A proper heir to the SBD

[yosimitesam]

Uh, Sam, the R-1820 gave 1000-1350 hp in various versions of the SBD. However, to your point, the speed never varied much. When they got the newer engines something was added (or several somethings) that added a bit more drag.

I just grabbed the 255/1600 numbers off of the wiki page for the SBD (-5 model), looking for a quick example to use. (Five point demerit for me for intellectual slot.) In my youth (a loonng time ago) I wondered why the "old" battleships (e.g. Perl Harbor) that had 25-28 knot top speeds could not be "juiced up" a little to match the 30-33 knot "fast" carriers. Then I learned that resistance (drag) is proportional to the square of the velocity. To increase the value of 'v', you have to overcome v*v^2 = v^3. I remember calculating (in physics class) the power increase required to go from 25knots to 30knots (1.73), which made it clear. It wasn't my greatest ephipony in life (such as there being no Santa Claus) but it impressed upon me the 'power' of the 'exponent' with regard to forces. (Unintentional pun.) It makes something like the receipt of radar echoes even more remarkable, since they decrease inversely to the FOURTH power, 1/d^2 going out and 1/d^2 coming back. This showed me the power of electronic resonance in circuits.

"How terrible is wisdom when it brings no profit to the wise."

 

[GrauGeist]

Japan bought two He118s (V4 and V5) and delivered them to Yokosuka.

Guess what they developed from those two examples?

 

[tomo pauk]

I just grabbed the 255/1600 numbers off of the wiki page for the SBD (-5 model), looking for a quick example to use.

Wikipedia article on the SBD does not have the 1600 number anywhere in their entry, or 1,600. They list 1,200 HP for the SBD-5.

 

[yosimitesam]

Wikipedia article on the SBD does not have the 1600 number anywhere in their entry, or 1,600. They list 1,200 HP for the SBD-5.

You are correct. I have no idea where I got 1600. Probably from another wiki page tab of "General Characteristics" of something else I had open at the time. In that case, a magic R-2800 would get to 307mph, assuming 2100hp. That's pretty decent and is SB2C speed range. Thanks for catching my error.

 

[Thumpalumpacus]

In my youth (a loonng time ago) I wondered why the "old" battleships (e.g. Perl Harbor) that had 25-28 knot top speeds could not be "juiced up" a little to match the 30-33 knot "fast" carriers.

Just a niggle, but those old BBs topped out at 21 kts. We'd have had to both lengthen them and install more/better machinery to even get 24 kts out of 'em.

That's what the Japanese did with the Kongos, FWIW. I think an extra 40 feet and more machinery bumped them from 25 to 28 kts? Working of the top of my head on them, and amenable to correction.

 

[Shortround6]

Just a niggle, but those old BBs topped out at 21 kts. We'd have had to both lengthen them and install more/better machinery to even get 24 kts out of 'em.

That's what the Japanese did with the Kongos, FWIW. I think an extra 40 feet and more machinery bumped them from 25 to 28 kts? Working of the top of my head on them, and amenable to correction.

You had the "middle" BBs from the North Carolina on. They were the short stubby ones.
The first 2 were 50 ft longer than the next 4. The "short" ones needed an extra 9,000hp to go 0.5 knots slower.

The older ones did to 21kts as you said and would have needed a total reconstruction to hit 24kts.
One of the "shorties"

Note the wave making and the wake here at 15kts.
Also note the lack of any space to put anything between B turret and Y turret.
Despite their large increase in power the Iowa's need their roughly 200 ft of extra length to not only provide room for the engines/boilers but to significantly change wave making resistance to reach 33kts.

 

[Thumpalumpacus]

You had the "middle" BBs from the North Carolina on. They were the short stubby ones.
The first 2 were 50 ft longer than the next 4. The "short" ones needed an extra 9,000hp to go 0.5 knots slower.

The older ones did to 21kts as you said and would have needed a total reconstruction to hit 24kts.
One of the "shorties"
View attachment 698597

Note the wave making and the wake here at 15kts.
Also note the lack of any space to put anything between B turret and Y turret.
Despite their large increase in power the Iowa's need their roughly 200 ft of extra length to not only provide room for the engines/boilers but to significantly change wave making resistance to reach 33kts.

