Akutan Zero

[pampa14]

In July 1942, the United States captured the first Japanese Zero fighter. The link below provides information and photos of this aircraft, called the Akutan Zero:


aviacaoemfloripa.blogspot.com.br/2011/02/akutan-zero.html



I hope you enjoy and I count on your visit!

[komata]

pampa14

Thanks for the images; as always, they are very interesting. It should be noted however that there are at least four different A6M's in the photographs: No.'s 1, 7, and 8 (and possibly EB-201, although that could be No.1 re-numbered), and that what are shown are various aircraft 'cobbled-together from captured wrecks. Such was the the American's desperation to get information about the 'Zero' that they got 'bits' from where-ever they could, and ultimately had at least five (of various variants)flying.

BTW(for the 'marking'enthusiasts): Note the different national markings and their locations; a study in itself.

[Dave Homewood]

New Zealander Don Nairn test flew and evaluated the first captured Zero in the USA for the Royal Navy. He was the second Allied pilot to fly one, after the US Navy's test pilot.

[nuuumannn]

Yes, great images. Komata, on the ball as always, although EB-201 is/was an A6M3-32 with clipped wingtips. TAIC was the Technical Air Intelligence Center at NAS Anacostia and its aircraft were numbered sequentially from when they arrived, the Aleutian Zero being TAIC 1. This department incorporated expertise from the Technical Air Intelligence Unit at Eagle Farm in Brisbane that had assembled and captured a number of Japanese aircraft there, including EB-201, which was captured in PNG and shipped to Australia for reassembly and trials before being sent to the USA, although EB-201 went to the USAAF at Wright Pat and not the navy TAIC.

TAIC 7 was captured at Saipan and survives today at the National Air and Space Museum, Washington DC. TAIC 8 was an A6M5 captured at Saipan also and was assigned to a unit trialling Bell P-59 and Lockheed P-80 jet fighters. Also visible in the fourth picture from the bottom is Nakajima B5N TAIC 6 which was captured in 1944 and was of immediate interest because it was fitted with ASV radar. The Zero in the foreground is possibly TAIC 5, an A6M5-52.

[komata]

nuumann

Many thanks. I noticed the TAIC marking on the fins of several of the machines, but could not recall what they meant. TAIU (Tech Air Int UNIT) I knew, TAIC, I had forgotten: too many acronyms .

Nice to know that TAIC 7 still survives. The P-80 / 'Zero' combat would have made for interesting viewing...

Again, thanks.

[davidd]

The first more or less complete Zero to fall into Allied hands was actually located in China, but this took longer to repair and get back into flying condition than the one from the Aleutians. The main problem they seemed to suffer was the production of faulty comparative performance figures, and these were the unintended consequences of (faulty) critical stop settings on the propeller, which was, as everyone knows, of the Hamilton Standard counterweight type. This prop type, which was very similar to those fitted to Harvards, Beavers, etc, although of the 3 rather than 2-bladed variety, was built in Japan under license by Sumitomo Heavy Industries, but its general design and operation would have been very familiar to Allied technical personnel. I can only presume that the American and Chinese technicians who dismantled this prop during a complete stripdown of this vital component, somehow lost the vital stop settings (or never recorded them in the first place), and on reassembly, guessed at what they should have been, and then presumed that the engine was performing "normally". Perhaps the "Never exceed" RPM was not a feature of the tachometer. As a result of this, the engine of the "China Zero" could never be persuaded to exceed about 2300 RPM, so the detailed technical report subsequently produced grossly underrated the performance of this aircraft. Needless to say, the Japanese had the correct settings set at the factory, and the standard maximum RPM of their engines was about 2700 RPM - what a difference! Thus the American report stated that the Zero possessed a general performance which was easily exceeded by practically all contemporary American fighters, and was therefore not to be feared. This probably came as a suprise to all American pilots who had actually been in combat with the type. Fortunately greater performance results were also coming forward from the Aleutians Zero, so eventually somebody must have compared the two and realized that something was wrong somewhere. I do not know what circualtion was given to the more or less contemporaneous (and conflicting) reports, but eventually the higher performance estimates must have prevailed. Neverthess some general statements based on the inferior results were widely circulated, and traces of them are still evident in subsequent publications.
David D

[nuuumannn]

Very interesting as always Dave. Wasn't aware of the prop issues with this aircraft; the Sumitomo props were copies of Ham Std props. That aircraft was distinctive in appearance as it had two sets of three louvres aft of the engine cowl and can be distinguished because of these. It was indeed captured intact in February 1941, more than a year before the Aleutian Zero. It's also often mistaken for the Aleutian Zero as well.

