Current engine power setting modeling seems too limited

[MANDO]

Actually we can go from idle to some maximum power setting called "MIL", and then we jump to max power switching on wep.

With the exception of having WEP switched on, any throttle position will have little negative effect during combat, except fuel consumption. Engine will not overheat at all even running forever at maximum military power. But what we have as MIL was not a safe power setting at all for most fighters. Every engine had what was called max continuous power, usually below than our current MIL power.
I understand that any throttle position above max continuous will start to raise the engine temperature, and the available WEP time should be reduced also.

We can use 190A5 as an example. At sea level, its engine had a max continuous power output of 1365 Hp. 1550 Hp was the normal "climb and combat" power setting (1.32 ata, what we call MIL), but it was limited to 40 mins. 1780 Hp (1.42 ata) was its maximum power output at sea level, but it was limited to 10-15 mins. Flying the 190A5 at MIL power for 20 mins should limit the WEP time to 5 or 7 mins. To effectively cold down the engine, we should reduce power output to 1.20 ata / 2300 rpm or less, not just switching off WEP and keeping MIL (1.32 ata 2400 rpm).

Modeling this in AH would impact the air combat much more than the current fine tuned fuel consumption per power setting.

[Karnak]

Originally posted by MANDO
Actually we can go from idle to some maximum power setting called "MIL", and then we jump to max power switching on wep.

With the exception of having WEP switched on, any throttle position will have little negative effect during combat, except fuel consumption. Engine will not overheat at all even running forever at maximum military power. But what we have as MIL was not a safe power setting at all for most fighters. Every engine had what was called max continuous power, usually below than our current MIL power.
I understand that any throttle position above max continuous will start to raise the engine temperature, and the available WEP time should be reduced also.

We can use 190A5 as an example. At sea level, its engine had a max continuous power output of 1365 Hp. 1550 Hp was the normal "climb and combat" power setting (1.32 ata, what we call MIL), but it was limited to 40 mins. 1780 Hp (1.42 ata) was its maximum power output at sea level, but it was limited to 10-15 mins. Flying the 190A5 at MIL power for 20 mins should limit the WEP time to 5 or 7 mins. To effectively cold down the engine, we should reduce power output to 1.20 ata / 2300 rpm or less, not just switching off WEP and keeping MIL (1.32 ata 2400 rpm).

Modeling this in AH would impact the air combat much more than the current fine tuned fuel consumption per power setting.

None of which actually means anything as they are almost always maintainance based rating limits.

For example there was a ground test of an R2800 that had it run at WEP boost for 100 hours straight, and it did so with no problems.

In fact, barring the cooling problems of early P-38s or the quality problems of later Axis engines, pretty much any aircraft could run at WEP for a lot longer than AH allows.  Heat was not the limiting factor on WEP.  Fuel, or MW50 / GM1 / NO2 reserves were usually the limitation.  Well, that and the hell your crew chief would give you after having to overhaul the engine early.

[Swoop]

Originally posted by Karnak
there was a ground test of an R2800 that had it run at WEP boost for 100 hours straight

Can you explain this one some more?


By ground test you mean the aircraft was either stationary on the tarmac or the engine had been ripped out and bolted to a workbench?

Were some very large fans used to create a simulation of air flow?

Come to think of it, is the R2800 air cooled or liquid cooled?


Help me out here cos I'm just having a hard time visualising any engine on the planet running at full power for 100 hours without the proper cooling of being in the air at 400mph.

[Crumpp]

Slick 50!!

You did not see that, Swoop?  In fact I think they removed the oil pan on that PW 2800 and soaked the crank down with water from the garden hose.....


Crumpp

[Captain Virgil Hilts]

Originally posted by Swoop
Can you explain this one some more?


By ground test you mean the aircraft was either stationary on the tarmac or the engine had been ripped out and bolted to a workbench?

Were some very large fans used to create a simulation of air flow?

Come to think of it, is the R2800 air cooled or liquid cooled?


Help me out here cos I'm just having a hard time visualising any engine on the planet running at full power for 100 hours without the proper cooling of being in the air at 400mph.

Swoop,
The test I saw was a dyno test, where they coupled the engine to a dynamometer (measures torque, and from there you calculate HP) and over boosted it to 3400HP and ran it for about 48 hours. And yes, they cool it with very large fans, and they also attach oversize oil coolers, and use them to keep the oil temprature at the same level as it would be in flight under power.

The R2800 is air cooled, it is a radial. They use large oil coolers because with non watercooled engines oil is even more important as a coolant. Even in watercooled engines, oil carries at least 50% of the heat load of the engine.

We have two dynos here in the shop I am partners in. For testing we use oversize radiators and oil coolers to keep the engines at temperatures they'd see in the vehicle operating at speed.

