Thursday, 30 July 2015

Dr Frank Mitchell's Nakajima B4N1 Prototype in 1/32nd scale


Ken Glass very kindly sent these photos of Dr Frank Mitchell's stunning 1/32nd scale scratchbuilt model of the Nakajima B4N1 prototype taken at the IPMS Atlanta Third Annual Model Contest held on 21 March this year.



In Ken's own words:-

"While at the show I renewed my too brief acquaintance with Dr. Frank Mitchell, well known for his large scale scratch built models. His work is shown at the HyperScale and Large Scale Planes websites.  Dr. Mitchell brought with him some old favorites for display, including his Nakajima B4N1 prototype model. The build was featured at HyperScale on 3 June 2004:-




"The B4N1 model is unusual, interesting and deserving of another look and Dr. Mitchell was kind enough to allow me to take photos of his build, now showing effects from extended storage since 2004. The laminated plastic sheeting covering the wings and fuselage has split at a few seams, visible in some of the photos.



"Dr. Mitchell related that his project began in the mid 1970s when he was then living in the Maryland area.  The only known photo of the B4N1 prototype was made known to him by his friend Robert Mikesh who was then working at the NASM restoration facility.  They consulted on a model project at some length but Dr. Mitchell's build did not proceed in earnest until the mid 1990s for various reasons.  In all that time to the present, no other photos of the original plane have appeared.  My thanks to Dr. Mitchell for graciously allowing me to photograph his model, reviewing the photo scans that resulted and allowing his model and build remembrances to be posted here at Nick's blog.



"The B4N type is interesting in that it demonstrates the logic used by Nakajima's early 1930s designers as they moved in incremental steps from the preceding biplane era configuration towards the then new monoplane arrangement, to be seen a few years later in their follow-on B5N design.  The B4N1 featured large cockpit sidewall gas tanks. This detail was detected by Dr. Mitchell using x4 enlargements of the B4N1 photo.  The HyperScale article shows how those gas tanks were depicted on the model.  That arrangement was dropped for the later B5N design.  It is likely the B4N1 prototype served to trial other then new design concepts, that either passed of failed during trials with the prototype.  The later B5N type was a success almost from the start, likely due in some measure to Nakajima's prior experience with their B4N design."

Dr Frank Mitchell


With special thanks to Ken and Dr Mitchell for sharing these images of a beautiful model of a most unusual aircraft with Aviation of Japan. More images from the Atlanta Contest to follow.

Update Notice

Following some recent correspondence Kit Trivia ~ Another Veteran Zero, a blog about the Frog 1/72nd scale Zero-Sen from 1959, has been updated with additional kitography, box art and the image of an excellent model.

Image credit: © 2015 Ken Glass with permission of Dr Frank Mitchell






Wednesday, 29 July 2015

Nate Special Attackers ~ Ki-27 Aces Extra 3


Tokubetsu kôgeki - special attack - was a Japanese military euphemism for the tactic where aircraft would be deliberately used as piloted flying bombs to destroy Allied ships, the pilots expected and expecting to die in the attempt. Towards the end of 1944 the Japanese military determined that special attacks would be the most effective way to destroy Allied surface fleets threatening invasion of the home islands. In pursuit of this doctrine they began to form special attack units (tokubetsu kôgeki tai usually abbreviated to tokkôtai), and undertook the wholesale conversion and preparation of obsolete types of aircraft with which to conduct the operations. By the time that the Air General Army was formed for the final defence of Japan in April, 1945, a total of 800 aircraft had been prepared for special attack. This total included large numbers of obsolete Ki-27 fighters and trainers, together with Mansyu Ki-79 single and two seat trainers. 

The programme, which was hampered by Allied air attacks, involved the conversion of bombs, mountings and detonators with which to arm the obsolete aircraft. In order to complete this work the Japanese Army had to suspend research and development work on new weapons, instead diverting facilities and personnel to work on the preparation of suitable bombs. Those included modified IJNAF bombs with the Type 99 No.25 250 kg bomb typically being adapted for the Ki-27. The heavy bombs on fixed racks had a profound effect on the performance of the aircraft. The pilots, mostly novice flyers with a scattering of more experienced airmen and leaders, were in the main volunteers. Their aircraft were otherwise unarmed and they depended on escort fighters, not always provided, in order to reach their targets safely. 

