Catapult Development

The basic concept of the aircraft carrier catapult hasn't changed much over the years. The airplane is fitted with something to hook it to the catapult and something to hold it back under full throttle until the catapult is activated. The hold back is designed to break (or nowadays release) when the airplane is being pulled forward at a force somewhat greater than that provided by full power and the catapult shuttle being pulled forward to tighten the hookup. However, the details have changed significantly.

Before World War II, although carriers were fitted with catapults, takeoffs were usually accomplished by a deck run rather a catapult launch. It was quicker and to a small extent safer since catapult failures were not unknown. However, as airplanes got heavier, requiring more distance to take off, and more of them were crowded on deck, resulting in less distance for a takeoff run, the catapult launch became more the rule than the exception.

The catapult bridle (two attach points on the aircraft) or pendant (one attach point) was considered disposable. It simply dropped from the aircraft and fell into the sea off the bow after the launch. It's not clear whether there was an alternative hookup during the war which retained the bridle/pendant on deck.

However, at some point the bridle/pendant was retained on deck by means of a heavy elastic strap that was attached to both the bridle/pendant and the catapult shuttle. After a certain number of launches or visible damage, the bridle/pendants were disposed of, either by a launch without a retainer when it was one launch short of the limit or being dropped over the side if damaged. This is an S2F which used a pendant.

It appears that there was little commonality among aircraft with respect to launch gear, including hold backs, particularly the strength of the "weak links" that broke when the catapult fired.

My guess is that pendants were more desirable than bridles from the deck crew's standpoint because they were lighter but bridles may have been necessary on some airplanes to accommodate a slightly off-center lineup.

Still later, somewhat after the introduction of the angled deck and the steam catapult, "bridle catchers" were added ahead of the catapult on some carriers. It appears that on those carriers without bridle catchers, the previous practice of using elastic straps to retain the bridle/pendant on deck was no longer used and it was disposed of with each launch.

The bridle arrester lanyards were attached to the bridle and a track on the deck parallel to the catapult track.

The bridle rig wound up on the bridle catcher following launch and were retrieved with the shuttle.

The bridle/pendant hookup process was somewhat labor-intensive, time-consuming, and dangerous. It also relied on the skill of the catapult crew for a proper hookup. In this case, the sailors who are going to hook up the hold back are lying on the deck. The bridle is lying on the deck already looped around the shuttle.

The solution was the integration of the launch and hold back hardware on the nose landing gear. Beginning with the Grumman E-2 Hawkeye, all new carrier-based airplanes were to be designed with this capability. The first at-sea E-2 launch was accomplished on 19 December 1962 from Enterprise, the first carrier equipped with the nose tow capability. (An adapter allowed the catapult to be used to launch airplanes that still required the bridle/pendant.)

The holdback is now reusable, although a specific one is required for each aircraft and are color coded accordingly.

Note that only one sailer is required in close proximity to the aircraft using the nose tow concept.

The Truculent(?) Turtle

An acquaintance recently asked me why the Lockheed P2V-1 Neptune that set a distance record in late 1946 was called the Truculent Turtle when the name on its nose was just "The Turtle". Moreover, the cartoon character on the nose, a turtle smoking a pipe and pedaling the propeller-driven equivalent of a unicycle, was anything but truculent.

In many places (copies of the Wikipedia entry), the interweb incorrectly states that "With time, the aircraft has come to be called 'Truculent Turtle'..." In fact, in press releases before the flight, the Navy was already referring to it as The Truculent Turtle as evidenced by a New York Times article dated the day that the flight began.

The name The Turtle and the cartoon character doubtless originated with the Navy/Lockheed plan, "Operation Turtle," to counter the publicity being garnered by the Army Air Force with long-range B-29 StratoFortress flights, one setting the long-distance record in November 1945. The Navy was concerned that the President and Congress might well overvalue the Army's ability to deliver the newly demonstrated atomic bomb and underfund the Navy's ship and airplane programs. "Turtle" was probably used by the engineers in recognition of the fact that the maximum-range cruise speed of a propeller-driven airplane, even high performance fighters, is slower than most people would think, only about 150 knots or 170 mph. They can cruise at higher speeds, of course, but not go as far.

