Why was the SBD such an effective aircraft?

Barrett · Jun 20, 2019

Ref. SBD v F4U bombing accuracy: LONG ago when writing The First Corsair Book I found a 4th MAW study of the subject. Long since lost the document but here's the summary from the Naval Institute volume:

SBD CEP: 175 feet Hits on 50-ft radius circle: 5.4%
F4U CEP: 195 feet Hits on 50-ft radius circle: 4.5%

Those seem reasonable indicators of each type's inherent accuracy due to the highly permissive environment in the Marshalls during 1944.

XBe02Drvr · Jun 20, 2019

pinsog said:
I've never seen a single engine stall speed for it.

That's not the speed that matters. Vmc, or Velocity minimum controllable is the speed below which there isn't enough rudder authority to keep the plane from yawing and rolling into the dead engine with the working engine at full power.

Schweik said:
rudder forces tended to be high in single engine configuration.

This is an indication of a rudder authority problem, which seems to be confirmed by the small size of the tailfeathers. This implies that Vmc might be rather high and likewise single engine landing speed. The TBF was still several years in the future, so this would likely be the heaviest and fastest and by far the highest energy the arresting gear had ever had to cope with.
Cheers,
Wes

Schweik · Jun 20, 2019

Barrett said:
Ref. SBD v F4U bombing accuracy: LONG ago when writing The First Corsair Book I found a 4th MAW study of the subject. Long since lost the document but here's the summary from the Naval Institute volume:

SBD CEP: 175 feet Hits on 50-ft radius circle: 5.4%
F4U CEP: 195 feet Hits on 50-ft radius circle: 4.5%

Those seem reasonable indicators of each type's inherent accuracy due to the highly permissive environment in the Marshalls during 1944.

Interesting.

CEP, circle of error probable? Was that dive bombing or "shallow dive" bombing?

Schweik · Jun 20, 2019

XBe02Drvr said:
That's not the speed that matters. Vmc, or Velocity minimum controllable is the speed below which there isn't enough rudder authority to keep the plane from yawing and rolling into the dead engine with the working engine at full power.

This is an indication of a rudder authority problem, which seems to be confirmed by the small size of the tailfeathers. This implies that Vmc might be rather high and likewise single engine landing speed. The TBF was still several years in the future, so this would likely be the heaviest and fastest and by far the highest energy the arresting gear had ever had to cope with.
Cheers,
Wes

Wait, what am I missing? There were TBF's at Midway. TBF first light was a year after the first XF5F and almost a year before the long nosed one flew.

The loaded weight of the F5F is barely more than an SBD and significantly less than a TBF.

pinsog · Jun 20, 2019

Schweik said:
I've never been able to find out much about the F5F except what is on the Wiki. The latter includes the test pilot report:

"Testing by Grumman test pilot "Connie" Converse indicated "the flying qualities for the XF5F-1 were good overall. The counter-rotating props were a nice feature, virtually eliminating the torque effect on takeoff ... single-engine performance was good, rudder forces tended to be high in single engine configuration. Spin recovery was positive but elevator forces required for recovery were unusually high. All acrobatics were easily performed, and of course forward visibility was excellent."

LCDR Crommelin, in charge of the test, stated in a 1985 letter to George Skurla, Grumman president:

"for instance, I remember testing the XF5F against the XF4U on climb to the 10,000 foot level. I pulled away from the Corsair so fast I thought he was having engine trouble. The F5F was a carrier pilot's dream, as opposite rotating propellers eliminated all torque and you had no large engine up front to look around to see the LSO (landing signal officer) ... The analysis of all the data definitely favored the F5F, and the Spitfire came in a distant second. ... ADM Towers told me that securing spare parts ... and other particulars which compounded the difficulty of building the twin-engine fighter, had ruled out the Skyrocket and that the Bureau had settled on the Wildcat for mass production"

This is also the same source which claims 382 mph. Sources for all this seem pretty marginal though. Do you have a good source on the F5F pinsog?

