A funny thing happened on the way to 30,000 feet...........

[chris455]

On 3/7/2024 at 4:52 AM, DD_Arthur said:

When my Renault 18's turbo died it became a slower but much nicer car to drive.....

?

[Charon]

How certain are we that turbo overspeed was the catalyst here?

 

I just completed a 20 minute run with the following parameters:

 

Plane: P-47D-22

Altitude: 32,000ft

RPM: ??

MP: (FT) 46"

Turbo RPM: 23800

Oil temperature: 55C

CHT: 200C

Carb Air: 0C

 

This is overspeed for the turbo, and after about 15 minutes I observed that the turbo dropped down to 20000 RPM. No engine failure.

 

I conducted a second trial:

 

Altitude: 32,000ft

RPM: 2700

MP: (FT + WEP): 48"

Turbo RPM: 25000

Oil Temperature: 50C

CHT: 200C

Carb Air: 0C

 

After about 10 minutes I noticed a small reduction of Turbo RPM, down to about 24000; this coincided with the water pressure dropping. At some point around the 15 minute mark, I observed the CHT had crept up to 230C, and the Oil to 60C. At 15 minutes on the dot, the turbo spooled down to 20000 RPM.

 

Difficulty settings: Only Spectators, Technochat, Warmed Up Engine, and Autopilot were checked.

 

I note that if spawning cold and dark, the oil cooler starts in the 'closed' position. Is it possible that you overheated this in the climb?

 

 

Edited March 13, 2024 by Charon

[chris455]

 "I note that if spawning cold and dark, the oil cooler starts in the 'closed' position. Is it possible that you overheated this in the climb?"

 

No, if you refer to my initial post you'll see I had oil temp in the green.

Your experiment certainly does raise eyebrows though. I too have noticed the oil shutters spawning in closed position, but I always check them. They weren't the problem. I have switches bound on my Thrustmaster Warthog to both the oil and the intercooler shutters to quickly adjust them if needed.

In what appeared to be the absence of any other possibility, I concluded that the turbo was the reason for the engine failure. That may have been an error. Maybe it was something else, but at thus point, I can't imagine what- 

I am intrigued by your report of the turbo spooling down by ca. 20,000 RPM after being oversped. If this is so, then it is evidence that the Devs chose to use this to portray turbo failure, and chose not to use a failure of the engine. This does nothing to explain what my engine failure was all about, but it does seem to indicate that the Devs put more thought into this than I originally assumed. 

QUESTION: When your turbo went to 2,000 RPM, could you then elevate it back up to normal speeds, or did it behave as thought it were "damaged"?

Edited March 11, 2024 by chris455

[56RAF_Stickz]

I have been able to climb to 34k at chris original settings, turbo only went to 20k ish to run 2550 and 44-45". Although I tend to go to full throttle by 4k and then just inc turbo to maintain MP. But as a thought triggered by charon showing his at 0C, I have found it is necessary to keep the carb temps noticeably above 0deg. Whilst il2 p47 has this green down to 0C the manuals I have for UK and US seem to say it should be kept over 10C. Every failure I have had appears to have been due to carb temp. It does not fail instantly - I never tried to time it, I just worked on keeping it 10-20C. I know manuals suggest keeping intercooler open unless very cold or at least neutral but from my experience climbing at continuous settings seldom needs it even at neutral. You may have froze the carb when you levelled out at alt and sped up.

[Charon]

Interesting thought @56RAF_Stickz. I took it up to 38k last night with the intercooler shutters fully open with no problems (beyond the expected handling fussiness at such altitudes), but now that you mention it I do remember the manuals talking about closing them up to combat icing. I don't think Il-2 models carb icing, though. My thinking was just that in a climb the drag wouldn't matter so much, but that the increased power from the colder air would help a little; this may have been a mistake.

[chris455]

23 hours ago, Charon said:

Interesting thought @56RAF_Stickz. I took it up to 38k last night with the intercooler shutters fully open with no problems (beyond the expected handling fussiness at such altitudes), but now that you mention it I do remember the manuals talking about closing them up to combat icing. I don't think Il-2 models carb icing, though. My thinking was just that in a climb the drag wouldn't matter so much, but that the increased power from the colder air would help a little; this may have been a mistake.

Charon, Can you address this question? 

"QUESTION: When your turbo went to 2,000 RPM, could you then elevate it back up to normal speeds, or did it behave as though it were "damaged"?"

Thank you!

Edited March 13, 2024 by chris455

[FeuerFliegen]

On 3/11/2024 at 12:27 AM, Charon said:

 

I just completed a 20 minute run with the following parameters:

 

Plane: P-47D-22

Altitude: 32,000ft

RPM: 23700

MP: (FT) 46"

Turbo RPM: 23800

Oil temperature: 55C

CHT: 200C

Carb Air: 0C

 

This is overspeed for the turbo, and after about 15 minutes I observed that the turbo dropped down to 2000 RPM. No engine failure.

