As the massive door groaned into motion, pivoting upwards behind one of a row of nondescript hangars at the eastern edge of Paine Field, in Everett, Washington, an extraordinary sight began to appear from within. The familiar shape of a Mitsubishi Zero is enough to quicken the pulse of almost any aviation enthusiast, but this example has even greater appeal, being the world’s only intact A6M3 Model 32. Legend Flyers has worked diligently on the restoration of this ultra-rare fighter for more than a decade, with the Military Aviation Museum becoming involved about two years ago. Was this the day we might finally witness the aircraft take to the skies again? I had journeyed out to the Pacific Northwest to find out, and to update our audience with the very latest news on our project!
The Call
Getting an aircraft ready for its first flight can be a far longer process than many people might expect. As we check through its systems to ensure they are functioning correctly, adjustments are sometimes required. And as with any complex machine, every aspect must be tuned carefully to enable sustained operation. The stresses which a first flight can place upon an aircraft must all be accounted for on the ground ahead of time. This is a major reason why five of us from the Museum flew out to Everett in the penultimate week of August to run through the A6M again, in anticipation of a first flight. This group included our Director of Maintenance, Al Lintz, and senior mechanic, Cody Busse. The two of them, joined by warbird experts, Brad Pilgrim and Gordon Page, Museum Chief Pilot Mike Spalding and the Legend Flyers team of technicians (lead by Bob Hammer) Bennett Johnson and Dan Hammer, pulled every panel from the Zero for a visual inspection on August 23rd - all under the watchful eye of Johnsons’ dog, Herman, perched atop a mobile gantry! To be sure, the aircraft looked magnificent, both inside and out.
A view of the Zero during inspection. The Museum's Cody Busse is examining the cockpit interior. (image by Richard Mallory Allnutt)
A topside view of the Zero's engine compartment with the upper cowling removed. (image by Richard Mallory Allnutt)
A close up of the carburetor air box intake for the Zero's Pratt & Whitney R-1830-92 engine. (image by Richard Mallory Allnutt)
A view of the Zero's engine accessory section with the cowling removed. (image by Richard Mallory Allnutt)
A closer view inside the Zero's engine accessory section showing the oil tank and various other components. (image by Richard Mallory Allnutt)
A closeup inside the Zero's engine accessory section revealing the astonishing eye for detail which the Legend Flyers team has approached this project. (image by Richard Mallory Allnutt)
A closeup of the rub-strips on the engine cowling mount. These pieces of heavy fabric help prevent abrasion of the cowlings during engine operation. (image by Richard Mallory Allnutt)
A view of the amazing detail which Legend Flyers has applied to the Zero. Here we see some of the Japanese instructions stenciled on the side of the propeller's spinner. Propeller spinners are incredibly difficult to refabricate, for obvious reasons, so Legend Flyers opted to adapt an existing example from a Lockheed Constellation. While some may fuss over this minor compromise, it is a route which a number of other warbird restorations, Hawker Hurricanes for example, have employed when an original example was unavailable at any price. (image by Richard Mallory Allnutt)
A closeup of a decal on the Zero's propeller. Interestingly, when they left the factory, the A6M3's propeller apparently had a polished forward face. The rear face is painted matt black so as not to blind the pilot on sunny days. (image by Richard Mallory Allnutt)
When the main landing gear is extended, a red-painted indicator rises up from each wing to provide the pilot with a physical indication that the associated landing gear leg has deployed. Note the two tan-colored rub strips at each extreme which make it easier for the strip to slide in its slot without jamming. When the lower rubstrip is visible, it also gives the pilot a level of confidence that the gear leg is fully extended. (image by Richard Mallory Allnutt)
Gear Swings
The landing gear was one of the key aircraft systems under test and observation during our visit. Before a first flight, there is always a healthy discussion about whether or not to leave the landing gear down for the duration of the trial. However, we learned that the original components which make up the Zero’s landing gear are susceptible to an overspeed, where higher-than-normal air velocities can damage the structure. Put simply, the A6M was not designed to fly with its landing gear extended for long.
In consultation with current Zero pilots and experts in the industry, it became obvious that the gear must be raised for most phases of the first flight, thereby placing enhanced emphasis on evaluating the system. Ground-testing the undercarriage involved placing the Zero on jacks to execute gear swing tests. Mike Spalding got a vigorous workout in the cockpit during this stage; operating the hydraulic hand pump to lower and raise the wheels took significant effort!