The addition of Truculent was probably belated recognition that The Turtle did not convey the impression of long-range weapon delivery capability that the Navy wished to make with this record-setting flight even though this was not its stated purpose.

It was, no question, a publicity stunt. Few if any airplanes were as modified for speed records as The Turtle was for the distance record. Lockheed removed as much equipment as possible to minimize the empty weight and parasite drag and then added as many fuel tanks as there was space available until the aircraft gross weight was almost 50% greater than the maximum allowed operationally. In addition to new tip tanks, there were additional tanks in the outboard wing panels, the forward fuselage, and the aft fuselage. The standard internal fuel capacity of the P2V-1, not counting auxiliary tanks in the bomb bay, was 2,350 gallons. The Turtle's fuel capacity, including bomb bay tanks, was 8,541 gallons, well over than three times more.

Hal Andrews collection via Jim Sullivan (The lower radome was removed prior to the record flight and the tip tanks were  dropped when empty.)

In order to accommodate an engine failure shortly after takeoff, a fuel jettison capability was developed to reduce the airplane's weight as quickly as possible in that event. The tip tanks were simply dropped. The fuselage tanks were ganged to a dump station manned by one of the relief pilots during the takeoff. In theory, once the P2V had climbed to 1,000 feet above the ground, he could empty those tanks while maintaining the center of gravity within an acceptable range and thereby reduce the gross weight to that permitting a climb before they lost more than 800 feet.

Even a new, well-broken-in piston engine burns oil. The engine oil capacity was therefore increased by 64 gallons. The oil in the tank added in the nose wheel well was pumped manually as required to one or the other of the standard 78-gallon tanks located in each engine nacelle.

Four JATO bottles were added for the takeoff. These minimized both the length of the takeoff roll and the time it would take to reach the minimum single-engine control speed. Another change was the substitution of heavier duty main landing gear tires because of the higher takeoff speed required at the higher gross weight. The resulting takeoff roll was 4,700 feet on a 6,000-foot long runway. (The normal takeoff distance was less than half that.)

JATO Takeoff Test at Lockheed Burbank

The takeoff from Perth, on the west coast of Australia, was made at dusk local time. One reason given was the desire to begin at night to allow celestial navigation. However, as plane commander CDR Thomas D. Davies admitted to the press before takeoff, a far more important consideration was minimization of the level of turbulence likely to be encountered. At its design gross weight of 54,000 pounds, the P2V was designed for a limit load factor of 2.6. At a takeoff weight of 85,500 pounds, the structure was theoretically capable of being loaded to only 1.64 gs before being damaged. Of course, catastrophic failure of the structure was not supposed to occur before a 50% higher load was encountered, with the likelihood that it would sustain even more than that, but it was best to avoid turbulent conditions until some fuel had been burned off.

An excellent color video of the Turtle at Perth and the JATO takeoff is here: https://www.youtube.com/watch?v=8cyQklgmfzE or see https://thanlont.blogspot.com/2016/09/the-turtles-takeoff.html

It would take almost 60 hours to burn this much fuel at the maximum range cruise speed. To reduce weight, the crew therefore consisted of only four pilots instead of the regular crew of eight, with two resting and two flying at any given time. The flight was not uneventful. The crew had to deal with bad weather crossing the equator northeast of Australia, turbulence and icing in the western US, and unexpected headwinds. The stated destination prior to takeoff was Seattle, Washington*, which would have set the record, but it seems clear that they intended to fly as far as they could, preferably all the way to Washington, D.C. However, after reviewing their fuel status and approaching Columbus, Ohio they prudently decided to land there after 55 hours in the air rather than pressing on to Anacostia where officials and family were waiting. That would set the record at 11,236 statue miles, almost halfway around the world.