I bought the paperback book on the F5F. Pretty interesting. Long periods between stuff happening on the project, I imagine that Grumman was busy working on the F4F-3 prototype. I'm sure the F5F wasn't perfect but the Corsair was full of flaws even after it deployed. There is a test on the F5F that is official, giving altitudes, horsepower, speed etc. 10,132 was light weight loading on fuel and apparently ammo. Top speed is listed as 357 at 17,000, with last hp given as 900 per engine at 14000 so what ever they would be down to at 17000. 10,892 was 'overload fighter' with 278 gallons of fuel and apparently ballast for a full ammo load. I broke all that down on I think 2 different threads on here as far as the weight of fuel, pilot, oil etc and there was about 900 pounds left over which had to be ballast for weapons. Search F5F and you should be able to find them. I'll look when I can and put the link on here.

It did not have armor (easy fix) and the 278 gallon tank was not self sealing (harder fix, or at least expensive fix). The entire wing between the 2 engines was a fuel tank and it was a single large aluminum extrusion. Evidently it had internal bracing which precluded the addition of a self sealing rubber bladder. Probably nothing a redesign wouldn't take care of, but that costs money and time and I think Grumman was just too busy with the F4F-3 to fix it. In my fantasy F5F I add 150 pounds of armor and 200 for a self sealing tank (the corsair tank was 177 pounds of self sealing material for a 237 gallon tank). It might have done fine without turbochargers, because it was fast up to 20,000 feet, but turbochargers give it 2400 hp up to 25000 feet or maybe 27000 feet depending on exactly which ones you choose. Quite an increase for 500 pounds. I figure while you at it you might as well add some 65 gallon or so sized fuel tanks in the outer fold up wings. It also folded up to about the same size as a Corsair or Wildcat, about 21.5 feet.

pinsog · Jun 20, 2019

XBe02Drvr said:
That's not the speed that matters. Vmc, or Velocity minimum controllable is the speed below which there isn't enough rudder authority to keep the plane from yawing and rolling into the dead engine with the working engine at full power.

This is an indication of a rudder authority problem, which seems to be confirmed by the small size of the tailfeathers. This implies that Vmc might be rather high and likewise single engine landing speed. The TBF was still several years in the future, so this would likely be the heaviest and fastest and by far the highest energy the arresting gear had ever had to cope with.
Cheers,
Wes

I know they increased the size of the rudders early on and the pilot reported good single engine control, although I completely understand "good single engine control' vs "lets get it down to 75 mph on a single engine and land on a carrier' is 2 totally different things and I understand that the first could be very good and the 2nd impossible. Its a shame that we have so little data on it. On the other hand, single engine control is why Grumman put the engines so close together and I imagine it is why they gave it a twin rudder setup with a rudder directly behind each engine. We all know the P38 if you lost an engine on takeoff was a nightmare for untrained pilots, but the engines were also far apart. Maybe the F5F wasn't too bad on a single engine at low speed. (Of course we all know that landing on a carrier is a crap your pants event under the best of circumstances so it would not be fun no matter how well the F5F handled on 1 engine)

pinsog · Jun 20, 2019

Schweik said:
Wait, what am I missing? There were TBF's at Midway. TBF first light was a year after the first XF5F and almost a year before the long nosed one flew.

The loaded weight of the F5F is barely more than an SBD and significantly less than a TBF.

He is specifically talking about the F5F on a single engine. Also, even though the TBF was the heaviest plane to operate from a carrier during the war, it also had an almost 500 square foot wing so it could fly REALLY slow and REALLY controllable. I think it was the easiest plane to land on a carrier that we had, especially empty

michael rauls · Jun 20, 2019

VBF-13 said:
I unequivocally agree. And while the SBD won't put a 500# bomb in a pickle barrel, it'll get it close enough, count on it, when it's given the chance. Let's also not forget to credit the F6F, which I see being referenced by implication in your last sentence, on its diving capabilities. There's a reason those were in VBF squadrons. Given that, and by that time in the War, at least, and with the F4U, I don't think we needed any SBDs over land. Still, given its track record, I'm at a loss as to why it couldn't have been put to land targets. In particular, what was it lacking, compared to the ones that were deployed over land? How do they rate as against those? Forget about the comparisons to the fighters. How do they compare as against the land dive bombers? Again, I don't know enough about the latter to form an opinion either way. Having said that, without more, I still don't see them handicapped in any material way.

Man, those pickle barrels sure took a beating durring the war. Seems everybody was always trying to drop a bomb in them.

