Saving fuel: making combat vehicles lighter

Preface. The military would like to lightweight equipment to save on fuel. Although Peak Oil isn’t mentioned, no other department of the U.S. government is more aware of future energy shortages, and the implications that has for their ability to wage wars (see posts here). Lightweighting vehicles would have the added advantage of enabling them to use roads rather than tracks, and I assume make better time to reach a battlefield.

Many of the workshop participants in this National Research council workshop were from companies such as Boeing, Lockheed, Alcoa, General Electric, touting materials the military might be interested in, and universities explaining their latest light weight materials research.

Several people commented on how long it takes to move from discovery to large-scale manufacturing, often 15 years or more. And once manufacturing starts, it is unlikely that new materials can or will be brought into the process.

Alice Friedemann  author of “When Trucks Stop Running: Energy and the Future of Transportation”, 2015, Springer and “Crunch! Whole Grain Artisan Chips and Crackers”. Podcasts: Derrick Jensen, Practical Prepping, KunstlerCast 253, KunstlerCast278, Peak Prosperity , XX2 report


NRC. 2018. Combat vehicle weight reduction by materials substitution. Proceedings of a workshop. National Research council, national academies press.

Vehicle weight reduction is an effective strategy for reducing fuel consumption in civilian vehicles. For combat vehicles, it presents not only an important opportunity to reduce fuel use and associated logistics, but also important advantages in transport and mobility on the battlefield. Although there have been numerous efforts in the past to reduce the overall weight of combat vehicles, combat vehicle weight has continued to increase over time due to new threats and missions. For example, whereas early combat vehicles had limited armor protection (located primarily in the front of the vehicle), the emergence of all-aspect threats has resulted in armor that is distributed throughout the vehicle and thus has increased the vehicle’s weight.  This workshop focused on materials substitution as a means toward weight reduction, considering options in a variety of vehicle systems (such as power train, structure, and armor). It also explored the potential impact of materials substitution on system performance and life-cycle requirements.

In the 1980s, the primary threat to vehicles was from the front, but over time the threats became hemispherical and, increasingly, fully spherical. They said that this change has required increased armor protection for vehicles and has thus increased their weight. Additionally, Carter pointed out that soldiers use ground vehicles beyond their design requirements due to combat needs. He said this includes climbing hills, busting through walls, fording water, and knocking down trees, among other field activities. In addition, vehicles should operate and be sustained in all environments; they have to withstand heat, cold, thermal cycling, solar radiation, rain, humidity, salt fog, sand and dust, vibration, shock, and other forces and environments. He noted that threats to vehicles include kinetic energy from bullets (small arms, medium cannon, and large caliber rounds), chemical energy from shape charge jets and explosively formed projectiles, and underbody threats from mines and improvised explosive devices.

Despite intensive effort, the materials efficiencies have not kept up with the vehicle weight. This has had numerous impacts, particularly on transportation. For instance, Carter stated that only a single M1 Abrams tank can be carried by a C-17 transport aircraft due to its weight.

Combat vehicle design requires a balance among many competing requirements. This includes protection, mobility, automotive requirements, deployment and transportability, and a host of other considerations. However, he also noted that cost has been a direct or indirect driver in ending each of the previous efforts to reduce weight.

Heavier vehicles have to use tracks and are more restricted in what roads and bridges they can use. Weight also affects fuel economy as well as transportation.

The Army is currently undertaking a Lightweight Combat Vehicle Science and Technology Campaign, he explained. The objective is to develop a portfolio plan to realize a 30- to 35-ton vehicle by 2030 that meets the capabilities and mission of today’s 40- to 75-ton fleet, such as the M1 Abrams tank, which weighs more than 70 tons and is the heaviest vehicle in the U.S. Army. He said that this will involve technology advances in survivability, lethality, materials, power, and energy, among other supporting areas, and that the plan is to identify technologies, materials, and vehicle and component designs that can meet this objective.

A 75 ton Abrams tank has 40.7 tons of armor and structure, 12 tons of running gear, 11.6 tons of weapons (i.e. main gun and ammunition), and 10.7 tons of powertrain, auxiliary automotive, and crew equipment.  One idea was to reduce the armor to 13.5 tons, but it is questionable if that would provide as much protection as 40.7 tons of material.

