Classic Jetliners: The Dassault Mercure

In the late 1960s and 1970s, the commercial passenger aircraft industry featured a diverse array of manufacturers, unlike today’s market, which is primarily dominated by Boeing and Airbus. Back then, companies such as Boeing, McDonnell Douglas, British Aerospace, Convair, Airbus, Sud Aviation, Vickers, Lockheed, and Dassault, among others, vied for a share of the market. In this post, I’d like to discuss a particular aircraft designed specifically for short-range flights, intended to compete with the Boeing 737: the Dassault Mercure.

The Dassault Mercure, a twin-engined narrow-body jet airliner, was developed and manufactured by the French aircraft firm Dassault Aviation. Despite being the first large-scale European cooperative civil aeronautics program, the Mercure experienced limited success in the commercial aviation market. Let’s take a closer look at the history and design of this lesser-known competitor to the popular Boeing 737.

A French Challenger to Boeing

In 1967, Dassault proposed the Mercure as a French alternative to the American Boeing 737. It marked Dassault’s first foray into the commercial jet airliner market, having primarily built fighters and executive jets before. The prototype took to the skies for the first time on May 28, 1971, and entered service with French airline Air Inter on June 4, 1974.

Dassault made attempts to market the aircraft in the US, even considering partnerships with American manufacturers such as Douglas, Lockheed, and General Dynamics. The idea was to manufacture the Mercure in the United States. Unfortunately, the aircraft’s lack of range compared to rival planes led to limited success, with only 12 Mercures built between 1971 and 1975. The final Mercure flight took place in 1995.

Design

The Dassault Mercure was optimized for short-haul routes, sacrificing fuel capacity to accommodate more passengers. As a result, the Mercure offered up to 17% more seats than the competing Boeing 737 while having a shorter range. The basic model of the Mercure featured built-in stretch potential, with many elements of the design, including the wing, cabin, and undercarriage, capable of supporting an expanded model with little or no modification.

The wing of the Mercure was relatively thick and was optimized using a combination of wind tunnel tests and computer-generated simulations. Production Mercures were powered by two Pratt & Whitney JT8D-15 turbofan engines, mounted on underwing pylons designed with anti-vibration mountings. The engines featured joint Snecma/Dassault-developed thrust reverser and noise suppression systems, anticipating potential noise regulations in the United States.

Dassault emphasized the Mercure’s commercial value, focusing on its low operating costs for short sectors due to its aerodynamic features and low structural weight. The aircraft also benefited from an advanced fail-safe structure, primarily milled in accordance with Dassault’s traditional military manufacturing practices. The Mercure featured a triplicated, fail-safe hydraulic flight control system with no manual reversion, and independent duplicated air conditioning systems.

Highlights

• Optimized for short-haul routes: The Mercure sacrificed fuel capacity for more passenger seats, offering up to 17% more seating capacity than the Boeing 737 but with a shorter range.
• Built-in stretch potential: Many design elements, including the wing, cabin, and undercarriage, could support an expanded model with minimal modification.
• Thick, optimized wing design: The wing was relatively thick and optimized using wind tunnel tests and computer-generated simulations.
• Twin Pratt & Whitney JT8D-15 turbofan engines: These engines were mounted on underwing pylons designed with anti-vibration mountings and featured joint Snecma/Dassault-developed thrust reverser and noise suppression systems.
• Advanced fail-safe structure: The Mercure’s structure was primarily milled according to Dassault’s traditional military manufacturing practices, providing increased safety and durability.
• Triplicated hydraulic flight control system: The aircraft featured a fail-safe hydraulic flight control system with no manual reversion.
• Independent duplicated air conditioning systems: The Mercure had separate air conditioning systems for redundancy, ensuring consistent temperature control for passengers and crew.
• Emphasis on low operating costs: The Mercure’s aerodynamic features and low structural weight contributed to its low operating costs, particularly for short sectors.

