P-47 Engine Management

[R33GZ]

I know this has kind of been discussed before... I guess I'm just looking for confirmation of my theory, or correction if applicable ?

 

I have only just begun flying the D 28, but there doesn't really seem to be much point in linking the turbo, throttle and propeller controls. I have only flown QMB missions so far,  but I don't imagine multiplayer will be much different.

 

The turbosupercharger should be set to full and only needs managing when up around 30,000 ft to avoid over revving the turbo. The propeller control doesn't appear to stay linked when decreasing throttle - which is hazardous to the engine if you're not aware of this (I may be doing something wrong here)

 

I tend to mostly fly in  cruise settings and manage my energy as opposed to managing my engine if that makes sense. I don't use technochat, so tend to have a pretty good cross check going... unless I've been drinking. Obviously there are going to be times in a flight when either emergency or combat power is used, bit then its just a case of bumping the rpm and throttle up and back down when going back to cruise settings.

 

Is this the case for other people? Or am I really missing something here?

[Charon]

2 hours ago, R33GZ said:

The turbosupercharger should be set to full

You can do this, but you'll experience higher intercooler temperatures and so reduced power relative to someone who links them. It doesn't matter at combat power, for which you pin all three levers fully forward anyway, but your procedure produces a measurable speed loss at some cruise settings.

 

https://www.reddit.com/r/il2sturmovik/comments/13kq4am/p47d_boost_lever_mythbusting/jkuyx1g/

 

Quote

Here's a test I just ran: P-47D-28 at 20,000ft, standard atmosphere, Oil Neutral, Intercooler Neutral, Cowl Flaps closed, Auto-Rich, Trim Neutral, 2280 RPM, full fuel, no mods, 34.4" MP. These are straight out of the Jan 1945 pilots manual, page 50, column III*. I ran three trials**:

Full Throttle, Boost as needed: 223mph indicated.

Interconnected: 221mph

Full boost and throttled back: 206mph (a 15mph penalty!)

I then did three more trials at 30,000ft, 2290rpm, and 35.0" MP.

Full Throttle, Boost as needed: 194mph

Interconnected: 194mph

20,000 turbo RPM and throttled back: 192mph.

It's clear from this that throttling losses are indeed being modeled. The penalty for interconnecting at cruise power is small, but is measurable at some power settings and altitudes. The penalty for running full boost and then throttling back is larger.

 

 

2 hours ago, R33GZ said:

The propeller control doesn't appear to stay linked when decreasing throttle - which is hazardous to the engine if you're not aware of this

 

This is correct. The cam is there to prevent you from accidentally going full boost at low RPM, which in real life is dangerous. It's always supposed to be engaged. Low power and full RPM doesn't have the same danger, so there's no need for a bi-directional lock.

 

FWIW, I never engage the RPM-throttle cam (it would be confusing since the in-game RPM lever would update but my physical axis would not). I usually fly with the throttle and turbo connected via the lock on my split throttle, except at extreme altitudes or when flying in formation.

 

In combat at high altitudes it may be better to reduce the throttle and turbo together to keep turbo RPM in check, rather than reducing only the turbo. Different versions of the manual say different things, but this is how it was originally intended to be operated and seems to work just fine in Il-2.

Edited July 10, 2023 by I./JG3_Charon

[FeuerFliegen]

At lower altitudes, you can get a decent amount of manifold pressure using just the supercharger that always runs, and leaving the turbocharger at 0%.

 

If you run the turbo on full and throttle back to not overboost, you are wasting some or all of the energy generated by the supercharger.

 

Most efficient scenario appears to be to always utilize the supercharger first to get the boost you need without using the turbo, and if that alone isn't enough at 100% throttle, then give just enough turbo to get the power output you need.  The biggest problem is that the turbo is slow to react to changes in the boost lever, unlike just using the throttle to modulate power.

[R33GZ]

15 minutes ago, I./JG3_Charon said:

You can do this, but you'll experience higher intercooler temperatures and so reduced power relative to someone who links them. It doesn't matter at combat power, for which you pin all three levers fully forward anyway, but your procedure produces a measurable speed loss at some cruise settings.

 

https://www.reddit.com/r/il2sturmovik/comments/13kq4am/p47d_boost_lever_mythbusting/jkuyx1g/

 

 

 

 

This is correct. The cam is there to prevent you from accidentally going full boost at low RPM, which in real life is dangerous. It's always supposed to be engaged. Low power and full RPM doesn't have the same danger, so there's no need for a bi-directional lock.

