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The General Dynamics Convair, which is a contraction of Consolidated Vultee Aircraft, was located in San Diego, and produced the B-24 Liberator and the B-36 Peacemaker, among other famous airplanes. The Convair-Liner project started with the Convair 110, CV-110 prototype, but even before the Model 110 had made its first flight, discussions with various airlines, and in particular American Airlines, indicated that an improved 40 seat medium range transport was desirable. Therefore, in 1945, Convair launched the 240 (2 engines 40 passengers) with an order for 100 aircraft from American Airlines. Additional contracts for over 50 more were signed with Western Airlines, Pan American Airways, Continental Airlines, KLM and Trans-Australia Airlines.
Of conventional all metal construction, except for a fiberglass rudder and elevator trailing edges, the 240 had a multi-spar wing with hydraulically-operated Fowler-type flaps. Fuel was contained in two 500 US gallon capacity tanks outboard of the two nacelles housing Pratt & Whitney Double Wasp R-2800 engines driving three-blade Hamilton Standard or Curtiss reversible pitch propellers.
The pressurized fuselage, the first for a twin-engined transport, accommodated 40 seats in a comfortable ten-row four-abreast layout with an 18 inch aisle despite a diameter of 113 inches, four less than the Model 110. Two pilot operation was normal, but some foreign customers also specified a radio operator.
Customers could choose from four basic interior and door arrangements. These were referred to as Type A, W, P and S respectively after the initial customer for each, American, Western, Pan American and Swissair. Subsequently, there were modifications to individual aircraft. All had a rear starboard side toilet but galley and carry-on baggage space varied.
The Convair 240 prototype (N90849) was first flown on March 16, 1947, from San Diego. Following a 16 week flight-test program, the CV-240 was approved for a gross operating weight of 40,500 lbs. with the P&W R-2800’s rated at 2300 HP for take-off. Deliveries to American (Model 240-0) started on February 23, 1948 with (NC94200 msn 2) and following the award of Type Certificate 793, entered service with the airline on June 1, 1948.
The following January, the 100th aircraft was rolled out. Because of the various configurations for each customer, dash numbers were applied to distinguish customers. In 1950, gross weight was increased to 41,790 lbs. and fuel capacity to 1550 US gallons with the addition of outer wing tanks.
The CV-240 fleet completed over 840,000 flight hours before its first fatal accident in 1952 which was, by far, the best safety record of any transport up to then.
Airline orders finally totaled 176 deliveries. The remainder of the 565 built were delivered to the USAF and USN in the following versions: T-29-CO Flying Classroom, T-29B-CO, T-29D-CO and the C-131A-CO Samaritan.
With the withdrawal of the CV-240 from the fleets of the initial airline customers, the aircraft passed to the secondhand airline market and corporate customers. In the mid-70’s when the USAF/USN started to dispose of its 391 aircraft, a large number converted to civil cargo use.
The last 15 CV-240’s proved difficult to sell and Convair had considered terminating to whole project. However, the sale of the pressurized Martin 404 to Eastern Airlines and Trans-World Airlines prompted Convair to refine its basic design. Originally designated 240-A, then 340, the new model was announced on November 28, 1950 as the Convair 340, with a fuselage lengthened by 54 inches to allow an extra four seat row in the cabin. To improve high altitude airport operational capability, the wing span was increased from 91 feet 9 inches to 105 feet 4 inches which also allowed an additional 750 US gallon fuel capacity, and the flaps divided into two sections.
More powerful R-2800-CB16/17 engines were installed in 7 inch longer nacelles, and propellers were standardized with Hamilton Standards, with a 4 inch increase in diameter to allow interchangability with those of the Douglas DC-6. Longer undercarrige legs and larger tires increased the height slightly. There were also modifications to the pressurization system and all passenger doors and integral stairs were positioned on the port side to be compatible with ramp docking facilities. Many of these improvements were made to satisfy United Airlines, this airline became the launch customer with an initial order of 30.
The prototype Model 340 (N3401 msn 1) made its first flight on October 5, 1951. Based on a T-29A airframe, this was the only 340 with a starboard side passenger door and was restricted to a gross weight of 46,725 lbs. In contrast, production 340’s were certified at 47,000 lbs. under ammended TC 6A6 issued on March 27, 1952. The first deliverey was made to United four days later and the type entered service on November 16, 1952.
