# J2M Raiden



## Sagittario64 (Nov 29, 2011)

How would the J2M stack up against the German and English (among other European) fighters of WWII, as well as the Russia's fighters? Like the Hurricane, Spitfire, Tempest/Typhoon, MiG-3, LaGG-3, La-5, Yak-1/3/7/9, Bf.109, Fw.190, IAR.80, Dewoitine D.520, Italian 5-series, C.202, and the Mosquito(the heavily armed fighter variant).


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## krieghund (Nov 29, 2011)

There is a combat comparison report between the F6F vs J2M3 here: http://www.ww2aircraft.net/forum/flight-test-data/f6f-5-vs-j2m3-26637.html


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## GregP (Nov 30, 2011)

The J2M is a very impressive aircraft. At the Planes of Fame, we have the last remaining example. It has some corrosion problems, and so would be a monumental effort, but it IS restorable to flying condition. The canopy area is large, unusual for Japanese types, and it is a very pleasing aircraft to look at, well proportioned and looks like it "flies right."

The pdf of the computer combat simulation makes me glad the Japanese didnlt produce them in large quantities. Thanks for the great comparison file!


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## davebender (Nov 30, 2011)

First batch serial built J2M2 delivered December 1943. These would have been J2M2 Model 11. Max speed is listed as 370mph @ 19,360 feet. That doesn't seem very fast for a fighter aircraft powered by a 1,820hp engine. IMO Japan would be better served by reserving those powerful engines for the IJA Ki-84 and Ki-100 programs.


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## krieghund (Dec 1, 2011)

davebender said:


> First batch serial built J2M2 delivered December 1943. These would have been J2M2 Model 11. Max speed is listed as 370mph @ 19,360 feet. That doesn't seem very fast for a fighter aircraft powered by a 1,820hp engine. IMO Japan would be better served by reserving those powerful engines for the IJA Ki-84 and Ki-100 programs.



I have recently read in a IJN forum that the speeds quoted in captured Japanese documents were at the engine military rating and not at the WEP rating. Some TAIC reports put the J2M2 speeds above 400 mph but these have been debated numerous times in many online forums. However, if the forum discussion was right then that needs a new look at the Japanese aircraft performance. 

I am working another angle using the aircraft rate of climb to calculate the CDo since the climb rates are not in dispute. Using the available horsepower verses quoted speed makes determining drag unreliable due to the controversy. 

I have included copies of the TAIC and ATAD reports of the J2M series as evaluated by the allies.

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## tomo pauk (Dec 1, 2011)

Krieghund, is the TAIC document available for dowload?


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## krieghund (Dec 1, 2011)

tomo pauk said:


> Krieghund, is the TAIC document available for dowload?



Unfortunately no, only excerpts here and there, however it can be purchased here: Amazon.com: Japanese Aircraft Performance and Characteristics - TAIC Manual: Edward T. Maloney: Books but I got mine at a fraction of the price plus I recently acquired the ATAD booklet but it is an early version and my TAIC manual was updated by the original owner up thru May 1945


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## tomo pauk (Dec 1, 2011)

Pretty big priced, but I reckon that's how it goes. Thanks anyway.


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## krieghund (Dec 2, 2011)

tomo pauk said:


> Pretty big priced, but I reckon that's how it goes. Thanks anyway.



Found a site that sells copies (either paper or download PDF) Japanese Aircraft Performance Characteristics Manual for about $31


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## tomo pauk (Dec 2, 2011)

Many thanks


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## alejandro_ (Dec 2, 2011)

> I have included copies of the TAIC and ATAD reports of the J2M series as evaluated by the allies.



When writing articles on the Ki-61 Tony and N1K I had the same problem. Its hard to compare the performance with allied types because there aren't much data available. Also, TAIC and ATAD reports are not always clear. Its hard to know if they are calculations or data recorded from an actual test.

J2M3 had good performance, but as most Japanese late war fighters it has 2 main problems: it became available too late and there were always reliability issues. At the end of the day, 343 Kokutai -Genda's elite squadron- chose the N1K2-J Shiden Kai.


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## vanir (Dec 2, 2011)

I heard something about the prop extension gear failing. Anyways about published figures, this occured right from the Zeros comparatively tested, it was specified by the DoD at the time that since a local fuel was being used, and tuning characteristics were unknown that the aircraft were restricted to a conservative military power setting for maximum performance testing. According to some Japanese enthusiasts doing the rounds at aviation sites the M21 Zero for example had about 300hp more on tap than published and that would mean several mph extra top speed at all heights, and possibly some underrated manoueuvring if that is even possible considering how highly it was rated on that score.

This held true with most of them, a combination of language and reluctance according to the New Zealand recovery team which went through the Solomons in 45 collecting up all the various models of abandoned fighters. Because so little could be ascertained about them, they actually had to disarm the plane, then put Japanese POWs in the cockpit just to ferry them home...with a heavily armed Corsair escort of course. One of the pilots of those escorts wrote an article I read about them.

Postwar, Wright-Patterson was given the job of evaluating Axis fighters from the Dora to the Ki-84 and specifically to comparatively test them against the P-51D Mustang (I think the reasoning was that they wanted to drop the P-51H from production and show the P-51D as having adequate performance in the immediate postwar environment, it was actually the P-47N which was presently the main USAF fighter).

First thing they recorded was performance greatly exceeding Japanese sourced military Intelligence on them. On all of them but especially the Ki-84 and N1K2-J, both those two they rated as superior to the P-51D at all heights up to 6000 metres, the Mustang was superior at that height. But at 5000 metres it couldn't even catch one.
I've no doubt the J2M has a similar story, but it's really the limited production M5 series that's the tough puppy. The M3 runs out of breath too quickly, at 5500 metres iirc.


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## renrich (Dec 3, 2011)

Went back and reviewed the computer simulation comparison of the Jack and the F6F5. A few things jumped out at me which destroys a lot of credibility of that comparison. Firstly the writer repeats the old myth of the AVG fighting against Zekes which is not true. Secondly it repeats the myth that Chennault transmitted intelligence about the Zeke to the US Military and it was ignored. Not true. If you read Lundstrom, "The First Team" the USN was aware of the Zeke before the war began and long before it encountered any but of course had no details of it's performance. Thirdly the performance chart gives the F6F5 a Vmax of 386 mph at best altitude. The F6F5 was a genuine 400 mph fighter at best altitude.


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## Vincenzo (Dec 3, 2011)

reinrich in WWII Aircraft Performance the are test and cards on F-6F5 and in none i can see a 400 mph speed


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## GregP (Dec 4, 2011)

Chenault DID transmit information on the Zero to the US Military and it WAS ignored. The information was not about the existence of the Zero, but about the performance of the Zero. 

The US Military simply refused to believe the performance level that was sent by Chenault, failed to pass it on to the active duty personnel, and it came as a great surprise to the uninformed when we encountered them in combat.

That comes from many AVG members who gave presentations at the Planes of Fame. We've had out share of WWII aviators giving talks out there and they ALL said Chenault told the US about the Zero and was not believed.


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## davebender (Dec 4, 2011)

Not sure that to be a good comparison.

The F6F was designed for fleet air defense at medium and low altitude. The Jack was designed to intercept bombers at high altitude. Chances are small these aircraft would meet in combat. P-47 and P-51 escort fighters are probably more likely to encounter a J2M.


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## tomo pauk (Dec 4, 2011)

F6F was carrying a hefty load of booth fuel ammo, plus a drop tank from day one - that would make it a good long range fighter; it's engine was featuring two-stage supercharger set - a sign of good high altitude capability.
Perhaps we could call F*8*F a fleet defender at medium and low altitudes?


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## davebender (Dec 4, 2011)

Was the F6F ever used as an escort for long range bombers?


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## tomo pauk (Dec 4, 2011)

A long-range fighter doesn't necessarily mean that plane's purpose was to strictly protect long range bombers; that's the task he may do. 
If the Hellcat was to provide air superiority over Rabaul, for example, he was doing that to protect his 'own' bomber force, and there he may meet Raiden, IJN plane defending IJN base. Now if some planes are escorting the Libs bound to Sumatra oil fields, those are likely to encounter Ki-44s, the IJA planes.

A capability never exploited does not mean it was not present.


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## Sagittario64 (Dec 4, 2011)

well this is all pretty interesting guys but my original thought still remains: compared to the western european fighters, can the Jack compete?


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## davebender (Dec 4, 2011)

That depends on how fast the Jack was. If the published speed of 370mph is correct then it was surpassed by the 1941 Me-109F and hopelessly obsolete by 1944. But is that max speed correct?


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## Jenisch (Dec 4, 2011)

Sagittario64 said:


> well this is all pretty interesting guys but my original thought still remains: compared to the western european fighters, can the Jack compete?



The J2M had all features of a modern aircraft for the time. The difference in performance must be relevant for the machine start to make difference, above all in power. For the typical combat speeds of 450-500 km/h WWII aircraft had, the Japanese fighter with a roughly 2000 hp engine was competitive in theory.

BTW, here's some Japanese footage about the Ki-84 and the J2M: 
_View: https://www.youtube.com/watch?v=FCfKUOj9ojI_


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## krieghund (Dec 4, 2011)

Vincenzo said:


> reinrich in WWII Aircraft Performance the are test and cards on F-6F5 and in none i can see a 400 mph speed



Here's the F6F-3 indicating 391 mph (close to 400)


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## Vincenzo (Dec 4, 2011)

i knewn they can go close to 400


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## gorizont (Dec 5, 2011)

krieghund said:


> Here's the F6F-3 indicating 391 mph (close to 400)



It's OK, but this speed was achieved at 8300 meters. I suppose one can't find any evidence of a single fight between Hellcats and japanese aircrafts at that altitude.
At the altitude there Raiden could achieve more than 400 miles per hour (about 5500 m.) Hellcat was 50 miles/hour slower according the documents attached to the topic.


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## renrich (Dec 5, 2011)

Page 556, AHT by Dean, the F6F5 could touch 400 mph at 20000 feet with combat power. Linnekin, page 67, "80 Knots to Mach Two," "The F6F5 was a legitimate 400 mph airplane at altitude." "The Great Book of WW2 Airplanes" page 628, in a comparison between the F6F5, F4U1D and the Zeke 52, the top speed attained by the F6F5 was 409 mph at 21600 feet.

GregP, with respect to WW2 pilots, if they were fighting in the Pacific, how would they know whether or not intelligence about the Zeke transmitted to the US Military was ignored or not back in the States? How could Chennault know exactly what the performance of the Zeke was without capturing one and putting it through it's paces? If the AVG in the first six months of 1942, which is all they operated did not encounter Zeros, how did Chennault come by his info about the airplane? Page 535, Lundstrom, "The First Team and the Guadalcanal Campaign," During the testing of the Aleutian Zero, in 1942, the Zero Project Commander, Frederick Trapnell made the following statement, "The general impression of the airplane is exactly as originally created by intelligence-including the performance."

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## Juha (Dec 5, 2011)

IMHO it is also important to note, that some Japanese sources, for ex Hata's Izawa's Japanese Naval Aces and Fighter Units in WWII (1989) give the max speed for J2M3 Raiden as 610km/h (379mph)

Juha


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## Vincenzo (Dec 5, 2011)

renrich said:


> Page 556, AHT by Dean, the F6F5 could touch 400 mph at 20000 feet with combat power. Linnekin, page 67, "80 Knots to Mach Two," "The F6F5 was a legitimate 400 mph airplane at altitude." "The Great Book of WW2 Airplanes" page 628, in a comparison between the F6F5, F4U1D and the Zeke 52, the top speed attained by the F6F5 was 409 mph at 21600 feet.



this are alla secondary sources, and when a secondary sources don't agree with a primary source i go to primary.
i seen too many times wrong info from secondary sources.


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## Sagittario64 (Dec 5, 2011)

Does it really matter the limits of their speeds? i cant really imagine 350+mph fights going on so much. the dewoitine d.520 wasnt a 400mph fighter, yet it could still compete in a dogfight with the p-38


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## vanir (Dec 5, 2011)

The performance envelope is what's important here fellers, not the apex test figures. Look up Wright-Patterson flight records for 45-46 they tested all the Japanese and German captured types, and any Soviet aircraft they could get their hands on as it so happens but that was down at the back hangars with nods and tarps over them, not that anyone would take much more notice of anything other than the German jets and Doras, they did tons of flying in those.

