correcting RPM/MAP -> reduced rpms (for longer WEP MAP time) with high/max MAP not allowed

[the_emperor]

Currently the time of use of certain Engine Settings (e.g. WEP) can be increased by decreasing rpms while keeping a high (maximum) MAP.

examples:

Spitfire IX 18lbs@2600rpm (instead of 3000) from 5min to 15min

La-5fn 1180m@ 2400rpm (instead of  2500) from 10min to 20min

Bf 109 G-14 1.7ata@2600rpm (instead of 2800) from 10 min to ~20min

 

This goes contrary to the  manuals. High MAPs need the correct corresponding rpms to prevent damage to the engine. You must always increase rpms first before increasing MAP / decrease MAP before decreasing rpms.

There should be no benefit like longer WEP time when using full MAP with reduced rpms. It should be quite the opposite. When operating high MAP with lower than recommended rpms you should fly with reduced time on your current setting (especially at full WEP MAP).

 

Pilot Training manual P-40 1943:

 

 

Pilot´s notes general, April 1943

 

 

 

 

 

P-40N/Kittyhawk Pilots flight operating instructions

September 1944

 

 

 

 

 

From Allison V-1710-F manual April 1943:

 

 

 

 

 

 

 

Spitfire Mk V

Air Publication 1565E & 2280 A, B & C

Pilot Note‘s Spitfire VA, VB and VC

And Seafire IB, II and III

 

 

 

Spitfire Mk IX

Pilot Notes‘s for Spitfire IX, XI, XVI

Merlin Engine 61, 66, 70 or 266

Air Publication 1556j

3rd Edition September 1946

page 33

 

Spitfire Mk VIX

Pilot Note‘s for

Spitfire XIV & XIX

Griffon 65 or 66 engine

Air Publication 1565T 2nd Edition April 1946

page 39

 

 

 

 

Pilots flight operating instructions P-51 D-5 April 1944,  AN 01-60JE-1:

 

Pilot training manual P-38, AAF Manual 51-127-1

 

They even installed auxiliary systems to prevent that from happening (IIRC later Spitfires also employed such system whit connected throttle and propeller)

 

 

 

 

 

 

Typhoon/Tempest

 

 

HANDBOOK OF Operation and Maintenance for Allison V-1710 "E" Type Engines April 1944

 

P-63 manual

 

P-39Q flight manual

 

 

 

 

Edited May 15, 2024 by the_emperor

[Sgt_Joch]

Hi, there seems to be a lot of confusion about this topic on the forum, what you say about the relationship between RPM and manifold pressure is true, but that only applies to naturally aspirated engines. This is not an issue in the game since every WW2 prop engine in the game has a supercharger/turbocharger/turbosupercharger, etc. This means that either MP stays fixed when RPM changes or the MP increases when RPM is increased or vice versa, i.e. P-40E.

 

more info here:

 

Now it is true that running an engine at a high MP with very low RPM could potentially cause detonation and damage the engine, but not sure that what players are doing, i.e. running at a RPM of 2600 instead of 3000 qualifies as that and will necessarily cause immediate damage.

 

Edited December 18, 2022 by Sgt_Joch

[Charon]

@Sgt_Joch, I think you're misunderstanding the request. It's not about MAP response to RPM changes (as you note, almost everything in the game has regulators), but rather about how readily engines should be destroyed by detonation when running at (absolutely forbidden) low RPM / high MAP settings.

Incidentally though, it's not correct to say that "either MP stays fixed when RPM changes or the MP increases when RPM is increased or vice versa". For instance, from "Pilot Trailing Manual for the P-40":

Spoiler

 

[=MERCS=JenkemJunkie]

It's very likely an unintended glitch/quirk from how the game calculates the timers. I've noticed that the RPM trick only works when the mode underneath it has a lower RPM value. Using the Spit 9 and 51 as examples, the trick works on the Spit because it's combat mode uses 2850 RPM, and WEP uses 3000. On the 51 it doesn't work because it uses 3000 RPM for WEP and combat. I'm guessing when the game is calculating how fast the timer is being used on the Spit 9, the game sees that the Spit is running combat RPM and adjusts the rate the timer is being eaten to a much slower value, but when the mustang is running a lower RPM the game doesn't recognize the lower RPM as combat RPM and doesn't adjust the rate to be slower. Oddly if you drop the RPM to the continuous level in the 51, the game won't recognize that as continuous RPM and give you a much longer timer, so it appears the game won't calculate the timer using the value 2 modes down (like from WEP to continuous), but will give you the bonus when you're only going down 1 mode (like from WEP to combat, or combat to continuous). As a solution 1C could just look at whatever game logic is causing the bonus not to apply 2 modes down, and just apply that to the game logic of going 1 mode down.

