 2013, at 18:45, "Sacha" <uuccio(at)gmail.com> wrote:



[quote] My fuel return line only goes back to the gascolatorâ€¦ but Iâ€™m hoping itâ€™s enough as it is at the bottom of the cowling and should get decent cooling from the airflow.

  

 I read Transport Canadaâ€™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 doesnâ€™t seem like there is any need for â€œsummerâ€ fuel this year so farâ€¦ 

  

 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 Iâ€™m concerned there was no BS involved. To say thereâ€™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>

 To: 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

Alan Carter

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

Posted: Tue Apr 09, 2013 12:54 pm Post subject: Re: Fuel return line

Hi All.

I can see the fire hoses on the metal fuel lines above the engine,

How can i tell if have the return or buy pass fuel line is already installed ?

I take it this is not part of the standard build ,914 built 2000.

Alan

rlborger(at)mac.com
Guest

Posted: Tue Apr 09, 2013 1:08 pm Post subject: Fuel return line

Alan,



If you have a 914, there should be a fuel return line as it is required for the 914 installation.

There should be a fuel return line coming off the fuel pressure regulator returning to the starboard side of the fuel tank.  

Go to Europa-Aircraft.com > Builder Assistance > Builders Manuals > Rotax 914 Installation for details.

Blue skies & tailwinds,Bob BorgerEuropa XS Tri, Rotax 914, Airmaster C/S Prop.Little Toot Sport Biplane, Lycoming Thunderbolt AEIO-320 EXP3705 Lynchburg Dr.Corinth, TX  76208-5331Cel: 817-992-1117rlborger(at)mac.com (rlborger(at)mac.com)



On Apr 9, 2013, at 3:54 PM, Alan Carter <alancarteresq(at)onetel.net (alancarteresq(at)onetel.net)> wrote:

[quote]--> RotaxEngines-List message posted by: "Alan Carter" <alancarteresq(at)onetel.net (alancarteresq(at)onetel.net)>



Hi All.

I can see the fire hoses on the metal fuel lines above the engine,

How can i tell if have the return or buy pass fuel line is already installed ?

I take it this is not part of the standard build ,914 built 2000.

Alan[b]

Alan Carter

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

Posted: Tue Apr 09, 2013 2:09 pm Post subject: Re: Fuel return line

Hi Bob.

I glad i have one, i have an inspector coming to see the aircraft and hoping he will give me a few pointer as im a bit of a green horn.

Alan

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