Shortround6 · Jun 20, 2019

Schweik said:
An "SBF" would have the merits, and drawbacks, of a proven design that was quickly adapted. Kind of like how the F4F was derived from the F3F, how the I-16 was a monoplane version of the I-15 / 153, how the Hurricane was more or less a monoplane version of the Hawker Fury, the Merlin P-51 was derived from the Allison P-51. Or how the P-40 was derived from the P-36. Or how (I think?) the F6F was at least partly derived from the F4F. Or was it? I'm not sure about that one.

Some of these examples are not correct.
The P-40 was a P-36 with a new engine (of course the P-36/Hawk 75 had already gone through 4 or 5 engines) and yes the P-51B was derived from the Allison P-51.
However some of the others like the Hurricane/Fury and and the F4F/F6F had nothing more in common than being made by the same company. Tales of the Fury monoplane notwithstanding. There was a fury monoplane on paper, it was tossed and the Hurricane was a fresh start.

The I-153 first flew about 3 1/2 to 4 years after the I-16. The I-16 used a wooden fuselage and metal wings (at least the structure) while the I-153 use a metal fuselage and fabric covered wooden wings.

F3F-3 (2nd engine)

XF4F-2

Which was being worked on before the last of the biplanes left the factory.
BTW it used a single speed, single stage supercharger,

You need more than a general shape in order to really trace what plane is derived from another.

Shortround6 · Jun 20, 2019

Dive bombing ships vs dive bombing land targets is a lot different.

Ships, if there wasn't a lot of cloud, stood out from the ocean pretty well, Large bridges might stand out but many targets on land didn't stand out very well. Especially in woods or jungle.

The ships were much larger even though they moved. There were darn few bunkers that were 300-400ft long.

GrauGeist · Jun 20, 2019

The XF4F-1 was actually a biplane and it's performance was dismal. In an attempt to salvage it, they redesigned it as a monoplane, which also had poor performance.
They stopped trying to "fix" what they had and after a complete overhaul, the XF4F-3 was the result.

Shortround6 · Jun 20, 2019

The XF4F-1 never flew, it's performance was dismal even on paper. In fact the amount of actual construction may be a subject of debate, has anyone seen a photograph of even a mock up?

RCAFson · Jun 20, 2019

Schweik said:
Yeah I tried to amend that post to note that there were different cruise speeds used for different circumstances. I wonder if they switched to higher speed cruise when closer to enemy territory / aircraft.

Yes, both at Guadalcanal and over Darwin, A6Ms and G4Ms would switch from a low altitude, range cruise to a high altitude, high speed cruise when approaching the target for a low-high-low mission profile. IIRC, this was not typically the case during carrier borne strikes, where a range cruise at medium altitude was more likely.

fliger747 · Jun 21, 2019

Somewhere along the way I accumulated about 20,000 hrs of multi time. We of course had the exciting simulator scenarios twice a year, but I also puked some real life engines. The F5F was an interesting aircraft though the climb specs aren't spectacular. In wartime a certain attrition rate was considered acceptable, just look at the number of operational accidents! On takeoff it's probably going to crash, just like a single engine would in case of an engine failure, in thins case due to not reaching VMCA. A more likely scenario is returning aboard on a single engine. This is not so much a problem on approach, but it better be a good one as being in close and taking a wave off would be very exciting, one needing a little altitude and judicious throttle application to accelerate out of it.

At some time or another I did flight dynamics for almost all of the WWII USN Carrier Aircraft for FSX, including the F7F. I did a lot of single engine carrier approaches with it. From my many years of flying, I think this was a fairly reasonable simulation. The Corsair was the most difficult to bring aboard, the F7F was easy just because you could see well, which reduced the probability of getting wave off. The view was about like the early jets like the Panther or Banjo, which really needed to get it right on a straight deck.

XBe02Drvr · Jun 21, 2019

Schweik said:
Wait, what am I missing? There were TBF's at Midway. TBF first light was a year after the first XF5F and almost a year before the long nosed one flew.

Right you are. I was thinking (without checking) the XF5F was earlier than it was. Good catch!