New York Times

The flight had the hoped-for impact and specific comparison with the Army Air Force B-29 flights. On 2 October 1946, a New York Times editorial stated "The 7,916-mile record that it shattered was that made by the Army's Boeing Super-Fortress Dreamboat. A plane like the P2V can carry an atomic warhead from any point on the earth's surface to a point half-way round the globe."

Of course, the Times neglected to note that delivering a bomb to a target 12,000 miles away would be a one-way trip for a P2V, it couldn't be a very big bomb (the crew debated the last-minute addition of a 37-pound kangaroo), and the enemy would have a couple of days to get ready to greet it...

*Seattle, Washington was on the great circle route to Washington, D.C. as shown here.

The great circle route is the shortest distance between two points on the globe, which does not appear as a straight line here because it is the depiction of the globe with a Mercator projection. However, winds aloft might (and did) dictate a deviation from this line, which on a long flight is established by a concept called pressure pattern flying (feel free to Google that). Moreover, the reported weather in Seattle dictated a mid-flight deviation to the south as shown on the map of the actual route of flight.

The Turtle is now on display, indoors, at the excellent National Naval Air Museum at NAS Pensacola, Florida.

And Now For Something Completely Different

The Coast Guard was responsible for helicopter development during World War II. One of their concerns was the rescue of the crew from a ship that had been sunk by German submarines off the U.S. east coast. Existing helicopters were too small to carry more than one or two rescuees. The Coast Guard wanted one that could carry eight in addition to a crew of two.

At the time, based on experience with autogiros, it was believed that the empty weight of a single rotor helicopter as a percentage of gross weight would increase with rotor diameter so quickly that large single rotor helicopters would have no payload capability. Frank Piasecki, a young engineer who had just flown his first helicopter, convinced the Coast Guard and the Navy that the answer was a tandem-rotor helicopter. He got a contract for a full-scale demonstrator in January 1944.

The first flight of what was designated the XHRP-X, Bureau Number (BuNo) 37968, was made in March 1945, little more than a year after go-ahead. It was powered by a 450-hp Continental R-975 radial engine and subsequently referred to as the Dogship at Piasecki. Unique features in addition to the tandem rotors were the castering wheels intended to minimize side loads in a touchdown with sideward motion; the pilot sitting aft of the front pylon (the copilot sat directly behind him); and the bottom of the forward fuselage being "skinned" with clear plexiglass panels for downward vision. Unlike subsequent tandem-rotor helicopters, the rotors did not overlap.

The XHRP-X was featured in this late 1945 newsreel as the "World's Largest Helicopter!". Following its successful development and demonstration, Piasecki received approval to build a Static-Dynamic Test Article for qualification testing of the drive and rotor systems. It did not receive a BuNo and the fuselage was never covered with fabric.  It was powered by a 600-hp engine P&W R-1340 engine.

 The XHRP-1, BuNo 37969, was also authorized.

 Its first flight was accomplished in March 1947. It initially had a aft fuselage without as much side area as the XHRP-X, possibly to reduce weight. Stability problems resulted in the addition of a small horizontal stabilizer and vertical fins.

Piasecki also received a production order for 10 HRP-1s in June 1946 and another 10 in April 1947.

The first production HRP-1 flew in September 1947 and was delivered later that year. The last of the total order of 20 was delivered in 1949. These were initially used by the Marine Corps to develop tactics for vertical assault and by the Coast Guard for its ongoing helicopter search and rescue development.

Five of the HRPs initially assigned to the Marines Corps were then used by the Navy for the development of dipping sonar and airborne minesweeping. The fabric was taken off to reduce weight (testing was done off Key West, Florida) and flotation bags were added so the helicopter could be recovered if its engine quit over the water.

Eventually a portion of the small fleet was acquired by civil operators from military surplus.

The Dogship is currently stored at the Smithsonian's Paul E. Garber Preservation, Restoration, and Storage Facility located at Silver Hill, Maryland.

