USN air combat data from Office of Naval Intelligence

[pry]

Taken from the AAF's "Official History" offered without comment just to add another point of view to the discussions.

(New Guinea - Northern Australia)

First priority naturally went to the defense of Allied bases, a burden
which fell upon the fighter units at Moresby and Darwin. Over both
points the enemy bombers usually came in at 20,000 feet and above, too
high for satisfactory interception by P-40’s, P-39’s, or P-400’s the
only fighters available to the AAF in the Southwest Pacific, and
their limitations seriously affected Allied operations. During July the
P-39 had made contact with enemy bombers only four times in a series
of nine raids despite a thirty-minute warning; in sixteen actual contacts
it never once enjoyed an altitude advantage and the Zero invariably
could outclimb and outmaneuver this fighter, which suffered the
additional disadvantage of increased vulnerability because of the location
of its motor behind the pilot. The P-40 was somewhat better, but
it, too, was outperformed by the more nimble enemy fighters, particularly
at high altitudes. Inferior performance of their planes lowered
the morale of the pilots. It was true that the Allied planes were more
rugged and less inflammable, they could outdive the Zero, and if given
warning to permit them to reach sufficient altitude they could achieve
creditable scores, as they did on 30 July over Darwin when twentyseven
P-40’s shot down six Zeros and two bombers at the cost of one
P-40. But pilots continued to be frustrated, as on 17 August, when
for the seventy-eighth time enemy bombers struck Moresby in an
attempt to disable their favorite target, Seven-Mile Airdrome. Although
defending fighters had received adequate warning, they were
unable to intercept.

(Page 24 Army Air Forces in World War II, Volume 4)

(Comments on Guadalcanal)

Much less acceptable to fighter pilots was the painfully
inadequate performance of the P-400, which was no match either
for the Zero or for the enemy bombers now striking Henderson from
altitudes above 20,000 feet. As an export version of the early P-39
originally destined for the British, the plane lacked proper supercharging
equipment and its oxygen system was of the high-pressure type.
Since no supply of high-pressure oxygen bottles was available on
Guadalcanal, regardless of the plane’s other deficiencies, pilots were
forced to do their flying at low levels, usually below 10,000 to 12,000
feet or less than half the altitude of the attacking bomber. As a consequence
the high-scoring honors on Guadalcanal easily passed to the
Marines in their rugged and effective Grumman Wildcats.
After only four days’ operations, no more than three P-400’s of the
original flight of fourteen remained in commission and squadron morale
scraped bottom. General Vandegrift, very quickly recognizing that the
P-400 was being called upon to perform a task quite beyond its ability,
altered its assignment. From 2 September forward the 67th sent its
P-400’s up and down the beaches and jungles of Guadalcanal, bombing,
strafing, and harassing the Japanese ground units in close support of the
Marine troops, and in this type of work the plane excelled. Soon its
pilots were dive-bombing transports, barges, and destroyers, and they
did everything but engage the enemy at high altitude. This last function
remained almost exclusively a province of the Marines until newer
models of the P-39’s and finally P-38’s arrived. Harmon continued to
press AAF Headquarters for better fighters, citing the inadequacies of
the P-400, and the War Department continued in its attempt to reassure
the South Pacific commander that the plane could be used successfully.
But Harmon well realized that his P-39 replacements could not
fight at high altitudes, which was his chief need if the Japanese attacks
were to be stopped. The P-38 was the only solution, but the P-38 was
not to be available for combat until November.

(Page 41-42 Army Air Forces in World War II, Volume 4)

[pry]

USAAF numbers on Japanese aircraft, pilots, training ETC.

USAAF Official History Volume 1 Pages 79-81

As the border fighting ended in September 1939, the poor record
of the Japanese Army Air Force led foreign observers to conclude
that the army's force was inferior in both training and efficiency to
the naval air force. There was some justification for such a belief.
Training in the army flying schools was devoted almost exclusively to
pilots, and training of other air crewmen was largely neglected until
their assignment to tactical units. The navy, on the other hand, gave
closer attention to the training of all members of the crew, and by
1941 its training program was designed to turn out annually some
2,500 navigators, bombardiers, gunners, and flight engineers. At the
same time, the navy was training about 2,000 pilots a year, while the
army was turning out pilots at the rate of approximately 750 a year.


By 7 December 1941 Japanese air strength consisted of some 2,700
aircraft assigned to fully trained air units. Approximately 6,000 pilots
had been graduated from air schools or training units, 3,500 of which
were assigned to the navy and the remainder to the army. About 50
per cent of the army pilots had been in combat either in China or in
the border fighting against the Soviet Air Force, while 10 per cent of
land-based navy pilots had participated in the Chinese operations.
Some 600 of the best navy pilots were assigned to aircraft carrier units.
In contrast to the 200 hours in primary, basic, and advanced training
then being given to Air Corps cadets in the United States, the Japanese
pilots were receiving about 300 hours in training units before being
assigned to tactical units. The average first-line Japanese pilot in 1941
had about 600 flying hours, and the average pilot in the carrier groups
which were destined to begin hostilities against the United States had
over 800 hours. Though somewhat discounted by officials of other
nations, the Japanese air forces had now reached a peak of efficiency,
at any rate in their first-line strength, which gave them a commanding
position in the Pacific.


