Hot weather and autogas?

"Michael" wrote in message
om...
That's the key question. Until I hear evidence to
the contrary, I'm going to keep on believing that gravity feed
carbureted systems that have a reasonable (say 2 ft or better)
vertical distance between tank pickup and carb inlet are immune to all
this vapor lock stuff.

Believe whatever you like.

Rich S.

"Michael" posted:

That's the key question. Until I hear evidence to
the contrary, I'm going to keep on believing that gravity feed
carbureted systems that have a reasonable (say 2 ft or better)
vertical distance between tank pickup and carb inlet are immune to all
this vapor lock stuff.

Believe whatever you like.

Rich S.
++++++++++++++++++++++++++++++++++++++++++++

Anecdotally speaking....

My GRAVITY fed RV3 has been totally immune to
vapor lock after logging more than 440 hours in it.
The vertical distance has remained less than 2 ft
for over 17 years.

P.S.
Not yet sure certain what can be believed.

P.P.S.
A greater 'fall' is certainly desirable.

YMMV.


Barnyard BOb --

Thanx Rich,
I think I will do the books one by one.
I am currently removing the engine from my Sonerai to redo the whole engine
installation.
I think I am going to hang on until I have gone through the book in detail.
Regards
Andre

"Rich S." wrote in message
...
"Andre" wrote in message
...
Thanx Rich!
I have just placed my orderfor the "Firewall Forward" book.
Hopefully UPS will have it here in South Africa by the end of the week.
Now I'm looking forward to some winter reading in front of the
fireplace!
:-)
Question: How does Tony Bingelis "Firewall Forward" book compare to
"Bingelis on Engines", considering that I'm running a VW engine?

The two books are comparable, Andre. "Firewall Forward" may be a bit more
comprehensive, but "TB on Engines" appears to be a later, slicker volume.
I
bought the whole series - as little as I knew about aircraft when I
started
my project, I needed all the help I could get!

Rich S.

"Rich S." wrote
That's the key question. Until I hear evidence to
the contrary, I'm going to keep on believing that gravity feed
carbureted systems that have a reasonable (say 2 ft or better)
vertical distance between tank pickup and carb inlet are immune to all
this vapor lock stuff.

Believe whatever you like.

So prove me wrong. Show me a counterexample.

Michael

"Dave" wrote in message
...

Summer vapor pressure figures are 9.0 PSI @ 100degrees

Typical undercowl temperatures on a 100° day can double that.

Rich S.

"Michael" wrote in message
om...
"Rich S." wrote
That's the key question. Until I hear evidence to
the contrary, I'm going to keep on believing that gravity feed
carbureted systems that have a reasonable (say 2 ft or better)
vertical distance between tank pickup and carb inlet are immune to all
this vapor lock stuff.

Believe whatever you like.

So prove me wrong. Show me a counterexample.

Michael

Michael..........

I went back and re-read the entire thread and, you're right, I failed to
identify my airplane and to describe the fuel system configuration. It is an
Emeraude, powered with a Lycoming O-320-E3D and having a mechanical fuel
pump on the engine. There is a Bendix electric fuel pump mounted on the
engine side of the firewall, downstream of a gascolator. All the lines are
firesleeved and are well clear of the exhaust system. There is no vapor
return line. There is a fuel pressure gauge teed in at the carburetor. A
manual primer pump takes its feed from the gascolator and is piped to all
four cylinders at the intake ports. The carb has a stock accelerator pump.

There are two 20 gallon fuel tanks, one located ahead of the instrument
panel and the other behind the seat. The nose tank has about 15" of head
above the carb inlet when the aircraft is level. There is a tank selector
valve mounted on the left kick panel. The rear tank is almost level with the
carb. The tank vents exit the bottom of the fuselage at 90° to the
slipstream and received no pressure "boost" from it. I have no idea how much
the restrictions in the fuel line (filters, check valves in the pumps,
fittings, etc.) affect the head pressure or fuel flow. The fuel system is
virtually identical with the one depicted in Fig. 4, Pg. 172 of "Firewall
Forward" by Tony Bingelis and titled "Typical Pump Fed Fuel System".

