A proper heir to the SBD

[EwenS]

I had to smile about the mention of only 2 limiting factors for carrier aircraft. There are many more.

First question which comes first chicken or egg? Carrier or aircraft?

During the interwar Treaty period a carrier had a Treaty limited minimum lifespan of 20 years (except the "experimental" ships). (By the way the USS Nimitz has passed its 47th birthday.) The replacement cycle for aircraft was maybe 5-7 years and accelerated in WW2. At a time when aircraft design was rapidly advancing. How far are you able to see into the future to build in some surplus capacity over 3-4 generations of aircraft? Even the Yorktown class designed in 1934 for an air group of 97 was seeing that reduced to 75-80 by 1941/2 due to increasing aircraft dimensions. The next carrier design, the Essex, had to grow from a standard displacement of 20,000 tons to 27,000 tons to accomodate that increase (OK there were some other factors at play as well).

So what factors need to be taken into account? (I'm not claiming this list is exhaustive)

Physical dimensions of aircraft - relates to lift size, hangar height, width etc. But it also relates to just how many aircraft you can spot for a strike on the limited flight deck space, especially if the wings need to be unfolded manually in advance. Standard practice for the USN was the "deck load strike" of about half the air group that took up about the after half of the flight deck, leaving the forward half for free take off runs (see below for the consequences of that). And carrier practice plays its part. For example how mauch of the airgroup do you want to keep in the hangar at any point in time.

For Britain with different operating criteria and environment hangar capacity was important. Bigger aircraft = less in the hangar. So the capacity of Illustrious fell from 36 when designed in 1936 (around the Swordfish / Skua) to 33 when she entered service in 1940 (around the Albacore / Fulmar)

Hangar height (generally 16ft) became an issue for the RN when it had to rely on US aircraft in WW2. It saw 8" cut from the wingtips of the F4U Corsair. In 1942 the RN accepted that its future carriers would need to match those of the USN for hangar height. So the Colossus class and Audacious class were designed with 17.5ft hangars from the outset to match the USN.

Width of the aircraft in the hangar is important relative to overall hangar width. Britain generally looked at c18ft folded. But in 1940 reduced the folded width in the Firebrand Spec to 13.5ft which the Seafire III/XV/XVII followed. That allowed 4 abreast stowage in an Illustrious / Implacable hangar rather than 3 abreast. Instantly more aircraft on bard but a designers nightmare to meet in attempting to meet everything else

The Japanese with so many fixed wing aircraft have particularly complicated hangar stowage arrangements to get every thing to fit.

Aircraft weight - this is actually pretty fundamental. It affects the strength of the flight and hangar decks and lifts (elevators) needed, not just to support a static aircraft (or maybe up to half the air group) but to take the impact of an aircraft landing (sometimes referred to as a controlled crash) somewhere near it max weight in an emergency. Stronger = heavier = potential problem when your carrier is weight limited by Treaty.

So in Britain the design limits were 10,500lb fully loaded until 1940 (e.g. Barracuda spec 1937) when they began to be relaxed (12,500lb Firebrand 1940) with 19,000lb for the Spearfish in 1943.

So for example the Implacables were built with stronger flight desks than the Illustrious class. That would have allowed operation of the Mosquito/Sea Mosquito. The Majestic class of light fleet carrier were built to handle heavier aircraft than the Colossus class. Post war conversions had to address that issue.

Take off and landing speeds - limits on these affect the design (see the flaps on the likes of the Barracuda & Firefly and variable incidence wing on the Supermarine Type 322 Dumbo to meet the RN limits) but are necessary to ensure an aircraft can get on and off the fligt deck safely.

Take of run required - bigger aircraft generally = longer take off run. In the 1930s and early in WW2 the USN rarely used its carrier catapults, where they were fitted (not all the carriers had them) because it slowed the launch rate (from roughly every 10 secs to 30 secs). So more time assembling the strike force = shorter range for that strike. By 1945 due to increasing aircraft weights and more aircraft having to be handled, catapults were being used in about 40% of take offs (generally the early launches in the strike to maximise the weight they could carry in what would otherwise have been a shorter take off run).

Capacity of the catapults to launch the required weight- These were steadily increased over time either by introducing new models or uprating existing ones. The alternative is for carriers to sail faster but that burns up huge amounts of fuel for them and the Task Group that they are part of = supply problem.

The British BH.III accelerator first fitted in Illustrious in 1940 was rated at 11,000lb at 66 knots (trolley lauch). It was steadily upgraded during the war to 16,000lb at 66 knots (trolley) or 20,000lb at 56 knots (tail down launch).

The type of catapult launch also makes a difference as the necessary equipment has to be built into the aircraft. Some are heavier than others. And note the Japanese carriers didnt employ catapults.

Capacity of the arrester gear to handle the returning aircraft - again there was an uprating during WW2.
Aircraft fuel capacity - bigger aircraft = bigger thirstier engines. Or do you trade air group size? Or do you accept the need to replenish more often?

A Yorktown was designed with 178,000 US gals of Avgas. The Essex increased that to 232,000 US gals. Remember both were designed around a similar sized air group. And wartime experience showed that petol stowage needed greater protection so in the later Essex class it reduced to 212,000 US gals. And it can't be stored in the ships' main fuel tanks (unlike jet fuel). It needs separate protected stowage due to its volatile nature.