Actually, the Japanese possessed neither the economic potential nor
the extensive technical skill necessary for developing and maintaining
a first-class air force. If other nations erred in underestimating the
strength of Japanese air power in 1941, the Japanese high command
for its part failed to appreciate the disparity between Japan’s air
potential and that of prospective opponents. In 1941, for example, the
aircraft industry in Japan turned out only 5,088 planes, while the
United States, though only in the initial stages of its conversion to a
wartime economy, produced 19,445. In comparison with the 11,000
pilots trained by the US. Army and Navy during 1941, the Japanese
training programs turned out about 3,000. The Japanese also seemed
to have had little appreciation of the problem of replacements, for
they sacrificed safety factors in aircraft to performance, and they
made relatively little provision for air-sea rescue of highly trained
personnel. In the matter of airfield construction and maintenance of
aircraft, the Japanese had only rudimentary conceptions of the problems
involved; no system had been developed for the rapid construction
of airfields, while only small supplies of spare parts were kept on
hand and the number of depots for major repairs was inadequate for
extensive operations.
The Japanese air forces were not prepared for a war of long duration.
Their major dependence would be placed on the element of surprise
and on a few well-trained airmen in the execution of skillfully
laid plans. Confident of an early victory, they discounted the potential
strength of their enemies.

[mdiehl]

Particularly the ones for the P-39 and A6M2 at 15k' I think you'll see that the Zero has an edge in turn rate, both instantaneous and sustained,

Only at optimum airspeed for turn. If you put both a P40 and an A6M2 at 330 mph, the P40 will out-turn it every time. The Zeke's low speed advantage was having huge control surfaces. The Zeke's high speed disadvantage was having huge control surfaces.

Rather nicely illustrate's the Zero pilot's dilemma. If you enter the fight at something close to your maximum airspeed, you lose any maneuverability advantage. If you enter the flight in your "sweet zone" you open yourself up to high-speed diving or head-on attacks by opponents who refuse to fly at your preferred airspeed.

[Tristanjohn]

I share this quote for two reasons

1. A few posts ago TJ doubted whether or not Zeros operated at this altitude. Clearly this shows that they did. But I would also submit that it was not the norm given Sakai's comments. Though attacking from this altitude to a lower altitude in the low to mid 20s would seem to be employing the Zero to its fullest given Sakai's comment on the "Element" of the Zero above. Does anyone want to contest that Saburo doesn't know what he's talking about?

Anecdotal evidence of the Sakai kind must always be treated carefully, sometimes taken with a grain of salt, especially when the language being translated from is 180^ out from our own, as is Japanese, and so the translation might not be accepted at face value.

As far as "element" goes: one need not turn to evidence of the anecdotal kind at all regarding matters of this kind unless it is to add some experiential meaning within some better context to our knowledge base of aeronautical-engineering theory. That is, a given airplane's best altitude for one aerobatic or another can be fairly extrapolated from published specifications of that plane's design and installed powerplant. Where the comments of a Sakai might stand us more usefully would be in the area of "he did that so I countered with this" sort of combat detail, none of which directly gets at the engineering truths of the situation but does tend to add to our context.

As for this action representing a "norm": well of course it wasn't any such thing, no more than could we accept an AAR of some strange "dogfight" conducted one afternoon twenty feet above a coral-sand beach over some forgotten atoll as "normal."

2. I think this shows that certainly at 20k' the Zero was "In it's element".

Your thinking is logically flawed and runs counter to known aeronautical engineering theory. Your thinking is, in a word, bad.

Further, if in fact these were P-39s on O2 at 30k' It could also illustrate the Airacobra and its pilots inability to take advantage of a Zero pilot who'd lost his vision at 30,000'. And then was broken in two around 20,000' once the Zero pilot had regained his vision!

Whatever. Sounds like a one-off to me, and at that this action involved the "best" fighter pilot Japan had in the "best" fighter plane it owned versus arguably the least suitable Allied aircraft to fly against it in this very special combat circumstance.

While I'm certainly surprised Sakai coaxed (or even wanted to coax) his "Zero" that high in the first place I'm nothing short of flabbergasted an Allied pilot was able to drive a P-39 to 30K as well--he'd need a crane!

But then again, who knows?

As far as modeling EVERY aircraft performance bands at every 1000' interval... I think choosing one aircraft that suffered severely from altitude and modeling that is reasonable. Elf

You would ape the simplistic method UV chooses, promise identically poor results, argue for maintenance of the status quo in the face of reasoned and articulate argument contrary to this stance.

Not so good, Elf.

Meanwhile, the fact remains that the P-39 was capable (more or less) of "high performance" (by its modest standards) up to some 15,000 feet (above that it was mincemeat, no argument at all on that score). What continues to be ignored is that the "Zero" itself was "out of its element" much above 12,000 feet and always stood in dire danger of being blown immediately out of the sky by a plane with the sort of heavy armament carried by a P-39 no matter what the altitude.

