Amiot 120

Amiot 120

The Amiot 120 emerged in the early 1920s as one of France’s most ambitious medium bomber prototypes. Built to meet a new generation of strategic reconnaissance and bombing requirements, it combined rugged construction with advanced aerodynamic features. Although it never entered large-scale production, the Amiot 120 paved the way for subsequent designs through its innovative structure and powerplant integration.

Design and Development

Concept and Requirements

In response to the French military’s 1921 specification for a fast, high-altitude bomber, Avions Amiot set out to create an aircraft capable of carrying a substantial bomb load over 1,000 kilometers. Key goals included:

• Cruising speeds above 200 km/h
• Service ceiling exceeding 7,000 meters
• Modular bomb racks for flexible ordinance configurations

Airframe and Materials

The Amiot 120’s structure married wood and metal to balance weight and durability. The primary load-bearing members—wing spars and fuselage longerons—were crafted from laminated spruce, while the forward fuselage and engine mounts employed welded steel tubing. Fabric coverings treated with doped linen enhanced smoothness and moisture resistance.

Wing Configuration

The biplane wings featured unequal spans and slight stagger to improve pilot visibility. Both upper and lower wings incorporated:

• Two solid spruce spars with plywood webbing
• Streamlined steel fittings at strut junctures
• Balanced ailerons on upper surfaces for precise roll control

Struts and bracing wires maintained wing alignment and transferred aerodynamic loads to the fuselage.

Powerplant and Propulsion

Engine Model

Powering the Amiot 120 was a single Lorraine-Dietrich 12Eb W-12 engine, chosen for its blend of reliability and output. Key characteristics included:

• Rated power: 450 kW (600 HP) at 1,900 RPM
• Liquid cooling via a twin-circuit radiator housed under the nose
• Dry weight: 500 kilograms

Propeller and Fuel System

A two-blade fixed-pitch wooden propeller translated engine torque into thrust. The fuel system comprised two 500-liter gravity-feed tanks located in the upper wing center section, offering:

• Total fuel capacity: 1,000 liters
• Endurance: approximately 5 hours at cruising power settings

Performance Characteristics

Flight Envelope

Designed to excel at medium-range missions, the Amiot 120 achieved:

• Maximum speed: 210 km/h at sea level
• Cruising speed: 185 km/h at 4,000 meters
• Service ceiling: 7,500 meters

Climb performance targeted 5,000 meters in under 18 minutes, granting tactical flexibility against early-generation anti-aircraft defenses.

Range and Endurance

Long-distance capability was a hallmark of the Amiot 120:

• Ferry range: 1,200 kilometers without bombs
• Combat radius: 600 kilometers with 800 kilograms of ordinance
• Loiter time: Two hours over target area

Armament and Payload

Offensive Load

The Amiot 120 carried its bombing load in an internal bomb bay beneath the lower wing root. Payload options included:

• Four 250-kilogram general-purpose bombs
• Twelve 50-kilogram fragmentation bombs
• Customizable racks for aerial mines or propaganda leaflets

Defensive Armament

To defend against fighter attacks, the crew managed three 7.7mm Lewis machine guns:

• One dorsal mount on a Scarff ring for the observer
• One ventral mount accessible through a trapdoor in the floor
• One fixed forward-firing gun synchronized through the propeller

Ammunition stores totaled 3,000 rounds, split evenly between mounting positions.

Crew Accommodations

Cockpit Layout

The two-man crew occupied tandem open cockpits:

• Pilot station forward with full engine and flight instrumentation
• Observer station aft equipped with compass, bomb-release levers, and camera mounts

A pneumatic intercom system facilitated communication under full throttle.

Ergonomics and Protection

Seats incorporated shock-absorbing spring mounts to reduce pilot fatigue. Transparent celluloid windshields shielded heads while preserving lateral visibility. Provision for armored panels beneath the pilot’s seat guarded against ground-fire fragments.

Avionics and Navigation

Instrument Suite

Basic flight instruments allowed precise navigation at altitude:

• Altimeter calibrated to 8,000 meters
• Airspeed indicator with 0–250 km/h range
• Inclinometer and turn-and-bank indicator

Long-Range Navigation

Optional equipment included:

• Drift sight mounted on the port wing struts
• Radio direction finder in the observer’s cockpit
• Celestial navigation sextant storage in a waterproof tube

Structural Reinforcement and Fatigue Life

Stress Analysis

Stress testing on prototypes identified high-load regions around wing root fittings and landing gear attachments. Reinforcements included:

• Steel gussets at fuselage longeron intersections
• Double-shear brackets on undercarriage struts

Service Life Projections

Engineers projected a fatigue life of 1,500 flight hours for primary structural members, with:

• Mandatory 100-hour inspection cycles
• Non-destructive testing of critical welds

Operational Trials and Modifications

Flight Testing

Initial flight trials uncovered engine cooling hotspots. Solutions involved enlarging radiator core area and adding cowl flaps for adjustable airflow control. Subsequent tests confirmed stable handling and improved engine temperatures.

Proposed Variants

Plans for stretched-fuselage and twin-engine derivatives were drafted but never finalized. One concept replaced the W-12 with twin 300 HP inline engines, aiming for increased payload at the expense of added complexity.

Technical Specifications

Legacy and Influence

Although only a handful of prototypes flew, the Amiot 120 influenced French bomber design throughout the 1920s. Its blended construction techniques and focus on high-altitude performance informed later models that ultimately equipped frontline squadrons in the decade that followed.