By Tommy H. Thomason

Monday, April 25, 2011

The Blue Angels Aircraft (Draft)

This is, again, a work in progress. Knowledgeable corrections and comments, as well as better pictures, are welcome.

1946, F6F-5: In April 1946, as described by Robert K. Wilcox in First Blue, Butch Voris was tasked with establishing an official U.S. Navy flight exhibition team. Among the aircraft he considered were the Grumman F7F Tigercat, the Vought F4U Corsair, and the Grumman F6F Hellcat. He thought that the Corsair was the “nicest looking” but was concerned that the possibility of it stalling and snap-rolling at the top of a loop precluded close formation flying. “The Tigercat, he felt, was too big and not agile enough.” Moreover, he and many of the candidates for the team were very familiar with the Hellcat so he requested four, modified by the removal of armament, etc. to reduce weight and painted in a new distinctive color scheme. (For more information on Blue Angel markings, click here.) Three were flown in close formation in the air shows with the fourth available as a spare. The first public display was on 15 June 1946 at Craig Field near Jacksonville, Florida.

In this photo reportedly taken at Grumman of a Blue Angel passing overhead during their final show in the F6Fs in August 1946, the bottom of the wing appears to be marked with US on one wing and NAVY on the other. (I’ve crudely enhanced the markings which are barely visible on the photo I have.)

1946-1949, F8F-1: The team was an immediate success and very shortly reequipped with the Navy’s frontline propeller driven fighter, the Grumman F8F Bearcat. Although powered by the same basic engine as the Hellcat, it was slightly smaller and lighter, with excellent climb and roll performance. Four were modified by Grumman to remove the guns, gun sights, tail hooks, etc. and delivered to the Blues in August 1946. These early production F8Fs did not have the turnover structure behind the pilot’s headrest. They flew their first show in the Bearcats only a week after ferrying them back to Jacksonville.
The show formation was soon expanded to four airplanes.

Later F8Fs had the turnover structure added, a polished aluminum or painted leading edge on the wing and tail surfaces, and “Blue Angels” in script on the cowling.

1949-1950, F9F-2: The Blue Angels entered the jet age with the Grumman F9F-2 Panther. They initially thought that removing the Panther’s tip tanks would provide better visibility for close formation flying as well as reduce weight. However, the Panther’s tanks were necessary for cross country flights and were not intended to be readily removable (they weren’t even jettisonable) so the concept was short-lived.
However, the fact that the tip tanks couldn't be jettisoned like they could on other jets turned out to be a feature. In lieu of being able to drop the tanks to lighten the aircraft, the fuel in them could be jettisoned. This was utilized to provide a spray of fluid to accentuate a maneuver, the predecessor of the smoke used today.

One of the show innovations implemented with the introduction of the jet was the use of a solo airplane to make passes to fill the time required for the faster jets to get turned around and back in front of the crowd for the formation's next maneuver..

When the Korean War broke out, the team’s pilots and airplanes were transferred to a fleet squadron which was converting to Panthers from Bearcats. They deployed aboard Princeton (CV-37) as the nucleus of VF-191.

1952-1954, F9F-5: The team was reformed with -5s after a hiatus for the Korean War. It had a more powerful engine than the -2. Its short stint with the team was indicative of the rapid succession of new jet fighter types in the early 1950s.

1952, F7U-1: Two Vought Cutlasses were assigned to the team in January 1952. The F7U-1 was a bit too overweight to be used as an operational airplane and was being redesigned with more powerful engines as the F7U-3. In accordance with its procurement practice, however, the Navy had begun low rate production before development was complete and had few more F7U-1s than they had test and evaluation requirements for. At the behest of Vought and with the approval of senior Navy management, two were assigned to the Blue Angels to generate publicity for the Navy's hottest new fighter. It was expected that they would be flown as opposing solos rather than be part of the formation of Panthers.
(If you look closely at the picture above, you'll note that the main landing gear is angled differently on the two F7Us. The selectable position provided better center of gravity location relative to the main landing gear wheels on takeoff versus landing .)

As it turned out, the new F9F-5s assigned to the Blues were effectively grounded for the first few months of the air show season. The Cutlasses were therefore the only airplanes available for flight demonstrations during that period and the necessary workup time after that. However, they weren’t really ready for prime time, suffering from hydraulic failures, engine fires, at least one landing gear malfunction, and excessive maintenance. In July the Blues were ready to resume shows with the Panthers so the Cutlasses were parked at NAS Memphis, the site of their last show and conveniently, a Navy training facility for aircraft mechanics.

