GHK-38 Wolverine

The Gyundoan-Han-Kansainyhteisön GHK-38 Wolverine is an advanced compound attack helicopter jointly developed by Hallia and Menghe. The Gyundoan-Han Helicopter Corporation contributed the powerplant and general layout, while Kansainyhteisön Ilmailu was responsible for the airframe materials and electronics. There are some minor differences between the baseline variants developed in Hallia and Menghe, including the type of autocannon mounted under the hull and the spacing of the bomb suspension locks on the pylons, but most of these parts can be swapped out in production to streamline parts commonality.

Development

Fast Attack Helicopter Program

In 2008, the Menghean Ministry of National Defense opened the Fast Attack Helicopter program. The goal of this program was to develop a new type of attack helicopter that would combine the speed and agility of the SS-32 Jamjari with the armor and payload of the GH-26 Agŏ. During the 2000s, the Menghean Army had used both of these helicopters in concert, with the SS-32 acting as a forward scout for the slower GH-26, but this division of labor had its drawbacks, including redundant sets of spare parts for two unrelated attack helicopter designs.

Menghe's two main design bureaus specializing in helicopters, Gyundoan-Han Helicopter Corporation and Saebyŏk Rotorcraft, both began work on competing prototypes. Gyundoan-Han, which had the most experience in original design work, was the initial favorite, but it struggled with many aspects of the design, particularly speed. By 2011, Gyundoan-Han had produced an independent design for a pushrotor-driven gunship with a coaxial rotor, but many of the components, including the engine, existed only on paper. No full-size prototypes of the Gyundoan-Han GH.347 design exist, but Gyundoan-Han did build a number of scale models for design expositions and wind tunnel testing; these show a stepped cockpit design and wider sponsons on either side of the cockpit.

Saebyŏk began with incremental improvements to its existing helicopter platform, the SS-32. A single SS-32 airframe was extensively modified during construction to feature a pusher propeller, a longer nose, and wider stub wings supporting three hardpoints each. This helicopter appeared at a Menghean military airshow in May 2014, and performed stunts for the audience while the announcer described it as a "new model of Army-Navy attack helicopter." Foreign press mistakenly assigned it the designation SS-36, and for a time the designation stuck, with the Menghean MoND issuing no corrections. In reality, Saebyŏk's SS.332 prototype was only meant as a testbed and concept demonstrator, and it never received a numeral designation from the MoND.

Joint development

Slow development continued until 2012, when representatives from Hallia expressed interest in merging the Fast Attack Helicopter program with their own plans for a new helicopter gunship. Under a division of labor negotiated the following year, Kansainyhteisön Ilmailu would contribute the airframe, electronics, and composite materials, while its Menghean partners would contribute the powerplant and general layout. Each country would then make their own modifications to the pylons and guidance systems to support locally made missiles.

At the outset, Kansainyhteisön Ilmailu opened joint development programs with both Saebyŏk and Gyundoan-Han, neither of which had produced a working prototype. By operating two redundant programs, the MoND hoped to encourage productive competition between its major design firms, while also leaving the option of choosing the final prototype with better overall characteristics.

Over the same time period, a separate department of Gyundoan-Han was working on what would later become the GH-36 Mulsuri. Impressed with this craft's performance, Gyundoan-Han decided to speed up the design process by adapting the GH-36's powerplant to fit on the new airframe. The entire rotor assembly is shared between the two types, and the pusher propeller was borrowed as well. The two Taesan turboshaft engines were moved behind the transmission, with their drive shafts leading forward rather than rearward on the GH-36, and the transmission was modified accordingly, but otherwise the two helicopters use an essentially identical propulsion system.

GH.405

Gyundoan-Han-Kansainyhteisön produced a working prototype under the designation GH.405. It conducted its first flight on 25 June 2016 at Menghe's Hŭksan test site.

Design

Overview

The GHK-38 uses a compound helicopter configuration, with a six-bladed pusher propeller in the rear to provide forward thrust. Its main rotor uses a coaxial configuration with four rigid blades per level. Both the coaxial lifting rotor and the pusher propeller are driven from the same transmission by a pair of Taesan T508-1 turboshaft engines, each one generating 2,400 kW (3,200 hp) of power. There is also an auxiliary power unit forward of the transmission which provides power during the startup process and while grounded, though this is normally turned off during flight.

As on other attack helicopters, the crew consists of two personnel sitting in a tandem cockpit. The pilot sits in the rear, upper position, while the gunner and weapon systems operator sits in the forward, lower position. Both crew members have a full set of controls, meaning that the gunner can take over flying the helicopter if the pilot is incapacitated and the pilot can target weapon systems directly if necessary.