Typical of those units was the 68th Shinbu-tai (振武 Shinbu - stirring the martial spirit and 隊 tai - unit) formed by the Hitachi Air Training Division on 23rd March 1945 and established at Tenryu airfield in Shizuoka Prefecture on Honshu with a complement of 12 Ki-27 Nates under the command of 2 Lt Iichi Yamaguchi, whose Ki-27 is the subject of the heading profile by Ronnie Olsthorn. The Ki-27 is shown painted in the late war olive brown # 7 colour but special attack Nates were also painted dark blue and dark grey. From photographs of this aircraft it appears that the lustrous paint was newly applied and there is little flaking or wear. The unit insignia consisted of the numbers '6' and '8' fashioned into the shape of a bomb, but might not have been applied to all aircraft of the unit. At the top of the rudder were the characters for the Yamaguchi family name. The 68th moved to Chiran on Kyushu in preparation for attacks on US shipping laying off Okinawa and commenced operations on 8th April 1945. Also participating in these attacks as part of the Dai Ni Kikusui Sakusen (2nd Floating Chrysanthemum Operation) was Nekohashi-tai, the 42nd Shinbu-tai consisting of 12 Ki-27 Nates under the command of 2 Lt Yoshiaki Nekohashi.  This unit was formed on 29th January 1945 at the Akeno Air Training Division and all its pilots were officers.  

The first clash between these units and the US Navy occurred on the morning of 11 April 1945 when several groups of Japanese aeroplanes began approaching the Radar Picket (RP) stations  protecting the fleet. Corsairs from USS Intrepid intercepted a formation of 12 Ki-27 Nates approaching from the north and claimed to have shot down all of them.  On 12 April at 1352 hrs five Nates attacked LCS(L) (Landing Craft Support - Large) 57, part of RP 2 which had already come under attack from Japanese naval special attack aircraft. Three of the Nates made a co-ordinated attack on the vessel and two were shot down whilst the third, badly damaged, crashed only ten feet from the ship and blew an eight foot hole in its hull. The ship’s steering was damaged and she began to list so her commander Lt Harry L Smith implemented emergency steering and ordered her to sail towards Okinawa. As the ship withdrew a fourth Nate attacked her but was shot down by CAP (Combat Air Patrol) fighters and the ship’s defensive fire. At 1430 hrs a fifth Nate managed to evade the CAP and survive the ship's defensive fire to crash into her bow, destroying a 40mm gun position and killing two of the crew.  Despite the damage and fire on board LCS(L) 57 managed to stay afloat and even to rescue survivors from LCS(L) 33 which had been sunk during the attack.

Ki-27 Special Attack damage to LCS(L) 57

On the same day the destroyer escort USS Rall DE 304, part of the submarine screen of Task Force 51.5, was attacked by two aircraft that had managed to penetrate the picket ships and CAPs. One of these aircraft, a Nate, approached Rall from her starboard side whilst the other approached simultaneously from port. The ship’s defensive fire brought down the port side attacker but the Nate kept coming only ten feet above the water and slammed into the hull just below deck level. The Nate’s 250 kg bomb was hurled through the ship during the impact, exited the far side and exploded 15 feet from the ship. Despite a continuation of attacks by other aircraft, including a strafing Ki-43 Hayabusa which set off a depth charge locker, Rall also survived.

Wreckage of Nate Special Attacker ~ Katakana character ヤ 'ya' on fin tip

In an attempt to prevent the bombs being thrown from the racks on impact and passing through the targeted ships before exploding the IJAAF began fitting extended strikers protruding ahead of the aircraft so that the bombs exploded on contact with the hull.

Damage to USS Rall recorded in USN Report

Other tokkôtai units know to have used the Ki-27 for suicide attacks were the 41st Makoto Hikotai (Honesty or loyalty air unit), the 76th Shinbu-tai and the 108th Shinbu-tai. Despite the determination  of the young Ki-27 pilots who had sacrificed themselves on 12 April, the fate of the special attackers encountered by the Corsairs of VMF-323 “Death Rattlers” on the late afternoon of 28 April 1945 was the more typical outcome. The 12 Corsairs under the command of Maj George C Axtell were assigned to picket duty over the radar picket destroyers north of Okinawa, flying at 12,000 ft when Lt Jeremiah J O’Keefe spotted five bogies at 8-10,000ft in clear, sunny weather. Obtaining permission for his division to investigate O’Keefe identified the enemy aircraft as bomb-laden Ki-27s. The three Corsairs, Axtell, O’Keefe and Hood circled the formation of Nates which made no attempt to evade and then attacked them from 5 and 7 o’clock. O’Keefe hit the lead aircraft in the cockpit from 300 yards, exploding it. Streaking past the falling debris in a shallow dive he saw another Nate diving towards the sea and lining up on its tail exploded that one too. Bill Hood also downed two Nates and Axtell one. None of the Ki-27s had made any attempt to defend themselves and their only evasive manouevres were to dive towards the sea when attacked.

(This article completes the publication of the omitted chapters from Ki-27 Aces.)

