On Mark Engineering Writen by Richard E Fulwiler In the early 1950s, Grand Central Air Terminal, Glendale, California, was a hot-bed of ex-military aircraft conversion and modification. This historic airport (which exists almost completely intact but is in threat of demolition by the Disney Corporation which now owns the property) was America's first west coast transcontinental terminal and over the years (it closed in 1959) had seen numerous historic aviation firsts. Grand Central Aircraft Company executives came up with the idea to modify an Invader to carry passengers. Several Invaders were completed when the employees split off and established On Mark Engineering at nearby Van Nuys Airport. The company obtained a Supplemental Type Certificate (STC) and began to produce a number of conversions. With conversion production getting underway in the late 1950s, the company created first the Executive, becoming the Marketeer in 1957, which were the unpressurized variants. Most had the rear spar carry-through (which limited cabin access) replaced by a strong and efficient circumferential "ring" spar of On Mark's patented design. By removing most of the original interior bulkheads and adding the ring spar, provided additional room for passengers in the new cabin space of the aircraft. The forward wing spar was not changed because of the magnitude of the re-engineering that would have been required, and would have altered the aircraft's design geometry and excellent flying qualities. With the wings mounted as with the original design, meant that crew members were left with the inconvenience of mounting the flight deck through a crawlway along the right side of the cabin beneath the forward spar. The customer would supply or either purchase a standard Invader which would be restructured in On Mark's spacious hangar. The cockpit would be removed and rebuilt to include dual controls, upgraded instruments and radios, a lengthened fiberglass nose for baggage and radar added, and, more importantly, the cabin was built to customer specifications, and added a number of large windows. The standard A-26 curved windshield design would be retained, with the upper canopy clamshells either painted or skinned over. Air stair doors were installed into the belly, or right side of the fuselage. Also offered, were distinctive 165 gallon wing tip fuel tanks added to increase range, and upgraded P&W R-2800's. Next came, perhaps the best-known of the civilian Invader conversions, the On Mark Marksman series in 1961. The Marksman was the pressurized variant and required a special Supplemental Type Certificate (STC). The airframes were restructured with a greatly altered fuselage, DC-6 / -7 canopy structure with heated windshields, radio/navigation/radar improvements, ring spar, lavatory and food service consoles, soundproofing, air conditioning, increased area vertical tail, long nose, wingtip fuel tanks, improved anti-skid brakes, deicing, and numerous other upgrades and systems included as standard. The pressurized Marksman series were offered in three versions; Marksman A, B, and C. The Marksman A had 2100 hp R-2800-83AM3 engines; the Marksman B had 2100 hp R-2800-83AM4A engines; whereas the premier Marksman C had a raised cabin top that provided a 6 foot walk-through full length cabin, 2500 hp R-2800-CB-16 / -17s and added internal wing auxiliary fuel tanks. Only 15 percent of the original fuselage remained, and dependant on customer options, were designed to carry from 6 to 8 passengers. The base price of the Marksman A was $257,430, up to $361,492 for the Marksman C. The On Mark Marksman was regarded as the best of the A-26 Invader conversions, providing up to eight business executives and a crew of two, an all-weather aircraft that was able to cruise up to 25,000 feet at 325 - 365 miles per hour with a range of  between 1200 and 2500 miles with normal reserves. At 20,000 feet, the pressurized, air-conditioned cabin was at a comfortable 7,500 feet. On Mark also built a model and partial mock-up of the Model 450 which was a greatly modified pressurized aircraft fitted with Allison 501 D turboprops but, after a lot of deliberation, the project was shut down. Oddly, there is no exact record of the number of converted Invaders built by On Mark but its thought to be up to 50 aircraft. Also, the reign of the On Mark aircraft was short - a new generation of business jets led by the Lockheed JetStar and Lear Jet quickly dominated the market and the On Marks were purchased in the late 1960s and 1970s by drug runners who respected the type's long range and load carrying abilities. The following is a quick look at On Mark Invader conversions.   