The first production HRP-1, BuNo 111809, that was at the New England Air Museum is currently being restored at Piasecki Aircraft Corporation in Essington, Pennsylvania for eventual display at the American Helicopter Museum in West Chester, Pennsylvania.

The HRP-2 utilized the same drive train and engine as the HRP-1 in an all-metal fuselage. The pilot and copilot now set side by side ahead of the front rotor mast. First flight was on 10 November 1949. Only five were produced. They were initially used by the Marines along with the HRP-1s and then all of the -2s were assigned to the Coast Guard. It was clear that they were underpowered with the same 600-hp engine installed in the HRP-1.

At least one surplus HRP-2 was procured and operated by Rick Helicopters, then the largest civil operator of rotorcraft, in the 1950s.

The Air Force and subsequently the Army recognized the value of the basic design for their emerging helicopter missions, however, and ordered modified versions of the HRP-2 as the H-21 with more powerful Wright engines with up to 1,425 horsepower.

The Davis Barrier, One More Time

For background and other information on the Davis barrier, see the following entries.
22 September 2008
1 October 2008
26 September 2009
4 October 2010
One of these days, I'll combine all this into one entry.

The FJ-2 and -3 Furies had a retractable barrier pickup device located aft of the nose gear wheel well. This insured that the activated barrier cable did not fall back down before it engaged the airplane's main landing gear struts. (It was subsequently removed from at least the -3s when the angled deck eliminated the need for the Davis barrier.)

There is a similar, albeit non-retractable, device on the belly of the Grumman S2F. I had assumed that it performed the same function, but it turns out that it corrected a different problem related to the Davis barrier function.

The initial S2F Davis barrier qualification at Naval Air Material Center (NAMC) had actually been accomplished with an F7F that had been modified with tubing shaped to simulate the S2F-1 belly. Surplus F7Fs were plentiful and surplus S2Fs, not. Moreover, in the interest of minimizing cost, nose-high, off-center, and lifter strap run-down by a dual nose wheel landing gear (the F7F had a single nose wheel) were not evaluated.

In early 1954, during one of the first S2F squadron carrier qualification periods aboard Siboney (CVE-112), a pilot failed to lower his tail hook, which wasn’t noticed by anyone on the LSO platform as it should have been. This guaranteed a trip into the barriers. The airplane also engaged nose high, which didn’t help matters. Things went badly after that. The cables didn't engage the left main landing gear as they should have. The nose gear failed when the airplane pitched down and the right wing was torn off when the airplane was yanked violently around by the engagement of only one landing gear strut by the barrier cable.

S2F-1 BuNo 129146 was therefore assigned to NAMC to provide a more representative test article for a series of more comprehensive tests. It was catapulted, unmanned, into a Davis barrier at speeds from 35 to 70 knots in five-knot increments. Normal, nose-high, and nose-low engagements were made as well as at 17 feet off of centerline. A total of 129 shots were accomplished between 30 May and 23 November 1954 to develop a configuration that provided a higher likelihood of a benign barrier encounter.

One of the problems encountered was that on a nose gear with two wheels, a lifter strap could conceivably be caught between them, preventing the lifting of the barrier cables. The S2F also had a relatively short wheelbase and a wide tread, which meant the cable might not always rise high enough across the width of the tread in time to engage both landing gear struts. If only one strut was engaged, a violent yaw resulted as it had in the Siboney incident.

S2F changes established during the testing included the addition of four pairs of small detents on a strengthened nose wheel door so the actuator strap would not slip down, affecting the rise of the barrier cable. The nose gear strut torque arms were modified and the tow fitting between the wheels was extended forward to reduce the likelihood that a lifter strap would be trapped between the nose wheels. A slanted fairing was also added ahead of the catapult hook so there was less likelihood that the cable would be deflected downward and not engage the main gear struts.

