Hi John,
While I've "had a run" at this subject several times in the past, this
was the first time everything seemed to "come together" between all
sources. I've certainly not had the opportunity to visually compare
the terneplate and aluminum tanks side by side that you have.
The depth (height?) of tanks is pretty much defined by the spar
attachments, cross-section (depth?) by the airfoil and outer "limit" by
the wing outer panel. The tank "outer side" and "spar side"
projections and projection into the fuselage (length?) would seem to be
the only possible variables.
It did sort of come to mind as I was going through my stuff that a
stainless/ternplate tank designed to go around the front-mounted main
gear would have to project further into the fuselage to have the same
capacity as an aluminum tank that didn't. But, again, without the
tanks to compare all I can do is speculate.
Anyone have measurements or pictures of any of these tanks for us to
play with?
Regards,
WRB
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On Feb 21, 2010, at 22:42, John Cooper wrote:
Bill:
I can't dispute anything you've said, but if you look at the
terneplate tanks, particularly those with the float gauge in the right
tank, they are clearly smaller on the outside compared to the later
aluminum tanks. I suppose there could be some sort of TARDIS effect
making them bigger on the inside, but I never noticed any time-space
distortion...
John
On 2/21/2010 11:21 PM, William R. Bayne wrote:
Hi Donald,
If you refer to the back of the Service Manual (about two thirds
down the listing of "Ercoupe Modifications"), you will see that
production wing tanks were changed (from terneplate) to aluminum with
serial number 2623. Your bird originally had all terneplate tanks.
Prewar Ercoupes are listed in brochures as having fourteen gallon
fuel capacity. That was with a five gallon nose tank and one nine
gallon wing tank. Early postwar brochures show a fuel capacity of 23
gallons with the same five gallon ternplate fuselage tank and two
nine gallon wing tanks. Later on this increased to 24 gallons when
the 6 gallon aluminum nose tank replaced the five gallon ones
(terneplate thru serials 2468 and stainless from 2469 to 2623).
The Parts Manual suggests that 415-48083-L/R tanks were stainless
replacements for original terneplate wing tanks. These stainless
replacement tanks were apparently designed and fabricated to fit
Ercoupes with serials up through 812 (with the main landing gear
mounted on the forward face of the main spar) as well as serials 813
through 2623 (with the gear mounting to the rear of the rear face of
the spar).
As of the issuance (on or after 9/26/46, per Fig. # 1) of Service
Memorandum No. 31, production was passing serial no. 3672. Paragraphs
3 and 4 make it clear that, as of this time, terneplate (or
replacement stainless wing tanks) or aluminum wing tanks installed in
a production (non-experimental) Ercoupe had a nominal capacity of
nine gallons.
As of the issuance of Service Memorandum No. 39, ERCO was receiving
requests to replace terneplate wing tanks with the aluminum tanks,
and item 8 confirms that each had the same (9 gal.) capacity. As
Richard has pointed out, the aluminum substitution is seven pounds
less. In order to install "current production" tanks (parts no.
415-48187L & R) a fuselage cutout was necessary (see Sketch A).
As of the issuance of Service Memorandum No. 43 (on or after
10/19/46 per drawings 48178-80), aluminum tanks 415-48187L & R were
installed "serials 3468 & subsequent". Sketches suggest that aluminum
wing tanks 48128L & R were originally fitted to serials 2623 thru
3467, and these were logically of nine gallon capacity.
We can see that ESM-49 came out subsequent to production of serial
no. 4729 on 5/13/47, with ESM-50 following. This describes
replacement of wing terneplate tanks with a replacement aluminum tank
"recently approved" by the CAA. Identified as part numbers 415-48197L
& R, ERCO should have said much more about these tanks here.
Aircraft Specification No. 718 offers more information, p. 4, item
No. 108. These are the elusive "eight gallon aluminum wing tanks"
that hold 7.7 gal. (ea.). They had less capacity so that installation
on serials 813 through 2623 (with the gear mounting to the rear of
the rear face of the spar) was possible without cutting the fuselage
skin (per ESM-39). System capacity is 20.4 gal. with these and a five
gallon fuselage tank.
Becoming available this "late in the game", it should be obvious
that aluminum replacement tanks 415-48197L & R were NEVER installed
during production on ANY Ercoupe.
I am aware of NO "eight gallon" stainless tanks being produced or
installed at any time.
Regards,
William R. Bayne
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(Copyright 2010)
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