Image credit: Profile © 2015 Ronnie Olsthoorn; Photos and schematic USN Archives




Friday, 17 July 2015

Rising Models - 1/72 Hayabusa Kits

Rising Models (aka Rising Decals) have released two complete Nakajima Ki-43 Hayabusa kits in 1/72nd scale. Based on the Special Hobby kits the new releases feature additional resin and photo-etch parts together with decal options to model two Hayabusa variants never previously kitted.


RM-01 Ki-43-II Early Model "Oscar" contains the Special Hobby Ki-43-II kit with a new resin cowling and replacement resin wing tips to make the first production variant of the II, together with a very neat five-part photo-etched annular oil cooler. The decal sheet offers four options:-
  • Ki-43-II of the 3rd Chutai leader, 64th Sentai in Burma, 1943 - in solid dark green over natural metal
  • Ki-43-II of 1st Rensei Hikotai at Sagami, Kanagawa Prefecture, Japan in 1944 - this aircraft has dark green tiger stripes over natural metal
  • Ki-43-II of 54th Sentai on Formosa in May 1943 - this aircraft in dark green dapple mottle over natural metal was flown by Sgt Mineta May
  • Ki-43-II of 54th Sentai at Okadama, Hokkaido, Japan in 1944 - this solid dark green over natural metal aircraft was flown by the Sentai commander Maj Naosuke Kurokawa


The early production version of the II can best be distinguished in photographs by the small wedge-shaped auxiliary oil cooler beneath the cowling. This variant had an upgraded Ha-115 engine driving a three-bladed propeller with a downdraft carburettor intake located internally in the upper lip of the cowling, a reflector-type gunsight and the revised canopy design, but retained the annular oil cooler and original long wingspan of the Ki-43-I. Two prototypes were constructed in February 1942 but quantity production did not begin until December of that year with the first examples reaching operational units in early 1943. Some early Ki-43-II 64th Sentai examples appear in photographs with their headrests removed. The exact point of changeover to the later production II variant with the larger honeycomb oil cooler under the cowling and shortened wingspan is not known for certain but it was noted in the HQ SEAC Weekly Intelligence Summary # 16 of 5th March 1944:-

"Recent information from Technical Intelligence has now settled satisfactorily the question of the fighters in Burma with 'square wing tips'. It will be recalled that over a period these fighters have been constantly reported as HAMPS presumably because of the common characteristic of wing tip shape. It has now been established that this is the final development of Type I Fighter Oscar Mark 2 which has a reduced wing span, with blunt rounded tips, and this may give the false impression of HAMP. This new type of fighter has been identified since the withdrawal recently of some fighter strength and a reasonable assumption is that OSCAR Mk 2 will for the present form part of the normal replacement to fighter units."

The 64th Sentai Hombu and 3rd Chutai had withdrawn to Malaya in September 1943 giving a tentative date for the arrival in Burma of the short wingspan Oscars as the autumn (fall) of 1943. This in turn suggests the production figures for the early II with long wingspan was approximately 800 aircraft from December 1942 to circa August 1943.

Rising Models early production II kit will be an excellent and unusual addition to any Hayabusa line up.


RM-02 Ki-43-III b "Oscar" contains the Special Hobby Ki-43-III Ko kit with parts to make the experimental Otsu variant armed with two Ho-5 20mm cannon in the cowling position. The conversion parts consist of a new resin cowling and the raised fairings for the Ho-5. Decals for four options are provided:-
  • Ki-43-III Otsu prototype at the Tachikawa factory in September 1945 - in olive brown over grey with no unit markings
  • Ki-43-III Otsu of 64th Sentai at Curakore, Cambodia in 1945 - a 'what if' in olive brown over grey with yellow 3rd Chutai tail emblem
  • Ki-43-III Otsu of Kumagaya Army Flying School in 1945 - also a 'what if' in olive brown over grey with white Homeland Defence 'bandages' on the fuselage
  • Ki-43-III Otsu of 24th Sentai at Ilan (Alian?), Formosa in 1945 - another 'what if' in olive brown over grey with white 1st Chutai tail emblem


The kit compromises on accuracy because on the real Otsu the fuselage forward of the windscreen was lengthened by 20cm (approx 2.77mm in 1/72nd scale) and this is not represented by the conversion. Panel lines behind the cowling were also altered and the flaps on the aircraft were modified to a rectangular split-type rather than retaining the eliptical 'butterfly' flaps of the original design so sticklers for absolute accuracy will have a bit of work to do if they want the model to be exact. The design of the Special Hobby kit should facilitate the addition of a laminated styrene plug in front of the firewall, a technique I used for the LS Oscar (below) and which permits both an accurate dimensional increase and the tapering behind the cowling flaps to be represented, but the new panel lines would be tricky to add.


