The UD-4L Cheyenne Dropship is a type of combat utility spacecraft used by the United States Colonial Marine Corps. The Cheyenne is primarily designed to be dropped from the belly of most USCM spacecraft while they are in orbit and deliver troops and equipment rapidly to a planet's surface. They typically carry the M577 Armoured Personnel Carrier, although they can also be used to transport other equipment and even Marines directly in the field.
The UD-4L has the ability to take off and land vertically from unprepared sites, and can also operate as a ship-to-ship transport. Additionally, the Cheyenne has many variable weapons hardpoints and a fixed internal cannon, allowing it to be used in a gunship role in support of ground troops.
All things considered, this is the ship of choice if you're getting into some heat. The payload bay is a 9.5 l x 4.5 w x 2.4 h meter (102.6 m3) volume with a 3.92 meter wide deck ramp suspended from four dual-hydraulic assemblies. The deck ramp can comfortable carry a fully-crewed M577 APC (with turret stowed) or a HALOS stores pallet, and is able to raise the cargo completely into the payload space from ground level. Within the bay, latches are automatically activated, extending to hold cargoes in place when the deck is raised. A 20 cm cavity to either side of the payload bay separates the cargo volume from the outer skin and contains the main structural members, cable runs and the blower pipes from the forward turbines to the aft lift nozzles. Aft of the payload bay, a step gantry can be lowered to the port side to allow crew access. Forward of the bay, a small volume accommodates three seats for passengers and additional crew.
The spacious pressurized cockpit is accessed from the payload bay and features two crew positions, seated in tandem. Both crew sit in Martin-Siekert R2102 zero-zero ejection seats which are cleared for operation at any altitude below 10,000 m and speeds below Mach 1. In the event of an emergency, explosive cord blows the canopy off and the crew are ejected clear of the ship. Canopy transparencies are made from single-crystal quartz, flash coated with gold, germanium, molybdenum and iridium to provide protection against bright light and short-wavelength lasers. The coatings also act as a radar reflecting surface, preventing the entire cockpit volume from becoming a radar reflecting cavity.
The main fuselage also features the mounting points for the main weapons pods and the secondary weapons bay. The main weapons pods are attached to cross-folded pylons just forward of the ramrocket intakes, which at supersonic speeds, the 4.4 m pylons can be deployed crosswise to secure the ordnance within the pods. The total span of the pods when deployed is 15.3 m. The pods cannot be deployed at speeds above transonic because of the adverse effects of drag and the torsion caused by dynamic pressure on the pylons. The secondary bays also fold flush against the sides of the lifting body, and can be sprung out to expose all the weapon hardpoints and allow exhaust space for weapons launch. Unlike the main weapon pods, the secondary bays can be deployed at super-sonic speeds up to Mach 2.4 without adverse effects on dropship handling.
It must be noted that even light damage can prevent a dropship from lifting into orbit. A breach of the fuselage skin will seriously compromise the ship's high-speed thermal protection, and even a tiny hole can cause oxidation or 'burn through' when atmospheric speeds exceed Mach 5.0. To prevent such accidents, a sensor net is bonded to the inside of the skinning to monitor for breaches, differential hull temperature and ionization. If a breach is detected, a warning is flashed to the cockpit monitors to notify the crew.
The UD-4L is a reliable craft in all realms of its aerospace operating platform, and is a popular craft with its pilots. It handles well above the specific purpose for which it was designed, but in the world of war, nothing can be expected to handle as it was designed, here the Cheyenne delivers above and beyond... but not as well as the pilots who push these craft to their limits would prefer.
