F8F Safety Tips—It Seemed Like a Good Idea at the Time

Much of this post was taken from Naval Fighter Number Eighty: Grumman F8F Bearcat, an excellent monograph on the Navy's last and arguably best propeller-driven fighter from the standpoint of air superiority.*

It is available directly from Steve Ginter (http://www.ginterbooks.com/NAVAL/NF80.htm), Sprue Brothers (http://store.spruebrothers.com/), or Amazon books.

In 1943, Grumman engineering was struggling to meet the weight goal for their new high-performance air-superiority fighter that was intended to replace the F6F Hellcat. In the process, they came up with a gimmick that would have been expected from their across-the-Sound rivals, Vought, but not from what was fondly referred to as the Grumman Iron Works.

The primary structural design requirement is specified as a limit load in gs at a design gross weight.  For fighters, the design gross weight was approximately the same as the combat weight, which was the operating weight (empty weight plus trapped fuel/oil, fixed armament, pilot, removable equipment, and other odds and ends) plus bullets and 60% of internal fuel. Application of the limit load was not to result in a permanent deformation of the structure. There was also an ultimate load requirement, which was expressed as a percentage of limit load, below which the structure might be permanently bent but would not break. If it was subjected to something greater than ultimate load the designer was no longer responsible for what happened.

At the time, according to Corky Meyer,  a longtime Grumman test pilot and one of the coauthors of the monograph, the limit load requirement was 7.5 gs and the ultimate load almost twice that, 13 gs. To minimize weight, the Grumman innovation was to have the outboard three feet of the wing, including that portion of the aileron, break off at 9 gs, which would allow the remaining, less-leveraged wing structure to sustain an ultimate load of 13 gs. The weight savings was 230 lbs, a significant reduction for an airplane with an empty weight of only 7,600 lbs.

The weak link, so to speak, was just outboard of middle hinge of the aileron so adequate roll control would still be available in the event that both tips broke off, which was the expectation. The concept was successfully tested in flight using an F4F Wildcat modified with breakaway wingtips. F8F flight tests were subsequently accomplished by Corky himself to include landings with only one wingtip broken off to demonstrate controllablity in the asymmetric condition. Demonstrated and proven, the safety tip was standard on production Bearcats.

It also worked in service, with pilots even landing on carriers after they had parted company with their wingtips by overloading their airplanes. "I made a wide gentle pass—had 100 knots at the 90-degree point. The pass felt very little different, just a little fast. The landing was normal with quite a bit more shock on catching the wire."

There were, however, fatal crashes associated with the breakaway of only one wingtip. One was a Blue Angel who failed to pull out of the downward finish to a Cuban 8 at an airshow in September 1946. Another was during pullout from a dive-bombing run. The resulting sudden roll reduced the effectiveness of a pullout to less than that needed to avoid hitting the ground.** That only one wingtip came off instead of both was ascribed to variation in manufacturing tolerance (size of rivet holes, clamp-up load, skin thickness, etc) in the structure and a difference in the weakening over time of the weak-link structure in each wing caused by carrier landings and buffet during high-g maneuvers.

The response was to add a ballistic backup to the weak link to insure that both tips came off at the same time. Primacord (a thin plastic tube filled with explosive) and a microswitch were added to the break point and the installations on each wing were connected electrically. If the microswitch opened on one wing, indicating that the wingtip had separated, a circuit would close to detonate the Primacord on the other wing, insuring that its wingtip separated as well.  Corky demonstrated the removal of one wingtip ballistically in flight.

If there was understandable nervousness about bombs embedded in aircraft structure, it wasn't enough to insure that adequate safety measures were established or observed although the installation was identified with a red line on at least some Bearcats.

 Capt Paul Anderson collection via Jan van Waarde

It was therefore probably inevitable that a short circuit during maintenance on an F8F caused the wing tip to separate, killing a sailor. According to the Flight Manual "it has not been possible to make and maintain a continuously reliable installation of the explosive wing-tip-shedding device in service airplanes." The result was an airframe change in early 1949 to delete the Primacord installation and eliminate the weak link with a structural beef-up of the wing.

* A somewhat different story of the genesis of the Bearcat than the one provided by Corky in his monograph can be read here: http://thanlont.blogspot.com/2011/02/conception-of-f8f-bearcat.html

** Contrary to what you might think, the loss of lift from the wing tip was usually accompanied by a net increase in lift from the rest of the wing rather than a decrease. The nose-down pitching moment of the wing was reduced by the loss of the wing area but the nose-up pitching moment of the horizontal tail remained the same, resulting in an increase in the angle of attack of the wing at the amount of aft stick when the tips came off. If the increase didn't exceed the angle of attack for stall, lift would therefore increase.