Aircraft lifts / elevators
The figure quoted for the Esssex class elevator was for the third deck edge lift. The two main ones were 48x44ft stressed to lift 28,000lb, intended to lift two aircraft at a time (it was written into the Design Spec) assuming all the hydraulic pumps worked, otherwise it was 14,000lb and a single aircraft.

Ark Royal III had two lifts 45x22ft and a third 45x25ft and the Illustrious class were 45x22ft to lift 14,000lb to lift a single aircraft. Indomitable & the Imlacables had the size of the forward lift increased to 45x33ft in order to handle the fixed wing aircraft expected to enter service.

The T shaped lifts of earlier British carriers actually represent a different and much slower pace of operations in the 1920s, where, without a crash barrier (the first in the RN was fitted in Ark Royal in 1938), an aircraft had to be cleared from the flight deck quickly to allow another to land. So a T shaped lift allowed it to be struck down into the hangar and folded once it got there. So

Eagle:- forward (T shaped) 46x47ft; aft (rectangular) 46x33ft
Hermes, C & G:- 46x47ft (T shaped)
Furious:- 34x45ft (T shaped)

For other ships
Yorktown class & Wasp - 48x44ft plus a rudimentary side lift affair in the last named
Ranger - 52ftx41ft
Lexingtons - 29x35ft

Akagi - 38.5x42.66ft & 42x29.5ft
Kaga - 37.66x39.5ft & 35x52ft
Soryu - 16x11.5m; 12x11.5m; 10x11.5m
Hiryu - 16x13m; 12x13m, 13x11.8m
Shokaku class - 13x16m; 13x12m & 13x12m
Taiho - 14x13.6m & 14x14m

But there comes a point when nations made a decision that new aircraft could just not be designed to fit existing carriers. So for the RN the 1943 designs such as the Fairey Spearfish was specified not to have a length greater than 45.5ft and a height stowed of 17ft. Same with the Short Sturgeon. These were never intended to operate from the Illustrious/Implacable/Colossus/Majestic classes but only from the newer Audacious & Centaur classes.

Same with the Japanese. The Aichi B7A Ryusei, aka Grace, designed to a 1941 spec was intended to operate from a new generation of carriers and so the length limit (then 11m = 36ft) was relaxed. The first of those ships was the Taiho laid down in July 1941 which was intended to be followed by another 7 modified ships.

Postwar the US increased the size of the remaining centreline lift on the Essex class and moved others to the side as well as enlarging them.

Too many people look at the Essex class and their long lives and ability to handle jets off Vietnam without understanding the huge changes that were made to them to allow that to happen. Many of those changes are not generally visible. So flight decks were strengthened. Would anyone have envisaged in 1940 that by 1960 they would be handling the Douglas A-3 Skywarrior? Bulged hulls for stability and more fuel, more jet fuel capacity, larger stronger elevators. Those vast changes were only possible because they were built as open hangar ships with the hangar as superstructure. Britain & Japan chose closed hangar ships with the flight deck as the strength deck making modernisation more difficult (see Victorious).

The pros & cons can be summarised thus at least so far as the RN was concerned (courtesy of D K Brown):-

Closed hangar gives a lighter & stronger hull
Fire protection is better in a closed hangar ship as it is contained and unlikely to spread to the rest of the ship. On the other hand it becomes an oven in the tropics.
Space is generally greater in an open hangar design unless you go to a double closed hangar
Aircraft engines can be run up in an open hangar design
Side lifts (elevators) are far easier to install on open hangar ships


But by the time the US reached the Forrestal class they had to move to a closed hangar for added strength and blast protection from nuclear blast..

Incidentally the spec for the SB2C stated "minimum weight and size are desirable, but consideration will be given to designs of of 9,000 to 9,500 pounds (in the 500lb bomb condition with sufficient fuel for 1,000 miles range at economical speed), if increased performance sufficient to warrant such weight increase proves attainable." But the weight exceeded that almost from the start.

Folded a Fulmar had the following dimensions (l x w x h) - 40ft 3in x 17ft 10in x 10ft 8in. Unfolded the span went up to 46ft 4.5in.
Swordfish folded - 36ft 1in x 17ft 3in x 12ft 10.5in
Albacore folded - 39ft 11.75 x 17ft 9in x 12ft 6in
Barracuda folded - 39ft 9in x 17ft 8in x 14ft 11in

 

[Shortround6]

See the other 1-seaters that gave birth to the 2-seaters during or just after the ww2: Spitfire, Hurricane, P-40, P-51, Bf 109, Fw 190, Yak-1/-7 - neither of these grew in length. Even the G.59 was just 4 in longer than the predecessor, G.55. Some of them lost fuel tankage (Bf 109, P-40, Spitfire), some have not. Note that all of these are much smaller A/C than the F4U or F6F.
Both F4U and F6F have had far more free volume to install extra fuel tanks in the wing than these aircraft, as well as leeway in juggling the CoG-related items, like oxygen bottles, batteries, etc.

Not quite the same thing.
Fighter trainers had different requirements for cockpit space.