In order to compete with the propeller-turbine Vickers Viscount, the Model 340B was announced in 1954 which soon became known as the Model 440 Metropolitan. The major change was to a rectangular exhaust outlet instead of the twin tubes of earlier versions in an effort to reduce cabin noise. More streamlined cowlings were fitted, extra soundproofing was added, and gross weight climbed to 49,100 lbs. (later 49,700 lbs.). Weather radar was offered as optional equipment, although most 440’s were delivered thus-equipped with a radome that increased the length by 28 inches. Cabin accomodation remained at 44 seats although a 52 passenger interior was also offered with an extra window on each side.
One CV-340 (N8431H msn 202) was retained by Convair to test these refinements and was first flown after modification on October 6, 1955. The initial production CV-440 (msn 312) first flew on December 16,1955 and certification was received on January 30, 1956 and the first delivery made to Swiflite (Cities Service Oil).
The first airline operator was Continental Airlines, which introduced the CV-440 on March 8, 1956. Other US airlines soon followed but the majority of the airline aircraft went to overseas customers, most of which found the improved Convair-Liner sufficiently effective to be able to pass by the propeller-turbine stage entirely.
The following military versions were completed to make a total of 199 aircraft and a final Convair-Liner total of 1,076. Military versions of the Model 440 were as follows: C-131D-CO, C-131E-CO and R4Y-2.
Convair also supplied kits for operators to modify 340’s to a standard close to that of the CV-440 and over 100 were so converted.
From the very beginning of the Convair-Liner program, the airframe was designed to take propeller turbines. The first conversion was made by the Allison Division of General Motors in cooperation with Convair. The prototype 240 (N24501 msn 1) was fitted with two 2,750 eshp Allison 501-A4’s (T-38s) and, as the Model 240-21 Turbo-Liner and the first US propeller-turbine transport. The aircraft made its first flight on December 29, 1950 with R.C. Loomis and Donald P. Germeraad at the controls. As it turned out this engine combination was not developed enough for commercial applications and after a decade of use as an engine test bed, it was converted back to Double Wasp power in 1959. It should also be noted that a second conversion had been applied to this aircraft in 1957 for the development of the Allison 501-D5C for the Lockheed Electra program and for USAF evaluation of the YC-131C. Upon completion of these programs the aircraft was then converted to Double Wasp power with the R-2800 CB-17’s installed and nacelles from (CV-340 msn 33) which now made the aircraft a CV-300.
The first commercial propeller-turbine conversion was made from a CV-340 (G-ANVP msn 153) by D. Napier and Son Limited at Luton in England in 1955. Fitted with 3,060 eshp Napier Eland N-E1-1’s and four blade De Havilland propellers, it was first flown on February 4, 1956. A crusing speed of 315 mph at 16,000 feet was recorded and on October 21,1957, the Napier Eland Convair Series 2 was awarded a certificate of airworthiness. The following month, the Eland Convair (re-registered N340EL) was delivered to PacAero Engineering Corporation of Santa Monica, who had been desgnated by Napier to handle US certification with 3,412 eshp N-E1-6 Eland 504 engines. This proved more difficult than anticipated, and a Supplemental Type Certificate (STC) was not issued until August 22, 1958 for the Napier Eland Convair 340/440 Mark I. A second aircraft known as the Mark II, was converted from a CV-440 (N440EL msn 445) with US components and received its STC on December 19, 1958, similarly with a gross weight of 53,200 lbs.
The first operator of the Convair 540 Cosmopolitan was Allegheny Airlines, which leased the second aircraft for three months starting, July 1, 1959, to become the first local service airline to fly a turbine-powered type. The Eland Convair was used on “Leilani” service (celebrating Hawaii’s statehood) to Atlantic City, NJ and resulted in an order for five which were converted by AirResearch.