The usual explanation for the lengthening of the fuselage is that the aircraft centre of gravity had to be altered but it seems more likely that it was just to enable the larger weapons to fit. The Ho-5 was just over 30lbs heavier and 13.3cm longer than the Ho-103. Two aircraft were converted in December 1944, one of which was c/n 7884, but the performance of the aircraft was found to be so degraded during flight testing that it was decided not to proceed with production of this variant. With some reservation over the compromises to accuracy this kit will make another fine and interesting addition to a Hayabusa line up.  

Image credit: Kit images © 2015 Rising Models; LS Hayabusa wip author

Monday, 13 July 2015

The Need for Speed: Developing and Delivering Saiun


In an extended article for Aviation of Japan correspondent Mark Smith and co-author Mike Quan explore the development of the Imperial Japanese Navy Air Service's elegant Nakajima C6N Saiun (彩雲 - vibrant cloud) carrier based reconnaissance aircraft. The article is illustrated with images of Mark's own Saiun prototype model, built from the Hasegawa kit.

From its inception the Imperial Japanese Navy Air Service (大日本帝國海軍航空隊 - Dai-Nippon Teikoku Kaigun Kōkū-tai)  had stringent demands and high expectations of those who designed and built its aircraft.  Performance specifications outlined for each new model required the highest level of innovation, financial risk, and imagination – and even then seemed impossible to meet. Successful designs like Mitsubishi’s A6M Zero fighter and Nakajima’s B5N torpedo bomber had proven the wisdom of such a course.  But in 1942, Nakajima’s design engineers were asked to deliver against a specification for a new experimental carrier reconnaissance plane that must have come as a jolt.


A top speed of 350 knots at 6,000 meters and a maximum range of 2,500 nautical miles would be required for a machine carrying three crewmen, state-of-the-art radio and camera gear, a rear-seat machine gun, and arresting gear for carrier operations.   The vaunted Zero-Sen, a pure fighter design unmatched in performance by any shipboard aircraft of any type then in service, had a top speed under 300 knots.


The need for speed was fundamental to long-range fleet reconnaissance, but had taken on a new urgency.  The Japanese knew that the Corsair and Hellcat would soon show up in the Pacific in significant numbers. Japan’s reconnaissance doctrine was heavily reliant upon catapult-launched floatplanes and long-range flying boats, and they had reliable aircraft and seasoned crews for these roles; against US forces in carrier versus carrier battles, however, they would not be enough.  While these aircraft had remarkable range, if spotted by Allied fighters, they seldom returned.  In the first few months of the Pacific war the Navy employed small numbers of carrier-based attack aircraft for reconnaissance to augment the reporting of “Jake” floatplanes and “Mavis” as well as the “Emily” flying boats just introduced to service.


But this would not prove the answer against the new foe.  Grumman F4F Wildcats, guided by Fighter Directors on American CVs who were quickly learning to exploit the USN’s critical edge in radar, kept showing up.  The risk of interception was high when enemy forces were known to be within the search radius.  If fighters did not score a kill, they could at least divert Japanese aircraft from their assigned search vectors.  Other factors pressed also.  IJN attack aircraft and their veteran crews were critically needed for their primary role when their own numbers were spread too thin, and the unforgiving nature of ocean navigation over trackless distances regularly claimed its own victims.  The hardest part of such a stressful mission came at the end, when weary crews had to find a carrier which might have changed course in their absence, usually under strictly imposed radio silence.  The absence of the air superiority the Japanese had known in China had changed the picture.   

JNAF carrier units were second to none in equipment, training, and skills.  But airborne reconnaissance missions that would give Combined Fleet the needed edge required greater range, speed, and a higher service ceiling than any IJN bird in the inventory. Where were the dedicated eyes of the fleet?


Right around the corner, some said; the scuttlebutt was that something special was on the way from Koizumi that would help Japan reclaim the initiative in the South Pacific.  Koizumi was a brand new facility, with Ohta Field and Nakajima’s Ohta plant virtually next door.  There the Navy and Nakajima had assembled their brightest lights in experimental flight-testing, as well as a crack team of mechanics and fitters.  Specific groups were assigned to investigate persistent problems critical to any new design’s success. According to Rene Francillon, the C6N design employed eighteen prototype and pre-production aircraft before production could commence.  But at Koizumi the Saiun improbably evolved into a viable design, as the airplane the Allies would come to know as “Myrt” came into its own.

Yasuo Fukuda was the project’s Airframe Section Chief. Instrumental in design and production of Nakajima’s the B5N (“Kate”) and its successor the B6N Tenzan (“Jill”), he knew what he was up against. Tenzan had held great promise, but was riddled with teething problems that had so far prevented it from attaining production status. The main problem was power.  The horsepower necessary to meet assigned requirements was unavailable in any Japanese engine of that time.  A three-seat carrier aircraft with a maximum speed of 250 knots, Tenzan was still mired in a long gestation period.  And in Saiun, the company was being asked to come up with a three-seat carrier aircraft 100 knots faster!