An SBD or successor being designed in 1939-41 needs a lot more space for the rear crewman who performs several functions, like radio operator. Long range radio operator. Which requires more than just twiddling knobs and a Morse code key balanced on his knee. We are back to the progress made with radios during the war. For instance two seat Mustangs had the original military spec radios replaced by newer, lighter, more compact equipment and that was before transistors showed up.
Remember the SBD stands for Scout Bomber Douglas. If the proposed plane cannot perform the scout function, as seen by the US Navy and not a different air force, it won't get a contract.
Douglas had this thing flying in April of 1943

They actually built 28-30 (in 1944-45) before it was canceled in 1945 in favor of the Skyraider.
I am NOT proposing this for Tomo's requirement.
Simply pointing out that the rear crewman requirement lasted for quite a while and shoehorning a 2nd man into a pretzel like configuration behind the pilot for missions of 6-8 hours was not going to be looked on with favor. The rear seater was also supposed to assist the pilot in "observing" and to do that he needed to be able to see the surface (land or water), at least to some extent.
2nd crewman was also expected to use the rear fire guns. Granted the pictured aircraft took that a bit far. Same flexible firepower as an A-26
But in more basic aircraft the gunner was going to have to use his whole upper body (and legs) to maneuver/aim the gun/s.

I would note that the old SBD had one advantage for carrier operations that is largely overlooked and may have been overlooked at the time.
It sipped fuel compared to some of the later aircraft. Granted a lot of the Navy planes figured their ranges at 160-180mph speeds with their R-2800s running a bit above idle but after 4-5 days of flight operations the SBDs might have made a smaller dent in the carrier fuel supply.

 

[Wild_Bill_Kelso]

I had to smile about the mention of only 2 limiting factors for carrier aircraft. There are many more.

First question which comes first chicken or egg? Carrier or aircraft?

During the interwar Treaty period a carrier had a Treaty limited minimum lifespan of 20 years (except the "experimental" ships). (By the way the USS Nimitz has passed its 47th birthday.) The replacement cycle for aircraft was maybe 5-7 years and accelerated in WW2. At a time when aircraft design was rapidly advancing. How far are you able to see into the future to build in some surplus capacity over 3-4 generations of aircraft? Even the Yorktown class designed in 1934 for an air group of 97 was seeing that reduced to 75-80 by 1941/2 due to increasing aircraft dimensions. The next carrier design, the Essex, had to grow from a standard displacement of 20,000 tons to 27,000 tons to accomodate that increase (OK there were some other factors at play as well).

So what factors need to be taken into account? (I'm not claiming this list is exhaustive)

Physical dimensions of aircraft - relates to lift size, hangar height, width etc. But it also relates to just how many aircraft you can spot for a strike on the limited flight deck space, especially if the wings need to be unfolded manually in advance. Standard practice for the USN was the "deck load strike" of about half the air group that took up about the after half of the flight deck, leaving the forward half for free take off runs (see below for the consequences of that). And carrier practice plays its part. For example how mauch of the airgroup do you want to keep in the hangar at any point in time.

For Britain with different operating criteria and environment hangar capacity was important. Bigger aircraft = less in the hangar. So the capacity of Illustrious fell from 36 when designed in 1936 (around the Swordfish / Skua) to 33 when she entered service in 1940 (around the Albacore / Fulmar)

Hangar height (generally 16ft) became an issue for the RN when it had to rely on US aircraft in WW2. It saw 8" cut from the wingtips of the F4U Corsair. In 1942 the RN accepted that its future carriers would need to match those of the USN for hangar height. So the Colossus class and Audacious class were designed with 17.5ft hangars from the outset to match the USN.

Width of the aircraft in the hangar is important relative to overall hangar width. Britain generally looked at c18ft folded. But in 1940 reduced the folded width in the Firebrand Spec to 13.5ft which the Seafire III/XV/XVII followed. That allowed 4 abreast stowage in an Illustrious / Implacable hangar rather than 3 abreast. Instantly more aircraft on bard but a designers nightmare to meet in attempting to meet everything else

The Japanese with so many fixed wing aircraft have particularly complicated hangar stowage arrangements to get every thing to fit.

Aircraft weight - this is actually pretty fundamental. It affects the strength of the flight and hangar decks and lifts (elevators) needed, not just to support a static aircraft (or maybe up to half the air group) but to take the impact of an aircraft landing (sometimes referred to as a controlled crash) somewhere near it max weight in an emergency. Stronger = heavier = potential problem when your carrier is weight limited by Treaty.

So in Britain the design limits were 10,500lb fully loaded until 1940 (e.g. Barracuda spec 1937) when they began to be relaxed (12,500lb Firebrand 1940) with 19,000lb for the Spearfish in 1943.

So for example the Implacables were built with stronger flight desks than the Illustrious class. That would have allowed operation of the Mosquito/Sea Mosquito. The Majestic class of light fleet carrier were built to handle heavier aircraft than the Colossus class. Post war conversions had to address that issue.

Take off and landing speeds - limits on these affect the design (see the flaps on the likes of the Barracuda & Firefly and variable incidence wing on the Supermarine Type 322 Dumbo to meet the RN limits) but are necessary to ensure an aircraft can get on and off the fligt deck safely.

Take of run required - bigger aircraft generally = longer take off run. In the 1930s and early in WW2 the USN rarely used its carrier catapults, where they were fitted (not all the carriers had them) because it slowed the launch rate (from roughly every 10 secs to 30 secs). So more time assembling the strike force = shorter range for that strike. By 1945 due to increasing aircraft weights and more aircraft having to be handled, catapults were being used in about 40% of take offs (generally the early launches in the strike to maximise the weight they could carry in what would otherwise have been a shorter take off run).