The post I was replying to specified "at Pearl Harbor", which includes nothing past a Colorado-class -- i.e., Standard battleship, and 21 kts.

You're absolutely right, the SDs were 680' (-50 ft from the Washingtons) and needed more shp to stay close in speed to the latter. Length-to-beam matters. Pearl Harbor BBs, at most 624 feet, weren't getting anywhere near 28 kts no matter the rebuild, you're better off building from the keel up than trying that. And my main point was that those Standards were 21 kts.

No way they're getting to 30.

 

[Shortround6]

The post I was replying to specified "at Pearl Harbor", which includes nothing past a Colorado-class -- i.e., Standard battleship, and 21 kts.

You're absolutely right, the SDs were 680' (-50 ft rom the Washingtons) and needed more shp to stay close. Length-to-beam matters. Pearl Harbor BBs, at most 624 feet, weren't getting anywhere near 28 kts no matter the rebuild, you're better off building from the keel up than trying that. And my main point was that those Standards were 21 kts.

No way they're getting to 30.

You are quite right.
Just pointing out that the 28 knotters would have been impossible to get to 30kts+ so the old ones really had no hope (tow by the Starship Enterprise?)

The Japanese rebuilt most of their old BB with new boilers and engines so people need to look at each class or even ship and see what was done.
Also note that the old Japanese battleships were usually 23-24kt ships to begin with (the Kongo class were 27-27.5 as built) so they had a much better head start.

I would also point out that over driving an existing hull shape leads to a point where the bow rises and the stern sinks and extreme cases leads to the ship (boat) taking in water over the stern. Transom hulls were used to "fake out" the water flow at speed.

Ship acted longer than it really was. Downside, they used more fuel at cruising speed.
Some of the Japanese (and Italian) rebuilds tried to modify the "lines" even it they didn't change the length that much.
Practical things like lengthened ship won't fit in as many dry docks for repair were also considered.

 

[Thumpalumpacus]

You are quite right.
Just pointing out that the 28 knotters would have been impossible to get to 30kts+ so the old ones really had no hope (tow by the Starship Enterprise?)

The Japanese rebuilt most of their old BB with new boilers and engines so people need to look at each class or even ship and see what was done.
Also note that the old Japanese battleships were usually 23-24kt ships to begin with (the Kongo class were 27-27.5 as built) so they had a much better head start.

I would also point out that over driving an existing hull shape leads to a point where the bow rises and the stern sinks and extreme cases leads to the ship (boat) taking in water over the stern. Transom hulls were used to "fake out" the water flow at speed.
View attachment 698603
Ship acted longer than it really was. Downside, they used more fuel at cruising speed.
Some of the Japanese (and Italian) rebuilds tried to modify the "lines" even it they didn't change the length that much.
Practical things like lengthened ship won't fit in as many dry docks for repair were also considered.

Right, Japanese battlewagons had lighter armor anyway and thus a couple of kts advantage even before rebuilds. I may well have been wrong about the numbers for the Kongos, working off of my shoddy memory, and your numbers are in the ballpark too, so I'll stipulate to that.

That said, there's no way we're getting Maryland or Oklahama to 30 kts. The USN saw as much and so they built the Washingtons, SDs, and then Iowas. Also allowed for better armament, not that these classes didn't have problems of their own. But 27-28 or 33 kts allowed them to perform both battle-line and carrier-guard duties.

I need to do more reading about transom sterns. I think I understand the principle, but it still is hard to make sense of for me. If you know of any good reading on the topic, I'll be happy to learn more. Thanks for the good convo.