[357th_KW]

2 hours ago, Charon said:

It's not about MAP response to RPM changes (as you note, almost everything in the game has regulators), but rather about how readily engines should be destroyed by detonation when running at (absolutely forbidden) low RPM / high MAP settings.

 

It's worth noting that not all engines were equivalent in this regard.  There are numerous accounts of P-38's suffering engine failures due to pilots increasing manifold pressure prior to mixture and RPM.  On the other hand, there are accounts of Spitfire and Mustang pilots intentionally using lower RPMs with high throttle settings.

 

" I found that with full throttle and 2800 revs. I did a steep climbing turn to starboard which easily out-turned the M.E. 109. "

 

"Automatically I have followed my self-imposed drill that I always do at times like this. Reflector sight on; gun button to fire; airscrew pitch to 2,650 revs; better response. Press the emergency boost override."

 

"Another effective form of evasion with the Spitfire was found to be a steep, climbing spiral at 120 mph, using +6 1/4 boost and 2,650 rpm"

 

"... I decided to break off combat.  I left the two FW 190s on top of the circle, dumped flaps, applied 60 Hg. and 2,700 R.P.M. and got the hell out of there.  Jerry still pursued but I left them entirely."

 

" The aileron turn threw them off and with over 500 m.p.h. on the clock I climbed like a rocket at 18 lbs. boost and 2,900 revs in a steep climbing turn."

Edited December 18, 2022 by 357th_KW

[=MERCS=JenkemJunkie]

The timers follow their own game logic, and aren't simulated based on real world logic. To understand what's going on with them it's better to forget everything you've read about real world examples.

[Charon]

By the way, "Pilot Training Manual for the P-38 Lightning" (AAF Manual 51-127-1) has the following illustration on page 72:

 

Edit: Did I overlook this chart in the original post, or did they go back and edit it to include this? I'm not sure.

Edited December 19, 2022 by Charon

[=MERCS=JenkemJunkie]

That's not how the P38 works in game, you can rapidly slam the RPM back and forth from 0-100% with max throttle and not break your engine (which can be helpful when you need to chop the throttle, and don't want to deal with the turbocharger winding up and down slowly). That chart shows you should reach detonation IRL if you run 54" / 2700 RPM, but in game you end up extending your combat timer like that. The trick doesn't extend your WEP timer because combat/WEP use the same RPM, but it also doesn't break your engine like it should IRL. 

[the_emperor]

16 hours ago, Sgt_Joch said:

Now it is true that running an engine at a high MP with very low RPM could potentially cause detonation and damage the engine, but not sure that what players are doing, i.e. running at a RPM of 2600 instead of 3000 qualifies as that and will necessarily cause immediate damage.

 

Yes, it probably will do you no good. As the manuals specifically describe, that must not increase MAP before rpm. and use of WEP is not allowed if you have not increased rpms to max. and as the game goes strictly by the manuals (not my preferred choice, but it is what it is) that should apply. So running WEP with the wrong rpms should reduce your WEP-time not increase.

[Sgt_Joch]

7 hours ago, the_emperor said:

 

Yes, it probably will do you no good. As the manuals specifically describe, that must not increase MAP before rpm. and use of WEP is not allowed if you have not increased rpms to max. and as the game goes strictly by the manuals (not my preferred choice, but it is what it is) that should apply. So running WEP with the wrong rpms should reduce your WEP-time not increase.

 

My understanding is that a low RPM/high MP combo is only potentially dangerous if taken to extreme.

