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Probably just what they have. The engine design bureau at Kharkov decamped for Chelyabinsk in 1941 and never returned. Most of the brain power behind engines was at either Leningrad or Chelyabinsk. Omsk and Stalin/Volgograd also had good teams for light tank engines. I think it is highly telling Kharkov didn't have an attached engine bureaus like the other factories did and did every thing in house. 

 

Also Uralmash did some cool stuff like the 16 cylinder engine in the Object 279. 

 

Edit: According to DAV Kharkov only did two noteworthy engine designs in the 45-65 period: 5TD and the 5TDF.

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Like I said, top-notch gas turbines are really hard to make.  As in, I can count on both hands the number of companies worldwide that can.

The Oplot seems to keep the original T-80UD engine bay dimensions, it might be too small to fit a V2-derived diesel in there.  So the two-stroke is probably their only option that gives enough power but fits into that envelope.

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Thanks to EE for the translation:



Technical documentation for the UTD-30 diesel was complete by the end of 1958. A prototype was finished in June of 1959. Compared to V-2 engines, it had better mass and size. The height was lowered by changing the cylinder angle. The piston travel distance was reduced from 180 to 150 mm, the RPM was increased from 1800-1900 to 2600. The fuel efficiency was comparable to the 5TD.

 

The overall heat transfer to water and oil was less than for the V-55 engine which had the same power. The UTD-30 was only inferior in heat transfer to the 5TD (200 kcal/h vs 150 kcal/h). The average piston speed of the UTD-30 was 13.5 m/s, which is higher than all production and experimental engines. The high power density of 435 kW/m3 was achieved by reaching higher cycle temperatures. Without applying pressure boost and by turbocharging the engine by adjusting the excess air coefficient, the developers simplified its design, but created difficulty with allowing components of the piston group to function due to higher temperatures. The temperature of discarded gases was 700 degrees and higher.

 

The pressure-boost-less variant of the UTD-30 had nearly no turbocharging reserve left. The engine needed more air, which could only be achieved by boost.

 

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  • 2 weeks later...
12 minutes ago, Ramlaen said:

Is there a simple explanation for how a transmission can get 800 HP out of a 675 HP engine?

 

That seem to defy the law of physics to me, there must be another power source.

Maybe something akin to a capacitor which would be used when you need a boost?

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18 minutes ago, Alzoc said:

 

That seem to defy the law of physics to me, there must be another power source.

Maybe something akin to a capacitor which would be used when you need a boost?

 

Perhaps I am misreading it, but I keep seeing references to 800 HP from transmission efficiencies with the new engine/transmission the Bradley family is getting.

 

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14 minutes ago, Ramlaen said:

 

Perhaps I am misreading it, but I keep seeing references to 800 HP from transmission efficiencies with the new engine/transmission the Bradley family is getting.

 

Maybe they mean that there is provision for a bigger engine if needed and that the transmissions won't be the limiting factor?

Mechanics isn't really my thing, but that's what I would say.

 

Or that the new engine have only a nominal 675 HP and can peak at 800 HP depending on the conditions and RPM (seem to be quite a far stretch though)?

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2 hours ago, Ramlaen said:

Is there a simple explanation for how a transmission can get 800 HP out of a 675 HP engine?

 

It might be the same type of logic used to defend the Merkava 3's 1,200 HP engine compared to the 1,500 HP AGT-1500C: the transmission is more efficient than the previous model, so that it can deliver more performance out of the 675 HP engine to the drive sprockets than the old transmission could extract out of a 800 HP engine. I.e. the old transmission would loose something like 150 HP out of 800 (thus effectively having 650 HP at the drive sprockets), while the new transmission would only loose 25 HP.

 

The same argument was being made by some IDF soldier in the ARMOR magazine quite a while ago - i.e. the Merkava 3's 1,200 HP would come a lot closer to the AGT-1500C due to the higher efficiency of the Renk 304S tansmission. Given that Hunnicutt claims that there are 1,232 net horsepower available in case of the Abrams', this statement was probably exaggerated.