The general consensus by Wright-Patterson was that all the late war Japanese aircraft, specifically J2M3, N1J2, Ki-44, Ki-84, Ki-100 and even Ki-61 all had surprisingly similar performance. Whilst they had limited altitude performance, they were all contemporary with or superior to Allied aircraft specifically the P-51D and P-47D based at Okinawa and Iwo Jima and F6F-4 and Sea Spitfire fighters at up to medium combat heights. At 3000 metres the combat report for a N1J2 runway attack at Okinawa was that local fighters on redirect could not even catch them at this height despite beginning the chase within eyeshot of the enemy formation.
The flight tests at Wright-Patterson not only confirmed this report of low-medium altitude superiority particularly of the N1J2 and Ki-84 types, but also states that the Japanese based Intelligence on these aircraft was understated due to shocking operating and maintenance conditions and general organisational disarray.

However, at altitudes exceeding 5500 metres all the Japanese aircraft were inferior to US-Allied contemporaries, except the J2M5 of which only dozens were ever built. Most Raidens were the J2M3 which has poor altitude performance as per all other Japanese fighters. They all run out of steam by 6000m, whilst US aircraft in the theatre pull strong at 7000m and upwards.


Now the important thing to consider here is that maximum level speed ratings describe altitude, not speed performance per se. Altitude. It says how much you can zoom climb or recover or what your cruise characteristics are like, how much your plane likes going upwards, stuff like that. The Ki-84 was faster than any Allied fighter at its design operational altitude, despite having a much lower maximum level speed rating, which again is a reflection of throttle heights moreso.

Think of it like pole racing versus altitude records. Set an altitude record and you have to fly fast just to stay up. Your IAS is actually very low, your TAS is very high. You seem to be going very slow, you just really go fast only because you're so high.
A pole racer accelerates with sheer grunt in thick air like butter off a hot knife. It will outdo the IAS of the altitude record plane easily, but it isn't likely to match its TAS.
Still, it is a faster plane. That's like a Ki-84 to a Mustang at 3000 metres. Although...the way I understand only the N1J2 and Ki-84 had advantage, the others were just contemporary, ie. highly competitive and dependent upon pilot skill alone against late war Allied fighters in the theatre. But again all tended to drop off performance capabilities above 5500m or thereabouts. Mustangs like to roam at 6-7000m normally, the P-47 is best above 6000m, etc. The F4U-4 is tremendous at all heights, but the F4U-1 gets sluggish low and slow. And combat over the islands ranged from ground height to 3500m typically.


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## Jenisch (Dec 6, 2011)

vanir said:


> The performance envelope is what's important here fellers, not the apex test figures. Look up Wright-Patterson flight records for 45-46 they tested all the Japanese and German captured types, and any Soviet aircraft they could get their hands on as it so happens but that was down at the back hangars with nods and tarps over them, not that anyone would take much more notice of anything other than the German jets and Doras, they did tons of flying in those.
> 
> The general consensus by Wright-Patterson was that all the late war Japanese aircraft, specifically J2M3, N1J2, Ki-44, Ki-84, Ki-100 and even Ki-61 all had surprisingly similar performance. Whilst they had limited altitude performance, they were all contemporary with or superior to Allied aircraft specifically the P-51D and P-47D based at Okinawa and Iwo Jima and F6F-4 and Sea Spitfire fighters at up to medium combat heights. At 3000 metres the combat report for a N1J2 runway attack at Okinawa was that local fighters on redirect could not even catch them at this height despite beginning the chase within eyeshot of the enemy formation.
> The flight tests at Wright-Patterson not only confirmed this report of low-medium altitude superiority particularly of the N1J2 and Ki-84 types, but also states that the Japanese based Intelligence on these aircraft was understated due to shocking operating and maintenance conditions and general organisational disarray.
> ...



Interview with a Soviet WWII pilot:

*A.S*. Nikolay Gerasimovich, you constantly say that the basic Soviet fighters, the Yak and the Lavochkin, were equal to the German fighters in speed, although reference books contradict this. According to reference data, German aircraft always have superiority in speed. How do you explain this difference between reference data and practical data?

*N.G*. Reference data is obtained under ideal conditions, in “ideal” aircraft. Tactical and technical characteristics are always lower under actual use conditions.

A.S. Yes, but we also determine the tactical and technical characteristics of our aircraft in ideal conditions. So let’s attempt to approach this phenomenon from another perspective. What kind of actual speed (by instrument) did German fighters attain in aerial combat?

*N.G*. The Bf-109E—from 450 to 500 kmh [270—300 mph]. The Bf-109F: 500—550 kmh [300—330 mph]. The Bf-109G was equal to the F in speed or perhaps just a bit faster. The superiority of the G over the F was in armament, not speed.
The FW-190 reached speeds of 470—550 kmh [280—330 mph]. All of these aircraft approached speeds 30 kph greater in a dive.
You know, we didn’t pay particular attention to our instruments during an aerial engagement. It was obvious without looking that your own aircraft was lagging behind in speed or it wasn’t. Therefore I can affirm that the Airacobra, Yak, and La [Lavochkin] were not surpassed by the German fighters in speed.

*A.S.* What can I say? Can we agree that the speeds you have indicated to me are somewhat lower than those listed in reference works?

*N.G.* What have we been talking about? You must understand that you have been making the same mistake as do all people who have no connection with combat aviation. You are confusing two concepts: maximum speed and combat speed. Maximum speed is attained under ideal conditions: horizontal flight, strict maintenance of altitude, calculated engine revolutions, and so on.
Combat speed is a range of maximum possible speeds that an aircraft can develop for the conduct of active maneuver aerial battle, and at which all forms of maneuver attendant to that battle can be executed.
When I speak to you about speed, I have in mind namely the combat speed at which I conducted battle. To me maximum speed is neither here nor there.

Part 4

I only understood this true/indicated speed stuff recentely. That's why I can catch Mustangs at low and medium altitude in the IL2 sim with the Fw 190 A without much problem, despite they being considerable faster in theory.


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## vanir (Dec 6, 2011)

I like the sims like IL2 and FC2 for things like the general components of service conditions (I once made an IL2 Pacific mission in Wildcats for a realistic start-finish real time experience and let me say it was exhausting, hours of mission time with stressed out navigation issues using full realism settings... and thoroughly enjoyable, it depicts the scope of open ocean for hundreds of kilometres in all directions very well, carriers and island bases are needles in a haystack...man those guys were brave doing it on fumes to get the enemy).

Of course one must keep in mind these arcade-sims can only scratch the surface of genuine complex evolutionary diversity inherent to real world tactical operations. The watchword of the army remains, if it doesn't work, think army. No battleplan survives enemy contact. Etcetera. An Eagle pilot will be the first to say it's between pilots unless terrifically disadvantaged by equipment, that's very uncommon in any major conflaguration. A Fulcrum is dangerous, just troublesome to operate but among the best it's dangerous. This is because theoretical technologies work in sims and often don't work due to solar flares and whoknowswhat on the day when you depend on it.

Somehow, it's historically always been as soon as you depend on it. Delete guns and in the very next conflaguration the enemy are all gunfighters. The real world always works like that, sims need a lot of very process heavy development to approach it, I understand DCS isn't bad, but knock around a physics forum with Caltech engineers and they'll laugh at it.
Have to keep that part in mind with them, no genuine reference. More an emotional insight potential, a learning tool certainly in that sense.



I'll tell a funny story, really I take it with good humour and laugh at myself for past ignorance (I suspect one could do that for a lifetime yes?), part of my research for flight modelling the Ta152C and manual boost regulated Kittyhawk in IL2 was visiting a physics forum with the javascript engine all laid out to try to emulate real world flight test records and engine manuals into the game shell. I got laughed off the forum by someone like a resident Caltech engineer when he looked at it. Okay, makes me smile now, I learned something.
What I did wind up with say for the kittyhawk was something which I used weeks of trial and error, value adjustments by increment to emulate the "feel" rather loosely, and so that in game operational regimés matched best historical figures but that's where you start the compromises due to shell limitations. It did get celebrated by a virtual kittyhawk online squadron who all installed it and loved it. You really had to govern the throttle for your altitudes and watch the boost guage with it, and I restored all the military, take off and war emergency ratings and overboost, it was a bit of a monster under 5000 feet. Had a lot of character that plane.

That was what I was aiming for in the end. Translating reliable sources of the character of a plane in service conditions. I suspect that's what most of the other modellers would've arrived at, I'm no genius. So it's really about emotions and immersion, these sims, any comparative renditions are extremely argumentative.


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## Jenisch (Dec 6, 2011)

Well, of course sims are far from perfection, but surely the modern ones give a considerable notion, if not for the aircrafts themselfs, the flight, specially if you follow the procedures realistically.


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## renrich (Dec 7, 2011)

From the Williams site, USN tested a production model of the F6F5 and it clocked 391 MPH at 23100 feet with military power. Same site at same altitude clocked 330 knots with combat power which is slightly more than 400 MPH. If I remember correctly that plane had launch rails for ordnance on the wings.


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## tomo pauk (Dec 7, 2011)

330 kts is 380 mph.
The specimen that achieved 391 mph (# 58310) did have only starboard pylon installed.
The only source that declares F6F making true 400 mph was the manufacturer, and that is stated in US hundred thousand book. 

I'm at loss why would the F6F-3/-5 be able to fly as fast as sleeker F4U-1/1D. 
The P-47D was even more streamlined, it had on disposal a full 2000 HP MIL at 23000 ft, yet it was able just to beat 400 mph mark at that altitude. If the F6F wants to have 2000 HP, that means going down to some 18000 ft - to the ticker air that, in F6F's case, easily cancels out most of HPs gained for going in WER. Meaning, 380-390 mph both at 23kft and 18 kft.


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## eagledad (Dec 8, 2011)

Gentlemen,

Please check the following address:

http://www.wwiiaircraftperformance.org/japan/ptr-1111.pdf

You will find that the US Navy clocked at least one Hellcat at 400+ mph.

May God fly your wing always!

Eaqledad


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## renrich (Dec 8, 2011)

The F4U1D, according to Boone Guyton, had a Vmax of 425 MPH with combat power. In the comparison flight test between the Zero 52 and the F4U1D and F6F5, the Vmax of the F4U1D was 413 MPH TAS at 20400 feet while the Vmax of the F6F5 was 409 MPH TAS at 21600 feet. However the speed advantage the F4U1D had over the Zero 52 at lower altitudes was significantly greater than that of the F6F5. I think the disparity of the Vmaxs indicated by Guyton points up the fact that individual AC had different performance characteristics and loads and exterior conditions had a significant impact on Vmaxs.
Sorry for misreading a graph comparing knots to miles. Can never remember the factor to use when converting.

The link that eagledad so kindly posted is what I have been quoting from which I have in a book, "The Great Book of WW2 Airplanes."


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## vanir (Dec 8, 2011)

Sorry I'm confused...it's been 20yrs since I had flight training or flew a plane. I thought Vmax was your maximum in a shallow dive. Maximum level speed tends to be lower, Vmax is more like partway to VNE. Modern jet fighter manufacturers rate Vmax in an altitude dip, there's guidelines, you can lose something like 2500 metres establishing Vmax or something like that. One of you guys should know, hence why I'm talking here.

Someone put me right?


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## krieghund (Dec 8, 2011)

vanir said:


> Sorry I'm confused...it's been 20yrs since I had flight training or flew a plane. I thought Vmax was your maximum in a shallow dive. Maximum level speed tends to be lower, Vmax is more like partway to VNE. Modern jet fighter manufacturers rate Vmax in an altitude dip, there's guidelines, you can lose something like 2500 metres establishing Vmax or something like that. One of you guys should know, hence why I'm talking here.
> 
> Someone put me right?



You're correct. If you look up 'V' speeds there isn't a 'Vmax' but in aerodynamics I take it to be the same as Vne. You exceed that speed and the 'Wing Off' light might illuminate. I searched for a 'V' speed which represents maximum power speed in level flight. The only 'V' speed that compares to this is 'Vh' which represents maximum speed in level flight at maximum continuous power.