Most importantly, a cable scoop, the “Fosdick,” was added on the bottom of the fuselage. Unlike the one on the FJ-2/3, it was not just there to keep the barrier cable up off the deck. It was primarily there to reduce the drag loads of the barrier cables on the landing gear and the violent yaw that would result if only one main landing gear was engaged by the cables, assuming that the cable scoop was engaged as well.

Here is an early S2F, flying with one engine shut down and the propeller feathered. Note that the only protuberances on the belly ahead of the retractable radar dome are two radio antennas and the catapult hook.

This is the belly of the S2F after the addition of the detents on the nose gear door, the fairing ahead of the catapult hook, and the cable scoop.

The existing main landing gear "scoops" were also modified to be more effective at diverting the cables onto the struts.

Steve Ginter is working on an S2F-1 monograph for publication in his Naval Fighters series.

Once Upon A Time

I rediscovered an interesting report in the Vought archives this week, Notes on Comparison of Carrier and Land-based Fighter Airplanes Incorporating Folding Wingtips dated 21 March 1952 and authored by John H. Quinn Jr. I had previously copied it from the George Spangenberg collection in the National Archives but hadn't taken the time to examine it closely.

The folding wingtips aspect of it was only of passing interest to me because it was never incorporated on a produced design, at least not for the original purpose, which was to provide a high aspect ratio wing for cruise flight with the wingtips lowered and a low aspect ratio wing for combat maneuvering with the wing tips raised as shown in the following artists concept.

Vought submitted an unsolicited informal proposal to the Navy for the V-381 which incorporated the feature in September 1952. The Navy passed, having already given Douglas a contract for the A4D Skyhawk.

The report, however, addressed a more pressing issue, which was the Navy's need to achieve performance parity with land-based jet fighters. Three predesigns were accomplished for the study: a carrier-based airplane designed to the existing limitations, a land-based airplane, and a carrier-based airplane taking advantage of relaxation of the existing limitations.

"It was assumed the airplanes were powered with a single J67W-1 engine... and were designed to combat radius of 600 nautical miles, approximately." The J67 was the designation of the Curtiss-Wright license-built Bristol Aero Engines Olympus; it was projected to provide 21,500 lbs of thrust. The mission radius was, of course, selected to highlight the cruise benefit of the folding wingtip feature.

At the time, carrier airplanes had to be designed for launch from the existing hydraulic catapults and recovery using the Mk 7 arresting gear; tactical airplanes, as opposed to the big nuclear bombers, could not be any longer than 56 feet (for straight spotting on Essex-class elevators) or taller than 17 feet and more than 24.4* feet wide when folded. (The folded height and width were Essex-class hangar deck constraints.)

Although there was no dimensional restriction on the land-based airplane, it was required to operate from a 5,000-ft runway with the takeoff roll not to exceed 3,000 feet. (Sounds short, but according to the F-100A Standard Aircraft Characteristics chart, it had a ground roll of 2,970 feet at its maximum gross weight of 29,000 lbs.) It was also required to have a combat ceiling of 55,000 feet as another constraint on wing loading. (The F-100A was bit short on that and woefully short of the range, not having folding wingtips.)

Because of the lift and size limitations imposed by the existing carrier-basing ground rules, the first carrier-based design was predicted to be 200 knots slower than the land-based one at 35,000 feet, about Mach 1.7 and 2.0 respectively. Analysis indicated that only two of the carrier-basing imposed constraints, takeoff wing loading and overall length, were the cause of the difference. The newly invented steam catapult was projected to eliminate the wing loading penalty; diagonal spotting was suggested to allow for more length and provide a better fineness ratio for less drag. The result was parity of performance with land-based airplanes. (It was recognized that the longer airplane would result in fewer being accommodated aboard, a shortcoming for carrier-basing.)

