Those IR temp sensors are a great idea and very useful for this type of
testing and for calibrating the EM2 if need be. Al G. tipped me off on one
thing about them however. If the object being measured is shiny, aluminum,
painted white, etc, you can get a false reading (lower than actual).
Put a small spot of flat black paint on whatever you want to measure and
they are spot on accurate. The red paint on my engine housings works well
too.
----- Original Message -----
Sent: Sunday, August 07, 2005 11:04
AM
Subject: [FlyRotary] Re: Vapor lock last
weekend
Thanks so much for sharing your experience. You've described the
conditions well.
Couple comments if I may.
Head on down to local hobby shop. Purchase one of those little $25 infra
red temperature sensors. You just point it at object and it tells you how hot
it is. They are pretty accurate, great way to gather facts. We know that fuel
pump temp is highly significant cause for vapor lock, so great value in
finding it's temp. Use hair dryer on it to measure your safety margin.
Assume you crashed, assume you have misidentified the cause(s). Seek ways
to prove your causes. A fundamental problem with vapor lock risk is we never
know how close we are to that condition, so we tend to make assumptions.
By gathering the facts we can get closer to measuring our vapor lock safety
margin. It is measurable.
I strongly suspect the fuel pressure bypass idea would have no positive
effect on your vapor lock risk.
-al wick
Artificial intelligence in cockpit, Cozy IV powered by stock
Subaru 2.5
N9032U 200+ hours on engine/airframe from Portland,
Oregon
Prop construct, Subaru install, Risk assessment, Glass panel design
info:
http://www.maddyhome.com/canardpages/pages/alwick/index.html
Thought I would share this with everyone since just about everyone is
getting some of this heat wave and most of us aren't used to it. Also,
it sounds very similar to what Kevin is putting up with in his
RV-6A.
Interesting experience this last Saturday in my RV-4.
Interesting because it didn't happen at 800 feet where it would have
probably made the news but while I was just starting my takeoff
roll.
Conditions:
90 deg F, about noon on Saturday
150 HP Lyc
O-320 with carb, gascolator, mechanical and Facet electric pumps.
Running
last winter's last few gallons of auto-gas from my storage
tanks.
Engine was all warmed up from three laps around the pattern
shooting landings at Hillsboro. I had taxied back to the hanger to
check for anything out of the ordinary since I had recently been working on
my carb. Everything was okay so I headed back out.
While
setting at an intersection for about 5 minutes waiting to be cleared for
takeoff my CHTs were heading for hotter than I like. The wind was at
my tail so the engine was not getting any cooling. CHT was passing 335
on the Electronics International UBG-16 engine monitor and I was about to
call the tower and tell them I was heading back. The controller beat
me to it and cleared me for takeoff. This airplane normally runs about
325 at power and I have to have a hot day to get it to 350 but I never see
it that hot prior to takeoff.
Okay, I thought, a little air through
the cowl and we'll be back to normal. So I answered the controller
"6RV cleared for TO", lined up and pushed in the throttle. I got
almost 2000 rpm and just enough of a push to make it to the next
intersection and coast off the runway. It was as if I had pulled the
mixture. The prop had stopped before I stopped rolling, I was looking
at everything thinking I had missed something like the fuel valve half
cocked or left the mixture mostly out (I taxi that way). Feeling
stupid I called the tower and said 6RV was NOT taking off.
After pushing it across the runway threshold I turned the electric
pump on and it was obviously empty from the noise it was making. I was
on the tank that was 95% full so I switched to the other tank and
viola. I recognized the sounds of the pump filling the apparently
empty fuel system and carb. Hopped in and after about 6 blades it lit
and ran fine. I called the tower and taxied back to the hanger.
Thankful this had not happened at about 800 feet leaving the 5 o'clock news
empty handed.
Pulling the cowling, the carb and fuel pump were so hot
you couldn't hold your hand on them. The gas had boiled enough that it
pushed it back through the mechanical pump, gascolator, Facet pump, and tank
selector valve. When I switched to the "cold" tank out on the
intersection the Facet could get hold of enough at that point to push fuel
back to the engine. From this tank the fuel was cold enough I could
get it started and taxi back to the hanger.
-->KEVIN:
I know
you run 100LL but at the temps you are describing, upwards of 400 degrees,
you can vapor lock 100LL, too. I think Dave's right, it could be that
you are getting some vapor generation on the ground when you're trying to
run at full power. You mentioned the problem only happens when the
engine is warmed up.
I'm going to try and duplicate last Saturday's
scenario this weekend (except the takeoff attempt) if the OAT is up
enough.
Bear in mind that since I have never had any problems like
this I never saw any need for blast tubes on the fuel pump and carb like
some people have done. The cowling on the RV is pretty tight and I
have four exhaust pipes down there next to the carb, pump, and
gascolator. And since I have thousands of hours running auto gas in
various planes, while the extra volatility certainly contributed I don't
believe it's bad stuff and will continue to use it. I may keep one
tank with mostly 100LL in it for ground ops on the very hot days for extra
margin but there were more things than fuel type that contributed to what
happened.
Obviously a fuel return line that would allow
purging the hot fuel would be another fix. We have another RV-4 on the
field that has a vapor bleed return line for just this reason.
Well,
sorry for the epistle but I thought it was something for people to keep in
mind while your waiting in a long taxi line at a busy airport.
Especially those of us who rarely see 90 degree ramp temps. It was a
real eye opener (and I've only got one eye..) P-)
Mike McGee, RV-4 N996RV, O320-E2G, Hillsboro, OR
13B in gestation
mode, RD-1C, EC-2
At 20:50 2005-08-03, you wrote:
Kevin, I agree with Ken Powell
that it still sounds mostly like fuel starvation, probably in the
carb. So I won't beat that horse... However, if following
those suggestions doesn't fix it, then consider:
Since you
have definitely identified temperature as a culprit, that points at 2
possible causes: fuel vaporization and detonation. Vaporized fuel
going to the carb could cause a scenario where the bowl cant fill.
Also, detonation could behave like what you describe. Maybe you
cooling flow is no sufficient.
Doubtful, but a bad
could maybe act that way. It's easy enough to test that as a
possibility.
--
Dave Leonard
Turbo Rotary RV-6 N4VY
http://members.aol.com/_ht_a/rotaryroster/index.html
http://members.aol.com/vp4skydoc/index.html