Westinghouse Redux

All this time, I had misidentified the jet engine under the F4U at Patuxent River in 1944 as the Westinghouse 9.5-inch engine instead of its original 19-inch Yankee engine. I'm not sure why I didn't compare it more closely to the airplane's tires to establish its diameter. However, it's clear to me now that it was the bigger Yankee engine so I've revised the post accordingly: http://thanlont.blogspot.com/2011/03/from-hero-to-zero.html

Baby Steps for the Tip of the Spear

One of the U.S. Navy's first airplanes was a swept-wing biplane with no horizontal tail. Burgess was a U.S. shipbuilding company that got into the airplane business in 1910. Beginning with Curtiss and Wright designs, it built airplanes under license for several years. It also bought a manufacturing license for the Dunne D.8 that was developed by John Dunne in England. The Navy bought at least a few as the Burgess-Dunne AH-7 in 1914.

NA 80-G-452496

The sweep of the wing was obviously not for speed but to move the pitch control surface far enough aft of the center of gravity to provide sufficient pitching moment for control of angle of attack.

At least one was fitted with bomb racks, one under each wing as evidenced in this picture taken at Pensacola in September 1916.

 NA 80-G-463263

The bomb looks almost home made...

Halcyon Days IV

In the summer of 1951 when this picture was taken by VF-51 squadron mate John Moore, Neil Armstrong was not yet 21 and had just been promoted to Ensign.  Air Group Five, of which VF-51 was a part, had just deployed on Essex and they were enjoying a day at the beach in Hawaii on their way to the Korean War.

Armstrong had completed four semesters of college at Purdue University, financed by the Navy under the Holloway Plan that obligated him to three years of service at that point before completing his degree. He was designated a Naval Aviator in August 1950, two weeks after his 20th birthday and two months after the start of the Korean War. Although still only a Midshipman, he had the good fortune to be assigned to VF-51 in November. The squadron was in the process of reforming with new personnel and equipment following a deployment on Valley Forge. Although jet transition units had been established to check out pilots, Neil's first flight in a jet was solo in a VF-51 F9F-2B Panther on 5 January 1951. (The Navy was more casual about training then and yet to realize that more rigor was necessary to avoid a horrendous loss of pilots and airplanes.)

Here, Midshipman Armstrong is flying F9F-2B number 116 as the wing man of Lt(jg) Ernie Russell in 107. John Moore took the picture.

Air Group Five deployed aboard Essex on 26 June 1951. The picture of young Armstrong at the beach was taken during final workups in July in Hawaii. On 29 August, little more than a year after becoming a Naval Aviator, he flew his first combat mission. Less than a week later, a cable strung between two hills as a crude antiaircraft booby trap cut off six feet of one of his wings. He managed to herd the badly damaged jet out over the water where he could eject without much risk of capture. He went on to fly a total of 78 combat missions.

Armstrong left the active Navy in the fall of 1952—although he  continued to fly in the Naval Reserve through late 1960—and returned to Purdue. He graduated with a bachelor's degree in Aeronautical Engineering and joined NACA. It was a most satisfactory beginning to a storied career.

Thanks to the staff at the Emil Buehler Library at the National Naval Aviation Museum for the pictures. Many of the facts included above were taken from First Man: The Life of Neil A. Armstrong by James R. Hansen.

Halcyon Days III

I'm not sure yet when this photo was taken but it is probably late 1955 or early 1956. The aircraft are all newly assigned to NATC for test and evaluation before being declared suitable for service use. Leading the echelon is an Douglas A3D-1 Skywarrior that was to be participate in at-sea carrier trials in June 1956 aboard Forrestal. The change from the overall blue to the gray/white scheme had just been decreed in February 1955, which is why its folding fin, rudder, folding wing sections, flaps, and ailerons are blue.

The two new all-weather fighters were the McDonnell F3H Demon that is next in the formation with a Douglas F4D Skyray below it. These are finally about to get to the fleet, having been in development since first flights in 1951. Both were delayed by the J40 engine fiasco (as was the A3D, but it had an earlier start) that required an engine substitution. The A3D and the F4D were subsequently powered by the P&W J57 while the F3H had to make do with the Allison J71.

