I'm building an RV, and am considering using mogas, or at least having the
option of using it. Problem is that mogas has a higher vapor pressure (among
other anomalies), and this in turn can cause vapor lock. Routing of the fuel
lines is quite important, as well as the proper cooling of the gascolator
and insulating the firewall forward lines.

Even with all the above, risk of vapor lock still exists, especially when
the bird has been heat soaking on a ramp during a flying intermission.

Anyone ever consider the use of a Peltier effect device (like the ones used
in those solid state coolers, or CPU coolers) to cool down the fuel as it
passes through the cockpit (lowest ambient temperature... lower than FWF
anyway).

Haven't done the BTU math yet and was wondering if anybody else is going
through this same exercise.

This device could be used when the risk of vapor locking is high (high
altitude, temperature etc.)

Comments?

I'm not sure your assumptions about vapor pressure are correct. I once saw
my blue 100LL fizzing furiously when I checked the drains on a hot afternoon
in Albuquerque. The homebuilt owner next to me showed me his Mogas sample
and there wasn't a bubble in it.

I delayed departure until the next morning to let my 100LL cool. He flew
away without delay.

Bill Daniels


"anaconda" > wrote in message
...
> I'm building an RV, and am considering using mogas, or at least having the
> option of using it. Problem is that mogas has a higher vapor pressure
(among
> other anomalies), and this in turn can cause vapor lock. Routing of the
fuel
> lines is quite important, as well as the proper cooling of the gascolator
> and insulating the firewall forward lines.
>
> Even with all the above, risk of vapor lock still exists, especially when
> the bird has been heat soaking on a ramp during a flying intermission.
>
> Anyone ever consider the use of a Peltier effect device (like the ones
used
> in those solid state coolers, or CPU coolers) to cool down the fuel as it
> passes through the cockpit (lowest ambient temperature... lower than FWF
> anyway).
>
> Haven't done the BTU math yet and was wondering if anybody else is going
> through this same exercise.
>
> This device could be used when the risk of vapor locking is high (high
> altitude, temperature etc.)
>
> Comments?
>
>
>

> I'm not sure your assumptions about vapor pressure are correct. I once
> saw
> my blue 100LL fizzing furiously when I checked the drains on a hot
> afternoon
> in Albuquerque. The homebuilt owner next to me showed me his Mogas sample
> and there wasn't a bubble in it.
>
> I delayed departure until the next morning to let my 100LL cool. He flew
> away without delay.

And I've flown our normally aspirated O-540-powered, mogas-fueled Cherokee
Pathfinder on days that you could fry eggs on the tarmac, at both high and
low altitudes...without difficulty.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

"anaconda" > wrote in message
...
> I'm building an RV, and am considering using mogas, or at least having the
> option of using it. Problem is that mogas has a higher vapor pressure
> (among
> other anomalies), and this in turn can cause vapor lock. Routing of the
> fuel
> lines is quite important, as well as the proper cooling of the gascolator
> and insulating the firewall forward lines.
>
> Even with all the above, risk of vapor lock still exists, especially when
> the bird has been heat soaking on a ramp during a flying intermission.
>
> Anyone ever consider the use of a Peltier effect device (like the ones
> used
> in those solid state coolers, or CPU coolers) to cool down the fuel as it
> passes through the cockpit (lowest ambient temperature... lower than FWF
> anyway).
>
> Haven't done the BTU math yet and was wondering if anybody else is going
> through this same exercise.
>
> This device could be used when the risk of vapor locking is high (high
> altitude, temperature etc.)
>
> Comments?

Comments? Certainly...

I built and now fly a 160 hp carburated RV-6. I always run 100 LL, and have
starting problems I attribute to vapor lock on hot days when I do a medium
length stay on the ground - say 20 to 45 minutes after flying for a while.
I think the starting problem would be much worse using mogas. I've never
had a problem with vapor lock once I got the plane started.

I've read the same thing you have about mogas - it typically has higher
vapor pressure, which is compounded if you happen to get some winter
formulation mogas with higher (winter) vapor pressure during the warm
months. Given my experience and flying patterns (I typically cruise at
10,000' or more during the warm months), I can't see me putting mogas in my
airplane during the summer months. Too many opportunities for trouble.
However, if I lived in a cool climate, or didn't plan on flying high, I
might use it in the winter.

If I was going to use mogas, I would consider a blast tube on the mechanical
fuel pump, plus I'd do everything possible to minimize heat build up inside
the cowling. Additionally, I would follow the EAA mogas STC's plan of
avoiding sharp bends in fuel lines. Beyond that, I might add a recirc line
or purge valve to purge the fuel lines firewall forward before a hot start.

You should be able to find a pretty good write up on mogas STC's using
google. There is some good information out there, particularly at the EAA
site, IIRC.