 

Reducing RPM moderately to reduce the strain on the engine is routine and should not cause any damage to the engine, i.e.:

 

Is High Manifold Pressure With Low RPM (Oversquare) Bad? – Airplane Academy

 

Savvy Maintenance - AOPA

 

Mustang and Spitfire pilots routinely set lower RPM than recommended, as posted above. Additionally, when Charles Lindbergh was sent to the South Pacific in 1944, he convinced P-38 pilots to adopt the following technique to extend their range:

 

"Mr. Lindbergh" wanted to explain how to gain more range from the P-38s. In a pleasant manner Lindbergh explained cruise control techniques he had worked out for the Lightnings: reduce the standard 2,200 rpm to 1,600, set fuel mixtures to "auto-lean," and slightly increase manifold pressures. This, Lindbergh predicted, would stretch the Lightning's radius by 400 hundred miles, a nine-hour flight.

 

Charles Lindbergh and the 475th Fighter Group

 

no reason why the settings listed as example, i.e. Spit at 2600 RPM instead of 3000 or La5fn at 2400 RPM instead of 2500 should damage the engine as long as temperatures are in the normal range.

 

So this is not an engine damage issue, it is a "timer" issue. Note that the technique of extending timers by lowering power is well known and can be used on all ACs. As I recall, you could extend the FW190 emergency power timer up to 15 minutes, up from 3 by setting RPM around 2550. 

 

Note also that there is no free ride, lowering RPM will also generally lower HP and speed.

 

Most players want timers to be loosened or have an option to turn them off altogether, I doubt anyone wants to make them more restrictive.

 

 

[=MERCS=JenkemJunkie]

The problem is that the RPM trick isnt something that was consciously put in place based on data, it's the result of a glitch in how the timer is calculated that I described above. Ideally it should either be implemented as a conscious decision based on real data, or it should be globally added or removed from all planes, instead of some planes getting lucky due to a glitch as it is now.

[Charon]

4 hours ago, Sgt_Joch said:

My understanding is that a low RPM/high MP combo is only potentially dangerous if taken to extreme.

 

Correct.

 

Look to your airplane academy link, for example, and you'll notice that they're talking almost exclusively about naturally aspirated engines running <30" (which most GA pilots these days are flying). This is a very safe regime. You'll note that the P-38 manual I screenshotted above lists everything under 34" as safe from detonation, even at lean mixture and 1600 RPM.

 

They do briefly touch on the Turbo Skylane RG (still at only 31") -- even then, of course, the POH calls for full(?) 2400 RPM when using take-off power.

 

Note also that they're rebutting a very extreme interpretation of this rule ("don't let MAP in inches of hg exceed engine RPM in hundreds"). That's clearly a nonsense rule, firstly because the units are totally unrelated, but also because it doesn't account for factors like compression ratio or carb air temp that we know are very relevant to detonation. GA pilots seem prone to this sort of thinking, because they're risk averse and also want to stretch TBO as long as is safe, so they sometimes adopt these stupidly conservative rules. They've got similar rules about never operating undersquare that are nonsense for similar reasons.

 

Rules like "always advance RPM before advancing throttle" aren't important because failing to do so causes detonation in all regimes. Rather, it's a good habit to establish so that you do things in the right order when in the high-power regime where it matters.

 

4 hours ago, Sgt_Joch said:

Additionally, when Charles Lindbergh was sent to the South Pacific in 1944, he convinced P-38 pilots to adopt the following technique to extend their range:

 

"Mr. Lindbergh" wanted to explain how to gain more range from the P-38s. In a pleasant manner Lindbergh explained cruise control techniques he had worked out for the Lightnings: reduce the standard 2,200 rpm to 1,600, set fuel mixtures to "auto-lean," and slightly increase manifold pressures. This, Lindbergh predicted, would stretch the Lightning's radius by 400 hundred miles, a nine-hour flight.

 

Charles Lindbergh and the 475th Fighter Group

 

Note maximum economy cruise is 30" and 2300 RPM, by the manual (maybe 2200 in some revisions, I'm not sure). 1600 and 33" would match his "slightly higher MAP", and is still within what the manuals lists as safe from detonation.

4 hours ago, Sgt_Joch said:

Reducing RPM moderately to reduce the strain on the engine is routine and should not cause any damage to the engine, i.e.:

 

Not in supercharged engines pulling full MAP it's not. We know that detonation was the limiting factor for power, the reason they didn't just jam 100" down the intake with big superchargers:

 

 

-- Harry Ricardo, The High Speed Internal Combustion Engine, p27.

 

Yes, it's true that a mild detonation can be tolerated for some time, but at high power settings it becomes dangerous. There's a reason that both of the USAAF's turbocharged fighters were fitted with throttle hooks to prevent pilot accidentally advancing throttles without RPM (as posted above).