XBe02Drvr · Jun 21, 2019

pinsog said:
the TBF was the heaviest plane to operate from a carrier during the war, it also had an almost 500 square foot wing so it could fly REALLY slow and REALLY controllable. I think it was the easiest plane to land on a carrier that we had, especially empty

My uncle Ned carrier qualled in the TBF on a 500 foot long converted paddle wheel steamer on Lake Michigan, then flew off jeep carriers in the North Atlantic. He said the bird was a real sweetheart for deck landings. He joked that when he had to land on a fleet carrier he got agoraphobia looking at all those acres of flight deck.
Cheers,
Wes

pinsog · Jun 21, 2019

fliger747 said:
Somewhere along the way I accumulated about 20,000 hrs of multi time. We of course had the exciting simulator scenarios twice a year, but I also puked some real life engines. The F5F was an interesting aircraft though the climb specs aren't spectacular. In wartime a certain attrition rate was considered acceptable, just look at the number of operational accidents! On takeoff it's probably going to crash, just like a single engine would in case of an engine failure, in thins case due to not reaching VMCA. A more likely scenario is returning aboard on a single engine. This is not so much a problem on approach, but it better be a good one as being in close and taking a wave off would be very exciting, one needing a little altitude and judicious throttle application to accelerate out of it.

At some time or another I did flight dynamics for almost all of the WWII USN Carrier Aircraft for FSX, including the F7F. I did a lot of single engine carrier approaches with it. From my many years of flying, I think this was a fairly reasonable simulation. The Corsair was the most difficult to bring aboard, the F7F was easy just because you could see well, which reduced the probability of getting wave off. The view was about like the early jets like the Panther or Banjo, which really needed to get it right on a straight deck.

Climb on the F5F was supposed to be 4,000 feet per minute. Shortround and I discussed this in another thread wondering if the over heating engine was the problem. The right hand engine on the F5F constantly ran hot, one of the reasons Grumman complained to the government about faulty government supplied equipment.

I figure if you add turbochargers, armor, self sealing tanks and even wing tanks bringing the weight of the F5F up to 12,750 pounds or so and 2400 hp and fuel up to 400 gallons, it's still around 2000 pounds lighter than a P38E that only has 2300 hp and 300 gallons of fuel. Climb should be amazing as would range. Reliability should be very good as well as durability.

fliger747 · Jun 21, 2019

On the F5F specs listed above it said 4 mins to 10,000' and 9+ to 20,000', which seems a little low for the weight and power. I am more inclined to agree with you. Are the above specs in error?

Perhaps a better supercharger, turbo's were a big hoopla to develop and manage. The Navy rejected the turbocharged F4U-3.

Kevin J · Jun 21, 2019

pinsog said:
These are the same guys that let the US fight 2 years without a working aerial torpedo, or submarine torpedo, and left the prototype P51 Mustang sitting on a runway for like a year and said it was a crap plane and built 8,000 pound fighters with 1200 hp. They definitely could have used some help from us!!!

We have the benefit of hindsight without bigotry.

Wildcat · Jun 21, 2019

Schweik said:
Plus Brewster seemed to be having some serious problems, they got taken over by the government in 1942. Buccaneer was fast for it's large size but apparently had a lot of build and production problems, everyone seemed to reject it. The similar Vultee Vengeance did a little bit of good in Australian service. This line from the Wiki is pretty much what I'd been saying about fighter bombers vs. dive bombers:

"Australian Vengeances flew their last operational sorties on 8 March 1944, as they were considered less efficient than fighter bombers, having a short range and requiring a long runway, and were withdrawn to allow more effective fighter bombers to move into the forward area.[18] The Vengeance squadrons were re-equipped with Consolidated B-24 Liberator heavy bombers.[19]

The view of the Vengeance's limitations is disputed by Peter Smith in Jungle Dive Bombers at War, "The precision and skill of the dive-bombing method...and its clear superiority over most other means of air attack when it came to destroying small and well-hidden targets in difficult country, was proven over and over again in the Asian jungle campaigns."

So fighter bombers generally more suitable but dive bombers more accurate. However the Vengeance seemed to be pretty second rate over all. Certainly by 1944 it was quite obsolete, even for Burma. Neither the Vengeance or the Buccaneer was small enough to make a good fighter IMO.

Actually the RAAF was quite happy with the vengeance and it's squadrons were doing good work up in New Guinea. The decision to withdraw the vengeance wing from combat came from USAAF orders, not RAAF. IIRC the RAAF leadership of these squadrons were not impressed...

Why was the SBD such an effective aircraft?

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