Aerodynamics of Japanese fighters

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spicmart

Staff Sergeant
907
190
May 11, 2008
How competitive were Japanese fighters in this field?
 
How competitive were Japanese fighters in this field?
In what regards?
And when?

Only trying to be a bit of a smart ass.
There is a lot of aerodynamics that go into even just fighters. Most of it is beyond me but even for wings we have
Aerodynamic section/airfoil which governs lift/drag ratio but the lift drag ratio, if I understand correctly can change a little bit at different speeds. Good L/D at low speed might cross over and not quite so good at high speed as a different airfoil.
Plan form, like tapered wing or plank wing or elliptical wing.
Taper, like for the plank wing where there is a constant size/shape airfoil from one end to the other or from root to tip. Other wings changed the airfoil to get thinner even as the wing tapered from front to back (cord).
Use of flaps of different types.
Use of any leading edge lift/flow devices. Many designers twisted the wing, tips were operating around 2 degrees less angle of attack than the wing roots, was it gradual or was all the twist done in the outer 1/2 (or around there?).
Retractable landing gear?

There may be more, but we can go on to the fuselage/engine cowling and engine intakes/ oil coolers and occasional radiators.
We can look at canopies? radio antennas and so on if we really want to get nit-picky.
The Zero and and Oscar were pretty darn good based on speed vs power. But they were operating in a good area. Drag for most planes is pretty predictable under or approaching mach 0.6(?) it can get really squirrely going higher.

It also doesn't matter very much how good your wing is if you hang a couple of airbrakes like this underneath
main-qimg-4987a8bdb8bcc81a282d2ce2e12be548-lq.jpg

Some times you got to do what you got to do ;)
 
My understanding is that the Japanese used their ESD series alloy for the more highly stressed load bearing structural members in the A6M - like spars, some stringers, some formers, some frames, etc - while the skinning (except directly behind the exhausts? - not sure what they used there) and the rest of the aluminum structure was all 2000 series. They would have liked to use their ESD series for almost every load bearing member in the structure but it was considerably more expensive to manufacture, and at the time more difficult to machine properly when dealing with stamped and formed or drawn parts in particular. I do not think it would have made much difference if used for the skin, even in the monocoque structures, considering the very thin section and the use of rivets for fastening.

Japan's ESD (Extra Super Duralumin} had almost the same composition and mechanical properties as today's 7076.

Japan started using ESD in a large scale in 1940, with production of the A6M2 being the first(?), gradually spreading to other aircraft as the war progressed. Japan subsequently developed and began using the ~equivalent of 7075 in early-1943.
 
As far as the extent and depth of Japan's knowledge of aerodynamic theory is concerned I think it is correct to say that their 'boffins' were just as capable as those of the other countries around the world. Their understanding of physics in general was on a par with the best of the other countries, as was their knowledge of hydrodynamics (when investigating the designs of the Japanese ships after the war the British considered them to be their equal in most areas, with a different focus in some areas due to their strategic needs).

As has been mentioned in many other threads involving different aspects of Japan's industry at the time, the main problem the Japanese had was getting their theories into practice, primarily due to a relatively small industrial base. Once the war started they had a hard time getting major programs all the way through to production and deployment.

This level of knowledge should not really come as a surprise as Japan paid attention to the developments in the rest of the world - just as other countries did. Many of their scientists and engineers spent time abroad and at foreign educational institutions, attended symposiums, and had an amicable relationship with foreign scientific and manufacturing communities. As far as the knowledge of the time goes it was only the very latest immediate pre-war developments that Japan did not have access to, due to restrictions place on the dissemination of information. But they developed most of the same knowledge on their own anyway.
 
T ThomasP my understanding is that it was 7075 not Alu 7076 but those are almost the same material anyway. Minor quibble on my part but totally agree with everything you wrote. EDIT: I misread and you did write that 7076 is essentially the same thing as ESD whereas 7075 was introduced by Japan in 1943. Mind blowing info. Thanks!

Regarding the primary discussion topic, aerodynamics, I believe the main things that we're all talking about are the zero-lift drag coefficient and wing area of an aircraft. I only have a low-level, mechanical understanding of these principles of flight, but a quick summary for WW2 aircraft is as follows:

In general, the major aerodynamic variables for drag are the zero-lift drag coefficient and the wing area. If you have both, then you can calculate how aerodynamically efficient an air frame is.

Japanese aircraft tended to have particularly good streamlining, but then they also had big wings relative to horsepower and weight, which watered down their excellent streamlining.

But this is all speculation as I have never seen a ZLDC calculated for any Japanese aircraft, not even the Zero. Although some aviation buffs have used estimated ZLDCs which were reverse engineered from TAIC records, these are of unknown pedigree as well. This video does a really great job of reverse engineering TAIC's calculations, and some Japanese sources, to get the ZLDC for the Ki-84. But as the video pointed out, TAIC appears to have just transplanted the Ki-43's ZLDC to the Ki-84's wing area. Additionally, Nakajima burned all of their records after the war, so the final drag estimate is also just an estimate with no valid sourcing. This is definitely not the right number. And we don't actually know how the Frank's aerodynamic efficiency was.

Just a side note: I'd love to see the zero lift drag coefficient calculated for the N1K2-J and the N1K1-J but my guess is that it doesn't exist. But because it has laminar airfoils and a large propeller, it's a good indicator of Japanese aerodynamic technology.

