Mailing List flyrotary@lancaironline.net Message #56219
From: Tom Walter <roundrocktom@yahoo.com>
Subject: Re: [FlyRotary] Re: vapor lock
Date: Sat, 13 Aug 2011 11:51:43 -0700 (PDT)
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
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Dennis,

What fuel valve are you using?

My plans on the Bearhawk (high wing taildragger):

Left and Right fuel lines flow into a "R-Both-L-off" single Andair valve.

Then to the gascolator (low point at rest)

Gascolator feeds header tank, then into two pumps (only one in flight).

Everything is under the floor of the planer, under a 0.032" 2024 floor board.

Fuel return though a small "T" (0.020" orifice) to header tank.

Where does the regulator return fuel to? 

With the high wing, any air bubble from the header tank should work it's way
back up the line into the tank.  -6 aluminum tubing (note tanks have for and
aft pickups, that meet up under the door.  Allow for flow at high angles of
attack.

Tom






From: Dennis Havarlah <clouduster@austin.rr.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Saturday, August 13, 2011 12:41 PM
Subject: [FlyRotary] Re: vapor lock

Right On Kelly!!
 
I have the fuel system Kelly described in my RV-7A.  I've used Mogas with and without ethanol with outdoor temperatures up to 105 ' F.
 
I have never had a vapor lock problem.  After stopping for fuel and the engine compartment  heat soaks I hear the vapors being pushed out of the fuel rails and thru the bypass orifice  when I turn on the pumps.  No Hot Start Problems!!  It takes less than 5 seconds for the vapors to be removed and returned to the tank.  That means that all the injectors see is cool fuel when I start the engine. 
 
My fuel pumps are located on the floor between the pilot and passenger.  Because the pumps are very low fuel from the left tank will flow into the pumps by gravity.   One -6 aluminum fuel line from the pumps runs to the firewall.  If any fuel leaks during flight I will smell it and turn off the pumps and start gliding.  If I have a leak in the engine compartment I may not detect it before it ignites.
 
Just my two cents worth.  It does work for me.
 
Dennis H.
 
 
 
 
----- Original Message -----
Sent: Saturday, August 13, 2011 9:22 AM
Subject: [FlyRotary] Re: vapor lock

Guys,
 
I vote for keeping high pressure pumps as close to the tanks and as low
as possible to fuel level...............I would not locate pumps and/or suppy
hoses firewall forward unless totally encapulated, insulated and cooled
by ram air...........And by all means use the bypass oriface...........Besides
helping to reprime pumps (as Mark says) it will relieve pressure on leaky
injectors to prevent flooding (if you have experienced this with the 13B
you know what I mean and the Renesis is even worse to clear) and to
allow a vapor lock to clear the high pressure supply lines from pump to
the regulator............One more thing I would install the regulator after the
fuel rails/injectors to allow any vapor to pass through the rails on their way
to the bypass oriface...........I have seen some fuel regulator installations
with the fuel rails "Dead Ended" after the regulator leaving vapor trapped
in the rail.................When flying vapor might clear with only an apparent
misfire to the pilot but after shutdown and after heat soak it could cause
"Hot Start" problems (has anyone tryed to hot-start an fuel injected  "Lyc"
lately............IMHO 
 
Kelly Troyer
"DYKE DELTA JD2" (Eventually)
"13B ROTARY"_ Engine
"RWS"_RD1C/EC2/EM2
"MISTRAL"_Backplate/Oil Manifold
"TURBONETICS"_TO4E50 Turbo

From: Ed Anderson <eanderson@carolina.rr.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Saturday, August 13, 2011 8:16 AM
Subject: [FlyRotary] Re: vapor lock

No question, Charlie - the more of your fuel line kept under EFI pump level pressures , the less chance for vapor lock.  In tank pumps certainly do that - but, as you point out there are other considerations.  Wing root sounds like a pretty good compromise in luie  of in-tank pumps.  I considered that but in the end decided against it as it would have high pressure fuel lines inside my cockpit - which I personally do not favor {:>)
 
Don't know for certain (and may never) the cause of the latest sputtering engine event - but, in absence of in-tank pumps and/or return to tank - I still believe that pressure applied by a boost pump can prevent vapor lock (based on my own personal experience with my unique installation)
 
Ed

Sent: Saturday, August 13, 2011 9:06 AM
Subject: [FlyRotary] Re: vapor lock

The really frustrating thing about all this is that every installation is different (not to mention that it's only speculation as to what caused this particular power loss).

Sixties-era cars (carb, engine mounted fuel pump) had vapor lock problems all the time in hot weather. Modern cars, almost never (in-tank high pressure pump). Keeping the pumps as low & as close to the tank(s) as practical would seem to be the best path. Van recommends mounting pumps on the floor in the cabin. That means that the max lift would be maybe 3-4 inches, through a -6 line, and nowhere near the high under-cowl temps. There's a guy flying an injected Lyc on ethanol-laced mogas who never has a problem with vapor lock. He removed the mech pump and uses wingroot mounted electric pumps.

If it weren't for the maintenance related inconveniences, I'd seriously consider in-tank pumps, as others have done.

But we still don't know whether this is what caused the recent power loss....

Charlie
 
On 08/13/2011 06:20 AM, Ed Anderson wrote:
I should have added - the best overall approach - returning hot fuel to the heat-sink tanks and drawing new cooler fuel into the lines.
 
Ed

Sent: Saturday, August 13, 2011 6:47 AM
Subject: [FlyRotary] Re: vapor lock

Ok, Finn,  that was my guess as well. 
 
 That then brings up a question - my understanding of "vapor lock" is that it is caused by a low pressure area/combined with hot fuel on the EFI pump intake which cause the gasoline to flash to vapor - naturally the EFI pumps can not pump vapor - therefore as fuel is injected from the high pressure side of the pump (reducing pressure on that side), vapor can form there as well.  In any case, insufficient fuel is injected into the engine.
 
Since the injectors are still clicking open, it would seem that any vapor on that side of the pump already has a chance to vacate the line (through the injector) - so my assessment is that it is not the relief of vapor/gas from the high pressure side that remedies the problem, it's removing the gas from the low pressure side (pump inlet) and thereby permitting liquid fuel to be pumped that "cures" a vapor lock situation. 
 
So I am puzzled why a gas vent on the high pressure side would have much (if any) effect on vapor lock.  IF there is pressure on the injector side - I question whether it would be as high as pump pressure - and even if it were, the injector opening would provide a path for it to be release - not to mention the pressure regulator.  So as I said -I'm a bit puzzled as to the mechanism that a vent in the high pressure side prevents vapor lock.
 
In my opinion, there are two ways to reduce/eliminate the vapor in the low pressure side - either cool the fuel sufficiently (somewhat difficult to do) or to increase the pressure in the low pressure line forcing the vapor back into the liquid - ergo - use  a boost pump.
 
FWIW
 
Ed
 

Sent: Saturday, August 13, 2011 2:53 AM
Subject: [FlyRotary] Re: vapor lock

Hi Ed,

I believe it's simply a return to the tank from the high-pressure side via a very small orifice. How small I do not know.

Finn

On 8/10/2011 9:28 AM, Ed Anderson wrote:
 
The one I potential preventive measure/fix I have not looked into is the vapor by-pass/dump that I know a few folks are using.  I search the archive but could not find a description of this method - anyone care to provide one?






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