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15 hours ago, SH_MM said:

 

It might be the same type of logic used to defend the Merkava 3's 1,200 HP engine compared to the 1,500 HP AGT-1500C: the transmission is more efficient than the previous model, so that it can deliver more performance out of the 675 HP engine to the drive sprockets than the old transmission could extract out of a 800 HP engine. I.e. the old transmission would loose something like 150 HP out of 800 (thus effectively having 650 HP at the drive sprockets), while the new transmission would only loose 25 HP.

 

The same argument was being made by some IDF soldier in the ARMOR magazine quite a while ago - i.e. the Merkava 3's 1,200 HP would come a lot closer to the AGT-1500C due to the higher efficiency of the Renk 304S tansmission. Given that Hunnicutt claims that there are 1,232 net horsepower available in case of the Abrams', this statement was probably exaggerated.

I think you misinterpreted that text. I believe I remember it quite well - the argument revolved around the suspension, and not the transmission. In some areas, the Abrams would have to intentionally limit its speed to avoid damage and excessive fatigue of the crew, whereas the Merkava 3 didn't need limitations as its suspension did a better job absorbing the shock. It was probably said in the context of the comparative trials between the Merkava 3 and M1A1 AIM a while ago. I remember nothing about comparison of the transmissions other than the intentional limitation.

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No, it wasn't an argument about the suspension. The article published in the ARMOR magazine talked about the available net horsepower at the drive sprockets - so the suspension and cross-country are not part of the equation. I.e. Richard M. Ogorkiewicz wrote in "Technology on Tanks" (published in 1991) that "in general" only up to 70% of the actual engine output are available at the drive sprockets. The author of the article in the ARMOR magazine cites this statement and claims that the Merkava 3's powerpack has a 71% efficiency, implying (because the statement referencing R. M. Ogorkiewicz said "not more than 70%") that the performance delta between the other tanks with 1,500 hp engines is smaller than the actual difference in engine output.

This is followed by a vague statement about "tanks powered by 1,500 hp engines" not performing better; the author failed to clarify if he meant in regards to efficiency, absolute net horsepower available or in regards to cross-country performance.

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That is indeed the argument that the Israeli's make in regards to the 1200hp engine in the Merkava 3.  And it's true that the Renk transmission is more efficient than the Allison transmission in the M1.  I suspect that when they claim to have similar power "at the drive sprocket", they are exaggerating a bit.  Not all the power loss is in the transmission, there is also power loss from cooling systems and other engine accessories, so even a powerpack with a 100% efficient transmission will not produce it's stated gross HP at the sprocket.  In case anyone ever wondered why the Merkava 1 has an engine with 908HP,  that figure was intentional on the part of Teledyne Continental.  The Israelis specified that they wanted a specific power output at the sprocket (I forget the number, but it was a round figure like 600 or 650) and the Teledyne engineers calculated they needed 908hp gross to get to that figure.  

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On 13/03/2018 at 2:36 PM, SH_MM said:

The author of the article in the ARMOR magazine cites this statement and claims that the Merkava 3's powerpack has a 71% efficiency, implying (because the statement referencing R. M. Ogorkiewicz said "not more than 70%") that the performance delta between the other tanks with 1,500 hp engines is smaller than the actual difference in engine output.

Tamir Eshel. It was 72% if I remember well.

 

He answered to the low horsepower per ton ratio generally considered about Merkava 3 when comparing  to others tanks. 

He noted that there is a miss understanding because the mesure must be made at the sproket level, not the engine one. 

 

I think I still have this 20 years old article. 

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This leads me to believe he was misunderstood. It is indeed illogical to say a 1200hp is just as fine but say a 1500hp provides better capabilities. Especially for a man like him.

 

Still, he points to the suspension as another key argument, and indeed many times Israeli sources like comparing the Merkava's mobility to that of the Abrams.

