Econo-Jet – the Model 73

Beech Aircraft Corporation’s Jet Mentor was built on a tight budget and performed well but lost its bid to be the U.S. Air Force’s first turbine-powered basic trainer to crosstown rival Cessna Aircraft Company’s Model 318.

During the early 1950s, excitement about the “Dawn of the Jet Age” was capturing the imagination of the American public. World War II, still a very fresh memory to millions of Americans who had fought in that global conflict or lived through it, had seen the jet fighter’s combat debut as the twin-engine Messerschmitt Me-262 tore through Allied bomber formations, wreaking havoc and easily evading Allied fighters with its 500-plus mph maximum speed. In response to the German threat, the British Royal Air Force soon fielded a twin-engine jet fighter of their own, the Gloster Meteor and by 1943-1944 the United States Army Air Forces was experimenting with the Bell XP-59 powered by two jet engines provided by the British.

The Model 51 was built by the Texas Engineering and Manufacturing Company to challenge Cessna’s Model 318 and the Beechcraft Model 73. A mid-wing design, it was evaluated by the U.S. Navy as the TT-1 Pinto primary jet trainer, but only 14 were built. (Edward H. Phillips Collection)

In addition, during 1950-1953 the escalating air war in the skies over Korea was often headline news as North American single-engine F-86 Sabre jet fighters clashed in dogfights with the much-vaunted Soviet MiG 15- and MiG 17-series jets flown by Russian and North Korean pilots. By the end of the Korean conflict in 1953, it had become painfully clear to the champions of United States military aviation that the day of the reciprocating piston engine as the “prime mover” of front-line fighter aircraft was rapidly drawing to a close.¹

As early as 1945 the Army Air Forces had begun taking delivery of the single-engine Lockheed F-80 Shooting Star – the service’s first combat jet fighter that also served with distinction as a fighter-bomber during the Korean War. A two-place, tandem-seat version designated T-33 eventually became the Air Force’s standard airframe for training new jet pilots who had already earned their wings in war-weary T-6 trainers that had been rebuilt. To bridge the wide gap between the Beechcraft T-34 and the T-33, in 1950 the Air Force began operating the North American T-28A Trojan as its basic and primary pilot training platform.²

In 1953-1954, however, the Air Force also had begun taking delivery of the Beechcraft Model 45 Mentor – a two-place, tandem-seat, piston-powered airplane that was much better suited to serve as a basic trainer than the T-28A. Recognizing that the time had finally come to bid farewell to the venerable T-6 and SNJ, in the early 1950s both the Air Force and Navy, working independently, began formulating plans to obtain a jet-powered basic trainer. Early in 1952 the Air Force conducted a design competition for a primary jet trainer and three manufacturers responded – Wichita, Kansas-based Beech Aircraft Corporation and Cessna Aircraft Company, and Dallas, Texas-based Texas Engineering & Manufacturing Company (TEMCO).

Cessna’s design was designated the Model 318 and was a “clean-sheet” airplane powered by two Turbomeca Marboré II centrifugal-flow turbojet engines, each rated at 920 pounds of static thrust. The compact powerplant was built in the United States under license by Continental Motors, which had obtained manufacturing rights in 1951. The engine was designated as the military J-69-T-7. The engines were buried in the wing root area. Inlet air screens extended when the tricycle landing gear was down and retracted when the gear was up.

The airframe was of all-metal, monocoque construction and the wings featured slotted flaps mounted inboard of the ailerons that were operated hydraulically. Wingspan was 33 feet, 9.5 inches, length 29 feet, 4 inches and height 9 feet, 2.5 inches. A speed brake was installed under the forward fuselage section below the cockpit and could be extended up to 50 degrees. The empennage was a semi-crucifix design with electrically operated trim tabs on the elevator panels and rudder, which were covered in fabric.

Cessna Aircraft Company’s Model 318 was a new design that featured two J-69-T-7 turbojet engines and side-by-side seating for the student and instructor pilot instead of the conventional tandem configuration. The Model 318 eventually became the U.S. Air Force’s T-37A primary jet trainer that served for decades until it was replaced by the turboprop-powered
Beechcraft T-6A Texan. (Textron Aviation)

The Model 318 departed from the Air Force’s conventional, tandem seating configuration by placing the student pilot and instructor side-by-side in ejection seats under a large canopy that could be jettisoned in an emergency. Dual controls were standard. At the design maximum gross weight of 6,250 pounds, maximum speed was 370 knots and the airplane could climb to an altitude of 35,100 feet. The twin-engine jet made its first flight Oct. 12, 1954, under the command of company test pilot Bob Hagan.

Temco’s proposed trainer, the Model 51, was powered by a single Continental-built J-69 turbojet engine rated at 920 pounds static thrust. Its all-metal airframe featured a molded fiberglass tail cone, and some wing panels and the landing gear doors were manufactured using metal honeycomb materials. The wing, which spanned 29 feet, 10 inches with an area of 150 square feet, was mounted midway up the fuselage and featured three different airfoil sections along the span to preserve airflow across the ailerons deep into a stall. The cantilever empennage was all-metal. The tricycle landing gear was operated hydraulically and was designed to extend and lock into place if a complete hydraulic failure occurred.

Dual ejection seats were installed with the rear seat raised slightly to improve the instructor’s forward field of view. The large canopy could be jettisoned. Temco officials claimed that the engine could be exposed for inspection in only 10 seconds and a complete engine change was possible in only 20 minutes. The prototype Model 51 took to the sky March 26, 1956, and later was flown to NAS Patuxent River, Maryland, where it was evaluated alongside the Beechcraft Model 73 Jet Mentor.

