March A6M-2 Zero Update | AirCorps Aviation

Texas Flying Legend’s Museum
by Chuck Cravens

Hunter and Randy continue to prepare the main portion of the rear fuselage for skinning

Update

They say if it doesn’t have guns, it isn’t a fighter. We all know that the nebulous “they” are never wrong, so Texas Flying Legends decided that guns were a definitely desirable addition to the fuselage in this repair and renovation of their Zero.

The Model 21 mounted two of the Type 97 aircraft machine guns in the top of the fuselage, just in front of the pilot, with the receivers and all but a little of the muzzle end of the guns faired over. Slots in the cowl ran forward for bullet clearance. This Japanese designation signified a licence-built version of the Vickers E model machine gun. There was a type 97 light machine gun used by the ground troops, but that was a completely different machine gun.

Naturally, since the FAA (not to mention the Bureau of Alcohol, Tobacco and Firearms) distinctly prefers that one doesn’t fly with functioning machine guns, these are inoperative replicas.

Steve is machining the pivot shaft or receiver lever shaft for the 7.7 mm machine gun replica.

Here you can see the part more clearly as the lathe turns it during the machining process.

Receivers were machined for the Type 97 fuselage machine guns. The tops and bottoms were from billet aluminum and the sides were sheet.

The top pieces of the receiver in the foreground and the bottom piece on the one behind show up well in this photo. To the right are the cooling sleeve and barrel replicas.

The parts in the foreground are the cocking handles.

In the lower right are two machined boxes that will hold modern radio equipment. They will fit in the rear of the receivers and will be removable for static show situations.

This receiver lever pivot will be mounted on the bottom of the machine gun.

In front is the rear gun mount, behind are the radio concealment boxes.

These are called cocking mechanism plates.

Here we have the rear gun mount finished and ready for installation.

Scanning

Stefan scans the leading edge area of the vertical fin.

The scanner picks up the stick-on dots, called position targets, and uses them to develop data that places them precisely in space. That data is used in creating rotatable CAD model of the scanned area.

The vertical stabilizer trailing edge and hinge attachments are the scanner’s target in this image.

The scanning produced the model shown here.

The scanned model is not in a format that allows for editing or modifications to its properties. It is but the first step in the reverse engineering process. Without software to clean, repair, and produce usable reference points that can be exported from the scan, it has little value. This next step of cleaning, repairing and generating reference is referred to as post-processing. This step is critical and not all scanners provide the software in order to perform this task.

Stefan scans the upper end of the rudder.

Here the horizontal stabilizer is being scanned.

One side of the horizontal stabilizer leading edge wasn’t damaged. So Stefan scanned it, mirror imaged the results and created the model for the other damaged side.

The good half as it sits on the bench with the location targets still affixed to it.

Framework & Empennage

The rear fuselage framework and the vertical and horizontal stabilizers are nearing completion.

After scanning, the vertical stabilizer’s leading edge remains in place.

Randy works behind the stabilizer attachment fittings.

Various rudder parts sit on the bench awaiting installation.

Ryan squeezes a rivet on the tip end of the rudder spar.

Here’s the same rudder spar in place in the fixture.

We can see the entire rudder going together in the fixture in this shot.

The horizontal stabilizer attachment fittings appear in this image, painted and ready to install permanently.

Here are the fittings in place in the end of the stabilizer carry through tubes.

One side of the horizontal stabilizer is ready to go on.

Ryan is repairing the elevator main spar and he also replaced the first 3 ribs counting out from the root end.

The front spar of the vertical stabilizer shown as it appears without the leading edge subassembly.

A wider angle shows us the way the vertical flows into the fuselage. That particular transition skin piece will be a complex one to make.

A wide angle gives us perspective on the scope of the repair.

What we see here is the main spar of the vertical stabilizer as it would appear looking back from the cockpit area.

This is the tailhook bay, the clecoes hold on the bracket mentioned earlier.

This odd looking object is a mock up model of the tail hook.

It is an inexpensive way to use two dimensional materials to represent the three dimensional tailhook for the purpose of fitting and testing operational clearances before machining the tail hook. The tail hook is an addition to the historical fidelity of the Zero added during this repair process.

Skin Fabrication

Accurately recreating the compound curves in the thin skin of the Zero is an exacting task.

Forming the metal to those curves requires the use of an English wheel.

The two wheels on the machine squeeze the sheet and stretch the surface, inducing a curve.

Wheeling is a process requiring skill. The curvature and size of the anvil wheel and the number of passes determine the amount of curve in the metal skin.

The anvil wheel is below the sheet skin and the wheeling wheel shows here

Ryan guides one end of a skin piece through the English wheel.

Once the skins have been formed, rivet holes are laid out on them.

Robb and Randy work on the rivet hole layout.

Skin Fitting & Trial Installation

The undamaged skin we are reusing is in place in this shot of the rear fuselage.

The skins are clamped in place and holes that already exist on reused structural members are drilled from the inside out through the new skin.

Every hole gets a cleco clamping the skin in place, working out from the center.

The skin fitting progresses from the top down and back toward the rear.

Work on new holes progressed out toward the edges.

New holes are drilled through the laid out skin holes into the new structural members that don’t yet have rivet holes. This has to be done after the skins are positioned tightly by clecos into the reused ribs.

Randy is working on making a piece that fits just in front of the vertical fin forward spar.

Here is that same piece being test fitted.

We can clearly see how the skin fits around the horizontal stabilizer attachment fittings in this closeup.

Once all holes have been located and drilled, the skins come off again.

That’s because the next step is to countersink the rivet holes. To do this on the very thin, light .020 skin panels of the Zero, the countersinks are formed by pressing in dimples rather than cutting material to a specified angle with a countersink bit. Then the protective paint will be applied to the inner side of the skins. The first Mitsubishi airplane to have flush riveting was the prototype 9 fighter that developed into the type 96 or A5M. This fighter was designed by the A6M’s designer, Jiro Horikoshi, and is the immediate ancestor of the Zero. The allies code named it “Claude”. When the flush riveting was done on the prototype 9, it was such a new innovation that the skill needed to create a smooth finished product was yet to be developed and the prototype 9 looked “quilted”. Body putty was used to smooth out its appearance for the Navy review board. By the time the A6M-2bs were manufactured, the flush riveting skills had progressed and produced a much more satisfactory result.

Every hole needs to be carefully dimpled. The A6M-2 tail section on its tubular fixture.

Behind it is the P-51C, Lope’s Hope 3rd. The original Lope’s Hope 3rd flew with the 75th Fighter Squadron in China. They never encountered actual A6M Zero fighters. However, their log book and combat report entries frequently listed the Oscar fighters they fought against as Zeros because of the similarities in appearance.

Texas Flying Legend’s Museum by Chuck Cravens