Capacity of the catapults to launch the required weight- These were steadily increased over time either by introducing new models or uprating existing ones. The alternative is for carriers to sail faster but that burns up huge amounts of fuel for them and the Task Group that they are part of = supply problem.

The British BH.III accelerator first fitted in Illustrious in 1940 was rated at 11,000lb at 66 knots (trolley lauch). It was steadily upgraded during the war to 16,000lb at 66 knots (trolley) or 20,000lb at 56 knots (tail down launch).

The type of catapult launch also makes a difference as the necessary equipment has to be built into the aircraft. Some are heavier than others. And note the Japanese carriers didnt employ catapults.

Capacity of the arrester gear to handle the returning aircraft - again there was an uprating during WW2.
Aircraft fuel capacity - bigger aircraft = bigger thirstier engines. Or do you trade air group size? Or do you accept the need to replenish more often?

A Yorktown was designed with 178,000 US gals of Avgas. The Essex increased that to 232,000 US gals. Remember both were designed around a similar sized air group. And wartime experience showed that petol stowage needed greater protection so in the later Essex class it reduced to 212,000 US gals. And it can't be stored in the ships' main fuel tanks (unlike jet fuel). It needs separate protected stowage due to its volatile nature.

Aircraft lifts / elevators
The figure quoted for the Esssex class elevator was for the third deck edge lift. The two main ones were 48x44ft stressed to lift 28,000lb, intended to lift two aircraft at a time (it was written into the Design Spec) assuming all the hydraulic pumps worked, otherwise it was 14,000lb and a single aircraft.

Ark Royal III had two lifts 45x22ft and a third 45x25ft and the Illustrious class were 45x22ft to lift 14,000lb to lift a single aircraft. Indomitable & the Imlacables had the size of the forward lift increased to 45x33ft in order to handle the fixed wing aircraft expected to enter service.

The T shaped lifts of earlier British carriers actually represent a different and much slower pace of operations in the 1920s, where, without a crash barrier (the first in the RN was fitted in Ark Royal in 1938), an aircraft had to be cleared from the flight deck quickly to allow another to land. So a T shaped lift allowed it to be struck down into the hangar and folded once it got there. So

Eagle:- forward (T shaped) 46x47ft; aft (rectangular) 46x33ft
Hermes, C & G:- 46x47ft (T shaped)
Furious:- 34x45ft (T shaped)

For other ships
Yorktown class & Wasp - 48x44ft plus a rudimentary side lift affair in the last named
Ranger - 52ftx41ft
Lexingtons - 29x35ft

Akagi - 38.5x42.66ft & 42x29.5ft
Kaga - 37.66x39.5ft & 35x52ft
Soryu - 16x11.5m; 12x11.5m; 10x11.5m
Hiryu - 16x13m; 12x13m, 13x11.8m
Shokaku class - 13x16m; 13x12m & 13x12m
Taiho - 14x13.6m & 14x14m

But there comes a point when nations made a decision that new aircraft could just not be designed to fit existing carriers. So for the RN the 1943 designs such as the Fairey Spearfish was specified not to have a length greater than 45.5ft and a height stowed of 17ft. Same with the Short Sturgeon. These were never intended to operate from the Illustrious/Implacable/Colossus/Majestic classes but only from the newer Audacious & Centaur classes.

Same with the Japanese. The Aichi B7A Ryusei, aka Grace, designed to a 1941 spec was intended to operate from a new generation of carriers and so the length limit (then 11m = 36ft) was relaxed. The first of those ships was the Taiho laid down in July 1941 which was intended to be followed by another 7 modified ships.

Postwar the US increased the size of the remaining centreline lift on the Essex class and moved others to the side as well as enlarging them.

Too many people look at the Essex class and their long lives and ability to handle jets off Vietnam without understanding the huge changes that were made to them to allow that to happen. Many of those changes are not generally visible. So flight decks were strengthened. Would anyone have envisaged in 1940 that by 1960 they would be handling the Douglas A-3 Skywarrior? Bulged hulls for stability and more fuel, more jet fuel capacity, larger stronger elevators. Those vast changes were only possible because they were built as open hangar ships with the hangar as superstructure. Britain & Japan chose closed hangar ships with the flight deck as the strength deck making modernisation more difficult (see Victorious).

The pros & cons can be summarised thus at least so far as the RN was concerned (courtesy of D K Brown):-

Closed hangar gives a lighter & stronger hull
Fire protection is better in a closed hangar ship as it is contained and unlikely to spread to the rest of the ship. On the other hand it becomes an oven in the tropics.
Space is generally greater in an open hangar design unless you go to a double closed hangar
Aircraft engines can be run up in an open hangar design
Side lifts (elevators) are far easier to install on open hangar ships


But by the time the US reached the Forrestal class they had to move to a closed hangar for added strength and blast protection from nuclear blast..

Incidentally the spec for the SB2C stated "minimum weight and size are desirable, but consideration will be given to designs of of 9,000 to 9,500 pounds (in the 500lb bomb condition with sufficient fuel for 1,000 miles range at economical speed), if increased performance sufficient to warrant such weight increase proves attainable." But the weight exceeded that almost from the start.