On Mark  -  Marketeer On Mark Marketeer: Prototype serial number: 44-35326 ( c/n: 28605 )  Registered as N40Y ( 1957 ) Unpressurised version of the executive transport produced by On Mark Engineering on almost production-line basis. After the airplane was stripped of its armament, it was entirely re-engineered, re-framed and altered. All surface metal of fuselage, wing and empennage structures were inspected. The aft wing-spar that passes through the fuselage was removed and was replaced by a ring of steel. Most of the partitions within the fuselage were removed to open up the cabin area. Skin, stringers and ribs were altered, added to and strengthened. Large 'picture windows' were installed, as was the side entrance. Thick Fiberglass insulation was packed in cabin and cockpit walls to quiet the cabin.. When changes in the structure were completed, the interior was finished off to customer's specification that included a lavatory and a seating capacity for up to seven passengers in clubroom comfort. Extra fuel tankage in the wings, tip tanks, an auxiliary power unit (APU), advanced radios, radar, and 2,500 hp (1865 kW)  R-2800-CB-16 / -17 radials were often installed to customer specifications. See feature by Richard E. Fulwiler           On Mark  -  Marksman A On Mark Marksman A: Prototype serial Number: 43-22416 ( c/n: 18563 )  Registered as N100Y ( early 1961 ) Pressurized, air conditioned version of the executive transport produced by On Mark. Cockpit windshields and side windows were flat panels from Douglas DC-6 / -7 airliners, while cabin windows became rounded-corner squares. Extra sound deadening materials were used to further quiet the cabin. Powered by 2,100 hp (1567 kW) R-2800-83AM3 engines.   On Mark  -  Marksman B Similar to the Marksman A apart from the provision of R-2800-83AM4A radials.           On Mark  -  Marksman C   On Mark Marksman C: Prototype Serial number: 44-34761  ( c/n: 28040 )  Registered as N400E ( late 1961 )   Vastly modified, premier version of the pressurized Marksman series. Cabin interior volume was increased by raising the fuselage top to provide a 6' 1" full length "walk-through" height. All "C" model Marksmans were powered by high output Pratt and Whitney R-2800-CB-16 / -17 radials developing 2,500 hp (1865 kW) for take-off with water injection. Also standard were fully reversible, broad chord Hamilton Standard propellers, and a "707" type anti-skid braking system. The Marksman C was the ultimate in executive transport only for a brief time until executive jets became available. The early radar-equipped Marketeers had fiberglass nosecaps that were round-ended conical sections, but otherwise "B" model gun-nose profile. But when they went to the 103" nose, it was a extended, sharply tapered, all fiberglass unit that mounted on fuselage station "0". All Marksmans and many of the Marketeers were equipped with the 103" nose.         Prices for these aircraft   On Mark Marksman A - $257,430.00 On Mark Marksman B - $314,715.00 On Mark Marksman C - $361,492.00 Note: These prices did not include for radio, electronics or sales tax       Early nose with radar (note the slight step in conical section)     103" Nose   Clarification by Richard E. Fulwiler

	L.B. Smith Aircraft Corporation   Based in Miami, Florida, this company specialized in conversions of the C-46 as well as producing airliner interior components. The company decided to completely reengineer the Invader and replaced both spars with ring spars built of aluminum. This also saw the increase of the wing center section which moved the engines on each side 20 inches from the cabin to reduce noise. The aircraft, like the On Marks, received DC-6 wheels and brakes, new canopy and cockpit, lengthened nose, rebuilt fuselage, and numerous other modifications. Named the Biscayne-26, it is thought that only one aircraft was built before the company decided to start with a clean sheet of paper. The new aircraft would have a completely new and much larger fuselage that would also be pressurized. Two variants were to be built, the Tempo I (unpressurized) and the Tempo II (all the bells and whistles). The Tempo II was ten feet longer than a standard Invader and had a 28-foot cabin that could accommodate up to 13 passengers. Every thing else on the first aircraft was completely modernized and it was a beast, making its first flight as N4204A during October 1959. Price was $375,000 but it appears only one was built and it eventually went to the University of Nevada and was lost over the Sierras when it came apart. The seven seat Super B-26, made its first appearance at the National Business Aircraft meeting in Philadelphia. The aircraft cruised at 325 m.p.h. on 60 per cent power, and had a range of 2,100 miles at a take-off gross weight of 