An article I found. Not for JFB's.

[mdiehl]

I think the article's claims about Pearl Harbor accuracy are suspect. To know the bombing accuracy the author would have to have reliable information about what bombs were released by whom, their intended target, and what they actually hit. If you target ship A and hit ship B that is a miss. A helpful one, perhaps, but still a miss.

To get a reall best approx of actual accuracy would require lining up all the Japanese sources (if there were any with that level of detail) with detailed US battle damage assessments. Ens whomever releases bomb at target X at time Y. Lance Corporal Shmoe standing near target X at time Y sees bomb burst on target... near target... way off target.. or whatever.

Generally speaking, Japanese level bombing accuracy using Kates was poor during the Guadalcanal campaign, and during the Darwin Raid. Hits during the latter were as much a product of target density as Japanese ability. Given the target density and non-moving targets at BB row at Pearl Harbor, the real issue is how often the Japanese missed. Their lack of success vs Doorman's force as au notes is illustrative.

Rest of the article has suspect comments. For ex USN were satisfied with 40% hit rates. Sure, but that was in open water at moving targets that were maneuvering to avoid bombs. So the Japanese success rate at PH with dense-packed, stationary, very large targets is not very impressive by comparison. Even US B-17s could accurately bomb stationary ships.

It looks like he's attributing declining accuracy apparent in the comparison between hit rates at PH with hit rates in Indonesia and at Midway to deteriorating pilot performance or something. IMO the correct perspective is to view the "normal" Japanese hit rate as 5-10% and the PH success rate largely as a product of a target rich environment full of oversize, stationary targets.

[ChezDaJez]

The wooden fins on the torps did not change the entry angle. They increased the drag after the torp hit the water, in effect increasing it's buoyancy. The idea was to prevent the torps from plunging to their normal plunge depth (how deep it goes into the water before the depth mechanisms could bring it to normal operating depth). Had they been less effectively buoyant they may have had problems sticking into the mud in the relatively shallow harbor.

Actually they did help change the water entry angle to a shallower one. Once the torp was released, the up angle of the fins also acted as miniature elevators by keeping the torp in a more horizontal position. These small wooden fins provided extremely little additional buoyancy. It was the flow of the water over the angled fins that brought the torp back towards the surface faster than it normally could. Adding buoyancy to the stern of a torpedo will make it angle down, not up. Pretty much a law of physics there.

Once water entry was made, the torp did not dive as deep due to the shallower anlge during water entry. As the torp began its run, it began to angle upwards. The Japanese wanted the torps hit at a depth of 5-10 feet and coupled with the greatly shortened runs, the fins did their job well.

BTW, one of the torps was seen by the USS Raleigh to porpoise several times and then sink at the end of its run near Ford Island. This torp was recovered and the fins examined. They found an up angle of 10 degrees.

Chez

[mdiehl]

Actually they did help change the water entry angle to a shallower one.

I've not seen any source that claims the fins flattened the angle entry in the air. If you have a source for that I'd be interested. For ex: http://www.combinedfleet.com/torps.htm

If you don't I'm going to assume that such was not their effect.

As make-shift canards go, they fins added to those torps are (a) very small relative to the size of the object that they're supposed to be controlling, (b) don't have much time to stabilize the torp in the air, and (c) are located on the wrong end of the torp if their only purpose was to change the pitch angle prior to water entry; vis the latter, increasing the drag on the back end of a torpedo would *elevate* the back, pitching the torp down, and *not* level out its flight in the air as you claim. Pretty much elementary physics there. To compensate for the increased drag the fins through a canard effect in the air those fins would have to be really huge. They're not. see:

http://www.j-aircraft.com/research/bill ... hmod21.pdf

Every source that I have seen indicates that the wooden fins were intended to do the following:

1. increase drag and buoyancy in the water to slow the torpedo down so that its depth control mechanisms could use its usual guidance vanes and gyro settings to get the torp to the desired shallow op depth.
2. detach/break off as the torpedo pitched up to operating depth

It was the flow of the water over the angled fins that brought the torp back towards the surface faster than it normally could.

Incorrect. It was the torpedo's standard fins, gyro, and depth setting devices that did these.

Adding buoyancy to the stern of a torpedo will make it angle down, not up.

Yes they will. The bouyancy and drag effect of the fins was primarily intended to slow the torp down anbd prevent it from bottoming out in the harbor before the torpedo's usual guidance system could take over.

Pretty much a law of physics there.

Of course, one has to correctly assess what the purpose of the device was in order to understand which laws of physics were most important to its operation.

