TECHNICAL READOUT
UD-4L 'CHEYENNE' UTILITY DROPSHIP


by Lee Brimmicombe-Wood and Dave Hughes

transcribed by Livius Halupczok

The UD-4 'Cheyenne' is a versatile dropship and tactical transport employed
in a primary role in the US Colonial Marines. Derived from an original
Department of Defense requirement for a multi-role shuttle capable of
lifting heavy payloads up to 16,000 kg, the UD-4 has become the definitive
dropship design, influencing the shape of many derivatives and successors.

The heart of the UD-4 is the power provided by the two General Dynamics TF-
900 Turbines, each producing 310 kN static thrust. This twin-engined
configuration gives a degree of redundancy by still allowing the vessel to
lift itself into orbit should one engine de damaged or shut down. Thrust can
be vectored either through the side-bleed rotating nozzles to give VTOL
capability, or through the stern nozzles for forward propulsion.

The UD-4 utilises a lifting body configuration centered on its 324 cubic-
metre payload bay. The bay is flanked by the two forward struts of the
tricycle undercarriage and its floor comprises a hydraulic loading ramp that
lowers directly to ground level. Froward of the loading bay is the spacious
twin seat cockpit and to the stern is the tail assembly which houses the
rear undercarriage strut, main fuel tanks and the contol surfaces. As far as
is possible, the fuselage has integrated stealth characteristics including
rounded leading surfaces, shielded compressor intakes, a butterfly tail and
flash-coated cockpit transparencies. These features, in addition to the
heavy use of rader and laser-absorbent composite materials throughout the
airframe, serve to reduce the vessel's forward radar cross-section and
thermal signature.

The Cheyenne has a crew of two, comprising a Pilot and a Crew Chief/Weapons
Officer. Control is fly-by-light with much of the pilot workload handled by
the triple-redundant flight computer. This system is designed for maximum
cockpit efficiency, registering all flight information on a bank of
integrated CRT displays. The comprehensive Westinghouse avionics suite
incorporates radar, optical, thermal and laser sensing arrays, and a
communications data-link. Electronic counter-measures (ECMs) are provided
internally by an ALQ-2004V multimode deception/barrage jammer, though this
is supplemented by stern-mounted decoy dispensers firing chaff, flares and
mini-jammers. The flight characteristics of the UD-4 prove it to be a stable
and reliable vessel in the atmosphere-to-orbit interface and it is popular
with its pilot. However, the airframe is only stressed to 6 g, and its air
combat manoeuvrability is severly limited. If the UD-4 is forced into Air
Combat Manoeuvring, a pilot's best option is to evade using the Cheyenne's
vectored thrust capability or ECM.

The 'L' variant tactical transport carries a wide array of powerful weaponry
that can be used in dedicated support of its troop complement. Two main
weapon bays fold out on extended pylons to deploy weapon hardpoints capable
of carrying 16 x 150 mm unguided rockets each. Two secondary bays on the
port and starboard side of the fuselage house a further 12 hardpoints for
Air-to-Air/Air-to-Surface missles. The dropship also mounts a dedicated 20
kW Gatling Laser in a powered turret benath the nose. Target acquisition and
weapons operation are handled by the Weapons Officer in the cockpit,
although direct fire tasks utilising the Gatling Laser and Rockets can be
carried out by the Pilot.

In the Colonial Marines, the UD-4 is employed mainly as a tactical
transport, having the capability to deploy troops and its own dedicated
firepower direct from orbit to the operational area. Typical payloads into
an operational Landing Zone (LZ) may include up to three fully equipped
infantry squads or one M577 APC. The Cheyenne also has the capcity to carry
up to 16,000 kg of stores. Typical mission profiles include Assault,
Transport, CasEvac, Search and Rescue, Forward Supply, Close Air Support and
Reconnaissance.
The design of the UD-4 has proved highly successful and through refinement
has prompted the production of several variants. These include the
following:

UD-4B - Original production variant powered by Avco Lycoming F23 Turbines
producing 243 kN thrust each. Shorter by 1.5 metres that the later variants
and with less payload space, this version was also equipped with the main
weapons bays only.

UD-4C - A gunship variant, this was the first to employ the secondary weapon
bays and a dedicated gatling laser system.

UD-4E - This was the UD-4B re-engined with F29-L-13 Turbines to gibe
extended atmosheric 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 41 cubic metres of payload space and the engines
were upgraded to TF-900 Turbines. The avionics fit was the first to include
a broad-spectrum sensing arry and command data-link. Secondary missle bays
and the Gatling Laser were now fitted as standard.

UD-4J - A USCM life-extension program upgraded all existing UD-4B airframes
to 'H' standard. This was designated the UD-4J.

UD-4L - An upgrade of the 'H' version assault transport, the UD-4L
incorporates an improved sensor and fire control system as well as being the
first to include a multimode ECM/ECCM fit.


Statistics for the UD-4L are as follows:

Type: UD-4L Utility Dropship

Crew: Pilot and Crew Chief/Weapons Officer

Engines: Two General Dynamics TF-900 Turbines each rated at 310 kN dry
thrust

Dimensions: Lenth 24.3 m, Beam 18.2 m, Height 4.7 m

Weights: Loaded 18,620 kg; Maximum Loaded 34,628 kg

Performance: Maximum Acceleration (Loaded) 3.33 g; Maximum Acceleration
(Fully Loaded) 1.79 g

Armament: (Typical) 1 x 20 kW Gatling Laser; 32 x 150 mm unguided rockets; 6
x AGM-220 Air-To-Ground Missles; 4 x HiSARM Anti-Radiation Missles; 2 x AIM-
90 Short Range Air-To-Air Missles


CMC - Colonial Marine Corps



Comments: For those who are familiar with military aircrafts, you will
notice that the UD-4L is a future mix of the UH-1 and the AH-64 
helicopter.


For any abbrevations look here.

Thanks to Livius Halupczok for this document.

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