 

[Shortround6]

Transom stern gets a bit confusing, It is done for several reasons in the "modern" world. Not the least of which is more deck space (or cargo space) for a given length of hull. Especially when you are paying dock fees based on hull length. Dock fee can wipe out any fuel saving

Some of the hull/stern shapes have changed since the very early 1900s. Very few ships/boats could plane like a modern speed boat.

for low speed vessels which is sort of the old hull speed is 1.34 times the square root of the water length rule. 600ft is 24.5 kts, different sterns affected things differently depend on where in the speed range they were. The closer you get to max hull speed the worse the old double ender (giant canoe) becomes. But down at hull speed 0.5 it is really quite efficient.
Actual transom stern on a non-planning hull is often a bit camouflaged

Unless the ship is running deep the transom doesn't do anything one way or the other (except lower hull cost and docking fees?)
Go back to the Cruiser and you will see a number of feet of immersion if she was running deep.
Once you get into planning hulls you need a transom stern but the water flow is straight out the back.

Low speed with a transom stern can produce quite a bit of burble (turbulence/drag) put the picture on the right has gone right through Destroyer/Cruiser speed and into MTB land.

They do make whole books on this stuff so I have probably mangled it pretty well.

 

[Shortround6]

Getting back out of deep water and going back to the beginning
"Or, something else to design and manufacture instead of the SB2C. The 1st flight needs to happen before March 1st 1941, ie. a tad later than it was the case with SB2C, so the engineers have a bit less of a pressure to make it work. It needs to have a bomb bay of at least same size like it was the case with the new-gen attackers for the USN. Powered by the engines that US industry can provide in good numbers, using aerodynamics, materials, propellers, guns and electronics of the day. At least a 2-seater, folding wings are mandatory."

Does anybody have the USN design requirements? Like what they wanted for bomb load, range, speed, deck performance etc.

We have a short list from the Avenger write ups but I don't remember what the Navy actually wanted the Helldiver to do. Or how bad it missed certain things or how much it may have gotten right.

Grumman missed the service ceiling on the Avenger by a good margin as it turns out.

So are we looking at a better Helldiver (or less bad) or are we looking at a product improved Dauntless (fold the wing, slap a fairing around the bomb, call it done and start working on the 1943-44 airplane)

What are the actual design targets/goals they were trying to hit?
We know were ended which is not the same thing.

 

[Thumpalumpacus]

Transom stern gets a bit confusing, It is done for several reasons in the "modern" world. Not the least of which is more deck space (or cargo space) for a given length of hull. Especially when you are paying dock fees based on hull length. Dock fee can wipe out any fuel saving

Some of the hull/stern shapes have changed since the very early 1900s. Very few ships/boats could plane like a modern speed boat.

for low speed vessels which is sort of the old hull speed is 1.34 times the square root of the water length rule. 600ft is 24.5 kts, different sterns affected things differently depend on where in the speed range they were. The closer you get to max hull speed the worse the old double ender (giant canoe) becomes. But down at hull speed 0.5 it is really quite efficient.
Actual transom stern on a non-planning hull is often a bit camouflaged
View attachment 698604
Unless the ship is running deep the transom doesn't do anything one way or the other (except lower hull cost and docking fees?)
Go back to the Cruiser and you will see a number of feet of immersion if she was running deep.
Once you get into planning hulls you need a transom stern but the water flow is straight out the back.
View attachment 698605
Low speed with a transom stern can produce quite a bit of burble (turbulence/drag) put the picture on the right has gone right through Destroyer/Cruiser speed and into MTB land.

They do make whole books on this stuff so I have probably mangled it pretty well.

Not to short-shrift your lengthy reply -- and I'll delve more into it tomorrow -- but yeah, I figured that the transom only matters if it butts in deep enough to affect hydrodynamics. As I said earlier, it's a learning thing for me.

 

[Shortround6]

I was introduced to this as boy. My uncle had 34 ft double ended life boat hull as a cabin cruiser powered by a 40hp Atomic four engine that would drive it at just about 7kts (hull speed).
He explained to me (coast of Maine and Lobster boat races) that each additional knot of speed required double the power (roughly) so 8kts=80hp, 9kts =160hp, 10kts=320hp, 11 kts= souped-up Olds 455 engine and the boat might sink

Winner of the annual lobster boat race was using an Olds 455 but didn't have a double ended hull. Had a transom stern but not a V hull/planning hull.

Scale it up for the Battleships. If your hull form is wrong you can used up a crap load of power for not a lot of speed.