 

4 hours ago, Sgt_Joch said:

Mustang and Spitfire pilots routinely set lower RPM than recommended, as posted above.

 

@357th_KW unfortunately doesn't provide much information about what particular models those are or what their RPM limits were. I do note these are generally still high RPM. Of the two reporting the lowest RPM (2650), note that one only pulls +6 1/4  Boost (still within permissible cruising power for at least some Spitfires) and the other never says they push full power, only that the press the boost override so they have power available should they need it.

 

My inclination though is to believe that some of these pilots probably should have been using higher RPM. I'm not saying 2700 RPM and 60" will always break an engine instantly... only that it's dangerous, that the manual likely warns against it, and that it has the potential to break the engine more quickly than most of the things the pilot can do to it. Maybe it's the sort of thing you can get away with at 30,000ft in the winter over Germany and that melts a piston at 1,000ft in the summer over Sicily. Ambient temperature affects this, too.

 

4 hours ago, Sgt_Joch said:

no reason why the settings listed as example, i.e. Spit at 2600 RPM instead of 3000 or La5fn at 2400 RPM instead of 2500 should damage the engine as long as temperatures are in the normal range.

The reason this damages the engine is that it advances peak pressure and puts it closer to TDC, which puts more heat into the cylinder walls and can contribute to runaway pre-ignition until a hole melts through the piston or the cylinder wall. Note that it's possible for this to happen in only a single cylinder, and it's difficult to catch this temperature increase from aggregate measurements like water temperature. This is why some planes have per-cylinder CHT indicators, as you'll find implemented in CloD: Tobruk.

 

4 hours ago, Sgt_Joch said:

Most players want timers to be loosened or have an option to turn them off altogether, I doubt anyone wants to make them more restrictive.

 

To be clear, I think making high, even full, RPM unrestricted is the sensible way to loosen timers. The manuals all make it clear that high MAP/low RPM is dangerous and forbidden, while carrying few or no warnings about high RPM settings. Let me put engines at full RPM when I enter combat and then operate purely by throttle.

 

If the timers are going to exist, they should at least break engines that are operated in ways that every manual agrees should never be done.

Edited December 19, 2022 by Charon

[the_emperor]

Thanks @Charon, very Informative.

4 hours ago, Sgt_Joch said:

Mustang and Spitfire pilots routinely set lower RPM than recommended, as posted above. Additionally, when Charles Lindbergh was sent to the South Pacific in 1944, he convinced P-38 pilots to adopt the following technique to extend their range:

IIRC this only applied to lower Cruise MAP settings never to combat or WEP  settings.

And again the game and devs made clear that the  manuals are the “law” and are applied strictly. And the manuals are clear on this and explain why.

 

[357th_KW]

The first few quotes were from early Spits, so that +6 lbs was a fairly high setting on that engine.  The last two were from a P-51B and a Spit IX respectively, and so the most applicable to us here.  60” is nearly the military power (15 minute limit) manifold pressure on the 51, but he ran it with 2700rpm.  And +18lbs was the emergency limit on a Merlin 63 or 66 (that quote is from 1943, could be either), running with 2900rpm.  
 

My point here is just like with the timers themselves, where we have pilot accounts and test data showing that the numbers in the manuals weren’t always hard limits, there’s a gray area.  I seem to recall there is even some Russian test data for the Yak showing that they achieved higher top speeds in testing by using an “over-square” setting with reduced rpm.  I’d hate to see yet another binary system implemented where doing things that we know were actually done in combat, causes your engine to immediately fail.

[Charon]

2 hours ago, dogefighter said:

P-51 pilots flying long range missions from Iwo Jima on the power settings they used:

 

Captain Howard Russell, 72nd Squadron:
Special power settings for our Merlin engines had been prescribed, but not really tested by us. High manifold pressure and low RPM were specified. It was said that these settings were developed and tested by Charles Lindbergh. A rather unsettling procedure resulted: Set the manifold pressure at 36 inches, RPM at 2,000. Reduce RPM until engine cuts out (about 1,750 to 1,800 RPM), then ease the RPM forward until you got a smooth engine, all this in auto-lean.

Sketchy! And note "high" manifold pressure here is still only 36".

