From: "Perry Mick" <pjmick@mail.viclink.com>
To: "Flyrotary" <flyrotary@lancaironline.net>
Subject: Fuel Stories
Date: Wed, 26 May 2004 07:41:22 -0800
Message-Id: <20040526153433.M33605@mail.viclink.com>
MIME-Version: 1.0
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>Perry -- How is your sump supplied... gravity? 

>Mark

I guess now is a good time to tell some of my fuel stories.

I've flown for 460 hours now in almost 5 years, and have yet to log any 
glider time.

I've had a couple close calls though, related to fuel flow. Hopefully this 
will help someone.

Yes, the selected main tank in my Long-EZ drains to the sump by gravity. But 
there is only about a 1 ft. head there. I really need to replumb the fuel 
line into the sump so it enters the sump at the bottom and not the top.

I have two vents to each main tank. One comes from the center of the tank 
per plans, the second is near the top of the tank when the nose is parked 
down. So a total of 4 vent lines for both tanks, that exit at the top of the 
fuselage just ahead of the firewall behind the passenger's head. These point 
forward into the oncoming air, but are only about 1/4" above the fuselage so 
they are really within boundary layer air.

I have a fifth vent line from the sump tank near these four, but it had a 
shallower bend in it and was higher, pointing into the airstream maybe 3/4" 
above the fuselage, so it was getting more ram air.

The first sign of trouble happened a couple years ago, flying locally near 
the airport and around 3500', so even if the engine had quit, it would have 
been no problem. The engine hiccuped. There is not a lot of room on my 
instrument panel so I have side panels, a lot of engine instrumentation and 
circuit breakers on the left side and intercom and avionics circuit breakers 
on the right side. So my fuel pressure gauge is on the left side. So when 
the engine starts running rough, I have to think "fuel-related? look at the 
fuel pressure". Well, I saw that fuel pressure was low. Throttled back and 
switched tanks and it cleared up. What was happening? This only occurred on 
very cold days, after I had been flying level at full throttle for an 
extended period, and when the selected tank was very low, less than 5 
gallons. The vent into the sump tank was getting more ram air pressure than 
the vents to the main tanks, and with very little head because of the low 
fuel level in the main tank, fuel flow into the sump tank stopped. I fixed 
this by crimping the sump tank inlet mostly closed, leaving a small slit for 
an opening.

Fast forward a year or so, and it happened again one very cold morning! So I 
thought, I'll just close off the vent completely to the sump tank. I put a 
rubber cap over the sump tank vent. According to Ed Anderson, this would 
allow the high pressure fuel pumps to actually suck fuel from the main tank, 
so I thought I would try it. I flew it this way for months with no problems.

Last February I flew to Puyallup Washington. They have a relatively short 
3600' field there with one single runway. I landed there early in the 
morning when it was cool, and parked it nose down as usual. Met my cousin 
and went to the WA State Airfair. Early afternoon, sun is out, it has warmed 
up considerably. I go out and hop in and taxi out for takeoff. Very 
fortunately I had to sit at the end of the runway waiting a couple minutes 
to takeoff because of two landing airplanes in the pattern. Finally, it is 
clear and I take the runway, push in full throttle, the engine surges to 
full power, and then dies! This has never happened before! I restart it and 
it runs a little and dies. I do this a couple more times and am able to get 
it off the runway at a taxiway exit. Park it and try to figure out what is 
going on. I notice fuel pressure is low. This is strange, how could both 
fuel pumps fail? Eventually I think of the cap on the sump tank vent, and 
pop it off. I hear a "poof" sound and I hear fuel flowing into the sump 
tank. That was it! Apparently parked nose down outside while the ambient 
temperatures were increasing, allowed a big air bubble to form in the fuel 
line into the sump tank, and because the vent to the sump tank had been 
purposely blocked, fuel stopped flowing into it. I am really glad there were 
some planes in the pattern and I had to wait for takeoff. Otherwise the 
engine probably would have quit right after takeoff, at the worst possible 
time, when there were no landing options.

When I got home, I lowered the sump tank vent inlet to the same low level as 
the other vents. This way the sump tank will not get higher ram pressure 
than the mains. And of course, I now maintain the sump must be vented!

My sump only holds one gallon. I really need to put a fuel level sensor 
inside the sump tank, to give early warning that it is not full and possibly 
draining.

Perry