On a hot day, oil temps may exceed 200° F in the climb and run about 180° F
at cruise. Long climbs at high altitudes will bump these numbers. My oil
temp gauge has not been calibrated, but I think it's pretty close. Cylinder
head temps run 400° - 425° F in climb and 350° - 375° at cruise.

The airplane had flown over 200 hours with no mechanical problems to speak
of. It had operated perfectly in 90° temperatures and at altitudes up to
13,500' - but never both at the same time.

I hold a commercial SEL ticket with an instrument rating. I still have a CFI
card, but it has not been renewed for 20 years or so. I have logged some
1500 hours over the last 55 years and haven't logged probably another thou.
I've scared myself more times than I like to remember but have somehow
managed to survive without ever putting a scratch on an airplane due to
pilot error. One of the reasons for this luck is that I keep an open mind
and listen to those who have gone before.

On the day I experienced vapor lock and loss of power, the selector valve
was set on the nose tank and it was at least 2/3 full, adding another 10" to
the head distance. We were at 9,500' and the OAT was 85°. The electric pump
was turned off in cruise and the fuel pressure gauge had been reading just
above red line at ~2 lbs. As I was scanning the gauges, I saw the fuel
pressure fall to zero while I watched. I immediately turned the plane
towards a soybean field I has just passed. By the time I completed the turn,
the engine lost power.

I turned on the electric pump and switched to the rear tank. Nothing. The
engine must have been getting little dribbles of fuel, because the vibration
was severe. There was no noticeable thrust from the prop, however. My wife
was becoming hysterical, adding to the situation. I put out a Mayday to Salt
Lake Center in order to get through on the frequency - it was quite busy and
I wanted someone apprised of our situation and location at once. As we
descended, I did indeed lose line-of-sight and relied on a relay through an
overflying cargo flight (Thanks again, Matt!)

We lost about 7,000' and I was just setting up to enter a downwind leg for
the bean field. All attempts at a restart had failed. I admit that I had
forgotten to try the manual prime pump. On the Emeraude, I have a fold-down
instrument panel and the primer is mounted under the panel, pretty much out
of sight. No excuse for forgetting to think of it, I know. But a
"contributing factor". I did remember the accelerator pump at that moment
and decided to pump the throttle. Perhaps there was some fuel left in the
pump itself even though the float bowl was dry. I intended to close the
throttle before landing to make sure that I didn't get a burst of power at
the wrong moment.

I pumped the throttle and was immediately rewarded with engine power. It
sagged a bit, coughed a couple of times and then burst into full song. We
climbed without leaving the vicinity until I was sure that we could reach a
private field marked on the sectional another 5-6 miles further away. The
engine ran perfectly as we flew to the location; only to find the airport
had been turned into fenced ag fields. We had continued the climb somewhat
and decided to try to reach Helena, MT, then some 15 miles to the South. We
reached Helena without incident. The temperature there was over a hundred.
There was no FAA report necessary, as the emergency was terminated while
still airborne and without incident. Center, Approach and Tower staff were
concerned, professional and helpful. I called and thanked them all.

I'm sorry to be so long-winded about this, but you asked for details. Feel
free to criticize my plane or my actions, but try to be kind. I am not
trying to force you to abandon autogas or fly near roads. I'm just letting
you know what may happen if you persist in the belief that your airplane is
*immune* to vapor lock. Trust me in this, though. You don't ever want to
hear the person you love screaming and sobbing in fear. Never.

Rich S.

On Tue, 29 Jul 2003 07:48:35 -0700, "Rich S."
Anecdotally speaking....

My GRAVITY fed RV3 has been totally immune to
vapor lock after logging more than 440 hours in it.
The vertical distance has remained less than 2 ft
for over 17 years.

P.S.
Not yet sure certain what can be believed.