 

FWIW, I never engage the RPM-throttle cam (it would be confusing since the in-game RPM lever would update but my physical axis would not). I usually fly with the throttle and turbo connected via the lock on my split throttle, except at extreme altitudes or when flying in formation.

 

In combat at high altitudes it may be better to reduce the throttle and turbo together to keep turbo RPM in check, rather than reducing only the turbo. Different versions of the manual say different things, but this is how it was originally intended to be operated and seems to work just fine in Il-2.

Thanks for the tips, much appreciated. By having a high turbo temp, the speed loss would be because of open cooling vents somewhere I assume? Might as well have it linked then in that case.

 

Still learning the beast, so I imagine there will be plenty of tweaking to come yet.

[Charon]

7 minutes ago, R33GZ said:

By having a high turbo temp, the speed loss would be because of open cooling vents somewhere I assume?

No, the intercooler shutters are manual. That eventually changed -- was it with the D-30 or only with the M/N models? I don't recall offhand.

 

I believe power is lost in two ways: one is that the air entering the engine is hotter, so there is less of it (pressure and volume stay constant, and PV=nRT) so less power is generated. Additionally, the turbo wastegates let less exhaust escape, so there is more exhaust backpressure that the engine has to work against.

 

The relative magnitude of these two effects, I don't know.

 

[LukeFF]

2 hours ago, SCG_FeuerFliegen said:

At lower altitudes, you can get a decent amount of manifold pressure using just the supercharger that always runs, and leaving the turbocharger at 0%.

 

If you run the turbo on full and throttle back to not overboost, you are wasting some or all of the energy generated by the supercharger.

 

Most efficient scenario appears to be to always utilize the supercharger first to get the boost you need without using the turbo, and if that alone isn't enough at 100% throttle, then give just enough turbo to get the power output you need.  The biggest problem is that the turbo is slow to react to changes in the boost lever, unlike just using the throttle to modulate power.

 

I don't know how practical this is in the game right now (been a while since I have flown the P-47), but at least one wartime pilot's manual suggests using the throttle alone up to the maximum power it can provide and then using the turbo lever as a second throttle when more boost pressure is needed.

 

Of course, then when the N model came out they just said, screw it, we'll have the throttle and turbo controls combined into one lever, like on the P-38.

[Charon]

1 hour ago, LukeFF said:

 

I don't know how practical this is in the game right now (been a while since I have flown the P-47), but at least one wartime pilot's manual suggests using the throttle alone up to the maximum power it can provide and then using the turbo lever as a second throttle when more boost pressure is needed.

 

Of course, then when the N model came out they just said, screw it, we'll have the throttle and turbo controls combined into one lever, like on the P-38.

 

I believe you're thinking of the April 1945 printing of the P-47N training manual, page 24 (they wouldn't adopt a unilever system until the P-47N-25). This is the one that makes the biggest deal of out using the throttle fully first.

 

You can do this, but the gains in game are very marginal: about 2mph in one test and <1mph in the other, and only apply at cruising power settings. And I think that's correct: As far as I can tell the intent when the interlocks were introduced in the C series was that they would be interlocked under most normal conditions. That didn't work out as well as hoped because of pulsation at altitude, but I think it's evidence that the performance loss from interlocking really wasn't substantial. If it was, I think the Nov 1943 printing of the pilots manual would have drawn more attention to it. I think it only gets called out in the N series manual because that was always intended as a very long-ranged model, and that inefficiency will add up when you're cruising from Iwo Jima to Japan on maximum economy settings.

 

Note that the M/N series also have a different control system under the hood, with the oil-driven A series regulators being replaced with electric C-series regulators that brought several advantages (as well as their own teething problems).

Edited July 10, 2023 by I./JG3_Charon

[R33GZ]

You've given me plenty of reasons to go for a fly gents! ?

[354thFG_Leifr]

Link throttle and turbo, and you don't have to worry about anything else other than maintaining power limits and occasional temperature blips. The supposed loss in power operating the 47 this way is negligible, the engine suffers zero repercussions for being handled incorrectly - you only have to watch temperatures. It won't blow or seize, so feel free to abuse.

Edited July 10, 2023 by 86th_Leifr

[spreckair]

...and all of this is why I have only flown the P-47 once...unsuccessfully, and not again.  Is there a good and friendly tutorial on P-47 engine management?

[easterling77]

 I would recomend Sheriff here

 

Once you got used to it - the 47 is really easy to fly

Edited July 10, 2023 by easterling77

[354thFG_Leifr]

1 hour ago, spreckair said:

...and all of this is why I have only flown the P-47 once...unsuccessfully, and not again.  Is there a good and friendly tutorial on P-47 engine management?