KB

In article >,
"Kyle Boatright" > wrote:

> "anaconda" > wrote in message
> ...
> > I'm building an RV, and am considering using mogas, or at least having the
> > option of using it. Problem is that mogas has a higher vapor pressure
> > (among
> > other anomalies), and this in turn can cause vapor lock. Routing of the
> > fuel
> > lines is quite important, as well as the proper cooling of the gascolator
> > and insulating the firewall forward lines.
> >
> > Even with all the above, risk of vapor lock still exists, especially when
> > the bird has been heat soaking on a ramp during a flying intermission.
> >
> > Anyone ever consider the use of a Peltier effect device (like the ones
> > used
> > in those solid state coolers, or CPU coolers) to cool down the fuel as it
> > passes through the cockpit (lowest ambient temperature... lower than FWF
> > anyway).
> >
> > Haven't done the BTU math yet and was wondering if anybody else is going
> > through this same exercise.
> >
> > This device could be used when the risk of vapor locking is high (high
> > altitude, temperature etc.)
> >
> > Comments?
>
> Comments? Certainly...
>
> I built and now fly a 160 hp carburated RV-6. I always run 100 LL, and have
> starting problems I attribute to vapor lock on hot days when I do a medium
> length stay on the ground - say 20 to 45 minutes after flying for a while.
> I think the starting problem would be much worse using mogas. I've never
> had a problem with vapor lock once I got the plane started.
>
> I've read the same thing you have about mogas - it typically has higher
> vapor pressure, which is compounded if you happen to get some winter
> formulation mogas with higher (winter) vapor pressure during the warm
> months. Given my experience and flying patterns (I typically cruise at
> 10,000' or more during the warm months), I can't see me putting mogas in my
> airplane during the summer months. Too many opportunities for trouble.
> However, if I lived in a cool climate, or didn't plan on flying high, I
> might use it in the winter.
>
> If I was going to use mogas, I would consider a blast tube on the mechanical
> fuel pump, plus I'd do everything possible to minimize heat build up inside
> the cowling. Additionally, I would follow the EAA mogas STC's plan of
> avoiding sharp bends in fuel lines. Beyond that, I might add a recirc line
> or purge valve to purge the fuel lines firewall forward before a hot start.


The above precautions are just good design/building practice and should
be a part of the plane in the first place. Add a boost pump aft of the
firewall, to help keep a positive head on the engine-driven pump, too.

IMHO, the purge valve might ad more problems than it solves, in case of
valve failure.

As a side note, the Varga has the most cockamamie (and certificated)
fuel plumbing under the cowl that I have ever seen.


> You should be able to find a pretty good write up on mogas STC's using
> google. There is some good information out there, particularly at the EAA
> site, IIRC.
>
> KB

--
Remove _'s from email address to talk to me.

"ORVAL FAIRBAIRN" > wrote in message
...
> In article >,
> "Kyle Boatright" > wrote:
<<<snip>>>
>>
>> If I was going to use mogas, I would consider a blast tube on the
>> mechanical
>> fuel pump, plus I'd do everything possible to minimize heat build up
>> inside
>> the cowling. Additionally, I would follow the EAA mogas STC's plan of
>> avoiding sharp bends in fuel lines. Beyond that, I might add a recirc
>> line
>> or purge valve to purge the fuel lines firewall forward before a hot
>> start.
>
>
> The above precautions are just good design/building practice and should
> be a part of the plane in the first place. Add a boost pump aft of the
> firewall, to help keep a positive head on the engine-driven pump, too.
>
> IMHO, the purge valve might ad more problems than it solves, in case of
> valve failure.

Certainly something to consider. I have a gascolator under the cowl which
allows me to purge *some* of the warm fuel from the system. On the other
hand, I think the gascolator serves as a heat exchanger to heat the fuel,
which ain't good... I don't think my next plane will include an under-cowl
gascolator.

KB

"Kyle Boatright" > wrote in message
...
>

> I built and now fly a 160 hp carburated RV-6. I always run 100 LL, and
> have starting problems I attribute to vapor lock on hot days when I do a
> medium length stay on the ground - say 20 to 45 minutes after flying for a
> while. I think the starting problem would be much worse using mogas. I've
> never had a problem with vapor lock once I got the plane started.
>
> I've read the same thing you have about mogas - it typically has higher
> vapor pressure, which is compounded if you happen to get some winter
> formulation mogas with higher (winter) vapor pressure during the warm
> months. Given my experience and flying patterns (I typically cruise at
> 10,000' or more during the warm months), I can't see me putting mogas in
> my airplane during the summer months. Too many opportunities for trouble.
> However, if I lived in a cool climate, or didn't plan on flying high, I
> might use it in the winter.
>
> If I was going to use mogas, I would consider a blast tube on the
> mechanical fuel pump, plus I'd do everything possible to minimize heat
> build up inside the cowling. Additionally, I would follow the EAA mogas
> STC's plan of avoiding sharp bends in fuel lines. Beyond that, I might
> add a recirc line or purge valve to purge the fuel lines firewall forward
> before a hot start.
>
> You should be able to find a pretty good write up on mogas STC's using
> google. There is some good information out there, particularly at the EAA
> site, IIRC.

You've got a good grasp of the situation.

Rich S.

>... I think the gascolator serves as a heat exchanger to heat the fuel,
>which ain't good... I don't think my next plane will include an under-cowl
>gascolator.

I've heard of some people placing their gascolators in the area between the
wing and fuselage. Requires a bit more plumbing. Along with fuel pumps at
each tank (will require to switch on fuel pump only at selected tank) would
probably mitigate the vapor lock issue.

My only problem is figuring out the reasoning for Van's original plumbing.
There's usually a reason Van's does something, and I'd like to fully
understand it before modifiyg it.