P.P.S.
A greater 'fall' is certainly desirable.

YMMV.


Barnyard BOb --

The quality of autofuel dispensed at a strange FBO may vary as well. I
prefer to buy from a known source and often test for alcohol content. The
fuel which boiled in the Emeraude came from a really crappy looking
tank/pump installation at the Pullman, WA airport. I have no idea if it was
fresh - or last Winter's blend.

Chances are that the Avgas is more consistent quality.

I think you said your RV-3 has an electric fuel pump in the line. Does it
also have a mechanical pump? Do the check valves in the pump(s) reduce the
head pressure at the carburetor? Seems like a direct, gravity fed line with
no restrictions or check valves would deliver a higher fuel flow.

Rich S.
++++++++++++++++++++++++++++++++++++++++++++++

GRAVITY... and only GRAVITY.
No mechanical engine driven or electric boost pump
No fuel pressure gage, either

You're dead nuts on about 'restrictions'....
hampering a gravity only system.

I dare NOT install an electric pump directly in the line.
Van's sez it's OK to do that with an RV3 gravity system,
but I doubt if they have ever tried it for themselves. The
check valve restriction through the electric pump
combined with the puny 14 inch or so head is asking
for HUGE troubles with the boost pump off or failed, IMO.
At least with a half tank of fuel and high AOA, like...
at take-off trying to feed 60-80 of the 150 hungry horses?
[Remember we are only spinning at 2200 rpm, not 2700.]

What I have in mind is a PARALLEL path for an electric
boost pump...PREFERABLY without a check valve in
the system.

Think I can get away without one? ---
Think CAREFULLY, before you answer.


Barnyard BOb -- engage brain before putting mouth into gear

"Barnyard BOb --" wrote in message
...

GRAVITY... and only GRAVITY.
No mechanical engine driven or electric boost pump
No fuel pressure gage, either

You're dead nuts on about 'restrictions'....
hampering a gravity only system.

I dare NOT install an electric pump directly in the line.
Van's sez it's OK to do that with an RV3 gravity system,
but I doubt if they have ever tried it for themselves. The
check valve restriction through the electric pump
combined with the puny 14 inch or so head is asking
for HUGE troubles with the boost pump off or failed, IMO.
At least with a half tank of fuel and high AOA, like...
at take-off trying to feed 60-80 of the 150 hungry horses?
[Remember we are only spinning at 2200 rpm, not 2700.]

What I have in mind is a PARALLEL path for an electric
boost pump...PREFERABLY without a check valve in
the system.

Think I can get away without one? ---
Think CAREFULLY, before you answer.


Barnyard BOb -- engage brain before putting mouth into gear

I have been mulling over several different questions regarding fuel system
plumbing in the last year or so - even up to the last resort of an extra one
gallon (or so) tank with a mechanical pump piped to the intake manifold
after the carb.

As for your concept, I think it would require a shutoff valve to keep the
electric pump from pumping in a circle. Unless the electric pump had
sufficient flow to create friction loss in the line leading back to the
tank, that is. I'd have to get out my tables for friction loss to figger
that one out. Used to be able to do it in my head with a fire engine roaring
next to me.

How about a solenoid operated valve tied to the electric pump switch?

Rich S.

the system.

Think I can get away without one? ---
Think CAREFULLY, before you answer.


Barnyard BOb -- engage brain before putting mouth into gear

BOb, I'm "Positive" you could get away without one. Me though, I would
want the 2nd and third way out! g

I got through my back surgery (fusion) so count on even more mistakes, now
that my fingers are stoned.
--
Jim in NC

Michael wrote:

So prove me wrong. Show me a counterexample.

No quantitative data to back it up, so I'm sure
it won't meet your idea of a counterexample,
but a search of NTSB records shows a few
accidents with high wing gravity-feed systems
where vapor lock was suspected or reported,
and there was no other obvious mechanical
defect.

Dave 'Plan for the worst, accept better results' Hyde