Aerodynamic Drag Properties of the A6M

GregP said:

Not according to the design report on the Zeke 32. The A6M5 might well be laid out differently.

But, if so, the one to the right of the joystick grip in post #70 reads to +450 and -250. If that is a manifold pressure gauge and not a vacuum gauge, it will read positive.

Click to expand...

I am getting more and more suspicious of the design report on the Zeke 32.
First it gets the fuel volumes wrong, now it mislabels gauges.

If you look really closely, you will see a minus sign in the black section of the manifold pressure gauge just to the left of the vertical pointer.
It is supposed to be showing 0 mm boost because the engine is off.
The Red section is Positive boost and goes up to +250 mm.
The Negative section goes down to -450 mm.
Manifold pressure gauges can run both positive and negative depending on throttle setting and whether you are running boost or not.
Read the posts between the one with the Smithsonian image and the recent posts. I believe one has an image of the Chino A6M5.
You have access to the Chino A6M5. Check your cockpit images.
The A6M2 has exactly the same kind of gauge which is described in the report Informational Intelligence Summary Number 59 on bottom of page 9.

Hello GregP,
I think I am starting to understand more about what was going on.
This "Design Analysis" was based on the A6M3 Type 32 rebuilt from captured wrecks at Eagle Farm.
The report can be found here:

I have already commented elsewhere that I believe the performance figures in this report are total garbage.
Now, I don't know what they had to work with as far as wrecks, but if you look at the instrument panel on page 24 of 31 in the A6M Evaluation,
you can see that they have the 0-350 gauge and Manifold Pressure gauge swapped. The 0-350 gauge is actually a Cylinder Head Temperature gauge.
The report makes for interesting reading, but I am not sure how much of it I would rely upon for actual performance data. These guys were guessing (wrongly) about the specifications of how to set up the reconstructed bird they had. It does seem to be a reasonable view into how the Model 32 handled at medium speeds though. I kind of wonder what it might have done if they actually had gotten the numbers correct.

I have often wondered why they confined it to such a low MAP setting in addition to other bits of stuff here and there.

DarrenW said:

I didn't realize that we were in disagreement here. Besides the reasons you mentioned, there were other factors (such low quality replacement parts) that added to the maintenance dilemma. Aircraft plants often used unskilled labor during manufacturing and cut corners in other areas as well. So yes I agree that, by the middle of 1944, IJN and IJAAF aircraft were in a much worse state of repair than any of their opposition.

Click to expand...

Why the middle of 1944, and what does "much worse state of repair" actually mean?

What you find, when you actually look at this objectively, was that even a very late aircraft like the Ki-84, at the end of 1944, a model with a supposedly very poor reliability record, found in the Phillipines, thus in rough frontline conditions, exhibited the following pattern:

The TAIC rounded up a few of the intact ones for testing. Being unaware of what they were doing, they concentrated on the ones that looked the most pristine.

And they had a mountain of problems with them.

Then they looked at one that looked like a battered hulk, and that one worked comparatively perfectly.

After doing very little flying with the lemons (less than an hour, with virtually no flight data gathered, even after the war in the US), they finally realized that the "pristine ones" were the lemons that rarely or never flew.

Which means that there was a vast difference in useage between airframes, and that the Japanese concentrated their maintenance efforts on the best ones. It also probably means that they hardly sent into combat the bad ones at all, because the pilots were simply too valuable for that kind of nonsense.

Another example of this bias is the claim I have read, in at least one major publication, that 70% of Ki-84s were in such bad condition they could not exceed 450 km/h on delivery. 450 km/h was the maximum speed without Water-Methanol, which was supplied as standard for any operational flight, but was probably not supplied for ferry flights. This is why I suspect the statement of a speed of 450 km/h had nothing to do with the condition of the aircraft, but it got lumped up in a detailed paragraph where a Japanese mechanic supposedly complains about this...

Many axis weapons get the exact same treatment, but you hardly ever hear about all those P-51Ds (yes Ds) being down to one gun working (or one wing, always the one outside the turn) in 1945...

Hey wrathofatlantis,
re

wrathofatlantis said:

Another example of this bias is the claim I have read, in at least one major publication, that 70% of Ki-84s were in such bad condition they could not exceed 450 km/h on delivery. 450 km/h was the maximum speed without Water-Methanol, which was supplied as standard for any operational flight, but was probably not supplied for ferry flights. This is why I suspect the statement of a speed of 450 km/h had nothing to do with the condition of the aircraft, but it got lumped up in a detailed paragraph where a Japanese mechanic supposedly complains about this...

Click to expand...

I am sorry, but this makes no sense. 450 km/h (280 mph) is about the Vmax of pre-war aircraft such as the Ki-27 and A5M. Since the Vmax of a reasonably good condition Ki-84 is supposed to be around 610 km/h (380 mph) without mater-methanol, that would mean that water-methanol injection was giving a minimum increase of 100 mph when used. This is not possible with the design practices used in the Ki-84 or with the engineering limitations of the time.

If the publication claiming "that 70% of Ki-84s were in such bad condition they could not exceed 450 km/h on delivery." is correct, then there was a different reason for the problem.