Hats off and a bow to Sakai, but at bottom he didn't say much to affect the central issue.

[mogami]

Hi You use Anecdotal evidence from unnamed Zero pilot and then discount Sakai. How interesting. Good thing you don't have any bias of your own.

[Tristanjohn]

Hi You use Anecdotal evidence from unnamed Zero pilot and then discount Sakai. How interesting. Good thing you don't have any bias of your own.

As usual you misunderstand and then misrepresent what I wrote.

Looks like another long day in the salt mine.

[Tristanjohn]

More gouge on the P-39 From the NASM (National Air and Space Museum)Website http://www.nasm.si.edu/nasm/aero/aircraft/bellp39q.htm

"Even more damning, NACA advised the Air Corps to remove the turbo-supercharger, and it apparently agreed, believing that an engine with a geared supercharger was close at hand. However, Allison was years away from fielding such a powerplant and when it did, newer and more advanced airframes became the logical recipients. Without this vital component, the P-39 became unsuitable for combat above about 6,080 m (20,000 ft).

It was actually worse still. Reports from Allied pilots (mostly American) make it clear that the Aircobra's performance took a serious hit at anything above 15,000 feet, began to erode noticeably in most circumstances above 12K (which coincides closely with Allison's published specs for that plane's 1942 powerplant).

[mogami]

Hi, You are still using your 1 quote from unidentified Zero pilot to state Zero was not effective above 12k dispite other people using ID pilots to state otherwise. Data suggests you are mistaken in claim (since Zeros best speed is over 14k) Now I realize Zeros best speed is not it's best 'fighting' speed still it says the props can 'bite' at higher altitudes then you claim. So perhaps the rest of your claims are also incorrect. (I think the Zero pilots would have fought lower if handicapped rather then using 14k for many of their missions)

They could have flown lower since their aircraft climbs better. Why allow enemy to dive on you?

[mogami]

It was actually worse still. Reports from Allied pilots (mostly American) make it clear that the Aircobra's performance took a serious hit at anything above 15,000 feet, began to erode noticeably in most circumstances above 12K (which coincides closely with Allison's published specs for that plane's 1942 powerplant).

So what you are saying here is UV/WITP is off by 2 points (rather then totally off the mark)

[Mr.Frag]

USAAF Official History Volume 1 Pages 79-81

Makes for an interesting read eh Pry?

How far into the 7 volumes are you?

[mdiehl]

I've never read anything that suggested that any Japanese aircraft was particularly ineffective or logy above 12K feet. Likewise I think the P39's performace was pretty lousy above 15K feet. In any case the lack of O2 bottles in P400s effectively limits its "reasonable" altitude to about 12K feet. Sure you can flay above that altitude, but incipient anoxia is going to take its toll on pilot reflexes etc etc.

[pry]

Makes for an interesting read eh Pry?

How far into the 7 volumes are you?

You got that right Mr. Fang, Great read with a ton of great material and facts!

I have not even cracked the volumes dealing with Europe yet and have just started on the Pacific ones in detail, finished 1 and 4 and started on 5.

I remembered the Japanese training hours and total pilots trained info from Volume 1 and thought it might prove useful here so I posted it. I also liked the "Official History" saying their aircraft were

"Outperformed by the more nimble enemy fighters, particularly at high altitudes. Inferior performance of their planes lowered the morale of the pilots."

Their words not mine and leave little doubt on the subject that the Zero performed well at higher altitudes.

I had already thought the Japanese had a tangible advantage in Trained/Experience pilots as opposed to their Allied counterpart's early war now I am convinced this advantage existed. In nearly every example the Allied pilots always perceived themselves disadvantaged when coming up against the Japanese until a noticeable drop off in Japanese skill during the Solomon campaign after the lower trained replacements started showing up in numbers once front line units were decimated.

I think the much debated kill ratio is skewed by fact of the survivability of US aircraft to damage and the return of the pilot to action wiser, smarter and much more focused and able to deal effectively with the Japanese the 2nd or 3rd time around.

Japanese pilots except in very rare occasions never get a second chance because of the IJN failure to put a means into effect to recover the vast number of downed pilots who crashed on the return flight from Guadalcanal after taking damage.

[TheElf]

The "Zero" had its own issues at altitudes greater than 12,000 feet; had a smallish engine, not turbocharged or for that matter truly "high performance," with little guts at high altitudes; a frame that was light as could be so diving wasn't its game; taking much punishment from enemy fire was a huge no-no; meanwhile its own armament was so-so at best. This plane was, in fact, an early-war very long-ranged fighter escort-type of rig that was on the fragile side and which had its hey-day before the close of 1941 and enjoyed its finest hour at medium and low altitudes against pilots flying inferior aircraft designs who were foolish enough to "dogfight" it, and when Japanese pilots ran out of those types the jig, as they say, was up.