Folded a Fulmar had the following dimensions (l x w x h) - 40ft 3in x 17ft 10in x 10ft 8in. Unfolded the span went up to 46ft 4.5in.
Swordfish folded - 36ft 1in x 17ft 3in x 12ft 10.5in
Albacore folded - 39ft 11.75 x 17ft 9in x 12ft 6in
Barracuda folded - 39ft 9in x 17ft 8in x 14ft 11in

Great post! Thanks for digging up all that data.

You make a lot of very good points here. The reasons I wasn't focusing so much on weight or overall size was largely due to the success of the TBF bomber, which seems to have been able to operate both from US 'jeep' carriers and from many of the RN carriers as well, in spite of it's huge size (height 16'5", length 40') and considerable weight (15k lb / 7k kg loaded per Wikipedia). This for me is an aircraft that kind of 'flies under the radar' as a design, and one I only reluctantly have come to appreciate.

It's not beautiful or graceful to behold. It's not a dive bomber, it is not that fast at about 270 mph, carried a moderate bomb load, has a 'decent' but not fantastic range as carrier planes go... and it's literally the size of a bus. But it could fly from almost every Allied carrier, in the Pacific seems to have a pretty good survival rate in combat and a decent level of strike accuracy. In spite of it's size and weight, with flaps etc. it seems to have had pretty easy flying traits and good carrier ops flight characteristics. Only the crap US torpedoes prevented it from being as important to the war effort as the SBD. Ultimately over the long haul it may have actualy been more damaging to the enemy both in the air to surface, air to land, and ASW role in terms of tonnage sunk. And it seems to have been of some use to the British as well.

I don't know what the dimensions of the TBF were with wings folded but it's probably somewhere around 20' x 40'. I'm sure it required the catapult to launch from those jeep carriers.

To make a proper dive bomber of course, seems like a taller order. Especially a nice fast one

 

[Wild_Bill_Kelso]

Not quite the same thing.
Fighter trainers had different requirements for cockpit space.

An SBD or successor being designed in 1939-41 needs a lot more space for the rear crewman who performs several functions, like radio operator. Long range radio operator. Which requires more than just twiddling knobs and a Morse code key balanced on his knee. We are back to the progress made with radios during the war. For instance two seat Mustangs had the original military spec radios replaced by newer, lighter, more compact equipment and that was before transistors showed up.
Remember the SBD stands for Scout Bomber Douglas. If the proposed plane cannot perform the scout function, as seen by the US Navy and not a different air force, it won't get a contract.
Douglas had this thing flying in April of 1943
View attachment 699060
They actually built 28-30 (in 1944-45) before it was canceled in 1945 in favor of the Skyraider.
I am NOT proposing this for Tomo's requirement.
Simply pointing out that the rear crewman requirement lasted for quite a while and shoehorning a 2nd man into a pretzel like configuration behind the pilot for missions of 6-8 hours was not going to be looked on with favor. The rear seater was also supposed to assist the pilot in "observing" and to do that he needed to be able to see the surface (land or water), at least to some extent.
2nd crewman was also expected to use the rear fire guns. Granted the pictured aircraft took that a bit far. Same flexible firepower as an A-26
But in more basic aircraft the gunner was going to have to use his whole upper body (and legs) to maneuver/aim the gun/s.

I would note that the old SBD had one advantage for carrier operations that is largely overlooked and may have been overlooked at the time.
It sipped fuel compared to some of the later aircraft. Granted a lot of the Navy planes figured their ranges at 160-180mph speeds with their R-2800s running a bit above idle but after 4-5 days of flight operations the SBDs might have made a smaller dent in the carrier fuel supply.

Yeah you beat me to it! I think a two seat trainer is one thing, putting another combat crewman means more armor, more space for radios and other gear, probably a gun or two (which means also gun mount and ammunition), and overall the need for a stretch. This is the main design problem with the SB2C IMO, it needed to be about three feet longer.

 

[Shortround6]

Everything is connected to everything else.
TBF had a bigger wing than the A-20. Use one R-2600 instead of two. The wing was bigger than an F7F Tigercat.
You need a big wing to give you the lift needed to get off the deck (reason the F4F used the same wing area as a Hurricane and almost 50% bigger than a 109).
However big wings mean more weight and a lot more drag. Trick flaps only get you so far, especially in 1940-41 when they are still being figured out.
Some credit it due to the Navy for asking for a 70mph stalling speed while carrying a torpedo and less than half fuel. Among a lot of other things.
Credit due to Grumman for delivering on most of what was wanted.
Missed on the 300mph speed and the not less than 30,000ft service ceiling (why?).
Take-Off distance was required to be 325ft with a 25kt wind over deck while carrying the torpedo and enough fuel for 1000 miles.
Speed and ceiling were sacrifice for deck performance and ceiling. Or perhaps ceiling was sacrificed for self sealing fuel tanks and armor?
B7A was speedy, it couldn't operate off most of the remaining Japanese carrier decks even if they had good pilots.
Which was the better carrier plane?

Edit: Grumman wanted to use a two stage R-2600 promised in Aug 1939 but Wright failed to deliver.
Grumman got a contract for 285 TBF-1s with R-2600-8s and one XTBF-2 with a R-2600-10 with two stage engine.
They were trying for the 300mph speed and the 30,000ft ceiling

 

[EwenS]

Great post! Thanks for digging up all that data.

