Hi Gordon,
You're right! I have carefully researched the subject and confirmed
that what I said was quite specifically wrong. Sorry if I confused
anyone.
Having never owned a F1, it simply never occurred to me that Forney
would consciously choose to repeat ERCO's original error in their
"redesign" of 1956. Such an error in print would live "forever" in a
book, and I greatly appreciate your helping me avoid that
embarrassment.
The diagram for the Fuel System in the F1 Instruction Manual, page 14,
is a direct copy of the 415-C fuel system diagram in the Ercoupe
Instruction manual. A note was added, stating that "Tank cap gaskets
must seal to permit proper flow of fuel". Presumably this would be
because a tank with a good cap seal would be pressurized somewhat by
the forward facing vent hole whereas a tank with a poor seal would
actually, in some cases be subject to a siphoning action by airflow
creating negative pressure above the wing. In both instances the
overflow from the fuselage tank goes to only one wing tank. The only
way such a system can feed fuel reliably is for each wing tank to be
vented via the vented fuel cap.
Unfortunately, I can find no statement in Forney owner or maintenance
information that describes F1 wing tank caps as being vented.
Undoubtedly the drawings do, but mechanics and owners seldom have
access to such information in the field. There are more than a few of
our birds happily buzzing around the skies with the wrong wing tank
caps for their installed fuel system. What "came with the plane" is
NOT always "right". Ercoupes, et al, have long proven to be "works in
progress".
ERCO/Univair do not cover themselves with glory in print. The Ercoupe
Parts Manual and the Bulletins and Memoranda rather unfortunately focus
on the specifics of certain piping arrangements rather than on the
simpler generalities of actual system operation.
That may have made sense at first, but as fuel system deficiencies
dictated change after change, including the change from terneplate
tanks to stainless or aluminum ones. With 20-20 hindsight in 2010 it
is safe to speculate that the number of airframes with a fuel system
strictly conforming to the drawings in the Parts Manual or Ercoupe
Service Memorandum 43 is likely less than half of those produced in the
overall.
The Ercoupe Parts Manual, pages 28 and 29, is very specific that
unvented caps are fitted to serial nos. 4424-up. That is wrong.
Over a hundred 415-C Models in dealer hands and unsold when the 415-CD
was announced were modified in the field by ERCO to 415-CD
specification. That would be the fuel system (right down to individual
fuel tanks and line part numbers) shown in the "FAA Approved Flight
Manual for the Ercoupe Model 415-D, which uses unvented wing tank caps.
Unfortunately there is NO "FAA Approved Flight Manual for the Ercoupe
Model 415-CD. Consider then the fact that only a couple of 415-D
Models left the factory, while hundreds of 415-CDs were produced.
Worse, the fuel system purportedly installed in serials 3468 and up,
Fig. 20 on p. 28, shows individual wing tank return/vent lines for each
wing tank joining at a tee fitting from the fuselage tank overflow.
Such a system is also functionally identical to that in the 415-D and
415-CD Models. It defies common sense to use vented wing tank caps on
this fuel system, yet that is precisely what the Parts Manual
specifies.
Even though Ercoupes 3467 and below presumably left the factory with a
wing tank and fuel line arrangement that only vented one wing tank,
that is no guarantee that an owner of an earlier Ercoupe frustrated
with fuel siphoning or uneven fuel flow problems did not have his/her
system modified in the field to the later system requiring unvented
caps.
I therefore put forth the proposition that the only reliable indicator
that unvented caps are appropriate is on any and all fuel systems WHERE
BOTH WING TANKS VENT TO THE FUSELAGE TANK in some manner. Whether wing
tank caps are vented or unvented, the seal between the wing tank fuel
tank cap and the tank "cap seat" must be effective if either system is
to deliver the most even and uniform fuel flow possible.
The diagram for the Fuel System in the F1A Flight and Operations
Manual, page 16, confirms that Forney saw the error of their ways and
corrected it. Just as in the later Ercoupes, each F1A wing tank has a
return/vent line rising to a tee which then rises and connects with the
fuselage tank overflow.