Though the C6N1 project was originally envisioned to use two yoked 1000 hp engines in order to provide the requisite power, Nakajima’s new air-cooled Homare, then being tested, promised almost as much power without the added weight and maintenance headaches such a complex design was bound to bring.  The decision was made for a more conventional single-engine design. Homare (“Honor”) was compact, its diameter only 30mm larger than the Zero’s reliable Sakae.  But at the necessary altitude of 6000 meters, it was found that the engine (which would always prove troublesome in service) would only yield 1600 horses.  However Nakajima’s design crew did the math, they needed the 400 additional hp originally promised in order to deliver the performance the JNAF demanded.  The only hope to make up the difference would require the simultaneous success of several radical design features.  While it was a longshot, there was no alternative due to the worsening war situation.

Nakajima would not regret choosing Homare, and concurrent events that supported its wisdom are worth relating here.  In 1943 the Kugisho (sometimes referred to as Yokosuka) had begun to test the 18-Shi Field Reconnaissance Aircraft assigned the name Keiun. Without the necessity of arresting gear or a short takeoff run, a land-based recon aircraft should have been able to match or exceed Saiun’s performance.  But early in its design stages a decision was made for the in-line installation of two German DB601 liquid-cooled engines, produced domestically in Japan as "Atsuta" (Type 30), in what was termed a "twin-type" mounting, with the two powerplants buried front-and-back in the fuselage. Navy engineers had a privately-purchased Heinkel 119 on hand for study which had the same arrangement.  The engines were connected, to each other and to the propeller, via a long extension shaft. It was a bold technique, but one dictated by the lack of a Japanese aero-engine equivalent to the Pratt & Whitney R-2800 or the later Rolls-Royce Merlins; and Keiun’s radical airframe design was not flexible enough to support a more typical powerplant.  The gremlins connected with the “twin-type” engine arrangement were never exorcised.  The Keiun program consumed precious time, personnel, and priorities for the sake of an airplane that accomplished one ten-minute test flight.


If the efforts expended on Keiun had been applied to existing Kugisho types suitably modified to undertake the land-based reconnaissance role, such as the D4Y Suisei (Judy) and P1Y Ginga (Francis), these aircraft could have been delivered to JNAF units badly needing them.  At least in Suisei’s case, this could have easily occurred by the beginning of 1944.  The earliest variant, the D4Y1-C, had proven an able purpose-built recon bird, with long range and high speed.  The fact that the first two were assigned to Soryu just in time for the Midway battle in mid-1942 indicates how early they might have been ready in numbers.  That battle marked the beginning of heavy Aichi D3A (Val) dive-bomber losses, however, and afterward Suisei production would concentrate solely on the dive-bomber version.  With later models of the D4Y, the removal of armament, carrier arresting gear, bomb load, and the hefty bomb release mechanism inside the bomb bay would have added significant speed for the recon mission, leaving only the need for radio and camera gear.  Just as importantly, the type was easily adapted to a radial engine (D4Y3) when the Atsuta inline models became unavailable, so the decision to continue so long with the Keiun program seems completely insupportable.  

The Navy would finally have the land-based reconnaissance aircraft it needed, but for all the wrong reasons: Keiun failed miserably, and by the time Saiun reached production, there were no Japanese carriers left from which to operate.  But these two aircraft represent what has often been the critical design decision: to build upon the proven and traditional, or to take the leap of faith for something new or revolutionary.


In a way, Saiun’s designers did both.  Airframe Section Chief Fukuda’s prime directive was to keep the airplane as small as possible, much the same way as the Zero was designed with constant emphasis on weight savings.  Special care was taken with an economically elegant cowling design to provide an exceptionally clean airflow entry.  The same attention was focused on the front fuselage area and the seven sections of the aircraft’s greenhouse canopy.  

The wing design, as originally submitted, was a shade less than two-thirds of Tenzan’s wing area, and appeared impossibly small to provide the necessary lift for carrier take-offs and landings while still meeting range and drag numbers.  It was agreed that only a laminar-flow wing could provide the necessary lift while reducing drag sufficiently to meet speed requirements.  Over 200 NACA airfoils were tested along with Nakajima's own K-Series airfoil, one of the latter being modified by 30-year-old engineer Naito Yasuo.  His successful creation resulted from what he called "sharpening" the leading edge profile.  As he explained in a two-part article printed in Koku-Fan magazine in the 1970s, this was a “delicate planing” of the leading edge of the airfoil shape that resulted in an increase in the lift coefficient at higher airflow regimes than the normally tested flow regimes then considered as ‘standard,’ as measured by Reynolds number.  Encyclopedia Britannica defines Reynolds number as a scientific, mathematical quantity that models/theorizes liquid or gas flow, measuring the aeronautically important factor of when airflow transitions from laminar to turbulent, at which point the drag increases on an airfoil.  (Lift coefficient equals drag forces divided by lift forces.)  Essentially, Naito was pinning his hopes on a combination of aeronautics and nascent technology which was then unproven in Japan - and in doing so, had stumbled into the same scientific area of research which NACA had conducted in the US that resulted in the laminar airfoil so successfully used most notably on the P-51 Mustang, endowing it with unusual speed and range.