The Bradley infantry fighting vehicle weighs 39.3 tons, with over half of that weight armor and structure. This vehicle too needs to be lighter.

The enemy is much faster at changing tactics than the military is at fielding new vehicles because modern communications make it possible for the enemy to communicate about tactics and adapt to new threats far more rapidly than in the past.

Making vehicles in the past hasn’t happened because lighter materials are too expensive, eventually reaching a point where political leaders would no longer fund them, and canceled, though cost wasn’t a factor five years ago when the military was in Iraq.  The extra cost to lightweight a vehicle would save money in the long run, since treating wounded soldiers the rest of their lives is very expensive.

Is the age of the tank over?  Several workshop participants thought the age of the tank might be over, since they are now defeatable in many ways.  The military speakers stressed they weren’t only interested in tanks, but artillery, armored fighting vehicles, the tankers that refuel vehicles, and the body armor that protects soldiers.

It’s very hard to see what happens when force is applied to a potential material, it happens in less than 100 microseconds or less, and without being able to observe how the material was impacted, it is hard to improve upon it.

Scaling up is also very difficult. A small amount of material scaled up to manufacturing on an industrial scale often has problems because no one has anticipated what might happen going from a small laboratory-scale sample to larger scales.  Sometimes scaling up doesn’t work due to thermal properties or chemical changes change the resulting material to something undesired and unexpected.

The complexity of armor systems makes them hard to design, none of them are just one material, but many, and anticipating or observing the interactions among these materials is crucial.

A speaker from Alcoa proposed various solutions such as a monolithic hull structure with fewer welds that could break.  He pointed out that a major part of a vehicle’s lifetime will be training, not combat. He said that aluminum corrodes and pits over time, a major consideration.

Some of the participants then discussed the view that the Army sometimes is a difficult customer and what the Army can do to be a better customer. A few participants believed that the Army changes requirements and can be very bureaucratic. In addition, the size of the market drives the technology, and the military is too small of a customer to really drive the development of new materials technology. Some participants at the workshop also noted that the military needs to be clearer about requirements. “How will we inspect it, certify, and qualify it?” one participant asked. This participant also said that, at the moment, the military is not clear about what it expects from the customer (i.e., materials producers) on these issues.

Bill Mullins, Office of Naval Research: “Lightweighting of military vehicles has long been a consideration for armies. He said that as early as 1500 BCE, advanced materials were incorporated into horse-drawn chariots and armies and navies have sought to reduce the mass of their vehicles throughout recorded history”.

Eric Nyberg, Pacific Northwest National Laboratory:  “Applying lightweight metals to defense applications has been common in the United States for nearly a century. For example, he noted that the B-36 bomber, which was first conceived in the closing years of World War II, had 19,000 pounds of magnesium sheet, forgings, and castings, covering 25 percent of its exterior. He said the M-116 amphibious carrier used 60 pounds of magnesium in its floor and that the German Luftwaffe also began using magnesium in its aircraft in the 1930s.

Nyberg discussed the possibility of a 30 to 50 % weight reduction in vehicles. Such weight reduction is unlikely to occur through optimization and trimming in existing designs or through material substitution in existing designs. Instead, it will require material-specific designs. He said it is also unlikely to occur using existing vehicle composition and will require advancements in multi-material technology.”

Coming up with new technology can take a long time.  It took 10 years and a billion dolars to develop a new commercial turbofan engine at General Electric.


The external tank provided the structural backbone for the launch vehicle and had to support the 2.9 million pounds of thrust exerted by each of the two solid rocket boosters, as well as the 1.1 million pounds of thrust exerted by the engines in the tail of the Space Shuttle Orbiter. He said that the tank consisted of three major subcomponents. At the top was the liquid oxygen tank, which held 145,138 gallons of oxidizer at −297°F. Below this was the intertank, which was an unpressurized structure. Below this was the liquid hydrogen tank, which held 309,139 gallons of fuel at −423°F. In addition, the tank had 38 miles of electrical wiring, more than half a mile of pressure vessel welds, and 4,000 pounds of thermal protection materials (spread over 16,750 square feet).  The space shuttle program existed for 38 years and 135 flights.

The Heavy Weight Tank weighed 76,000 pounds and was flown six times. The Light Weight Tank weighed 66,000 pounds and flew 86 times. The Super Light Weight Tank weighed 58,500 pounds and flew 43 times.

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