 

Can you fix the typos?  I'm confused.  I'm sure you didn't mean to put 23700 engine RPM.   And only 2k RPM on the turbo?   That's barely running. 

 

On 3/11/2024 at 12:27 AM, Charon said:

 

I conducted a second trial:

 

Altitude: 32,000ft

RPM: 2700

MP: (FT + WEP): 48"

Turbo RPM: 25000

Oil Temperature: 50C

CHT: 200C

Carb Air: 0C

 

After about 10 minutes I noticed a small reduction of Turbo RPM, down to about 2400; this coincided with the water pressure dropping. At some point around the 15 minute mark, I observed the CHT had crept up to 230C, and the Oil to 60C. At 15 minutes on the dot, the turbo spooled down to 2000 RPM.

 

And here you say you were doing turbo RPM of 25k RPM, and noticed a small reduction down to 2.4k RPM (over 90% reduction being small?   Then it spooled down to 2k RPM?)  Did you mean it dropped from 25k, to 24k, then to 20k?

[Charon]

4 minutes ago, FeuerFliegen said:

Can you fix the typos? 

Corrected. Sorry, Turbo RPM is about 10x faster than the numbers I'm accustomed to thinking of and I guess I didn't proofread.

 

In the first trial I think I must have forgotten to write down engine RPM. From memory I think I had set it to the limit for continuous operation, so about 2550, but I've left that unmarked as I'm not certain.

[Charon]

1 hour ago, chris455 said:

"QUESTION: When your turbo went to 2,000 RPM, could you then elevate it back up to normal speeds, or did it behave as though it were "damaged"?"

As FeuerFliegen noticed, there was a mistake in my notes. The turbo only backed off to 20,000 rpm.

 

I did not test if there was any way to get it back above 20,000 again. My guess is that it simply throttles itself if run past a 15 minute timer, and I would guess that if you brought it to lower altitudes you would be able to make full power, since the turbo need not exceed 20,000.

[FeuerFliegen]

I'm looking forward to doing some testing again next time I get a chance to play.  I recall testing the P47 at high altitude a while ago, and I blew the engine from what I later assumed to be turbo overspeed.

 

I've also wondered how accurately the drag from the intercooler shutters are modeled.  The only thing I've noticed is that (when you're using the turbocharger) top speed is achieved when open anywhere between 40-60%.  When at low altitude, and no need to do more than 52" MP, it can be most efficient to keep the turbocharger off as the engine's supercharger is able to achieve that on it's own.   I tested the max speed at low altitude (about 1000ft) with 100% throttle,  and 0% turbo, which have me 52" MP.  I then linked the throttle to the turbo lever, and moved it to the point where it would equal 52" (can't remember exactly what % it was at,  but that's besides the point;  probably around 87-92%).  It's top speed was slower than with 0% turbo, which is accurate to real life... which I was happy to see.   Back to my main point- how accurate the drag is regarding intercooler shutters...   when I tested top speed at low altitude and no turbo, it did NOT gain any speed by closing them, vs. having them at a neutral (anywhere between 40-60%), which does not sound accurate.  Either way,  whether or not I'm using turbo,  it does slow down when opening them above 60%.

 

I do wonder if there's ever a benefit to having them fully opened though, such as in a climb, or acceleration from a low speed,  but that is much harder to test without variables, compared to just sleeving autoclaves and seeing where it ends up. 

[Charon]

2 hours ago, FeuerFliegen said:

Back to my main point- how accurate the drag is regarding intercooler shutters...   when I tested top speed at low altitude and no turbo, it did NOT gain any speed by closing them, vs. having them at a neutral (anywhere between 40-60%), which does not sound accurate.  Either way,  whether or not I'm using turbo,  it does slow down when opening them above 60%.

This behavior sounds reasonable to me. They're funny shutters that have two phases. At 0% they are fully shut, at 50% (neutral) they are flush but open, and at 100% they're open and sticking out into the slipstream.

 

Between closed and neutral they basically function as carb heat (indeed, I believe the only reason the manuals suggest closing them beyond neutral is to combat carb icing). You might get a small reduction in drag, but higher carb air temp means less air flowing through the engine even with RPM and manifold pressure held constant (remember the ideal gas law, PV = nRT) and so the engine will produce less power. (In real life doing this at high power settings is also a good way to destroy the engine very rapidly).

 

From neutral to open they stick out into the slipstream and I imagine produce a whole lot more drag. The engine will also produce a bit more power, but it makes sense to me that the drag would outweigh the power boost.

 

My intuition for when to open them matches yours. I don't know that it's optimal, but it's what I do. I never close the intercoolers below neutral (carb ice isn't modeled), I leave them neutral when I expect to be drag limited (cruise, dive, most combat) and only open them when I'm pulling high power at low airspeed, such as in a climb.