Some business pressures never change.  The IJNAF, the ones who had mandated such stringent requirements, balked at approving the new technology Nakajima would require in meeting them.  Naito was briskly summoned to explain himself, as the Navy’s own engineers felt that precious time would be wasted in banking on an untested and seemingly impractical design.  As a result of these discussions, however, a new wooden model was made, and the wind tunnel tests Naito requested were granted.  There his calculations and daring were vindicated; the maximum lift-over-drag coefficient increased, while stall characteristics decreased.  This was the key basis for selling the Navy on such a controversially small wing, and Nakajima now set to work to make it as efficient as humanly possible.  

Leading edge slats and sophisticated double-slotted Fowler flaps were incorporated into the wing to further increase lift, and the ailerons could be lowered in conjunction with the flaps.  The slats were unlike those seen on most aircraft of the period such as the Fieseler Storch or Me109, which deployed automatically at a certain speed above stall; those on Saiun these were operated hydraulically by the pilot through the use of springs.


The inevitable down-side of all these efforts to make the airplane controllable for carrier operations was that the “center of lift” shifted dangerously aft, causing the nose to pitch down perilously at deck landing speed.  Nakajima engineers devised an ingenious solution that was to be reflected in many later jet designs: again using oil pressure, the entire horizontal stabilizer was made hydraulically articulated so that its angle could be changed upon final approach and arrest.  The tiny square cutout underneath these surfaces is the only external evidence of this critical innovation.   

Lift or no lift, though, Saiun would need increased acceleration for that short carrier take-off run, and the largest-diameter propeller feasible (3.5 meters) was chosen for the sake of its additional thrust (3.5 meters).  This helped take Saiun from zero to six thousand meters in 6 minutes, 20 seconds.  (Nakajima’s Hayate, a single-seat fighter using the same engine, climbed to the same height only ten seconds sooner).  In a way that mirrored the Vought Corsair’s needs and development, this in turn mandated a long set of landing gear legs for ground clearance.  Due to the selection of a laminar-flow wing, these would have to retract between the spars (instead of forward of the main spar as was the general design practice of the time), so as to least compromise the critical laminar shape of the airfoil.  Though this pushed the main gear legs back far enough to give the aircraft an awkward ‘sit’ and made for slightly more difficult ground handling, it was yet another make-or-break point in the airplane’s development.  It also mandated another unusual feature. A “smooth” oleo strut was designed by Engineer Sakamoto, an element that Naito Yasuo, writing thirty years after the war, would cite as critical to the aircraft’s success.  These struts, when retracted, were raked forward dramatically to compensate for being mounted so far aft.  


Unusually large panels of thicker gauge metal were used to skin the Saiun.  This would seem an odd choice in an aircraft where speed was essential and any weight savings important.  Yet the benefits proved otherwise: Saiun needed less than half of the number of rivets used in Tenzan, and the larger panels cut skin drag and speeded production.  An innovative wing spar utilized super-extruded duralumin for the upper and lower spar caps.  These features made for an exceptionally strong wing structure (required for the larger panels), and one capable of mounting three fuel tanks in each wing totaling 1300 liters.  The under-wing external fuel tank, the largest carried by any Japanese aircraft, added 730 liters.  Thus loaded, Saiun could roam for an astonishing 5300 kilometers.

Nakajima had completed the first prototype in March 1943 and flown it on May 15.  Flight test results suggested several changes that might refine performance, even as Nakajima was feeling increasing pressure to standardize the aircraft for production as the front pushed further north toward Japan.  Significant changes to the design included a new three-blade propeller of different section to replace the original four-blade unit, cowling and oil cooler refinements, and modified horizontal tail surfaces.  Originally unable to meet the critical speed requirement for its mission, after these changes the sleek Saiun was finally accepted for production in the spring of 1944, and first deliveries made to operational units in September.


The C6N1 made its combat debut during the battle for the Marianas, an unmitigated disaster for Japan.  By then of course it was far too late; though the Saiun was a sterling performer and could usually accomplish its mission well and safely, the photographs and reports it brought back were inevitably disheartening.  It was ironic that by war’s end, the only Japanese aircraft in production possessing truly exceptional performance by international standards were not ones bringing bullets or bombs to the fight, but types designed to spy on the enemy: the Army’s late-model Ki-46 Type 100s and the Navy’s C6N1 Saiun.  However elegant their design or elusive their performance, they could only bring home bad news.  Soon many were flying as pathfinders for Tokko and Kamikaze missions, and a ‘successful’ mission meant coming home alone.        

