discord wrote:pinhead: i will accept that the 40mm is a lightweight gun, but the flak 88 was pretty much the heaviest gun put on a tank in its day, and still today would not exactly be a 'light weight', middle weight sure, but not light.
sen:
1. admitted. the turbine is also quite a bit thirstier.
2. fewer parts, yes, less maintenance, no. higher stress on high speed systems equals less tolerance.
in reality however, you get a failure you handle it the same way, lift out engine unit, plug in a new one, tank drives away engineers check faulty unit at leisure.
lighter, yes, smaller, yes, however, it is more sensitive to FOD and this is probably the major reason russia said 'fuck this shit!', they are not known for tolerating things with low grit tolerance.
3 turbines and diesel are different, yes, the abrams was designed in the 70's and since then the diesel has made rather amazing improvements, the turbine not so much.
4. this is a problem for the gearbox in a normal engine, it is STILL a gearbox(although includes a reductor on a turbine) problem for the turbine, since a turbine needs to operate at very high speeds, turbines have a slightly different problem, since what you generally want is torque, and the torque curve on a turbine IS peaky, which gives you basically the same problem of staying inside a rather small powerband for optimal performance in accel, and another for top speed...and as far as i know, neither is the optimal for fuel efficiency.
the powerplant was designed to run on autobahn, and do fast 'thunder runs' from base to base...that is basically what the design called for, it gets that job done, other scenarios....not so good.
5. not sure about acoustic differences, not had the opportunity to compare, but turbines in my experience are not exactly quiet, the signature is rather different, but not quiet.
6. cold weather problems? all the scandinavian countries use diesel, and it gets pretty damned cold here at times, and nemo is quite correct in that it can be managed.
1. Yes, yes it is. Part of the tradeoff, and a noted disadvantage.
2. You ignored that the Challenger 2 had the same issues, serving right alongside the M1. Since then, I've heard very little that didn't originate with those who have never used or worked on the M1 regarding any problems with reliability or maintenance. Honeywell didn't automatically build their engine with less tolerance to the requirements of it's own use for no particular reason. When you design a system to do something, you design it to withstand the stress of such to a reasonable degree, unless we're just assuming it's deliberately under-engineered? If so, why?
3. Have diesel engines stopped being piston driven when I stopped looking? And if not, how do they resolve the fact that a piston engine of any sort has to build up to it's optimal power band before generating maximum horsepower? I've not seen one yet that doesn't have an optimal range of operation, and a need to spin up to get there.
Turbines are spun up once, on start up, then spun back down on shutdown. Once in their operating range, which is narrow compared to a diesel, they can be kept there within a reasonable margin, delivering constant horsepower. The fact that they deliver very little deviation is the advantage in this case. Effectively, with a turbine, you're starting it, running it up, then dumping it into the drive train via reduction gears, wholesale, with the power plant delivering it's full output immediately, translating to a LOT of torque off the starting blocks with the right setup, but more importantly, a consistent power curve. With a diesel, you start it up, engage the transmission, then hit the accelerator, and the engine builds up it's RPM's from there. No question that diesel engines have excellent torque... But they don't deliver their full horsepower at lower RPM's, and thus don't have as consistent a power curve. Irony, really, that having a wider range, in terms of operational speed, means that a diesel, like all other piston engines, has a less consistent delivery of power.
On the subject of turbines not advancing... I suggest further reading on the matter.
4. It's actually a simple reference to the basic design of any piston engine setup. In all fairness, it's a point I should have rolled into 3. However, since we're on the subject... The only European MBT that has a better 0-20 mph rating is the LeClerc, which can do so in 6 seconds. Both the Leopard 2 and Abrams are rated at 7. Not too shabby.
