An error in IJN CV capacities?

[Saburo Kurusu]

Well, at least everyone might feel free to change the numbers via the editor in the way he assumes to really fit reality best...... But I think the developers might have done that to the best possible knowledge. I also have three books with three different numbers on this, that's annoying, I can understand the poster very much...... I think in the end a definite answer to this is perhaps impossible......

[Local Yokel]

I have extrapolated some of the figures given in Herwin’s post #19 in an attempt to relate space required by carrier aircraft to the hangar space available.

I assumed a complement of 81 aircraft for Kaga broken down into three 9-plane chutai apiece of A6M, D3A and B5N. Applying Herwin’s figures, 27 A6M and 27 D3A require 19,800 square feet apiece, whilst the 27 B5N require 15,000 square feet. Combined, these give a total of 54,600 square feet. This is slightly more than one half of the available hangar space provided by Kaga’s upper and middle level hangars. Put another way, it is almost possible to house the carrier’s entire airgroup in one of her two principal hangars.

If you reduce the airgroup size to the game maximum for Kaga of 72 aircraft by taking away one chutai either of A6M or D3A, the hangar space requirement drops to 48,000 – substantially less than half the available hangar space.

I have two reservations about the figures given by Herwin as the space required for individual carrier aircraft. First, I think he may have underestimated the area taken up by a single D3A. I also suspect that there may be a significant difference between the minimum theoretical area into which an aeroplane can be crammed and the minimum area required for practical handling purposes – you can’t park an aircraft by moving it sideways! I am aware that Herwin made some allowance for this by increasing the area required for parking each 9-plane element, but I think that allowance may not been large enough.

Even if one allows a generous increase in the amount of hangar space required for parking a chutai of any given aircraft model, you still seem to be left with ample space within Kaga’s hangars. On Herwin’s figures a single A6M or D3A takes up about 720 square feet, a B5N about 500. Contrast that with a figure of 1,336 square feet per individual aircraft if the upper and middle level hangars’ area is divided evenly amongst 81 aircraft. All this without any resort being made to the additional area of 5,568 square feet that is available in the lower level hangar.

The conclusion I draw from this is that there is no obvious reason for limiting Kaga’s capacity to 72 aircraft by reference to the space available within her hangars. Even with a manoeuvring/parking area per aircraft about double the space allowed for by Herwin, I see no reason to think that Kaga could not have accommodated an hikokitai of 81 1941-era aircraft in her hangars. This implies that some other reason was adopted by the developers for constraining her capacity to 72. What can that reason be?

I’m well aware that I can modify the data to restore Kaga’s capacity to a figure closer to Akagi’s, if I think it better reflects her historical capability. But I would much prefer to understand why the developers limited her capacity to 72 when both the historical record (91 aircraft capacity) and calculations of her available hangar area point to a different conclusion. So far, the only explanations I have seen suggested for such a reduction have been related to such factors as the maximum size strike she could spot. This, however, is to confuse her ability to conduct various forms of air operations with her staying power over a battle that may last several days, for which total aircraft embarked (and therefore maximum capacity) becomes much more significant.

Sad to say, still no response on my question about how reserve aircraft are related to carrier capacity.

[Fishbed]

Tell me if I am wrong (for I don't have the book with me and it's been a very long time), but I seem to remember that Shattered Sword (or was it Sunburst?) had an interesting graph of some IJN carrier hangar storage in its annex (I think it was Akagi's) with its airgroup as an overlay seen from the top. Maybe it could answer some questions, or at least give a better picture of the whole thing.

[DivePac88]

Local Yokel,

you have to remember that the Hanger space figures provided, did not take into account the lift-wells. The spaces on either side of the lift-wells could not be used for aircraft storage, and were generally used for aircraft and engine parts. Also some of the older carriers had lifts that could not handle all aircraft types available, and this dictated the storage arrangements also.

[spence]

It's "Shattered Sword" but it's only a partial view of the hangar deck. It's pretty crowded in there. Tall people would get lots of bumps on their heads unless they were very careful. IIRC there is considerable text describing hangar deck operations.