 

If you're happy to fly online, the 47 is all we tend to fly in the 86th - happy to help if ya wanna shout out in the online world. ?

[I./JG52_Woutwocampe]

I always interconnect the turbo with the throttle before taking off personally. I dont think that managing it apart is worth it. 

[spreckair]

@easterling77 @86th_Leifr Thank you both.  I will study the Sheriff's video and see if it gives me the courage to press on.

[CUJO_1970]

You can pick up some bad habits there because the game let's you get away with stuff you couldn't in real life.

 

For example you can run the turbo flat out in the P-47 and pull back on the throttle with essentially no repercussions. You couldn't do this IRL. You can also run full boost with lower prop pitch in the game which in real life leads to detonation and then engine damage. In the game it just makes the P-47 go faster, lol.

 

If the developers ever make the P-47 more realistic those things are going to bite you.

[the_emperor]

28 minutes ago, CUJO_1970 said:

For example you can run the turbo flat out in the P-47 and pull back on the throttle with essentially no repercussions. You couldn't do this IRL. You can also run full boost with lower prop pitch in the game which in real life leads to detonation and then engine damage. In the game it just makes the P-47 go faster, lol.

 

If the developers ever make the P-47 more realistic those things are going to bite you.

 

I problem that plagues all planes...the way engines are modelled and can be abused is something that should be dearly looked into 

as it also creates weird glitches with the arcade timer mechanic.

 

 

[FuriousMeow]

It would be nice to get more detailed engine simulation and fuel simulation, but at this price point I highly doubt it'll get through all details and intricacies. If we were paying $40+ per plane, then yeah that would be expected.

[354thFG_Rails]

The prop pitch thing really depends on the grade of fuel and other factors. To simply say that you can’t do that isn’t true. There are AAR’s of guys running lower rpm’s with high manifold pressures. The turbo full forward and throttle full back, would be true if the turbo was a straight waste gate controller. In the 47 it doesn’t control this directly. So I’m not sure it would be another risk to the pilot if operated this way. It would be very inefficient though. 

Edited July 14, 2023 by 86th_Rails

[R33GZ]

Having flown the D28 a bit more now, I link the turbo and throttle because.... well, I can just forget about it. But the propeller I leave as unlinked. Because it doesn't stay linked, I find it better to have full manual control so I don't forget about it. I can't imagine a scenario where I would engage WEP and I haven't already got every other control 'through the gate'.

 

I might try some different power settings for climbing with a heavy load next, trying to get that thing to climb with a load on is like pushing a brick uphill ?

[354thFG_Rails]

30 minutes ago, R33GZ said:

Having flown the D28 a bit more now, I link the turbo and throttle because.... well, I can just forget about it. But the propeller I leave as unlinked. Because it doesn't stay linked, I find it better to have full manual control so I don't forget about it. I can't imagine a scenario where I would engage WEP and I haven't already got every other control 'through the gate'.

 

I might try some different power settings for climbing with a heavy load next, trying to get that thing to climb with a load on is like pushing a brick uphill ?

Keep her light but don’t expect more than 2k ft/min with a decent load. Fully loaded she’ll be lucky to do 1.5k. Mind you this is at 52” and full rpm. Until they give it more lift and the correct prop don’t expect much more. 

Edited July 14, 2023 by 86th_Rails

[Charon]

9 hours ago, CUJO_1970 said:

For example you can run the turbo flat out in the P-47 and pull back on the throttle with essentially no repercussions. You couldn't do this IRL.

It's not as bad as you might think. The N series manual, for example, has instructions for how to operate the plane with the wastegates stuck fully shut (the C-series turbo regulator teething troubles I mentioned), so it can clearly be flown that way.

 

 

As far as I can tell, the P-47 runs into the following problems when operated with the boost lever full forward:

 

* Increased carburetor air temperature will result in it producing less power (this is modeled).

* At high altitude and low power settings, the engine will surge and potentially stop (I've not been able to reproduce this).

* At high altitudes this will cause the turbo to overspeed (I believe this is modeled, although I've not tested how well).

* Their may be damage to the induction system if you slam the throttle *fully* shut while the turbo is running at full speed; or the impeller may just stall. The sources are unclear on what happens. Interestingly, if you try this in game, you'll see the turbo RPM *increase*, just as sources say should happen.

 

 

[69th_chuter]

The P-47N (and M) use the C series engine which, as far as durability goes, is a different beast the the P-47D's B series engine.

[R33GZ]

On 7/15/2023 at 1:13 PM, I./JG3_Charon said:

* Increased carburetor air temperature will result in it producing less power (this is modeled).

