Project 904 A-90 Orlyonok Ekranoplan S-21 3D print model

Herewith a 3D printable model of the Orlyonok ekranoplan, as it was developed by the CHDB (Central Hydrofoil Design Bureau) from 1992 onwards. The model has been created in Solidworks, I've included STEP and IGES files, next to seperate STL files for all printable parts. All parts are sized to be printed on print beds of 30x30cm upwards and of course can be resized accordingly. In the standard size the assembled model is quite large, namely 784 x 426 x 221 mm. It consists of some larger parts and many seperately printable periphery. This allows the model to be tailored and presented in different configurations and flight modes. All flight control surfaces are seperate parts.

A short history: The A-90 Orlyonok originates from the 904 project which was started in the sixties, with the first flight of the first prototype in 1972, on the Volga river (close to the warf). This was the first large-scale implementation of Alexeyev's WIG technology, in a vehicle concept which was from the start designed to go into series production. Due to the unknown territory and lack of prior experience, the first unit was highly experimental and differed significantly from the later series machines and it was upgraded several times during the testing programm. In general, the project 904 was supposed to provide a WIG machine aimed at troop-carrying capabilities with high-speed beach landing capacity. As such, the machine was required to be fully amphibic, beeing able to access unprepared shorelines and beaches, unloading rapidly and turning around. Where a practical military WIG vehicle was already uncharted territory, the additional operational requirements called for even more innovative & unusual solutions. During the course of the testing programme the prototype's aerodynamic configuration was reworked. Also, two hydroski's were installed to reduce the unexpectedly high loads on the vehicle during the landing phase. The hydroski's doubled as the main interface for the beaching gear, which was designed and installed in the same period.

The propulsive layout was revised in comparison to earlier designs. The speed requirement was a bit lower for the Orylonok and it's amphibic requirements sought for a different layout alltogether. The PAR turbofan engines were installed in a 'flush' configuration inside the nose, providing it with an unusual but distinctive appearance. These engines were burried deep inside the nose and were somewhat more protected from the elements. A navalized version of the famous NK-12 turboprop was fitted to the top of the vertical tail, completed by an up-lifting, sharply swept horizontal tail plane. The amphibic capabilities required the main wings to be mounted unusualy low on the airframe, causing them to be almost completely below the waterline during rest. To aid the PAR (power-assisted-ram) during the take-off phase, the Orlyonok had quite unique underwing panels, located chordwise just behind the leading edge. When extended these prevented most of the PAR exhaust gasses to escape forward at low speeds.

Flying the Orlyonok was similarly unusual. The machine was capable of flying both in & out of groundeffect, but performed sluggishly in the latter regime. Although equipped with a 'conventional' set of flight controls, in ground-effect the elevators were solely used to maintain the pitch at a neutral setting (keel on an even/level trim). Altitude was controlled by lowering/retracting the flaperons, instead of changing pitch attitude. The machine could be flown without electronic stabilization, although a custom-developed naval autopilot was fitted and performed well. The machine could make high-speed banked turns safely even whith a sponson skimming along the water during the turns.

This 3D model represents the S-21 (hull number 610), basically the first of the three manufactured series machines. The S-21 was the only machine which went through extensive update/overhaul in the late 80's / begin 90's. This sought to bring the Orlyonok machines forward for another 20 years, in a modern - 'post Soviet' navy. Due to a lack of funding and lack of knowledgeable workforce remaining at the time, the overhaul dragged along for several years, by which time all three machines were supposed to be updated already. Shortly after the final update, the S-21 was lost in a crash on the 12th of september 1992 and was sunk in the Caspian sea. As a result of this loss, the other machines were not overhauled and eventually written off. The S-21 differed in several ways from the only remaining machine (S-26, hull number 650, Moscow naval museum), especially after the final overhaul/update. It's radar altimeter suite underneath the forward traffic radar was different (more aerodynamicaly shaped), it's elevator actuator fairings were of a different design, it was equipped with a bird-ingestion protection case in front of the PAR engines, it has a rear-facing FOF radar on the tail etc. The machine sported a new color scheme and eagle nose-art on the side of the fuselage. The model is presented in the S-21's layout and configuration as it was on its very last flight in 1992.

The model does not future all individual panel lines, but all protruding featres, panel overlaps etc. are nicely modeled as embossed features. The landing gear consists of many seperate components allowing it to be assembled in any of the desirable operational states. The tires are left off, the bogies are designed to fit small O-rings as tires. The geometry of the model is based on the original drawings & sections as they were prepared for international delegations in 1992, and as such the model is highly accurate & correct.