[davidd]

Grant,
A small point, but the Japanese actually had a license to manufacture the Hamilton Standard counterweight prop (as did DHs in UK) and like the DH version they showed some differences in detail. Interestingly, the DH-built props were manufactured in greater numbers than those eqivalents built by the parent company in USA, although this probably due to the British company keeping this early type in production until 1944 in large sizes (as for the Sunderland). DH's also delivered Hydromatic props (full feathering for most part, and mostly assembled from components supplied by USA parent under Lend-Lease) to RAF aircraft manuafacturerd from about 1941, such as Beaufighter, Stirling, also Lancastr, Mosquito, York, and the later Albemarle. The Japanese (and the British) also manufactured very large numbers of other American patented accessories under license prior to and during WW2, including many instruments (including gyro), machine guns, de-icing systems, fuel gauges, electrical items such as starter motors, generators, and brakes, and automatic pilots, among others. All Japanese heavy aircraft apparently used Jack & Heintz autopilots. One British development that I know of was manufactured under license in USA by Sperry of New York - this was the Exactor hydraulic control system, used in British aircraft for engine controls, but main employment for the USA-built examples seems to have been for controlling moveable radar antanae, such as the Yagis carried under the outer wings of US Navy a/c such as TBF, SBD, SB2C for their ASB radar, in distinct search and homing modes.
David D

[davidd]

Grant.
I have revisited my version of the comparative combat tests of the China Zero (dated 6th February 1943, Kumning, China), and the maximum RPM the USAAF officer test pilot could wring out of his engine was only 2075!!!! No wonder the P-40K and the P-43 he "fought" with were able to best this rather compromised machine. This pilot even notes that he had been advised that the prop settings were strongly suspected of not being representative (the technicians would have realized that such an engine should have been capable of 2,700 RPM), yet he still maintained that the generic Zero could be quite easily beaten by the P-40K, P-43 and even the P-36A types, based purely on the performance of this aircraft. I think somebody had a huge blind spot in offering these opinions, in spite of the doubts of his own technical staff, and I wonder if he was ever chastized for offering such opinions. However the slightly earlier Aleutians Zero test results would have been available by this time so the China Zero recommendations were probably realized to be very suspect too, and would not have been promulgated generally so no harm should have resulted.
David D

[komata]

davidd

Re: 'I think somebody had a huge blind spot....'

The test pilot's viewpoint could well have been a case of 'you will see what you want to see' and find answers that would be supportive of that view. To do so would have been totally in accordance with the prevailing American view was that the Japanese were incapable of building anything, much less a high-powered combat fighter that was superior to anything extant in Europe and America.

Claire Chenault tried to tell them, but, as we know, no-one took any notice...

[nuuumannn]

Thanks for the info Dave, I'm aware the Japanese licence built the Ham Std props as did de Havilland. The Hydromatic prop differences between the US and British built was/is on the splines on the engine prop shafts are different on the British and American engines, therefore the spiders, which attach the prop to the engine has different splines and key way as well. Otherwise, there's little or no difference between them. The standard 23E50 prop for the DC-3 is the same as the 23EX for the Mosquito. There are minor differences in breather tubes in the centre of the hub and distributor valves between prop models and fit to aircraft, as well as the location of pitch stop mechanisms, but the parts are nominally the same. You can remove the piston from inside the hub of a Ham Std 23E50 and fit it to a de Havilland 23EX.

These props also have largely the same blade part numbers as well and often blades were cropped to size to fit different applications. This was done by hand, literally drawing the blade profile onto the metal and cutting it out, them profiling it to shape again by hand. Here's an example, the Yak-3 flying at Omaka has a Ham Std Hydromatic prop, the hub comes from a DC-3 23E50 (if my memory serves me correctly), the blades from a PB4Y Privateer, which were trimmed to size to fit the Allison installed under the hood.