Attempts were made to transform both designs into fighters, utilizing diagonally-mounted cannon neither airframe had been designed to support.  The handful of examples of Saiun that were turned into night-fighters to protect Japan’s industrial cities against B-29s saw little if any success.   Mounting large-caliber weapons mid-cockpit of such a specialized design was merely a measure of Japan’s desperation.


Counting prototypes and production airframes, 463 examples of Saiun were built.  While the Zero was the pride of the Navy for much of the war, Saiun was easily the fastest and most exotic aircraft in its inventory in WWII.  It was a remarkable accomplishment of imagination and innovation in the face of Japan’s most crippling aviation shortcoming - horsepower.  American testing of at least one aircraft was undertaken after the war upon arrival of several airframes aboard jeep carriers.  “Myrt” had earned a deservedly high reputation among USAAF and USN pilots and intelligence officers in its brief time of service; with new plugs and the Homare perfectly tuned, for instance, it could not be caught by Hellcat pilots in a tail chase.  While the design elicited admiration stateside for its clean lines and performance, interest was academic; by war’s end American reconnaissance doctrine was firmly established in combat-ready fighter types also equipped with cameras, as had been ably vindicated by the P-38, Hellcat, and P-51.  And the new technology of the jet engine was here to stay.

The only surviving example of Saiun is now held in storage by the National Air and Space Museum in Washington D.C.  Found at Atsugi Air Base at war’s end, it had been converted to the night fighter role. Some of its cockpit appointments are long lost, and many of those that remain are unique to the armed version, to which only a handful were converted.  Roughly disassembled, it is still sadly derelict, and if restored, some areas would need re-fabrication.  It was last flown at Middletown, Pennsylvania, after which it sat at its tie-downs for many months through hard Northern weather, its tires soon flat and its once-polished metal surfaces chalking to gray - an ignominious end for a brilliant design.


Engineer Naito Yasuo’s account, as abstracted in English in Koku-Fan magazine, was the central source used for this article. I had only a photocopy of that article obtained long ago, which gave no clue to the particular issues where it appeared. That information would be greatly appreciated so we can provide it here. As this project became more ambitious and I struggled with a translation that had its own problems, and that treated subjects where my knowledge was insufficient, I was out of my depth.  In clarifying certain vagaries of that translation as they related to technical matters, in correcting my own mistakes regarding terminology, and particularly in rewriting the section about Reynolds number, I was greatly aided by Mike Quan’s careful reading and editing of the manuscript. His professional knowledge of the subject made such a difference. Errors that remain are entirely mine.          

Mark Smith

Image credit: All model photos © 2015 Mark Smith; Interior colour chips © 2015 Aviation of Japan 



Wednesday, 8 July 2015

Arawasi International Magazine Issue 12 and Eagle Eye Series No.2


The appearance of Arawasi International magazine, Issue 12 for Spring 2015, is a welcome delight. Issue 11 was published in the Summer of 2009 and the long interval that followed was a cause for concern. The latest issue is, as usual, packed with interesting articles, photographs and superb profiles by Zygmunt Szereneta, with a definite civil focus as follows:-

  • Japanese Staggerwings - a thorough examination of the licence-built Beech 17E with full story, many interesting photographs, schematics, interior details, contemporary colour and profiles - almost a mini monograph in its own right and essential for anyone interested in this machine.
  • Human Bomb Ohka Pilots Ready For Take Off - a fascinating first hand account by Saeki Masaaki with several previously unpublished photos.
  • Through Furnaces and Freezers - an account of the exploits of pioneer civilian pilot Kumakawa Ryôrarô flying the Stinson Reliant and Messerschmitt Bf108 Taifun in the 1930s with photographs and three colour profiles - the camouflaged 108 J-BACC offering excellent inspiration for a model.
  • Experimental 6-Shi Two-seat Fighter - interesting account of a little known and unsuccessful biplane carrier fighter for the IJN.
  • Tachikawa Ki-36 Accident Report - another gem of an article illustrating a damaged aircraft of the 206th Dokuritsu Hikôtai in photographs and profiles, although the camouflage was probably the standard China-based Chokkyo unit green and brown rather than the grey and green depicted. In monochrome photographs the brown, with its red content, often appears the darker of the two colours although intuitively it is assumed to be the green.
  • Model Commentary - a superb and beautifully rendered model of the Experimental 11-Shi Special Reconnaissance Seaplane E11K1 by Bill Sanborn in 1/72 scale using the A&V resin kit. Colour photographs throughout and plenty of them.
  • On Location: Matsuyama, Ehime Prefecture, Japan - a potted history and colour photographs of surviving structures at the former IJN base. 
Arawasi magazine, available directly from the publisher, retails at US$12 (about £7.80) plus $3.00 postage and packing and is worth every cent. It has far more substance (and less advertising) than many mainstream aviation magazines and a quality and depth of presentation that puts it firmly in the serious journal category. Very highly recommended.


