HELLCAT VERSUS CORSAIR
GRUMMAN TEST PILOT FLIES THE COMPETITION
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, sealevel, 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 forwardfacing 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.
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 lowspeed 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
During this time, our flight-control engineers designed all kinds of aileron contours and shapes. We tested them to their limits but to no avail. We just could not get the same delightful low forces and high rolling performance as the Corsair had so ably demonstrated. We eventually realized that the high dihedral angle of the Hellcat’s wing produced exceptionally high lateral stability, which was the cause of the low rolling rate of our ailerons. To change the dihedral of the wing meant completely redesigning the complicated wing-fold mechanism where the dihedral angle of the wing was formed. That was a real nono in wartime production. We even went as far as making an exact set of molded plywood ailerons to the Corsair’s contours, but we met with zero success. The very low lateral stability that we measured in the Corsair gave its ailerons great power and produced the fabulous rolling rate. They were simply not fighting as much inherent lateral stability as we were. We finally incorporated the newly invented NACA spring tab for the aileron; it did the trick by lowering the aileron stick forces over 50 percent, thus allowing the pilot to get full aileron deflections at speeds of 100 knots faster than he could before. Navy pilots agreed that the spring-tab ailerons did close the rolling performance gap of the two competitors.
To everybody’s happiness (except that of the Japanese), these ailerons were introduced on the F6F-5 early in 1944. To further increase Japanese joy, we retrofitted many of the 3,000-plus F6F-3s that had been delivered to the Navy without springtab ailerons with spring tabs.
On one flight during full-power performance testing at 25,000 feet, I had the chance to see just what the practical benefits of the Corsair’s low lateral stability would be in an emergency. Pat Gallo, one of our other experimental test pilots, was flying the Corsair; I was flying the Hellcat.
We were at full power heading toward Bermuda when I noticed that Pat no longer answered my radio calls. I was trying to remind him to check his estimate of the differences between our speeds. When I finally passed his Corsair, I saw him peering at me very glassy-eyed, in a real daze.
I also noted that he was wearing one of the unsafe, light gray Mine Safety oxygen masks. I thought we had destroyed those masks many months before, after having serious problems with them at high altitude. We were now using the dark green Navy
WHEN I FINALLY PASSED HIS CORSAIR, I SAW HIM PEERING AT ME VERY GLASSY-EYED, IN A REAL DAZE ... I IMMEDIATELY REALIZED THAT I WAS FACED WITH MAKING ONE OF THE MOST CRITICAL DECISIONS I WOULD EVER HAVE TO MAKE FOR A FELLOW TEST PILOT.
issue masks with the balloon bag under the pilot’s chin; the bag clearly showed the oxygen flow by its expansion and contraction with each breath.
I immediately realized that I was faced with making one of the most critical decisions I would ever have to make for a fellow test pilot. I was unable to communicate with Pat and I knew that in another 10 minutes at full power he would be halfway to Bermuda. He would then run out of gasoline over a very cold and unwelcoming winter Atlantic Ocean. It became quite clear what I had to do, but I worried that my actions could have dire consequences.
I slowed to formation speed on his left side and closed in to him until my right wingtip was just under his left wingtip. I then gave a strong left push to my stick and rolled him into a 30-degree right bank. His Corsair started down in a long, slow spiral with me in trail. I did not know whether my actions would lead to a steep dive to the water or not, but I knew I had to do something. With the luck of the century, the Corsair’s very weak pitch and roll stability slowly took over, and we leveled out heading back to Long Island at about 19,000 feet. Much less hesitantly, I then repeated the maneuver twice until, at about 9,000 feet, he started talking to me in a most querulous and angry tone inquiring
which damn maneuver we were going to do next. Using my most diplomatic tone, I told him that we were very low on fuel and that he should reduce power from full throttle to cruise and return to base with me. His regular fiery temperament seemed all too docile until he said that he wasn’t feeling too well and suggested that I talk him through his landing. On the ground, he confessed that he didn’t remember anything about the flight from climbing through 10,000 feet to awaking at 9,000 feet before we landed. Needless to say, I now had great comments about the Corsair’s weak lateral stability and many more foul ones about the Mine Safety masks still in our ready-room lockers.
A Very Jumpy Takeoff
Before measuring Corsair takeoff performance, I performed the usual required stalls in all configurations. This model of the Corsair had the new and improved stall tripper wedge on the right wing to improve stalls. It was quite clear to me that the Hellcat was much more docile and controllable during and after stalls, especially in the landing-condition accelerated stalls. The Corsair had more of an abrupt wing drop in the normal stalls and was more difficult to un-stall than the Hellcat. Even worse, the Corsair did a totally unexpected double snap roll when performing a 5G accelerated stall in the clean condition. During these tests, I should have been more impressed with the Corsair’s reactions than I was. The Corsair was really talking to me.
