Yemac-Tonal T3 Ahuimani

T3 Ahuimani
T3 Ahuimani medivac transport in 1963
Role	Compound gyroplane
National origin	Aztapamatlan
Manufacturer	Yemac-Tonal
First flight	6 November 1961
Introduction	3 January 1963
Status	In service
Number built	149

The Yemac-Tonal T3 Ahuimani is a gyroplane aircraft designed and developed by the Yemac-Tonal corporation. The T3 was initially designed for civilian use by private helicopter airlines, but was never used for this purpose as such private companies proved to be financially non-viable. After a period of disuse, the T3 would then be adopted by the military forces of Aztapamatlan as a military transport and medical evacuation aircraft, with an armed variant also being commissioned by the military. The gyroplane concept used by the T3 was previously demonstrated by less succesful prototype designs built by Yemac-Tonal and other companies such as rival Axinitlan, and revolved around a hybrid design using both a rotary and fixed wing layout. Such a design would give it the vertical take-off functionality of a helicopter while retaining the greater energetic efficiency and speed enjoyed by fixed wing aircraft, features which were originally envisioned as the perfect solution to the high cost issues faced by transport helicopters. The hybrid design of the T3 enjoys greater lift than an equivalent fixed wing aircraft thanks to its autogyro-style unpowered rotor while also benefitting from far lower cost per kilometer of flight compared to a helicopter.

Development

Background

The developmental prototype of the T3 Ahuimani, then known as the O1, was originally marketed as a more efficient and cost effective helicopter transport for civilian airlines. At the time of the O1 project undertaken by Yemac-Tonal designers in the late 1950s and early 1960s, many airlines were experimenting with helicopter transports as the new solution for city to city air transport. This was in large part due to the problem of large modern airports being increasingly moved far away from the city center, adding significant door to door travel time for passengers leaving from the downtown of one city to travel to the downtown of another city. For short distances inside a region, it would often be the case that travel time to and from the airport was equivalent or longer than the flight itself. In an attempt to circumvent this, helicopters were used because of their vertical take-off capability to travel directly to and from landing pads located downtown, eliminating travel delays caused by the commute to the distant airport facilities. However, the airlines which experimented with this concept ran into problems with costs. It was quickly discovered that a passenger route flying helicopters, which have very high operating costs but often very low passenger capacity, would not be profitable and in many cases would become a net loss for the airline. The YT O1 project for a gyroplane design would attempt to resolve the issue by reducing the operating cost and increasing the passenger capacity compared to a helicopter transport through the use of its hybrid design with fixed wings and conventional forward facing turboprop engines.

Civilian Contracts

Interest in the YT O1 was significant from many helicopter airlines, many of which were quickly loosing money due to the cost of helicopter operations but by the late 1950s many were still very much invested in making their routes profitable. Responding to the interest shown by airlines, Yemac-Tonal doubled its efforts to develop the O1 expecting an open market free for the taking if they could crack the helicopter transport problem. The company appealed and successfully secured a state subsidy for the development of O1, which facilitated the engineering of the aircrafts new technology including the rotor tip jets. However, in the early 1960s the helicopter airline industry had already begun to collapse under the weight of its financial non-viability, causing demand for the soon to be finished O1 prototype to dry up. With it, government subsidies declined and then vanished, leaving Yemac-Tonal with a fully functional and flight tested prototype with no prospective buyers left.

Military Interest

Yemac-Tonal appealed to the Aztapaman military, especially to Air Force and Army Aviation officials, in an attempt to secure a buyer for their finished prototype and recuperate the significant losses the company had taken in development of the unusual vehicle. The unique characteristics of the gyroplane design indeed were of interest to military officials, who were interested in the improved speed and performance of the craft compared to competing tandem rotor helicopter designs being considered for the role of a heavy lift vehicle. The O1 prototype was submitted to rigorous field tests and found to be satisfactory as a transport craft. Although the O1 would go to be destroyed in a particularly damaging crash test in which the vehicle was shot by high caliber anti-aircraft weapons, the military expressed an interest in the concept and began to collaborate with Yemac-Tonal to improve on the survivability of the design through the addition of redundant controls and partially armored engines and cockpit. It was found that the autogyro design of the craft enabled it to hover down to earth without crashing even if both of its powered turboprop engines were destroyed, dramatically improving the aircraft's survivability. The resulting design, dubbed the T3 Ahuimani, was adopted by the Aztapaman Air Force as a transport craft and would find use as both a regular troop transport and medivac craft which could ferry wounded troops directly from the front line to hospital facilities in the rear. The T3 entered service in 1963. In 1965, a gunship variant dubbed the T5 would designed with four rocket pods, a chin mointed rotary canon and space for a limited number of passengers. The 1980 modification known as the T5B did away with the passenger cabin of the T5 in order to add a payload of guided missiles for anti-tank purposes.