Moving the gantry in over the Zero's tail in preparation for hoisting the rear fuselage for the gear swing tests. (image by Richard Mallory Allnutt)
Preparing the gantry for lifting the Zero's rear fuselage. (image by Richard Mallory Allnutt)
Dan Hammer (left) and Bennett Johnson begin the delicate process of hoisting the Zero's rear fuselage off the hangar floor. (image by Richard Mallory Allnutt)
Raising the rear fuselage took a great deal of focus, as stress on Dan Hammer's face reveals here! (image by Richard Mallory Allnutt)
The Zero's rear fuselage fully raised. The team is about to begin lifting the forward fuselage via under-wing jacks. (image by Richard Mallory Allnutt)
A closeup of the Zero's rear fuselage showing the straps holding it up (and down) for the gear swing tests. (image by Richard Mallory Allnutt)
Bob Hammer (left), Bennett Johnson and Cody Busse (right) attaching a jacking block to the underside of the Zero's port wing to provide a secure hard point for lifting the aircraft off the ground. They attached a similar device for identical purposes to the starboard wing as well. (image by Richard Mallory Allnutt)
A view of the jacking block after it was attached to the starboard wing. (image by Richard Mallory Allnutt)
Bennett Johnson carefully jacking up the Zero's port wing while Dan Hammer works on the starboard wing. (image by Richard Mallory Allnutt)
The undercarriage and gear door sequencing performed flawlessly, however the limit switches which (in part) trigger the cockpit warning lights to inform the pilot whether the landing gear is properly locked up or down needed minor adjustments. While that might seem a simple task to those unfamiliar with the procedure, nothing with the Zero is straightforward!
Instead of making it easy to get at the necessary components by placing them in the wheel wells, Mitsubishi buried them deeper inside the airframe. As a result, the Legend Flyers team had to unfasten underwing stress panels and remove the aircraft’s tail cone to access the adjustment mechanisms for the main and rear landing legs respectively. The iterative process of tweaking and verifying limit switch settings with repeated gear swing operations consumed the best part of a day before it concluded successfully!
Bennett Johnson (left) and Gordon Page (right) unfastening the stress panels beside the main gear to allow adjustment of the gear position limit switches. (image by Richard Mallory Allnutt)
Bennett Johnson removing fasteners from the underwing stress panel while Dan Hammer observes from the right. (image by Richard Mallory Allnutt)
A side view of the Zero's uncovered rear undercarriage. (image by Richard Mallory Allnutt)
A closeup of the Zero's tail gear. (image by Richard Mallory Allnutt)
Brad Pilgrim (left) working on the Zero's tail gear, while photographer Jim Larsen looks on. (image by Richard Mallory Allnutt)
Gordon Page reinstalling the screws on the underwing stress panels following the successful conclusion of the gear swing tests. (image by Richard Mallory Allnutt)
Preparing for Engine Tests
Thankfully, by about 4pm local time on August 24th, we were finally ready to wheel the A6M outside for some engine runs. A successful taxi test conducted some months earlier indicated that a few engine sensors needed fine tuning, so the initial intent behind this latest run was to give those adjustments a once over. It would also provide an opportunity to look for any additional items which might impede a first flight.
Legend Flyers opened a storage hangar next door to retrieve their aircraft tug, a 1940s Willy’s Jeep! Suitably attired in WWII-era US Army markings, it was an unexpected surprise, tucked away in the same building as the fuselages of two replica Boeing P-26 Peashooters; Legend Flyers’ project-in-waiting.
An interesting fact about the P-26 which many may not realize is that the type was still in US and Philippine service (albeit in small numbers) at the time of the Imperial Japanese Navy’s attack on Pearl Harbor in December 1941. While no American Peashooters took part in that battle, several Philippine P-26 pilots bravely engaged with Zeros during the Japanese invasion of their Pacific island nation that same month. Despite overwhelming odds, Captain Jesùs Villamor of the Philippine Army Air Corps is reported to have bagged a brace of the heretofore near-invincible fighter.
The two partially completed Boeing P-26 Peashooter fuselages which will form Legend Flyers' next project. These replicas are the legacy of the late Tim O’Connor who conceived this project and spent twenty years working on it using original Boeing blueprints and manufacturing photographs. (image by Richard Mallory Allnutt)
A Philippine Army Air Corps Boeing P-26 seen here in the Philippines during 1941. Several Philippine P-26's confronted Zeros in the skies during the Japanese invasion in December, 1941. (image San Diego Air & Space Museum)
As the Jeep eased our A6M from the workshop, via straps attached to the main gear, it wasn’t hard to imagine a similar scene taking place 81 years earlier outside Hangar 7 at Eagle Farm near Brisbane, Australia. An Allied Technical Air Intelligence Unit once used this airfield to repair and evaluate a Model 32 Zero captured at Buna, New Guinea in late 1942. Knowing what the Legend Flyers team has been through in restoring our A6M3 to flight, gives everyone on the project an enhanced appreciation for just how difficult these wartime Zero restorations must have been. Vital to the war effort, certainly, but getting one back together and flown could not have been easy without factory drawings and the associated knowledge of how it was constructed - details which are now more available.
Clear Prop!