Since we seem to agree on the P-39D, can we move on to what seems to be the biggest point of contention? That would be the "Sluggish" performance of the Zero as it begins to lose performance above a randomly slected 12K'(unless I missed your documentation there TJ )

To that end let me offer the following Intell memorandum "Japanese Fighter plane Tactics," NOV 19, 1942. This was as a result of testing done with captured Zeros by Allied Engineers, and hardly Anecdotal. By the way I feel anecdotal evidence goes a long way toward truisms, especially with regard to Pilots and their own Aircraft. I wouldn't be so hasty to dismiss it TJ unless it made you nervous

Here we go. You'll notice the P-39D actually does quite well...at first.

"P-39D-1 Airacobra vs. A6M2 Model 21
Takeoff was accomplished in formation on signal to initiate a climb from sea level to 5k'. The P-39D-1 was drawing 3000rpm and 70in manifold pressure on takeoff when the engine started to detonate, so manifold press was reduced to 52in. The Airacobra left the ground first and arrived at 5k' just as the Zero was passing 4k'. This manifold pressure of 52in could be maintained to 4,500' just as the Zero was passing 4k'. At 5k' from a cruising speed of 230mph (200kt) indicated airspeed(IAS), the P-39 had a marked acceleration away from the Zero. Climb from 5k' to 10k' at the respective best climbing speeds(thus eliminating zoom effect), the P-39 reached 10k' approximately 6sec before the Zero. At 10k' form acruising speed of 220mph (191kt)IAS, the Airacobra still accelerated away from 10k' tp 15k', both aircraft maintained equal rates of climb to 12,500'. Above this altitude, the Zero walked away from the P-39.
In the climb from 15k' to 20k', the Zero took immediate advantage and left the Airacobra. The climb from 20k' to 25k' was not completed since the P-39 was running low on fuel. :rolleyes:
On a straight climb to altitude from takeoff under the same conditions as before, the Airacobra maintained the advantage of the climb until 14,800'. Above this altitude the P-39 was left behind, reaching 25k' approximately 5min behind the Zero. At 25k' from a cruising speed of 180mph(156ky)IAS, the Zero accelerated awayfrom the P-39 for three ship lengths. This lead was maintained by the Zero for one and a half minutes and it took the P-39 another 30saec to gain a lead of 1 ship length.
An experienced Japanese pilot had already learned how to cope with the P-39. Their tactic was to begin a climb, just out of firing range of the P-39. At the point of stall for the P-39, the lighter weight Zero, which still had manuevering airspeed, would turn quickly toward the P-39 and attack while the Airacobra was defenseless without airspeed. "

As the analysis has already been done I'll just let you all mull this over. Keep in mind this was done by Allied pilots, engineers, and Intel in 1942.

v/r
Elf

[HMSWarspite]

Hi, this discussion has got a lot of issues flying around, so here are a few facts about engines and aircraft!
(Forgive me if this is preaching to the converted, or too off topic, but I think it might explain a few things for a few people)
As the air pressure falls off with altitude, the power delivered by a normally aspirated piston engine at a given speed (rpm) falls. The easiest way to think of it is that the power is generated by the mass (weight) of fuel:air mixture it can swallow, and use. As the air pressure falls, the volume occupied by a given mass of air rises, so an engine, with fixed size cylinders, running at constant speed, can swallow less of it. The only way to counter this is to run the engine faster. This is not usually possible (due to the stresses in the engine), or desirable (due to the propellor - see on)

A supercharger is a compressor, connected to the crankshaft of the engine that provides additional compression, and can increase the mass of air into the cylinders and hence the power. You can use it in one of two ways: by running the engine at full throttle at sea level, and the supercharger at max boost (pressure increase), you can increase the power of a given engine considerably, however the output will still decrease with altitude. You will have to considerably strengthen the engine (particularly conrods, crank shaft, and bearings, oil system, and cooling), otherwise all you do is break it very quickly;). If the engine is one that is used at altitude, and altitude performance is important, you can do the other trick, which is to keep the power unchanged at sea level by throttling back, thus avoid any strengthening (and weight increase) relative to an unsupercharged engine. You actually do this by allowing the supercharger to run at your desired boost level, and throttling back the engine (reducing the amount of fuel you put in to the fuel:air mixture. Then, as the engine climbs, you can progressively open the throttle, and maintain the engine power output constant despite the loss in air pressure. By the late 1930's, engine controllers could do this automatically, so that the pilot put the throttle to max, and the engine sorted out how to deliver the (constant) power. This is fine until that engine reaches a certain altitude, where the throttle is fully open. This is a 'full throttle height', and is the highest point at which full rated power is delivered. After this the output falls with further climbing.

Since aircraft drag falls with pressure as well, an aircraft's highest speed will almost always be at its full throttle altitude (FTA). Above this performance will fall off since the loss of engine power outweighs the drag reduction. The quality of aerodynamic design of the supercharger impeller goes some way to define the FTA, but more rigid issues prevent it rising too high (for example, it has to go round at a fixed speed relative to the crank shaft). Best FTA for a simple superchargers are up to 19000ft (Merlin 45, 1940 - compare with Merlin III, 16000ft, 1938). This almost certainly explains the A6M2 best speed at 14000ft, and the A6M3, and later, at c19000ft.

