THE "ZVENO" PROJECT

The Zveno-1a was a Soviet experimental project from the 1930s that used a Tupolev TB-1 heavy bomber as a "mother ship" for two Tupolev ANT5 fighters. The Zveno concept (which means “link” in Russian) was designed to provide protection for a bomber group by extending the operational range of the escort fighters attached to a bomber. In the Zveno-1a configuration, the two I-4 (ANT5) fighters were mounted above the wings of a TB-1 modified for this purpose.

The fighters could detach from the bomber in flight, and, in certain configurations, it was planned that they could eventually reattach to it.

The Zveno-1a successfully completed several test flights, demonstrating the feasibility of the concept. Subsequent Zveno projects involved larger bombers and more modern fighters. Although innovative, the Zveno concept faced practical difficulties and saw limited operational use during a few combat deployments early in World War II.

The origins of this project date back to 2023, with the goal of achieving something that had never been done before while making the most of the lessons learned from previous projects, without exceeding a weight of 25 kilograms.

Since the team did not have all the necessary technical expertise, the novel nature of the Zveno project required the following division of roles:
- Our friend Bertrand Pujin was responsible for defining and creating all the DXF drawings needed for the collaborative effort.
- Roland Galley was responsible for the digital cutting and rib assemblies, as well as the milling of composite parts based on the DXF files provided by Bertrand
.- Nicolas Schneider was responsible for the lamination of the engine cowlings and other composite parts.

The aircraft mounts must be functionally flawless to ensure 100% success in the deployment of the satellite aircraft. The assemblies were professionally constructed using jigs.

- The so-called metallurgical work, including aluminum brazing, was entrusted to a specialized company.

It took Bertrand nearly a year to model and refine this project, finding the best possible compromises.

To determine the scale, the Tupolev I-4 (ANT5) satellite fighter was chosen, with a wingspan of 1.90 m, to achieve the following characteristics for the carrier aircraft:

• Scale 1:6
• Wingspan 4.80 m
• Wing area: 340 dm²

To best preserve the proportions as they appeared in the 1930s, a more modern 17% root-section airfoil was chosen to ensure optimal flight characteristics, given that the root chord measures no less than 90 cm.

The wing, which has a very classic appearance, consists of a semi-box-section spar onto which 3-mm-thick poplar ribs and wing spar tubes are strung, while minimizing the variety of materials as much as possible. Previous experience building a large 3.30-meter Hurricane highlighted the advantages of using 0.3-mm-thick epoxy sheet formwork bonded with PU adhesive, as it eliminates the need for finishing work, the time saved, and an appearance very close to that of period aluminum sheet metal.

The two carbon-fiber wing spars measure 50 mm × 1.25 m.

The challenge of this build is made significantly more complex here because, in addition to the two planned 60-cm³ Fiala 4-stroke engines and the struts for the fixed landing gear, it was necessary to fabricate three three-legged aluminum trapezoids using welding jigs, each with three tabs for attachment to the wing, to ensure the secure mounting and in-flight release of the two satellite fighters.

The 3-meter-long fuselage is typical of its era: not very aerodynamic and openwork, it consists of a poplar and balsa lattice reinforced with Kevlar struts and partially covered with 0.3 mm fiberglass panels.

Two models of this sesquiplane fighter with a 1.90-meter wingspan were built. For practical reasons, they are powered by electric motors. Here again, a great deal of modeling work was required for the engine cowlings and fittings. Their all-wood, fabric-covered construction was

carried out by Richard. Not everything is finished yet, and the fighter is currently... undergoing repairs!!!!

A separate article may be devoted to the detailed construction of the Tupolev I-4 (ANT5).