35,000 lb. The new interior of the machine was designed by Charles Butler Associates in a colour scheme featuring gold, wheat and tones of blue. "Cabinetry is of smooth, hand-rubbed blond walnut," and "the instrument panel and overhead panel was finished in turquoise with eyebrowtype lighting. Smith Biscayne 26 A high-speed transport version developed by the L.B. Smith Company and able to seat up to 15 passengers         Smith Super 26 Standard Invader airframe converted with wingtip tanks and an executive interior. Both spars were replaced with ring spars built of aluminum. This also saw the increase of the wing center section which moved the engines on each side 20 inches from the cabin to reduce noise. The aircraft, like the On Marks, received DC-6 wheels and brakes, new canopy and cockpit, lengthened nose, rebuilt fuselage, and numerous other modifications. Named the Biscayne-26, it is thought that only one aircraft was built before the company decided to start with a clean sheet of paper.         Smith Tempo I Unpressurised executive conversion with R-2800 B series engines.         Smith Tempo II Prototype serial number: 44-35640 Second prototype Serial number: 44-34127 - N4214A A pressurised executive conversion with a new fuselage which was 9 ft 7 1/2 in (2.93 m) longer than the standard and able to seat up to 13 passengers. The Tempo II was ten feet longer than a standard Invader and had a 28-foot cabin that could accommodate up to 13 passengers. Every thing else on the first aircraft was completely modernized and it was a beast, making its first flight as N4204A during October 1959. Price was $375,000 but it appears only one was built and it eventually went to the University of Nevada and was lost over the Sierras when it came apart.

	Lockheed Air Service (LAS), California conversion   A separate arm of Lockheed Aircraft, LAS operated from Ontario, California, and specialized in the conversion of airframes. In the late 1950s, the company created the Super 26 which utilized just the wings, engines, tail, and landing gear of the Invader. A new fuselage with a pressurized cabin that was 22 feet long and six feet high was built and this could carry six-to-nine passengers. Constellation windows and cockpit sections were utilized and the first example, N5052N, flew in mid-1960. Apparently only one was built and the hulk finally wound up with Air Spray in Canada as a parts source. Super 26 The above shot shows N5052N, s/n 44-35994, when the plane was at Spaatz Field, Reading, Pennsylvania, on 29 September 1968. At that time it was owned by Mesta Machine Co. of Pittsburgh.   Prototype serial number: 44-35994 The Super 26 utilized just the wings, engines, tail, and landing gear of the A-26 Invader. A new fuselage with a pressurized cabin that was 22 feet long and six feet high was built and this could carry six-to-nine passengers. Constellation windows and cockpit sections were utilized and the first example, N5052N, flew in mid-1960. Apparently only one was built and the hulk finally wound up with Air Spray in Canada as a parts source.   The modifications in detail consisted of: Increased interior height by raising the fuselage top ( looks like a foot above the normal A-26 ) - and - deepening the belly ( by 6 to 9 inches - starting with a fairing at the nose landing gear well / forward bomb bay lower-partial bulkhead ) carrying this height section aft to the break in the parallel longitudinal reference ( tapering to the tail ). Increased the interior cabin length by adding what appears to be a 6 foot " plug " in the fuselage aft of the wing. This configuration is remarkably similar to the L.B. Smith Tempo II conversion design. With the incorporation of the " ring spar " to replace the rear wing spar carry-through structure, the interior would be open from the rear face of the forward wing spar, all the way back to the rear pressure bulkhead ( behind the rear-most cabin side window ).   LAS was said to have used Constellation L-1049 Super G cabin windows in conjunction with pressurization. These can be identified by the square shape with generously rounded corners as seen on the aft fuselage ( 4 on each side, includes the entrance "Airstair" to starboard and the escape panel opposite ) and the pair below the right wing. The oval windows above the wing appear to be horizontally sectioned from the side window size. The cockpit windshield appears to be the normal A-26 curved units but with small cockpit side windows, both incorporating heavier framing to withstand pressurization loads. This configuration can also be found on the L.B. Smith Tempo II conversion.   