The way round this was to either fit a 2 speed supercharger (when you get to the full throttle altitude, change gear on the supercharger, increasing its speed to get more boost, and resume the climb. Alternatively fit a second supercharger in series with the first, to increase the total boost. The Merlin 60 series did both, and raised the FTA to 29000ft. This is, of course additional complexity/technology, and you need intercooling (which together with Turbosupercharging I will leave for another day!:sleep:)

Up to now, I have ignored the propellor: the engine power is converted in to useful work on the aircraft by the prop. You can think of a propellor blade as like a wing. The efficiency of a propellor is largely determined by it's angle of attack (the direction of the air relative to the leading edge of the blade - OK and it's basic shape). This is a function of the propellor speed and the aircraft speed. Cutting a long story short (TOO LATE THEY ALL CRY), it is a good idea that the propellor operates at constant speed, and modifies its blade angle with power, or aircraft speed. In actual fact, early propellors were fixed pitch, and varied their speed with the engine power. This meant you had to compromise on pitch angle for low a/c speed (take-off), and high a/c speed, and it probably wasn't optimum for either. These props struggled to use an engines power effectively throughout the envelope. Early Spit 1s had a fixed pitch 2 bladed prop. The next step was 2 pitch air screws (fine and coarse pitch), Spits being retrofitted almost immediately, with constant speed props being the final development (as fitted to most a/c mid war).

Aircraft manoeuvreabilty also comes in to fighter's effectiveness. This is split in to two sorts: instantaneous manoeuvres (i.e. how quickly can the a/c turn for example ignoring what happens to speed), and sustained manoeuvres (i.e. how fast can the a/c turn whilst maintaining speed). The first is a function mostly of the aircraft geometry - wing loading, control surface size, deflection (loads) and position. The second is down to engine power, since all manoeuvres cause extra drag, and the more 'spare' power you have, the tighter turn (or whatever) you can sustain.

OK, so where does this leave us with the game. I will make my points quickly.

1) A fighter without a supercharger (or turbocharger) is at a significant disadvantage relative to any a/c with one, as soon as you start getting up much in altitude. At 5000ft, the pressure is already down 17%, and at 15000, t is down 44%. Crudely, these are the losses in output for an engine at constant throttle. Admittedly, you can counter them a little by the same part throttle at sea level trick, but you have still basically got a heavy engine for the power output. The Allison does not strike me as particularly throttled back at sea level (and of course was actually designed for a blower. Thus, penalising the P39 exceptionally relative to 'normal' fighers does not strike me as unreasonable. Any other fighers without blowers should also be hit, of course (are there any in UV?)

2)There is no reason that I can think of why the A6M2 should have any penalty below 14000 (or, in RL for its performance to be suspect there). It has got manoeuverabilty problems at medium/high speeds (as the figures posted previously illustrate rather well). This is due to the poor control surface design (although it is actually a good design, but for the wrong sort of air combat post 1942). It is possible that the air screw was not very sophisticated (was it fixed pitch? Or 2 position, but compromised? Generally such a compromise would result in a disappointing high speed, or take off performance, rather than just an altitude issue. Given that the Zero's max speed is not unreasonable, I don't know how it would have a dodgy prop. Source/reference please. I will confess to having no specific knowledge on this point, I am working from 1st principles.

3) The idea of debiting all aircraft manoeuvre/speed/climb ratings above the FTA has potential. It would need careful examination to make sure that 2 poorly rated a/c struggle to kill each other rather than producing a blood bath or anything silly, and I am sure we could argue all year about how much debit etc. However, the same logic that says P39 should be debitted, logically means that a single stage blower a/c ought to suffer against a Spit8, P51, P47 with their 30000ft (ish) FTA. The P39 only option is (just about) OK for UV, but I think WitP would need review.


Interesting link to a site that seems to have the development story of the P39 (can't vouch for accuracy) http://home.att.net/~C.C.Jordan/XP-39.html

Sorry if this is all :sleep: :sleep: :sleep: :sleep: :sleep: :sleep:

[Tristanjohn]

Hi, You are still using your 1 quote from unidentified Zero pilot to state Zero was not effective above 12k dispite other people using ID pilots to state otherwise. Data suggests you are mistaken in claim (since Zeros best speed is over 14k) Now I realize Zeros best speed is not it's best 'fighting' speed still it says the props can 'bite' at higher altitudes then you claim. So perhaps the rest of your claims are also incorrect. (I think the Zero pilots would have fought lower if handicapped rather then using 14k for many of their missions)

They could have flown lower since their aircraft climbs better. Why allow enemy to dive on you?

Why indeed! And the smart ones did not allow this to happen to them. Which is why we often found "Zero" pilots plying altitudes not especially well suited to their airplane's design--perhaps at altitudes even less sutied to an enemy airplane's design.