F9F-6, 1953: The team picked up six Cougars, the swept-wing successor to the Panther, from Grumman in August 1953. The ferry flight home was marred to say the least because the team leader, Ray Hawkins, experienced a runaway pitch trim at 42,000 feet. He had to make a near-sonic ejection when the airplane bunted into an outside loop. He wasn’t badly hurt but the Cougar control system had to be modified so the Blues returned the F9F-6s to Grumman without ever performing a show in them and flew the F9F-5 for another year.

1955-1957, F9F-8: The successor to the F9F-6 was received in December 1954. Their first F9F-8s did not have the splitter plate on the fuselage in front of the engine intake. It’s not clear why the Cougar’s time with the team was not only relatively short, it was replaced at mid-season, which required the team to transition to a new airplane while still flying air shows in the old one.

1957-1958, F11F-1 (early): Before committing to the F11F Tiger, the team also considered both the North American FJ-3 and the Douglas A4D. However, neither were afterburner equipped, which added an extra element of showmanship and maneuver capability to the flight demonstration. Moreover, F11Fs from the first production lot, characterized by a shorter nose with a refueling probe at its tip, were readily available since design improvements were in work.

1959-1968, F11F-1 (late): As it turned out, the marginally improved F11Fs in the second production lot were no more in demand in the fleet than those in the first due to the superior performance of the Vought F8U Crusader, so the early short-nose F11Fs were replaced with the later long-nose version.

1969-1973, F-4J: In the late 1960s, two situations resulted in the F11F finally being replaced. First, the Navy was running out of F11Fs. Second, the Navy had bought an improved version of its front line fighter, the McDonnell F-4 Phantom, but its new radar and improved engine were not available in time to be installed in the first production F-4Js. As a result, the Navy had brand-new Phantoms with lead ballast in the nose and the prior version of the J79 engine. Twelve or so of these were made available to the Blues to replace the F11F. To improve handling qualities in the very close formation maneuvers, the control system was modified, including a change to allow afterburner to be selected at a lower engine rpm. A smoke system was also added.

Although the Phantom was a terrific air show airplane, the Blues experienced a series of unfortunate events with them. Nine of the lead-nosed Js were lost in accidents between September 1969 and March 1973, requiring replacement with a few “real” Js with the J79-GE-10 engine. Another was destroyed in early July 1973 at an air show. However, the 1973 season ended in tragedy on 26 July when a midair between the team leader and a wing man occurred during an arrival display at NAS Lakehurst NJ. The boss, the pilot of the other F-4, and a Chief Petty Office in the backseat of one of the F-4s were killed. The other Chief Petty Officer riding along was able to eject successfully.

1974-1986, A-4F: After the Lakehurst disaster with the F-4Js, the benefit versus the cost of the team was questioned at the highest level of the Navy. The debate was resolved in favor of continuing but not with the fuel-guzzling and accident-prone Phantoms. The Grumman F-14 Tomcat was deemed too expensive. The Vought A-7 Corsair II was or was not favored, depending on who is telling the story, but in any event was in short supply as the more capable strike replacement for the Douglas A-4 Skyhawk. Not only was the A-4 available, the latest variant, known as the Super Fox, had a very good thrust-to-weight ratio with its uprated J52 engine in addition to an excellent roll rate. After control system modifications, bolting up the aerodynamically actuated slats, removing unneeded equipment, and adding a smoke system and a braking parachute, it proved to be an excellent air show airplane in addition to being relatively simple and easy to maintain. Its diminutive size, relatively low approach speed, and excellent handling qualities allowed the Blues to land with all six aircraft in formation.

1987-present, F-18: By mid-1985, considering that the A-7, the A-4’s replacement in the fleet, had itself been replaced, the Blues were overdue for a change of airplane. However, options included an A-4 service life extension program as well as the new trainer, the McDonnell T-45A based on the British Aerospace Hawk. However, the Navy once again had a set of airplanes, Lot IV production McDonnell F-18A Hornets that did not have the landing gear modifications necessary for carrier operations. The F-18 required control system modifications in addition to the usual weight reduction removals and unique Blue Angel show requirement additions like a smoke system and inverted fuel system capability. The conversion to a more complicated airplane was accomplished between seasons in part by retaining the same pilots, some of whom would normally be replaced, in order that there would be no pilots who would be learning both the Blues maneuvers and the characteristics of a modified F-18. The reinstatement of an airplane with afterburners added to the crowd appeal and maneuver options.
Unlike past two-seaters operated by the Blues, the F-18B could fill in as part of the diamond if required.

