A new, greener Bradley?
The Washington Post writes the Army is considering buying a hybrid Bradley which runs on diesel but is assisted with batteries for power. The expected weight is 70 tons, which the Post says is double the weight of the current Brad, but that’s wrong, as far as I know. I was one of the first Bradley squad leaders and as far as I know, the IFV weighs 26 tons, so a 70 ton Brad would be nearly three times the weight of the initial configuration.
In the article, the author calls the Infantry Fighting Vehicle a tank, luckily his readers straightened him out. It’s like calling an AR rifle a machine gun like the media is so fond of doing. We infantrymen stop listening to people who call an Infantry Fighting Vehicle a tank. We’re not tankers, we’re infantrymen first.
So back to the Bradley; I remember when the Bradley was first issued to TO&E units in 1983 after years of testing and we still received the systems with technical and design problems, so I can only imagine the problems that will handed to infantrymen when you’re talking about an entirely new power train system. When we got the Bradley, we had been accustomed to the M113 battle taxi which had no complicated weapons system to maintain and employ, a relatively new type of power train, fire suppression systems, fueling system, new weapons, etc… In other words, it was like moving from a bi-plane to the space shuttle. We were in training mode for over a year.
When Toyota rolled out it’s Prius, there were problems with the relatively uncomplicated system, it had problems which appear to have been fixed, but it seems to me that a 70-ton IFV would have even more problems with it’s hybrid power system than a soldier under fire, needing some organic firepower would care to deal with.
I do, however, like the idea of a “stealthy” Bradley, if it could arrive at the battle on battery power without the usual noise associated with the current diesel engine. But, I’m pretty sure that the problems with the new power train, and the Army’s traditional inability to work out problems before the vehicle is handed over to the troops, would outweigh any advantage like that.
Category: Military issues
@50- diesel electric can and has worked in fighting vehicles before. The failed Porsche bid for the tiger tank in ww2 was diesel electric. (The krauts turned the prototype models into the jadgpanzer elefant, which had significant drive train issues because it was designed to power a tiger tank, not a mobile gun bunker. I believe the drive train would have been sound in a 40 ton vehicle).
Diesel electric responds well to changes in demand, Hondo. The diesel runs balls out regardless of electric motor rpm, as it is powering the generator. Electric motors make maximum torque as soon as they start turning, so acceleration is great. A good top speed, however, requires more windings and will significantly increase the size and weight of the motors.
teddy996: correct. And therein lies two possible reasons that you don’t see more use of diesel-electric drives in machinery that has to both accelerate quickly at times plus have a reasonable top end speed.
First: if a diesel runs continuously but doesn’t run under sufficient load, it tends to “wet stack”. That can lead to crankcase dilution – not good for longevity. Trains and construction machinery (and most diesel generators) run at sufficient loads that this isn’t a problem. A vehicle that runs while immobile a large portion of the time may be a different story. Probably only a minor consideration, but could be an issue.
A more serious potential problem is power/weight ratio. Even a heavy-duty transmission can be made reasonably light. A generator capable of generating several hundred horsepower, not so much. One HP is about 3/4 kw. If you need 400 peak HP, that means you need a generator capable of putting out 300 kw electrical – minimum. Those kinds of generators don’t tend to be very light. Add in 4ea 100hp electrical motors with enough windings capable of allowing a top end of 50+MPH and the requisite power control and synchronization systems, and you may well end up with the combination being much heavier than an equivalent transmission. That means the vehicle’s acceleration, fuel economy, and (to a slight degree) top end will suffer.
In a piece of construction equipment or train, you’re not usually worried much about weight/power ratio – because snappy acceleration isn’t usually a consideration. In a vehicle that has to scoot at times to save the occupants’ asses, you are.
@53- The diesel loading problem you mention (my knowledge of diesel engines is rudimentary- I serviced the generator end only) can be handled easily by resistor banks or bullshit loads to put counter torque on the generator when the vehicle is at idle, but again, it adds weight to something whose main survival tactic is its mobility.
Diesel electric’s big turn off, and the main reason the krauts did not go with the Porsche design for the tiger, is that it adds complexity and it sucks fuel. Waiting in battery to attack? You’re at 4000 rpm. Creeping at 2mph to be loaded on a transport? 4000 rpm. Hauling ass to support the left flank? 4000 rpm, like a conventional drive setup. That’s the only time diesel electric could possibly compete in fuel efficiency- when a conventional setup would be running balls out. That doesn’t happen often.
But diesel electric can handle changes in speed very well, within their set range. As I mentioned, electric motors put out maximum torque from the jump. They also are capable of stopping fast, through the use of dynamic breaking (turns your electric motor into a generator, and uses the counter torque that it produces to stop the rotor, which would be directly coupled to the drivetrain. Very effective). But electric drive will never have the range of functional top speed that a conventional gearbox setup will have within a comparatively sized package.
But that’s not the system they’re talking about for the 70 ton Brad, so its moot. They want battery operated DC motors assisting the diesel engine. Completely asinine.
Pentagon Wars 2 – Return of Teh Stupid
teddy996: yep. That’s precisely why many larger tactical diesel generators years ago had load banks, and presumably still have them today – to add electrical (and thus engine) load when the electrical demand wasn’t high enough to do the trick. As you point out, they add substantial weight and some additional complexity. Using dynamic or regenerative braking also adds at least the latter.
You’re also correct that a straight diesel-electric setup isn’t what’s being proposed here. They’re talking a battery-assisted hybrid. IMO, that’s a VERY stupid idea for a tactical vehicle given today’s battery technology.