 

2 hours ago, dogefighter said:

This was historically murder on engines and against all the rules we had been taught about engine care. But it worked, even though some engines were ruined by the time the flight was over. Severe piston burning was often the result, but most of the engines made it.

 

I stand by my assertion that this is hard on engines. "Most of the engines made it", lol.

 

2 hours ago, dogefighter said:

Harry Crim explained "We set the rpm on about 1 800 with full throttle at 10,000 feet, pulled the mixture back until our wingman signaled the coolant shutter was coming open, then eased it forward just a tad. This setting worked like a charm, though the mixture control was set up to fly only in selected places. We would indicate about 210 and burn about 40 gallons per hour. This would burn up a set of plugs but it didn't seem to bother the engines."

 

https://www.506thfightergroup.org/index.asp

 

Oh, this is really cool.

 

I'm not sure why this works, but I suspect it's because the overall power output is so low (as evidenced by the low indicated speed, much lower than at maximum cruise). I expect the combination of altitude and low RPM prevents the supercharger from actually delivering all that much manifold pressure to the engine. I'd guesstimate much closer to 36" than to 60", even with the throttle wide open. The fact that they burned up plugs doing this suggests to me that they probably were pre-igniting the whole way, because overheating spark-plug electrodes usually go hand-in-hand with pre-ignition

 

-- Ricardo, p41

 

Fun party trick: cut the magnetos off and watch your engine keep running:

 

-- Ricardo, p40

 

In fact, I see now these are not so different than the "Column V" (maximum range) power settings for the -7 engine given at the back of "Pilot Training Manual for the P-51 Mustang" (51-127-5):

 

 

Note this calls for a slightly higher altitude (15k vs 10k) before going full throttle at 1,800 rpm. MP at full throttle (F.T.) is probably only a little higher than the 10k value, so probably 33-34". The manual leaning seems to have gained them about 10gph, at the cost of burning out the plugs.

 

----

 

Don't get me wrong, I think I find this sort of engine nerd stuff way more interesting than the average simmer, and I'd be absolutely delighted by an engine model that handled all these weird edge cases. But I'm trying to be realistic about it: long-range economy cruising isn't a focal point of the sim, and I don't expect the devs want to focus on realistic low power operations.

 

What is very prominent is high-power operations. The sim right now is in the very weird position of encouraging players to dogfight using very high power settings but reduced RPM, even as the manuals loudly scream not to do this. And this seems amenable to a simple quick fix, even if full fidelity engine modeling is deferred to some other day.

Edited December 20, 2022 by Charon

[Charon]

2 hours ago, 357th_KW said:

 I seem to recall there is even some Russian test data for the Yak showing that they achieved higher top speeds in testing by using an “over-square” setting with reduced rpm. 

Something about power curves? This may just be a case of the governor being configured to permit RPMs on the high side of peak power, even while other aircraft designers saw no reason to ever run the engine that fast. I admit that power bands aren't something I know much about.

[the_emperor]

7 hours ago, 357th_KW said:

I seem to recall there is even some Russian test data for the Yak showing that they achieved higher top speeds in testing by using an “over-square” setting with reduced rpm.  I’d hate to see yet another binary system implemented where doing things that we know were actually done in combat, causes your engine to immediately fail.

 

(for 1050mm (~41inches) mercury I would guess.)

 

I would like to make clear, that I did open this thread to question (again, I know) the current engine modelling and behaviour/shenanigans in regards to full/very high MAPs (in some cases directly contradicting the manuals),

therefore my suggestions to give us an the option the turn of the current engine timer mechanic:

 

Edited December 20, 2022 by the_emperor

[Sgt_Joch]

14 hours ago, Charon said:

My inclination though is to believe that some of these pilots probably should have been using higher RPM. I'm not saying 2700 RPM and 60" will always break an engine instantly... only that it's dangerous, that the manual likely warns against it, and that it has the potential to break the engine more quickly than most of the things the pilot can do to it. Maybe it's the sort of thing you can get away with at 30,000ft in the winter over Germany and that melts a piston at 1,000ft in the summer over Sicily. Ambient temperature affects this, too.

 

 

The reason this damages the engine is that it advances peak pressure and puts it closer to TDC, which puts more heat into the cylinder walls and can contribute to runaway pre-ignition until a hole melts through the piston or the cylinder wall. Note that it's possible for this to happen in only a single cylinder, and it's difficult to catch this temperature increase from aggregate measurements like water temperature. This is why some planes have per-cylinder CHT indicators, as you'll find implemented in CloD: Tobruk.