In the last year or so, the Blues have begun to replace their As with the newer C model, newer being relative since the last C built by McDonnell was delivered in 1999. The Bs were to be replaced by Ds. Hopefully, the changeover to "new" aircraft will allow the Blues to continue to be a powerful recruitment tool and good-will ambassadors for the U.S. Navy for many years to come.

Saturday, April 23, 2011

NATF: Better is the Enemy of Good Enough

Once upon a time, the Navy was developing a plan to replace the F-14 and the A-6. The Air Force needed to replace the F-15 and the F-111. In 1986, Congress essentially directed that the Navy’s fighter be the Air Force’s Advanced Tactical Fighter (ATF), its F-15 replacement, and the Air Force’s strike airplane be the Navy’s Advanced Tactical Aircraft (ATA), its A-6 replacement. The Air Force planned to buy 750 ATFs and the Navy, 618 NATFs.

The Air Force and its contractors had been planning the replacement for the F-15 for several years. A formal requirements document was first issued in January 1973. The design studies considered incorporation of the latest advancements in structures, aerodynamics, propulsion, avionics, etc to maximize mission effectiveness, with stealth being a major differentiator.

This effort culminated in a formal competition in 1986. The Air Force selected Lockheed (teamed with Boeing and General Dynamics) and Northrop (teamed with McDonnell) to build demonstrators, the YF-22 and the YF-23 respectively.

The Navy subsequently established a three-person NATF program office collocated with the Air Force program office at Wright-Patterson Air Force Base, Ohio. In September 1988, Lockheed and Northrop received contracts from the Navy to study carrier-based derivatives of their proposed aircraft.

Carrier basing imposes specific design requirements for low-speed capability, low-speed handling qualities, over-the-nose visibility, compactness, corrosion protection, structure and hardware for catapult launches and arrested landings, etc. For example, in the case of the NATF, the Navy specified a maximum takeoff weight of 65,000 lbs and a landing weight of 52,000 lbs. (The Navy estimated that the difference in requirements would result in an NATF empty weight of 4,000 lbs more than the ATF’s and a gross weight difference of two to three times that.) It was to be no longer than the F-14 (62 ft) or take up more space when folded.

The basic mission requirements of the Air Force and Navy were also different. At the risk of oversimplifying, the Air Force ATF was to be an air superiority fighter; the Navy ATF also had to have the capability to shoot down enemy bombers before they could launch cruise missiles. This fleet air defense role required long range sensors, weapons, and endurance. It also inclined the Navy toward a second crewman, whereas the Air Force wanted a single-seat fighter.

As a result, the NATF designs only superficially resembled the land-based ATF demonstrators. The Lockheed NATF had variable-sweep wings like the F-14.

The Northrop NATF retained the basic wing planform of the YF-23 but replaced the stealthy ruddervators with a canard forward and vertical fins aft.

Nevertheless, the engines and much of the avionics and aircraft systems were to be common even if the airframe was not. The Air Force estimated that the engines and avionics represented 44 percent of the ATF’s unit flyaway cost.

The Northrop YF-23 was the first to fly, lifting off on 27 August 1990. The Lockheed YF-22 flew a month later. The development and evaluation programs ran almost concurrently, with the Air Force selecting Lockheed's F-22 for qualification and production in April 1991.
The Navy, however, had withdrawn from the program before then, citing the unaffordability of the ATF, its weight, and program schedule delays. At the point, the Admirals expected to keep the F-14 in service through 2015, giving them time to develop their own advanced fighter with minimal overlap of A-12 development expenditures. Unfortunately, the Secretary of Defense unexpectedly cancelled the A-12 program in January 1991. It had gotten unacceptably behind schedule and over weight. There was no push back from Congress on the complete failure of the joint program concept.
The Navy then had to deal with OSD's disagreement with its plans for an A-12 replacement and continued F-14 production. The result was the F-18E/F program, with the F being a two-seat variant of the single-seat E. The design was based on the so-called legacy F-18 Hornet, ironically a development of the losing airplane in the Air Force’s so-called light-weight fighter competition that was supposed to result in a common Navy/Air Force fighter.
The early retirement of the F-14 with its long-range Phoenix missile capability and the A-6 with its all-weather strike capability caused a furor in the Naval Aviation community but to no avail. The F-18E/F Super Hornet was decreed to be good enough.