You make a lot of very good points here. The reasons I wasn't focusing so much on weight or overall size was largely due to the success of the TBF bomber, which seems to have been able to operate both from US 'jeep' carriers and from many of the RN carriers as well, in spite of it's huge size (height 16'5", length 40') and considerable weight (15k lb / 7k kg loaded per Wikipedia). This for me is an aircraft that kind of 'flies under the radar' as a design, and one I only reluctantly have come to appreciate.

It's not beautiful or graceful to behold. It's not a dive bomber, it is not that fast at about 270 mph, carried a moderate bomb load, has a 'decent' but not fantastic range as carrier planes go... and it's literally the size of a bus. But it could fly from almost every Allied carrier, in the Pacific seems to have a pretty good survival rate in combat and a decent level of strike accuracy. In spite of it's size and weight, with flaps etc. it seems to have had pretty easy flying traits and good carrier ops flight characteristics. Only the crap US torpedoes prevented it from being as important to the war effort as the SBD. Ultimately over the long haul it may have actualy been more damaging to the enemy both in the air to surface, air to land, and ASW role in terms of tonnage sunk. And it seems to have been of some use to the British as well.

I don't know what the dimensions of the TBF were with wings folded but it's probably somewhere around 20' x 40'. I'm sure it required the catapult to launch from those jeep carriers.

To make a proper dive bomber of course, seems like a taller order. Especially a nice fast one

TBF/TBM Avenger folded span = 19ft
SB2C = 22ft 6.5in

As for getting an Avenger off an escort carrier deck, free take offs were the norm in the RN subject to wind over the deck (natural or augmented by ship speed say 16-18 knots) and load to be carried. IO operations were a bit more difficult calling for the catapult.

The US aircraft are coming in around the 16,000lb mark. SB2C 16,800lb. TBM 16,400lb. Barracuda was a bit lighter but was from a slightly earlier design era at 14,250lb MTOW

Avenger taking off unassisted from HMS Tracker 1944 in the Atlantic

 

[Wild_Bill_Kelso]

Everything is connected to everything else.
TBF had a bigger wing than the A-20. Use one R-2600 instead of two. The wing was bigger than an F7F Tigercat.
You need a big wing to give you the lift needed to get off the deck (reason the F4F used the same wing area as a Hurricane and almost 50% bigger than a 109).
However big wings mean more weight and a lot more drag. Trick flaps only get you so far, especially in 1940-41 when they are still being figured out.
Some credit it due to the Navy for asking for a 70mph stalling speed while carrying a torpedo and less than half fuel. Among a lot of other things.
Credit due to Grumman for delivering on most of what was wanted.
Missed on the 300mph speed and the not less than 30,000ft service ceiling (why?).
Take-Off distance was required to be 325ft with a 25kt wind over deck while carrying the torpedo and enough fuel for 1000 miles.
Speed and ceiling were sacrifice for deck performance and ceiling. Or perhaps ceiling was sacrificed for self sealing fuel tanks and armor?
B7A was speedy, it couldn't operate off most of the remaining Japanese carrier decks even if they had good pilots.
Which was the better carrier plane?

Edit: Grumman wanted to use a two stage R-2600 promised in Aug 1939 but Wright failed to deliver.
Grumman got a contract for 285 TBF-1s with R-2600-8s and one XTBF-2 with a R-2600-10 with two stage engine.
They were trying for the 300mph speed and the 30,000ft ceiling

Yeah that's a fair question - to me the TBF is kind of the 'ugly duckling' that worked, which is something you could say for a lot of WW2 era Grumman aircraft.

 

[Wild_Bill_Kelso]

So speaking of ugly ducklings, the Vultee Vengeance, especially the A-35 version which dispensed with the strange flying attitude of the original (at the expense of vertical dive bombing) seems to be the closest thing to an actual possible replacement for the SBD that was flying and operational in time, and was a viable combat aircraft. I was trying to figure out if it had folding wings or not and I guess it didn't. With folding wings it's viable as a Navy plane, without it's too big (and thwould explain why it was never used on carriers).

But it is pretty similar to the TBF in size seems to have done better in combat as used by land units (RAF, IAF and briefly RAAF) than the Army version of the SBD (A-24) did operationally, especially vis a vis losses. This may be attributable to the superior speed and the R-2600 engine. The A-24 seemed to get slaughtered every time they tried to use them operationally.

Something like a Vengeance with folding wings may have been a sufficient (if not ideal) replacement for the SBD. Or just an SB2C either 3 feet longer or designed by another firm.

Once the various problems were (mostly) worked out for the SB2C it actually seems to have done fairly well, it was fast and well armed. Though I am sure a better design could have been made. I think Curtis was having major organizational problems which contributed to the issues it had.

 

[Shortround6]

I think Curtis was having major organizational problems which contributed to the issues it had.

Possibly.
Curtiss was in a weird position. It was the largest aircraft company in the US. It had perhaps the most expertise (?). It was trying to maintain it's position.
It bid on a lot of projects (of all types) and the government was often a bit stuck. Go with the Curtiss bid (and suspect their engineering staff was getting a bit thin) or give to contract to Johnny Come-Lately or Irving Upstart. Some of those did quite well, others not so well (Vultee). Many of these companies had to expand production capacity many times over prewar size. Republic/Seversky had only built about 100 planes total when they got the contract for the P-47 (the later P-43 contracts were to keep the work force together and pay for more factory space).