The most successful of the propeller-turbine conversions was the Allison “Prop-Jet Super Convair” powered by 3,750 eshp 501-D13 engines (civil version of the T-56), which resulted in 170 aircraft being modified. In order to gain operating experience, Allison obtained YC-131C (msn 91/53-7886) from the USAF on loan and installed 501-D13 engines. Testing under the name Operation Hourglass, started on November 1, 1957, and, 1000 hours were logged by January 23, 1958. To counteract the effect of the more powerful engines, 340/440 conversions (240’s were not considered structurally suitable) required a 12 inch taller tail and a 40 inch increase in tailplane span. Four blade, 13 ft. 6 inch diameter square tipped Aeroproducts propellers were fitted and additional soundproofing material installed along with a revised cockpit layout. Operating weights and performance were increased substantially and an optional modification was the increase of wing fuel tank capacity to a maximum of 2,908 US gallons. Modifications were also made to the exhaust ducts from those fitted to the YC-131C.
Because Convair was fully occupied with the 880 program, Allison contracted conversion work to PacAero at Santa Barbara and the first aircraft (N5100 msn 33) was flown on January 19,1960. An STC was awarded on April 21, 1960. All the early conversions, made at Burbank from October 1962, were completed for corporate customers and the initial delivery was made to General Motors. The first airline operator was Frontier Airlines which specified 501-D13H engines for high altitude operations and a 52 seat interior. Frontier also choose the name Convair 580 for marketing purposes, and unofficial designation that was widely adopted, and put the type into service in June 1964. It was followed by Allegheny, Lake Central and North Central. Still a popular and efficient aircraft today, CV-580’s are operated by several US airlines including Aspen Airways, which now does business as United Express carrier.
Four VC-131D’s were converted for the USAF and became VC-131H’s for the 89th MAW, Andrews AFB, Maryland. Three were transferred to the Navy at the same base in 1979 for VR-52 (later VR-48). A fifth conversion was made from a C-131B (53-7793 msn 245) as part of the modifications to transform it into an NC-131H for the Total In-Flight Simulator (TIFS) program developed by Cornell Aeronautical Laboratory in Buffalo, NY for advanced transport aircraft. A lengthened nose incorporated a separate cockpit, and movable control surfaces were mounted vertically above and below the wings and in this configuration a first flight was made on July 8, 1970. In 1979, it was fitted with a digital computer in connection with the Space Shuttle program and remained in use until 1986. In February 1987, it was used by Boeing to test flight control computer software and control configurations for its proposed 757 transport.
In 1967, the RCAF decided to convert eight of its Canadair 540’s to Allison power with 4,050 eshp 501-D36 engines and Hamilton Standard propellers (comparable to the C-130E) which increased cruising speed by 58 mph over other 580’s. The only other military operator was Bolivia, which acquired four ex-North Central aircraft in 1974.
The structural integrity of the Convair-Liner airframe and the excellent record of the Allison 501 kept up the demand for the CV-580 well after conversion worked stopped in July 1969. In 1984, Allison proposed a Super 580 (unofficially referred to as the 580A) with 4,269 eshp 501-D22G Series 3 engines to increase maximum cruise by almost 40 mph to 361 mph with decreased fuel flow and modem avionics. As Aeroproducts propellers are now scarce, these were replaced with round tipped Hamilton Standard ones. Two aircraft were so-modified, the first making a maiden flight on March 21, 1984 at Tucson, AZ. A 14 ft 3 inch stretched fuselage version for up to 76 passengers, called the Allison Turbo Flagship (ATF) 580S, was marketed by Super 580 Aircraft Inc., a subsidiary of Flight Trails, parent company of Air Resorts Airlines of Carlsbad who ordered three. Tracer Aviation, Santa Barbara, also proposed building a similar stretched version, as has Kelowna Flightcraft, British Columbia, Canada, but no 580S aircraft has yet been built. NOTE (Two stretched CV-5800’s were converted by Kelowna Flightcraft).
A third, more simple and less powerful propeller-turbine conversion program was initiated in 1964 by Convair for all three series of Convair-Liners with 3,000 eshp Rolls-Royce Dart R.Da 10/1 (Mk-542 4) engines. Initially refered to as the 240-D, 340-D and 440-D respectively, the designation Convair 600 (for ex-240’s) was adopted in 1965 and Convair 640 (for ex-340/440’s) in 1966. The first 600 (N94294 msn 178) mades its initial flight from San Diego on May 20, 1965, followed by the 640 (N73137 msn 88) on August 20, 1965, and STC’s were awarded on November 18th and December 7, 1965, respectively.
