Message-Id: <5.1.1.5.2.20040526105137.023dc850@localhost>
Date: Wed, 26 May 2004 10:55:19 -0500
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
From: Mark Steitle <msteitle@mail.utexas.edu>
Subject: Re: [FlyRotary] Fuel Stories
In-Reply-To: <list-90999@logan.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"; format=flowed

Perry,
Thanks for that detailed explanation of your fuel system.  I assume you 
return excess fuel to the sump tank?  If this is the case, have you ever 
experienced a condition where the fuel got hot enough to cause vapor lock?

Thanks,
Mark


  At 07:41 AM 5/26/2004 -0800, you wrote:


> >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
>
>
> >>  Homepage:  http://www.flyrotary.com/
> >>  Archive:   http://lancaironline.net/lists/flyrotary/List.html