Also from Arawasi, No.2 in their superlative Eagle Eye series features the Yokosuka/Kawanishi K5Y1 and K5Y2 Akatombo training biplane of the IJN in both its land and float configurations. This is a most complete and authoritative account of the type in 81 pages, packed with photographs, schematics and charts as well as fold-out plan drawings and profiles. Anyone who thinks that colour schemes for this particular aircraft are limited will be inspired by Zygmunt Szereneta's 18 superb and colourful profiles.

Fortunately the famous Akatombo is well served by good kits in 1/72, 1/48 and 1/32 scales, the various box arts for which are shown inside the rear cover. There is also a colour feature of a wonderful 1/25 scratch-built model by Tanaka Shôichi. Eagle Eye No.2 retails at US$25 (about £16) which is a bargain for the amount and quality of content provided. The book is an absolute must for anyone contemplating building the type in any scale and is very highly recommended.

Image credit: All © 2015 Arawasi





Saturday, 4 July 2015

Chinese Aircraft ~ Part 2


John Haas kindly shared these images of his splendid Curtiss Hawk 75 built from the 1/48th scale Hobbycraft kit  in Republic of China markings. The story of the Curtiss Hawk monoplanes in Chinese service may be found here and here.



John's model represents the Curtiss 'Hawk Special', also known as the 'China Demonstrator', NR1276, (c/n 12327), as photographed at the Curtiss factory on 16th April 1937. Although NR1276 is often referred to as the first H75-H it actually appears to be the pattern aircraft for the H75-M, an export version of the Curtiss Hawk specific to China.



Les Moore kindly provided these images of his excellent Martin B-10 bomber wearing Chinese insignia and representing an aircraft of the 30th Squadron. The model was built from the classic 1/72nd scale Williams Brothers kit and constructed from the box except for the machine gun and pitot tube which were fabricated from .016 guitar string.  Les painted it with War Birds acrylic and Testors enamel paints. 


The Chinese government purchased nine Martin M-139WC-1 and M-139WC-2 export versions of the bomber, the first six delivered in two batches of three in February and May 1936. The final three arrived at the end of 1936 via Manila and Hong Kong. The first six bombers were assigned to the 8th Air Group's 30th Squadron and the subsequent three bombers to the 14th Squadron, also known variously as the 14th International Volunteer Squadron or the 14th Volunteer Bombardment Squadron. This unit, commanded by Vincent Schmidt, a First World War veteran from New York, consisted of foreign volunteer pilots from the USA, France and New Zealand flying with Chinese bombardiers and gunners, and was also equipped with Vultee A-19, Northrop A-17 and Gamma 2E types.   


In May 1938 the two surviving Martin bombers from the 14th Squadron, 1403 and 1404, were assigned to an Air Expeditionary Force under the command of Captain Hsu Huang-sheng to fly over Japan and drop peace leaflets. The bombers were equipped with enhanced radio and radio direction finding equipment which had been co-ordinated with ground stations established along the primary and secondary routes. 


The two Martins were on stand by for the mission at their Hankow base from 15 May awaiting suitable weather conditions. At 1523 hrs on 19 May the two aircraft, piloted by Captain Hsu and 1Lt Tung Yen-po (the executive officer of the 8th Air Group's 19th Squadron), departed on the first stage of the mission, flying to Ningpo via Nanchang and Chuchow. They landed there at 1755 hrs and after final preparations and refuelling took off for Japan at 2348 hrs. After dodging the searchlights of Japanese warships the Martins arrived over the fully lit city of Nagasaki at 0245 hrs and from an altitude of 11,500 ft first dropped a flare which triggered an immediate blackout and then scattered leaflets.  They then flew on to Fukuoka where from 0325 hrs they began dropping more flares and leaflets. At 0332 hrs they started for home.     



On the return journey the two bombers encountered bad weather and became separated in cloud but were able to find their way to the Chinese coast by means of continuous radio communications with the ground stations and each other. Both aircraft made landfall at Sanmen Wan at 0712 hrs coming under fire from Japanese ships anchored in the bay, the first hostile fire they had encountered on the mission. Martin 1404 finally landed intact at Yushan airfield at 0848 hrs  and at 0924 hrs 1403 landed at Nanchang. After refuelling the bombers flew on to Hankow, rendezvoused over the city at 1113 hrs and both landed there safely. 

More on Chinese bombers and bomber operations in due course.

Image credits: All Curtiss Hawk 75 © 2015 John Haas; All Martin B-10 © 2015 Les Moore