Also, many times these pilots were obliged to fly their "Zeroes" at higher alltitudes in escort of their own bombers. That was their mission and no one ever said combat was "fair." You usually do what you have to do out there--at least the ones who come back alive usually do.

But none of that changes the fact that the "Zero" performed worse and worse the higher it clawed into the atmosphere above some 12,000 feet. Same same for the early P-39s and the Wildcats and so on, except each aircraft had its own handling characteristics and so each suffered in varying degree and according to circumstance.

No one could defeat the laws of physics through sheer will any more than he could hold back the hands of time. Some things in life are absolute. Physics are one of those things. (So to speak--let us not get into the minutiea of Newtonian physics.)

[mdiehl]

I find some tangential evidence to support Tristanjohn's post. Ghost Squadron has one of Zuikaku's 1942 A6M2s recovered from some jungle infested place in 1968. The max-speed altitude is 15,000 feet -- seems very low if the plane did indeed have a supercharger. Will see however what more I can dredge before I make up my mind on this.

Here's Ghost Squadrons' claim

One Nakajima NK1C Sakai 12 Engine
Twin-row 14 cylinder Air-cooled Radial
950 hp @ 3,100 rpm

Two 37 mm Cannons
(Type 99 mounted in the wings)
Two 7.7 mm Machine Guns
(Type 97 mounted in the upper fuselage decking)

Max. Speed 332 mph @ 15,000 feet
Cruise Speed 207 mph

Climb to 20,000 ft in 7.5 minutes
Service Ceiling 32,800 ft

But there is one page that gives it a 2-stage supercharger.
[url]http://mitsubishi_zero.tripod.com/powerplant.htm[/url]

[Tristanjohn]

Hi, this discussion has got a lot of issues flying around, so here are a few facts about engines and aircraft!
(Forgive me if this is preaching to the converted, or too off topic, but I think it might explain a few things for a few people)
As the air pressure falls off with altitude, the power delivered by a normally aspirated piston engine at a given speed (rpm) falls. The easiest way to think of it is that the power is generated by the mass (weight) of fuel:air mixture it can swallow, and use. As the air pressure falls, the volume occupied by a given mass of air rises, so an engine, with fixed size cylinders, running at constant speed, can swallow less of it. The only way to counter this is to run the engine faster. This is not usually possible (due to the stresses in the engine), or desirable (due to the propellor - see on)

A supercharger is a compressor, connected to the crankshaft of the engine that provides additional compression, and can increase the mass of air into the cylinders and hence the power. You can use it in one of two ways: by running the engine at full throttle at sea level, and the supercharger at max boost (pressure increase), you can increase the power of a given engine considerably, however the output will still decrease with altitude. You will have to considerably strengthen the engine (particularly conrods, crank shaft, and bearings, oil system, and cooling), otherwise all you do is break it very quickly;). If the engine is one that is used at altitude, and altitude performance is important, you can do the other trick, which is to keep the power unchanged at sea level by throttling back, thus avoid any strengthening (and weight increase) relative to an unsupercharged engine. You actually do this by allowing the supercharger to run at your desired boost level, and throttling back the engine (reducing the amount of fuel you put in to the fuel:air mixture. Then, as the engine climbs, you can progressively open the throttle, and maintain the engine power output constant despite the loss in air pressure. By the late 1930's, engine controllers could do this automatically, so that the pilot put the throttle to max, and the engine sorted out how to deliver the (constant) power. This is fine until that engine reaches a certain altitude, where the throttle is fully open. This is a 'full throttle height', and is the highest point at which full rated power is delivered. After this the output falls with further climbing.

Since aircraft drag falls with pressure as well, an aircraft's highest speed will almost always be at its full throttle altitude (FTA). Above this performance will fall off since the loss of engine power outweighs the drag reduction. The quality of aerodynamic design of the supercharger impeller goes some way to define the FTA, but more rigid issues prevent it rising too high (for example, it has to go round at a fixed speed relative to the crank shaft). Best FTA for a simple superchargers are up to 19000ft (Merlin 45, 1940 - compare with Merlin III, 16000ft, 1938). This almost certainly explains the A6M2 best speed at 14000ft, and the A6M3, and later, at c19000ft.

The way round this was to either fit a 2 speed supercharger (when you get to the full throttle altitude, change gear on the supercharger, increasing its speed to get more boost, and resume the climb. Alternatively fit a second supercharger in series with the first, to increase the total boost. The Merlin 60 series did both, and raised the FTA to 29000ft. This is, of course additional complexity/technology, and you need intercooling (which together with Turbosupercharging I will leave for another day!:sleep:)

Up to now, I have ignored the propellor: the engine power is converted in to useful work on the aircraft by the prop. You can think of a propellor blade as like a wing. The efficiency of a propellor is largely determined by it's angle of attack (the direction of the air relative to the leading edge of the blade - OK and it's basic shape). This is a function of the propellor speed and the aircraft speed. Cutting a long story short (TOO LATE THEY ALL CRY), it is a good idea that the propellor operates at constant speed, and modifies its blade angle with power, or aircraft speed. In actual fact, early propellors were fixed pitch, and varied their speed with the engine power. This meant you had to compromise on pitch angle for low a/c speed (take-off), and high a/c speed, and it probably wasn't optimum for either. These props struggled to use an engines power effectively throughout the envelope. Early Spit 1s had a fixed pitch 2 bladed prop. The next step was 2 pitch air screws (fine and coarse pitch), Spits being retrofitted almost immediately, with constant speed props being the final development (as fitted to most a/c mid war).