The pilot and gunner both use a version of the Keikō-II helmet-mounted display, which projects target markers, threat markers, and avionics information in front of the user's eyes and allows the user to "see" icons through the floor of the cockpit. This allows either crew member to look at a target and promptly redirect the autocannon and under-nose optical unit to face it. The Keikō-II HMD also provides both crew members with night vision, allowing all-day and all-weather operations.

In the rear fuselage, just behind the engines, there is an electronics access compartment with two rudimentary seats. Typically, this compartment would be used to rescue the pilot and copilot of another downed helicopter, a feature also retained on later models of the GH-26 Agŏ. In addition to electronics boxes, this rear compartment contains a basic first aid and survival kit and self-defense weapons for the downed aircrew. If no other helicopters are available, the GHK-38 can also rescue other ground personnel, including special forces and civilian VIPs, though the small size and limited amenities of the rear compartment make the GHK-38 inefficient as a transport helicopter. Outside of rescue missions, the crew can use the rear compartment to transport spare parts and personal effects when ferrying to a new base, or to deliver and recover high-value cargo. On most missions, however, the crew leave the rear compartment empty.

An unusual detail on the GHK-38 is the location of its exhaust. While most helicopters place the exhaust directly behind the turbines, the GHK-38 places it at the end of the tail boom, facing upward. Inside the fuselage, exhaust from the turbines combines with cool air drawn in through a set of vents on the roof, and the hot and cool air mix while proceeding through a pair of wide tubes in the tail, bringing the temperature of the exhaust closer to atmospheric temperature. The exhaust vent itself is beyond the main coaxial rotor, meaning that the rotor downwash does not blow the exhaust back onto the fuselage and heat up the helicopter's skin. While heavier and more complex than a conventional turbine exhaust, this system makes it harder for heat-seeking missiles to lock onto the helicopter, and also impairs detection and targeting by land-based infrared optics.

Protection and countermeasures

The designers of the GHK-38 placed a heavy emphasis on survivability. A composite metal "bathtub" surrounds the cockpit, protecting the pilot and copilot against 23mm fire from the front and 14.5mm fire from the sides. The canopy is made of bulletproof armor glass, and is able to withstand 14.5mm ammunition. While still vulnerable to direct hits, these armor plates can also resist kinetic subminitions from airbursting 35mm and 40mm anti-aircraft rounds, as well as shrapnel from lightweight surface-to-air missiles. Gyundoan-Han claims that the rotor blades can withstand glancing hits from 23mm autocannon projectiles.

In addition to its outside protection, the cockpit has a heavy metal armor plate behind the gunner's seat, with a heavy bulletproof glass plate above it. Both are purported to resist 14.5mm fire, though they may be able to stop 23mm projectiles slowed by the previous layer of armor. These plates help ensure that if one crew member is incapacitated, the other will still be able to fly the helicopter to safety.

As a final protective measure, the GHK-38 has a high level of crashworthiness. The crew seats are designed to sink into the cockpit floor on impact with the ground, and the armored cockpit bed itself can sink into the fuselage. In the event of engine failure, a backup tension system automatically deploys the forward landing gear to further cushion an impact with the ground; the pilot and copilot can also activate this system manually. The seats in the emergency rear compartment are simple cushioned panels bolted to the floor, and meet no crashworthiness requirements.

Gyundoan-Han chose a twin-engine layout in part because it offered greater redundancy than Saebyŏk's single-engine competitor. The two turboshaft engines are separated by metal plates and fireproofing equipment, and each one has a fire-suppression system that can be triggered automatically or activated manually from the cockpit. If either engine is damaged, especially by gunfire or proximity-fused missile warheads, the helicopter is able to fly at reduced speed on a single engine in order to return to a safe landing site.

The lack of a horizontal tail rotor somewhat improves survivability: unlike a conventional helicopter, the coaxial-rotor GHK-38 will not enter a tailspin if the tail rotor or its driveshaft are damaged, though it will have to transition to conventional helicopter flight. Even if the tail is completely lost, the Wolverine can still maintain a minimal degree of control through adjusting the main rotor blades, though this is only adequate for a controlled descent to the ground.

Fuel is divided between six tanks: two in the stub wings, two in the large wing roots, one forward of the gun ammunition magazine, and one aft of the rotor hub. All of these tanks are self-sealing and constructed with ballistic foam to reduce the risk of fire and leakage. An active two-way pump system transfers fuel between tanks to maintain stability around the center of gravity and recover fuel from leaking tanks.