Flight Journal|Annual 2020

Whenever Navy and Marine Corps aviators who flew and fought in propeller-driven fighters gather, there is always the argument about which was the better airplane: the “bent-wing bastard,” as we lovingly dubbed the Chance Vought F4U-lD Corsair, or the Grumman Hellcat? I am sure that many beers have been consumed and many loud, emotional discussions have taken place on this subject.

In the desperate climate of WW II, the Navy decided that the easiest, quickest, and least costly way to tweak the utmost performance out of its fighter planes would be to let rival manufacturers test the latest versions of one another’s products. So, in the summer of 1943, the Navy delivered into Grumman hands the newest Corsair (F4UlD Buno 17781). I was privileged to be the project engineering test pilot for the F6F-3 Hellcat at the time.

Grumman’s specific orders from the Navy were to improve the Hellcat’s speed by 20 knots and put better ailerons on it so that it would compare favorably with the incomparable Corsair. We were motivated by the strongly implied “or else” in between the lines.

We were also pleased to learn that we had not been singled out for harassment of our sterling product when we heard that Chance Vought, our friendly competitor from the other side of Long Island Sound, was sent an F6F-3 Hellcat and ordered to improve the Corsair’s visibility, cockpit internal layout, and stall characteristics and to redesign the landing-gear Oleos (the Corsair bounced badly on landing). In other words, make the Corsair fly as well as its friendly competitor, the Grumman Hellcat.

If the contest between the two airplanes had been for beauty of design, we would have given in immediately. Our baby, the Hellcat, was beautiful to us, but in comparison with the graceful lines of the Corsair, the Hellcat looked more like the box it came in than a new Navy fighter. We always used the euphemism “functional-looking” instead of “ugly” to describe it.

We were sure that Vought would have a difficult time meeting the Navy’s demands, as most of the Corsair’s deficiencies would require major changes in configuration. We were also steeped in the tradition that Grummanites could always make better Navy fighters than Connecticut clam diggers; thus, our tasks would be accomplished in a trice. Our performance improvement challenge turned out to be much easier than we ever hoped, but the aileron problem turned out to be nearly impossible.

The Navy Was Right

As long as we had the enemy in our hangar, we decided to conduct a witch hunt into its entrails. On my first flight, I discovered the Corsair did indeed indicate 20 knots faster and did have really smooth and powerful ailerons compared with our Hellcat’s. But as we had heard and as was completely obvious, the cockpit was wretched from many standpoints. The most glaring deficiency was the absence of a cockpit floor! Behind the rudder pedals, only two small heel panels offered any protection against dropping a pencil, a chart, or earphones, etc., into a 3-foot-deep, yawning black hole. Consider the havoc this would cause if the pilot’s relief tube dropped down there on a very, very long mission!

To simplify the evaluation and reduce data, we decided to test-fly the Hellcat and the Corsair in close formation. Instead of comparing complex calculations, performance could then be compared directly at the critical altitudes of the main stage, high and low blower altitudes of the engine’s superchargers, and from cruise to high-speed level flight with water injection. We also included some formation dives to learn which airplane was the slickest.

Performance Almost Equal

Except for the Corsair being 20 knots faster than the Hellcat in the main, sea level, supercharger stage, both fighters had almost exactly the same speed at the low and high blower stages from 5,000 feet altitude up to service ceiling! In essence, they had the same performance. Our formation flights showed that both airplanes (with similar power settings) were in closely stabilized formation at all altitudes tested above 5,000 feet. Sometimes, the Corsair would slowly gain a lead of 100 to 200 feet after five minutes of stabilized power flight, and sometimes, the Hellcat would do the same. Considering that both airplanes had the same engine, propeller, gross weight, wingspan, etc., they should have had about the same performance. We did notice that during these runs, the Corsair always had about a 20-knot indicated airspeed (IAS) advantage! We didn’t realize just how embarrassing it would be to solve that dilemma.