 

[EwenS]

Britain adopted the transom stern for many of its larger warship designs from around 1937. So we had the 1937 Colony class cruisers and subsequent developments, the never built 1938 Lion class Battleships, the 1941 designed battleship Vanguard, the 1942 Audacious class and 1943 Centaur class carriers.

Vanguard

Audacious class Ark Royal

 

[Macandy]

The SBD was of its time, but its time, and that of the scout bomber had passed.
F-4U-1 Corsairs were carrying as much weaponry, a long way and were excellent fighters by 1944/45.
The later versions was able to haul 4,000+lbs of bombs and packing 4 x 20mm cannon - a mini 'Skyraider'

 

[Wild_Bill_Kelso]

IMO the biggest problem was actually the carrier. You could make a fast dive bomber (hard but doable), even a fast dive / torpedo bomber (very hard, but still apparently doable), but they all faced the problem of the size of the carriers, and specifically the size of the elevator on the carrier. Making a fast dive / torpedo bomber that could also fit on a standard carrier elevator was a big challenge. The elevator drastically limited the length of new aircraft which is a big problem especially if you are trying to put a torpedo in a bomb bay (or even semi-recessed), and in general for aircraft with big high-torque engines like an R-2600.

The TBF was kind of amazing in that they made a functional, fairly good aircraft that could fit on those small elevators, and had folding wings. The TBF was 40' long but it had nicely folding wings so it's an easier fit.

Sea Gladiator was 27' 3" long
Bearcat was 28' 3" long
Wildcat was 28' 9" long
Seafire was 30' 2.5" long
Sea Hurricane was 32' 3" long
D4Y bomber 33' 6" long (this varied obviously by engine)
Corsair was 33' 8' long (I was a little surprised by this!)
B5N bomber was 33' 10" long
Devastator was 35' long
Swordfish was 35' 8" long
SBD was 33' long
Hellcat was 33' 7" long
D3A was 33' 5" long
B6N bomber 35' 8"
B7A was 37' 8" long
Firefly was 37' 11" long
Barracuda was 39' 9" long
Albacore was 40' 1" long (I was surprised by this)
Fulmar was 40' 2"

The aircraft elevator on the Kaga was 35' x 52', Essex class had 60' x 34' elevator. Obviously folding wings helped fit something on one of these.

But elevator size was apparently the reason for the forward bent tail and rudder on the B6N, it was the reason the B7A never flew from a carriers (the only two IJN carriers big enough for it got sunk too quickly) and it was the main reason for a lot of the problems with the SB2C - it just really needed to be about 3' longer. I think this would have been an issue for a theoretical two seat Corsair or Hellcat.

I'm a little confused how they fit all those Fulmars on early carriers... I guess the folding wings helped like with the TBF. I assume by the time Albacore was around they had the bigger elevators?

 

[tomo pauk]

and it was the main reason for a lot of the problems with the SB2C - it just really needed to be about 3' longer. I think this would have been an issue for a theoretical two seat Corsair or Hellcat.

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

I'm a little confused how they fit all those Fulmars on early carriers... I guess the folding wings helped like with the TBF. I assume by the time Albacore was around they had the bigger elevators?

Albacore have had the same layout of the fold as the Swordfish.

 

[GrauGeist]

Hangar height belowdeck also had an impact of how high the wings could be in the folded position.

 

[Wild_Bill_Kelso]

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

Are you sure about that? I mean, I know it's possible to make a two seat bomber roughly the same size (the SBD isn't too much bigger than a Corsair), but this would definitely add a lot of weight, add drag (especially if the rear seater has a gun mount), take away space used for fuel or oil other needed things, and change the CG.

For that matter, looking at my 1/72 USN air fleet here, the diameter of the R-1820 on the SBD looks about the same as the R-2600 on the Corsair... maybe you could put the bigger engine on it...? But then I assume you have a fuel and maybe CG problem. And you can't lengthen it much without folding wings....

 

[tomo pauk]

Are you sure about that? I mean, I know it's possible to make a two seat bomber roughly the same size (the SBD isn't too much bigger than a Corsair), but this would definitely add a lot of weight, add drag (especially if the rear seater has a gun mount), take away space used for fuel or oil other needed things, and change the CG.

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.