The Model 720, named the “Alti-Cruiser,” was the eighth Commander model to be placed into production, but only 13 aircraft were built. The first six were produced by the Aero Design & Engineering Company at Tulakes Airport (later re-named Wiley Post), in Bethany, Oklahoma, and the last seven by the Aero Design & Engineering Company as a subsidiary of the Rockwell-Standard Corporation. The Alti-Cruiser was the last of the so-called Bathtub Commanders because of the distinctive shape of the engine nacelles.
The 13 examples were built between October 1957 and June 1960, with serial numbers in the range 720-501-1 through 720-850-13, although serial number 720-501-1 was converted from a Model 680, serial number 680-501-1.
Of these, one was initially certified in 1957; two in 1958; eight in 1959; and two in 1960.
The Model 720 was proudly proclaimed as “The World’s first pressurized light-twin executive aircraft.” R. J. White, Vice President-Director of Sales, is quoted as commenting, “They said that you couldn’t pressurize a slab-sided fuselage. But we did.”
A factory document describes the Model 720, under Wing Drawing 5170023 with a 32-inch wing tip extension, as a pressurized model 680E. It is the same as the Model 680 except for increased weight, the extended wing, a pressurized cabin, and some fuselage changes.
The Model 720 was certified on December 5, 1958 under Type Certificate 2A4. Power came from 340 hp Lycoming GSO-480-B1A6 engines. The first seven aircraft used 93-inch-diameter Hartzell HC-83X20-2C/9333C propellers, while the last six used the Dash 2C1-variant hub.
Maximum gross weight is 7,500 lb and the cabin pressurization differential is 2.8 psi, giving a 17,632-foot cabin at 28,600 feet, and a sea-level cabin at 5,733 feet.
If the viewing angle is right, the Model 720 can be distinguished from other Bathtub-nacelle models by the dorsal scoop mounted on top of the fuselage aft of the wing trailing edge. The scoop is for the pressurization system. Also, the windshield installation uses glass panes, and to limit the curvature to a single plane an aluminum “eyelid” was added to fill in the upper four-to-five inches of the normal Aero Commander windshield opening. Additionally, the Model 720 does not have nose-mounted lights; instead, retractable units are mounted under the wings.
The pressurized cabin door is secured with a number of bayonet pins, each of which is actuated by small individual gearboxes that in turn are all powered by a single, very long, bicycle-type chain routed around the inside periphery of the door frame. Some muscle is required to operate the door because of the very long door handle with a relatively large throw.
Pressurization is provided by a single-stage hydraulically-driven centrifugal compressor, manufactured by the Stratos Division of the Fairchild Engine and Airplane Corporation. Variable delivery engine-driven hydraulic pumps, one on each engine, provide power to drive the compressor. A cabin pressure control system allows selection of cabin altitudes, normally from 5,000 feet to 7,000 feet below the actual aircraft altitude. Automatic cabin air-conditioning, both on the ground and in flight, is maintained by a Stratos BUR-20 turbine cooling unit, while heating is provided by a Janitrol 40,000 BTU gasoline heater.
One of the first things designed for the Model 720 interior was a separate toilet compartment at the rear of the cabin, but this reduced the six-place passenger cabin to a four-place. Strangely, the FAA Type Certificate Data Sheet shows the Model 720 as having six seats, but then amplifies this by saying “2 at +94, 2 at +128, and 3 at +168” which gives a total of seven seats. However, an article in Business Flying magazine in January 1958 appears to clarify things by saying that the 720 was being offered in two configurations: straight seven-place or four seats plus lavatory. The $183,750 price tag included everything for all-weather operation except de-icer systems and weather-avoidance radar. These were optional items, as was an autopilot.
Barry Collman’s lifelong interest in airplanes began when he was growing up in a house located underneath the downwind leg to busy Northolt aerodrome, an R.A.F. base near London-Heathrow airport. As a young teenager he discovered airplane “spotting”–hobbyists’ observation and logging of aircraft by make, model, and registration number. The hobby began to grow into a passion as Collman joined a club of like-minded spotters. At one point he purchased a copy of the January 1966 U.S. Civil Aircraft Register, and thumbing through it came upon the Aero Commander. He was hooked. Eventually he acquired every available FAA microfiche file on Commanders, and since 1995 has made annual pilgrimages to Oklahoma City to sift through FAA records. He now has a database with more than 96,100 records as well as a collection of negatives, slides, photographs, digital images, magazines, brochures, knick-knacks–and a very understanding wife. This series on Commander production history originally was written for the Twin Commander Flight Group, of which he is an enthusiastic member.