Swinging the Zero’s tail clockwise to the south, Dan Hammer positioned the fighter so its propeller blast would flow away from the open hangars. Mike Spalding then climbed aboard the fighter, while our team began pulling through the propeller, counting off each blade until it had exceeded eight revolutions. This process helps redistribute any oil which may have pooled in the radial engine's lower cylinders, thus preventing 'hydraulic lock' stressing the powerplant on startup.
With all of us, save Mike Spalding, now standing a safe distance from the Zero’s propeller, the pilot yelled the familiar warning “Clear Prop!” before engaging the starter motor. The polished aluminum propeller blades gleamed as they rotated, slowly at first, then with a rush once Spalding initiated ignition. The engine bellowed into life, puffs of grey smoke gouting from the exhaust manifold briefly as excess oil burned off. Mike cycled the engine and propeller through various settings, gradually increasing power and revolutions. A throaty roar soon enveloped our ears, magnified further by a resonance scattering from the hangar walls. As the crescendo grew, the Zero’s fuselage began to shimmy to its beat, seemingly urging us to free the fighter from its chocks. But just as quickly as the tension arose, Mike eased back on the throttle, and then cut the engine into silence. Our technicians quickly moved in to examine the engine for leaks and to take oil temperature readings. When Mike climbed down from his cockpit, it was clear that some work remained to be done, a typical scenario for warbird restorations even as they near the finish line. Each rebuild produces what is essentially a unique, hand-built aircraft, so it is rare that a project fails to reveal niggling issues once testing begins.
Over the course of the following day, we ran the engine several more times as components and accessories were adjusted. The focus reduced quickly down to two Squawks – an industry term for issues which require remediation.
The ‘Squawks’
Two distinct issues arose following the engine runs. Firstly, the propeller governor showed signs of an oil leak which would ultimately evolve into inconsistent blade pitch control. Secondly, there was a significant disparity between the temperature readings reported by cockpit instrumentation, and what was physically verifiable using an external infrared sensor measuring the engine directly.
The Prop Governor
Our Zero uses an American-made Pratt & Whitney R-1830-92 engine driving a cut-down Hamilton Standard 23E50 hydromatic propeller from a Douglas DC-3. Legend Flyers opted to use this power train due to its relatively similar size, weight and performance in comparison to the Nakajima NK1F Sakae 21 engine which the A6M3 Model 32 used during WWII. Rebuildable Sakae engines and spare parts are ‘as rare as hens teeth’ as the saying goes, so it made sense for a flying restoration to go with a far more readily available (not to mention maintainable) American powerplant despite the slight, if regrettable sacrifice to authenticity.
A badly damage Nakajima NK1 Sakae 14-cylinder radial engine which came with the project sits forlornly on a pallet outside the Legend Flyers workshop. (image by Richard Mallory Allnutt)
A closeup of the Nakajima NK1 Sakae engine at Legend Flyers. Rebuildable examples of this engine are incredibly rare, and nearly impossible to maintain economically, which is why Legend Flyers, reluctantly, chose to replace the powerplant with an American Pratt&Whitney R-1830-92, which is both available in relatively large numbers and with a significant supply of spare parts. Maintenance knowledge of the R-1830 is also far better understood in the USA as well. (image by Richard Mallory Allnutt)
Another view of the beleaguered Sakae. Note that it retains its propeller governor on the nose case. (image by Richard Mallory Allnutt)
A side view of the heavily damaged Nakajima NK1 Sakae engine at Paine Field. Given the level of corrosion present, it is unlikely that this engine could ever be restored to airworthy condition. It should make for an interesting display once it arrives at the Museum though. (image by Richard Mallory Allnutt)
To control propeller pitch (and moderate engine revolutions) the R-1830 features a propellor governor atop its nose case. The device is essentially a variable flow oil pump which the pilot can adjust to, as its name implies, govern the propellor’s blade pitch (how much “Bite” the propeller takes out of the air). This, in turn, affects engine revolutions as well. While our Zero’s prop’ governor functioned normally during prior engine runs earlier this year, it chose this occasion to misbehave. Had the governor failed during flight, or even high speed taxi trials, the consequences to both plane and pilot could have been disastrous. It was obvious, therefore, that this issue had to be fixed before either of those operations could be attempted.
After troubleshooting the problem, and identifying the recalcitrant governor as the weakest link, the team made the decision to replace the unit. However, sourcing an airworthy substitute on short notice required some ingenuity. After calling around various local workshops without result, Gordon Page elected to make the journey down to AeroMetal International in Aurora, Oregon to see if they could help. Aurora is more than 220 miles by road from Everett, a four hour ride at the best of times. Thankfully, Page was able to enlist the help of locally-based, former U.S. Navy P-3 pilot, Mark Darrow, to make the journey by air in his ex-Gabonese Air Force Beechcraft T-34C Turbo-Mentor. This reduced the travel time to just an hour each way, so after the brief hop down to Aurora, Darrow and Page successfully retrieved an operable prop governor for our Zero - with much thanks to Mark Darrow and the team at AeroMetal!