A newly designed fiber glass nose with considerable length and contour revisions over the standard A-26. The added length of the nose was certainly increased to compensate for the added fuselage length aft of the wing. This would bring the C. G. back to the correct location and aerodynamically improve the shape. An added benefit would be an increased capacity to carry luggage and baggage in the nose along with the aft compartment ( note the small open doors on the right side, nose and tail ). A half-dome transition shape to the aft end of the cabin top to blend with the standard A-26 tail section. Note how the vertical stabilizer leading edge blends into a horizontal dorsal spine, ending at the half-dome transition. These shapes can be found on the On Mark Marksman " C " configuration. As the LAS Super 26 preceded the Marksman series, it seems that there were many design elements used by the various conversion companies, especially those operating from the San Fernando Valley area of California. It must be noted, however, that On Mark Engineering dominated the A-26 Invader conversion business, and was successful beyond measure compared with their competition.

	Rhodes Berry, California conversion   Possibly the ugliest of all Invader conversions, the Rhodes Berry Silver 60 was built at Whiteman Airpark in the San Fernando Valley of southern California during the late 1950s. The fuselage was completely redone resulting in a swollen unit that could accommodate up to 16 passengers. Also, because of the deeper fuselage, the nose gear could now retract straight back without first swiveling as on stock Invaders. The first Silver 60 flew on 25 June 1960 with the registration N5510V. Some sources state another example was built but we can't find photos of just the first and its final history is not known.   Silver Sixty Prototype serial number: 41-39262 1960 Conversion. The fuselage was completely redone resulting in a swollen unit that could accommodate up to 16 passengers. Also, because of the deeper fuselage, the nose gear could now retract straight back without first swiveling as on stock Invaders. The first Silver 60 flew on 25 June 1960 with the registration N5510V.

	Rock Island Oil & Refining Co., Kansas conversion   Oddly named company had an aviation division that in the 1960s produced the very attractive Monarch-26s. The company purchased several dozen surplus Invaders and moved them to their aviation facility at Hutchinson, Kansas. A number of Rock Island aircraft were built up and they were basically stock looking but had a lengthened nose, passengers cabin with extra windows, and upgrade cockpit and avionics. Monarch 26 Prototype serial number: 44-35911 The company purchased six surplus Invaders (ex-French AF aircraft that had served in Indochina) out of the Clark Field storage facility. The original Invader airframe was extensively reconfigured with re-contouring and extensive re-skinning. In order to provide for more interior cabin space, an new wing spar was designed to replace the original straight-through configuration and new upper and lower fuselage structures were extended from the rear spar to the fin root fillet. The new cabin could accommodate up to six passengers in a low-density arrangement, and featured floor heating, a restroom, catering facilities, and panoramic windows. There was an airstair door on the rear starboard side. The extended nose was 30 inches longer than the original. Because of a fear of wing failures, the Rock Island engineers decided not to add wingtip fuel tanks, but added additional fuel cells in the outer wing panels, which raised the total fuel capacity to 1012 US gallons. The cockpit was fitted with dual controls, new instrument and overhead panels, and "metalized" double-paned cockpit canopies. Anticipating more orders, Rock Island acquired 30 more surplus Invader airframes, this time from storage at Davis Monthan AFB. However, the Monarch had only limited success in the corporate aircraft marketplace, with only 4 being completed, including three in-house.     Consort 26 The Consort 26, was designed for research and development purposes. All military equipment was removed, the bomb bay was sealed up, and a reinforced floor was added. Three Invader airframes were modified in this way and were sold or leased to aerospace companies as platforms for system development programs. Prototype serial number: 44-34121

	LeTourneau   Based in Long View, Texas, this company did some very early Invader executive conversions. There modifications basically included a six-place cabin in the rear fuselage and an air stair door. Number of conversions is not known. Prototype serial number: 44-34134 DOUGLAS A-26 Modifications basically included a six-place cabin in the rear fuselage and an air stair door. Number of conversions is not known.

