War Emergency Power

[Ivan]

Hello All,

I have been debating on the best method of representing in Combat Flight Simulator Flight Models the various kinds of Maximum / Limited Duration power that are available in real aircraft.

In CFS, there are three kinds of War Emergency Power (WEP):
1. Supercharger:
Maximum duration is 5 minutes. 10 seconds past that, the engine is damaged.
2. Water Injection:
Maximum duration is 5 minutes. After 5 minutes of total use, WEP is no longer available.
3. Water-Methanol Injection:
Maximum duration is 10 minutes. After 10 minutes of total use, WEP is no longer available.

The problem that I see is that there are so many different kinds of actual "emergency" or limited duration power that these choices do not cover. Also, from reading various aircraft and engine manuals and descriptions, unless there is a limited supply of an additive that is required for a power setting, there are really no hard time limits. The "hard" limit is reached when the engine exceeds other operating (typically temperature) limits.

With my recent work on a Messerschmitt 109E flight model, I found that the following settings were available for its Daimler Benz DB 601Aa engine:

1.45 ATA (42.14 inches Hg) - 2500 RPM - Take-Off Rating (One Minute Maximum)
1.35 ATA (39.24 inches Hg) - 2400 RPM - Emergency Power (Five Minute Limit)
1.27 ATA (36.91 inches Hg) - 2400 RPM - Climb (30 Minute Limit)
1.23 ATA (35.75 inches Hg) - 2400 RPM - Maximum Continuous
1.23 ATA (35.75 inches Hg) - 2250 RPM - Economy Cruise

The RPM Limits are simplified. The climb and cruise RPMs are about 100 less at low altitude.

For the Me 109E, even though there is a 2500 RPM limit for Take-Off, we can not simulate that without allowing 2500 RPM in regular us

The stock flight model has no WEP setting at all. It allows 41.0 inches Hg for continuous use. This works out to be 1.41 ATA which is somewhere above "Emergency" power but below the Take-Off rating. Its RPM limit is 2400.

....

 

[Ivan]

What is the Best Method?

For those who might be wondering, this discussion is not intended to be a complaint about existing flight models or how something was done wrong. It is intended to work out the best method of representing actual engine emergency power settings within the limitations of the simulator.

For some kinds of engines, the solution is easy:

For an aircraft that requires anti-detonant injection to achieve its "Emergency Power" and we know the duration of the anti-detonant, the answer would be VERY easy: Use the stock solution.
An example of this would be the P-47 Thunderbolt. It needs Water Injection to achieve its WEP and the amount of water carried along with the injection rate work out pretty close to 5 minutes.

If there is enough anti-detonant (or some other power adder) to last over 5 minutes, we can use "Water-Methanol" injection.

With some aircraft the engine durability was good enough so that the "Emergency Power" restrictions were pretty much a procedural matter. It was the way by which the engine manufacturer could ensure that the engines would last as long as claimed between overhauls. In this case, there should be no WEP limitation. I believe this should be the case with the Merlin Mustang as it is with the Merlin Spitfires.

In some cases, there is a reason to believe that the engine is not durable enough to allow unlimited use of emergency power. The engine manufacturer may not even authorise the use of such high manifold pressure. This was initially the case with the Allison engine in the Hawk 87 - P-40 series. Eventually the company agreed to authorise the higher throttle settings.... after they had been used in operations for quite some time. I believe in this case, the use of WEP should be limited but not necessarily to 5 minutes. The only possible choice here would be "Water-Methanol" even though the aircraft never had any kind of anti-detonant injection.

Those are the fairly obvious cases.
Here is where things get interesting.

How should we handle the case of the Late-War FW 190s? They had a normal "Combat" rating of 1.42 ATA for 1750 HP (US Tests). Some were equipped with a system for injecting fuel into the supercharger as a charge cooler / anti-detonant (C3-Einspritzung). Although the system could only be used only for 10 minutes at a time with 5 minute pauses in between, it could be used multiple times during a flight. As for the amount of anti-detonant, it was fuel, so as long as there was fuel to run the engine, there was anti-detonant to use.

The case becomes even more messy with late-war Japanese fighters. Japanes fuel quality was never very good. Their standard fuel was only 91 Octane for the Army and 92 Octane for the Navy. Toward the end of the war, often the fuel was closer to 85 Octane even on the home islands.
With this level of fuel quality, the more powerful engines would typically be set up to automatically start water-methanol injection as soon as a certain throttle setting was reached. This setting was well below the engine's non emergency rating.

How should we handle a case like this? There is enough anti-detonant to allow nearly continuous use. In fact it is intended to be used continuously. Should we set the maximum non-WEP manifold pressure below even a "Maximum Continuous" rating???

If we know what reality is, how do we represent it within this game?

- Ivan.

 

[hubbabubba]

Well, Ivan, as far as I know, you simply can't...

... unless you have a trick up your sleeve that we don't know about. Do you?

As for manufacturer's limitations, they pretty much went by the window when a bandit was about to mow your tail.

