Probably more important than where a person decides to place the
filters, valves, etc., is the decision to do a flow test after all
the plumbing is done. That might reveal more than all the theory in
the world. If the flow test shows marginal flow, change something! If
it doesn't......
One of the discoveries that I made while changing to the TBI in place
of the Bing carb, was I hadn't realized how far up the "flow chart"
the carb/TBI was located. With my gravity flow ONLY system, if I have
to point the nose up very steeply with low fuel....like when the
header tank supply is the only fuel available....that fuel will not
make it up to the TBI/carb. You folks with high-mounted carbs are
almost certain candidates for a pumped system.
If in doubt about the flow of your particular system, lay some
masking paper on the side of the aircraft, and measure and plot where
the various parts of the fuel system lie, and where the lines run.
Draw these components onto the paper, then imagine the plane
climbing, diving, banking, etc., and see where the fuel goes and also
imagine a lower than normal fuel supply, and see where that leads you.
Lynn Matteson
Kitfox IV Speedster, taildragger
Jabiru 2200, #2062, 805.4 hrs
Countdown to 1000 hrs--195 to go
Sensenich 62"x46" Wood prop
Electroair direct-fire ignition system
Rotec TBI-40 injection
Status: flying (and learning)
On Nov 1, 2009, at 10:28 AM, fox5flyer wrote:
> <fox5flyer@idealwifi.net>
>
> I know this thread has been going on forever and those who have
> wing tank filters will probably keep them. Fuel flow is probably
> one of the most important parts of our airplane so talking this to
> death can't hurt a thing. Here's my take, for whatever it's worth.
> Ideally, "IMO" the lines from the wing tanks to the header should
> be as large as practicable...3/8 ID would be good. To keep the
> head pressure as high as possible there should be no (unnecessary)
> restrictions between the tanks and the header, meaning no filters,
> valves, unnecessary fittings, or reducing fittings that restrict
> flow. After the header, the same applies, however, it's obvious
> that one needs at minimum a shutoff valve and usually a fuel pump
> of some sort. Since most fuel pumps are meant to push fuel, not
> suck, it should be at the lowest point in the system, generally
> just after the header and as close to it as practical. After the
> fuel pump things are not so critical as most pumps can push fuel
> pressure and volume far beyond what static flow can provide.
> Obviously, the 582s with diaphragm pumps wouldn't be very practical
> to be placed at this point, but to continue. There should be a shut
> off valve, generally on the console or wherever it's located that
> is easy to reach, again, IMO, the next restriction should be the
> filter. This should be a high flow filter and could be located on
> the firewall and be the last line of defense before it goes to the
> carb/TB/etc. Again, I stated "ideally" and is only my opinion.
> There are many other methods that work and some that don't, but as
> I recall a study was done at some point about forced landings and
> most were caused by fuel starvation. Everything that is put into
> the system between the fuel tanks and the engine is a restriction
> of some sort. Add them all up and it can be significant and even
> though the system may be working it may be marginally close to
> failure without one knowing it.
> Personally, I don't feel the filters in the lines from the tanks to
> the header are necessary at all. Between the finger strainers and
> the natural settling action of the header, plus the fuel sump at
> the bottom of the header, there is more than enough there to clean
> up the big stuff. The final filter at the firewall will take care
> of anything that somehow reaches that point.
> I expect that some will take issue with this, and that is fine and
> I'd like to hear it. Just be nice. :-)
> Have a great day!
> Deke Morisse
> Mikado Michigan
> S5/Subaru/CAP 438+ TT
> "If you put the federal government in charge of the Sahara
> Desert, in five years there'd be a shortage of sand."
> -- Nobel prize-winning economist Milton Friedman (1912-2006)
>
> ----- Original Message ----- From: "FlyboyTR" <flyboytr@bellsouth.net>
> To: <kitfox-list@matronics.com>
> Sent: Sunday, November 01, 2009 8:43 AM
> Subject: Re: Fuel Flow Problems, Again! (Vixen, Series-5)