[spence]

I have a picture (not very clear) of a PV-1 making a torpedo drop at Whidbey Island.  The caption reads:
 

To assure acceptable water-entry angles, aircraft torpedoes were were equipped with box-like auxiliary tail fins made from plywood, which broke away on impact.

 
On the facing page there's another photo showing "a plywood nose cap which improved the torpedo's flight ATTITUDE during free fall and cushioned water entry as it broke away."

[rtrapasso]

ORIGINAL: spence

I have a picture (not very clear) of a PV-1 making a torpedo drop at Whidbey Island. The caption reads:

To assure acceptable water-entry angles, aircraft torpedoes were were equipped with box-like auxiliary tail fins made from plywood, which broke away on impact.

On the facing page there's another photo showing "a plywood nose cap which improved the torpedo's flight ATTITUDE during free fall and cushioned water entry as it broke away."

EDITED:
The final standard modification of the Mark-13 air-dropped torpedo was a plywood ring snugged around the head of the torpedo. This decreased the air-speed of the torpedo by nearly 40%, reduced airborne oscillations, and acted as a shock absorber as noted above. This ring was known as the "pickle barrel".

There was also the shroud ring, aka the "ring tail" that fitted over the aft the torp. It was said to act as feathers on an arrow, and suppressed snags and underwater rolls. This appears to have been made of metal. (Source: Hellions of the Deep: The Development of American Torpedoes of World War II - Robert Gannon)

[ChezDaJez]

Every source that I have seen indicates that the wooden fins were intended to do the following:

1. increase drag and buoyancy in the water to slow the torpedo down so that its depth control mechanisms could use its usual guidance vanes and gyro settings to get the torp to the desired shallow op depth.
2. detach/break off as the torpedo pitched up to operating depth

You must not have seen many sources. The two sources you listed hardly discuss the subject. They contain a total of ONE sentence between them that mentions the function of the fins.

They were actually designed to break off on water entry and were used for air stabliization only. I should have been clearer on this point in my post. So they couldn't produce drag and buoyancy to slow the torpedo down as you described.

Upon water entry and the fins breaking off, the Type 91 torpedo's own control surfaces were designed to give an immediate up order on motor start up. This coupled with their superb antiroll fins allowed the torp to reach run depth and maintain direction much faster than comparable US torps. The antiroll fins also allowed them to use the entire warhead chamber for explosive charges hence the greater explosive effect. US torps required that an airchamber be left in the top of each torpedo section as part of their antiroll system. US torps also had a nasty habit of hooking on water entry because of poor air stabilization early war..

The best launch speed and height for the Type 91 was 140 knots and 15-20 meters. The wooden fins kept the torpedo from assuming too great a down angle and helped stabilize in the air. At this launch speed and height, with the wooden fins detaching on water entry, the torpedo would reach a maximum depth of 30-35 feet. The Type 91 Mod 1 (4-fin) could reach run depth within 380 yards while the Type 91 Mod 2 (8-fins) took over 800 yards to do so and the Mod 2 had the added disadvantage that it couldn't be loaded in a bombbay with fins attached. It was quickly dropped. BTW, the Type 91 was so robust that it could be launched from 1000 feet and 250 knots.

My source? US Naval Technical Mission to Japan report O-01-2 titled "Article 2: Japanese Aircraft Torpedoes" dated March 1946. Excellent data complete with indepth design, engineering diagrams and performance specifications from Japanese sources as well as US testing. One of the most definitive works on Japanese aerial torpedoes available.

Chez

[Hipper]

Is not the entire article pointing out that Level bombing was not very accurate against moving targets  (although it could be effective against stationary targets ) , torpedo bombing was better
 
and though not stated Dive bombing was best of all   (I think the Hermes was hit by half the bombs aimed at her ! )  

[mdiehl]

You must not have seen many sources.

You are, as usual, incorrect. The basic flaw in your logic is in assuming that the sources I've listed are the only ones I've seen. These were listed because they are widely accessible. The NTM-Japan documents are not widely accessible.

The two sources you listed hardly discuss the subject. They contain a total of ONE sentence between them that mentions the function of the fins.

Indeed they do not. The illustration however provides a very accurate rendition of the attachment on the torpedoes. Your claim that the wooden devices leveled out the flight of the torpedo in the air is unsubstantiated. Certainly they were not angled in any way to function other than as mere fins. They're not aerodynamic (that is, they're not shaped to produced lift or thrust, like a wing or a propellor). And they're on the wrong end of the torpedo to lift the nose: the increased drag aft would point the torpedo down, not up. Your assertion that they "leveled the torpedo in the air" is not supported by the evidence to hand. To believe your claim requires that basic laws of physics and aerodynamics be ignored.