Navy Length and Wing Area Constrained

Air Force Land-Based

Navy Diagonal Spotting and High Wing Loading

As it happened, the F8U-1 achieved parity (even superiority) with the F-100, also powered by the P&W J57, based on the benefit of the steam catapult alone. (It was just within the 56-foot length limit.) The F8U-3 exceeded 56 feet in length by a little less than three feet but it had Mach 2 performance in part due to the rediscovery of the area rule by Whitcomb in 1952; it too had performance parity with the land-based J75-powered fighters.

*The maximum folded width was in the process of being increased to 27.5 feet, in part perhaps to allow the Douglas A4D Skyhawk to go below without having to fold its wings.

F-111B Colossal Weight Improvement Program

This assessment is based on a 1/50th scale model in the Grumman History Archives on Long Island and a three-page summary of Grumman's CWIP (Colossal Weight Improvement Program) study provided to General Dynamics.

The empty weight proposed for the F-111 was even more optimistic than usual in winner-take-all paper competitions. As is customary, Grumman and General Dynamics initiated a two-pronged F-111B weight reduction study effort, the Super Weight Improvement Program and the Colossal Weight Improvement Program, even before first flight. Roughly speaking, the ground rules for the SWIP were to reduce the weight but not significantly depart from the design and mission requirements. The CWIP allowed a great deal more flexibility, basically tossing out anything imposed only by the Air Force low-altitude strike mission and preferences like the crew escape capsule.

For the CWIP configuration, Grumman engineers deleted the bomb bay and escape capsule and reduced the volume required for the main landing gear by not allowing for the large high-flotation tires required for operation from unprepared fields. That enabled them to shorten the forward fuselage by about five feet. The shorter forward fuselage presumably allowed them to delete the ventral fins, with the original vertical fin now adequate for directional stability even at high angles of attack. However, the horizontal stabilizers were slightly increased in size, presumably for improved low-speed handling qualities for the carrier approach.

All six Phoenix missiles were now carried on the fuselage, four semi-submerged and two on short pylons on the lower sides of the fuselage. This arrangement eliminated both the wing pylons and swivel mechanisms required to keep the missiles aligned when the wings were swept. I haven't yet found any information on the main landing gear configuration change required by putting two missiles on the centerline of the belly, but presumably it resembled that on either the Grumman F11F Tiger or the North American A3J Vigilante.

The center fuselage with the engine inlets and wing mounting structure were basically unchanged except for the main landing gear bay. The wings were also unchanged. The engines appear to have been moved forward by about two feet to restore the center of gravity after the nose was shortened.

Although the canopy appears to be bulged upwards, my preliminary assessment is that the visibility over the nose was no better than it was on the original F-111B, which was determined to be unsatisfactory. However, the lower weight would have resulted in a lower angle of attack for the same lift, possibly providing the same over-the-nose visibility improvement as the raised cockpit that was eventually required.

The government program team elected to incorporate most if not all of the SWIP changes in the 12th F-111A and the 4th F-111B. The CWIP specification changes stayed on the drawing board until Grumman was able to apply them to what became the F-14.

One if by Land, Two if by Sea

“One if by land, and two if by sea.” That line from Longfellow’s poem commemorating Paul Revere’s famous ride in 1775 was one of the justifications used by the Navy in 1976 to select the twin-engine McDonnell F-18 over the single-engine F-16 for its VFAX program. Some viewed it as dissembling on the Navy's part since the desirability, much less necessity, for twin-engine carrier-based aircraft had not been very evident up until then. In fact, although single-engine airplanes were in the minority in the air wings at the time, that was a relatively recent change from past practice. A year earlier there was still an air wing aboard Hancock (CV-19) that was almost entirely comprised of single-engine aircraft. Now, of course, there are no single-engine airplanes in the carrier air wings.

The major benefit of twins, the capability to return to base after an engine failure, was initially problematic for a carrier-based airplane. The pilots approached power-on in level flight at the lowest safe speed and minimum altitude, cutting the engine just when the airplane would settle onto the deck. This was essentially the same technique used for a short-field landing ashore, where it assured a touchdown very close to the approach end of the runway, allowing the maximum distance for stopping.