At subsonic speeds, the lifting body configuration generates little lift and the pilot becomes increasingly reliant on the flight software and lift from the vectored thrust engines to keep the dropship stable in the air. Stall speed is very high, and as the Cheyenne approaches the stall it tends to fly increasingly nose-high. As transition is made through the stall speed, vertical lift from the nose and stern nozzles are bled in to prevent departure. Though the airframe is nominally stressed to +6 g, manoeuvre's in conventional flight greater than +3 g are prohibited due to the excessive stall speed, which can cause the Cheyenne to prematurely depart controlled flight. When fully loaded, turns greater than +1 g are prohibited. At very low speeds and at altitudes below 500m, VTOL hovering flight is recommended. The Cheyenne is at its nimblest in the hover; here, response is crisp in all axes and the dropship is a very steady weapons platform.
The Cheyenne has a crew of two, comprising a pilot and a Crew Chief / Weapons Officer. Flight control is quadruplex digital fly-by-light with automatic self-monitoring and reversion to back-up modes, all handled through the Herriman-Weston 5 / 480 flight computer. There is no manual reversion since the dropship is too unstable to be flown with direct control inputs. Engine thrust and nozzle settings are automatically moved to their optimum positions depending on speed, altitude, throttle and stick settings. An intelligent autopilot facility allows the automatics to fly all phases of the mission profile, including ingress and egress to the target zone as well as landing and docking cycles.
Two main weapons bays fold out on extended pylons to deploy weapon hardpoints each capable of carrying 16x150mm unguided rockets, 6x7mm unguided rockets and 4x120mm guided rockets. Two secondary weapon bays on the port side and starboard side of the fuselarge house a further 14 hardpoints for ATA and ATS missiles. The dropship mounts a dedicated 25mm gatling gun in a powered cuploa beneath the nose, which can be rotated 180 degrees side to side and by an angle of 60 degrees downwards.
The GAU-113/B is a six barrel weapon driven by a pneumatic motor turned by the engines at 6000 rpm and geared down to the rear of the gun. Rounds are caseless, and do not carry their own propellant. Instead, the GAU-113/B system uses hypergolic liquid fuels, stored and loaded separtely, as a binary propellent. When fed into the chamber via the spray nozzles, they react simultaneously to explode and propel the shell.
Ammunition comprises a mix of Armour Piercing Incendiary (API), Armour Piercing Discarding Sabot (APDS) and High Explosive Incendiary (HEI) and is fed from a 900-round drum beneath the cockpit. It is standard practice to carry at least two spare ammo drums on board. These can be reloaded manually by a crew member from inside the cockpit.
- AGM-204A TSAM: The TSAM (Threat Suppression Attack Missile) is a low-cost self-protection weapon designed to defend strikeships and dropships against airborne missiles, early warning radars, SAM sites and AAA. Small, short ranged and lightweight, the TSAM design trades off the loiter mode of most modern Threat Suppression Missiles for speed, in order to eliminate a threat rapidly. The Tekell solid motor is a high impulse unit that will accelerate the missile to hyper velocity in less than two seconds; after burnout, the missile coasts to the target. Range varies considerably with launch speed and altitude, though practical limits in an Earth-density atmosphere are 20 km at sea-level up to 60 km at high altitude. The TSAM is guided but cannot be fired at. It is designed to attack incoming missiles. It locks on automatically.
- AGM-220C Hellhound II: The Hellhound II is a multi-role tactical missile designed for use against point targets such as vehicles, armor, buildings and bunkers. Based around a greatly enlarged version of the Hellhound I airframe, the missile employs a three-stage motor consisting of a launch boost engine, and in flight sustained motor and a third-stage booster designed to accelerate the weapon during its terminal attack phase. The weapon can be launched in two different modes: in the first, the dropship Weapons Officer locks the missile's seeker onto a target before launch and provided he maintains the lock until the moment of launch the weapon will then be guided to that target; in the second, the weapon is directed to a grid reference where it then commences a search for a pre-designated target, or one selected from an internal menu of potential targets, or for a target of opportunity. The dual-seeker system combines a high-resolution millimeter-wave radar and infrared imager linked to a sophisticated 12 Mb processor which determines the missile's optimal attack profile and warhead fusing to ensure a kill. The 'C' variant of the AGM-220 incorporates a new, jam-resistant radar and improved countermeasures refection logic to bring it in line with the 'F' version employed by the USASF. This is a guided weapon.
