U.S. Army mulls hybrid-engine model for next mainstay tank

The Washington Post

Next year, the U.S. Army is expected to choose a larger tank to replace its Bradley Infantry Fighting Vehicle, which has been in service since 1981. If the army accepts one contractor’s proposal, its armored brigades could be relying heavily on a tank with a hybrid engine for several decades.

General Dynamics currently manufactures the army’s main battle tank, the Abrams, and BAE Systems builds the Bradley. Those two companies are now competing for the new contract, which the Congressional Budget Office predicts will be worth approximately $29 billion.

The new tank will ideally seat nine passengers instead of the seven who can fit in a Bradley, and it will probably weigh around 70 tons. That’s about twice as much as the Bradley and around the same as the Abrams. BAE’s proposed vehicle, which it would build with help from Northrop Grumman, would be among the largest land vehicles ever constructed with an electric battery in a hybrid engine.

For their part, representatives of General Dynamics are skeptical of the idea of equipping a large tank with a hybrid engine, but Venkat Srinivasan, a staff scientist at Lawrence Berkeley National Laboratory and an expert on energy storage, said there are reasons to think BAE’s approach might work.

“I would argue that, in these sorts of heavy gasoline use applications, hybridizing things makes a lot of sense,” Srinivasan said.

He noted that large, heavy vehicles use enough gasoline to justify the expense of a battery system, and that they have plenty of space as well as a need for power at low engine speeds, which an electric motor can provide.

Most of the time, the power in BAE’s tank would come from diesel generators that would deliver electricity to the motor and to the batteries. When extra power is needed, such as when the tank is accelerating, the batteries would engage. According to BAE, the tank would use 10 to 20 percent less fuel than a vehicle of the same size with a conventional engine.

Because of its sheer mass, it would still be inefficient relative to other kinds of vehicles. Despite its hybrid engine and 255-gallon (965-liter) gas tank, the tank would be able to go no more than 186 miles (299 km) without refueling, according to the company.

All the same, even a small increase in fuel efficiency would be valuable for the army because of the danger of transporting fuel through war zones. Soldiers and equipment used to protect convoys are diverted from more important missions, and Pentagon officials have long called for a more fuel-efficient military.

Also, while an internal combustion engine typically has to reach a few thousand revolutions per minute before it begins running efficiently, an electric motor can provide torque immediately. As a result, vehicles with electric drive can provide better acceleration.

“Electric motors are fantastically zippy,” Srinivasan said.

BAE is also touting the tank’s stealth. The crew could, says the company, shut down the generators entirely and run the tank’s sensors and communications equipment on the batteries alone while observing an enemy. With the generators off, the tank would be silent and would give off little heat.

Yet it’s still unclear whether idling only on battery power would be a practical option for commanders in the field. That’s because BAE isn’t permitted to disclose how long the batteries would last in this state, according to a company representative. The company also wouldn’t reveal how much electricity the batteries can store, or how much they weigh — information that would give a sense of their durability.

While most people probably wouldn’t boast about the acceleration or the stealth of a Toyota Prius, there is at least one thing a Prius would probably be able to do better than a hybrid tank. While passenger-car hybrids can recover some of the car’s momentum as charge when the driver applies the brakes, a tank’s tracks naturally absorb much more forward momentum than wheels do, limiting the energy that could be reclaimed.

Bob Sorge, a program director at General Dynamics, said that his company had decided against including a hybrid engine in their proposal for this reason, among others. “For this particular application, we decided it doesn’t make sense,” he said.

Instead, his company plans to use an engine and a transmission that have already been produced and used in other tanks, which would, he argued, allow the army to predict the cost of the vehicle with more certainty. “You can guess, when you have something that’s never been done before, how much it’s going to end up costing, but it’s a guess,” he said.

Sorge said if General Dynamics’s proposal is accepted, each new tank will cost around $9 million. Mark Signorelli, a vice president at BAE, predicted each of its hybrid tanks would cost between $9.5 million and $11 million.

The costs of military procurement projects are notoriously difficult to anticipate, and they typically run 50 percent over budget, as the Congressional Budget Office noted in a recent report critical of the army’s plans to replace the Bradley. The CBO questioned why the army needed such a large tank and suggested the service consider keeping the Bradley or buying one of two new, smaller models that have recently been developed for the German and Israeli militaries.