Specifications at a Glance

• Crew: Three flight crew members
• Capacity: 162 passengers in an all-economy configuration
• Length: 34.84 meters (114 feet 4 inches)
• Wingspan: 30.55 meters (100 feet 3 inches)
• Height: 11.36 meters (37 feet 3 inches)
• Wing area: 116 square meters (1,250 square feet)
• Aspect ratio: 8
• Airfoil: Dassault sections
• Empty weight: 31,800 kilograms (70,107 pounds)
• Maximum takeoff weight: 56,500 kilograms (124,561 pounds)
• Fuel capacity: 18,400 liters (4,900 US gallons; 4,000 imperial gallons)
• Powerplant: 2 x Pratt & Whitney JT8D-15 low bypass turbofan engines, producing 69 kN (15,500 lbf) of thrust each
• Performance:
  • Maximum speed: 704 km/h (437 mph, 380 kn) EAS up to 6,100 meters (20,000 feet)
  • Maximum speed: Mach 0.85 (1,041 km/h) at 6,100 meters (20,000 feet)
  • Cruise speed: 926 km/h (575 mph, 500 kn) at 6,100 meters (20,000 feet)
  • Range: 2,084 kilometers (1,295 miles, 1,125 nautical miles) with 4,100 kg (9,000 lb) fuel reserves
  • Service ceiling: 12,000 meters (39,000 feet)
  • Rate of climb: 17 meters/second (3,300 feet/minute) at sea level, at 45,000 kg (100,000 lb) weight
  • Fuel consumption: 2.96–5.03 kg/km (10.5–17.8 lb/mi) (2,440 kg / 825 km to 4,700kg / 935km)
  • Takeoff roll: 2,100 meters (6,900 feet)
  • Landing roll: 1,755 meters (5,670 feet)

Development of the Dassault Mercure

In the mid-1960s, Marcel Dassault, founder of French aircraft company Dassault Aviation, observed a gap in the civil aviation market. Along with the French Directorate General for Civil Aviation (DGAC), they noticed a lack of aircraft specifically designed for low-distance air routes. The DGAC was eager to introduce a French alternative to the American Boeing 737 and proposed a 140-seat airliner to Dassault.

With support from the French government, Dassault began working on its short-haul airliner concept in 1967. Initial studies focused on a 110 to 120-seat aircraft powered by two rear-mounted Rolls-Royce Spey turbofan engines. Eventually, the specifications evolved to accommodate a 150-seat aircraft with a 1,000-km (540 nm) range, targeting the upper end of the market segment against the 100-seat Boeing 737-100 and the 115-seat Boeing 737-200.

In April 1969, the development program was officially launched. The French government funded 56% of the program’s total development costs, expecting repayment through levies on airliner sales. Dassault also invested $10 million of its own money and bore the majority of manufacturing costs. The program’s total cost was $75 million, with each unit costing $6 million in 1971.

The aircraft’s design aimed to fill the gap in the market with Dassault’s expertise in high-speed aerodynamics and low-speed lift capability, honed through the development of jet fighters like the Ouragan, Mystère, and Mirage. Marcel Dassault named the aircraft Mercure (French for Mercury), inspired by the winged god of mythology. Utilizing advanced computer tools for the time, the Mercure 100’s wing was developed, making it larger and faster than the Boeing 737. In June 1969, a full-scale mockup was presented at the Paris Air Show, and on April 4, 1971, the prototype Mercure 01 rolled out of Dassault’s Bordeaux-Merignac plant.

Operation and Decline

Dassault envisioned mass production of the Mercure, with the 300th aircraft projected for delivery by the end of 1979. To achieve this, Dassault established four plants dedicated to the Mercure program in Martignas, Poitiers, Seclin, and Istres. Additionally, manufacturing work was distributed throughout Europe, involving companies like Fiat Aviazione of Italy, SABCA of Belgium, CASA of Spain, and the Swiss National Aircraft Factory at Emmen, all acting as risk-sharing partners in the venture.

Air Inter placed an order for ten Mercures on January 30, 1972, with delivery scheduled between October 30, 1973, and December 13, 1975. The anticipated break-even point was around 125-150 aircraft. However, due to a lack of additional orders, the production line closed on December 15, 1975. Only two prototypes and ten production aircraft were built, with one of the prototypes eventually refurbished and added to Air Inter’s fleet.

On April 29, 1995, the last two Mercures in service completed their final commercial flights. The Mercure fleet logged a combined total of 360,000 flight hours, carrying 44 million passengers across 440,000 individual flights without any accidents, and achieved a 98% in-service reliability. Despite its remarkable performance, the Mercure’s production run came to an early end due to insufficient demand.

The Dassault Mercure was a unique and ambitious project that aimed to challenge the popular Boeing 737 in the short-range flight market. Despite its advanced design and impressive performance, the Mercure ultimately struggled to gain a foothold in the industry. Nevertheless, it remains an important milestone in aviation history, highlighting the innovative spirit of the era and Dassault’s commitment to pushing the boundaries of aircraft design.