- Mk. 16 150mm BANSHEE 70: The Banshee 70 system constitutes one of the most important unguided weapons in US service. In the Colonial Marines, it is most commonly associated with the LAU-190/A 16-tube launcher mounted on the UD-4L Cheyenne dropship. Each rocket is spin stabilized by a fluted exhaust nozzle and has three spring-mounted wrap-around fins at the rear. The Mk. 16 model has a high-impulse rocket motor, giving a burnout velocity in excess of 1800 m per second, providing excellent stand-off range and accuracy in the air-to-surface role.
- AIM-90E Headlock: The AIM-90E is a short-ranged air-to-air missile optimized for dogfight engagements. Guided by a dual optical / active radar seeker, the Headlock missile accelerates to hyper velocity speeds after launch and then glides the remaining distance to the target. The warhead consists of thirty four explosive darts that are released by the missile as it approaches the target. To ensure a kill, the AIM-90's unique fusing system directs these flechettes into an optimum attack pattern upon release, dependent on the target's current aspect. The 'E' variant of the missile incorporates changes to the countermeasures software and enlarged aerodynamic surfaces to improve lift at high altitudes.
- Mk. 10 70mm ZEUS: The Mk. 10 ZEUS is a 70mm unguided rocket system that has been the mainstay of USCM service for some sixty years, in its various forms. A small, spin-stabilized rocket, the ZEUS is now supplied with only two types of warhead: a smart fused antipersonnel fragmenting warhead and a smoke warhead for laying particulate smoke screens.
- Mk. 88 120mm SGW: The Mk. 88 is a 120mm, short ranged (under 1500m) weapon designed as a low-cost alternative to the Hellhound versus light armor and prepared positions such as hangars or gun emplacements. A simple weapon, it comprises a rocket with a low-impulse motor steered by fold-out fins. Guidance is by an imaging infra-red seeker in the nose, and a 2.2 kg shaped-charge warhead is positioned just behind. The SGW is a fire-and-forget weapon - once locked-up by the dropship, the missile self-guides to the target.
- UD-4B: Original production variant powered by Atco Wyoming F23 lift turbines, producing 243 kN thrust each. Shorter by 1.5 m than the later variants and with less payload space, this version was also equipped with the main weapons pods only.
- UD-4C: A gunship variant, this was the first to employ the secondary weapon bays and a dedicated Gatling gun system.
- UD-4E: This was the UD-4B re-engined with F29-L-13 turbines to give extended atmospheric range.
- UD-4H: The definitive production variant of this type, the UD-4H included a major redesign of many systems and components. The fuselage was stretched by 1.5 m to allow an extra 16 m3 of payload space, making it the first variant capable of carrying the M577 APC, and the lift engines were upgraded to a broad-spectrum sensing array and command datalink. Secondary missile bays and the Gatling guns were now fitted as standard.
- UD-4J: A USCMC life-extension program upgraded all existing UD-4B airframes to 'H' standard. This was designated the UD-4J.
- The Cheyenne's legacy includes providing a hefty amount of inspiration to the game development company Bungie, resulting in the famous Pelican dropships from Halo, which draw many features from the Cheyenne.
- The Cheyenne also inspired the Quantradyne APOD-33 Dropships of StarCraft fame; in fact, the pilots seen in StarCraft are directly inspired by Colette Ferro, the dropship pilot seen in Aliens.
- The UD-4L is also operated as a close-support gunship for Marine ground forces. While this is only implied in Aliens, the craft has been used in this role in several video games from the franchise.
- In Aliens versus Predator 2, dropships are seen using their rockets against Aliens/Predators.
- In Aliens vs. Predator, during the player's trek through the jungle as the Rookie, the dropship Typhoon is seen firing at ground targets before being shot down.
- In Aliens: Colonial Marines, a Cheyenne is seen firing upon the second Acheron Queen when it has the player trapped inside a shipping container. Before this, it also engaged other airborne units.