I hope this gives you some idea about how the tests work.

[HoHun]

Hi Hilts,

>Even in watercooled engines, oil carries at least 50% of the heat load of the engine.

Well, not in the sense of transmitting it to the ambient temperature.

The power breakdown of the DB605A at Climb/Combat power looks like this:

Energy content of fuel: 3420 kW
Power at the shaft: 920 kW
Oil cooling: 50 kW
Water cooling: 400 kW
Exhaust energy: 2050 kW

(From Daimler-Benz documents.)

So the oil carries about 2.4% of the heat load of the engine to the ambient air, or 11% if you only look at the heat load dissipated by the radiators.

Regards,

Henning (HoHun)

[Captain Virgil Hilts]

Originally posted by HoHun
Hi Hilts,

>Even in watercooled engines, oil carries at least 50% of the heat load of the engine.

Well, not in the sense of transmitting it to the ambient temperature.

The power breakdown of the DB605A at Climb/Combat power looks like this:

Energy content of fuel: 3420 kW
Power at the shaft: 920 kW
Oil cooling: 50 kW
Water cooling: 400 kW
Exhaust energy: 2050 kW

(From Daimler-Benz documents.)

So the oil carries about 2.4% of the heat load of the engine to the ambient air, or 11% if you only look at the heat load dissipated by the radiators.

Regards,

Henning (HoHun)

It does depend on the engine and the installation. Sometimes you'll find that the cooling system in a water cooled engine installation is designed to make up for the fact it doesn't have a good oil cooling system.

It is actually the oil itself that transfers heat out of the pistons, rings, valves, and bearings. Now, you can cool the oil itself with an external oil cooling system, or you can allow the oil to transfer the heat to a water jacket and use water to carry off the heat. It depends on the desires of the engineers and the parameters they have to work with.

[HoHun]

Hi Hilts,

>It is actually the oil itself that transfers heat out of the pistons, rings, valves, and bearings. Now, you can cool the oil itself with an external oil cooling system, or you can allow the oil to transfer the heat to a water jacket and use water to carry off the heat.

Hm, according to von Gersdorff et al., the oil cooling amounts to 10% or slightly above (which would match the DB605A example), while the remaining 90% are transferred by wall cooling.

Regards,

Henning (HoHun)

[gwshaw]

Originally posted by HoHun
Hi Hilts,

>It is actually the oil itself that transfers heat out of the pistons, rings, valves, and bearings. Now, you can cool the oil itself with an external oil cooling system, or you can allow the oil to transfer the heat to a water jacket and use water to carry off the heat.

Hm, according to von Gersdorff et al., the oil cooling amounts to 10% or slightly above (which would match the DB605A example), while the remaining 90% are transferred by wall cooling.

Regards,

Henning (HoHun)

Depends on the engine. The Allison dumped about 2x as much of its heat load into the oil as the Merlin did. I'll see if I can find the figures, but it seems like it was something on the order of 25-30% for the Allison, vs 10-15% for the Merlin. Helped make the Allison much less vulnerable to coolant loss than the Merlin. Along with the liquid phase vs vapor cooling the Merlin used.

Greg Shaw

[gwshaw]

Originally posted by Swoop
Can you explain this one some more?


By ground test you mean the aircraft was either stationary on the tarmac or the engine had been ripped out and bolted to a workbench?

Were some very large fans used to create a simulation of air flow?

Come to think of it, is the R2800 air cooled or liquid cooled?


Help me out here cos I'm just having a hard time visualising any engine on the planet running at full power for 100 hours without the proper cooling of being in the air at 400mph.

The US standard was to run any engine on the test stand for 100 or 150 hours at a rating before authorizing it. Put a load on it, either a dynometer or some used them for generators, then run em till they broke or passed. Then tear it down and see what broke. IIRC the British standard was half the time the US required. Not sure about the German standards.

Air-cooled would be cooled by fans of some sort, liquid cooled would have oversized radiators or heat exchangers setup.

Greg Shaw

[joeblogs]

If you look for articles at enginehistory.org, you'll see a number of stories by a Rolls Royce engineer describing how these engines are run through their paces. By WWII, the minimum test was 100 hour and a good part of that was at rated power.

WEP is actually easier than military power on the engine as you get better cooling in the cylinder. But it does affect the valves and the plane will come to an overhaul faster.

-Blogs

Originally posted by Swoop
Can you explain this one some more?


By ground test you mean the aircraft was either stationary on the tarmac or the engine had been ripped out and bolted to a workbench?

Were some very large fans used to create a simulation of air flow?

Come to think of it, is the R2800 air cooled or liquid cooled?


Help me out here cos I'm just having a hard time visualising any engine on the planet running at full power for 100 hours without the proper cooling of being in the air at 400mph.