	Grand Central Aircraft Company h The above photo is by courtesy of W.J. Balogh via W.T.Larkins The early days of air travel in Los Angeles have essentially nothing to do with those often dreaded letters L-A-X. In fact, the origins of commercial air travel in America began in Glendale in the early portion of the 20th century in what eventually became Grand Central Air Terminal (GCAT). In the early 1930s, work began on the Aviation Trade School at the airport, “the Curtiss-Wright Technical Institute was founded in 1931 as an aviation trades school and occupied a corner of the Air Terminal building. It gradually expanded, occupying portions of the aircraft hangars at the airport and various industrial buildings along Air Way. Directed by Major Moseley, the Institute was a school for aircraft technicians, mechanics, and engineers. It did not have a flight-training program. Flight instruction was available from the Curtiss-Wright Flying Service as an adjunct to courses offered by the Institute.” Moseley then leased the airport in 1934 and along with other partners formed Aircraft Industries, Inc. which served as an “authorized service (aircraft repair and engine overhaul), sales and distributor agent for several aircraft manufacturers” (City of Glendale). In the early 1950s, Grand Central Air Terminal, Glendale, California, was a hot-bed of ex-military aircraft conversion and modification. This historic airport (which exists almost completely intact but is in threat of demolition by the Disney Corporation which now owns the property) was America's first west coast transcontinental terminal and over the years (it closed in 1959) had seen numerous historic aviation firsts. Grand Central Aircraft Company executives came up with the idea to modify an Invader to carry passengers. Several Invaders were completed when the employees split off and established On Mark Engineering at nearby Van Nuys Airport. The shot below shows conversion work at Grand Central on A-26's in the 50's   Prototype serial number: 44-34758

	Aero Trades Inc.   h 1951 Serial number. 44-35950   Garrett Corp, Los Angeles, CA & Phoenix, AZ - Modified for turboprop engine in nose position.

	Wold Corp.   The Wold Invader is powered by two Pratt and Whitney R-2800-CB-16 engines, rated at 2,400 h.p. with water injection, and driving Hamilton Standard reversing propellers. Although of somewhat small cross-section, the fuselage is luxuriously furnished for eight passengers in four large reclining chairs and a divan. The cabin is "super-soundproofed" and provided with a toilet and extensive storage facilities, and optional equipment includes the following: Sperry A-12 autopilot; Bendix X-band and weather radar; Collins Integrated Flight System; Bendix D.M.E.; Sperry engine analyzers, and the following radio equipment—sufficient to take the aircraft anywhere in the world—Collins 51R3 Omni receiver, Bendix Omni receiver, 17L3 Collins transmitter, series 440 Wilcox 50W V.H.F. transmitter simplexed with Wilcox receiver, dual Collins R.M.I., dual A.D.F. Bendix MN62, Bendix markerbeacon receiver, F-ll A isolation amplifier, cockpit and cabin speakers, Collins 51V glideslope receiver, and R89 glide-slope receiver. More than 80 multi-engined executive and airline transports, with a total value exceeding £5m, were sold by William C. Wold Associates, an American company specializing in transport aircraft sales. The simple but highly successful Wold technique centred on the production of a small brochure describing the aircraft, which was circulated to a mailing list of 7,000 company executives, pilots, purchasing agents, export and import firms and operators, both in the U.S. and abroad. The companies flag ship conversion identified in the Wold brochure was the 300- m.p.h. Douglas B-26 Invader conversion with a luxurious fiveseat cabin and toilet. A Wold Corporation B-26 Serial number: 44-34762 ( Only one No. conversion undertaken )         The majority of the information above was furnished by the National Museum of the USAF

