Silent shadow: marines looking at hybrid vehicle for greater fuel economy, more stealth on the battlefield

Diesel Progress North American Edition, Sept, 2004 by Bill Siuru

when the U.S. military is deployed in combat, as much as 70% of the supplies by tonnage consist of furl to keep the forces rolling. The standard fuel, JP-8, can be used both by diesel engines in ground vehicles and turbine engines in aircraft and helicopters. And if you think $2.50/gal. for gasoline is outrageous, consider that JP-8 can cost $400 to $600/gal. by the time it gets into the field.

So like the civilian world, the U.S. military is very interested in furl economy and is taking a serious look at hybrid electric vehicles (HEVs) to reduce fuel costs and logistical problems, along with extending the range so vehicles can stay engaged in battle longer.

HEVs also offer important benefits beyond just more mpgs for the military. They can operate more stealthily with reduced infrared and acoustic signatures. Indeed, many military experts believe that "silent running" is much more important than better fuel economy on the battlefield. Additionally, generators and batteries in hybrid vehicle can help provide the large amount of electrical power needed by a modern military.

While prototype hybrid electric armored vehicles, trucks, buses and even Humvees have been built and demonstrated, the U.S. Marine Corps could be the first to have a hybrid electric combat vehicle in its inventory. The Reconnaissance, Surveillance and Targeting Vehicle (RST-V), also called the Shadow, is being developed by General Dynamics Land Systems under sponsorship of the Office of Naval Research (ONR), the Defense Advanced Research Projects Agency (DARPA) and the Marine Corps Warfighting Laboratory (MCWL).

The series hybrid system used in the Shadow features a lightweight diesel engine coupled to a generator that supplies electric power to in hub electric wheel motors in all four wheels to give 4 x 4 capability. The RST-V can operate in stealth, hybrid and engine-only modes, in stealth mode, the Shadow, powered only by batteries, can travel about 20 miles with extremely low thermal and acoustic signatures. When rapid acceleration or maximum torque for climbing steep hills is called for, the Shadow operates in the hybrid mode with power from both the diesel engine/generator and energy from the batteries. The RST-V can also run on the diesel engine alone.

At the heart of the hybrid system is a 2.5 L Detroit Diesel TD DI-4V automotive diesel engine. The engine, which incorporates an electronically controlled Bosch common rail fuel injection system and electronically controlled modular EGR, is an in-line four-cylinder rated 138 hp at 4000 rpm. Peak torque is 251 lb.ft. at 1800 rpm.

The engine directly drives a Magnet Motors 110 kW permanent magnet generator. Power from the generator is delivered to four 50 kW (67 hp) permanent magnetic hub motors--also supplied by Magnet Motors--positioned at each wheal. Excess electrical energy is stored in twin SAFT Lithium-Ion (Li-Ion) battery packs with total rated output of 20 kW-hr and a peak power output or 80 kW.

This configuration gives the Shadow a top speed on improved roads of 70 mph. With 25 gal. of fuel onboard, the Shadow has a range of 470 miles at 30 mph. This equates to nearly 19 mpg.

The size and layout of the Shadow was determined by the need for it to be air transportable in CH-53 or CH--46 helicopters, V-22 Osprey flit rotor aircraft and C-130 Hercules transports. As many as 21 RST-V Shadows could be carried in a C-5 Galaxy or 12 in the C-17 Globemaster.

Fitting the Shadow into the narrow Osprey represented the greatest challenge. To do this, the RST-V has a pneumatic suspension system that can be lowered to reduce the Shadow's dimensions. The tires are also pulled in to reduce the vehicle's width to a mere 62 in. and the vehicle's height can be dropped so that the clearance is only about 3 in. The bottom of the Shadow is also arched so it can move over an aircraft ramp. This feature also helps in climbing over obstacles such as fallen trees.

Without a conventional mechanical drivetrain to take up space, the RST-V has the same cubic storage capacity as a Humvee.

The USMC sees the Shadow as a replacement for both the aging M151-A2 Fast Attack Vehicle and the Humvee, where it would be used for reconnaissance, surveillance, targeting and C3I (command, control, communications and intelligence) missions. Other possible tasks include carrying forward observers and forward air controllers; a battlefield ambulance, cargo or personnel transport; or a platform for anti-armor and mortar weapons.

It can be armed with a 7.62 mm or 12.7 mm machine gun, 40 mm grenade launcher, Objective Crew Served Weapon (OCSW) or Javelin or TOW anti-tank missiles. The Shadow can also be fitted with defensive aids including radar and laser warning receivers, and missile detectors.

The Shadow RST-V carries a crew of four who enter and exit through the vehicle's two doors. A rear ramp provides access to the cargo area. While the RST-V has an aluminum body, an optional armor package is available for protection against small arms fire. Bulletproof windows can also be installed on the front and sides.