Kits were also sold for airlines to make their own conversions which entailed few changes aft of the engine firewall. The Dart and four blade Dowty-Rotol 13 ft. diameter propeller unit was attached to the original cowling but offset 8 inches from the original centerline to provide adequate airscrew clearance. Some structural strenghtening was necessary, particularly for the 600, and two air compressors were added for pressurization at the higher operating altitudes. An AiRsearch APU in the starboard nacelle was optional. After initial flight tests, the beaver-tail fairing of the nacelle and exhaust tailpipe was extended to prevent interference of the engine exhaust to the flaps.
The first customer for the 600 was Central Airlines which ordered 10 (converted by Convair). The first delivery was made on September 19, 1965 (for crew training) and services began on November 30, 1965.
These were followed by 25 for Trans-Texas Airways (later Texas International Airlines) converted by the airline, and three others for a total of 38 aircraft.
Hawaiian Airlines placed the first order for the 640 and the first of eight entered service on December 20, 1965. However, a day earlier, the forth Dart Convair customer, Caribair, had operated the first 640 service. Caribair’s seven aircraft retained the two JATO units previously fitted to their 340’s. In 1966, the 640 was re-certificated with a reduction in exhaust duct area to increase thrust by 1001 lbs. and a Hydroaire anti-skid system. Larger diameter propellers with reverse pitch were offered as options.
The first of the re-certificated aircraft was delivered to
Hawaiian. The first conversion in Europe was made by Aviolanda at Woensdrecht
in the Netherlands, in 1966 for Martin’s Air Charter and this had extra fuel
capacity and seating increased to 56 passengers. Aviolanda also converted
aircraft for Air Algerie and SATA of Switzerland. Scottish Aviation Limited
converted two for General Dynamics as demonstrators and the first (N7262 msn 9)
was flown on September 19, 1966. In 1973, California Airmotive (later American
Jet Industries) converted five of the Hawaiian aircraft to 640 Freighter standard
for Zantop International with a heavy duty floor and a port side aft fuselage
door. This modification is also available for the CV-580. A similar conversion
with a 108 inch by 73 inch door was undertaken by Airfreighters Int’l of
Addison, TX in 1975. Subsequently, another four ex-Navy C-131F’s have been
converted to 640’s to bring the total to 31 aircraft.
The following narrative was taken verbatim from the publication, “The United
States Air Force in Southeast Asia: Development and deployment of Fixed-Wing
Gunships 1962-72” by Jack S. Ballard, Office of Air Force History, Chapter
One: Origin and Early development, pages 5-9……near the end of June, Captain Simons and Captain Boren flew a C-131 for
three hours to check lateral sighting techniques in a cargo aircraft. Flying
low over Central Ohio, the pilot banked the aircraft about ten degrees
and with rudder control followed a road, keeping it in view with the single
horizontal line on the left side of the cockpit window. Tracking this continuous
target proved easy both from the standpoint of flying and sighting. Next
the pilot singled out silos, barns, moving horses, and even flighting geese
as point targets. The aircraft rolled into a pylon turn around the objects
selected. Finally he changed the horizontal line on the window to a vertical
one. This did not affect case of tracking but precise sighting along a
line was lost. From this flight Simons concluded that cargo aircraft could
acquire and keep targets in the sight during a pylon turn, and saturate
them with assumed ballistic dispersion patterns…..” (Memo,
Capt. John C. Simons, Ch/Crew Stns Br, Human Engrg Div, subj: Lateral Sighting
Study (ca 2 Jul 1963)
Plans to verify sight and gun
alignments followed. In June 1963 one of the C-131B’s at Wright-Patterson was
fitted with a new sight, mounted at the pilot’s left cockpit window. The sights
optical axis was perpendicular to the aircrafts flight path. Next, three
synchronized cameras were installed. One 16mm motion-picture camera was
positioned to record the sight alignment. Another in the cargo compartment back
of the wing, aimed through a window where a gun might be positioned. A third
camera was placed to photograph the special flight instrument panel in the cargo
compartment. The panel showed altitude, airspeed, turn and bank, and altitude
factors. From this test equipment Simons hoped to obtain enough data to plot
pilot error involving altitude, line-of-sight distance, wind, indicated
airspeed, and to secure realistic inputs for firing geometry. (Simons et al, Project Tailchaser:
Development of a Lateral Firing Concept, AMRL-TR-66-202 pp 12-14). Later a second version of a camera installation was prepared including
one camera to record the pilot’s sight alignment and three cameras to represent guns. This concept was presented to the Aeronautical Systems Division flight test organization but was delayed indefinitely because of lack of priority.