The pilot of a twin-engine propeller-driven airplane with one engine inoperative had to take into account the minimum control speed in that situation. Since the engines were almost always placed out on the wing, when one failed the other produced a significant turning moment which had to be counteracted by the rudder. Since rudder effectiveness varied with airspeed, at some point the pilot could no longer stop the airplane from turning with the engine at full power. What’s worse, the turning generated a roll because of the difference in the lift on the wing on the outside of the turn versus the one moving slower on the inside. Since the ailerons also lost effectiveness with decreasing airspeed, a loss of control in roll would result as well if the engine power was not immediately reduced.

Unfortunately, the minimum-control speed at the power required to climb with the gear and flaps down was almost certainly higher than the required approach speed dictated by arresting gear, which made a successful wave-off an iffy proposition.

The tyranny of minimum-control speed was also imposed on an airplane taking off, but it was more draconian at sea than ashore. If the pilot taking off from a runway lost an engine while still below minimum-control speed, he would simply close the throttle on the good engine and reject the takeoff. The outcome varied with the length of the runway and if it came to that, the landscape beyond its end, but was rarely as dire as faced by the pilot of an airplane less than one hundred feet above the sea after being launched from an aircraft carrier at less than the minimum-control speed with full power on the operating engine. If he reduced power on it engine to maintain control, he almost certainly would not have enough for level flight, much less to climb or accelerate to a speed at which he could use all the power available.

Having a second engine was therefore not as good a deal for a pilot flying from an aircraft carrier as it was for one flying from an airport. Although it enabled one to divert to a land base or get back to friendly ships and ditch if an engine was lost in flight, it doubled the risk of an engine failure during a critical, albeit short, time during takeoff and landing. Twin-engine airplanes also tended to be bigger than singles whereas compactness was a virtue on an aircraft carrier.

Nevertheless, there were benefits beyond the ability to continue flight after an engine failure. The easy way to improve the performance of fighter airplanes is to incorporate more powerful engines in new or existing designs. Increasing power in piston engines basically meant adding more and/or bigger cylinders and supercharging. By the late 1930s, the engine manufacturers were beginning to approach the limits of existing technology and incremental horsepower increases were resulting in increasingly smaller increases in speed and greater engine complexity. The obvious next step was the twin-engine fighter, a doubling of power available without requiring the time and expense of a new engine development.

The U.S. Navy solicited proposals for a twin-engine carrier-based fighter in 1937 but none of the submittals were deemed to be acceptable. In 1938, the Navy had Lockheed modify an Electra Junior to have a fixed tricycle landing gear and tail hook. It was designated XJO-3 and delivered in October 1938. On 30 August 1939, Navy pilots made 11 takeoffs and landings from Lexington (CV-2) to evaluate it from both twin engine and tricycle landing gear standpoints.

In parallel with this research program, the 1938 competition for a new fighter was opened to both single and twin-engine designs. This time, the Grumman design number G-34 was considered worthy of evaluation by the Navy as the XF5F along with single-engine designs from Vought, the XF4U-1 powered by the big new P&W R-2800; and Bell, offering a derivative of the Army Air Forces P-39, the XFL-1.

The XF5F, probably in consideration of the one-engine-inoperative requirement, had the engines mounted as far inboard as possible and twin vertical fins, one in each engine’s slipstream. One-engine-inoperative wave offs were evaluated at altitude: "(A wave-off) might be accomplished (on one engine) provided the airspeed is about 80 knots or more and no more the 1/2 power on the operative engine were used." The "proper" approach speed based on stall speed, however, was defined as about 74 knots.

In spite of having as much or a little more installed horsepower than the XF4U, the XF5F was slower and couldn’t climb as high although its rate of climb through 20,000 feet was essentially the same. As a result, the Navy elected to proceed with the F4U for development and production. Nevertheless, the Bureau of Aeronautics continued to be interested in a twin-engine carrier-based fighter. On 30 June 1941, Grumman received a contract for the two XF6Fs and two XF7Fs. The F7F program suffered from the priority on F6F Hellcat development but the prototype Tigercat finally flew for the first time on 3 November 1943.

