Boardroom bombers

Air Classics, Oct 2002

WITH ITS EXCEPTIONAL RANGE AND

PERFORMANCE, MODIFIED INVADERS BECAME THE LEAR JETS OF THEIR DAY

At the end of World War Two, surplus Invaders were not common but those that became available were quickly purchased for a variety of reasons. Some were supplied to foreign air forces but the need for a high-performance business aircraft in post-war America was evident and conversions were undertaken to modify the Invader to haul business executives. In this brief guide, we shall start with the most prominent:

ON MARK ENGINEERING

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 production getting underway in the late 1950s, the company created the Marketeer which was an unpressurized variant that had the rear spar (which limited cabin access) replaced by a strong and efficient ring spar. The customer would supply or either purchase a standard Invader which would be torn apart in On Mark's vintage hangar. The cockpit would be removed and rebuild, a lengthened nose for baggage added, and, more importantly, a cabin was built in the rear fuselage to customer specifications - easily identified by a number of windows. Air stair doors were also added to the side of the fuselage or in the belly. Also, distinctive wing tip fuel tanks were added to increase range and upgraded P&W R-2800s were offered. Next came the Marksman, a pressurized variant with greatly expanded fuselage, increased vertical tail, long nose, DC-7 canopy structure, and numerous other upgrades. Only 15 percent of the original fuselage remained in the Marksman. 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 around 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 1960s and 1970s by drug runners who respected the type's long range and load carrying abilities. The following is a quick look at other Invader conversions.

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.

ROCK ISLAND OIL & REFINING CO.

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.

RHODES BERRY

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 NSS 10V. Some sources state another example was built but we can't find photos of just the first and its final history is not known.

LOCKHEED AIR SERVICE

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.

L.B. SMITH

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.