In July, 1963 Captain Simons gave his supervisor a progress report on test
flights and preparation of test equipment. He highlighted his success in
tracking various targets and urged that the next step be turnover of the
C-131 to ASD cargo flight-test personnel. Suggested test equipment was
installed in this aircraft. Flexman believed two flights should supply
ample data to analyze the essential firing functions before actual firing
tests. Looking to the future he foresaw ASD research into minimum and maximum
tumbling characteristics of ammunition fired from the waist gun, the prospect
of using the on-pylon technique for pickup and delivery, and possible use
of a laser beam to designate targets, or side-looking infrared equipment
to acquire night targets during the pylon turn (Memo, Simons to Christensen,
ca 2 Jul 1963).
As a fallout from the Simons
proposal of 20 May 1963, a meeting was held on 1 July. Attending were Captain Simons, Lt. Col.
James L. Hight and Captains Birt and Boren, the latter three from ASD’s
Directorate of Crew Subsystems Engineering. On 3 July this group officially
supported testing the concept. (Ind, Lt. Col J L. Hight, Ch/Pers Subsys
Div, Dir.Crew Subsys Engrg, to 6570th AMRL, 3 Jul 1963). By August Captain Simons had the part-time services
of Captains Birt and Boren to help set-up sighting-definition flights.
On 28 October a new flight-test plan changed Project Tailchaser from a
lateral-firing to a lateral-sighting project because of resistance to the
firing phase. The plan prescribed use of a C-131 and later a T-28 in flights
from Wright-Patterson AFB, possibly Ft.Rucker, AL., and Eglin AFB, FL. Captain Boren became project manager with
Captains Birt and Simons and Sergeant Bunch as designated engineers. Capt.
Edwin J. Hartzenbuehler was named project pilot (Flight Test Plan ASNM-63,
Project Tailchaser - Lateral Sighting Study, 28 October 1963).
Crablike progress ensued and the C-131B camera test equipment stood idle.
The part-time officers, Captains Birt and Boren, were recalled by their
units for higher-priority duties. Project Tailchaser was virtually at the
bottom of the list of priorities and was likely to stay there, in view
of the increased attention given Vietnam-related counterinsurgency developments.
Test flights were hard to arrange. In seven months the C-131B made just
two flights and these were preliminary procedure checkouts. Not a single
actual or camera-verified firing test had taken place. People remained
skeptical of the whole concept. Frustrations mounted with seemingly endless
With undimmed enthusiasm,
Captain Simons, Sergeant Bunch, and other pioneer of the concepts early testing,
remained convinced of Tailchaser’s potential. On 10 February
1964 they were
cheered by news from Captain’s Boren and Birt of a flight test set for the near
future, “hopefully in February.” Technicians reinstalled the cameras (they had
been removed from the C-131B) and boresighted them like guns. Test pilots
scanned aerial photos of Ohio’s ClintonCounty seeking test targets. But over this activity loomed the priorities
problem, a roadblock to the tests. At one point ASD returned the sighting-project
files to the medical research laboratory, commenting the project deserved
total attention of several people whom it could not provide and admitting
“limited surveillance and informal management of the project” had fostered
delays. Again the planned flights failed to take place.
Finally a few flights were made
in the summer of 1964. By this time, however, the press of his other duties
forced Captain Simons to give up his gunship responsibilities. He picked
1st Lt. Edwin Sasaki, a fellow medical laboratory researcher interested in the project, to act in his stead as human performance engineer on the lateral-firing team. In addition, the project pilot, Captain Hartzenbuehler, was replaced by Maj. Richard M. Gough and he in turn by Captain Ronald W. Terry. Despite these changes, Simons kept up his interest in Project Tailchaser’s development, reiterating that the concept’s acceptance hinged on live-firing tests.