Unfortunately institutionalised racism gave the Allies as a whole a false view of the Japanese and what they were capable of.

[davidd]

For interest, I have copied parts of the American report which have been personally chosen to illustrate what I consider are some of the warning signs which should have alerted the Americans (and particularly the test pilot), who does seem to have an-above average engineering knowledge for a service pilot at this time. I also question his interpretation of the term 'semi-monococque' in relation to the main structure of the Zero (which is correct in the purest sense), then he states that the wing and fuselage skinning is unstressed (which is certainly a completely false statement!) However only about half the actual report is included below - the rest of the text I have no dispute with.

I have left the original American spellings as found (airplane, carburetor, etc.) Most of the earlier part I have left out, but Sections 6 to 9 are complete. It is revealing that this pilot ocnsiderd the Zero a structurally weak aircraft, and this was probably based on his examiniation of the aircraft and its structure. However the designer (and most pilots) seem to have regarded it as strong enough for all maneouvres and situations, although its lack of armour and self-sealing tanks possibly inhibited approaches to heavily armed American aircraft to a certain extent - it certainly did later in the war. Later models of the Zero fighter (Reisen) were deliverd to the Navy fitted with various amounts of armour protection and certain types of protected fuel tanks 'by popular demand'.

Unfortunately the tabulated information has not survived the conversion process onto the Board, so you will have to reconstruct the columns yourself if you wish to download them - however the general layout is about right - just the compression.

Despite my concerns with the main recommendations of this report, it is nevertheless an interesting document of it's time.


CAUSE FOR CONCERN?

2:- All tests were carried out at Kunming, China, and comparative performance with P-40K and P-43A1 aircraft was tabulated. Insomuch as the elevation of the Kunming airdrome is above 5,000 feet, the minimum altitude at which performance tests were run was 10,000 feet.


4:- GENERAL TECHNICAL DATA
a. The Japanese Navy Zero airplane is a low wing, single radial engine, single seat, all metal, flush riveted monoplane of very light construction. The fuselage is of semi-monocoque design. The thickness of wing and fuselage skin covering is .02 inch, and is unstressed. The landing gear is fully retractable. The weight of the airplane, fully serviced, with belly tank installed is approximately 5,600 pounds.

b. Engine: The engine is a 14 cylinder, twin row radial of almost identical design to our own Pratt & Whitney R-1535 series, and is tightly cowled. Accessories and accessory drive are similar to our own engine, the chief differences being in the oil cooler design and the float type carburetor. This engine, contrary to opinion and data expressed elsewhere, will not develop 900 H.P., nor is its altitude performance superior to our own standard fighter craft engines of single stage, single speed, mechanically driven blowers. This engine at full throttle and full r.p.m. with the aid of 160 indicated mph of ram, will hold zero boost only to 16,000 feet indicated. Our own P-40K Allison V-1710-73 will, at 3,000 r.p.m., hold zero boost, with benefit of 230 indicated m.p.h. of ram, to 22,000 feet indicated. However, it is believed that the propellor on this particular Zero airplane is not set to permit maximum allowable r.p.m. (maximum obtainable r.p.m. was 2,075).

c. Fuel System: The fuel system consists of two wing tanks of 55 gallons capacity each, one fuselage tank mounted ahead of the instrument panel of 37 gallons capacity, and one non-streamlined detachable belly tank of 88 gallons capacity (total fuel capacity 235 U.S. gallons). All tanks are non-bullet proof. A motor driven fuel pump of similar design to our own furnishes fuel to the carburetor at a pressure of .33 kg/sq. cm. This is believed to be normal pressure; the pressure increases markedly with positive acceleration forces on the airplane. A wobble pump of similar design to our own supplements the motor driven pump. Two fuel cocks control the selection of tanks (the forward cock is shown in the lower left hand corner of attached cockpit picture, just aft of the two fuel gages). One cock controls selection between the belly and fuselage tanks; its third position is "off". The other cock controls selection between the two wing tanks; its four positions are; "left wing, right wing, both and off". The systems controlled by the two cocks are in parallel, but should not be used simultaneously as fuel will drain from the higher fuselage tank to the lower wing tanks when the two systems are inter-connected. Thus, if such draining fills the wing tanks, the action will continue with fuel running thru the wing tank overflows until the fuselage tank is completely drained. 91 octane fuel was used in the conduct of all tests, and at full throttle at 10,000 feet no detonation was experienced. This indicates that timing was probably slow, insomuch as engine is reportedly designed to operate on 100 octane fuel; normal performance probably was still further reduced thereby.