Again, in my considered opinion, all fuel systems functionally
conforming to this design require unvented caps. The Forney Service
Manual, likely written before the F1A Model came out, is silent on this
subject; as is the Forney Parts Manual. I suppose the financial
situation at Forney in the transition of ownership and production
location from Ft. Collins, CO to Carlsbad, NM is the reason. Perhaps
Air Products intended to clarify the matter but never had the chance.
From both an engineering and maintenance perspective, this is a glaring
deficiency that should be officially clarified and corrected by
appropriate means in applicable documentation.
Alon and Mooney can legitimately ignore the "issue since all of their
production had one "system" (respectively). You just ordered what each
manufacturer sold and you couldn't go wrong ;<)
The Alon Service Manual shows a fuel system identical to the F1A. The
A-2A Owners Manual, however, on page 2-8, identifies a "Fuel Line (LH
Wing Tank to RH Wing Tank) as #16, a "Fuel Line (Fuselage Tank to RH
Wing Tank) as #19 and a "Fuel Line (Fuselage Tank to LH Wing Tank) as
#20. So each A-2A wing tank has an entirely separate return/vent line
to the fuselage tank and no tee. Alon, in their Service Manual, says:
"Wing tank caps must be used with the special gasket as they came from
the factory.
A mechanic trying to help an owner with a fuel problem can be easily
misled by the serial number of the airframe and the Parts Catalog. I
he/she instead properly understands how the system installed SHOULD
function a successful solution to the problem is much more likely.
Understand in all that I post on this list that I'm NOT a mechanic! I
discuss matters such as this in the strict academic sense with the
single desire that in every case the truth of each and every matter
emerge and improve our collective understanding.
To that end, thanks again, Gordon, for your input.
Regards,
William R. Bayne
.____|-(o)-|____.
(Copyright 2010)
--
On Aug 17, 2010, at 21:06, Gordon Smith wrote:
I have a Forney F1. Both wing tanksd have vented caps.
Gordon Smith (JOT) IL.
Socialism will eventually run out of other peoples money.
--- On Tue, 8/17/10, William R. Bayne <ercog...@txercoupemuseum.org>
wrote:
From: William R. Bayne <ercog...@txercoupemuseum.org>
Subject: Re: [ercoupe-tech] Re: Fuel System Problems parts 1 and 2 of
3?
To: ercoupe-tech@yahoogroups.com
Date: Tuesday, August 17, 2010, 7:50 PM
This confuses me as well.
All Ercoupes after the 415-C model have unvented fuel caps. The wing
tanks are "treated as a single tank" insofar as the balancing tube
between them which maintains the same level in each tank, and each
wing tank has a separate "overflow/fuel return/vent line into a tee
from the fuselage tank standpipe which maintains the fuel level in
that tank. All that has changed is that the fuselage tank is no
longer present.
I would think "...appropriate plumbing to connect the air spaces in
the two [wing] tanks could be much as Eliacim suggests, i.e. a vent
line from each tank to a tee venting to the outside on the right or
left side of the fuselage at or above the level of the bottom of the
original fuselage tank. Fly the plane with a manometer connected to
such a fitting and angle it forward or backward for neutral or
slightly negative pressure, and Voila! (?)
Regards,
WRB
--
On Aug 17, 2010, at 19:02, <heave...@wt.net> wrote:
>
>
> John
> Maybe I am missing something obvious, but wouldn't simply venting
both tanks connect the air spaces through the atmosphere?
> That works for our normal (small) wing tanks. What am I missing
here?
> Eliacim
>
>
> --- j...@skyportservices.net wrote:
>
> As previous owner of the "30 Gallon STC", the reason I didn't put it
> into production is because it treats both tanks as a single tank but
> does not include the appropriate plumbing to connect the air spaces
in
> the two tanks.
> -- John Cooper
> Skyport East
> www.skyportservices.net