[herwin]

Thanks for the critical comments. The other thing is that Japanese carriers had workshops along the edges of the hangar deck--much like RN carriers. I did the original work 30 years ago, and my notes are back in America in the condo (if they still exist). I suspect the big constraints were flight deck operations and aircraft availability.

Shattered sword shows 13 Zeros and Kates ranged between the amidships and rear lifts, apparently on Hiryu or Soryu. Four rows of three aircraft plus one. The A6M2 had a wingspan of 36 feet 2" with wingtips folded and a length of 29 feet 9 inches. Three took up about 75 by 30 = 2250 square feet. The B5N2 had a wingspan of 24-25 feet folded and a length of 33 feet 9.5 inches. Seven in the picture took up a bit more than 75 by 70 = 5250 square feet. Based on the figure, 61740 minus the space for the three elevators and adjoining shops (about 75x30x6=13500 square feet) was about enough space for 48000/750 = 64 aircraft. Sounds like the quoted capacity. The flight deck was 711 x 75 feet. Subtract 650 feet for landing and takeoff operations gives 61 x 75 = room for six A6M2s in a deck park. Theoretical maximum of 70 aircraft.

[Local Yokel]

DivePac makes the entirely valid point that the lift wells and the space laterally adjacent to them have to be left out of any reckoning of hangar space, and Spence rightly directs attention to Figure 7-1 in Shattered Sword. The authors don't say which carrier is being illustrated, but judging by the offset of the centre lift and the sponson arrangement I'd say it's a plan of Hiryu, whose hangar area is shown by shading on Fig. 17-6.

The plan of the aft section of Hiryu's hangar (assuming that's correct) shows 13 aircraft. Given that this is a double deck hangar, a similar number of aircraft would be accomodated on the deck above or below - add another 13 aircraft: 26 in total so far. Ahead of the middle lift shown in the plan there's another section of double deck hangar of comparable length - add another 26 aircraft, and we are up to 52. Finally, there's a further section of hangar ahead of the forward lift. The upper level of this is longer than the aft section illustrated in Shattered Sword, but the double-deck portion below is shorter. The upper area was probably used for A6M's - from memory their cannon arming station was near the front of the carrier and it makes sense to bring them up to the flight deck via the forward lift. Even if this forward section can accomodate, say, only 20 rather than 26 aircraft, the total has gone up to 72. This in a carrier having a hangar area only 57% of that of Kaga, so when scaling up to the hangar space available in the larger carrier I have no difficulty in visualising capacity for more than eighty aircraft.

Once again, this assessment of the available hangar space in Kaga is without recourse to the small lower level hangar. Indeed, if my extrapolation from the Shattered Sword plan of the number of aircraft that Hiryu can take into her hangars is correct, Hiryu herself has an aircraft capacity equal to that attributed to Kaga in the game.

[Local Yokel]

My previous post made before I saw Herwin's.

Harry, the workshops flanking the hangars may well have a bearing on available space, although in the midships hangar section we are dealing with the area of maximum beam. So 72 in the hangar may be too high an estimate. I think we are moving closer on the area required per aircraft; it's a pity we don't have a full hangar plan with which the part plan in Shattered Sword can be compared.

Nevertheless, when the substantially greater size of Kaga is taken into account I don't see a reason to revise my conclusion that she could take more than 72 aircraft into her hangars.

Incidentally, I think the plan in Shattered Sword is showing D3A carrier bombers rather than A6M's. The obvious place to strike below the Zeroes is the forward end, given that they will normally go to the front of the flight deck spot because of their short take-off run.

[spence]

Incidentally, I think the plan in Shattered Sword is showing D3A carrier bombers rather than A6M's. The obvious place to strike below the Zeroes is the forward end, given that they will normally go to the front of the flight deck spot because of their short take-off run.

They are not D3As since the Vals did not have folding wings. Folding wings were inherently weaker wings and dive bombers needed every bit of the strength of a one-piece wing in order to withstand the G forces of pullout (that is; in order to make more than one dive per airframe [:D]).