The reason the Corsair was faster in the main stage blower was that its engine and carburetor were provided with ram air coming in directly from the forward facing wing duct, whereas the Hellcat had the carburetor air coming in from the accessory compartment of the fuselage just behind the engine, with no ram air effect. Our airplane was getting carburetor air at the same pressure as it would have were it motionless on the ground, and the Corsair was getting carburetor air supercharged by the speed of the airplane giving it more power (speed) in the main stage blower. In both aircraft, however, the designs were similar in that they provided ram air to the low and high blower stages. Our engineering department defended its position because taking the warmer air for the main stage blower would prevent inadvertent carburetor-icing engine failures. Many Wildcats that had ram air in the main stage like the Corsair were lost because pilots failed to take precautions in time to avert this type of disaster. The Hellcat design was reviewed and approved by the Navy. I had had a carburetor-icing accident during final approach on my first flight in a Wildcat a few months previously; it resulted in my first deadstick landing and a vertical ground loop. I therefore heartily agreed with the Navy’s decision.


THE F4U-4 WAS BLESSED with the more powerful Pratt & Whitney R-2800-34W, which gave it a great boost in high-speed performance. This provided the necessary edge over the newer Japanese fighters that were coming into squadrons when the F4U-4 arrived in the Pacific Theater.

Grumman also had a version of the Hellcat, the XF6F-6, with the same engine, and from what we learned in our 1943 evaluation, it demonstrated a comparable high-speed performance to the F4U-4 model Corsair’s.

The F6F-6 Hellcat caused an interesting internal fracas on “mahogany row” in Grumman headquarters. Our very capable director of production, George Titterton, wanted to put the F6F-6 into production. Bob Hall, director of experimental, who had flown the Focke-Wulf 190 in 1943 and was very impressed with that airplane, wanted to put the 445mph XF8F-1 Bearcat into production. The brouhaha went up the line to Mr. Grumman (he was the only person in Grumman who wasn’t called by his first name or a nickname), and he took it up with the Navy. The decision, as we all know, was made for F8F-1 production. Although the XF6F-6 was abandoned, the F6F-5 Hellcat continued in production throughout the remainder of the war. The Navy made a wise decision by having both the F6F-5 continue production and the F4U-4 start squadrons operations as a backup for the yet unproven Bearcat—the Navy’s third option.

IAS Performance Equalized, the Hard Way

After noting the 20 knots IAS difference that had caused all the “lower performance” ruckus for our Hellcat, we eagerly decided to change the airspeed system so that it would read evenly with the Corsair when they were in formation. We had taken a lot of flak from all who had flown both airplanes (but not in formation), and therefore, everybody “knew” that the Hellcat was inferior in highspeed performance. We liked our simple and less complicated airspeed system with the static and dynamic orifices on the same boom, but we decided to go whole hog and put the static orifice on the fuselage (like the Corsair) to tailor the system to read 20 knots higher. We tried several orifice locations to get the required reading. After I had done a thorough testing of the final system over the entire flight envelope—or so I thought—I proudly flew the airplane to the Naval Air Test Center at Patuxent, Maryland, for an evaluation. We soon found out that we had not purloined the Corsair airspeed system design thoroughly enough.

We soon received the Navy’s glowing report of the new system; it went on to say that the Air Test Center had never tested an airplane with such remarkable low speed performance in its entire history. They found that in a left side slip with the wheels and flaps extended, the Hellcat could fly at zero airspeed. Wonder of wonders— Grumman led the industry again! Upon re-evaluation, we found that the engineers, inexperienced with flush static airspeed systems, had designed ours with only one orifice on the left side of the airplane, and it was very unbalanced with the flaps down. As the senior engineering test pilot, I was in deep doo-doo for not testing the new system in all side-slip conditions. A dualorifice system way behind the lowered flaps (similar to the Corsair’s) finally provided a satisfactory means to give the Hellcat a cockpit IAS reading comparable to the vaunted Corsair’s. That was the last we heard of the Hellcat’s performance gap with the Corsair. Performance case closed.

Hellcat Ailerons Improved— The NACA Way

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