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## Sagittario64 (Dec 8, 2011)

People please. I understand the Hellcat trumps the J2M in combat and apparently in conversation popularity now. I know well enough about the Hellcat already. tnhe purpose of this thread was to get opinions on whether or not the J2M could be put up against planes other than its typical USA opponents


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## krieghund (Dec 9, 2011)

Sagittario64 said:


> People please. I understand the Hellcat trumps the J2M in combat and apparently in conversation popularity now. I know well enough about the Hellcat already. tnhe purpose of this thread was to get opinions on whether or not the J2M could be put up against planes other than its typical USA opponents



HOLD THE PHONE!!! My previous posting FIGHTER COMBAT COMPARISON ; F6F-5 vs J2M3 combat comparison report between the F6F vs J2M3 here: http://www.ww2aircraft.net/forum/fli...2m3-26637.html (F6F-5 vs J2M3) I believe answers the question that the J2M3 kicks butt!

However, this comparison is not equally paired up. The two fighters are designed for two different missions. The Raiden can't do the Hellcat's mission and the Hellcat is not as good as the Raiden for the point defense interceptor mission. I believe the better match up would be the Ki-84 against the Hellcat or even the N1K1-J as they would have been encountered more frequently.

To plainly answer your question, the J2M3 when functioning adequately would be superior to anything in the US inventory from medium to low altitudes until the advent of the Bearcat or the Seafire 47. This relates to the performance of the aircraft and doesn't address maintenance difficulties, training shortfalls, and other mitigating factors at the time of the Raiden's introduction. If you wish to use those factors then the question is answered by history already.

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## renrich (Dec 9, 2011)

I find it extremely doubtful that the Raiden, based on performance numbers was superior to the F4U4. At SL it could do 380 mph which according to Dean, AHT, was the best that any US WW2 fighter could do and at altitude it could get almost 450 mph. At combat power and SL it's climb rate was almost 3900 FPM. It was a superb gun platform, had a very high roll rate and was a great maneuvering fighter( not talking about rate of turn.) It could carry six 50s with lots of ammo and the F4U4B carried four 20 mms with lots of ammo.


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## Sagittario64 (Dec 9, 2011)

once again my point has been missed. i know how the hellcat and raiden stack up against each other. what im wanting to know is, if a yak was superior to it or was a 109 inferior to the raiden? pitch these and other european aircraft against the raiden.


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## CORSNING (Dec 10, 2011)

krieghund, 
Thank you for posting the sight on manuals. Awsome find buddy. I punched it up and shelled out the best $31 spent in quite a while. Thanks again, Jeff.

renrich,
The F4U-4 maximum TASs were 383mph/S.L. climbing to 464mph/20,600ft. See www.wwiiaircraftperformance.com. Click on F4U and scroll to the bottom and click on F4U-4 performance summery. The -4 initial climb: 4,770fpm gradually climbing to 4,825fpm just over 10,000ft. The J2M3's (according to 105B) maximum speeds were 359mph/S.L. climbing to 417mph/16,600ft. (F4U-4 at 16,600ft= 433mph). The Jack 21's initial climb: 4,835fpm climbing to 5,000fpm just over 4,000ft. U.S. pilots that flew the J2M3 praised its handling up to 325mph. I do not know exact roll rates of the J2M but in the compairison against the Hellcat it was found to have quicker response. I do not have exact figures but have formed the opinion that at low and medium altitudes and speeds these two fighters were close enough in performance that the pilot skill and luck would be the determining factor in a close in dogfight. At high speed or high altitude the fight would be a whole different game where I believe the F4U-4 would hold a fair advantage.

Sagittario64,
My files are at home so I'm going to have to use my memory (this ought to be good). The Yak-3P with 3 x B-20 cannon did operate against the Japanese in the closing months of the war. It could climb initially: 4,450fpm and had a maximum speed of 401mph (16,400ft.?) and a sea level speed of 350mph (?) The VVS considered it to have a roll rate equalling the FW-190A and at medium and high speeds (up to about 360mph) to be able to outturn most anything. It was considered to have a very high combat speed (see N. Golodnikov). It was a very quick and responsive aircraft. If pilots of each aircraft used their planes best qualities I believe the outcome of combat would be close. If you would like to learn more about the Bf.109's capabilities check out Kurfurst's sight. Its an awsome sight filled with 109 information. I am going to refrain from posting my opinion of the Bf.109's capabilities because I have only recently started to research it's capabilities and there are a lot more people on this sight with much greater knowledge of this aircraft at this time.


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## vanir (Dec 10, 2011)

Just tossing out there off the top of my head, the 109 will get trumped in every area except two: performance generally above 6000 metres, and dive. Every other area you'll have to work very hard, but all late war fighters from every belligerent nation are competitive with only a few exceptions. Spits, US types, Russian, German, Japanese all very very good planes. The problems, the advantages, they were industrial and achieved by strategic superiority for whatever reason, sometimes luck, sometimes disadvantage.


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## renrich (Dec 10, 2011)

Corsning, your post really illuminates how performance tests vary from one source or another. I think the different numbers are the result of different test conditions, load, exterior conditions, climatic differences, perhaps fuel, individual aircraft, etc. My figures I quoted came from Dean, AHT, which I regard as kind of the bible on WW2 US fighters. The handling qualities come from Boone Guyton, Vought test pilot and Linnekin, "80 Knots to Mach Two," who flew the F4U4 operationally, as well as the F6F5 and F8F. He rates the Corsair, overall, the better handling AC over the Hellcat and Bearcat. To me, with equal pilot skill, the numbers indicate that the Jack would be at a disadvantage at all the above.

An anecdote, which illustrates how important pilot skill was in ACM. Guyton, who probably had more time in a Corsair than anyone living and who was an ex USN pilot flew in a mock dogfight in 1944, against a Marine ace in another Corsair. The Marine had the standard 10 gallon water tank for WEP where as Guyton had a 60 gallon( from memory) tank. Guyton tried every thing he knew and the Marine waxed him every time.


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## CORSNING (Dec 10, 2011)

renrich,
I agree with you 100%. I believe the Corsair had the edge overall in the horizontal plane and the J2M3 had a slight edge in the vertigal (at lower levels).
When I research a particular A/C, I strive to find out the absolute limits of a combat ready A/C in interceptor/air superiority mode. The amount of boost level used and everything you mentioned all have a direct outcome on the final performance figures. I have always felt if you are going to compare an interceptor (Yak-3, Spit XIV, J2M3, Ki.44...etc.) to a fighter bomber or escort fighter (P-51, P-38, P-47, F4U-4..etc.) it can only be apples to apples if you equip the latter in their lightest combat mode without pylons and shackles. This unfortunately is not how they met in combat but is a more true representation of the individual A/C's comparative performance. Many fighter A/C were handicapped because of the necessities of war (FW-190G) and the gunship Bf-109s. Utilization was everything in a battle in order for victory. What happened where in WW2 I leave to the historians. I am more interested in what the aircraft was actually capable of IF it was properly manufactured/maintained. The Ki.84 had to deal with a lower grade of fuel. I strive to find out its true capabilities in good condition with this fuel and not all the conditions it had to suffer under (poor construction by unskilled workers, poor maintenance from lack of parts). I would really like to get my hands on a technical performace report of the Ki-44-IIIa with the 2,000hp. Nakajima Ha. 145. It had an increased wing (204.514sq.in) and enlarged tail surface. The Ki-44-II had a max. climb of 4,286fpm at 6,888ft. the -III must have been a sky rocket............Ahaaaaaaaaa, I went and got off topic, didn't I......sorry.

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## CORSNING (Dec 10, 2011)

vanir,
Now you went and did it. You got me curious about the 109 so I strolled over to the Kurfurst sight (awesome by the way) and looked up the 109K-4. Best I can tell the true limits of the K-4 in combat ready gear is as follows: Max. Speed: 377mph/S.L. 396/3280ft. 413/6560ft. 423/9840ft. 432/13,120ft. 442/16,400ft. 452/19,352ft. 447/19,680ft. 449/22,960ft. 437/26,240ft. Max. Climb: 4,723fpm/S.L. 4,880fpm/2,625ft. 4822/3,280ft. 4,625/6,560ft. 4,428/9,840ft. 4,310/13,120ft. The 109 used MW-50. 
The Bf.109K-4 had a definite maximum speed advantage at all altitudes and good handling up to 325mph (max. combat speed?) Its climb was close enough for close in fighting at very low altitudes and it eclipsed the climbing ability of the J2M3 just over 6,000ft. The Jack may have outturned the 109 under 20,000ft. but the leading edge wing slats of the 109 must have made it close.

Sagittario64,
Sorry I got carried away. Any plane can beat another fighter if the pilot skill difference is great enough or if a pilot is taken by surprise. But on equal terms, and if the pilot uses the best abilities of his aircraft you can cross off the Hurricane, Typhoon, Lagg-3, La-5FN, IAR.80, D.520, Mosquito, Yak-1, Yak-7 and probably the Mig-3 as being contenders with the J2M3 or even J2M2. The performance levels are too great. I'll have to do more digging to comment on the Spitfire 14, FW-190D, Yak-9U, Tempest, 2005 and MC.205. I read the post on the P-38L vs J2M3 and I believe the contest between them was a lot closer than the conclusion of that post noted.


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## vanir (Dec 11, 2011)

The epitomised performance figures for the K-4 are commonly swung favourably by enthusiasts of this bird and given for the 2000PS engine at 1.98ata of which no conclusive evidence exists being in service, and it was not cleared for service until the last few weeks of the war. Most units operating the K-4 were at airfields that were only receiving B4 fuel, and operated them alongside Doras. They had to be the 1850PS 1.8ata version.
Two airfields notably operated K-4 in March 45 and were receiving C3 fuel only, they operated alongside Fw-190A/F types. These may very well have been the 1.8ata 1850PS motor as it could use either fuel interchangeably and nobody has yet provided evidence that they indeed operated at 1.98ata.

So you need the figures for the DB-605DB engine for K-4 aircraft, at 1.8ata overboost calibration. Still from aces, what I've arrived at is Erla G10, fastest of the wartime 109, around 425mph often seen in the field or about as fast as a Mustang but of course they have completely different handling personalities and flying qualities. Räll said the Erla G10 had no trouble exceeding 400mph, but it was the only one which could. Still, if someone said what about the K he very well might've said, oh yes the K too. That's the thing about personal stories.

K models were heavier than a G-10 in clean fighter configuration in any case from all repute. A dutch team did a nice research project on Erla G10 and late series G14/AS using the 605ASB motor (which is virtually identical to a 605DB but has a different blower). K models were serially fitted with all the rustätze equipment, just not the external fittings unless you specified the installation (but they actually could be fitted or swapped in the field where the Gustavs had to have it done at the factory despite nomenclature). No idea what else but it's pilots who said it was lighter and fastest and they're pretty believable. Oh I think the K had more oxygen bottles in the starboard wing too, like twice as many. The Dutch confirmed reports before such evidence existed and all we had was the word of the vets, so that's doubly convincing.


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## CORSNING (Dec 11, 2011)

Thanks for the info vanir. See there, you proved my point. There are several people on this sight that know a heck-of-a lot more about the Bf.109 than I do. I'm more of a Russian, Japanese and U.S. aircraft type of guy.


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## renrich (Dec 11, 2011)

Here is another factor which most of us either ignore or either are unaware of. The R2800 powered a lot of US AC including the Corsair, Thunderbolt and Hellcat. The Corsair was in combat in February, 1943, the Thunderbolt in April, 1943, and the Hellcat in August, 1943. The R2800 was a good engine, almost legendary for power, ruggedness and reliability. The vast majority of pilots at the 1944 Fighter Conference picked the R2800 as their favorite. The P47, when it became operational was plagued with many problems. A lot of them crashed. The Corsair had many teething problems, including engine issues. A number of times test pilots had to abandon burning Corsairs or were forced to dead stick land or were killed.

Get this! In March, 1943, (look at the dates when the above fighters went into combat) Boone Guyton and Vought were still trying to ferret out the problem which caused number thirteen cylinder in the R2800 to overheat, seize up and blow the engine. The engine in the Corsair, number 02157, Guyton was flying was all instrumented. At 25000 feet a full power run was begun. Guyton leveled off at normal power and began a shallow dive to 24500 to shorten the time spent at military( not combat) power. After four minutes, military power, he was approaching the speed designated for the test. The temperature of number thirteen was nearly 260 degrees, the limit. A little shudder, he grabbed the throttle, prop control, the engine blew, oil covered the canopy, the plane caught on fire. He thought he could make the runway but did not quite make it. He was in the hospital three months and was lucky to live.