I have tried counting it up before but Curtiss was involved with 12-15 different projects during the war. From trainers to fighters, from transports to floatplanes.
Some of them were world class turkeys.

 

[Wild_Bill_Kelso]

Possibly.
Curtiss was in a weird position. It was the largest aircraft company in the US. It had perhaps the most expertise (?). It was trying to maintain it's position.
It bid on a lot of projects (of all types) and the government was often a bit stuck. Go with the Curtiss bid (and suspect their engineering staff was getting a bit thin) or give to contract to Johnny Come-Lately or Irving Upstart. Some of those did quite well, others not so well (Vultee). Many of these companies had to expand production capacity many times over prewar size. Republic/Seversky had only built about 100 planes total when they got the contract for the P-47 (the later P-43 contracts were to keep the work force together and pay for more factory space).

I have tried counting it up before but Curtiss was involved with 12-15 different projects during the war. From trainers to fighters, from transports to floatplanes.
Some of them were world class turkeys.

I think Vultee did alright, the big disaster was Brewster, especially with the Buccaneer and I think they had to cancel the F3A version of the Corsair.

Vultee made the Valiant which was was pretty successful trainer (over 10,000 produced), the Vanguard wasn't that bad really, and the Vengeance actually did fairly well in combat as we have discussed. I think dive bombers just went out of fashion nearly as fast as they went into. Then they merged with Consolidated to become Convair which did alright (especially with the Stinson 108).

Curtiss started the war strong with the P-36 and P-40, maybe attributable to Don Berlin in large part (before he left), but then definitely spread themselves too thin with zany or poorly designed projects (things like the P-55, and all the ostensible P-40 successors), and I don't know if that was fully the fault of the company or the specs they got, the bribery scandal and production issues that they seem to have been sneaking by War dept doesn't look to good for them. Some of those they produced just turned out terrible (SOC-3, C-76) and others ultimately functional but problematic (C-46, SB2C)

Maybe the most successful 'new' companies besides Seversky / Republic were North American and Lockheed.

 

[VBF-13]

A 2-seat F4U and F6F do not need to be any longer than their 1-seat brethren.

Why do you need a rear on those, anyway, they're not going anywhere. Especially the F6, it's a bomber-fighter by design. And I'm sure the F4U could dive bomb, too, although I'm less familiar with those training logs.

EDIT TO ADD: And while they're in their 70 degree dives, nobody is chasing them, shooting them down, they're going too fast. The ships' guns are all they're up against. And then they're coming up fighters.

 

[EwenS]

There was a thread on here about the F4U Corsair as a dive bomber

Corsair as Dive Bomber?

I saw this mentioned on a different forum - the Corsair's landing gear extended as dive brakes? Was this really a viable option? And was this intended by design, or battlefield improvisation? Was it commonly done? F4U using gear as dive brakes

ww2aircraft.net

Note the use of the undercarriage as a dive brake.

 

[EwenS]

When you look back at the development of the various dive bomber projects of this period the only one that seems to have been relatively trouble free was the Douglas SBD Dauntless. Look at the others:-

Curtiss SB2C Helldiver / A-25 Shrike - initial structural weakness, handling issues, directional instability, bad stall characteristics. All required sorted before the aircraft finally reached the front line.

Brewster SB2A Buccaneer - significant changes had to be made to the design, but the real problems arose from setting up a new factory to build it, bad management at Brewster and significant labour problems leading to awful quality control. The whole project was eventually cancelled with the aircraft only of use for second line duties.

Vultee Vengeance - its development was not trouble free. Handling problems, dive brake issues etc, not to mention a strike in July 1941, which all led to delays in the programme. Then the problem that because Northrop were brought in as a second source while development was still going on there effectively became two versions of the aircraft. Northrop actually had the first production aircraft. They became Vengeance I/IA. Vultee built aircraft with modifications became Vengeance II. These were all A-31 models. Unfortunately not everything was interchangeable.

Then war with Japan broke out. The USAAF took over a chunk of the A-31 production and demanded its own modifications, and the A-35 version was born. With production lasting until mid-1944 despite no one wanting the aircraft for some time before that.

Vultee itself was not without its own management and labour problems. Some of these were no doubt caused by expanding from its Downey, California base, to a new plant in Nashville Tennessee in 1941 to build the Vengeance. Unlike Brewster, Vultee was able to overcome these issues. In 1944 it retooled and began to produce P-38L aircraft in 1945 but only produced about 115 before the end of WW2 saw the order cancelled.

All the aviation manufacturers, big and small, had to expand rapidly from 1940 to cope with vastly increased orders from France, Britain and then the USAAF/USN. New plants dispersed across the country. New workforces requiring relocated and trained. And the accompanying rapid expansion of management to control it all. It is hardly surprising some did better than others.

 

[elbmc1969]

That last line makes me wonder. The SDB probably didn't have room or weight allowance for a proper bomb bay but what about a semi-recessed bomb bay where half the bomb was inside the aircraft to decrease the amount of drag out in the slipstream? Similar to how some modern fighters have recessed missile hardpoints to reduce drag?