We had found that the Hellcat could shorten its takeoff roll by about 100 feet in a calm wind if the tail was raised to levelflight position during the first part of the roll and then slammed down at minimum takeoff speed. We named this a “jump takeoff” (versus the normal three-point type). This became the standard way to make a short takeoff in the Hellcat—not so in the mighty Corsair.
My Army doctor brother was visiting me at Grumman on the day we were to perform minimum-distance measured takeoffs in the Corsair, and he was out on the runway to watch the proceedings.
After making 10 measured three-point takeoffs in the Corsair, I told the engineers that I was going to start jump takeoffs. I pushed the stick forward and waited until the airspeed indicated 66 knots; then I slammed the tail down onto the runway as I had many, many times in the Hellcat. Lo and behold! As the tailwheel went down on the runway, I got a very strong wind from the left side of the cockpit because the airplane prematurely left the ground, instantly yawed 30 degrees left, stalled, dropped the left wing, fell to the ground, and departed the runway promptly to the left without any help from me. We were headed at full power straight into a batch of Hellcats on the delivery line. Navy delivery pilots who have flown from Grumman’s Bethpage airport know there isn’t much empty space there, and they would thus understand the interesting but unplanned path the Corsair was grinding out for me.
The Corsair’s action was so precipitate that it seemed as if it took me way too much time to start taking prudent defensive actions. I finally yanked the throttle back, raised the tail so that I could see what the near future held for me, and began a frantic braking on what happily proved to be hardpacked, dry ground. I stopped about 50 feet from the nearest Hellcat in the delivery-line area! I sat there for a while until the earth stopped trembling, then I slowly taxied back to our experimental flightline and decided to call it a day for jump takeoffs.
While we were having cocktails that evening, my brother hesitantly asked me if I did that for a living every day.
Epilogue
The Corsair’s production line benefited in many ways from its Hellcat evaluation. Reducing the oleo bounce, making further improvements to its harsh stall characteristics, and enhancing the forward visibility by extending the tailwheel and raising the seat were easy ones to
THE LACK OF SATISFACTORY FORWARD VISIBILITY CAUSED MANY CARRIER-LANDING ACCIDENTS IN THE EARLY CORSAIR SERIES UNTIL THE F4U-4 CAME INTO SQUADRONS LATE IN THE WAR.
incorporate into the production line. But several of the needed fixes were impossible to insert into the production line until the major changeover of the F4U-4 model in late 1944. The Corsair’s cockpit internal layout, for instance, required a complete redesign, and that was impossible to do with the high wartime production rate that Vought was striving for in 1943.
Forward visibility for the Corsair was never as good as the Hellcat’s because of the design of its wing center section. In a fighter, fuel is usually required to be on its center of gravity (CG) to keep the flight characteristics within satisfactory limits. The Corsair was originally designed to have the fuel in the wing center section, and the first few prototypes did have it there. But the inverted-gull-wing design was so complicated to manufacture that those tanks had to be removed and a fuel tank had to be placed on top of the wing in a fuselage extension—where the cockpit had been. Placing the cockpit 4 feet farther aft gave the Corsair its very impaired forward visibility, especially in the landing configuration. This poor forward visibility also greatly reduced pilot lead estimation capabilities in deflection gunnery runs. The long nose was as endemic to poor visibility in the Corsair as the design of the wing dihedral was to the low rolling performance in the Hellcat.
The Hellcat, with its straight wing center section, could be designed with all of the fuel on the CG. Thus, the cockpit could be positioned just behind the engine to provide excellent forward visibility for aerial gunnery, carrier approach, and even after flare-out on landing. It was also attached to so much structure around the CG that it gave the pilot excellent crash protection. Hellcat pilots gave Grumman its nickname “the Grumman Ironworks.”
The lack of satisfactory forward visibility caused many carrier-landing accidents in the early Corsair series until the F4U-4 came into squadrons late in the war. Because of high accident rates, Corsairs were pulled from carrier operations three times during the war. In land-based operations, where higher-speed wheel landings could be used to improve forward visibility, the Corsair had a very good safety record.
In summary, any objective analysis must acknowledge that the United States and the U.S. Navy were fortunate indeed to have Grumman and Vought to produce the “Fustess with the mostess” so soon after Pearl Harbor. Part of the heat in the discussion to decide which was the better airplane was generated by the fact that both planes met the requirements for carrier and land-based uses extremely well.
This writer just might have been a little less biased if the Chance Vought Corp. was sending him a monthly retirement check of the same size as Grumman has been doing. If, however, the late Boone Guyton, who was the project test pilot for all models of the Corsair (and was an old friend) was buying the beer, I would agree heartily with him that the “bent-wing bastard” was the “greatest fighter in aviation history!”