Here is the point. The R2800 turned out to be a good engine but in 1943, it still was troublesome and our fighters were flying with it. Eventually that problem with number thirteen was eliminated and the F4U4 could with water injection use 75 inches of MP, safely. On this forum, we talk about this or that wunderairplane, the TA152 and many others and we quote all these performance figures we get from books or online. Maybe those performance figures are true or maybe not. But could those performance numbers be produced in production airplanes with production engines, over and over again, safely? If not, comparing those wunderairplanes to the proven models does not make much sense.


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## fastmongrel (Dec 11, 2011)

renrich said:


> Get this! In March, 1943, Boone Guyton and Vought were still trying to ferret out the problem which caused number thirteen cylinder in the R2800 to overheat, seize up and blow the engine.



renrich what was the problem with the 13th cylinder and how was it sorted. Also how were the cylinders numbered.


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## renrich (Dec 11, 2011)

FM, in his book, he did not describe what the problem other than it overheated, was, or how it was corrected. He had several engines blow while he was flying the Corsair. From memory I believe number thirteen was on the aft bank of cylinders. His book," Whistling Death" is a good one. Guyton was six feet four inches and was a star football player in college. The engine had lots of teething problems during the development of the airplane and the Corsair kind of blazed the trail for the later use of that engine in fighters since it was among the first AC to use the engine and both Vought and Pratt and Whitney were owned at that time by United Aircraft.


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## GregP (Dec 11, 2011)

Sagittario64,

There is no account of a J2M Raiden going up aginst the Me 109 or other German fighters. The data on the J2M that remains is self contradictory. Many sources cannot agree if the climb rate was 2950 feet per minute, 3900 feet per minute, or 4800 feet per minute. These same self-contradictory sources don't even say if the quoted climb rate is the initial climb rate, climb rate at, say, 5000 feet or 25000 feet, and the rate of roll is not published anywhere I have been able to uncover with any degree of relaibility.

Our museum does have a Raiden, and it is a very good-looking aircraft. That doesn't mean we have a reliable flight test report on iot that details the real-life performance of it. I have heard talks given by pilots at the time who said that some of the evaluation pilots were VERY biased and didn't report accurately on the performance of captured equipment because they wanted history to think otherwise. So, we were warned not to believe all the flight test evaluation reports. 

That leaves me in a bit of a quandry. Which tests ARE a reflection of real performance? I don't even believe we have more than a very few tests of the J2M to look at.

What we have left is a description of the basic aircraft weight and power, the fact that it used a rather short, 4-blade propeller, and a few combat reports.

I, for one, decry simulators becuse many people seem to feel the sims are a good indiction of real performance! Not ture. The sims give a decent indication of the equations used by the progrtammer, and if we cannot find a real performance analysis, what makes you think the programmer could? Sims are games, pure and simple, and have nothing whatsoever to do with flying a real warbird. I sometimes fly WWII simulators for fun, and you can easily pull full aft sick at high speeds. Thry that ina real warbird and you will break the plane or break up first.

I'm afraid this question, which is interesting to me, will have be left in the area of conjecture. What we DO klnow is that the Raiden was a pretty good performer when it was running well. We also know that probability of any particular Raiden running well at a point in time when it needed to do so was less then stellar. Still, a good design from the designer of the Zero, that was put into production less than completely successfully, through no fault of the designer.


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## krieghund (Dec 11, 2011)

It would appear the only way to get an accurate performance would be to use a software program such as "Basic Aircraft Performance" by Sid Powers (KERN International, Inc) which requires the input of all physical parameters of the aircraft in question. Of course it was originally designed to compute jet aircraft performance but it does an excellent job of drag prediction. It just takes so bloody long to input the parameters and it is a Basic language program.

I have included the output samples from this program, One for the J37 Viggen and a Cessna 172.


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## barney (Dec 11, 2011)

fastmongrel said:


> renrich what was the problem with the 13th cylinder and how was it sorted. Also how were the cylinders numbered.



I don't know what the problem was with the 13th cylinder either. However, in a general sense, I believe I can explain what was going on. 

The Pratt Whitney R-2800 was the first air cooled engine to produce more than 100 horse power per cylinder. Engineers in the 30's believed that 100 horse power per cylinder would never be achieved. The problem was cooling. That, and back when the design of this engine was begun, the quality of the fuel was not good. But, mostly, it was cooling. You have to have sufficient fin surface to dissipate the heat.

So, on a tightly cowled engine, as was the case with the F4U, air for cooling would be at a premium and careful baffling would be required. I can imagine problems arising here as bugs were worked out.


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## CORSNING (Dec 12, 2011)

I coudn't locate any report specifically directing the overheating problem of the R-2800 to the 13th cylinder (that doesn't mean it doesn't exist). I do know that a lot of the cooling problems were corrected by replacing the cast cylinder heads with forged heads allowing deeper, closer-pitched cooling fins. Ganged slitting saws following cams were used to creat the correct depth and pitch for the fins. This substatially increased the cooling fin area and heat rejection capability of the engine.


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## Sagittario64 (Dec 12, 2011)

Greg and corsning i thank you for your professional opinions. It seems that there are too many factors to come close to a definitive conclusion, the validity of test data included.


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## CORSNING (Jan 9, 2012)

Sagittario 64,
Sorry I took so long to get back to your original question. I have moved all my files and books to a new room in my house and they are a complete mess. The holidays took a lot out of me also.
I pulled what I had on the Spitfire Mk.XIV and did a side by side comparison against the J2M3. The Jack 21 compares favorably up to about 20,000ft. The Griffin Engine just proved to be too much after that. I used power figures from the Griffin 65 at +18 boost sinse that was the boost used from January 8, 1944 to March 21, 1945. The Jack has the advantage in power loading 3.77 lbs./hp vs. 4.15 lbs./hp. The Jack has the advantage in wing loading 33.89 lbs./sq.ft. vs. 35.1 lbs./sq.ft. 
Don't have time now to post all the figures, but if your interested I could post them this weekend. I'm still trying to find all my info on the Tempest, MiG, La-5FN, La-7., Yak-3 9U and MC 202.


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## GregP (Jan 9, 2012)

Renrich,

From several pages back (sorry, I was moving ...) the WWII pilots would know if the data got transmitted because they got answers from back home of disbelief. How would they know the performance? Easy, they fought with them and could either catch or not catch the enemy, climb with or not climb with the enemy, etc. Their talks are of the lecture variety, not Q&A, but if you come down when we have these pilots give their talks, you can always ask them yourself.

One of our guest speakers was Corky Meyer, Grumman test pilot. He says the F6F and the F4U performed almost identically. They had the same engine, same prop (at least in the F4U-1 variant) and equivalent frontal area. The only real difference was the fact that Vought use ram air and Grumman did not due to concerns about carb icing. According to Corky, it you flew an F4U-1 and an F6F-3 side by side at identical power settings, they would cruise right together except in the main stage due to ram air in the Corsair. He says if you ran them in any other stage, side by side, at the same power one or the other would usually gradually pull away, and it wasn't always the same aircraft.

He stated categorically that the Vought Corsair had what he called an "optomistic pitot-static system" and always indicated a bit faster than the Hellcat even when they were flying side by side.

Many of the veteran WWII pilots from the Pacific have a great respect for the late-war Japanese aircraft. I say "respect," not affection ... I see someone above quoted the J2M3 as having a climb rate of 3900 fpm. We have heard anywhere from 2950 to 4800 fpm from WWII combat veterans for the Jack, and they said it was "very fast and could disappear vertically with ease." I believe the 370 mph was, in fact, a sea level speed at conservative power. It could easily have been a major player in Europe if deployed there ... just my opinion. Yours may vary.

The J2M, Ki-84 and Ki-100 were as good as anything we had. Ask anyone who fought them; I have and that's what they said. Add the N1K-2J Shiden to the list, too ... the only great fighter developed from a floatplane.

Vanir touched on something that has been my thought for a LONG time. Top speed is not exactly important. Combat speed is important. Top speed is almost never actually achieved. Combat speed and the ability to climb and dive to engage or disengage combat is important, as is maneuverability. Top speed is for factory test pilots. Almost nobody else pays any attention to it. Military pilots almost never attain the listed top speed without facing difficulty for aircraft abuse. The Military wants to fly their planes for a long time, not wear them out in a few flights. It's Ok to pull some g's but, if you over-g a plane, you are in for a tough time from your commander.

Take the McDonnell F4 Phantom. Officially it is a Mach 2.5 aircraft, and can do that if you configure it right, fly it clean except for a couple of sidewinders, and follow a specific flight profile. In real combat, it is a Mach 1.6 - 1.8 airplane. Big difference, huh? And most Phantom pilots never SAW Mach 2.5 ... they saw Mach 1.6 - 1.8 or so, max. particularly if carrying drop tanks. Ever see a pic of a Phantom without drop tanks? If so, not many. It's fuel flow is like a small creek.


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## CORSNING (Jan 10, 2012)

Vanir is correct. Top speed is only used to get to or away from a fight in combat. TAIC reported the War Emergency top speed of the J2M3 as 359 mph./S.L. As I stated before pilots who flew the Jack praised its ease of handling up to 325 mph. I have never read anything that said the controls on the J2M3 get so stiff that it could not be manuevered at higher speeds. The Spitfires 14's top speed at +18 lbs. is 359 mph./S.L. also.


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## Vincenzo (Jan 10, 2012)

CORSNING said:


> . I used power figures from the Griffin 65 at +18 boost sinse that was the boost used from January 8, 1944 to March 21, 1945.



i can ask what boost was used before and after of this ?


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## CORSNING (Jan 10, 2012)

January 8, 1944 the Mk.14 entered combat. In 1945 a few were prepared to handled +21. It is not known if +25 was ever used in combat.


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## Vincenzo (Jan 10, 2012)

thank you


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## CORSNING (Jan 10, 2012)

The figures that follow relate to any given Spitfire. She was a beautiful bird and one of the absolute best to ever sail the skies. Within her realm she was supreme. The Jack was an after thought that was close to being abandoned at one time. It was resurrected because of its exceptional climb. In the latter stages of the Pacific war a lot of Japanese fighters suffered from lack of quality and maintenance. So while the following figures relate to the standard Mk.14 Spitfire, the figures for the Raiden apply to those in excellent condition only: The figures are for War Emergency Speed (mph) / Maximum Climb Rate (fpm).

Height.........Spitfire Mk.XIV...J2M3

Sea Level......359/4,700.......359/4,835
.1,000m........376/4,675.......374/4,940
.2,000m........390/4,625.......380/4,650
.3,000m........405/4,510.......382/4,270
.4,000m........416/3,850.......403/4,320
.5,000m........415/3,690.......415/4,350
.6,000m........422/3,670.......410/3,760
.7,000m........434/3,510.......404/3,160
.8,000m........448/2,960.......394/2,440
.9,000m........444/2,400.......383/1,850
10,000m........437/1,875.......368/1,150

Power and wing loading were on the Jack 21's side as long as the engine held out. Above 20,000 ft. (6,000m+) the mighty Griffin 61 or 65 took over.


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## GregP (Jan 10, 2012)

Kreighund, I am astounded. You say the only way to get a real performance analysis is by SOFTWARE?

Software implies a thorough analysis of the aircraft, which results in performance equations and accurate performance graphs. Exactly where do you think the performance analysis will come from?

If we had the performance results, we wouldn't be having this discussion, we'd know.

There seems to be whole generations that think a flight sim is accurate, but it really isn't accurate unless the model is correct. The only aircraft with accurate models are well documented. WWII prototypes or short-run production types cannot possibly be accurately modeled unless we restore one and test it rather thoroughly. VERY unlikely. If anyone restores one, they fly it very carefully. They don't thrash it to see what it can do!

Software is only as good as the programmer, and always will be only that good, I think ... at least until the software starts self-learning. When it does, we are done as a species.


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## krieghund (Jan 11, 2012)

GregP said:


> Kreighund, I am astounded. You say the only way to get a real performance analysis is by SOFTWARE?



Greg, I wasn't talking about software that costs $19.95. I talking about the stuff we use here to calculate mods to aircraft and fitting stores. It must be thoroughly investigated and substantiated before we go to flight trials. By inputting all the physical attributes a reliable drag value can be obtained.



GregP said:


> If we had the performance results, we wouldn't be having this discussion, we'd know.