* At high altitude and low power settings, the engine will surge and potentially stop (I've not been able to reproduce this).

* At high altitudes this will cause the turbo to overspeed (I believe this is modeled, although I've not tested how well).

* Their may be damage to the induction system if you slam the throttle *fully* shut while the turbo is running at full speed; or the impeller may just stall. The sources are unclear on what happens. Interestingly, if you try this in game, you'll see the turbo RPM *increase*, just as sources say should happen.

First point seems to be the only plausible reason in this game for why you would link the turbo and throttle then?

 

Point  2, I cant imagine a scenario where you would have  low power settings at high altitudes. You would have nearly full throttle at high alt to maintain appropriate manifold pressure?

 

Point 3, I only found I had to manage the turbo around 30,000ft which is way outside the operating alt in online and singleplayer. Generally I use the P-47 as a strike aircraft.

 

Point 4, again I just can't imagine a scenario where this would happen. Maybe an engine fire? But in that case I would have a much bigger problem than a damaged induction system.

 

Interesting info though. Where the hell did you find a pilots manual. It's an original copy?

[LukeFF]

5 hours ago, R33GZ said:

Interesting info though. Where the hell did you find a pilots manual. It's an original copy?

 

Scanned copies of pilots' manuals can be found fairly easily, and they're typically free of charge. WW2Aircraft.net is one good place to look.

[R33GZ]

1 hour ago, LukeFF said:

 

Scanned copies of pilots' manuals can be found fairly easily, and they're typically free of charge. WW2Aircraft.net is one good place to look.

Thanks Luke, I'll check it out. You did however, burst the bubble I had..... believing charon had an original copy and had scanned a section for my reading pleasure ? yes, I am an eedjit sometimes.

[Charon]

11 hours ago, R33GZ said:

First point seems to be the only plausible reason in this game for why you would link the turbo and throttle then?

 

Put another way, why wouldn't you link them? It's a system to reduce pilot workload, it's more efficient, and it doesn't even suffer defects at high altitude.

 

11 hours ago, R33GZ said:

Point  2, I cant imagine a scenario where you would have  low power settings at high altitudes. You would have nearly full throttle at high alt to maintain appropriate manifold pressure?

The P-47 will happily cruise at 30,000ft. Since the turbo lever (and not the throttle lever!) is linked to a regulator you won't even need to move the levers much as you climb.

 

11 hours ago, R33GZ said:

 

Point 4, again I just can't imagine a scenario where this would happen. Maybe an engine fire? But in that case I would have a much bigger problem than a damaged induction system.

 

Maybe cutting power abruptly in a P-47M/N which, unbeknownst to the pilot, has suffered the failure of the wastegate motors? I certainly can't think of a reason you would want to do this.

 

11 hours ago, R33GZ said:

Interesting info though. Where the hell did you find a pilots manual. It's an original copy?

 

Like Luke said, they're floating around the net. If you click through my Reddit link above, you'll find several of them bundled at the bottom of the original post.

 

[Charon]

Some other observations about how the P-47 is modeled:

 

If you leave the boost lever fully forward, cut to external view, and watch the wastegates  as you manipulate the throttle, you'll see that they open when the throttle is opened and close when the throttle is closed. This is exactly correct: the turbo regulator on the P-47 responds to exhaust backpressure. Opening the throttle lets more air in, will open to try to maintain constant exhaust pressure. The wastegates do not appear to respond when RPM is varied. This seems like a bug to me: lower RPM should also produce less exhaust pressure and so the wastegates ought to close up in response.

 

With the boost lever fully forward and the throttle held constant, the BoX version of the P-47 will maintain constant manifold pressure as altitude varies. That seems weird to me, but may be correct. I'll need to think about it more.

 

It's possible to break the engine at high altitude by closing the throttle and keeping the boost full forward, waiting for the prop to enter full fine pitch, and then advancing the throttle rapidly. This causes power to surge in just a fraction of a second, and the engine will overspeed up to around 3200. This seems dubious to me, because the later printings of the pilot's manual describe how it may take up to 30 seconds for power to return if the throttle is closed at altitude.

 

Edited July 18, 2023 by I./JG3_Charon

[354thFG_Rails]

10 hours ago, I./JG3_Charon said:

With the boost lever fully forward and the throttle held constant, the BoX version of the P-47 will maintain constant manifold pressure as altitude varies. That seems weird to me, but may be correct. I'll need to think about it more.

 

Seems right to me if the turbo is what’s being used to regulate the pressure. Turbo speed would increase as you gain altitude to maintain the set manifold. Unless it’s operating differently?