Design

The T3's main feature was its very large four bladed main rotor, which was unpowered similar to the rotor of an autogyro. Instead of a motor spinning the rotor blades as in a helicopter, the rotor would autorotate driven by aerodynamic forces during cruise flight thereby generating additional lift for the craft and greatly supplementing the lift of the relatively short fixed wings without incurring the fuel cost of powered rotation. For vertical take-off and landing, rocket jets attached to the tips of the rotors would be ignited for a short burst to rotate the blades and generate the required lift to land or take off from a small landing zone or helicopter pad. Transitioned from this VTOL flight mode to the cruising mode would take place under 100 km/h as the main turboprop engines would engage and begin to drive the craft. Once in cruising, roughly half of the aerodynamic lift would be provided by the fixed wings while the autorotating rotor blades would provide the rest. An autogyro flight mode enabled the craft to descend vertically with its turboprop engines disengaged, generating lift exclusively with its autorotating blades which would transition to being driven by gravity while in autogyro mode. It was found that this would enabled a severely damaged T3 transport to land without crashing or endangering any passengers or crew as the autogyro functionality would allow the craft to land if engine power were cut and in some cases even if the fixed wings and turboprop engines had been totally destroyed. The long rectangular body of the craft allowed for a maximum capacity of 50 persons of which 2 would be the air crew, giving the craft and large troop transport capacity of 48. The T5 Gunship variant only had capacity for up to 15 due to significant modifications to the hull in order to improve its effectiveness as a combat vehicle.

Specifications

Transport

Data from YT Aeronautics Statistics

General characteristics

• Crew: 2
• Capacity: 40-48 passengers
• Length: 17.88 m (58 ft 8 in) Fuselage
• Wingspan: 14.17 m (46 ft 6 in) Fixed wings
• Height: 6.76 m (22 ft 2 in) Top of rotor pylon
• Wing area: 44.1 m² (475 sq ft) >
• Airfoil: 2B-8673
• Empty weight: 9,979 kg (22,000 lb)
• Gross weight: 14,969 kg (33,000 lb)
• Fuel capacity: 7,500 lb (3,402 kg)
• Powerplant: 2 × TB 11A Turboprops, 2,100 kW (2,800 shp) each
• Powerplant: 4 × Rotor tip jet , 4.4 kN (1,000 lbf) thrust each
• Main rotor diameter: 27.43 m (90 ft 0 in)
• Main rotor area: 591.0 m² (6,362 sq ft) Rotor Aerofoil
• Blade tip speed: 219 m/s (720 ft/s)
• Disc loading: 30 kg/m² (6.14 lb/ft²)
• Propellers: 4-bladed, 4.0 m (13 ft) diameter

Performance

• Maximum speed: 321.8 km/h (200 mph; 174 kn) speed record
• Cruise speed: 295 km/h (183 mph; 159 kn)
• Range: 724 km; 391 nmi (450 mi)
• Service ceiling: 4,000 m (13,000 ft)

Gunship Variant

Data from YT Aeronautics Statistics

General characteristics

• Crew: 4
• Capacity: 10-15 passengers
• Length: 17.88 m (58 ft 8 in) Fuselage
• Wingspan: 14.17 m (46 ft 6 in) Fixed wings
• Height: 6.76 m (22 ft 2 in) Top of rotor pylon
• Wing area: 44.1 m² (475 sq ft) >
• Airfoil: 2B-8673
• Empty weight: 11,340 kg (25,000 lb)
• Gross weight: 16,329 kg (36,000 lb)
• Fuel capacity: 7,500 lb (3,402 kg)
• Powerplant: 2 × TB 11A Turboprops, 2,100 kW (2,800 shp) each
• Powerplant: 4 × Rotor tip jet , 4.4 kN (1,000 lbf) thrust each
• Main rotor diameter: 27.43 m (90 ft 0 in)
• Main rotor area: 591.0 m² (6,362 sq ft) Rotor Aerofoil
• Blade tip speed: 219 m/s (720 ft/s)
• Disc loading: 30 kg/m² (6.14 lb/ft²)
• Propellers: 4-bladed, 4.0 m (13 ft) diameter

Performance

• Maximum speed: 300 km/h (186 mph; 162 kn)
• Cruise speed: 280 km/h (174 mph; 151 kn)
• Range: 724 km; 391 nmi (450 mi)
• Service ceiling: 3,800 m (12,500 ft)