CFS1 AIR files are particularly poor when it comes to damages caused by over-stress of any kind. Another M$ game released about the same time (I think its name was "Aces High") could be adjusted to mimic over-stress damages, but nothing was more frustrating than breaking a wing trying to follow a target in a sharp turn, I can tell you that!

So, all in all, the 5 minutes is not so bad. BTW- I never use WEP and, from my readings, so was the case of most Allied pilots deep in enemy territory. They would let go a "sure kill" rather than pass the rest of the war in a POW camp because of overheating seized engine.

But, again, I'm really curious to know if you have found something on the subject.

 

[Ivan]

Hello Hubbabubba,

Yes, I KNOW we can't simulate all the different ways Emergency power was implemented. I was just wondering what others thought about the having to use anti-detonant during high speed cruise (maximum continuous) and military power settings.

Wings breaking off is a pretty extreme thing. On quite a few fighters (P-51 and Me 109 come to mind), the maximum load was 8G which would easily black out a pilot without a G suit, but the wings would not break until 1.5 times that load or at 12G. I dunno how you would go about doing that in the game. Now there are others such as the Ki-43-I Hayabusa which might shed a wing at a much lower G load.

Your post actually is a bit contradictory: You state that a pilot might ignore the manufacturer's limitations when he is in danger of getting shot down but state a bit later that while deep in enemy territory, a pilot would generally NOT use WEP to avoid overstressing the engine.

From accounts I have read, there generally was no lack of willingness to use War Emergency power or Water Injection if the situation seemed apropriate. In the case of the mid production P-40 series, pilots had no reluctance to use power settings that greatly exceeded manufacturers recommendations to the point that the manufacturer (Allison) eventually sent a letter authorising some of the settings that were already being used.

Imagine getting 1745 HP out of an engine that was only capable of 1150 HP. At this power level, my own testing of my P-40K flight model was showing 385 mph which is about 20 - 30 mph faster than any speed claims for the aircraft. That testing also showed another CFS WEP issue that is beyond the scope of this discussion.

- Ivan.

 

[hubbabubba]

Hi Ivan

Not a contradiction at all. A pilot who's life was in the balance would "trip the wire" of his P-51 to get out of harms' way, but would certainly hesitate to do the same just to get a kill. In many accounts, pilots would let go a Me-262 rather than risk turning their warbird into a very heavy glider on their way back. Of course, personality comes into play here and some adventurous-minded pilots would go for it, but they were less of them left to tell their stories afterward.

In a dogfight, speed cease to be the paramount ingredient and agility takes precedent. Speed is essential during the approach and, if necessary, while egressing from a bad situation.

Manufacturer's recommendations are quite another story. In the heat of a fight, you tend to "throw the book by the window". And P-40 pilots in China, if they're the ones you read the accounts, had very good odds of landing on friendly soil.

In CFS1, the chances of getting "jumped" by surprise are quite slim because of the padlock mode and the situation window (and for those who like it, the green cone...).

As for Aces' High, the "realistic" mode was quite unrealistic. In a tight turn, you would hear the creaking of the controls cables then, almost always, the snap. Game over. That's why I finally played only in "arcade" mode. It was even more frustrating because the AI aircraft you were pursuing never lost a wing!

I wish there would be a "in between" compromise. I've heard that IL-2 was pretty much there, but I never played it, so...

 

[Ivan]

Hi Hubbabubba,

The combat reports involving a Me 262 are rather poor examples of whether or not pilots choose to use Emergency Power. The fight will just about always end up as a tail chase with your target having nearly 100 mph advantage in maximum speed. If you don't get close enough to shoot in the first minute or two, you're not going to get any closer with a sustained chase.
From a tactical standpoint, the same applies but just a little less so with any of the other first line Luftwaffe fighters. If you have a late model 109G or even a 190A running from you, you certainly have a 20-30 mph speed advantage in all out maximum speed, but you would be burning up a lot of fuel and probably headed away from home for the duration of the chase. Think about how many times you have encountered this in a game. I have seen it a lot.
If the enemy stays to fight, then using WEP makes sense, if they are running from you, it does not.

If your engine doesn't destroy itself during the use of emergency power (which it probably will not), it is hardly likely to destroy itself on the cruise home. Your crew chief may hate you for forcing him to change out the plugs or schedule an overhaul sooner, but that is about it.
The thing to remember is that most non-additive Emergency Power is a procedural thing to ensure that the engine lives up to manufacturers' claims. Other than exceeding operating limits such as oil pressure, temperature, etc, there is nothing that should destroy your engine immediately. Emergency power may exceed the cooling system's ability to reject waste heat, but until the operating temperature itself is exceeded, there should be no damage other than increased wear. The exception to this would be if you need an anti-detonant to operate at emergency throttle settings and run out of it. Destruction in that case comes pretty quickly.

I am a bit surprised by your comment about speed in a dogfight. Even disregarding discussions about "Energy-Maneuverability Theory", increased engine power afffects acceleration and climb a lot more than it does maximum speed. Climb rate and Acceleration are two of the most important Agility factors IMO. (Actually are these just a single agility factor because they are basically the same thing).