 

I am aware of how detonation work, but I have yet to see any evidence that lowering RPM by 5-10% will keeping boost constant would lead to detonation and immediate destruction of the engine. If anything, lowering the RPM while keeping MP constant would reduce the engine workload and should lead to cooler engine temperatures which would lower the risk of detonation. If the engines are running cooler, that may be part of the reason why the P51 spark plugs were fouling when using their low RPM/high MP regime.

 

If lowering RPM 5-10% while keeping MP at 100% lead to quick destruction of the engine, we would have the empirical evidence for that, i.e. pilot accounts, field reports, test results, etc. Here we have no empirical evidence to back up this theory. If anything the "evidence" presented so far is that there are actually benefits to running an engine at lower RPMs.

 

Contrast that with the situation of the early DB605 used in the 109G. We have multiple accounts of engine fires, engine failures in the air, reports of pilot deaths like the ace Hans-Joachim Marseille, LW reports on the failures and the reason why using 1.42 ata was prohibited, etc.

 

The Devs are not going to make changes to the game when there is no evidence to show that it was actually a problem in real life especially when the only net effect of the change is to give MP players who fly German planes an advantage over players who fly western allied/Russian planes.

 

Edited December 20, 2022 by Sgt_Joch

[=MERCS=JenkemJunkie]

The issue is that this trick works due to a glitch. Where is the documentation that says for example a spit 9 should work for 5 minutes at 3000 / +18 and 15 minutes at 2850 / +18, but that this same trick doesnt apply to a 51? The games timer logic is all over the place, and could use an update that standardizes them and makes them more transparent, and ideally also an option to remove them. It's not a red vs blue issue either, because it works for the blue boys too using the same glitch rules. For example all 3 MW 50 109s can get 20 minutes on the deck if you run 2650 RPM with manual prop pitch. It's a glitch and should be cleaned up.

[CUJO_1970]

High pressure - low  RPM lol - it's nothing but an engine hack. Been that way for years.

 

High MAP, low RPM leads to detonation in real life. In the sim = longer WEP use, higher top speeds (in some cases way higher) by doing things that would ruin an engine in real life. I do hope they fix it soon

[Hitcher]

Blue mains HATE this one simple trick! Click to find out why!

[=MERCS=JenkemJunkie]

On 12/20/2022 at 10:44 AM, =MERCS=JenkemJunkie said:

It's not a red vs blue issue either, because it works for the blue boys too using the same glitch rules. For example all 3 MW 50 109s can get 20 minutes on the deck if you run 2650 RPM with manual prop pitch. It's a glitch and should be cleaned up.

I know you're just joking, but 1C will be less likely to take a second look at timers, if it all just gets dismissed as whiny blues.

[Charon]

Just to throw a wrench in things:

 

Pratt and Whitney, "The Aircraft Engine and it's operation".

 

This seems weird to me, as it's the inverse of what other sources instruct. My first thought was that it was all down to carburetor air temp (the P-38 manual specifies it's at a constant 60C CAT). But... the carburetor is (always?) placed before the impeller, for best fuel distribution, which means carburetor air temp isn't affected by the impeller. Any ideas?

 

On 12/19/2022 at 4:00 PM, 357th_KW said:

I seem to recall there is even some Russian test data for the Yak showing that they achieved higher top speeds in testing by using an “over-square” setting with reduced rpm.  I’d hate to see yet another binary system implemented where doing things that we know were actually done in combat, causes your engine to immediately fail.

 

Note that literally all of these engines are run "over-square". Even the high-revving Sabre runs at 3150/38" (cruise) or 3700/43" (climb), both "over-square". The Sturmoviks will run 2050 and 47" in cruise. "Over-square" is a rule of thumb for your Piper or your Cessna, don't pay it any mind here.

 

I think the altitude graph clarifies this a lot. They're also pulling only 1050mmHg (41"Hg) compared to the 60" the P-38 can use. I suppose that makes it less of an issue? Note the P-38 is rated for 34" on auto-lean and ANF 28 (100/130 octane), and is almost RPM independent in that range. Perhaps the graph for the M-105PF looks like the  Auto-Lean side of the P-38's graph? In that case, they can safely reduce RPM to reduce power lost driving the impeller (up to critical altitude, at which point they need to speed it up to maintain MP).

