P-47 engine might be less susceptible to overspeed failures now (?).

[Art-J]

With Wolfpack 2 campaign getting closer to release, I've decided to refresh my P-47 knowledge a bit, engine "torture-tests" included.

Most of us remember heated debates in (closed now) threads about max RPM the engine could temporarily sustain before suffering from the dreaded master bearing failure. 3050'ish RPM being mentioned in real wartime manuals, but us not being able to get anywhere near that figure in DCS etc etc.

Well, I don't want to jinx it, but it appears that this aspect of engine simulation might've been tweaked somewhat again by ED in one of recent patches, without being mentioned in the patch notes.

I've just done a dozen or so high speed dives from 40k ft in an air-start mission I used in the past to investigate the controversial engine durability. Back in the day, letting the engine overspeed in a dive anywhere above 2750 RPM was a guaranteed damage, with extent of damage depending on how far and how long above 2750 you were. Steep 50+ degree dives were causing 100% reproducible failures after 12-15 seconds above the 2750 redline, every single time even in power-on condition.

Today, out of these dozen'ish attempts, I've got engine failure only twice, both possibly slightly above 3100 RPM. In the other attempts, the engine kept running fine even after 20+ seconds of 3000-3100 RPM (I ran out of altitude to keep it overrevving longer  ), oil temp within limits and all. I even did one 3000 RPM overspeed test with power reduced to increase master rod force reversal effect and "encourage" master bearing failure. That didn't happen though.

So, a risk of random engine failure due to overspeed still exists and has to be considered in combat, but it seems to be much smaller now.

All and all, thanks to ED for making the engine more durable (even though a relevant patch note would be nice)....

....unless it's an unwanted side-effect of February WEP-code change - in that case, please for the love of Flying Spaghetti Monster DO NOT "fix" it to where it was  .

EDIT: my test mission was using D-30 "Early". I don't think there's any difference in engine code between that one and "Late" or D-40, but you guys feel free to test these two as well.

Edited March 30 by Art-J

[grafspee]

Thank you @Art-J for noticing that.

[Gunfreak]

I'm honestly now sure how a constant speed prop cam over rev at all. 

Especially in an engine known to be indestructible. Yet the P47 engine is the most delicate engine on any warbird in DCS.

I haven't tested much in a whiile but some 7-8 months ago. I would break the engine in 10 second dives from 30k feet diving after a 190. It happened if I ran at max WEP with water on. And happened if I throttled back. A few seconds in a dive and the engine broke.

I even had it happen at low altitude shallow dives from bombing.

Dividing 20-30 degrees from 12 000 feet to 3000 feet. Would break it some 6-8 months back(this I didn't experience last time I flew the P47 a month or so back.)

[grafspee]

9 hours ago, Gunfreak said:

I'm honestly now sure how a constant speed prop cam over rev at all. 

Especially in an engine known to be indestructible. Yet the P47 engine is the most delicate engine on any warbird in DCS.

I haven't tested much in a whiile but some 7-8 months ago. I would break the engine in 10 second dives from 30k feet diving after a 190. It happened if I ran at max WEP with water on. And happened if I throttled back. A few seconds in a dive and the engine broke.

I even had it happen at low altitude shallow dives from bombing.

Dividing 20-30 degrees from 12 000 feet to 3000 feet. Would break it some 6-8 months back(this I didn't experience last time I flew the P47 a month or so back.)

Unlike every single warbird in DCS P-47 very easily over-revs prop.  You can switch to manual mode and drop rpm but in auto mode maximum pitch is lower then maximum pitch in manual mode. I didn't find any data about that but it looks suspicious that P-47 known as excellent diver  has this problem and this is only artificial problem because prop it self is capable of reaching higher pitch but auto mode don't do that for some reason. Just couple degrees more and engine dying in dive would be gone in no time.

Edited May 17 by grafspee

[Gunfreak]

1 hour ago, grafspee said:

Unlike every single warbird in DCS P-47 very easily over-revs prop.  You can switch to manual mode and drop rpm but in auto mode maximum pitch is lower then maximum pitch in manual mode. I didn't find any data about that but it looks suspicious that P-47 known as excellent diver  has this problem and this is only artificial problem because prop it self is capable of reaching higher pitch but auto mode don't do that for some reason. Just couple degrees more and engine dying in dive would be gone in no time.

I've been harping on that all warbird engines in all modern fight sims seems to be way too sensitive to surive real life and death between young men.

And doesn't seem to match any first hand accounts I've read. And I've read quite a few.

But I'm not gonna go on yet another long rant.

I still don't understand how an engine can overrev when I pull the RPM back. If I pull the RPM back to 2000rpm. In a  dive abd the needle never goes over 2000. How can i overrev it? 

Yet it the only excuse I can find for my engine dying within 30 seconds after diving after a 190.

[Andurula]

Are you sure it was failing because of an overspeed?

I would have to go back and look at the details but I remember those big round engines had a problem when there was insufficient load on the thrust bearing at otherwise normal operating speeds.

It was something about the oil flow through the bearing was stopped when in an "unloaded" condition.  Keeping some power in and forward thrust generated was the solution.

[grafspee]

8 hours ago, Gunfreak said:

I've been harping on that all warbird engines in all modern fight sims seems to be way too sensitive to surive real life and death between young men.

And doesn't seem to match any first hand accounts I've read. And I've read quite a few.

But I'm not gonna go on yet another long rant.

I still don't understand how an engine can overrev when I pull the RPM back. If I pull the RPM back to 2000rpm. In a  dive abd the needle never goes over 2000. How can i overrev it? 

Yet it the only excuse I can find for my engine dying within 30 seconds after diving after a 190.

From my experience if i over rev not higher then 2700 the  engine is fine i avod over revving above 2700. If you pulling rpm to 2000 that doesn't change max pitch in automatic mode and this will make engine over rev even at lower speeds. I mean over rev rpm above what you set not above 2700.

[Art-J]

21 hours ago, Gunfreak said:

I'm honestly now sure how a constant speed prop cam over rev at all. 

Every constant speed prop in the world has pitch limiters: fine and coarse.

In DCS interpretation of Curtiss prop the coarse limit is pretty high, so available range of blade angle adjustment is narrow, compared to other warbirds (In automatic mode at least, yes we can go past limiter in manual mode, but that's a different mystery altogether).

As airspeed goes up, governor in auto mode continuously rotates the blades towards more coarse angle to maintain RPM - but only until it hits coarse limit and cannot adjust anymore. At that point CSP effectively becomes fixed pitch prop (locked at coarse limit), thus, if airspeed still increases in a dive, so will the RPM, no matter what it was initially set to.

The prop windmills and aforementioned ED simulation of master bearing damage kicks in.

Previously the irreversible damage always happened above 2750 RPM (tacho redline). Amount of it depended on how far and how long above 2750 you were plus what the MAP was in relation to RPM was, so it could kill the engine, or not.

Maybe in current game version the damage simulation still starts at 2750, only coders know, but all and all, the engine appears to be somewhat more robust now and reliably survives short overspeeding up to about 3050'ish. That's enough for a single dive from 35000 ft to sea level, which is all we really need in realistic combat scenarios. I admit I haven't tried multiple such dives in a row in a single flight, but that would not be realistic scenario to be honest, so I don't see any sense in testing it.