Building the perfect Jeep

Illustration by Razvan Maftei
Date:27 October 2011 Tags:, , , ,

By combining ideas and tech from industry experts, our editors create the Popular Mechanics Light Tactical Vehicle (PMLTV). By Joe Pappalardo

One of the world’s best-loved vehicles developed out of a need for compact, agile and tough transport in the theatre of war. Just how fit-for-purpose the original Jeep was became apparent as it did yeoman duty in World War 2 and subsequent conflicts before it was finally supplanted by a modern equivalent dictated by the ever-changing requirements of modern warfare: the Humvee.

Those same changing requirements now make it once more necessary to update the template of a vehicle that will be called on to do everything from hauling gear to ferrying troops and conducting patrols.

Thing is, the military is having a devilishly hard time building a light tactical vehicle to replace the Humvee, which was introduced in the early 1980s. Contractors are vying to produce the next-generation all-purpose vehicle, called the Joint Light Tactical Vehicle (JLTV), for the US army and the Marine Corps. But with R2 billion already invested – and at least R4 billion more in projected development costs through 2015 – the only options thus far have been expensive, overweight prototypes.

In February, the US army’s product manager of the JLTV programme revealed to attendees of a National Defence Industrial Association wheeled-vehicle conference that each of the 21 JLTV designs submitted by contractors was as much as 450 kg too heavy. This degrades the vehicles’ performance and, since JLTVs will be built to be carried by specific helicopters and fixed-wing aircraft, restricts their deployment. The cost is also rising. Replacing steel with lighter composites and metal alloys drives up the price; the JLTV options are already topping the $300 000 (about R2 million) goal set by the Pentagon. Existing Humvees cost R525 000; with an extra armour kit, the price is around R1,5 million.

Not willing to sit by while the defence industry that created the Jeep flounders, PM took action. We called on the best military-vehicle designers to help us create the PMLTV, a rugged, menacing piece of machinery. Even if we do say so ourselves.

1. Chimney blast

To save the weight of armour, the PMLTV instead uses a flue to channel energy from an explosion through the centre of the vehicle, guiding the damaging blast away from the occupants. The downward thrust produced by the blast rushing through the chimney also helps keep the PMLTV from flipping. Hardwire LLC is pitching the chimneys to the military; the Pentagon is blast-testing the tech now.

2. Diesel-Electric powertrain

The PMLTV's diesel engine is connected to an electrical generator, which creates power for a traction motor driving each axle. This eliminates the need for a transmission and a conventional drivetrain, creating more room under the crew compartment for 360 degrees of armour. For a scout vehicle operating far ahead of the front lines, the option of switching to nearly silent propulsion is very appealing. We like vehicle manufacturer Oshkosh's ProPulse system, a 335-kW engine that can also export enough power to run a fi eld hospital.

3. Ford F-450 frame

Most military-vehicle companies prefer the flexibility offered by their homegrown chassis, but purchasing an available and trusted vehicle frame from a commercial production line can save billions. In 2005, vehicle designer Scott Badenoch and the Georgia Tech Research Institute developed an armoured patrol vehicle using a Ford F-350 truck frame; we opted for the wider F-450. At about 2 300 kg, the F-450 chassis is heavy, but it can handle thousands of kilograms of payload without going over the specified 6 000-kg kerb weight limit.

4. Tak-4 Suspension

It’s hard to build an active suspension system that is both agile and tough enough to handle on-and off-road conditions. The F-450 suspension is certainly not up to the task, so the PMLTV adopts the new version of TAK-4, made by Oshkosh. This independent suspension system uses high-pressure gas to raise and lower the vehicle 50 cm with the flick of a switch on the frontseat dashboard. The government is now testing the new TAK-4, says Chris Yakes, Oshkosh’s vicepresident of advanced products.

5. Crew compartment

Many new armoured vehicles have steering wheels in the centre of the dash, which allows greater visibility. The layout of the ballistic-resistant windows provides a better field of vision. Inside, a cage of tubular steel protects occupants during rollovers, and seats are suspended to halt the transmission of explosive shock waves to occupants.

Related video:
Watch how to dismantle and rebuild a Jeep in less than 4 minutes


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