The Ryujo and other CVLs never carried D3As because they were much larger to accommodate in the hangar and on the elevator because of their non-folding wings.

[herwin]

ORIGINAL: spence

Incidentally, I think the plan in Shattered Sword is showing D3A carrier bombers rather than A6M's. The obvious place to strike below the Zeroes is the forward end, given that they will normally go to the front of the flight deck spot because of their short take-off run.

They are not D3As since the Vals did not have folding wings. Folding wings were inherently weaker wings and dive bombers needed every bit of the strength of a one-piece wing in order to withstand the G forces of pullout (that is; in order to make more than one dive per airframe [:D]).

The Ryujo and other CVLs never carried D3As because they were much larger to accommodate in the hangar and on the elevator because of their non-folding wings.

The aircraft with the folding wingtips were A6M2s. The wingtips were removed in later models. The ones with the folding wings were B5N1s or B5N2s.

[JWE]

Interesting perspective, Mr. Palmer. Sent you a pm.

Ciao. John

[Gilbert]

ORIGINAL: spence

Incidentally, I think the plan in Shattered Sword is showing D3A carrier bombers rather than A6M's. The obvious place to strike below the Zeroes is the forward end, given that they will normally go to the front of the flight deck spot because of their short take-off run.

They are not D3As since the Vals did not have folding wings. Folding wings were inherently weaker wings and dive bombers needed every bit of the strength of a one-piece wing in order to withstand the G forces of pullout (that is; in order to make more than one dive per airframe [:D]).
The Ryujo and other CVLs never carried D3As because they were much larger to accommodate in the hangar and on the elevator because of their non-folding wings.

The aircraft with the folding wingtips were A6M2s. The wingtips were removed in later models. The ones with the folding wings were B5N1s or B5N2s.
[/quote]


The Val had folding wings see drawing below

Gilbert

[Local Yokel]

ORIGINAL: spence

Incidentally, I think the plan in Shattered Sword is showing D3A carrier bombers rather than A6M's. The obvious place to strike below the Zeroes is the forward end, given that they will normally go to the front of the flight deck spot because of their short take-off run.

They are not D3As since the Vals did not have folding wings. Folding wings were inherently weaker wings and dive bombers needed every bit of the strength of a one-piece wing in order to withstand the G forces of pullout (that is; in order to make more than one dive per airframe [:D]).

The Ryujo and other CVLs never carried D3As because they were much larger to accommodate in the hangar and on the elevator because of their non-folding wings.

That had me worried - I thought I knew my Japanese carrier aircraft. Fortunately Parshall and Tully come to my rescue[8D]. From p.120 of Shattered Sword:

'Because of the placement of the Type 99's control surfaces and dive brakes, not to mention its need for structural strength, Aichi's designers had decided not to place a folding mechanism too near the center of the wing. Instead, the Type 99's wings folded very near the tips, making it difficult to stow, tricky to maneuver through tight spaces, and a hog of precious parking "real estate."'

If you look closely at the aircraft with folded wingtips in SS Figure 7-1, you can just make out the tips of the wheel spats peeping out below the wings. But those elliptical wings are a giveaway in any case.

[herwin]

What would an A6M2 look like on the same scale?

[Local Yokel]

I've just run a 1:76 scale rule over my 1:72 plans of a Model 21 Zero and D3A1 and D3A2 variants of the Type 99. It would tax my tired brain too much to convert the result to an accurate dimension, but, interestingly, the D3A2 with tips folded appears to have the same span as the Model 21, also with tips folded. This must be coincidental because the D3A1 wing appears to be hinged further outboard, thus giving it a slightly larger span with tips folded than the other two aircraft mentioned. At first I thought the coincidence of spans might have been dictated by something like size of lift well, but since the earlier D3A1 has a bigger span with tips folded and therefore requires a bigger well I don't think that can be the case.