When dealing with diesel, the ENGINE itself doesn't provide it's full, rated output until a certain RPM is reached. The MTU 873 only provides its full 1473 shp at 2,600 rpm (coincidentally, MTU's own information states that this is the maximum RPM for the engine, which is typical for a big turbo-diesel). Before you actually are getting 1473 shp, the engine has to get to 2,600 RPM. At a more modest 1000 RPM, you're getting approximately 740-870 shp (Rough calculation. MTU's site didn't have everything I needed, so I figured it from the displacement of 478.6 l, at 1000 RPM, both at 14:1 and 16:1 given that it's a direct injection engine. I'd favor the higher compression and resulting higher horsepower, given that I think highly of German engineering). The AGT-1500 is putting out 1500 shp from the moment you hit the gas, to the moment it peaks. Yes, it has a narrow powerband, which requires a slightly more complicated, heavier gearbox to regulate it, but the advantage is clear; the turbine runs entirely within it's powerband during operation, and has considerably more torque at lower speeds.
The resulting torque calculations from the shp comparison (effectively a situation where the tanks are accelerating) is;
M1 and variants using the AGT-1500 turbine: 3,939 ft-lb at 2,000 shaft RPM
Leo 2 using the MB 873 Ka-501 turbo-diesel: 2,284 ft-lb at 2,000 shaft RPM
Both numbers are a rough comparison, but the rating for the M1 is only 39 ft-lb off from whats officially claimed. It makes the point regarding torque, which equals acceleration, which equals life. For a 'thunder run' over any distance, I'd actually prefer the Leopard 2, with it's higher top speed. In the end, the M1, and Leopard 2A5, which are of similar weight in many instances (surprised? The Leo 2A5 lists it's weight as 55 t to 62.5 t, with the M1A2 listed at 62 t, and the original M1 at 54t), have similar specs on paper in regards to their power plant output. But the way those power plants deliver said horsepower is what sets them apart.
So...
You've got the choice of diesel, which doesn't give full power until it hits it's optimum range, or you've got the choice of a turbine, which provides it all from the get go but is less efficient.
And no, revving your engine to top speed is never optimal for fuel efficiency, regardless of what type of engine you have. One of the big drawbacks, as we agree, with turbines, is that they suck up gas no matter what, rather than sipping at idle. So, the tradeoff is efficiency versus capability. Pick your poison.
I'm not making a case of turbine engines being BETTER. Merely that they provide advantages that you can't match with diesel. There are situations in which a diesel is flat out better, in turn.
5. I have. It whines, with a slightly muffled quality to it, and a lot of examples can be found on Youtube. It doesn't sound like a jet airliner at full power, but it does have a high pitched whine. No tank is really 'stealthy' in terms of close range acoustics, but over the horizon? You won't hear it. You might not hear it at all if you're in a vehicle with a diesel running, until it drives up. During training exercises with Canadian units using diesel driven Leo 2 tanks, this happened time and again.
6. Nemo's entire post is correct, actually, including the part about it being a more complicated logistics chain. You can adapt a diesel to cold weather using additives, and building or adapting it for that region. Pre-heaters are a necessity... Now go and try and run that cold weather adapted diesel in the desert, or the subtropics... You'll have to change it up, every time.
You don't need to do anything for the M1's turbine to function just as well in the same conditions, without additives, or modifications, or much of a warm up period. That's the advantage. You paint the tank in the proper camouflage pattern, and send it off into the Sahara or Siberia with equal effectiveness. It won't make a difference in how the power pack functions.
His point regarding deployment is spot on. One type of fuel is all that's needed, regardless of where you're going, simplifying logistics. Can't get your fuel? No problem, burn whatever you can get your hands on from allied stockpiles until it gets there, or whatever you can scrounge up in the short term.
7. I feel the need to digress a moment. I'm not trying to make a case for the Abrams being some sort of godmobile... Nothing is invincible, perfect, or without drawbacks. It's simply one of many good tanks. And the reason I used the Leo 2 as the comparison here is simple; I consider it to be a monumentally fine example of modern armor in it's own right, and is my absolute favorite. It, too, has it's flaws.