Since there are many sources that claim that the purpose of the wooden fins was to slow the torpedo after it entered the water (thereby limiting the depth to which it would fall underwater) one would suppose that, for example, that you have a unique understanding of their purpose. Apparently the author contracted by Osprey, and Ballantine (Barker), and the guys at combinedfleet.com (who are collectively quite knowledgeable) have all been fooled.

[spence]

     A significant point made in the article, perhaps buried in the text in a way that it escaped many people's notice, was that the Ryujo repeatedly launched ineffective high level bombing attacks against Doorman's fleet rather than torpedo attacks and that it was because the Ryujo pilots were not practiced in that type of attack (plus their torpedos were poorly maintained).  I had noted in some other threads that torpedo attacks were not nearly as common IRL as they are in WitP (the article does seem to indicate that the Betty/Nells would have attacked Doorman with torpedos if they could have lifted off their airfields (soggy) with that loading though).  
 
I pretty sure that the TROM of Ryujo at Combined Fleet shows not one real torpedo attack launched by that ship in its lifetime.  Perhaps that explains its "bait" status at the Battle of the Eastern Solomons as opposed to operating in conjunction with the "real carriers", Shokaku and Zuikaku (as would almost assuredly happen in the game).     

[ChezDaJez]

ORIGINAL: mdiehl

You must not have seen many sources.

You are, as usual, incorrect. The basic flaw in your logic is in assuming that the sources I've listed are the only ones I've seen. These were listed because they are widely accessible. The NTM-Japan documents are not widely accessible.

The two sources you listed hardly discuss the subject. They contain a total of ONE sentence between them that mentions the function of the fins.

Indeed they do not. The illustration however provides a very accurate rendition of the attachment on the torpedoes. Your claim that the wooden devices leveled out the flight of the torpedo in the air is unsubstantiated. Certainly they were not angled in any way to function other than as mere fins. They're not aerodynamic (that is, they're not shaped to produced lift or thrust, like a wing or a propellor). And they're on the wrong end of the torpedo to lift the nose: the increased drag aft would point the torpedo down, not up. Your assertion that they "leveled the torpedo in the air" is not supported by the evidence to hand. To believe your claim requires that basic laws of physics and aerodynamics be ignored.

Since there are many sources that claim that the purpose of the wooden fins was to slow the torpedo after it entered the water (thereby limiting the depth to which it would fall underwater) one would suppose that, for example, that you have a unique understanding of their purpose. Apparently the author contracted by Osprey, and Ballantine (Barker), and the guys at combinedfleet.com (who are collectively quite knowledgeable) have all been fooled.

Well, then how about listing the other sources you have... if any. Doing a simple internet search and finding ONE sentence that refers to their function is hardly the way to present your erroneous point of view.

You listed combinedfleet.com as a source. I will quote what they said about the fins for your edification and education:

"The Japanese managed to deploy them in some pretty interesting places, most notably in Pearl Harbor, where the shallow depth of the water necessitated the modification of the existing torps with wooden fins so as to as make them dive less deeply upon entry into the water.
"

Nowhere in this sentence does it mention when the fins detach or how they provide for a reduced dive after water entry.

The other source you listed (j-aircraft-com) is a modeling site dedicated to accurately modeling Japanese aircraft. It mentions nothing as to the purpose of the fins. It only shows an artist conception of the top and side view of them.

This is hardly a definitive discussion of their design, purpose or performance.

So, let me provide that for you.

O-01-2 "Article 2- Japanese Aerial Torpedoes" page 25 and 26:

O. Anti-Roll Stabilizers

With the exception of the Type 91 mod 1, all Japanese aircraft torpedoes are fitted with small, gyro-controlled anti-roll flippers. This method was adopted in 1940 on the Type 91 Mod 2 torpedo and has been a permanent feature in all the later designs of aircraft torpedoes.

Before 1940, it was necessary to lower the torpedoe's center of gravity as much as possible to minimize rolling. This resulted in partial filling of the warheads with explosive charge in order to concentrate the weight below the axis of the torpedo. The introduction of anti-roll flippers, however made complete filling of warheads possible and gave this torpedo greater destructive capacity.

The torpedo is kept from rolling during air travel with the aid of wooden frames attached to the anti-roll flippers (see figure 7). If rolling occurs, the horizontal rudders, which have an "up rudder", act as steering rudders and cause the torpedo to "hook" sharply when it enters the water. The use of roll-stabilizers eliminated the "hook" and gave the torpedo excellent launching characteristics.

