Several style main tanks

Over the time there have been several different style main tanks for the Ercoupe and Forneys and Alons. These are interchangeable to a certain extend, but some Ercoupes will need an exact replacement. Early prewar Ercoupes up to serial number 112 featured only one 7 gallon main tank on the right side. Ercoupes up to serial number 812 used two main tanks with openings to fit the main gear that was mounted on front of the main spar.

When changing the gear to mount to the rear of the spar, the tanks were changed, featuring now slightly more than 8 Gallons.

Earlier Ercoupes had fuel tanks fabricated from terneplate sheet. The fuselage/header tank 415-48025 overflow line ran to the right wing tank (where the fuel gauge is located on these ships). From serial no. 2469 through s/n 2622, fuselage/header tank 415-48025 was fabricated from stainless steel sheet (the material only being changed by revision on the original drawings, following the same original drawings as modified by notation).

Note: When the mounting of the main landing gear legs changed from the front of the main spar to the back of the main spar at s/n 813, there was no change to the terneplate wing tanks or related plumbing. Beginning with s/n 2469 the fuselage/header tank was fabricated to the original drawing(s) from stainless steel sheet (no piping changes).

As of about 07/29/46, all replacement tanks for the original terneplate tanks (to s/n 2622) were thereafter fabricated to the original drawings from stainless steel sheet (no piping changes). These tanks and lines are shown in the Ercoupe Parts Catalog, p.26, Fig. 19.

Beginning with s/n 2623, all production fuel tanks were fabricated from aluminum sheet. The fuselage/header tank capacity increased from five gallons to six gallons (nominal).

Through serial number 2622 Ercoupes originally had terneplate tanks, but were changed to stainless steel tanks of identical construction at the last of this series. Terneplate tanks were steel with a thin coat of lead; not what one wants in a light aircraft! Their advantage is that they could be soldered shut with assurance that they would not leek. Below an example.


Early Style 9 Gallon tank with cutout for main gear left side

Early Style 9 Gallon tank with fuel sender unit right side Early Style 9 Gallon tank left side
The early style gauge as seen from the cockpit

These tanks came also as stainless steel tanks:"I did some additional research on the stainless steel material used in the tanks that replaced the ternplate tanks. The specification is AN-QQ-S-772-A.
It turns out that material is either 302 or 316 stainless steel. It is suitable for spot welding but NOT suitable for gas or arc welding.
The tanks are riveted together and sealed on the edges by what appears to be brazing - not welded.
If you have a leak on one of those tanks or otherwise need to repair it, do not try to weld it!"
Wayne


With the fuel gauge moved to the left tank, the very common 9 Gallon aluminum tanks were introduced. These are made from aluminum.


Left a 9 Gallon tank versus the 8 Gallon tank, both right side

The 9-gallon installation requires cutting a specially shaped hole in the fuselage. Service bulletin 39 is describing the procedure for this upgrade.

Intermediate style 9 Gallon tank with fuel gauge

Later Style M10 tanks

Had the pleasure of working on a Mooney M10 (August, 2018) and couldn't help but notice the different wing tanks it had. This is a top view of the right-hand tank. One notices the boss on the tank input, which varies from the standard ERCO models.

This shows the difference very well. The Mooney tank has an extension, where standard tanks are cut flat on the inboard side. Another difference is that the tanks are welded construction, not riveted. But yes, they still can leak. Rivets are particularly prone.

This is the left hand tank. The filler caps are "thermout bottle" style, instead of the ERCO tang kind.


From the left front, one notices to the right of the fuel boss, a larger protrusion. This is for the fuel quantity gauge. These tanks are marked as holding 9 gallons.

Shown here is the left side of the cockpit. The fuel quantity has a nice bezel right behind the throttle. This M10 cadet is fully instrument capable!
Percy