The appearance of Captain Terry
as a project pilot proved a propitious development. His personality projected a
subtle blending of tact and tenacity, self-confidence and openness, intelligence
and common sense, and most significant for the progress of the gunship, an
uncommonly convincing salesmanship. Also his past mental conditioning made him
keenly receptive to the gunship’s possibilities. In the spring of 1963 he had
served on an Air Force Systems Command (AFSC) team in
South Vietnam. It’ job was to assess problems in the field and suggest hardware developments to deal with them, the overall goal being a five-year development program to satisfy Southeast Asia requirements. The team, probed for almost six weeks, visiting bases and talking with the men who worked alongside of and advised the South Vietnamese. Combined with the firsthand knowledge was Terry’s fighter pilot experience. He knew how hard it was to place ordnance on a target in bad weather, at night, and in tight tactical situations.
Captain Terry first came across
Project Tailchaser while perusing the files in Flight Test Operations at ASD.
Obviously, the project had been dormant for some time. Yet, as he read, Terry
was intrigued by the potential of the idea for development and use in
Vietnam. Disregarding the ballistic skeptics who branded the concept unworkable,
he obtained permission to work on Tailchaser. Immersed in the project,
Terry’s interest heightened and he gained approval at several points to
evaluate the idea further. Finally, he drafted a scenario for a tactical
operation employing a side-firing weapon system, mainly in defense of hamlets
and forts. He viewed this system as performing a policemen-on-the-corner
or prowl-car role, prepared for anything and able to respond anywhere at
most anytime. ASD’s Limited War Office warmly welcomed the scenario and
promised to sponsor it. This achievement, together with Terry’s first C-131
flight where he practiced lateral-firing techniques, fueled his enthusiasm.
He became primarily responsible for restoring momentum to the gunship idea.
In August 1964 the ASD Limited War Office and Flight Test Operations, together
with the Aerospace Medical Research Laboratory, took a significant step
in the testing of the lateral-sighting study. An amendment to the flight
test plan specified that one or two small-caliber guns, remotely fired
by the pilot, be installed in the cargo doorway of a C-131 “to determine
the feasibility of firing guns with the lateral-sighting system.” Eglin
AFB would help install the guns and conduct the ground tests, firing blanks
to determine if the mounts could stand the recoil. The amendment also prescribed
preflight boresighting and safety precautions. Groundwork had been laid
for the long-awaited firing test.
The C-131 was flown to Eglin to become the testbed for the firing. A relatively
new weapon was selected and installed on the left side of the aircraft’s
cargo compartment. The General Electric GAU-2B 7.62mm Gatling minigun (In
a SUU-11A pod) could fire 6000 rounds-per-minute. Sergeant Bunch, who worked
on fabricating the sight and other test equipment, played a key part in
mounting the Gatling gun.
The first live-firing tests occurred in late summer. The pilot flew the
C-131 with line-of sight distance to the target varying from 1,750 to 9,000
feet and airspeed from 115 to 250 knots. On Eglin’s water range a one-second
firing burst scored twenty-five hits on a minimum ten-foot-square raft
and seventy-five hits on a maximum fifty-foot square one (Simons, et al,
Project Tailchaser: Development of a Lateral Firing Concept, AMRL-TR-66-202,
pp14-15). A testing phase on the land range saw twenty-five manikins scattered
in different positions over three-quarters of an acre. A three-second firing
run on this area target hit nineteen manikins, ten of them considered “killed.”
The test results exceeded expectations. As Captain Simons had long predicted,
they adequately confirmed the concepts feasibility and convinced many of
the skeptics that this was indeed a worthwhile weapon system. At this point
ASD assumed management of the program.
The C-131 test results aroused the interest of 1st Combat Application Group personnel at Eglin AFB. They asked Captain Terry, Sergeant Bunch, and other Tailchaser crewmembers if a gun kit in side-firing mode could be built into other aircraft. Specifically they wanted to modify a C-47 or C-123, since Air Force Special Forces units in South Vietnam were using these aircraft. Captain Terry jumped at this opportunity and in short order three of the Gatling guns (called miniguns) were installed in a C-47 cargo compartment. The C-47 side-firing tests in September 1964 repeated the successes of the C-131 tests.