According to Beech Aircraft Corporation historian William H. McDaniel, the Model 73 was proposed as a private entry based largely on the Model 45 Mentor piston-powered primary trainer that was serving with the Air Force and Navy. Billed by Beech as “the most economical jet trainer in the world,” the Jet Mentor was designed from the outset as a low-cost, economical yet high performance aircraft, and could lay claim to being the first lightweight, single-engine jet aircraft manufactured in the United States.

To minimize design and development costs, Beech Aircraft’s engineering department took a few pages from its ubiquitous airframe “cookbook” to build the Jet Mentor. Because acquisition and operating factors were such important considerations in the competition, the airframe borrowed major assemblies from the Model 45 Mentor (USAF T-34A and T-34B), such as the outboard wing sections and the empennage. The tricycle landing gear was operated electrically (same as the Model 45) and featured single-disc brakes (as did the Mentor). As with the Temco Model 51 and the Cessna Model 318, the Model 73 was propelled by the Turbomeca Marboré II turbojet engine. It was built in America by Continental under license from the French manufacturer as the military J-69-T-7, rated at 920 pounds static thrust.

Basic specifications of the Jet Mentor included:

Walter H. Beech was chiefly responsible for development of the Beechcraft Model 45 Mentor in the late 1940s. The tandem-seat trainer was economical to operate and easy to maintain, unlike the U.S. Air Force’s North American T-6G and the U.S. Navy’s SNJ that had outlived their mission. In 1954 the Model 45 served as a baseline for development of the Model 73 Jet Mentor. (Textron Aviation)

Wingspan – 32 feet, 9 inches
Wing area – 177.6 square feet
Aspect ratio – 6.05
Chord – 65.33 inches
Dihedral – 7 degrees
Single-slotted flaps
Speed brakes
Length – 30 feet
Height – 9 feet, 9.5 inches
Fuel tanks – Total capacity of 180 gallons in two wing tanks
Empty weight – 2,925 pounds
Useful load – 1,596 pounds
Maximum gross weight – 4,521 pounds

The first flight of the Jet Mentor occurred Dec. 18, 1955, with company test pilot Tom Gillespie at the controls.

The air-conditioned cockpit featured a conventional, two-seat tandem configuration for the student and instructor pilot. Both were seated under a large canopy that, if an emergency occurred, could be jettisoned before both pilots activated the ejection seats to leave the airplane. In addition, the clamshell-type canopy was powered open and closed.

In terms of performance the Model 73 could attain a maximum speed of 295 mph at an altitude of 15,000 feet and cruised at 245 mph. Stall speed (flaps fully extended) was a benign 65 mph. Service ceiling was 28,000 feet with a rate of climb (at sea level) of 1,400 feet per minute. Maximum range was 450 statute miles.

On Dec. 18, 1955, Beech Aircraft Corporation president and CEO Olive Ann Beech took time from her busy schedule to shake hands with test pilot Tom Gillespie shortly before the Jet Mentor’s first flight. (Wichita State University Libraries and Archives, Department of Special Collections)

In comparing the Beechcraft, Cessna and Temco candidates for the lucrative Air Force contract, all three were similar in size, met military equipment requirements and were very comparable in their overall capabilities. In April 1953 the Air Force selected Cessna’s entry that was developed into the XT-37, and by 1956 three prototype airplanes had logged more than 1,000 test flights. These were followed by an order in 1954-1955 for 11 T-37A trainers and full-scale production of 270 aircraft was underway during 1957-1958. Initial deliveries of the T-37A began in 1957, and the first all-jet pilot training class began flying the trainer in November 1958 and in 1961 the Air Force ceased all primary flight training in piston-powered airplanes.

In 1957 the Temco Model 51 was eventually selected by the U.S. Navy to be evaluated as the service’s primary jet trainer. A total of 14 aircraft designated TT-1 were built and assigned to the U.S. Naval Air Training Command, NAS Pensacola, Florida. The TT-1 would serve as a platform in the Navy’s quest to “determine the feasibility of beginning a student pilot’s flight training in jet-propelled aircraft.” Deliveries began in July 1957. By December 1960, however, the Navy discontinued use of the TT-1 and resumed primary training in the Beechcraft T-34B and North American T-28. During the 1980s both of those aging airframes would be replaced by the turboprop-powered T-34C.

As time went by the Beechcraft Model 73 did not attract any further attention from the Air Force, but Navy and U.S. Marine pilots who evaluated the Beechcraft were impressed by its systems, handling qualities, cockpit comfort and performance. The Navy, however, chose the Temco design chiefly because of its low price tag. As Beechcraft historian McDaniel wrote, “That was the beginning of the end for the Jet Mentor, but to pilots who saw and flew the swift, maneuverable little ship, it remains even today “The airplane I’d like most like to own—just for fun!”³

Notes:

“Prime mover” is a term long used by the FAA to describe a powerplant, whether piston, turbine or electric, that is the chief means of propulsion for an aircraft.
Throughout the late 1940s and into the early 1950s hundreds of war-weary North American T-6 (U.S. Navy SNJ) trainers were rebuilt and soldiered on as advanced trainers, but despite being refurbished, Air Force and Navy officials recognized that their aging airframes and thirsty static air-cooled radial engines would eventually become increasingly expensive to operate, repair and replace.
As of 2018 the sole Jet Mentor airframe is in storage at the Kansas Aviation Museum in Wichita awaiting restoration. For more information go to www.kansasaviationmuseum.org

Econo-Jet – the Model 73