On 12/20/2022 at 4:03 AM, Sgt_Joch said:

 If the engines are running cooler, that may be part of the reason why the P51 spark plugs were fouling when using their low RPM/high MP regime.

 

Note that you're misquoting Crim. Burnt plugs and fouled plugs aren't the same thing. This site is focused on modern auto engines, but the principles are the same. Fouled plugs are associated with rich mixture and low temperatures*. They certainly weren't running rich. Burnt plugs are associated with lean mixtures, overheating, and pre-ignition, which is what they appeared to have.

 

 

On 12/20/2022 at 4:03 AM, Sgt_Joch said:

If lowering RPM 5-10% while keeping MP at 100% lead to quick destruction of the engine, we would have the empirical evidence for that, i.e. pilot accounts, field reports, test results, etc. Here we have no empirical evidence to back up this theory. If anything the "evidence" presented so far is that there are actually benefits to running an engine at lower RPMs.

 

 

There are a few accounts of pilots using marginal settings, but I've yet to see an account of anyone deliberately operating under conditions of severe detonation. And why would they? That's not a useful test, that's just vandalism. If it happened, it was probably by accident, and the accounts would probably sound a lot like Dave Hastie's: "I had the throttle through the gate, and the engine blew up." He then bailed out and any evidence as to the cause went to the bottom of the straight.

Edited December 27, 2022 by Charon

[the_emperor]

On 12/27/2022 at 12:04 AM, Charon said:

Any ideas?

That also got me a bit confused. I thought here the rpms of the impeller/charger are meant? But I am not sure.

I also dont think that it does apply to the general problem of discussion here, running full/max MAP and the reduce rpms without any consequences though manuals state you must not do this.

 

On 12/27/2022 at 12:04 AM, Charon said:

Perhaps the graph for the M-105PF looks like the  Auto-Lean side of the P-38's graph?

unfortunately the manuals for soviet aircraft/engines are not as detailed as one might wish. But I would say that compared to other engines the M-105PF is a  "low performance" engine and can tolerate a bit more abuse in that regards.

[the_emperor]

Spitfire Mk V

Air Publication 1565E & 2280 A, B & C

Pilot Note‘s Spitfire VA, VB and VC

And Seafire IB, II and III

 

 

 

Spitfire Mk IX

Pilot Notes‘s for Spitfire IX, XI, XVI

Merlin Engine 61, 66, 70 or 266

Air Publication 1556j

3rd Edition September 1946

page 33

 

Spitfire Mk VIX

Pilot Note‘s for

Spitfire XIV & XIX

Griffon 65 or 66 engine

Air Publication 1565T 2nd Edition April 1946

page 39

 

 

Edited April 11, 2023 by the_emperor

[the_emperor]

Typhoon/Tempest

[=MERCS=JenkemJunkie]

Just gonna add that the extended WEP glitch won't work on the tempest/typhoon because it doesn't fit the glitch rules I described in a post above, and not due to any intentional modeling by 1C. Just in case anyone tries this on those planes then wonders what this threads about.

[Charon]

Well, I stand corrected:

 

 

 

From P&W OP Info No. 19: Detonation and Preignition, available to AEHS members.

[Charon]

It occurs to me that what we may be seeing with the P-38 and the P-47, which unlike most planes get the RPM hooks, is specific to turbocharging and not piston engines in general. In a conventionally boosted engine, we expect a reduction of RPM to also lead to lower impeller speed and thus reduced carb air temp. But in the case of a turbocharged engine, with the boost on, the boost regulator should close the wastegates to maintain MAP as RPM is reduced, which means the turbocharged engine, operating at high power, will not benefit from reduced temperatures when RPM is reduced. But I don't know, I've been wrong before. Does anyone have other theories?

[354thFG_Rails]

Leaving the turbo full forward in the P-47 will definitely lead to increased temps. It’s why it’s recommended to link it to the throttle or work it separately after the throttle is full forward and can’t maintain manifold pressure with the throttle alone. The problem is with the 47 in game is the supercharger is not modeled correctly so you can’t maintain manifold pressure correctly at lower altitudes. The 38’s turbos are automatic though, so the throttle has to be pulled back to maintain pressures and temps. 
 