	Slick Airways Slick Airways was founded in January 1946 by Earl F. Slick. It began operations on 4th March 1946. At that time Slick operated a fleet of ten Curtiss C-46E aircarft purchased from the Reconstruction Finance Corporation. During the first few years, the airline was the first U.S. freight carrier and was selected as one of the scheduled freight carriers in 1949. The DC-6B passenger aircaft entered service with United Air Lines on April 11th 1951, and Slick Airways was the first airline to operate the DC-6A freighter on April 16th 1951. By 1951-52 Slick Airways was the largest all-cargo commercial operator, as Flying Tigers supported their operations mainly with financially interesting military contracts. With the everincreasing competition of passenger airlines trying to sell their excessive freight capacities, Slick was forced to enter into merger negotiations with Flying Tigers. The two airlines agreed to merge on March 26th 1953. Approvel of their respective shareholders was obtained on August 6th 1953. Against the protests of the passenger airline competition, the CAB approved the merger on January 7th 1954. But then the CAB own lawyers objected the deal, and finally labour problems in both companies became very acute. Therefore, the companies decided reluctantly to drop the merger proposals on September 20th 1954. With the financial situation degrading constantly on its scheduled services, Slick decided to abandon all scheduled commitments as from February 24th 1958. The airline managed to survive financially and decided to diversify by buying the Illinois Shade Cloth Company in July 1960 for $6.350.000. Simultaneously it ordered six Lockheed GL 207 Super Hercules freighter aircrafts, but this deal never materialized. Instead four Canadair CL-44D4-6 were ordered on October 16th 1959. First commercial flight of this aircraft for Slick Airlines was made on February 11th 1962 on a military contract flight from San Francisco to Manila. On October 1st 1962 the airline's route 101, a transcontinental scheduled service was reinstated. However the airline's fortunes declined once again and on August 27th 1965, the CAB authorized suspension of scheduled services. Airlift International acquired the assets being used on Slick's military operations on July 1st 1966 and route 101 on July 22nd 1968. Slick became a financial holding company called Slick Corporation owning beside the Illinois Shade business also the Drew Chemical Company, which was purchased on February 19th 1968, and a Pulverising Machinery Plant. Slick Corporation was also a minority shareholder in Airlift International.     Prototype Serial number: 44-34759 NX67834, N67834, N28W, N956, N956R   This A-26 was one of the brand new, never AAF accepted Invaders that went direct from Douglas to Kingman, to the RFC for disposal. There is no AAF record card for the airplane since it was never accepted. Charles Babb purchased a bunch of them for $2000 each...brand new airplanes with the cushions still wrapped in plastic, or so I've heard. This A-26 went to Milton Reynolds and registered with his company then, the Printasign Corp. of America. After his round-the-world 1947 flights with Bill Odom at the controls, it went to Phillips Drilling in 1948. They had a large window installed in the aft fuselage and a cabin door installed. In 1954 it went to Earl Slick of Slick Airways, of Burbank, CA. Aviation Power Supply of Burbank installed the tip tanks in January 1956, and also did some other fuel system work and other modifications. In July 1956 On Mark at Glendale installed a weather radar unit with the radome on the nose. In October 1956, a company in Denver replaced the Bendix brakes with new Goodyear brakes. In August 1957, On Mark did some aft fuselage mods, including lowering the aft floor. In July 1961, On Mark did some more fuel tank work. In March 1967, the airplane went to the Ventura Division of Northrop, and pylons were installed to handle "Horkey Moore launcher" rails to mount RP-78 targets. Not sure about these items but it appears the Invader was used as a launcher of new target drones. Shortly afterwards, or maybe when the wing racks were added, the airplane went to On Mark again to have fatigue straps added to the front wing spars and shear plates added to the rear spars, and the wing structure and attach points were also inspected with the wings and engines off the fuselage.