It certainly was not nearly as advanced as the F-22, particularly with respect to stealth. Moreover, the Navy chose to initially qualify and deploy the first Super Hornets with less avionics capability than it was planned to have, which even then would be less than that of the production F-22. The uncharacteristic restraint, however, resulted in a development/qualification program that was essentially on cost and schedule and met the Navy's near-term need for F-14 and A-6 replacements. The first F-18Es deployed in 2001 while the F-22 was only then being approved for low-rate production, several years behind schedule. The Super Hornet went into action in Iraq in 2002; the F-22 was finally declared to be operationally capable in December 2005. Its first assignment? To guard the east coast of the United States, a mission that didn't require the advanced technology and capability it possessed. However, it still wasn't called to action several years later to establish a no-fly zone in Libya, with the F-22's stealthiness having been touted beforehand as being tailor made for the purpose. The reason for its no-show, according to an Air Force spokesman, Lt.Col John Haynes, was that "[the joint task force] needed to look realistically at the fighter assets already within Europe to execute operations...Because there are no F-22 Raptors based in the European theater, they were not included in the initial stages of the operation."

To be fair, the combat-proven Super Hornets were not employed in Operation Odyssey Dawn either. There were no U.S. Navy aircraft carriers in the Mediterranean at the time, Enterprise having departed in mid-February for the Arabian Sea.

The F-22 finally dropped bombs in combat for the first time in September 2014, almost 12 years after VFA-115 went into combat with its Super Hornets.

In large part because of the F-22’s very high unit cost, its production was curtailed at only 187 aircraft. In contrast, the 500th F-18E/F /G was delivered on 20 April 2011. As of mid 2015, production of the F-18E/F/G was to continue through 2017. There is a possibility that the line will continue to be kept open because of ongoing program delays with the F-35C.

The Super Hornet doesn't have the mission capability of the F-22 or the A-12, not to mention the F-14 or the A-6, but so far it is good enough.

Saturday, April 16, 2011

Bell L-39 Wing Sweep Evaluation

Early in 1946, BuAer had solicited proposals for a high-speed (jet) day fighter defined by Outline Specification 105. Cdr A.B. Metsger was the fighter class desk officer. According to his unpublished memoir:

“At that time no representative airplane had flown with significant sweep. Extensive wind tunnel data, mostly captured German reports, gave us reasonable confidence at operating speeds, but there were no data to insure satisfactory low speed flying characteristics—essential in carrier operations. “

Captain Walter S. Diehl, BuAer’s chief aerodynamicist, expressed doubt to Metsger that useful low-speed data could be obtained in subscale wind tunnel testing. However, Ivan Driggs, Head of Design Research, suggested an airplane could be built for that specific purpose quickly and economically.

Metsger therefore called his contacts at four aircraft companies that he thought would be interested in building a low-speed, swept-wing demonstrator. Bell proposed a 10-week, $100,000 modification of two surplus Army Air Force P-63As; Grumman, an ugly modification of an F4F Wildcat, including a nose landing gear, and a more expensive, all-new design that included a second seat for a test engineer and the capability to be configured with both swept and straight wings.
Grumman assumed that if a swept wing were to be substituted for a straight wing on an existing airplane, it would have to be positioned further forward so that the location of the mean aerodynamic chords was not changed.
With its tricycle landing gear, the Bell P-63 already resembled a jet airplane in configuration.

The Bell-proposed approach consisted of modifying the outer wing panels to attach to the center wing stub with a 35–degree sweep and zero dihedral. In effect, this moved the wings slightly forward relative to just mounting them at the side of body but not nearly as far forward as Grumman thought was required. Bell engineering calculated that the removal of the cannon and machine guns mounted in the P-63’s nose and the ammunition along with the addition of ballast in the aft fuselage would suffice to move the center of gravity aft so that a minimal forward shift of the wings would be adequate.