I still don’t understand the point of this topic. The only planes it really affects are the American birds with their limited timers. The speed gain is very minor. The only plane that it helps a lot is the P-47. But I’d argue that it’s so broken that abusing the engine timers is the least broken thing with it. Plus how many people here actually worry about running into 47’s in game?(pains me to ask this)

[=MERCS=JenkemJunkie]

1 hour ago, 86th_Rails said:

I still don’t understand the point of this topic. The only planes it really affects are the American birds with their limited timers. The speed gain is very minor. The only plane that it helps a lot is the P-47. But I’d argue that it’s so broken that abusing the engine timers is the least broken thing with it. Plus how many people here actually worry about running into 47’s in game?(pains me to ask this)

The glitch will help you massively extend timers for planes from every country, including the German planes like the 109. It's less effective for blue though as you have to use manual prop pitch for most of their planes to use the glitch. It does benefit Red more than blue, but I don't hate this glitch as a balance issue. Working with the timers is an ugly unrealistic system to be dealing with on it's own, and the RPM glitch just adds more ugliness and variables to it. I'd prefer to fly without having multiple fantasy clocks and math formulas ticking in my mind, and the RPM glitch just adds more variables to the fantasy math. I don't think many people have the P47 in mind at all with this, or any balance discussion really unless we bring up fla... mmm better not go there.

[the_emperor]

The problem is, that in one case they chose to slavishly bind themself to the manuals in case of engine timers and on the other hand ignore the same  manuals when they forbid the use of max MAP without max rpms  furthermore you are „rewarded“ with longer WEP time with this timer mechanic. 

[354thFG_Rails]

But like I said the speed glitch isn’t that much. And the extended timer isn’t that much btw. You’re talking about maybe an extra minute or two at slightly lower rpm’s but same manifold for WEP. You get a big extension in time with decreased manifolds as well. In the case of the 51 if you set the power settings the same as the spit 9 for combat power you can get 1 hour as opposed to if you set the power to 61” and the rpm to 2850 you might get 20-25 mins before damage occurs( I’m guessing btw, I know more of what timers do what for the 47 than the 51) in the case of the 47 the speed is nothing special. You can maintain 300 mph IAS for longer is all. I don’t know, unless a new system gets implemented people will find ways to get more speed and time out of the planes. It’s no different with the cool down timers before, or people deploying flaps at speeds well above what they should be do they can slow down or out turn folks. Personally I hope timers don’t go away for emergency but do for combat power. And the devs develop some sort of system that relies more on temps and pressures. I don’t know how dcs did it but their detonation systems works pretty well. 

Edited May 13, 2023 by 86th_Rails

[the_emperor]

I dont know, if I can double/triple WEP MAP time with a rpm reduction I wouldnt call that „not much“. 
Eg the P51 cant do that trick while the Spitfire can though both have essentially the same engine. 
This complain is not about more/less speed with rpm reduction but time extension on max MAP.

[=MERCS=JenkemJunkie]

To better understand people's complaints you should forget the P47. It's the other planes like the 100 Octane Spit IX getting it's WEP boosted to 14 minutes, or the LA5 and MW-50 109s getting their WEP timers boosted to 20 minutes are what people are talking about. The extra speed isn't a glitch though, depending on the plane there should be a speed increase.

[354thFG_Rails]

I’ll need to test this then. I’m very skeptical of double or triple wep times. What are the rpm settings to test with?

[=MERCS=JenkemJunkie]

If the mode underneath uses a lower RPM value, then using that RPM value will give you a massively extended timer. So just use 2850 for the 100 Spit IX, 2400 on the FN or manual 2600 on the MW 109s. If you want to mix/max you can use the max combat RPM and the glitch will still work, but to keep it simple for testing just use the by book combat RPM. Won't work to extend the P47's WEP because it uses 3000 RPM for both combat and WEP.

[the_emperor]

You will find my main examples in the starting post. 
I have not yet tested the MW50s 109s yet. Would be niceto know how much rpm reduction can do there

Edited May 13, 2023 by the_emperor

[=MERCS=JenkemJunkie]

2650 is the sweetspot for time/performance, it will also give you +1 or 2 kph on the deck in the G6L but not the K4/G14 last time I checked just to add more weirdness. Haven't tried with lower RPM to get a 20min+ timer, if a chase is lasting longer than that I'd rather uninstall.

[the_emperor]

Pilot´s notes general, April 1943