ThomasP said:

Hey wrathofatlantis,
re


I am sorry, but this makes no sense. 450 km/h (280 mph) is about the Vmax of pre-war aircraft such as the Ki-27 and A5M. Since the Vmax of a reasonably good condition Ki-84 is supposed to be around 610 km/h (380 mph), that would mean that water-methanol injection was giving an increase of about 100 mph when used. This is not possible with the design practices used in the Ki-84 or with the engineering limitations of the time.

If the publication claiming "that 70% of Ki-84s were in such bad condition they could not exceed 450 km/h on delivery." is correct, then there was a different reason for the problem.

Click to expand...

The Ki-84 had a "full time" MW-50 system and it could not get above that speed (425 or 450 km/h) without MW-50 automatically engaging.

It is not a matter of how much the MW-50 adds, it has to do with the design of the Ki-84 engine: The Ki-84 engine cannot operate normally above 450 km/h without MW-50 (this I think may apply to all Japanese aircrafts with the Homare engine). MW-50 is not an "added boost" like in other engines (like the Me-109G-14): The engine literally cannot reach above certain cruise power levels without MW-50, because the MW-50 water injection is part of its basic design function.

The Ha-45 (as used in the Ki-84) only ran water-methanol at above 80% power. Depending on which variant of the Ha-45 and Ki-84 this would mean that the Ki-84 was capable of around 610 km/h (380 mph) at ~1600 BHP (ie 80%) without water-methanol, upto about 655 kp/h (405 mph) at ~2000 HP with water-methanol.

450 km/h (280 mph) would be about the maximum weak mixture economical cruise for the Ki-84.

Just a comment on the "that 70% of Ki-84s were in such bad condition they could not exceed 450 km/h on delivery." statement: This was probably what they read off on the cockpit dial, i.e. the IAS speed and not the TAS. And to take an example, if they really did read this off at the purported Ki-84 FTH of 7000 m, this would correspond to a TAS of only around 635 km/h TAS, so well below the 427 mph (687 km/h) top speed the US TAIC credits "Frank" with. So yes, the Japanese acceptance pilots would be right to be disappointed to see only 450 km/h IAS on the dial, but that this is maybe then not as hair-raisingly bad as it may first appear to be.

Then about the Zero's manifold pressure gauge: If this goes from -450 mm and the red section ends at +250 mm that makes perfect sense: I have an original Sakae engine power chart which lists the engine power as a function of different rpms all the way from -350 mm to +300 mm in boost.

Discussing the lemons or hangar queens, one of the C-119s in our Reserve squadron always flew in a slight crab or slip according to the pilots. The 119, Triple Nickel I think, always used more fuel than the others and was more difficult in formations. The last year I was in, 1965, a fellow from Fairchild showed up and he took mechanics into the wing. A special seven point 3/4 inch drive socket was made in the machine shop and with it the internal wing structure was retrimmed so that ole 555 was now the fastest and easiest to fly. Just in time for the flight to the boneyard the next year with the rest of the C-119s.

ThomasP said:

The Ha-45 (as used in the Ki-84) only ran water-methanol at above 80% power. Depending on which variant of the Ha-45 and Ki-84 this would mean that the Ki-84 was capable of around 610 km/h (380 mph) at ~1600 BHP (ie 80%) without water-methanol, upto about 655 kp/h (405 mph) at ~2000 HP with water-methanol.

450 km/h (280 mph) would be about the maximum weak mixture economical cruise for the Ki-84.

Click to expand...

Hello ThomasP,
Your data isn't quite correct regarding the engines in the Ki-84.
The fuel quality used by the IJA was relatively poor, standard was 92 octane. The Ha-45 had enough boost that could not run at anything past a fast cruise or max continuous without Water Injection.
It could not achieve even Rated Power without Water Injection.
This is why the water tanks are so large relative to the aircraft's internal fuel in most late war Japanese fighters.
The testing of the Middletown Ki-84 documents that the system came on at +180 mm boost or 37 inches Hg.
This is for an engine that uses +350 mm for Military Power and +500 mm for Takeoff power.
280 MPH TAS (not IAS) sounds about right on such low engine power.
Also for context, the Ha-45-21 was making 1550 HP in Low Blower at low altitude at +200 mm boost.

The Ha-45 was a great engine when it actually ran correctly but there were usually numerous manufacturing faults.
That is why there were considerations late in the war to re-equip the airframe with a Kinsei engine of 1500 HP because the Ha-45 in actual service often didn't achieve any more than about 1300 HP.
When the faults are corrected, as they were in the engine from the Middletown Ki-84, the Ha-45 lived up to the claims made for it as the test engine generally did after a few repairs.

- Ivan.

Holtzauge said:

Then about the Zero's manifold pressure gauge: If this goes from -450 mm and the red section ends at +250 mm that makes perfect sense: I have an original Sakae engine power chart which lists the engine power as a function of different rpms all the way from -350 mm to +300 mm in boost.

Click to expand...

The Type 0 Mk.I (A6M2 Model 21) had a maximum boost of +250 mm for Takeoff power.
For it to have a Manifold Pressure gauge that only reads up to +250 mm makes perfect sense.
The Type 0 Mk.II (A6M3 and A6M5) had a maximum boost of +300 mm for Takeoff power.
It had the SAME Manifold Pressure gauge that only reads up to +250 mm DOESN'T make much sense.

- Ivan.