The real dimensional difference lies in the length: both variants of D3A are at or close to 10.2 metres in length, whilst the Model 21 comes in appreciably smaller at 9.05 metres. I estimate the D3A1 to have a span of about 12.4 metres between wingtip hinge points, so it's a bit bigger (but not that much) than the Zero in all plan axes. Perhaps Parshall and Tully make too much of it being a space hog.

[herwin]

ORIGINAL: Local Yokel

I've just run a 1:76 scale rule over my 1:72 plans of a Model 21 Zero and D3A1 and D3A2 variants of the Type 99. It would tax my tired brain too much to convert the result to an accurate dimension, but, interestingly, the D3A2 with tips folded appears to have the same span as the Model 21, also with tips folded. This must be coincidental because the D3A1 wing appears to be hinged further outboard, thus giving it a slightly larger span with tips folded than the other two aircraft mentioned. At first I thought the coincidence of spans might have been dictated by something like size of lift well, but since the earlier D3A1 has a bigger span with tips folded and therefore requires a bigger well I don't think that can be the case.

The real dimensional difference lies in the length: both variants of D3A are at or close to 10.2 metres in length, whilst the Model 21 comes in appreciably smaller at 9.05 metres. I estimate the D3A1 to have a span of about 12.4 metres between wingtip hinge points, so it's a bit bigger (but not that much) than the Zero in all plan axes. Perhaps Parshall and Tully make too much of it being a space hog.

Well, the analysis seems to hold up--750 square feet for a Japanese carrier aircraft, with an added 10-20% more Zeros if you squeeze them in. 64x750 square feet of aircraft can live in the Hiryu's hangar. However, the Kaga is quoted at 108,240 square feet and 5,568 square feet, and the Akagi with 93,000 square feet for the upper and middle level hangars combined, and 8,515 square feet for the lower level hangar. Subtract 18000 square feet from the Kaga's upper hangars, and you get 90000 square feet for planes--120 or so! The Akagi comes in at 100! I don't trust those figures...

Suppose the quoted figures don't include elevators, and not all the area is usable. Does it work then?

[Feltan]

herwin,

Don't you need to account for, hmmmm, looking for a term here: hallways, alleyways, paths, etc. What happens if the plane in the very back row pops an oil leak and you need to bring it forward for maintenance? I'd expect a pathway to get planes in the back out of the crowd. My expectation is not definitive, but certainly not every sq ft of real estate could be used for plane storage.

Regards,
Feltan

[herwin]

ORIGINAL: Feltan

herwin,

Don't you need to account for, hmmmm, looking for a term here: hallways, alleyways, paths, etc. What happens if the plane in the very back row pops an oil leak and you need to bring it forward for maintenance? I'd expect a pathway to get planes in the back out of the crowd. My expectation is not definitive, but certainly not every sq ft of real estate could be used for plane storage.

Regards,
Feltan

As close as they could. Look at that figure in Shattered Sword.

[DivePac88]

I think that when you are working-out the airgroup capacity of the Japanese carriers, you also have to take into account the structure of their carrier air squadrons. I know that on an administration level, the Japanese carrier air squadrons had to sizings. The standard squadron size was 18 operational aircraft, with 3 dismantled spare aircraft. Then there was the 'oversize' squadron of 27 operational aircraft, also with 3 dismantled spare aircraft.

I also think that a lot of the confusion arround the Japanese carrier aircraft capacity, is the inability of their air-industry to supply sufficient numbers of aircraft. So then you would be looking at an airgroup on AKAGI/KAGA of 27+27+27=91 operational airframes, and 9 spare airframe. HIRYU of 27+27+18=72 operational + 9 spare, and SORYU 27+18+18=63 operational + 9 spare.

[Pascal_slith]

For illustrations, including line drawings and interior drawings, I've gone and bought some Japanese sources.

Check this page at Amazon (I use the Google translate button often on these).

http://www.amazon.co.jp/%E6%97%A5%E6%9C ... pd_sim_b_6

You'd be surprised the wealth of detail you can find sometimes. I have a few people around me that can speak and read Japanese, so I can get help with some of the text. That is the best method to get some superficial translation at times.