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napierm(at)cisco.com
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 Posted: Mon Oct 26, 2009 7:58 am Post subject: Fuel Flow Problems, Again! |
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Hey Travis,
On advice from Tom Olenik I run the Rotax brand fuel filters. They are
big white plastic things. They are very high flow/low head loss and
won't block due to water.
If the filters/hoses are OK and the vent line has no obstruction then I
would check your tank caps. The gaskets are not hard and make a good
seal?
I can't think of anything else. If you make it a fly-in around Atlanta
please let me know; I would like to see your bird.
Good luck,
Mark Napier
Time: 05:55:37 PM PST US
Subject: Fuel Flow Problems, Again! (Vixen, Series-5)
From: "FlyboyTR" <flyboytr(at)bellsouth.net>
We just returned from an 800 mile trip to our favorite flying
destination, High
Valley Resort in north GA. We developed a fuel flow problem while
enroute.
A little history. Two years ago I had a fuel flow problem (actually on
the same
trip!) that was caused by my new paper filters (located between the wing
tanks
and the header tank) air locking and not allowing fuel to flow. We
completed
the trip using just one tank. After returning home, I discovered that
if I
blew up through the fuel line, causing the filter to fill with air, it
would
not gravity flow! After either sucking on the line ( or blowing on the
gas cap
vent tube) to force the fuel to flow, it would flow without restriction.
This
was repeated numerous times, on both tanks with the exact same results!
The
filters had been replaced just prior to this event. This was also
tested with
new filters with the same results. After that, I returned to using the
filters
with the glass sight tubes.
OKpresent day... I filled both tanks to the brim prior to our 400 mile,
one way,
flight. After about 45 minutes Kathy noticed there was no fuel in the
header
tank vent line. The right tank level was low and the left one was full
(could
not see the fuel levelabove the sight gauge). We checked and both fuel
valves
were on and we cycled them several times. I reduced power to the engine
and set it up lean of peak to reduce the fuel flow. Shortly, fuel
appeared in
the vent tube (yes that was a relief!). Fortunately we were at 9,500,
talking
the Atlanta Center and had an airport with easy gliding distance (which
also
provided some peace of mind).
After going back to full cruise power, the fuel level in the vent line
started
dropping. We turned the working tank off, pinched the vent line so it
would force,
hopefully, the fuel in the right tank to be sucked. After a few
seconds,
the left tank filter (which was filed with air) starting showing some
fuel movement
and slowly filled about way. I kept the vent line pinched for about
a minute. Fuel flow was established on the left tank, but still not
enough to
fill the vent line. I turned the right tank back on and the vent line
filled.
I closed it again and then slowly opened it to allow partial flow and
kept
the fuel level in the vent line visible for about 30 minutes. After
several gallons
of fuel was pulled from the left tank, I opened the right valve
completely
and the vent tube filled. After that fuel flowed from both tanks and
was
not a problem.
Heading Home We stopped for fuel while heading home. This time the
same thing
happened, except the tanks were reversed! Right tank would not flow.
We did
the same thingpinching off the vent line and forcing the system to suck
from
the non-flowing tank. Again, this was met with success.
I am at a complete loss! The vent lines on the gas caps are open
(checked with
each fill-up and also with a pipe cleaner, etc). All my flexible fuel
lines
are 3/8 marine grade lines (vent line is clear Tygon). No lines are
pinched.
Once flowing, they flow with no restriction. There are no loops, etc in
any
of the lines. I would appreciate any helpful information regarding this
problem!
AlsoOn the return leg home this afternoonMy charging system went out! I
just hope
it's not another alternator coupling/clutch thats gone bad!
Travis
--------
Travis Rayner
Mobile, AL
Skystar Vixen, N-789DF
Continental IO-240, Prince P-Tip Prop
ADI-II Autopilot
AnyWhereMap Navigation with weather
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p 69410#269410
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FlyboyTR
Joined: 04 Nov 2006
Posts: 215
Location: Mobile, Alabama
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| Posted: Mon Oct 26, 2009 12:28 pm Post subject: Re: Fuel Flow Problems, Again! |
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Mark,
What is the part number on the fuel filter. What is the element made of?