Aircraft manoeuvreabilty also comes in to fighter's effectiveness. This is split in to two sorts: instantaneous manoeuvres (i.e. how quickly can the a/c turn for example ignoring what happens to speed), and sustained manoeuvres (i.e. how fast can the a/c turn whilst maintaining speed). The first is a function mostly of the aircraft geometry - wing loading, control surface size, deflection (loads) and position. The second is down to engine power, since all manoeuvres cause extra drag, and the more 'spare' power you have, the tighter turn (or whatever) you can sustain.

OK, so where does this leave us with the game. I will make my points quickly.

1) A fighter without a supercharger (or turbocharger) is at a significant disadvantage relative to any a/c with one, as soon as you start getting up much in altitude. At 5000ft, the pressure is already down 17%, and at 15000, t is down 44%. Crudely, these are the losses in output for an engine at constant throttle. Admittedly, you can counter them a little by the same part throttle at sea level trick, but you have still basically got a heavy engine for the power output. The Allison does not strike me as particularly throttled back at sea level (and of course was actually designed for a blower. Thus, penalising the P39 exceptionally relative to 'normal' fighers does not strike me as unreasonable. Any other fighers without blowers should also be hit, of course (are there any in UV?)

2)There is no reason that I can think of why the A6M2 should have any penalty below 14000 (or, in RL for its performance to be suspect there). It has got manoeuverabilty problems at medium/high speeds (as the figures posted previously illustrate rather well). This is due to the poor control surface design (although it is actually a good design, but for the wrong sort of air combat post 1942). It is possible that the air screw was not very sophisticated (was it fixed pitch? Or 2 position, but compromised? Generally such a compromise would result in a disappointing high speed, or take off performance, rather than just an altitude issue. Given that the Zero's max speed is not unreasonable, I don't know how it would have a dodgy prop. Source/reference please. I will confess to having no specific knowledge on this point, I am working from 1st principles.

3) The idea of debiting all aircraft manoeuvre/speed/climb ratings above the FTA has potential. It would need careful examination to make sure that 2 poorly rated a/c struggle to kill each other rather than producing a blood bath or anything silly, and I am sure we could argue all year about how much debit etc. However, the same logic that says P39 should be debitted, logically means that a single stage blower a/c ought to suffer against a Spit8, P51, P47 with their 30000ft (ish) FTA. The P39 only option is (just about) OK for UV, but I think WitP would need review.


Interesting link to a site that seems to have the development story of the P39 (can't vouch for accuracy) http://home.att.net/~C.C.Jordan/XP-39.html

I've been to that site before but never used it for much and don't have it bookmarked. The P-39 history as written (having just scanned it quickly, mind you) reads familiarly and I'd guess nothing much is amiss--I didn't catch anything in transit.

The problem with the UV altitude penalty is that it's mistated in terms of altitude by a whopping 2,000-5,000 feet from the point of view of the P-39 and doesn't begin to address the "Zero's" own relative disadvantage (vis-a-vis its "sweet zone" of performance) at higher altitudes but continues apace as always with the same old false "maneuver+speed=superiority" idiocy.

Bottomline: it's poppycock.

This does not mean I think the P-39 was as good as or better than the "Zero." At least not as an interceptor or escort plane. The P-39 made for a much better ground-support type of aircraft than did the "Zero," and was rather mediocre in all other roles it undertook.

I'll attempt some more research on the "Zero" with regard to its engineering specifics, anecdotal accounts of former pilots and whatnot. The main problem there is that credible sites for this sort of information are few and far between. Many of the so-called "Zero" sites are run by idiots with hard-ons for all things Axis and the material found there must be taken with a lot of salt. Also, if there are any primary-source sites for "Zeroes' other than the ones I've been able to already unearth (and these are mostly US Government-type sites, or sites run privately which all tend to quote the same previous-mentioned US governmental material) would be of Japanese origin and with the sole exception of one I can think of are not presented in English--and I don't read Japanese.

My experience is that one needs to spend a lot of time painstakingly pasting together as best he might the "truth" about the Japanese side of World War II. It's much easier to arrive at a reasonable Allied POV of "reality" and as a matter of fact "our" statistics on "their" activities are pretty much all that exist!

I've said it once and I'll say it again: Japanese records of WWII are not reliable and the numbers checked, re-checked and then re-re-checked and then finally published by Morsion well over 50 years ago are about all that we can expect in that regard this far down the road. Indeed, for all the ballyhoo over the works of Frank and Lundstrom these authors inevitably arrive at the same kill ratios, just for instance, as did Morison.

Reason?