This is the problem, you have one set of data that says the J2M3 goes 369 mph and another that goes 400+. That is a wide variance to calculate the drag.

Of course the other options are to fly the surviving aircraft, have one duplicated or put it into a full scale wind tunnel. Without knowing the drag value we will be discussing this until the cows come home.


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## CORSNING (Feb 18, 2012)

Sagittario64,
Are you still out there buddy? I have been working on graphs and figures for the J2m3 vs. La-7 of 1945. The La-7 was one of the top four VVS fighters at the end of the war. The side by side comparison was actually suprising to me. The Raiden compares very well to the Lavochkin. The following figures are for the La-7 No.452132-76 production test trials of April 1945: Height (meters) / Speed (mph) / Climb Rate (fpm):

S.L........383 / 4762
.1,000...397 / 4762
.2,000...411 / 3936
.3,000...408 / 3660
.4,000...401 / 2952
.5,000...405 / 2952
.6,000...418 / 2499
.7,000...414 / 2007
.8,000...405 / 1495

The Raiden could outclimb the La-7 at any altitude. Maximum speed was fairly close. The La-7 had a 24 mph advantage at sea level, speed was even around 3,000m and the J2m3 had a 10 mph advantage around 6,050m. The la-7 regained the advantage above 5,500m. Both planes had excellent turning ability. The La-7 had an advantage in roll rate from what I can tell. It was comparable to the Fw-190. Just an opinion: the Raiden probably ruled the vertical and the La-7 probably had a slight advantage in the horizontal.


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## GregP (Feb 20, 2012)

My entire contention is that the J2M Raiden was never documented with accuracy, with the power settings, propeller settings, any boost settings, or any OTHER settings. What we have is factory basic data.

And it is self contradictory. Logically, it looks very much like a P-47 (we have the only J2M in existence at the Planes of Fame) and it is very slick. If would be fast and would climb well. The J2M pilots we have had speak at the museum say they could disappear vertically from any American figher they encountered, but were not quite as fast ... but could catch a B-29 ... barely.

I'd really like to restore the J2M to flight status, but intergrannular corrosion on the wing spar (or spar caps) is the issue. Someone has to fund the resto ... and nobody has stepped up to do so.


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## spicmart (Feb 1, 2017)

I wonder how the Raiden would have fared if it had gotten the same enignes as the Hellcat and Corsair?
Or any of the other top japanese fighters.


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## tomo pauk (Feb 1, 2017)

In case they can fit it, we'd probably see a 700 km/h fighter.


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## spicmart (Feb 1, 2017)

With a much better power to weight ratio. Would be the question if it can take the enormous horse power structurally to use full potential. It certainly could challenge a Bearcat then.


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## GregP (Feb 1, 2017)

Part of the disparity in J2M performance might perhaps be due to the fact that when we tested it over here, we used our own fuel. The Japanese may well have achieved only 369 mph if they were running on 87-Octane type fuels, I have no way to verify at this late date, but the reports are that the fuel wasn't the best for most of the last half of the war.

Perhaps we are hashing over things that are easily accounted for, perhaps not.

Stranger things have happened.


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## Shortround6 (Feb 1, 2017)

spicmart said:


> I wonder how the Raiden would have fared if it had gotten the same enignes as the Hellcat and Corsair?
> Or any of the other top japanese fighters.





tomo pauk said:


> In case they can fit it, we'd probably see a 700 km/h fighter.



As Tomo has noted *In case they can fit it.
*
The engine in a Raiden went a bit over 1700lbs. The engines in the Hellcat and Corsair went 2480lbs. Then to make use of the power you need a propeller like the Hellcat and Corsair used. About 480lbs for the big 3 blade units. 
Engine used in the F8F-1 Bearcat weighed a mere 2359lbs despite loosing the auxiliary supercharger. 

A Raiden loaded but clean weighs around 500lbs more than an F8F-1 does empty. 

Interesting photo:





The Raiden was actually a pretty small airplane compared to the American aircraft.

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## tomo pauk (Feb 1, 2017)

Shortround6 said:


> As Tomo has noted *In case they can fit it.
> *
> The engine in a Raiden went a bit over 1700lbs. The engines in the Hellcat and Corsair went 2480lbs. Then to make use of the power you need a propeller like the Hellcat and Corsair used. About 480lbs for the big 3 blade units.
> Engine used in the F8F-1 Bearcat weighed a mere 2359lbs despite loosing the auxiliary supercharger.
> ...



Yes, it was a small aircraft when compared with US mid-war stuff, even the Wildcat was bigger.
The Raiden's engine went to almost 1900 lbs due to the extension shaft, fan, gearing for fan and neccessary strengthening. The single-stage R-2800 'B', as used on B-26 or A-26, was as wide and as heavy, so it should've been an easier fit than the two-stage version. Ditto for the 12.2 ft four bladed unit vs. bigger 3-bladed ones.
The Kasei was making better altitude power than 1-stage R-2800, however.


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## GregP (Feb 1, 2017)

I can tell you this. In person, the cockpit is enormous!

American fighters had big cockpits relative to British fighters. Most Japanese fighters had small cockpits, too. But the cockpit on the J2M has more room in it than any other cockpit I have seen on any other WW2 or post-WW2 fighter. You might be able to get two people in there, side by side!

Look at the pic above and compare the cockpits of the Hellcat and Spitfire with the J2M with them.

Below is the Planes of Fame J2M-3 sitting outside Fighter Rebuilders at Chino last time we had it out for an event.

The Yokosuka D4Y is in the background. The J2M is static and the D4Y is a bit better than static. You can start it up and taxi it, but the structure is not airworthy at this time. It would need new longerons and a new wing spar. Who knows, it could happen someday.

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## BiffF15 (Feb 1, 2017)

Greg,
Do you guys have any history on yours? Also, do you have any cockpit shots?
Cheers,
Biff


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## GregP (Feb 2, 2017)

Hi Biff,

We know when and where it was captured, and we know the manufacturer's serial numbers bacause the data plate is still attached. We also know the unit it was assigned to and the markings because they were still on the plane when it was captured. From that, we can dig out other items of interest, but we have no specific combat history on the airframe as far as I know. To be complete, I'll check again this coming weekend.

I sent you a PM about cockpit shots.

All the best, - Greg

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## Laurelix97 (Feb 10, 2018)

From Jiro Horikoshi's book (The designer of A5M, A6M, J2M, A7M)

All performance is with Japanese 92 octane fuel. The engine wasn't built to run on higher fuel.

J2M2:
Wing Area: 20.05m2
Loaded Weight: 3210kg
Engine: Kasei-13
(1820hp at sea level at WEP / 1420hp at 2,600m at military power / 1300hp at 6,000m at military power)
Max Speed: 596km/h at 5,450m at military power
Time to 6,000m: 5:38 at military power
-
J2M3:
Wing Area: 20.05m2
Loaded Weight: 3440kg
Engine: Kasei-23A
(1820hp take off power / 1600hp at 1,300m at military / 1510hp at 4,150m at military)
Max speed: 596km/h at 5,450m at military power
Time to 6,000m: 5:40 at military power
-
J2M4:
Wing Area: 20.05m2
Loaded Weight: 3947kg
Engine: Kasei-23c
(1820hp take off power / 1420hp at 9,200m at military power)
Max speed: 590km/h at 9,200m at military power
Time to 10,000m: 19:30 at military power
-
J2M5:
Wing Area: 20.05m2
Loaded Weight: 3507kg
Engine: Kasei-26
(1820hp take off power / 1400hp at 7,200m at military power)
Max speed: 615km/h at 6,585m at military power
Time to 6,000m: 6:20 at military power
-
J2M6:
Wing Area: 20.05m2
Loaded Weight: 3435kg
Engine: Kasei-23A
(1820hp take off power / 1600hp at 1,300m at military / 1510hp at 4,150m at military)
Max Speed: 589km/h at 5450m at military power
Time to 6000m: 5:38 at military power

Note: Performance figures are at military power, thus you should compare it to US fighters at military power.
Based on weight, wing area, wing lift coefficient, stall speed and air density, I calculated their sustained turn time at WEP, 1000m alt no flaps used

J2M2 - 18 seconds
J2M3 - 19 seconds
J2M4 - 22 seconds
J2M5 - 19 seconds
J2M6 - 19 seconds
-
F4U-1a - 21 seconds
BF-109G-10 - 19 seconds
La-7 - 19 seconds
Yak-3 - 18 seconds
Ki-44-II - 18 seconds
Ki-84 (Ha-45-21) - 17 seconds
N1K2-J - 17 seconds
F6F-5 - 21.5 seconds
F4U-4 - 20 seconds


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## Ivan1GFP (Feb 13, 2018)

Hello Gentlemen,
The original question was how would the J2M Raiden have done if it had fought in Europe instead of the Pacific.
I take this to mean how did its performance compare to contemporary fighters in Europe.

My own opinion is that it would have done quite well and would not have been out of place but it would also depend on what altitude it had to fight at. At low altitudes, it was pretty hot, but typical combat against bomber escorts was much higher in Europe and although its altitude performance was good by Japanese standards, it wasn't good by European standards. 
(1560 HP @ 17,900 feet Military Rating)
Then again, if it was operated in Europe, it probably would have had better than the Japanese Navy 92 octane fuel and would not have needed water-methanol injection most of the time.

The J2M seems to have had a lot of problems with its engine installation but the basic engine was a proven design that powered many other aircraft such as the G4M Bomber, B6N Torpedo Plane and H8K Flying Boat. This might have had something to do with the time it was produced more than the design itself.

As for swapping engines, the whole concept of this aeroplane was to fit a very large diameter high powered bomber engine into a fighter.
The engine was very wide but not very deep, so I am guessing that to convert to a P&W R-2800 would require quite a bit of structural modification.
As for using the additional power, I do not believe this would have been a bit deal.
Note that there were two different propeller blade designs used on Raiden. They are noticeably different at the root of the blade.
The propeller is 3.30 meters (10 feet 10 inch) diameter but apparently was sufficient to handle 1870 HP in its current state... and that was for the "lower activity factor" version that was installed in the aeroplane tested by TAIC.
The biggest issue that it was having for performance was that Kasei 23 did not make that much power at altitude and that is where the P&W R-2800 (two stage) would have helped.
The change would most likely have cascaded into a bunch of other quite feasible changes such as
A Higher Activity Factor propeller as mentioned
A change in the reduction gear to address the higher RPM of the R-2800. (The Kasei only ran at 2500-2600 RPM max.)
and probably a serious adjustment in propeller pitch range to account for differences in power coefficients between the two installations.
There might be some differences in fuel consumption to address.
The J2M3 carried 390 liters in the main tank ahead of the cockpit along with a 90 liter tank in each wing root....
...but it also carried a 120 liter water-methanol tank ahead of the fuel tank.
With better fuel, perhaps the volume taken by this 120 liter tank could be used for additional fuel.

Comments and Thoughts?

- Ivan.

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## tomo pauk (Feb 13, 2018)

Ivan1GFP said:


> ...
> Comments and Thoughts?
> 
> - Ivan.



Usage of 100 oct and better fuel allows for one big fuel tank instead of the fuselage tank and ADI tank - 500L total in fuselage, 680 L (180 US gals) total per A/C internal. In WAllied use, stick the 165 gal tank under fuselage (make the tail wheel strut longer need be). Fuel consumption a bit higher than the 2-stage Merlin? Not that rangy for ETO LR escort work, but still much rangier than Spitfire or Typhoon/Tempest - 400 to 500 miles, depending on cruise altitude and speed?
Engine power is no worse than of the german fighters before mid 1944. I'd try to switch to the Kinsei 24 model, with slightly improved altitude performance. Compression ratio of 6.5 might allow for 50-55 in Hg of manifold pressure with 100/130 or C3 fuel.
'Butterfly flaps' shuld make it possible to out-turn any Western fighter of the era.


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## Shortround6 (Feb 13, 2018)

Ivan1GFP said:


> My own opinion is that it would have done quite well and would not have been out of place but it would also depend on what altitude it had to fight at. At low altitudes, it was pretty hot, but typical combat against bomber escorts was much higher in Europe and although its altitude performance was good by Japanese standards, it wasn't good by European standards.
> (1560 HP @ 17,900 feet Military Rating)
> Then again, if it was operated in Europe, it probably would have had better than the Japanese Navy 92 octane fuel and would not have needed water-methanol injection most of the time.
> 
> ...