I don't think my fuel cap gaskets are leaking. I can blow through the vent and don't hear air escaping. However...the gaskets are fairly hard..but appear to fit tight. Thanks!
Travis 
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_________________
Travis Rayner
Mobile, AL
Skystar Vixen, N-789DF
Continental IO-240, Prince P-Tip Prop
ADI-II Autopilot
AnyWhereMap Navigation with weather
www.enotam.net (My Flying Info Website) |
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napierm(at)cisco.com
Guest
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| Posted: Tue Oct 27, 2009 7:44 am Post subject: Fuel Flow Problems, Again! |
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Hey Travis,
The Rotax part number is 414-3636. The shape of the thing has changed
since I bought it last but I suppose the function is the same.
http://store.leadingedgeairfoils.com/index.php?cPath=548_436_447
The gasket around the tank is a Mercedes Benz fuel cap gasket #
140-471-00-79 seal ring. It should be somewhat pliable.
I'm changing my fuel system over to the current KF one for the KF IV
fuse I'm working on now. I did use a pump to establish flow though my
filter but the problem was the location the header tank. At takeoff it
wasn't "downhill" from the wing tanks.
The fuel management for my KF III was "interesting". It had a metal
header tank mounted behind the instrument panel at the fire-wall. The
vent line from the header had a large diameter, short length Tygon tube
that ran just over the glare shield with a floating red ball in it to
improve visibility and then a smaller 5/16" diameter hose ran up to vent
into the right tank. The 5/16" diameter wing tank fuel lines went over
to two over-head fuel cutoff valves and then teed together. Then
through a filter and down a line under the left door that fed a fuel
pump up under the panel. The fuel pump had a bypass one-way valve
around it and both fed into the header tank. Finally there was a fuel
cutoff valve from the header tank that fed a fire-wall forward mounted
gascolator.
So what you did was select a tank and turn on the pump. It would suck
fuel through the tee and filter and push into the header and from there
back up into the right tank through the header vent line. In level
flight the fuel would flow normally w/o the pump. The red ball would
witness the fuel in the vent line. I used the left tank for range only.
As it got low I would turn on the pump, select the left tank only and
put the rest of the fuel into the right tank through the vent line and
use a little left rudder to get the last of it. The right tank only is
selected for take-off and landing and the pump is on. This works well
since I always slip in using right rudder. I rarely if ever run with
both tanks selected.
The down side it that I did need that pump. I took off a few times and
forgot to turn it on. Then I would look at that empty vent line right
in front of me and practically break my finger on the switch turning the
pump on.
It sounds complicated and it was but I got used to it. The system was
completely reliable as long as the human element worked right.
Modifying the fuel system is considered a major change so I flew it "as
is". Add to that the HACMan leaning adjustment that I fiddled with
occasionally to keep the EGT's at around 1100. And the 6 gallons per
hour it took for the 582 to push the KF III to ~87mph.
So I'm looking forward to flying the HKS with the simpler set up and
much lower fuel burn even if it is no faster.
Cheers,
Mark Napier
-------------------------------------------------------------
Time: 01:31:27 PM PST US Subject: Re: Fuel Flow Problems, Again! From:
"FlyboyTR" <flyboytr(at)bellsouth.net>
Mark,
What is the part number on the fuel filter. What is the element
made of?
I don't think my fuel cap gaskets are leaking. I can blow through
the vent and
don't hear air escaping. However...the gaskets are fairly
hard..but appear to
fit tight. Thanks!
