Hi John,
I appreciate the knowledge you share, as time permits, with the group.
All "progress" is utterly dependent upon "unreasonable"
individuals...i.e. those unsatisfied with the "way things are". Theirs
is the never-ending challenge to "think out loud"...to identify and
explore problems and speculate as to possible resolutions without
inconveniencing or offending those content with the "status quo". In
this context, I hope my continuing questions are not taken as being
"nibbled to death by a duck" ;<)
The CAR 4.a.606 requirement is that interconnected tanks have
interconnected air spaces to prevent difference in pressure at the air
vents of each tank of sufficient magnitude to cause fuel flow between
tanks. My attention is attracted to the illusion of a "special ruling
from the administrator". If the usual "Administrator" is a political
appointee not a pilot and utterly lacking aviation experience somewhere
in the huge and horrendously expensive FAA bureaucracy some person of
sufficient competency to which to delegate such matters must exist.
Let's speculate a bit "in theory" even if the anticipated expense in
time and money to Skyport would likely never be offset by potential
sales of the "30 Gallon STC".
I would expect vented caps to perform just fine, as Eliacim suggested.
"Subtle differences" significant in a gravity-fed high wing fuel system
should have no measurable effect in a low wing pressure fed fuel system
with redundant fuel pumps capable of significant suction (regulated as
to output volume by an orifice in the line from the pumps to the
carburetor). If such caps vented side-to side (instead of a forward
facing hole), would not a slight positive or negative pressure
essentially equal between the tanks constitute less risk of malfunction
than the differential pressure between tanks as would occur if anything
obstructs one of two forward facing vents in flight?
I must confess that the "30 Gallon STC" has always struck me as a
solution in search of a problem considering the rather large investment
and associated major modifications necessary. What was the original
design purpose? Extra fuel? There are numerous ways of doing that
much easier.
More room behind the panel? The F-1A panel "solution" would be a
viable retrofit. Even those with the panel mounted quadrant Throttle
and Trim could easily revert back to the late 415-C arrangements for
these two functions.
To eliminate the "danger" the fuselage tank poses in case of a crash?
If only unplanned landings otherwise survivable are evaluated, I
believe such accidents to be sufficiently rare as to be of little
statistical significance.
Perhaps "all of the above"?
Best regards,
William R. Bayne
.____|-(o)-|____.
(Copyright 2010)
--
On Aug 18, 2010, at 17:52, John Cooper wrote:
On 8/18/2010 2:00 PM, William R. Bayne wrote:
The Ercoupe fuel system with unvented caps accepted by the CAA for use
on a production aircraft under CAR 3 in the normal category, which
vents wing tanks from the inboard end (well below the fuel level of
full wing tanks), would have been excepted from your CAR 4a.606 rule
by virtue of the engine being fed by gravity from the nose tank
CAR 4a.606 only applys to tanks from which the engine can (directly)
draw fuel. The Ercoupe wing tanks are transfer tanks and do not fall
under the same rules. They are not critical to flight safety. A
temporary interruption in fuel flow from the wing tanks to the header
tank would likely go completely unnoticed (which begs the question of
whether and how often it happens...)
When the header tank is removed then the regulations come into play and
the wing tanks move up to the critical list. Due to the wing dihedral,
there is no easy way to configure an effective vent line to connect the
air spaces of the two wing tanks, hence no easy way to meet the
regulations other than introducing a valve that prevents drawing fuel
from both tanks simultaneously.
--
John Cooper
Skyport East
www.skyportservices.net