Cody Busse in the process of removing the troublesome propeller governor from the engine nose casing. (image by Richard Mallory Allnutt)
The offending propeller governor following its removal from the engine. (image by Richard Mallory Allnutt)
Four studs atop the R-1830's nose casing awaiting the arrival of the engine's new propeller governor. (image by Richard Mallory Allnutt)
Al Lintz preparing a seal for the new propeller governor mounting pad on the R-1830's nose casing. (image by Richard Mallory Allnutt)
Al Lintz placing the new seal on the propeller governor's mounting pad. (image by Richard Mallory Allnutt)
Gordon Page (left) and Mark Darrow (right) exiting the Turbo Mentor after their return from AeroMetal's workshop in Aurora, Oregon. (image by Richard Mallory Allnutt)
Brad Pilgrim (left) holding the new propeller governor for our Zero which Gordon Page (center) and Mark Darrow (right) collected from Aurora, Oregon.
Brad Pilgrim (foreground) and Cody Busse unpacking the Zero's newly-arrived propeller governor in preparation for its installation and engine trials. (image by Richard Mallory Allnutt)
Cody and Al soon had the new governor mounted to the Zero’s R-1830, and we wheeled the fighter out for another engine test. Success! The prop governor performed precisely as intended! However, while we had finally overcome one concern, we still had to resolve the engine temperature issue.
Tugging the Zero from the Legend Flyers hangar following the installation of the new propeller governor (and a rain shower!). (image by Richard Mallory Allnutt)
Pulling the propeller through prior to engine start with the new propeller governor. (image by Richard Mallory Allnutt)
The Zero outside following the installation of the new propeller governor. Prior to engine start, we spun the fighter 180 degrees to avoid whipping the T-34 with its propeller wash. (image by Richard Mallory Allnutt)
Temperature Trouble
Throughout the period Gordon was en route with the prop governor, the team at Legend Flyers focused intensely on resolving the temperature sensing issues. As mentioned, Mike Spalding had noted what he considered unusually high cylinder head temperature (CHT) readings on the cockpit gauge relative to the engine settings he had employed while running the Zero’s R-1830. This had occurred on previous engine runs as well, and we believed that the original Japanese CHT gauge was the likely culprit. Mindful of this, Al Lintz used a laser gauge to measure the oil temperature in the fuselage tank behind the engine. The numbers Lintz recorded were roughly half what the cockpit gauge reported, so it was clear that something was amiss.
The maintenance team considered a number of potential causes for the measurement disparity, with their process being a window behind the scenes at what troubleshooting in a warbird looks like. It is of course possible for the gauge itself to be the issue. Could it be the probe? Certainly. What about the wires that run between them? Also possible. Is it grounded correctly? You get the point. Tracing the systems involved focusing everyone on Oil Temperature and Cylinder Head Temperature indications.
Of the three most plausible explanations for the problem which we had considered, the simplest potential solution involved replacing the engine mounted sensors to see whether that made a difference. It did not, unfortunately. The notion of replacing the instruments themselves was complicated somewhat by the limited space to access the instrument panel without disassembling the aircraft. In the Zero, getting behind the instrument panel is no easy task. While that would be straightforward on most contemporary American aircraft designs, the Zero’s instrument panel cannot be removed from the cockpit, nor even tipped forwards. This means that the only way maintenance personnel can change a gauge is to first remove the oil tank (after draining it!) and then remove the firewall so that someone small (and nimble) can get at the back of the instrument panel. As mentioned earlier… nothing about the Zero is straightforward!
Some might ask, well, its only a couple of faulty temperature gauges, if the airplane is running fine, why not fly it? Without knowing how hot the engine is, on takeoff in particular, you run the risk of overheating it and damaging it, perhaps irreparably.
A Teachable Moment
Given the nature of this last technical obstacle, and with the window of Mike’s availability closing rapidly (he had to fly home that evening for his real job – remember, all of our pilots are volunteers!), we had to come to grips with the realization that we were not going to get the aircraft in the air on this trip as planned. There is always a lot of anticipation and excitement wrapped up in these moments, and it can be exceptionally difficult to recognize when it’s time to step back – especially when everyone is working so hard together to make it happen.
Everyone handles disappointment differently, after all it is an emotional moment for all involved, but in the end, it was an easy decision. We chose to come home without having quite achieved everything we initially set out to accomplish - despite the enormous effort contributed by all concerned. While it was a quiet car ride to the airport, and a long flight home, it was a choice we could all live with comfortably, and a perfect example of how complex a task it is to get one of these vintage aircraft in the skies again. We are close though… watch this space!