Just so we are all on the same page fuel wise.

87 oct.......68.29 PN
91 oct...... 75.68 PN
92 oct...... 77.78 PN
95 oct.......84.85 PN
96 oct.......87.50 PN
100 oct......100 PN

Use of JM2 by Italians is problematic due to the Italian fuel situation.
Use of JM2 by the Germans is also problematic. Results on B4 fuel even with water/alcohol is not going to be good. Results with C3 fuel may be better?
Use of JM2 By Russians is probably still going to call for water/alcohol.
Use of JM2 by British/Americans _might _be limited by the strength of the engine rather than fuel. Will the Kasei actually stand up to the pressures the allied fuel will allow? 
Granted not everybody measured fuel the exact same way. I would also remind people that the Germans, Russians and Japanese never actually measured or rated the fuels for rich response. Japanese, *if *getting their fuel from the Dutch east indies *may* have had a bit better than 92 octane for rich response. Depends on aromatic content. 
The Wright R-2600 is the closest western equivalent. it was 200-300lbs heavier depending on version which makes one wonder about the life of the Kasei at high power levels. The Wright may not have had a very good supercharger, or they didn't change it much on the 1900hp BB series? 

As to propellers, they were sometimes matched to expected altitudes. The prop that works at sea level for take-off or sea level speed runs often doesn't work so well at higher altitudes (over 20,000ft?) depending on the power of the engine. The big props on the R-2800s were to transmit 1800hp at 15,500ft (no water injection and no RAM) or 1650hp at 22,500ft. The air at 22,500ft is roughly 80% as dense as the air at 16,000ft. 

The R-2800 "B"s ran 2700rpm max so difference in reduction gear is minor. 

Another problem is cooling on these radials, not so much in high speed level flight but when climbing. Please note the "C" series R-2800s required about 10% less cooling air _at the same power _as the "B" series engines. Also note that the 1900hp Wright R-2600s used a massive increase in cylinder and head fin area compared to the 1700hp versions. You not only have to make the power, you have to survive making the power. 
A Kasei given Allied 100/130 fuel might very well be able to make much higher power for a few moments, the question is for how long? And under what flight conditions? Flying straight and level or trying to climb at max climb rate? or running at military power (or WEP) while banked over and doing a hard turn at low speed? How long before temperature needle goes into the red zone?

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## Ivan1GFP (Feb 13, 2018)

Shortround6 said:


> As to propellers, they were sometimes matched to expected altitudes. The prop that works at sea level for take-off or sea level speed runs often doesn't work so well at higher altitudes (over 20,000ft?) depending on the power of the engine. The big props on the R-2800s were to transmit 1800hp at 15,500ft (no water injection and no RAM) or 1650hp at 22,500ft. The air at 22,500ft is roughly 80% as dense as the air at 16,000ft.
> 
> The R-2800 "B"s ran 2700rpm max so difference in reduction gear is minor.



This is what I meant by Propeller Power Coefficient. Designed operating altitude influences propeller "size" as shown by the P-47 versus Corsair with engines generating approximately the same power but operating at different altitudes.
I was thinking 2500 RPM to 2700 RPM would require some changes in gearing to be optimal, but I also have never really looked at what kinds of advance ratios the Raiden has at various speeds.



Shortround6 said:


> Another problem is cooling on these radials, not so much in high speed level flight but when climbing. Please note the "C" series R-2800s required about 10% less cooling air _at the same power _as the "B" series engines. Also note that the 1900hp Wright R-2600s used a massive increase in cylinder and head fin area compared to the 1700hp versions. You not only have to make the power, you have to survive making the power.
> A Kasei given Allied 100/130 fuel might very well be able to make much higher power for a few moments, the question is for how long? And under what flight conditions? Flying straight and level or trying to climb at max climb rate? or running at military power (or WEP) while banked over and doing a hard turn at low speed? How long before temperature needle goes into the red zone?



This aeroplane had an engine driven fan operating through a very small cowl opening. If necessary, the gear ratios could be changed.

- Ivan.


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## Shortround6 (Feb 13, 2018)

Most of the time fans were needed for ground running and initial climb out. Any fixed gear ratio fan is only going to optimised for a narrow speed range. This gets a bit of a boost in air flow as the speed of the plane increases. 
However I don't believe fans were the magic cure all that some people seem to think. There are a wide variation in both the heat load of the engine in different flight situations and a wide variation in airflow through the cowl at different airspeeds. Very few aircraft had any cooling troubles at high speed in level flight (high speed was always done with radiator/cowl flaps fully closed), the over heating problems came while taking-off, (max power and below stalling speed), initial climb out (trying to gain altitude with undercarriage still hanging down) and climbing with a heavy load and most of the time such flight was done with radiator/cowl flaps fully open. Fans could help at the low speed, needing less exit area (flaps) and smaller inlet openings. I would note that very few post war commercial aircraft used fans on their air cooled engines. While top speed may not have been important to the airlines fuel economy (low drag) and easy of maintenance was. 

How many people here have any experience with clutch fans in cars? These provided cooling air flow with the car stopped or moving in traffic but at high speeds 945-60mph) the airflow, even after going through the radiator, was fast enough to drive the fan faster than the engine. The fan went into free wheel and imposed no load on the engine. Of course if the fan clutch crapped out the fan flopped around on the end of the shaft and the imbalance soon took out the water pump. 
Now cars use electric fans and some cars only run one fan out of two if one fan will keep the coolant with temperature.


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## Ivan1GFP (Feb 13, 2018)

Hello Shortround6,
I am in pretty good agreement with most of your post, but post war prop liners are not really operating under the same parameters.
As you noted, cost, economy of operation and ease of maintenance are the most important things. A couple hundred Horse Power less for maximum power won't be more important than an economical cruise and time between overhauls.
As such, they are not really comparable.
If engineered properly, a cooling fan (such as on the FW 190A) doesn't cost anything more than a little weight and mechanical complexity.
Obviously the Mitsubishi engineers figured out enough to get things right at least according to the Allied Test Pilot's report.

Now keep in mind we are arguing the fine points of a hypothetical. I never claimed the idea would be easy to implement, but certainly it would be easier than to design a sleek fighter around the Kasei engine.
....and we haven't even mentioned what the additional weight of a heavier R-2800 engine would do to wing loading, maneuverability and climb rates.

I am actually quite familiar with automotive clutch fans and water pumps. I have had to replace each a few times. Once it was due to worn out engine mounts which allowed the fan to contact the fan shroud under hard acceleration. Some were done in the quest for improved performance and some were general maintenance. Water pumps should never be driven by the timing belt, but I have seen it done that way. Do you know what your water pump bearings look like? I do. I found a few of the roller bearings sitting on top of my battery and radiator when a water pump seized and threw the serpentine belt.

- Ivan.


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## GregP (Feb 17, 2018)

What are you using to convert PN to Octane and back, Shortround? Not saying you are incorrect ... am asking.

A reference of some wort would be nice for formula background. I find a lot of stuff on it, but little that explains WWII avgas ratings, other than the numbers themselves.


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## Shortround6 (Feb 17, 2018)

I am using a chart in a booklet/book provided by the Ethyl corporation to the USAF and US Navy around 1950. The book was written/prepared by Sam Heron who was one of the leaders in developing the PN scale. 
The PN scale may not be exactly linear but it is a lot better than the octane scale. 





Airplane Fuels and their Effects on Engine Performance Book, NAVAER, USAF 1951

I am not the seller 
I recommend it to anyone really interested in aviation fuel regardless of where you purchase it from or library access.

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## swampyankee (Feb 17, 2018)

Ivan1GFP said:


> If engineered properly, a cooling fan (such as on the FW 190A) doesn't cost anything more than a little weight and mechanical complexity.
> 
> 
> - Ivan.




... and power absorption which is greatest in high power, low speed operation. I read somewhere (on this forum) that the FW190 fan used 70 hp in climb; this means that the FW190A's "clever" little fan cooling cost something around 250 fpm in rate of climb. The additional weight is probably on the order of 0.1% to 0.5% of operating empty weight, which is in the noise. Engine cooling fans are a feature (or misfeature) that some designers thought beneficial, probably because they made different decisions to satisfy customers. I don't think any mass-produced US or UK fighter or bomber used cooling fans; this may mean that FW and Mitsubishi engineers were not as good at cooling system design as their American or British counterparts or it may have meant that the German and Japanese engineers didn't have access to the design tools that were available to the English-speaking world: NACA, especially, and ARC devoted quite a lot of effort towards improving the cooling of air-cooled engines, the former largely to improve the performance of commercial aircraft, which are going to spend significant time at high-power settings at low speed for climb and single-engine operations.

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## Shortround6 (Feb 17, 2018)

Surprisingly (or not?) the ability to manufacture air cooled engines with huge amounts of finning was not as easy at it seems. The "C" series R-2800 needed 10% less air flowing the cowling/baffles as a "B" series engine due the greater amount of fin area on the heads and cylinder barrels. However to manufacture the heads and barrels with such finning _in quantity _required new manufacturing techniques. Wright also came up with new methods of enlarging fin area. The technique of machining groves in the cylinder barrels and then rolling/caulking sheet metal fins into the groves also required a fair degree of investment in specialized tooling. 




If you don't have the ability to manufacture such heads and cylinders in quantity (hand work is not going to cut it) you are either limited in power or have to resort to extra tricky cooling systems (or both).

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## tomo pauk (Feb 17, 2018)

swampyankee said:


> ... and power absorption which is greatest in high power, low speed operation. I read somewhere (on this forum) that the FW190 fan used 70 hp in climb; this means that the FW190A's "clever" little fan cooling cost something around 250 fpm in rate of climb. The additional weight is probably on the order of 0.1% to 0.5% of operating empty weight, which is in the noise. Engine cooling fans are a feature (or misfeature) that some designers thought beneficial, probably because they made different decisions to satisfy customers.
> ...



The cost was 70 PS on sea level for the BMW 801S engine - 2000 PS at the prop reduction gear, 1930 available for prop after deduction of 70 PS is mande for the prop. Other exmaple is the BMW 801D - around 40 PS at 5.7 km, or 1440 for the prop vs. ~1490 PS after reduction gear. It is a percentage of total power, not a flat value. Bill/drgondog will probably know more about this, but, once we're at 400+ mph speed, a drag reduction (provided by tight cowling that was provided by fan) gives better return than extra 20-40-60 PS on the 801D. 
I don't think that extra 2-3% more HP will net you a 7-8% increase in rate of climb.


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## Ivan1GFP (Feb 17, 2018)

swampyankee said:


> ... and power absorption which is greatest in high power, low speed operation. I read somewhere (on this forum) that the FW190 fan used 70 hp in climb; this means that the FW190A's "clever" little fan cooling cost something around 250 fpm in rate of climb. The additional weight is probably on the order of 0.1% to 0.5% of operating empty weight, which is in the noise. Engine cooling fans are a feature (or misfeature) that some designers thought beneficial, probably because they made different decisions to satisfy customers. I don't think any mass-produced US or UK fighter or bomber used cooling fans; this may mean that FW and Mitsubishi engineers were not as good at cooling system design as their American or British counterparts or it may have meant that the German and Japanese engineers didn't have access to the design tools that were available to the English-speaking world: NACA, especially, and ARC devoted quite a lot of effort towards improving the cooling of air-cooled engines, the former largely to improve the performance of commercial aircraft, which are going to spend significant time at high-power settings at low speed for climb and single-engine operations.



Hello Swampyankee,
It all comes down to a matter of design choice rather than quality of engineering in my opinion.
The design choices by Japanese and German engineers were not the same as the one by American engineers.
The requirements that resulted in the A6M are a perfect example of compromise using the available technology to meet a requirement.

In my opinion, Mitsubishi did pretty well to fit a medium / high horsepower engine with a very large frontal area to a sleek fighter. Without fan cooling, they never would have achieved this.

American aircraft tried many times to use spinners on radial engines but were never successful because it interfered with cooling. If you consider this to be an indication of superior engineering for cooling a radial engine, I would have to disagree. 
As mentioned earlier, the requirements for a prop liner engine are pretty different from that of a combat aircraft, so what was used there isn't really terribly relevant. Do you really think a commercial airliner is designed with the intent of sustained single engine operation in mind? It should be able to stay in the air, but with a lot of other compromises. They certainly won't be running (War) Emergency Power to climb away from someone shooting at them. You would adjust the flight profile to suit what you have for optimum maintenance and overhaul cycles and not eat up the life of your engines trying to impress anyone. Also keep in mind that the prop liners came along quite a few years after their engines had been developed for war time use. The typical R-3350 didn't catch fire all that often by that time.