Slats were considered to be a very important part of providing adequate lift with a swept wing so the wing leading edge was modified to have five separate slat sections, any of which could be configured open or closed for flight. In the following picture, the four most outboard slats are open and the most inboard one is closed.

The aft part of the canopy was closed off for research instrumentation purposes. A panel with several gauges was mounted aft of the canopy door frame with a camera to photograph it.

This setup recorded data from instrumentation including those on booms mounted on each wingtip. The wings were marked with white lines and tufted so that cameras mounted on the canopy and horizontal tail could record the direction of the air flow as the airplane was stalled.

Since only low-speed flight characteristics were to be evaluated, the main landing gear attachment was reoriented but not required to be retractable. The wheel wells were covered over. The nose gear was still retractable.

Bell had referred internally to the aircraft as the XP-63N but the Navy formally designated it L-39 on 19 April 1946. This was consistent with the Navy’s practice for research aircraft, with the L being the letter assigned to Bell by the Navy and 39 being the Bell design number, as opposed to a model number. However, the number of at least one of Bell’s L-39 flight test reports began with 33, which was the model number of the early P-63s. L-39-1 was assigned BuNo 90060 and L-39-2, BuNo 90061.* (For more on U.S. Navy research aircraft designations, click Here.).

First flight of L-39-1 was on 23 April 1946. At some point, a lighter three-bladed P-39 propeller was substituted for the four-bladed P-63 propeller and a ventral fin similar to the P-63C's was added.

Eight flights were made by 3 May, when it was briefly laid up to incorporate a four-foot plug in the aft fuselage and a large ventral fin. The plug also reduced the stabilizer incidence by four degrees, building in more nose-up trim. The changes improved the longitudinal and directional stability.

Flight tests with different slat configurations quickly established that the stall characteristics with no slats extended were very poor: no warning and an abrupt and significant roll off. With most outboard (20%) slats open, there was no improvement. With the two most outboard (40%) slats open, there was some improvement. There was significant improvement with 60% and 80% slats, with excellent stall characteristics, as well as with a 40% slat configuration with the most outboard slat closed and the next two inboard open (60%-20%) as shown here.

With 100% slats, however, the airplane response was so bad that the test pilot recommended that testing with 100% flaps “be discontinued until further wind tunnel spin data is obtained.”

L-39-2 first flew on 29 May, configured with the fuselage plug and an even larger ventral fin.

It was also equipped with an automatic fuel distribution equalizer to maintain a desired center of gravity. It was used to evaluate a slightly different slat configuration with a narrower slot.

After Bell's short development program was complete, both aircraft were made available for evaluation flights by Navy and industry pilots. At one point, L-39-1 was configured with a "good" slat configuration and L-39-2 was set up with no slats, so pilots could make back-to-back evaluation flights. Grumman test pilot Corky Meyer flew the L-39s in late June 1946: "My flight ... with no leading-edge devices was short. It cavorted like a cat on catnip during the stalls and required excessive altitude for recovery. The second ... with leading-edge slats was docile during stalls and accelerated stalls. These stalls could be done with little wing dropping and the usual loss of altitude. The two prototypes made it clear that slatted, swept wings would provide carrier-suitable flight characteristics and stall-speed performance for fighters."

Flight test and evaluation using L-39-1 was completed at Bell on 26 August 1946, after which it was ferried to NACA Langley, Virginia, for a wind tunnel and flight correlation test program.

That concluded the Navy’s participation in the program. According to Cdr Metsger: “Our flights, including simulated carrier approaches and landings, assured us that sweeping the wings would not adversely affect carrier operations. We had the data in time for our (day fighter) competition evaluation.”

L-39-2 was repurposed in mid 1946 to support Bell’s X-2 program. The wing was modified to represent a swept wing with a circular-arc airfoil and the leading edge was extended forward to the side of body.

Bell engineering failed to appreciate the aerodynamic implications of a planform change. The center of lift was shifted far enough forward that the test pilot made most of the short flight on 20 July 1946 with full forward stick. Following reballasting, including reinstatement of the heavier four-bladed propeller, it was used by Bell for low-speed handling qualities and performance evaluation of the X-2 wing. L-39-2 was ferried to NACA Langley on 11 December, where it remained for three years. In December 1949, both aircraft were reportedly transferred to NACA Lewis where they were scrapped.

For drawings and other information of interest to modelers, click Here.

*The Navy History Center lists these two BuNos as P-63s that were cancelled.