The Japanese were early adopters of "laminar" flow airfoils. Kawanishi was the first company to fly such an aircraft outside of the US, but the J2M1 Raiden also had a semi-laminar airfoil (according to Japanese Wikipedia, which sources Maru Mechanic IIRC for this). However, except for the Suisei dive bomber and the Ki-61, all Japanese aircraft were relatively high drag radial aircraft, with extra emphasis spent on streamlining to compensate for their lower horsepower output as well as extensive hand finishing using machinists.

The Mustang (D model), as far as I'm aware, has the lowest Zero-Lift Drag Coefficient out of all aircraft produced in large quantities during the war. I think much of that is because it uses a liquid-cooled engine. The Ki-64 probably had an overall lower zero-lift drag coefficient though but that was a prototype.
 
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The Japanese were way ahead of the US and Britain in many aspects both aerodynamically and mechanically and this is best shown in things like the drop tanks of the A6M and Ki-43 and the tail landing gear of the A6M.

The care they took to make these items aerodynamically clean is an example of their whole design philosophy.

Using data from the thread greg-of-auto-and-airplanes-has-asked-for-a-debate it appears that the P-47 lost some 20-25 mph from the fixed bomb racks and stays used to support the drop tank. The P-51 reputedly lost 4-8 mph. Add to that all US aircraft lost range from the drag produced by the pylons and/or sway braces etc that were stayed on the aircraft when the tank was dropped.

The Ki-43 and A6M were contemporaries of the P-39 and P-40. Look at these four photos, all showing the aircraft without the drop tank fitted. Note all the aerodynamic a---holes (sway braces) hanging from the bottom of the P-39 and P-40 and the total lack of such drag producing hardware on the Ki-43 and A6M.

all photos from net.
1719647651846.png
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The reason the Japanese aircraft were so clean when the tank was dropped was that the sway braces (used on the Ki-43 installation) were all attached to the tank and the single point shackle was totally contained on the inside of the structure. Add to that the Japanese had self seal couplings that were again flush mounted while the Americans had, for a long while, hoses with breakaway fittings that were external to the aircraft.

This is the Ki-43 installation and a photo of the side stays and fuel transfer fitting on a damaged Ki-43 tank. The Ki-43 vent line is hidden in the front attachment fitting and produces no drag. On the early P-39 and P-40 tanks the vent line was a long tube that was welded externally to the tank and curled around the side producing drag. Likewise the Ki-43 and A6M had flush mounted filler caps from day one whereas the P-39 and P-40 had drag producing gooseneck fillers. Not shown here is the streamline fitting that covered the shackle and fuel fitting that was also discarded with the tank.

1719648893163.png

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The A6M drop tank was supported on a tube that went up inside the belly of the aircraft and therefore it did not require sway braces. Diagram and photo from https://ww2aircraft.net/forum/members/thomasp.72399/

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P-40 drop tank. You can see the gooseneck filler and the vent pipe, starting at the non aerodynamic welded fitting and angle fitting, is clearly marked. All the sway braces and barrels and the external shackle remain on the aircraft when the tank is dropped. All US aircraft had either drag creating hardware like this or drag creating pylons that stayed on the aircraft.
1719650368892.png
 
My understanding is that the Japanese used their ESD series alloy for the more highly stressed load bearing structural members in the A6M - like spars, some stringers, some formers, some frames, etc - while the skinning (except directly behind the exhausts? - not sure what they used there) and the rest of the aluminum structure was all 2000 series. They would have liked to use their ESD series for almost every load bearing member in the structure but it was considerably more expensive to manufacture, and at the time more difficult to machine properly when dealing with stamped and formed or drawn parts in particular. I do not think it would have made much difference if used for the skin, even in the monocoque structures, considering the very thin section and the use of rivets for fastening.

Japan's ESD (Extra Super Duralumin} had almost the same composition and mechanical properties as today's 7076.

Japan started using ESD in a large scale in 1940, with production of the A6M2 being the first(?), gradually spreading to other aircraft as the war progressed. Japan subsequently developed and began using the ~equivalent of 7075 in early-1943.
Schmued at NAA was intrigued by the findings of the A6M. Alcoa reverse engineered the ESD, but told Schmued that it was not available in early 1943 so NAA stretch formed and heat treated 24ST for the XP-51F.
 
That makes sense because that A6M is not flown anywhere near limits. Does anyone other than Steve, Jr even fly it?
There are a number of people who fly it when it gets flown. I'd say we have 4 - 5 pilots qualified and approved to fly it.

Most often it is John Maloney or Steve Hinton, either Sr. or Jr. I'm pretty sure Kevin Eldridge is also on that list, too.

The last few times I have seen it fly, it was John Maloney.


View: https://youtu.be/HjzY-CAc2iY
 
Off topic but I thought I would make a comment in regards to Shortround 6's post.
"It also doesn't matter very much how good your wing is if you hang a couple of airbrakes like this underneath
main-qimg-4987a8bdb8bcc81a282d2ce2e12be548-lq-jpg.jpg

Some times you got to do what you got to do ;)"

In Douglas Calum's book the Secret Horsepower Race, The: Western Fighter Engine Development: Western Front Fighter Engine Development, he discusses a German meeting, with Willy Messerschmitt present, where the discussion centres on the Bf109 having larger radiators relative to the comparable period Spitfire. (The reason is that the Merlin had a higher pressure radiator cooling system and thus was more efficient and smaller radiators.)

PS Great photo!
 

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