As for the FW 190A, I thought we had covered this already when discussing the comparison between Corsair, Hellcat, and FW 190:
The 70 HP consumed by the fan was at very low speed. By the time the FW 190 was at best climbing speed, there was already enough airflow to drive the fan and thus it did not absorb any significant power from the engine.

- Ivan.


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## swampyankee (Feb 17, 2018)

Pratt & Whitney, Curtiss-Wright, and their customers went to a great deal of effort to maximize cooling effectiveness without using fans and would likely consider them a crutch. Since, as you say, the FW190 didn't need the fan in normal climb, it seems to be a device of very limited utility. Possibly, the US used lubricants and materials. which could better tolerate short periods of high temperature and so the engines could tolerate temperature excursions better than either German or Japanese ones in those periods when cooling airflow was insufficient. Possibly, they spent more time and effort on cooling system design, or had more experience (my hypothesis) or they were simply better at this aspect of design. I suspect it's a mix of experience and materials, and a customer base that would not tolerate fans.

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## Ivan1GFP (Feb 17, 2018)

swampyankee said:


> Pratt & Whitney, Curtiss-Wright, and their customers went to a great deal of effort to maximize cooling effectiveness without using fans and would likely consider them a crutch. Since, as you say, the FW190 didn't need the fan in normal climb, it seems to be a device of very limited utility. Possibly, the US used lubricants and materials. which could better tolerate short periods of high temperature and so the engines could tolerate temperature excursions better than either German or Japanese ones in those periods when cooling airflow was insufficient. Possibly, they spent more time and effort on cooling system design, or had more experience (my hypothesis) or they were simply better at this aspect of design. I suspect it's a mix of experience and materials, and a customer base that would not tolerate fans.



Hello Swampyankee,
As I commented before, it is really a matter of choices. With a cooling fan, you need it really just for low speed and ground operation.
Without the cooling fan, you end up with a larger cowl opening, no spinner for reduced drag, and perhaps even propeller cuffs.
With one idea, there is a small power penalty at low speed. With the other, you have extra drag at all speeds.

I know what my choice would be.

- Ivan.


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## swampyankee (Feb 17, 2018)

tomo pauk said:


> The cost was 70 PS on sea level for the BMW 801S engine - 2000 PS at the prop reduction gear, 1930 available for prop after deduction of 70 PS is mande for the prop. Other exmaple is the BMW 801D - around 40 PS at 5.7 km, or 1440 for the prop vs. ~1490 PS after reduction gear. It is a percentage of total power, not a flat value. Bill/drgondog will probably know more about this, but, once we're at 400+ mph speed, a drag reduction (provided by tight cowling that was provided by fan) gives better return than extra 20-40-60 PS on the 801D.
> I don't think that extra 2-3% more HP will net you a 7-8% increase in rate of climb.


An FW190 had an operating weight of about 9,500 lbf. Seventy PS is about 32,500 ft-lbf/min. Multiply 70 PS by 32,500 and divide by the weight, one gets 240 ft/min.


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## tomo pauk (Feb 17, 2018)

swampyankee said:


> An FW190 had an operating weight of about 9,500 lbf. Seventy PS is about 32,500 ft-lbf/min. Multiply 70 PS by 32,500 and divide by the weight, one gets 240 ft/min.



The Fw 190A-8 with 1400-1440 PS climbed at 12 - 12.5 m/s between 2.5 and 5 km. With greater power in overboost, 1600-1650 PS, (a 15% increase), RoC went to 14 -14.5m/s, a 16% increase. Say we delete the fan, and cooling is still okay. We get 1450-1490 PS at that altitude band, +50PS or ~5% increase, that nets us a 5+% increase in RoC, 12.7-13.2 m/s. 
0.7 m/s extra = 2.3ft/s = 138 fpm.
Granted, 50 PS != 70 PS.
If cooling is not okay now, and we need to 'widen' the cowling so it is not that tight - how much of extra drag is that worth?


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## DarrenW (Feb 17, 2018)

Ivan1GFP said:


> With one idea, there is a small power penalty at low speed. With the other, you have extra drag at all speeds.
> 
> I know what my choice would be.



Hi Ivan,
So basically what you are saying is that without this cooling fan arrangement the FW-190A would have been even more 'draggy', when compared to it's American radial-engined counterparts?


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## swampyankee (Feb 17, 2018)

tomo pauk said:


> The Fw 190A-8 with 1400-1440 PS climbed at 12 - 12.5 m/s between 2.5 and 5 km. With greater power in overboost, 1600-1650 PS, (a 15% increase), RoC went to 14 -14.5m/s, a 16% increase. Say we delete the fan, and cooling is still okay. We get 1450-1490 PS at that altitude band, +50PS or ~5% increase, that nets us a 5+% increase in RoC, 12.7-13.2 m/s.
> 0.7 m/s extra = 2.3ft/s = 138 fpm.
> Granted, 50 PS != 70 PS.
> If cooling is not okay now, and we need to 'widen' the cowling so it is not that tight - how much of extra drag is that worth?



Probably not enough to notice; nose shape of subsonic aircraft, a category that includes all WW2-era aircraft, is not that important as long as there's no separation. There may be a small increase due to wetted area. Check out the zero-lift drag coefficients of US radial-engined aircraft vs the FW190.


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## Shortround6 (Feb 17, 2018)

A lot of US aircraft had spinners on the prototypes. most lost them on the production versions. 

Now for a quiz, what was the purpose of the discs behind the props on the Boeing 307.


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## tomo pauk (Feb 17, 2018)

swampyankee said:


> Probably not enough to notice; nose shape of subsonic aircraft, a category that includes all WW2-era aircraft, is not that important as long as there's no separation. There may be a small increase due to wetted area. Check out the zero-lift drag coefficients of US radial-engined aircraft vs the FW190.



Shape of the nose of Fw 190D made it 10% less draggier than the Fw 190A.
US fighters? Seems like Cd with "Cl as required for high speed" was greater than 0.028 for Corsair, greater than 0.029 for Hellcat, service condition. Link, table on pg 75 of report, FWIW.



Shortround6 said:


> ...
> Now for a quiz, what was the purpose of the discs behind the props on the Boeing 307.



To improve cooling? Just a wild guess.


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## DarrenW (Feb 17, 2018)

Hi Tomo the link didn't work for me. Is it perhaps for NACA report L5A30?


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## DarrenW (Feb 17, 2018)

I apologize as the link worked fine on my laptop but not on my phone. Thanks for posting it as it seems to include more airplane types than what can be found in the L5A30 report.


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## Ivan1GFP (Feb 17, 2018)

DarrenW said:


> Hi Ivan,
> So basically what you are saying is that without this cooling fan arrangement the FW-190A would have been even more 'draggy', when compared to it's American radial-engined counterparts?



My GUESS would be that they would have had to do something else to improve cooling during ground and low speed operation.
Then again, perhaps with a different engine (not that they had many choices), they may not have needed the cooling fan.
Note that even with the cooling fan, the BMW 801 tended to run hot.
Note also that there were other radial engine fighters with similar sized engines that did not need a cooling fan.
I am not convinced that the FW 190A was all that draggy in comparison to American radial engined fighters. Do you remember the discussion about equivalent flat plate area back in your FW 190 thread? Basing the CD on wing area is a bit misleading and makes aircraft with small wings look particularly bad.

For a practical example of this, consider the Unlimited class racing planes. Many of them have reduced sized canopies modified cowls and drastically reduced wing area. I am guessing that their CD values are fairly high in comparison to their unmodified cousins but their overall (equivalent flat plate) drag is much less.



swampyankee said:


> Probably not enough to notice; nose shape of subsonic aircraft, a category that includes all WW2-era aircraft, is not that important as long as there's no separation. There may be a small increase due to wetted area. Check out the zero-lift drag coefficients of US radial-engined aircraft vs the FW190.



Hello Swampyankee,
Actual testing results do not seem to support your assertion. Also, as I commented to DarrenW, I do not believe that coefficient of drag is always a good comparison.

Hello Shortround6,
My guess would be to reduce airflow through the cowl possibly because the engines had a tendency to run too cool?
Just a guess.......

- Ivan.


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## DarrenW (Feb 18, 2018)

Ivan1GFP said:


> Do you remember the discussion about equivalent flat plate area back in your FW 190 thread? Basing the CD on wing area is a bit misleading and makes aircraft with small wings look particularly bad.



Yes I remember that discussion. Basically we were talking about two different concepts. I was looking at zero-lift drag coefficient which gives an indication of an aircraft's aerodynamic refinement, and you were talking mostly about drag area. I think the CD0 formula tries to separate the drag component produced by lift alone in order to see how much parasitic drag the airframe produces. The formula will produce low drag figures for aircraft with small wings if the speed attained is high enough. Apparently the FW-190A just wasn't fast enough to allow this to happen, given all the variables.

But of course until we can get these airplanes together in the same wind tunnel, under similar test conditions in order to take some real world calculations, we are basically stuck with formulas to work with.


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## Ivan1GFP (Feb 18, 2018)

DarrenW said:


> Yes I remember that discussion. Basically we were talking about two different concepts. I was looking at zero-lift drag coefficient which gives an indication of an aircraft's aerodynamic refinement, and you were talking mostly about drag area. I think the CD0 formula tries to separate the drag component produced by lift alone in order to see how much parasitic drag the airframe produces. The formula will produce low drag figures for aircraft with small wings if the speed attained is high enough. Apparently the FW-190A just wasn't fast enough to allow this to happen, given all the variables.



I still don't think you understand the point I was getting at.
The meaning of the Coefficient of Drag is that when multiplied by some area value, it gives a number which when multiplied by the aerodynamic force (1/2 Rho V^2) gives the actual drag force. The problem is that the reference area is usually the Wing Area, thus if you have two aeroplanes with the same actual drag but one has a larger wing, the one with smaller wing has a lower coefficient of drag.

My earlier example was intended to illustrate this point.
Imagine that I just got a stock Grumman Bearcat and want to race it.
I do just a few things to clean up the airframe a bit: Reduce the size of the canopy, Align and seal panels and gaps, gun ports, etc.
Let's say that my racing Bearcat new has about a 5% decrease in drag force as shown in a wind tunnel test.
The Coefficient of Drag obviously just went down, right? I should go faster than stock....
But I am not satisfied.
Next, I chop several feet off each wing tip because this will be a pylon racer and not a fighter.
Let's say the wind tunnel test now shows a 8% decrease in drag from stock instead of the prior 5%....
Removing the wing tips also removed some wing area, let's say 12%.
What do you suppose just happened to my Coefficient of Drag if the Wing Area is the reference area?
I have an aeroplane that now has substantially less absolute drag but has a higher Coefficient of Drag.
The induced drag probably went up just a touch, but at high speed, it tends to be much lower than parasitic drag.
These numbers may or may not be realistic, but I believe they illustrate my point about why CD doesn't always tell the full story.
Equivalent Flat Plate Area tells a better story when there is a substantial difference in wing area.



DarrenW said:


> But of course until we can get these airplanes together in the same wind tunnel, under similar test conditions in order to take some real world calculations, we are basically stuck with formulas to work with.



No argument here.
The problem is that sometimes it makes sense to get into the details and sometimes the details hide the overall picture.

- Ivan.

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## DarrenW (Feb 18, 2018)

I appreciate your example concerning the modified racing aircraft and I can see where you find problems with how CD0 is calculated. Do you have actual aerodynamic data of modified WWII aircraft used for pylon racing to support your assumptions? Not that I'm dismissing your ideas as I don't know the answer either. You just peaked my curiosity on the subject, that's all.


Why do you feel that flat plate drag calculations are a better way to understand parasitic drag figures? Wouldn't larger aircraft be at an automatic disadvantage using this approach when looking at overall aerodynamic refinement? I would say aircraft with similar wing areas could be compared with such calculations but as the differences grow it becomes more problematic.

Case in point. Which aircraft would you say is more aerodynamically refined, a Lockheed Constellation or a Sopwith Camel?