The much-maligned Skua used this approach. Problem is, you have to set the dimensions of the bomb when you design the fuselage. The Skua ended up stuck with an utterly inadequate 500 lb bomb. If you design for a 1000 lb bomb and then you want to load a 500 lb bomb because you need more range, or target type, you end up with open space behind the leading edge, around the sides, etc. The front lip, especially, can produce a lot of turbulence, and you end up with a great deal of drag.

You may also simply want a longer bomb at some point, or fatter (demolition bombs?), etc., etc.

One of those things that's obviously a great idea, until it isn't.

The great benefit of the TBM's bomb bay was that you could carry four 500 lb bombs without multiple pylons, interference drag, etc.

 

[Shortround6]

Just got a book on the SB2C.
The requirement was issued on 29th of June, 1938. Six manufacturers were invited to submit proposals, only two did using the R-2600 engine, Curtiss and Brewster. Things start going down hill
Stuff that was wanted included rubber de-icing equipment, and rebreather oxygen equipment. Navy also wanted the double split flaps and high capacity air brakes which starts to restrict Curtiss choices. Already mentioned buy others was the requirement to fit two planes on one elevator.

"Consideration would be given to designs weight 9000 to 9500lbs while carrying a 500lb bomb and enough fuel for 1000 miles at economical speed. " (doesn't fit with a R-2600 engine very well).
Navy wanted a power turret/gun mount for rear defense.
minimum speed was to be 71mph and max (with 1700hp R-2600) was to be 313mph.
Take-off was to be 265ft with a 25kt wind.

It was not until Feb 1942 that the Navy gave up on the powered defensive gun set up and allowed Curtiss to substitute a pair of .30 cal guns.
Escalating weights caused the wing to go from 385 sq ft to 422sq ft.
This was after they tried going all the way to full span leading edge slats (in a wind tunnel) and trying drooped ailerons.
The original wing section was not giving the expected max lift co-efficient.
The larger wing went through a number of changes including a large number of magnesium parts (which didn't work and and had to be be redone).
Another solution was the use of more aluminum forgings for the wing but Alcoa was having troubles of their own with vast expansion of the aluminum industry and delayed things further. And Wright was late delivering the R-2600 engine for the prototype.

 

[tomo pauk]

Stuff that was wanted included rubber de-icing equipment, and rebreather oxygen equipment. Navy also wanted the double split flaps and high capacity air brakes which starts to restrict Curtiss choices. Already mentioned buy others was the requirement to fit two planes on one elevator.

Navy didn't get these flaps, not even the 'normal' Fowler flaps.
This will drive the size of the wing up, meaning greater weight and drag, as well as lower mileage.

"Consideration would be given to designs weight 9000 to 9500lbs while carrying a 500lb bomb and enough fuel for 1000 miles at economical speed. " (doesn't fit with a R-2600 engine very well).

9000-9500 lbs is a fully-laden P-40F with a 500 lb bomb... Ain't gonna fly long enough, I'm afraid.

 

[Shortround6]

Navy didn't get these flaps, not even the 'normal' Fowler flaps.

they got the split dive flaps, just like an SBD, they just don't do a lot for lift. But if that is what the Navy wants for dive brakes????

9000-9500 lbs is a fully-laden P-40F with a 500 lb bomb... Ain't gonna fly long enough, I'm afraid.

There was a lot of over optimistic estimating going on.
The XBT-2 (SBD prototype) first flew on 25 April 1938, just two months before the SB2C initial requirement was issued. Where they thought the R-2600 and power turret were going to go on plane that didn't weigh much more I have no idea.

 

[tomo pauk]

they got the split dive flaps, just like an SBD, they just don't do a lot for lift. But if that is what the Navy wants for dive brakes????

Vultee Vengeance dive brakes.
Use undercarriage as dive brakes (will require U/C like what P-36/-40, F4U or F6F had).
Dive brakes (A) and Fowler flaps (B) on the D4Y:

 

[Shortround6]

True but if the Navy is the one requesting the split flap dive brakes like the SBD used they may not accept substitutes.
It turned out that due to weight gain the early dive flaps/brakes didn't give the speed reduction the Navy was looking for.
Book does not say what that was.
An SBD could dive at a constant 240kts(?) for thousands of feet.
The Navy many have been wrong but that is what they were looking for.
It didn't matter what somebody else did several years later.

This is part of the problem with "what iffing" a peace time aircraft and a war time aircraft or a new aircraft vs an adapted in production aircraft.
In Peace Time the Army or Navy want what they want. They may or may not give in on some things (Navy held out out for over 3 years on the rear gun turret).
In war time an extra 3-5mph of landing speed or failing to hit the service ceiling by several thousand ft may be pushed aside in order to speed up production/delivery by months.
good enough NOW is better than perfect 9 months later.

The SB2C gained thousands of pounds before seeing service and that is after they got rid of the turret.
They also changed operating procedures and never (or almost never) tried to fit two aircraft on one elevator which would have simplified a bunch of things. (longer fuselage, smaller tail fins, better stability).

 

[EwenS]

They also changed operating procedures and never (or almost never) tried to fit two aircraft on one elevator which would have simplified a bunch of things. (longer fuselage, smaller tail fins, better stability).

Because they discovered that the extra time taken to carefully position 2 aircraft on the lift in close proximity, outweighed the time for the extra lift cycle.

Thing is, the TBF Avenger being designed around the same time to fit the same lifts on the same carriers was 40ft long.