(20) Mixture control – Use of this control is not fully understood, as in the rear position of this lever, mixture control is automatic. Movement of the lever to any forward position at any altitude causes no perceptible change in engine operation.

(22) Idling mixture control – This lever is spring loaded with normal position to the rear. Pushing the lever forward leans the idling mixture and prevents fouling of the engine during engine warm up. Apparently there is no thermostatically controlled by-pass around the oil cooler, for it requires about five minutes for the oil to warm up sufficiently for take off (at an air temperature of 50 deg. F).


5:- The materials used in the Zero airplane are of excellent quality. Generally, the workmanship of both airplane and power plant is rather mediocre. The most notable feature of the construction of this airplane is its utter lack of sectionalization. Any damage inflicted necessitates a major depot overhaul for repair.


6: - PERFORMANCE:-

a. High speed tests were as follows:

ALTITUDE (Feet) 10,000 15,000 20,000 25,000

IND AIR SPEED (mph) 238 219 190 171

TRUE AIR SPEED (mph) 286 289 270 265

R.P.M. 2,050 2,050 2,050 2,050

MAN PRESS (cm Hg) +12 +2 -8 -13

Cyl Head Temp (deg C) 235 228 226 225

OIL TEMP (deg.C) 55 55 55 55

OIL Press (Kg/Sq cm) 5 5 5 4.8

FUEL Press )Kg/Sq Cm) 0.42 0.4 0.4 0.38

Notes:
1. All of above performances were run at full throttle and maximum r.p.m. propellor setting.
2. It is believed that oil temperature gage was inaccurate.
3. True air speed was computed by estimating temperature at the various altitudes. A free air temperature gage was not available.

b. Maximum climb tests were as follows:
ALTITUDE (Feet) 10,000 – 15,000 15,000 – 20,000 20,000 – 25,000

AVERAGE I.A.S. 130 125 118

AVERAGE Rate/Climb 2690 Ft./S 2410 Ft./S 1785 Ft./S

c. Estimated normal cruising at 12,000 feet indicated is 1,700 r.p.m. and -7 cm. Hg. boost. The power output under these conditions is unknown; the indicated air speed was 197 mph, or a true air speed of approximately 245 mph. Fuel consumption under these conditions was 37 gallons per hour. Fuel consumption at other power output conditions was not tested due to limited time and a very limited supply of fuel.


7:- RELATIVE PERFORMANCE WITH P-40K AND P-43A-1 AIRCRAFT

a. Climb - The Zero airplane maintains a higher rate of climb than the P-40K-1 at all altitudes in excess of 10,000 feet. However, it is believed that below 5,000 feet, the P-40K-1 would climb faster. The P-43 A-1 will maintain a higher rate of climb than the Zero at any altitude above 12,500 feet. In climb tests with this airplane, the P-43 was operated at 2,500 r.p.m. and 42" Hg., and with this output did not achieve the advantage in climb until 12,500 feet was reached. However, with maximum allowable output of the P-43 engine (2,700 r.p.m. and 48.5 in. Hg.) it is believed this airplane would outclimb the Zero at any altitude. The P-43 was not operated at maximum engine performance on account of the extreme importance of conservation of equipment in this theatre.

b. High Speed and Acceleration. Both the P-40K-1 and the P-43A-1 are considerably faster than the Zero at any altitude. Acceleration tests were run at 13,000 feet indicated with the following results:

(1) P-40K-1 versus Zero. Airplanes were flown side by side at 200 m.p.h. indicated. On signal, both engines were given full throttle and full r.p.m. For seven seconds the two planes accelerated equally, at which time the P-40 began to pull away very rapidly. Twelve seconds after acceleration signal was given, the differential speed was estimated at ten m.p.h.

