Vought SBU Corsair; The ACTUAL Second One!

June 25, 2024

Everyone knows the Corsair II, right? Built by LTV, the successor to the legendary Vought company, the A-7 Corsair II was the replacement for the also legendary A-4 Skyhawk and served, rather remarkably, with the US Navy, Marines AND Air Force. Indeed, I’ll get around to covering the Corsair II one day in the future, when it isn’t so well remembered.

But I must now point out one problem with the naming conventions of Vought. Because the A-7 wasn’t the second, or even the third aircraft created by Vought to bear the name Corsair. It’s actually the fourth!

In a previous article I wrote about the first Corsair, the O2-and-3U, which served just about everywhere and with just about everyone throughout the 1930’s and ‘40’s, a handsome service tradition that was closely mirrored by the third Corsair, the also super famous F4U. But today I’m going to tell you about the first Corsair II…you get what I mean.

The Vought SBU Corsair.

This two-seat dive bomber had several remarkable features in its day, but to get there were a bunch of hoops to go through first.

The origins of the Vought SBU go back to the US Navy requesting that Pratt & Whitney develop for them a new engine. The Navy liked the company’s Wasp series of engines, plus their big, powerful Hornet. But what they wanted was a version of the new Twin Wasp that Pratt & Whitney was working on, but with a smaller diameter. This would give the pilot a better view forward and cut down on the drag of the larger radials but still, with a twin-row design, match the power output of its bigger single-row siblings.

Thus was born the Pratt & Whitney Twin Wasp Junior, which was first introduced in 1932.

Obviously, the Navy wanted a nice new fighter to go along with their new powerplant, and Vought was commissioned to build the XFU-3 two-seat fighter. This they promptly did, with the new aircraft flying in May 1933.

Unfortunately for Vought the US Navy then had a change of heart on the viability and need for two-seat fighters, and in November that year the requirement was dropped, leaving Vought with an aircraft but no buyer. However, all was not lost as Vought, canny operators that they were, had anticipated that this might occur and deliberately built the XFU-3 with an airframe over strengthened for possible use in a dive bomber role.

So, when the Navy promptly turned round and said they wanted instead a new attack aircraft, Vought was prepared.

The company decided that though the XFU-3 was a good basis for the new aircraft, they would build a dedicated prototype from scratch using the salvaged engine and equipment from one of the XFU-3’s. And so was created the Vought SBU Corsair.

Because it was modelled closely on an already built aircraft, the SBU was pretty quick through development. Flight testing was completed in 1934 and a production order for the new scout/dive-bomber, the next generation Corsair, was placed in January 1935.

And because of its high-performance origins, it was by all accounts a pretty good aircraft that was rather advanced for its role. It retained the Twin Wasp Junior engine which produced 700hp, comparable to the much larger Hornet.

It combined this with another innovation, the Hamilton Standard variable-pitch propellor, as well as being the first aircraft to have adjustable flaps on the trailing edge of its NACA cowling. Prior to this, cowls were designed to provide maximum cooling when aircraft were in take-off and climbing when their engines generated the most heat. But these also created a lot of excess drag at high speeds when simple air flow would suffice.

The SBU’s adjustable flaps meant that the aircraft could operate efficiently in both flight ranges, with maximum air flow for take-off but reduced drag for high-speed flight. The combination of all this meant that the SBU was surprisingly fast, with a listed top speed of 205mph (330km/h). This made it the first carrier dive bomber to be capable of more than 200mph.

If there was one element that was somewhat conservative, it was the construction method. Many online sources state that the SBU Corsair was of all-metal construction, which I am certain is not true.

Instead, I am pretty sure that, if you study pictures of the aircraft, you can see the ribs from the steel tube framework that formed the structure of the fuselage quite clearly.

I suspect that the SBU copied the same build standard of the proceeding O3U Corsair – which after all was still in production at the time – and had metal-skinning for the engine bay running back to behind the pilot’s seat, while the rear fuselage and wings were fabric-covered.

But it must be said that while the SBU used, I am fairly sure, the mixed construction of its predecessor, as well as a fixed undercarriage, that isn’t really a bad thing, as the O3U’s were extremely popular and durable aircraft in service. And like the final variant of the O3U, the -6, the SBU also had an enclosed canopy for the crew.

With an armament of one forward firing .30-calibre Browning for the pilot and a pintle mounted gun for the observer to cover the rear, plus a bombload of 500lb (227kg) the SBU Corsair was as advanced and as formidable as any comparative aircraft of its day when it entered service in 1935.

In fact, the combination of older design elements combined with new innovations shows just what was intended with the SBU Corsair; it was both a developmental design to start bringing new aeronautic technologies into service while having enough conservative elements to ensure that it shouldn’t fail and thus provide a hedge against new designs and concepts that were in development at the same time.

If there is one thing I am constantly repeating in these Forgotten Aircraft articles it’s that the 1930’s was absolutely crazy for aeronautic development. It is basically the standard to be already working on an aircraft’s next generation replacement when it first comes into service. But in the ‘30’s many aircraft went from cutting edge to outdated in a couple of years, to completely obsolete in five!

And the Corsair was largely in that category.

Even as the requirement was being issued for the creation of the SBU Corsair, another requirement was being placed for a monoplane successor; requirements that turned into the Vought SB2U Vindicator and the Douglas Dauntless. Even these aircraft, though they provided sterling service in the first years of the Second World War, were rapidly replaced in turn due to the gallop of aeronautic development in the prewar years.

But to return to the SBU, this all meant that it experienced a short life in service, as well as limited sales. In total, eighty-four Vought SBU’s were initially ordered for the US Navy.

In 1936 the one export order that was achieved for the type was placed by Argentina, who procured fourteen aircraft under the designation of V-142A. The Argentine Navy seems to have been happy with their Corsairs and used them well into the 1940’s until replaced by more modern types.

In 1937 the US Navy placed a follow order for another forty Corsairs, these the SBU-2’s, which were fitted with the improved Pratt & Whitney R-1535-98 Twin Wasp Junior engine. These replaced the last of the old Vought SU two-seat fighters in service but as said, did not last much longer themselves.

The obvious superiority of both the monoplane and retractable undercarriage had been recognized as the future, and even before the second order was being placed the Vought SB2-U was already entering squadron service with the US Navy.

Though Vought was already building this more advanced aircraft, they again thought it prudent to offer a simpler alternative if the new-fangled monoplanes proved a flop, and so they built a single XSB3U-1. This was essentially the SBU-2 but converted to have a retractable undercarriage and some additional streamlining. The new model was indeed some 10mph faster than the SBU, but was still outclassed by its monoplane sibling, and though the Navy was impressed by some it’s design elements, it was plain that this time Vought’s hedging on a conservative option – though probably sensible – was not going to pay off.

The supremacy of the newer Vindicator and Dauntless meant that though the Corsairs would carry on in service as a supplement to the newer aircraft as their numbers built up, by 1941 the last SBU’s were taken out of front-line squadrons and the survivors all switched over to training duties.

And that concludes the history of the Vought SBU, the actual Corsair II; an aircraft both innovative and conservative and nowadays an almost completely forgotten aircraft.

Sources/Related:

https://en.wikipedia.org/wiki/Vought_SBU_Corsair

https://www.jstor.org/stable/3100919

https://www.vought.org/products/html/sbu.html

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