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His specific argument is that a tank's actual power to weight ratio is not the gross horsepower of the motor divided by the weight of the tank, but rather the sprocket horsepower divided by the weight of the tank.  Sprocket horsepower is the gross horsepower of the engine minus losses from the cooling system and the transmission.  Since the Merkava mk III is supposed to have a particularly efficient transmission, its actual power to weight ratio isn't as bad as the more simplistic numbers would suggest, and in fact the merk has no worse of a power to weight ratio than tanks that have more powerful engines, but less efficient transmissions.

 

I don't buy it.  Here is the full quote from Technology of Tanks concerning the difference between gross horsepower and horsepower available at the sprocket:

 

Quote

   The power available for propelling tanks is not however that normally quotes, which is the maximum gross engine power.  It is considerably lower than the latter, first of all because of the power absorbed by the fans required to circulate air for cooling the engine and the transmission.  With the comonly used diesel engines this amounts to between 8 and 17 percent of the gross engine power.  Some power is also absorbed by the electrical generator and any ancillary equipment that may be fitted.  Thus, net engine power is generally taken to be not more than 85 percent of the gross engine power.

  More power is lost in the transmission.  As a percentage of the power throughput, the amount lost in a typical, well-designed automatic transmission in top gear and at full load is of the order of 10 percent.  But in lower gears and at a part load, when internal losses represent a greater proportion of the power flow, it is significantly more.  The best efficiency of such a transmission is therefore no more than about 90 percent, at best.  Additional losses occur in the final drives, the efficiency of which is typically about 97 percent.  As a result, the power available at the sprocket to drive a tank amounts to only 70, or at most 74 percent of the gross engine power.  However, even at full load, it can only be 61 percent of the gross power.

 

So the Merkava has a transmission that never dips below 71% (he claims), and it's up against transmissions that are only doing 61% efficiency.  That's a 16% improvement in power actually delivered to the sprocket.  But so what?  A 1500 horsepower engine has 25% more gross horsepower than a 1200 horsepower engine, so a 1500 horsepower engine through a shitty Allison transmission is still going to be putting more ponies into the drive sprocket than a 1200 horsepower engine going through a magical Israeli transmission.  The numbers don't add up.  It's horseshit.

On top of that, in the particular instance of the Abrams vs the Merkava, the Abrams has a higher percentage of gross engine horsepower available as net engine horsepower because turbines are (nearly) self-cooling, and don't loose significant power to radiators or fans.

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Turbines also have a neat trick for battlefield mobility, as the turbine generates the most torque when it's stalled. The power output from a turbine more closely approximates the output from a magic constant-power source, whereas a piston engine (petrol or diesel) approximates a magic constant torque source. This means that a turbine puts down a much greater fraction of the peak power at low RPM, which is useful for pulling away.

 

I wonder what the suspension comparison in the first page was to? 9g at half the speed compared to 1g in the merk is a big gulf. Maybe a sherman?

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2 hours ago, Xlucine said:

Turbines also have a neat trick for battlefield mobility, as the turbine generates the most torque when it's stalled. The power output from a turbine more closely approximates the output from a magic constant-power source, whereas a piston engine (petrol or diesel) approximates a magic constant torque source. This means that a turbine puts down a much greater fraction of the peak power at low RPM, which is useful for pulling away.

 

I wonder what the suspension comparison in the first page was to? 9g at half the speed compared to 1g in the merk is a big gulf. Maybe a sherman?

How much can you stall a turbine engine before it dies? 

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2 minutes ago, Xoon said:

How much can you stall a turbine engine before it dies? 

 

There's usually more than one shaft.  The AGT-1500, for instance, has two shafts taking power from the high and low pressure turbines to the compressors, and a third, completely separate power turbine with variable inlet geometry that actually delivers the power to the transmission.  So the power turbine could be at or near stall but the rest of the engine wouldn't necessarily.

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