The last three are all powered by the Wright J65 engine. From top to bottom, they are the North American FJ-4 Fury, Grumman F11F-1 Tiger, and Douglas A4D-1 Skyhawk. None of these three (or the F4D for that matter) were selected for development after a formal competition. The FJ-4 and the F11F (as the F9F-8 and then F9F-9) were initiated with budget designated for product improvement of a production airplane, the FJ-3 and F9F-6 respectively. The A4D rose from the ashes of the A2D program and was the beneficiary of its budget. (Before McNamara, the services had a lot more flexibility in airplane development.)

Most of the six were not as successful as hoped. The FJ-4 and the F11F were what the fighter class-desk officer at the time believed to be most appropriate for a day fighter: light, small, simple (inexpensive), maneuverable. The FJ-4 didn't even have an afterburner although Grumman had the foresight to add one to its F11F. As a result, the F8U, which was won a true competition against a specification that emphasized speed, almost literally blew them away. The FJ-4 fighter was relegated to the Marine Corps; the Navy subsequently bought some FJ-4Bs as an attack aircraft to give Ed Heinemann something to think about during early A4D development and production when it felt that Douglas wasn't being responsive to its concerns.

The F4D never got an armament capability that made it an effective all-weather aircraft. Although it deployed several times, it was really not suited for defending the carrier if the skies were cloudy. The Marine Corps operated it longer and didn't mind its shortcomings. The F3H wound up armed with the Sparrow missile, so it had a true all-weather capability. It also begat the McDonnell F4H Phantom and that alone justified its existence.

As for the big A3D and the little A4D, they both enjoyed long and honored careers, the A3D in part because it was big and the A4D, because it was little...

The Vought F5U: Missed it by that much...

Once upon a time, NACA engineer Charles Zimmerman postulated that a very low-aspect-ratio wing would provide low-speed lift and short takeoff and landing performance. The wing ultimately became a disc with large propellers mounted at the forward outboard edges and rotating in opposite directions to the wingtip vortices. These made the wing even more effective at low speeds and increased the effective aspect ratio for cruise. Wind tunnel testing established the feasibility of the concept. Zimmerman joined Vought in 1937 where he designed and flew a model that demonstrated the configuration's potential for very low speed flight. Vought proposed a concept demonstrator, its V-173, to the Navy, which was intrigued enough to provide Vought with a contract for one in May 1940.

The V-173 was not small but fortunately it was light, a wooden and metal frame covered by fabric, since it was only powered by two 80-hp Continental engines.

Its first flight was on 23 November 1942. It was almost its last, since Boone Guyton found it difficult to get it turned back around to return for landing. Control modifications were made before its next flight that provided better handling qualities.

The Navy had already ordered a production version, the F5U. It was exactly the same size as the V-173, but of all-metal construction and powered by two 1,350-hp P&W R-2000 engines.

The mockup had three-bladed propellers but it was soon apparent to the engineers that the installed power and necessary rotor-hub gimbal (the blades had to "flap" to relieve root bending loads) dictated a design with four blades.

The development of the propellers and qualification of the gearboxes that interconnected the engines and the propellers delayed the program. It may have made its first low-power ground runs with F4U propellers. (The left-hand one appears to have the propeller blades rotated 180 degrees in the hub.)

The F5U's propellers had a much larger root chord and the opposed blades were paired. Note that the blade pairs were also staggered fore and aft.

The F5U was finally ready to fly in March 1947 but by then it was apparent that new fighters would be jet propelled. Although the F5U reportedly made short hops down the runway at Sikorsky Field, a first flight was not accomplished before the Navy terminated the program and directed that the prototype be destroyed.

Fortunately for aviation enthusiasts, Vought donated the V-173 to the Smithsonian. It languished at the Silver Hill storage facility for many years before being shipped to Grand Prairie, Texas where Vought Heritage volunteers restored it to like-new condition. It is now on display at the Frontiers of Flight Museum in Dallas, Texas. See http://www.flightmuseum.com/

Tailhook? We don't need no stinking tailhook...

When an aircraft carrier deploys, it departs with an air wing comprised of several specialized squadrons to provide a full offensive and defensive capability.  The exact composition of the air wing has varied over the years, but in addition to fighter and attack squadrons, there are always airborne early warning and reconnaissance airplanes as well plane guard/utility helicopters. Now electronic warfare airplanes are a standard part of the air wing.