Regarding manufacturers' recommendations and the likelihood of landing on friendly territory, the Allison letter I posted here isn't about P-40s in China. It specifically mentions Australia and Africa. The desert in North Africa is only a little less inhospitable than the ocean. If your engine quits working and you end up on the ground, a POW camp would look quite inviting. Look at the cases of the "Lady Be Good" and the recent P-40E.
It took 15 years before anyone found the B-24 "Lady Be Good" and 70 years before Dennis Copping's P-40 was found.

- Ivan.

 

[papingo]

papingo here....
suppose you have a plane--with no boost.
then give the air file small spoilers-invisible of course
then you adjusted air file to give plane the original
performance(with the spoilers deployed.)
this would then mean that turning spoilers 'off'
would give the plane 'boost' performance (it may be
that we can devise a 4minute timer to turn them
back on ie 'boost off'

 

[Ivan]

Emergency Power Time Limits

Hi Papingo,

That is a very interesting idea. I don't have a clue as to where to start though. Perhaps it may be done with a gauge, but I don't know how to program gauges.

The problem is that actual use of emergency power is a bit different than we see here in CFS.
The time limit depends on the type of WEP, but all the limits are too short.
With a Supercharger Boost, you have 5 minutes 10 seconds before engine damage.
With Water Injection, you also have 5 minutes before Anti Detonant runs out.
With Water Methanol, the limit is still only 10 minutes before ADI runs out.

The Japanese engines probably had longer time limits because they were using ADI even at rated power as well as emergency power. So how do we put in a 2 hour time limit?

Another thing to note is that there are two kinds of additive used for emergency power:
An Anti Detonant such as Water, Water-Methanol, or even (!) Fuel. The amounts carried varied a lot between different installations.
An Oxidizer was also used by the Germans: GM1 (Nitrous Oxide).

Anti Detonant allows you to use excess supercharger capacity that would normally not be available because of charge air temperature or detonation or other factors related to the engine's structural strength.
Because it uses only the supercharger's excess capacity, it does nothing above the engine's critical altitude. In other words, using Water or MW50 injection to increase your service ceiling simply will not work.

An oxidizer is pretty much an additional supercharger in a bottle. Below the engine's critical altitude, it can't be used because the engine already has more supercharger than it can use. It can only be used to increase high altitude performance.

With CFS, WEP is a combination of both types. It works at all altitudes....

- Ivan.

 

[hubbabubba]

Quite ingenious, papingo

I like your "out of the box" thinking.

As for you, Ivan, I'm still waiting for your ideas on the subject. Anything you're tinkering with?

 

[papingo]

papingo here

nice to hear from you Hubba.
**********
Does anyone know a tame guage mechanic?
someone who can explain 'tokens'
in making gauges?
*****************
I have a helo and it has gauge switches for
pause and slew on the dashboard!!!
*************
e.g. in the hud gauge they tell the time at the
top of the'info' bit but I reckon that 'zoom factor '
would be more usefull here.(I like to feel that I'm
quite close to my victim)
***
I notice that (in quick-combat) if you come upon
your opponent --say from side/above if you aim
ahead of him by 3-4 plane lengths he seems to slow down!!!!
papingo

 

[Ivan]

Hello Hubbabubba,

Sorry, I have no solutions other than to use the Game WEP and pick the one that best fits the aircraft being designed. Sometimes that may be no solution at all. In other words, my most likely approach to doing Japanese aeroplanes that used anti-detonant even for military power would be simply ignore that fact entirely. Not optimal, but probably the most fair since they apparently carried quite a lot of antidetonant and the system was automatic in that the injection would turn on when a particular manifold pressure was exceeded.

Hello Papingo,

The gauge idea was one I was also thinking of but along a different approach. I was thinking of resetting the WEP timer according to how long WEP was NOT used. In other words, the engine would only allow 5 minutes of CONTINUOUS WEP but perhaps for every minute it was turned off, the remaining WEP time would increase by 15 seconds. There should also be a warning of how long WEP has been running.
The problem here is that I can't find a good compiler that will allow me to compile a DLL (gauge file) in a way that it will run on the old Windows 98 machines. I have been able to compile a simple tachometer that will run on a Windows 2000 machine but will crash my CFS game instantly on the Windows 98 system.
If you have a workable idea for a compiler, I have a lot of gauge ideas. One of the reasons my B-25 Mitchell is stuck is that I need some manifold pressure and tachometer gauges and I want to program them myself. I also need a few very specific fuel switching gauges for various aeroplanes including a PBY Catalina.

- Ivan.

 

[papingo]

dear Ivan....
did you try that Pelles.4.5 compiler
I got it to compile messageboxes and
simple windows .But I can't get it to do
resources yet (for an example SDK gauge
(temperature))
Now really what I know about 'C' can be
written on the back of a stamp and leave
plenty of space.

papingo
if you can see a .jpg it' just me experimenting