Flapping wings anyone? The Riout 102T Alérion Ornithopter

Built in 1937 by René Riout, the Riout 102T Alérion was an ornithopter, a type of aircraft designed to fly by flapping its wings.

The Alérion underwent various ground tests, including trials in the Chalais-Meudon wind tunnel in 1938, where it experienced a structural failure in its wings.

The onset of World War II halted further development of the aircraft, and it never achieved flight. The Alérion remained in storage until 2005, when it was discovered and transported to the Musée Régional de l’Air in Angers. There, it underwent partial restoration.

 

Flapping Wings

Following World War II, René Riout continued his work in aviation design, creating a new ornithopter featuring two sets of flapping wings. Despite his ongoing efforts to refine this unique design, he found little interest in the production of such machines.

Riout’s career also included stints at other companies, notably with Société des Avions Bernard (Bernard Aircraft Company) from 1927 to 1933, where he contributed to their projects for the Schneider Trophy race.

Type of Aircraft: It was an ornithopter, a type of aircraft designed to fly by flapping its wings, mimicking the flight of birds.

In 1933, Riout showcased his ornithopter research and designs to the Service Technique de l’Aéronautique (STAé or Technical Service of Aeronautics). His presentation to the STAé included both designs and models of ornithopters with two and four wings.



 

These models, weighing 3.5 and 17.6 oz (100 and 500 g) respectively, were capable of flights reaching up to 328 ft (100 m). Impressed by these demonstrations, STAé commissioned a 1/5-scale model of the ornithopter, to be powered by an electric motor.

Riout 102T Alérion Tests Were Successful

In 1934, a 1/5-scale model of René Riout’s ornithopter design was constructed. Between 11 November 1934 and 1 February 1935, this model was subjected to extensive testing, totaling 200 hours, in the wind tunnel at Issy-les-Moulineaux, near Paris, France.

The tests were successful, demonstrating the practicality of Riout’s concept and suggesting that a full-scale version, powered by a 90 hp (67 kW) engine, could potentially reach speeds of up to 124 mph (200 km/h).

Encouraged by these findings, the STAé commissioned the construction of a full-scale ornithopter for further wind tunnel research. Riout was officially contracted to build this prototype ornithopter on 23 April 1937.

Wind Tunnel Testing: The ornithopter underwent extensive wind tunnel testing at Chalais-Meudon in early 1938, including tests with both stationary and flapping wings.

This full-scale ornithopter was named the Riout 102T Alérion, with “alérion” or “avalerion” referring to a mythical bird similar in size to an eagle. The design featured a single-seat, cigar-shaped fuselage constructed from tubular steel and covered with aluminum.

The cockpit was located at the front of the aircraft, with a landing gear comprising two wheels on each side that retracted into the fuselage.

Riout 102T Alérion Ornithopter Wings

The ornithopter had two pairs of flapping wings positioned behind the cockpit. These wings, featuring a metal frame with two spars and covered with fabric, were attached to the fuselage via hinges at each spar.

Powering the aircraft was a 75 hp (56 kW) JAP (John Alfred Prestwich) overhead valve , installed behind the wings with its cylinders exposed for air cooling.

 

While the exact engine model is unknown, the 61 cu in (996 cc) JAP 8/75 is believed to be a close match. The ornithopter also included conventional vertical and horizontal stabilizers, made from tubu

The design of the Riout 102T Alérion’s wings allowed for a 50-degree range of motion—40 degrees above the horizontal and 10 degrees below. While a comprehensive explanation of the wing-flapping mechanism is missing, it seems to have been somewhat akin to the system used in the DuBois-Riout ornithopter of 1913.

In that design, the engine powered a crankshaft situated between the wings, with each wing attached to the crankshaft by a connecting rod. Each wing was connected to a separate crankpin, positioned 180 degrees opposite the other wing.

Riout 102T Alérion Ornithopter Wing Warping

However, photographs of the 102T show both sets of wings raised simultaneously, as well as one set raised and the other lowered.

This suggests that if a crankshaft was indeed used, it likely incorporated clutches and separate sections for each wing pair, operating so that one pair was up while the other was down. Wing warping, the movement of the part of the wing behind the rear spar, was utilized to generate forward thrust.

The 102T ornithopter had a wingspan of 26 ft 3 in (8.0 m) and a length of 21 ft (6.4 m). The lowest point of the wing stood 2 ft 2 in (.67 m) from the ground, while the highest wingtip reached 13 ft 5 in (4.1 m) above ground.

 

The tail of the aircraft measured 8 ft 2 in (2.5 m) in height. The ornithopter weighed 1,102 lb (500 kg) empty and 1,389 lb (630 kg) when fully loaded.

The aircraft was constructed in Courbevoie at the workshop of coachbuilder Émile Tonnelline (sometimes spelled Tonneline). Final assembly was completed by late 1937 at Bréguet (Société des Ateliers d’Aviation Louis Bréguet or Luis Bréguet Aviation Workshop) in Villacoublay. With its unique four-wing configuration and side-mounted landing gear, the completed ornithopter bore a striking resemblance to a dragonfly.

Riout 102T Alérion Ornithopter and a Wind Tunnel

The Riout 102T Alérion underwent preliminary testing before being transported to the Chalais-Meudon wind tunnel in early 1938. The initial tests involved running the engine with the wings stationary for two-minute intervals.

These were followed by tests where the wings were set to flap. Gradually, the testing sessions extended to a continuous 20 minutes, though these were conducted without activating the wing warping mechanism (which would have provided thrust). It was observed that the engine was underperforming, producing only about 60 hp (45 kW), but testing continued regardless.

On 12 April 1938, during a wind tunnel test with the wind speed set at 81 mph (130 km/h), a wing flapping test at 4,500 rpm led to a structural failure.

One wing collapsed, swiftly followed by the other three, resulting in the outer third of all wings bending, with the right wings folding upwards and the left downwards. At the time of this incident, the ornithopter had completed approximately three hours of wind tunnel testing and had passed initial stability evaluations.

Prior to this failure, Riout had proposed some modifications to the STAé for the ornithopter, but after the accident, there was no interest in funding repairs or continuing the project. The damaged wings were removed, but the fuselage of the 102T was preserved.

Where is it Now?

Presently, the Riout 102T Alérion is being restored and is displayed at the Espace Air Passion Musée Régional de l’Air in Angers, France. Although there have been a few manned ornithopter flights, the aircraft type has largely been unsuccessful.