Fighter and attack squadrons were typically assigned to a specific air wing for an extended period of time. At one point, in the late 1950s and early 1960s there were usually three fighter squadrons per air wing even though only two were required for a deployment. Because of the rapid development of new or improved fighter types at the time, one of the three was likely to be in transition to a new type and not ready to deploy.

For various reasons, a squadron might not be ready for deployment with its air wing and a substitute was required. Often, this would be a Marine Corps squadron since its pilots would all be naval aviators, qualified for carrier takeoffs and landings. VMFA-333 deployed several times, for example flying F-4s with Carrier Air Wing Eight aboard Nimitz in 1976.

 Official U.S. Navy photo via Johan A. (Hans) Engels (see http://www.thunderstreaks.com/)

One very non-traditional Marine Corps squadron deployment took place on the last cruise of Roosevelt. VMA-231, flying AV-8A Harriers, was assigned to Carrier Air Wing 19 for its cruise in the Mediterranean from October 1976 to April 1977. Also aboard were two squadrons of F-4Ns and three of A-7Bs, along with detachments of E-1Bs (for the last deployment of this type), RF-8Gs, and SH-3Gs.

In the mid 1970s, the Navy was seriously evaluating a transition to V/STOL aircraft for all sea-based, manned, tactical air missions instead of building more big aircraft carriers equipped with catapults and arresting gear. In early 1976, the CNO briefed OSD on a tentative plan to do so.  The assignment of VMA-231 to the Roosevelt’s air wing was intended to provide insight into the feasibility and benefits of a operating a V/STOL fighter/bomber at sea.

The Harrier had been in service with the Marine Corps since 1971 and had already been evaluated in an extended series of at-sea trials aboard, among others, the amphibious assault ship Guam (LPH-9) that was serving as an Interim Sea Control Ship. This resulted in the development of a corrosion control plan for an extended deployment among other operational procedures. However, there were still concerns about the Harrier’s maintenance requirements, hot exhaust, lack of endurance, etc.

VMA-231 worked up to the deployment via a series of mini-cruises aboard Franklin D. Roosevelt beginning in late June 1976. These established operating procedures and familiarized the ship’s company with the unique characteristics of the Harrier, like the downward-directed engine exhaust in VTOL mode.

 U.S. Naval Institute Proceedings October 1977

V/STOL advocates considered the experiment a virtually unqualified success. Complying with standard carrier cyclic operations (90-minute flight period for the conventional takeoff and landing airplanes) proved to be unnecessary since the Harriers could land in any open space during a launch/land cycle. Benefits demonstrated early on included no time or crew required to hook up to the catapult for takeoff, virtually no waveoffs (and zero bolters), and the ability to back into a designated parking space. The Harriers could also land with the ship steaming out of the wind in conditions that precluded the operation of its conventional airplanes.

Rolling takeoffs were a bit more problematical in some wind over deck conditions but a vertical takeoff was almost always possible. Flight time, however, was limited to 20 minutes by the reduction in fuel required.

Over 2,000 sorties and landings, 15% at night, were accomplished by VMA-231 during the deployment. There were no aircrew or aircraft losses, a non-trivial accomplishment given the accident rate of carrier operations. The promise of V/STOL seemed to have been clearly demonstrated and V/STOL aircraft welcome aboard.

In parallel with and supported by this evaluation, the Navy initiated a set of V/STOL development programs, with V/STOL A being a subsonic multi-mission aircraft and V/STOL B, a supersonic fighter and attack aircraft. (There was also a V/STOL C, which was to be a smaller ASW aircraft to replace the LAMPS Mk III helicopter operating from frigates and destroyers.)

Except for Bell's tiltrotor and Sikorsky's ABC, the V/STOL A concepts used various forms of lift fans and/or high-bypass-ratio jet engines like this Vought proposal.

The V/STOL B designs were equally innovative, in some cases using lift fans for more efficient vertical lift like this McDonnell Douglas concept.

After only a couple of years of studies, however, the Navy reversed course after completing its Sea-Based Air Master Study in 1980. It concluded that an all-V/STOL approach incorporating existing technology was high risk and in any event would cost more than utilizing conventional airplanes.

Two aircraft, the V-22 Osprey and the F-35B, did eventually result from the Navy's flirtation with V/STOL, however. The tiltrotor had been proposed for V/STOL A and thereby attracted the attention of the Marine Corps. The F-35B resulted from follow-on research programs to advance V/STOL technology. It's therefore possible that the U.S. Navy might yet transition to V/STOL carriers...