As soon as Grumman test pilots flew the XF7F-1, they realized that it did not have a big enough fin and rudder for an acceptable minimum control speed in the event of an engine failure on takeoff or a wave-off. Design of a bigger fin and rudder was initiated and introduced on the F7F-3. Although all models of the F7F were carrier qualified, the likelihood of and/or concern about a successful single-engine wave-off must have been low as there was no description of the technique for a single-engine carrier landing in the flight manual. In any event, the Tigercat never deployed with an air group on a carrier, probably due to its size as much as anything else.

One of the Navy’s first carrier-based jets, the McDonnell FD-1 Phantom was a twin, mainly because the Westinghouse-provided engine wasn’t very big. It grew to become the F2H Banshee, the first twin-engine airplane to regularly deploy on carriers. Two of its contemporaries, the Douglas F3D Skyknight and the North American AJ Savage, were also multi-engined. The AJ had three engines, two turning propellers and a jet. Like the F7F Tigercat, the Skynight was primarily operated by the Marines and made very few deployments. The Savage did deploy because of its critical mission of long-range nuclear strike, but because of its size, it generally was held in readiness at nearby Naval air stations during a carrier’s deployment. These jets were less limited from a minimum control speed standpoint in the event of a one-engine-inoperative situation than previous twin-engine propeller-driven airplanes because the engines were located close to the centerline; the AJs were slightly better off if one of its piston engines failed because the jet engine was located on its centerline.

However, North American was concerned about minimum control speed as evidenced by the size of the AJ’s original fin and rudder, made even bigger because carrier basing necessitated a fairly short airplane. Unfortunately, the rudder proved to be too big for high speed flight and resulted in a fatal accident when it broke the tail off in a flight test maneuver. The empennage was redesigned to increase the size of the fin, reduce the size of the rudder, and delete the dihedral in the horizontal stabilizer.

The lack of U.S. Navy concern about engine failures in the late 1940s was evident by the initiation of single-engine airplane programs, the Douglas F4D Skyray and the McDonnell F3H Demon, to replace the twin-engine all-weather Banshee. It was still true in 1958, when the Navy had to choose between the single-engine Vought F8U-3 and the twin-engine McDonnell F4H. The safety record of twin versus single-engine airplanes was examined and determined to not be a deciding factor. In fact, the only twin-engine airplane in the deployed carrier air groups at the time was the Douglas A3D Skywarrior, which had two engines because it was too big to be powered by only one. The F4H was selected because it had a dedicated radar operator, not because it had two engines.

The Navy did regularly deploy one twin-engine propeller-driven airplane at sea for more than two decades beginning in the mid-1950s on axial deck carriers, in part because Grumman had learned a lot about operating twin-engine airplanes from aircraft carriers with the F7F program. Its S2F (S-2) was as short-coupled as carrier airplanes get, so in order to size the rudder both for the single engine takeoff and wave-off condition and—relatively speaking—high-speed flight, it had a two-piece rudder. Up and away, the forward portion of the rudder was just used for directional trim and only the aft portion of the rudder moved with the rudder pedals. For takeoffs and landings, the forward and aft portions of the rudder could be selected to move as a unit, doubling the width of the rudder and reducing the S2F's  minimum control speed to one suitable for carrier launches and wave-offs.

The introduction of steam catapults, angled decks, and descending, constant angle of attack approaches also reduced the degree of difficulty of one-engine-inoperative takeoffs and landings.

By the time Grumman engineers designed the F-14, they felt confident enough in their handling qualities analysis to widely separate its engines to provide a "tunnel" where two of the big Phoenix missiles could be carried side-by-side.

However, minimum control speed would still prove fatal to the unwary: Hultgreen Crash

Finally, click HERE for a great tale of how a second engine and a naval aviator saved an airplane...