The 680T was the sixteenth Commander model, and the first turbine-powered model—to be placed in production. The first 56 were built by the Aero Commander Division of Rockwell-Standard Corporation at Bethany (Wiley Post Airport), in Oklahoma City, and the last 10 by the Aero Commander-Bethany Division of Rockwell-Standard Corporation.
The 66 examples were built between December 1964 and July 1967, with serial numbers in the range 1473-1 through 1707-82, although the first example was actually converted from a Model 680FLP, s/n 1473-3.
Of these, one was initially certified in 1964 followed by 17 in 1965, 34 in 1966, and 14 in 1967. Additionally, 51 models 680Ts were later converted to 680Vs.
The 680T and 680V share a common “unit” number sequence, hence the last 680T was s/n 1707-82 even though only 66 built.
A factory document describes the Model 680T, under Wing Drawing 5170045 with removed 32-inch wing tip extension, as “originally certified on September 15, 1965 per CAR 3, May 15, 1956, Amendments 3-2, 3-3, 3-4, 3-6, 3.197, 3.395, 3.396 and Special Conditions. At this time, it was an 8500-pound aircraft identical to the 680FL with the following exceptions: a) AiResearch engines Model TPE-331-29A; b) revised fuel system; c) pressurized to 4 psi; and d) revised air design speeds. In 1966 the 680T was recertified with the following changes: a) Gross weight increased to 8950 pounds; b) the 32-inch wing tip extension was removed; c) increased take-off power; d) new propellers; e) increase of operating limits; and f) airframe configuration changes, resulting in changes in flight characteristics. At 8500-pound gross weight, 680T aircraft was reworked to this new configuration.”
(Note: “At 8500-pound gross weight 680T aircraft was reworked to this new configuration” probably should read: All 8500-pound gross weight 680T aircraft were reworked to this new configuration.)
The Model 680T was indeed certified on September 15, 1965 under Type Certificate 2A4. The first example originally had AiResearch TPE331-29 engines, with the next 19 examples originally having TPE331-29As and the last 46 having the TPE331-43s. The 90-inch-diameter Hamilton Standard 33LF-325/1033A-0 propeller was eventually used, after various other 84-inch-diameter Hamilton Standard propellers had been used in the early stages of the model’s development.
Originally, the TPE331-43 was a military engine designated T-76. The civilian variant was test-flown in the nose of a Douglas A-26, s/n 27802, N9174Z, formerly 44-34523.
Some 680Ts have been modified to a “Century Turbo” with the TPE331-43 engines replaced by TPE331-1-151Ks.
Gross weight was originally 8,500 pounds, but this was later increased to 8,950 pounds.
Cabin pressure differential is quoted as 4.0 psi as a minimum and 4.2 psi as a maximum. At 4.2 psi, the cabin altitude is 13,000 feet at an aircraft altitude of 27,955 feet, and a sea-level cabin at 9,025 feet.
In its early stages of development the 680T had TPE331-29 engines; a wing span of 49 feet 0.56 inches; 84-inch-diameter Hamilton Standard propellers; a relatively small intake at the front of the nacelle; and exhaust tail pipes trimmed almost flush with the nacelle contour. Also, the main landing gear wheel doors attached to the wheel hub and articulated such that the lower portion hinged into a horizontal position when the gear was extended; these were quickly dubbed “daisy cutters.” Deliveries had started when it was announced that all 680T aircraft were being withdrawn due to their inability to meet certain guaranteed operational and performance numbers.
Under the 680T re-work program that followed, called Project 90, the 680T was modified to have: TPE331-43 engines; a wing span of 44 feet 0.70 inches; 90-inch-diameter Hamilton Standard propellers; a larger intake at the front of the nacelle, affectionately dubbed the “Garrett smile”; and exhaust stacks that were now routed aft and downward, almost clear of the flap and enclosed in a shroud that acted as a cooling eductor. Later, the “daisy cutter” main landing gear wheel doors were replaced by the “clam shell” style doors that were installed on the aft nacelle and hydraulically operated. These doors were used on all subsequent Turbo Commanders.
Additionally, gross weight increased from 8,500 pounds to 8,950 pounds; take-off horsepower increased (CAA description doesn’t state how much); aerodynamic flap gap seals were added (other gaps may also have been sealed); and the dorsal scoop for the pressurization system was deleted and a flush-type introduced.
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 about 100,000 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.