Here's another argument against header tanks that occurred to me
yesterday as I was struggling to access some wiring on a plane with a
header tank. All of the space that a header tank (mounted in the
"forward deck") occupies gobbles up a lot of valuable space that could
otherwise be used for battery, coils, voltage regulator, system
electrical bus, and most importantly.....easy access to all of this
stuff. Future additions, alterations, repairs, panel upgrades,
electrical bus connections, troubleshooting....all of that stuff is a
lot easier to access, with that space available if the fuel is out in
the wings instead, in low vertical CG voids that are normally empty
anyway! And if you make the front deck easily removable with piano
hinges like I did, access is about 30 seconds away from the decision to
open it.
The unattractive alternative is often to put some of this engine-related
stuff on the engine side of the firewall, which really starts crowding
things out there, and subjects the components to constant heat
(requiring cooling) and perhaps oil contamination....and will likely
result in much more difficult access, and perhaps less opportunity for
inspection and troubleshooting.
See the photo at http://www.n56ml.com/electrical/index.html for what all
I had under the front deck, long before I ever even flew the plane. At
first flight it had a lot more out there, like the EIS static/pitot
sensor, transponder altitude encoder, fuel pumps and regulator fastened
to the aft side of the firewall, etc, and nowadays it could have all
the ADS B stuff under there....with very easy access.
I've said this before and I'll say it again, I'm not a big fan of
"gravity feed" fuel systems. The head pressure (and therefore fuel
pressure supplied to the carburetor) varies depending on the level of
fuel in the tank, how well the tank is vented (plugged by an insect),
and even on what kind of maneuvers the plane is doing (stick back or
forward). Some carbs are more sensitive than others to these pressure
changes. A fuel pump and regulator solves this problem by providing
constant pressure and flow rate, and also adds the potential for an
electric primer without introducing a potential fuel leak (a mechanical
primer) into the panel. A backup battery and a double-pole double throw
switch adds redundancy to a level that I consider to be quite
adequate....it swaps out both ignition system and fuel pumps to a backup
battery that is always fully charged by the alternator, and isolated
(one-way) with a 40A diode.
And most of all, if I were to tear a plane up in an off-airport landing
(although I'm sure that would never happen to me......), I'd much rather
have the wings on fire than the cockpit, especially surrounded by a
hundred "hot" electrical wires right in front of me!
See http://www.n56ml.com/electrical/index.html
Mark Langford
[email protected]
http://www.n56ml.com
Huntsville, AL
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