World Heritage Encyclopedia:

_....In another comparison with the Camel, a very large but streamlined aircraft such as the __Lockheed Constellation__ has a considerably smaller zero-lift drag coefficient (0.0211 vs. 0.0378) in spite of having a much larger drag area (34.82 ft² vs. 8.73 ft²).
_
So you can see why I have my reservations with flat plate drag calculations when discussing aerodynamic refinement of a particular aircraft, just as you are suspect of zero lift drag calculations. If the wing areas of two aircraft are close than drag area would be more ideal, but this is not the case with all comparisons.


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## KiwiBiggles (Feb 18, 2018)

DarrenW said:


> Why do you feel that flat plate drag calculations are a better way to understand parasitic drag figures? Wouldn't larger aircraft be at an automatic disadvantage using this approach when looking at overall aerodynamic refinement?



Because it's not a beauty contest; what matters is how much parasitic drag is generated by the non-lifting parts of the aeroplane. And for comparing this, the equivalent flat plate area is far more relevant than the Cd. Comparing drag coefficients related to an irrelevant reference like wing area, means that fatties like the P-47 or F6F end up looking similar to planes as svelte as the Bf 109. You can easily lower your Cd by increasing your wing area, but it's not going to help you at all.

Parasitic Cd is a useful measure for examining changes to a particular design, or for comparing aeroplanes of similar size. Using it to compare planes of different sizes is an exercise in navel-gazing.

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## DarrenW (Feb 18, 2018)

KiwiBiggles said:


> You can easily lower your Cd by increasing your wing area, but it's not going to help you at all.



Yes, but with increased wing area usually comes reduced speeds, all other things being equal. This will effect the CD0 calculations as well, increasing it incrementally. But like what I posted concerning the comparison of the Camel to the Constellation (and I believe we are in agreement about this) you can use flat plate area calculations to help compare overall parasitic drag (or aerodynamic refinement) IF the wings are of similar area. The larger the difference gets the less accurate the comparison becomes.


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## Ivan1GFP (Feb 18, 2018)

DarrenW said:


> I appreciate your example concerning the modified racing aircraft and I can see where you find problems with how CD0 is calculated. Do you have actual aerodynamic data of modified WWII aircraft used for pylon racing to support your assumptions? Not that I'm dismissing your ideas as I don't know the answer either. You just peaked my curiosity on the subject, that's all.



I was getting a little too fancy with my example I guess. How about we just consider the same stock Bearcat but with no other changes than chopping a couple feet from each wing tip? I doubt it would reduce drag by much but certainly would reduce CD.
I can think of a couple real life examples but need to think of where I would get the aerodynamic data to illustrate.



DarrenW said:


> Why do you feel that flat plate drag calculations are a better way to understand parasitic drag figures? Wouldn't larger aircraft be at an automatic disadvantage using this approach when looking at overall aerodynamic refinement? I would say aircraft with similar wing areas could be compared with such calculations but as the differences grow it becomes more problematic.



First of all, it is not "Flat Plate Drag", but "Equivalent Flat Plate Area". An actual Flat Plate of the Equivalent Flat Plate Area would have much more drag (around 1.3x to 1.5x IIRC). It is a good measure because it is representative of the drag of the actual aircraft that you are trying to move through the air. The fact that a larger aircraft would have more drag is exactly what we are missing with a simple expression of CD.



DarrenW said:


> Case in point. Which aircraft would you say is more aerodynamically refined, a Lockheed Constellation or a Sopwith Camel?
> 
> World Heritage Encyclopedia:
> 
> ...



Your Sopwith Camel versus Lockheed Constellation is actually a great example. Imagine that we have the two airframes sitting side by side in a hangar but without engines. I give each aeroplane a 200 HP radial engine. Which one do you suppose will be flyable with that kind of power and which would not? Why would the Constellation with such aerodynamic refinement not ever get off the ground?

As I see it, when you take two aircraft that can both accomplish the same mission, then one compares other factors such as straight line performance and maneuverability, durability, and other abilities. If one aircraft has measurably better performance and maneuverability, do we really care that it has more or less wing area or that has a different coefficient of drag?
If there is no difference from a performance standpoint, and there is a significant difference in size and weight, is there an advantage of one over the other? I believe the answer is that for equivalent capabilities, choose the smaller, lighter one because it will be easier to transport and store.

-Ivan.


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## DarrenW (Feb 18, 2018)

Hi Ivan,
Yes, I understand the simple concept that a larger aircraft will produce more overall drag, thus requiring more power to gain the desired performance. But again other factors such as weight should be considered too (using the Camel/Constellation comparison again). Is that what you've been trying to explain all along? If it is than I agree with your points. And thanks for correcting my verbiage concerning flat plate area. I was being a bit sloppy in my choice of words.

I'm also positive that you will agree that a biplane built in 1917 is less aerodynamically 'clean' than most if not all modern built monoplanes. I've only looked to the CD0 formula to derive refinement of an aircraft design, not how much overall drag it may have (which takes in to affect the wing design of course). Newer aircraft may have larger aerodynamic 'foot prints' but they are still far more advanced designs nevertheless. This is the only point that I was trying to make concerning zero-lift drag coefficient calculations.

So my next question would be is how do fans, such as what was used on the BMW 801 radial, affect cooling at higher speeds? Could there be a point where the blades themselves block airflow that otherwise would pass though and around the cylinder heads?


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## DarrenW (Feb 18, 2018)

Sometimes it's nice to get two exceptionally well engineered aircraft engines side by side and marvel at the technology of the day:

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## KiwiBiggles (Feb 18, 2018)

Ivan1GFP said:


> How about we just consider the same stock Bearcat but with no other changes than chopping a couple feet from each wing tip? I doubt it would reduce drag by much but certainly would reduce CD


Wouldn't that _increase _the Cd, as the wing area has decreased with no real decrease in drag?


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## Ivan1GFP (Feb 18, 2018)

DarrenW said:


> And thanks for correcting my verbiage concerning flat plate area. I was being a bit sloppy in my choice of words.



I am glad you understand the difference. In this case wording is important because the drag of a flat plate and Equivalent Flat Plate Area are not really the same thing and I am sure there are folks that don't know the difference.



DarrenW said:


> I'm also positive that you will agree that a biplane built in 1917 is less aerodynamically 'clean' than most if not all modern built monoplanes. I've only looked to the CD0 formula to derive refinement of an aircraft design, not how much overall drag it may have (which takes in to affect the wing design of course). Newer aircraft may have larger aerodynamic 'foot prints' but they are still far more advanced designs nevertheless. This is the only point that I was trying to make concerning zero-lift drag coefficient calculations.



Agreed regarding aerodynamic quality difference between Constellation and Camel. I am guessing that the Camel simply could not go nearly as fast as the Constellation regardless of power that was installed.
The point I was trying to make was that actual performance beats the heck out of minor differences in "Aerodynamic Quality".



DarrenW said:


> So my next question would be is how do fans, such as what was used on the BMW 801 radial, affect cooling at higher speeds? Could there be a point where the blades themselves block airflow that otherwise would pass though and around the cylinder heads?



You kind of answered your own question with the photographs of BMW 801 and R-2800.
My own opinion is that the R-2800 is superior to the BMW 801 in most ways.

Hello KiwiBiggles,
Thanks for finding my error. What I actually typed would not be very coherent and not even support the point I was trying to make.
Chopping Wing Tips would obviously reduce wing area and INCREASE Coefficient of Drag.

- Ivan.


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## chuter (Feb 18, 2018)

The last production variants of the 801 was the F and minor variations of that . Those engines were to have a 14 blade cooling fan which would be an external identifier but this fan was later abandoned (and the 12 blade reverted) to when it was found that it interfered with high speed cooling. (Due to the small inlet size on the 801 cowl the fan was apparently only for ground and climb cooling.) Most American radial cooling relied on a large opening and cowl flaps which, when closed, built up a high pressure bubble in front of the engine forcing most air around the cowl achieving a similar, if much less aesthetic, result as the small inlet but still had much better ground cooling and was ridiculously simpler. Small gains could be had the BMW way but large aircraft formation ground and flight ops made the extra effort too much ... I guess.

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## Ivan1GFP (Feb 19, 2018)

chuter said:


> The last production variants of the 801 was the F and minor variations of that . Those engines were to have a 14 blade cooling fan which would be an external identifier but this fan was later abandoned (and the 12 blade reverted) to when it was found that it interfered with high speed cooling. (Due to the small inlet size on the 801 cowl the fan was apparently only for ground and climb cooling.) Most American radial cooling relied on a large opening and cowl flaps which, when closed, built up a high pressure bubble in front of the engine forcing most air around the cowl achieving a similar, if much less aesthetic, result as the small inlet but still had much better ground cooling and was ridiculously simpler. Small gains could be had the BMW way but large aircraft formation ground and flight ops made the extra effort too much ... I guess.



Hello Chuter,
My understanding was that the BMW 801F was never actually produced.
Perhaps you are discussing the BMW 801TS version that was fitted to the A-9 and F-9 series?
Those engines did have a greater number of fan blades.
Do you happen to know what versions came after those that reverted to the 12 blade cooling fan?

The high pressure bubble you are describing would certainly vary with dynamic pressure and thus would become less effective as speed increased, or is there something I am not seeing here?
If this lack of a spinner worked so well, then why did the P-47J and P-72 use spinners for their installations?
Note also that the radial versions of P-60 also wore spinners.

Why would the BMW method affect large aircraft formations? Are you describing the single engine control lever from the Kommandogerat?
If so, there was also a control for fine tuning RPM which could be used for formation flying.

- Ivan.


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## Shortround6 (Feb 19, 2018)

For the Boeing 307 the flat disk behind propeller helped the cooling in ground running. It was found that with the aircraft stationary (or moving slowly/taxing?) some of the air, instead of going reward through the cowl/baffles actually flowed forward around the propeller hub and blade roots, mixed with the incoming air and recycled. a fair amount of churning going on right in front of the propeller. 
At some point the discs were dispensed with. I have no information on why or what other modifications were done.

SB2C Helldivers have pictures both with and without spinners. Please note a large spinner may perform a similar function to the flat disk and help prevent air from bleeding out around the prop hub in ground running. 

However I would be very leery of making much in the way of generalizations. 
Early SB2C.




Later version.




Difference in engine was 200hp for take-off and less at altitude. The higher powered engine had better fining and _should _have cooled better at idle/warm up settings. What we don't know is what (if any) changes were made to the cowl flaps and what changes were made to the internal baffles of the cowl or between cylinders. 

Please note the Martin PBM-3D patrol bomber used _fan cooled _1900 hp R-2600s instead of the non fan 1700 R-2600s of earlier versions. However the PBM-5 used non-fan 2100hp R-2800s which pretty much solved the overheating on take-off problem. 

There are a lot of variables in cooling an air cooled engine and some designers attack the problem with different approaches. 

Also spinners were used for several reasons. Including shrouding the blade roots and those large blade attachment sleeves from simply churning the air. 
How much was theory and how much was actual tested fact I don't know. 

A lot of spinner use seemed to involve trial and error in actual test flights. I would also note that even propeller 'theory" was far from exact as early trials aircraft using contra-rotating propellers on high powered aircraft (like the P-47J and P-72) often failed to show any improvement in performance and often slight decreases (6-8mph?).


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## MiTasol (Dec 30, 2019)

Shortround6 said:


> I am using a chart in a booklet/book provided by the Ethyl corporation to the USAF and US Navy around 1950. The book was written/prepared by Sam Heron who was one of the leaders in developing the PN scale.
> The PN scale may not be exactly linear but it is a lot better than the octane scale.
> 
> Airplane Fuels and their Effects on Engine Performance Book, NAVAER, USAF 1951
> ...



Good find Shortround

It appears that copy is sold but the NASM has a copy of the 1945 edition and they will provide quality photocopies for a modest price.
Aviation fuels and their effects on engine performance / / prepared for U.S. Army Air Forces on purchase order (33-038) 44-5908-E and Bureau of Aeronautics, United States Navy on requisition P.D. ENII-28528-45.

There is a google copy of the 1951 edition at Aviation fuels and their effects on engine performance, prepared by Ethyl Corporation. Supplied to U. S. Air Forces on purchase order AF-33(600)5312; ... - download using the Hathi Download Helper - 277mb so it is actually a reasonable copy tho as always with google copies foldouts are butchered.


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