P. Air Stabilization

Japanese aircraft torpedoes are stabilized during air travel by means of wooden frames attached to the tail and to the anti-roll flippers on the sides of the afterbody. These frames break off when the torpedo enters the water.
Two types of aerial tail frames were used:

1. Box-Type Tail Frame: (See figure 5): This type was similar to the wooden stabilizers used on U.S. aircraft torpedoes. It was very large and could not be used when the torpedo was carried in the bomb bay of an aircraft. For this reason, and also because of the scarcity of large sheets of plywood, the Japanese planned to use the X-Type tail frames in the future. The box-type frame, however, gave better performance and was used occasionally on torpedoes which were slung under the fuselage of the aircraft.

The frame was tilted diagonally and slid over the tail fins then righted and slid back until the fins fitted into the grooves on the frame. Air pressure held the frame firmly against the fins during air travel.

2. X-Type Tail Frame (See figure 6): This type was slightly less efffective but cheaper and easier to produce. It was held in place by small wooden blocks which were bolted on after the frame was placed over the tail fins. The main advantage was in its adap[tability to all types of torpedo planes.

There were also two sizes of wooden frames for the anti-roll flippers (see figure 7). They were wing-shaped and consisted of two half sections bolted around the flippers. The larger size was used originally but a smaller type was finally adopted because of the restricted openings in bomb bays.

Bolded, underlined and italicized sections are mine.

BTW, these documents are available online and their links have been posted on many occasions by many forum members. They are an excellent source of information concerning Japanese equipment and form the basis for much of the latter day writings concerning Japanese capabilities. Anyone who wishes to intelligently discuss Japanese weapons needs to be familiar with them. I am.

Do a search on the forum or search the internet for the link. Beware that several sites list the available titles for ordering but only one (that I know of) that contains the actual documents.

Chez

[DuckofTindalos]

Here we go again...[8|]

[spence]

[ChezDaJez]

ORIGINAL: spence

     A significant point made in the article, perhaps buried in the text in a way that it escaped many people's notice, was that the Ryujo repeatedly launched ineffective high level bombing attacks against Doorman's fleet rather than torpedo attacks and that it was because the Ryujo pilots were not practiced in that type of attack (plus their torpedos were poorly maintained).  I had noted in some other threads that torpedo attacks were not nearly as common IRL as they are in WitP (the article does seem to indicate that the Betty/Nells would have attacked Doorman with torpedos if they could have lifted off their airfields (soggy) with that loading though).  

I pretty sure that the TROM of Ryujo at Combined Fleet shows not one real torpedo attack launched by that ship in its lifetime.  Perhaps that explains its "bait" status at the Battle of the Eastern Solomons as opposed to operating in conjunction with the "real carriers", Shokaku and Zuikaku (as would almost assuredly happen in the game).     

I agree with you, Spence. Aerial torpedo attacks by all types of torpedo aircraft are too numerous. That's one of the reasons I support having torps as a tracked production item. I would also want the ability to select between torps or bombs for the weapon loadout.

It's not just an issue with the Betty/Nell/Kate/etc either. The problem extends to the Allied side as well. With a few exceptions, the Avengers were primarily used as bombers during the latter half of the war and Beauforts also primarily carried bombs.

Chez

[ChezDaJez]

Can I have some that popcorn? [:D]

Actually, I think I'll back off. I've made my point.

Chez

[Big B]

ORIGINAL: ChezDaJez

ORIGINAL: spence

A significant point made in the article, perhaps buried in the text in a way that it escaped many people's notice, was that the Ryujo repeatedly launched ineffective high level bombing attacks against Doorman's fleet rather than torpedo attacks and that it was because the Ryujo pilots were not practiced in that type of attack (plus their torpedos were poorly maintained). I had noted in some other threads that torpedo attacks were not nearly as common IRL as they are in WitP (the article does seem to indicate that the Betty/Nells would have attacked Doorman with torpedos if they could have lifted off their airfields (soggy) with that loading though).

I pretty sure that the TROM of Ryujo at Combined Fleet shows not one real torpedo attack launched by that ship in its lifetime. Perhaps that explains its "bait" status at the Battle of the Eastern Solomons as opposed to operating in conjunction with the "real carriers", Shokaku and Zuikaku (as would almost assuredly happen in the game).

I agree with you, Spence. Aerial torpedo attacks by all types of torpedo aircraft are too numerous. That's one of the reasons I support having torps as a tracked production item. I would also want the ability to select between torps or bombs for the weapon loadout.

It's not just an issue with the Betty/Nell/Kate/etc either. The problem extends to the Allied side as well. With a few exceptions, the Avengers were primarily used as bombers during the latter half of the war and Beauforts also primarily carried bombs.