 

2 hours ago, FeuerFliegen said:

When at low altitude, and no need to do more than 52" MP, it can be most efficient to keep the turbocharger off as the engine's supercharger is able to achieve that on it's own.   I tested the max speed at low altitude (about 1000ft) with 100% throttle,  and 0% turbo, which have me 52" MP.  I then linked the throttle to the turbo lever, and moved it to the point where it would equal 52" (can't remember exactly what % it was at,  but that's besides the point;  probably around 87-92%).  It's top speed was slower than with 0% turbo, which is accurate to real life... which I was happy to see.

That doesn't sound right to me. The turbo lever only controls a regulator; if you're truly already making 52" (and I'm doubtful that you can make 52" at SL except perhaps on a very cold day) advancing the turbo lever shouldn't do anything at all. I've got a long post over on reddit about this, but my advice is to interlock the turbo and throttle under almost all circumstances, and that's how it was done in real life too. For combat power you simply push them both to the stop, and for even more power you do nothing but turn on the water. The losses you get from interlocking them are barely measurable and even then only at low power settings.

 

The only cases where you ought to disconnect them, as far as I can tell, are for start-up, economy-cruise, when in formation (it's easier to hold position in formation by using just the throttle), if you're dealing with icing and want to advance the turbo for hot carb air, and if the engine starts to surge at high altitude and low power-settings (high turbo speed with low airflow causes problems). In theory it's more efficient to split them at high altitude, once turbo overspeed becomes a concern, but at high power settings in high altitude combat I would guess that the power lost is negligible and I don't bother. Admittedly I've not run high-altitude speed tests yet.

Edited March 13, 2024 by Charon

[chris455]

Somewhere I thought I had heard that ground-boosting was to be avoided........................

[FeuerFliegen]

18 hours ago, Charon said:

The turbo lever only controls a regulator; if you're truly already making 52" (and I'm doubtful that you can make 52" at SL except perhaps on a very cold day) advancing the turbo lever shouldn't do anything at all.

 

Why not?   It takes engine power to keep the turbos spooled up.  When you spool up a turbo and don't gain any manifold pressure, all your doing is diverting power that would be used to spin the prop and putting it into other systems (the turbo).  When that turbo isn't running, the engine doesn't use extra effort needed to force exhaust gasses through the turbo-supercharger.

[Charon]

@FeuerFliegen  In an ideal world, the procedure you describe doesn't spin the turbo at all. The Boost lever doesn't directly control turbo RPM or even the wastegate position, instead it's linked to a regulator that controls the wastegates. Full boost is commanding the regulator: "spin the turbo as fast as needed to produce 52 inches of manifold pressure". That's why the boost lever has such a huge dead zone at low altitude: if you advance the boost lever to 3/4ths of its throw, you're only asking for maybe 40 inches, which you can easily achieve without spinning the turbo at all. It's only at high altitude that the lower reaches of the boost lever become live.

 

In reality the regulator isn't perfect and you may need to throttle back very slightly at low altitude to keep under 52". That's what the take-off stop is for in real life, although it's not really functional in game. But pragmatically, the speed difference between 52" interlinked and 52" at full-throttle with partial turbo is minuscule -- I challenge you to find any set of parameters where the speed loss from this exceeds 2mph. In almost all practical circumstances you're going to handicap yourself far more by micromanaging an extra throttle. The designers recognize that, which is why the pilot manuals (not the training manuals, which are for use with 91 octane fuel) all encourage the pilot to use the interlink whenever possible.

[FeuerFliegen]

I know that the turbo lever doesn't directly control the wastegate or turbo RPM, but by throttling down less than 100%, you lose the full potential of the engine's S/C and have to make it up with the turbo, so the fact is that you are more efficient at low altitude by using 100% throttle and no turbo (unless you want to push high boosted MP), vs 90% throttle-90%turbo.  That is not the same as if I tested the plane at 500ft, 100% throttle, 52", 0% turbo, and then did the same test, still 100% throttle,  but just added turbo, and still got 52" because the plane limits full combat boost to that MP anyway.  Which I will test just to see how the sim reacts.

 

Linking them, and that being more simple for most people is a different argument , which I agree that for the average person who has a hard time understanding how these systems operate, may be best.  Personally it's not over-micromanagement for me; I simply leave the throttle at 100% the vast majority of the time and just use the turbo to control power, which does give me a little bit more performance, even if it's not a massive difference; it's not taking the slightest bit more focus from me as I am still just using one lever- no different from before.  It's not as if it's using the brain power of micromanaging a plane without controllable RPM/constant speed prop such as a Bf109 E-1/E-3, or IAR-80.

 

Honestly none of that was even a point I was trying to get into;  I was only using it to point out that closing the intercooler shutters does not seem to lower drag in-game as the carb-air temps are perfectly normal with it closed when the turbo is not spooled up; there is zero difference in top speed when you move the intercooler shutters between 0-60% in this situation.

[FeuerFliegen]

I did the same test at over 30k feet, seeing what would happen with the turbo if it was left overrevving for excessive time; same thing happened to me where it dropped to 20kRPM.

 

I feel like this is a change in the engine modeling, as I recall doing a similar test a few years ago and it destroyed the engine.