Travis
--------
Travis Rayner
Mobile, AL
Skystar Vixen, N-789DF
Continental IO-240, Prince P-Tip Prop
ADI-II Autopilot
AnyWhereMap Navigation with weather
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p 69545#269545
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FlyboyTR
Joined: 04 Nov 2006
Posts: 215
Location: Mobile, Alabama
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| Posted: Tue Oct 27, 2009 12:19 pm Post subject: Re: Fuel Flow Problems, Again! |
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Mark,
Thanks for the info on the filters and fuel cap gasket. Even though testing hasn't shown any leaks in my fuel caps, I plan to replace them. My local autoparts dealer is trying to round up a couple for me.
The fuel system on your III sounds a little confusing at first glance. Many times the human element can get us pilots in trouble...quickly!
Thanks again...
Travis
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_________________
Travis Rayner
Mobile, AL
Skystar Vixen, N-789DF
Continental IO-240, Prince P-Tip Prop
ADI-II Autopilot
AnyWhereMap Navigation with weather
www.enotam.net (My Flying Info Website) |
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ruebd(at)skymail.csus.edu
Guest
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| Posted: Tue Oct 27, 2009 1:32 pm Post subject: Fuel Flow Problems, Again! |
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Travis:
Your story is one that gives me the puckers. As we all know, fuel system problems are the major malfunctions that cause accidents in light aircraft. I would strongly recommend eliminating the filters that are up high in the system. There is such a low head pressure up there that any resistance to flow is too much. Filters do have a pressure drop across them and great care needs to be used to place them in a system where that drop is not a problem. If they are large this is not as important as the drop due to the material used. Large only counts for a large capacity to store debris and for large fuel flows; not helping much if any for initial conduction of flow.
I would leave the valves in place (since they are already there) and either not put any more filters in the system than the one at the front of the engine, or if you insist on another one, put it on the output side of your starting pump. You will then have two filters in series, with the first one being out of sight unless the seat is removed, which should tell something about the need for it. While glass is tempting to think about, remember that the glass gas collators that we used to have on our old factory jobs with carburetors were of a very well thought out design, quite sturdy (the glass is tempered and thick) and placed just in front of the carb where there is room for a nice big glass thing. It had a very low pressure drop and due to its effective mesh size and configuration, had a pretty high capacity for debris. We didn't drain it every time we flew, but used it as an indicator of our fuel quality. It is also in front of the fire wall and definitely not in the cabin, so we could look at it when doing things up front. Our fuel system is rather large in the cabin, which is not the greatest thing to have, but necessary due to the folding wing idea. And since it is inside where we ride, I recommend making as few connections in our fuel systems as necessary and inspecting that system regularly, even more often than I do. (I will take note of this)
Some of that inspection occurs easily due to either the presence of or lack of fumes. If no fumes, no leaks in the cabin, but we still need to look at the lines that are covered with a sleeve to inspect the flex portion for impending cracks or anything that doesn't look good about them, remembering how that we have had the experience in cars that one day no leaks, the next day leaks and when we found them we said wow, how did I not notice how bad this line was?!
Have you checked the finger strainers in the tanks? I am planning to do this at this annual and then to rig a vacuum system to pull any debris off of them and from anywhere else I may find it. Please remember to be careful when doing this inspection to use a non-sparking light, and non sparking vacuum tools as well. Of course, you will make sure that the tank is drained and have enough vacuum hose to not have the vacuum motor close to the tanks. While I write this to you, I am also talking to myself and everyone on the list so that I (we) will think before doing something dumb and regrettable. Fuel is highly flammable. It won't hurt all of us to review our fuel system and methods for working on them, and if I have missed something important, please someone chime in.
I am also very aware of the fact that our kitfox factory has great experience and advice and the proper parts to use on our aircraft and I do also recommend supporting them by using their parts and wisdom.
Sorry to hear of still another alternator problem, and I would appreciate learning what failed.
I hope to hear a report soon that speaks of a beautifully flowing fuel system in your bird, and my intent is to inspire all of us to turn up the gain on our fuel system awareness, please do not take this as a critical lecture. It is kind of an open letter on our fuel system in our delightful little sky toys.
Sincerely, and warmly, Duane Rueb
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