The numbers they have to work with are only available in a limited number of places, Morison's already been there as a rule, and in any event these numbers haven't changed over the years. (At least I hope not. )

Anyway, if and when I can I'll be happy to foward to the forum any more light I can possibly shed on the "Zero" propeller issue. Don't hold your breath, though. I'm not getting paid for this misery.

[HMSWarspite]

I've been to that site before but never used it for much and don't have it bookmarked. The P-39 history as written (having just scanned it quickly, mind you) reads familiarly and I'd guess nothing much is amiss--I didn't catch anything in transit.

The problem with the UV altitude penalty is that it's mistated in terms of altitude by a whopping 2,000-5,000 feet from the point of view of the P-39 and doesn't begin to address the "Zero's" own relative disadvantage (vis-a-vis its "sweet zone" of performance) at higher altitudes but continues apace as always with the same old false "maneuver+speed=superiority" idiocy.

Bottomline: it's poppycock.

The P39 MAY be hard done by in UV, however, if the Zero peroformance penalty cuts in badly at say 20000ft, what effect does it's omission have in UV. Apart from the odd recce, I have never seen/used a/c of any type above about 15-17kft

This does not mean I think the P-39 was as good as or better than the "Zero." At least not as an interceptor or escort plane. The P-39 made for a much better ground-support type of aircraft than did the "Zero," and was rather mediocre in all other roles it undertook.

I'll attempt some more research on the "Zero" with regard to its engineering specifics, anecdotal accounts of former pilots and whatnot. The main problem there is that credible sites for this sort of information are few and far between. Many of the so-called "Zero" sites are run by idiots with hard-ons for all things Axis and the material found there must be taken with a lot of salt. Also, if there are any primary-source sites for "Zeroes' other than the ones I've been able to already unearth (and these are mostly US Government-type sites, or sites run privately which all tend to quote the same previous-mentioned US governmental material) would be of Japanese origin and with the sole exception of one I can think of are not presented in English--and I don't read Japanese.

Indeed, this is a problem with Jn research

My experience is that one needs to spend a lot of time painstakingly pasting together as best he might the "truth" about the Japanese side of World War II. It's much easier to arrive at a reasonable Allied POV of "reality" and as a matter of fact "our" statistics on "their" activities are pretty much all that exist!

I've said it once and I'll say it again: Japanese records of WWII are not reliable and the numbers checked, re-checked and then re-re-checked and then finally published by Morsion well over 50 years ago are about all that we can expect in that regard this far down the road. Indeed, for all the ballyhoo over the works of Frank and Lundstrom these authors inevitably arrive at the same kill ratios, just for instance, as did Morison.

Reason?

The numbers they have to work with are only available in a limited number of places, Morison's already been there as a rule, and in any event these numbers haven't changed over the years. (At least I hope not. )

Anyway, if and when I can I'll be happy to foward to the forum any more light I can possibly shed on the "Zero" propeller issue. Don't hold your breath, though. I'm not getting paid for this misery.

Accepted that it is difficult to get details like the propellor design and performance for Jn a/c like the Zero....

So where did you get the info about the 12000ft effective fighting altitude, the prop behaviour at 30Kft, the inability to dive up there.....? :rolleyes:

[HMSWarspite]

I find some tangential evidence to support Tristanjohn's post. Ghost Squadron has one of Zuikaku's 1942 A6M2s recovered from some jungle infested place in 1968. The max-speed altitude is 15,000 feet -- seems very low if the plane did indeed have a supercharger. Will see however what more I can dredge before I make up my mind on this.

Here's Ghost Squadrons' claim



But there is one page that gives it a 2-stage supercharger.
[url]http://mitsubishi_zero.tripod.com/powerplant.htm[/url]

The max spd alt of 15000ft has been quoted before - it is not inconsistant with a slightly badly designed supercharger (ref Merlin III of 16000ft).

The ref you give actually says a 2 SPEED blower (a 2 stage blower that gives 15000ft WOULD be bad!)

[Tristanjohn]

The P39 MAY be hard done by in UV, however, if the Zero peroformance penalty cuts in badly at say 20000ft, what effect does it's omission have in UV. Apart from the odd recce, I have never seen/used a/c of any type above about 15-17kft



Indeed, this is a problem with Jn research



Accepted that it is difficult to get details like the propellor design and performance for Jn a/c like the Zero....

So where did you get the info about the 12000ft effective fighting altitude, the prop behaviour at 30Kft, the inability to dive up there.....? :rolleyes:

That anecdotal account is, regretably, lost to me for the time being, though it's "finitely available" to anyone who cares to do a search of "A6M Zero" through Google or Alta Vista or All the Web. I hit it by accident some time ago when I was in one of those sessions where "something went wrong" and so rebooted without having saved that page in my Military History/WWII/Air/Japanese/A6M folder. (Not happy about that.)

When I wrote that piece in reply to Mogami (I think) I did so from memory, and I believe I mentioned this at that time.

In any event the page does exist (somewhere) and for all I know other accounts that might further qualify this pilot's memoir, either way, exist as well. All it takes to run this stuff down is untold time and the willingess to persevere.