Chez

Interesting you should mention that. I have been reading the Enterprise's After Action Reports, and after Santa Cruz, the commanders were suggesting dropping VT squadrons down to 12 a/c and carrying more VF and VB.
The prime reason to their thinking was that torpedo bombers of both sides - though valuable - had proven too vulnerable to that point in the war. It seems that they were recommending their employment in the torpedo attack role was to be restricted to favorable circumstances - with more reliance on dive bombing for future CV vs CV action.

B

[ChezDaJez]

It seems that they were recommending their employment in the torpedo attack role was to be restricted to favorable circumstances - with more reliance on dive bombing for future CV vs CV action.

I think doing that gave them greater flexibility in tasking. A bomb-loaded Avenger can be retasked from a land to sea target and vice versa quite quickly. The Avenger actually made for a pretty good glide bomber. Certainly a better flying airplane that the Helldiver.

Chez

[mlees]

I pretty sure that the TROM of Ryujo at Combined Fleet shows not one real torpedo attack launched by that ship in its lifetime.

As a side note, I would not be surprised if the Ryujo's magazines were kinda cramped, limiting the number of large volume weapons carried.

A carrier's physical construction, in regards to the layout of the spaces, size of deck hatches (where ammo and such passes up from the mags), size, location, and capacity of aircraft elevators, and so on, limit that carriers ability to carry a usefull number of aircraft, as much, if not more, than the size of the hangarbay and flight deck. (How's that for a run-on sentence?)

[mdiehl]

Chez, the illustrations used on that modeling web page are from a Japanese ordnance manual, IIRC. They're not "artist renditions" unless by that you mean a "scale drawing made by a Japanese engineer to illustrate the assembly and configuration of the torpedo."

As to the rest. Exactly. A fin *does* indeed stabilize ordnance in the air. That's what fins do. They do not, however, provide lift on any part of air dropped ordnance. All they do is provide drag (which provides stability).

That is why this:

Japanese aircraft torpedoes are stabilized during air travel by means of wooden frames attached to the tail and to the anti-roll flippers on the sides of the afterbody. These frames break off when the torpedo enters the water

Specifically and glaringly does not state that the torpedo is kept level in the air by the attachment of the fins, as you have claimed they do. They *will* provide additional drag once the torpedo hits the water, at least for however long they remain attached. And that is what keeps them from plunging as deeply. In all cases, the drag from the fins will tend to result in the torpedo pitching downward, either in the air or in the water. It is the torpedo's steering and depth setting mechanisms that level out the torpedo, once it has entered the water.

If you wanted to keep the nose of a torpedo UP while in the air you would have to put a very large horizontal stabilizer on the ass end and it would have to be subtantialy canted to the angle of attack of the torpedo in the air. Or, alternatively, if keeping the nose up while in the air is desired you could use a smaller canard like feature somewhere near the nose of the torpedo.

Your argument that the torpedo is kept level while falling through the air is something that you seem to have read (erroneously) from the information to hand.

[spence]

A carrier's physical construction, in regards to the layout of the spaces, size of deck hatches (where ammo and such passes up from the mags), size, location, and capacity of aircraft elevators, and so on, limit that carriers ability to carry a usefull number of aircraft, as much, if not more, than the size of the hangarbay and flight deck. (How's that for a run-on sentence?)

Very nice!

[ChezDaJez]

Chez, the illustrations used on that modeling web page are from a Japanese ordnance manual, IIRC. They're not "artist renditions" unless by that you mean a "scale drawing made by a Japanese engineer to illustrate the assembly and configuration of the torpedo."

Those are not engineering drawings. However, I can provide you with those if you so desire. They are shown in the Nav Tech Intel article.

Your argument that the torpedo is kept level while falling through the air is something that you seem to have read (erroneously) from the information to hand.

Where in the following statements did I say they were used to keep the torp level in flight? The following is what I said:

Second, the wooden fins on the torpedoes were not for buoyancy. As they were only installed at the rear of the torpedo, they would tend to make the torp angle downwards if buoyancy was the issue. The fins were angled upwards to allow the torp a shallower water entry, dive and run.

Actually they did help change the water entry angle to a shallower one.

Once water entry was made, the torp did not dive as deep due to the shallower anlge during water entry.

The wooden fins kept the torpedo from assuming too great a down angle and helped stabilize in the air.

I never said they were to keep the torp level in the air and certainly not to give it a nose-up attitude. What I said was they were designed to stabilize it in the air and to reduce the angle at which the torp hit the water. The ideal entry angle when a shallow run was desired was around 10-15 degrees down angle. Anything less and the torp could skip on the surface, anything greater and it would stick in the shallow bottom.

Keep dancing but I think you need some new taps on those shoes. [>:]

Chez