(2) P-43 A-1 vs. Zero. The same test was performed as with the P-40K-1, but at an initial speed of 190 m.p.h. indicated. After signal was given, Zero gained about one quarter plane length on the P-43, after which P-43 pulled away, but not as rapidly as the P-40. Again the P-43 was operated at 42 in.,Hg. and 2,500 r.p.m. - as compared to 3,000 r.p.m. and 41 in. Hg. with the P-40.

c. Individual Combat. - Several dog fights were carried out with both the P-40K-1 and P-43A-1, using various tactics. The Zero is, of course, vastly superior in maneuverability. It was found that the P-40 can, however, effectively fight the Zero without necessarily diving away. This is accomplished by proceeding away from the Zero on initial pass at high speed until approximately one and a half miles away, at which time a maximum turn is begun back into the path of the pursuing Zero. This turn can be completed just in time for the P-40 to pass thru the path of the Zero and barely miss a collision. If the Zero does not dodge from his own attack, the P-40 can fire a very effective head on burst in this manner. Of course, the Zero can take evasive action, but he cannot maneuver into such a position as to get effective fire into the P-40 without also getting return fire.
With the P-43, the same tactics can be used, but head on runs are not advisable with this airplane due to lack of both fire-power and protection. It is believed that the best tactics for engaging the Zero in individual combat with the P-43 is to climb away from the Zero and attempt to gain an advantageous position for a diving attack. The P-43 has a slight advantage in rate of climb, as before mentioned, and has a considerably higher best climbing speed.
It is advised never to engage in a turning fight with the Zero with either a P-40 or P-43 type airplane – but the above tactics may be effectively used provided the combat involves only two single airplanes.


8:- FLYING CHARACTERISTICS
a. Maneuverability - The Zero is very maneuverable. It will turn a little shorter than our own P-36A, but is slightly slower than this airplane and has a lower rate of climb. At altitudes below 12,000 feet, the P-36A has a much better rate of climb and is almost as maneuverable.

b. Dives - The highest speed attained in diving was 300 m.p.h. indicated. Above 200 m.p.h., the Zero became increasingly hard to maneuver, and at 300 m.p.h. requires a great deal of force on the controls for even a gentle turn. At these speeds, the airplane is very stable, and especially so about the longitudinal axis. It has no tendency whatever to roll in a dive, and at 300 m.p.h. it is practically impossible to make it roll. Above 226 m.p.h. indicated the P-40 will out maneuver the Zero – thus a Zero airplane pursuing one of our own airplanes in a dive is completely at the mercy of any following P-40's or similar pursuit aircraft. This probably explains why they rarely if ever follow our own aircraft in even a shallow dive where they could keep up for a short while.

c. Stalls - The Zero stalls very smoothly, even in tight turns. It has no tendency to whip on stalling, nor does it have any “squashing” tendencies like the P-26. At speeds above about 200 m.p.h. indicated, it is believed impossible to exert enough pressure on the elevators to cause the airplane to stall. This was not actually tried, however, for fear of a structural failure.

d. Landing - The airplane glides at 85 m.p.h. with flaps down and lands at about 65. It is very easy to land and has no ground looping tendencies whatever. The tail wheel is non-steerable and non-lockable.

e. Generally, the Zero is a very simple and easy airplane to operate. It has a high power loading and is consequently easy to get out of “tight spots” or difficult situations. It is structurally very weak, however, and must be handled with respect. It would be very foolish to attempt a forced landing with the Zero in any but very smooth terrain.


9:- REMARKS

a. Visibility is very poor directly ahead and down. Otherwise, visibility is good.

b. Best engine warm-up speed is 900 – 950 r.p.m.

c. The engine will not run under any conditions of negative acceleration, inverted, or in a steep skid. A Zero is unable to follow any airplane which does a sharp pushover unless it rolls and it cannot roll at high speed.

d. The Zero is manufactured of excellent materials, but it exhibits mediocre workmanship throughout.