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XyZspineZyX
10-05-2003, 04:11 AM
There has been some discussion & some confusion regarding manifold pressure on the boards lately. So I thought I'd chime in with some thoughts & suggestions.

First, manifold pressure.

At sea level sitting on the runway with the engine not running we should see approx. 30 in/hg in the American planes, 1.0ATA in the German planes, 100kPa in the Russian planes & 0psi boost in the Hurricane. On the runway at idle we should see approx. 13in/hg in the American planes, .45ATA in the German planes, 45kPa in the Russian planes & -8psi boost in the Hurricane. At this time only the German planes are close. They should be pegged low off the gauge though. Normal cruise settings for most of the planes in the game are around 27-30in/hg for American, 1.0-1.1ATA for German & I haven't seen any charts for Russian planes but it can be assumed they're similar. Max manifold pressure such as it is seems to be ok for most planes in the game. The other thing that is incorrect about the way it's modeled is that at a given Throttle setting decreasing RPM should cause MP to increase. And increasing RPM should cause MP to decrease.

In the original IL2 Sturmovik game the MP gauge was directly connected to your throttle. This would be a good starting point for modeling MP in Forgotten Battles. The MP gauge reading should be modeled primarily on Throttle position & modified by RPM. Something like this;

Throttle position.....10% @ 1000rpm = .47ATA
Throttle position.....20% @ 1560 " = .72 "
Throttle position.....30% @ 1810 " = .87 "
Throttle position.....40% @ 1990 " = .97 "
Throttle position.....50% @ 2150 " = 1.06"
Throttle position.....60% @ 2260 " = 1.12"
Throttle position.....70% @ 2380 " = 1.17"
Throttle position.....80% @ 2500 " = 1.25"
Throttle position.....90% @ 2600 " = 1.30"
Throttle position....100% @ 2710 " = 1.37"
Throttle position....110% @ 2800 " = 1.42"

Now if you are at 80% throttle & you have the prop pitch or CSP set so that your RPM is 20% below the RPM on this chart. Then your MP would read 20% higher, Like this;

Throttle position...80% @ 2000rpm = 1.5ATA

Or the other way around, RPM 10% higher, MP 10% lower, like this;

Throttle position...80% @ 2750rpm = 1.12ATA

This is a chart I made up for a generic German aircraft. The ranges & numbers would have to be changed for each specific model based on historic figures & settings for cruise, Max. continuous & military power. But the basic formula is very simple & would work for every plane in the game.

I don't know how Difficult this would be to impliment but in addition to adding realism it would give the developers a parameter on which to base two things. One is overboost damage, something that is currently not modeled. & the other is a "minor" change to the engine sound. Currently the engine sound varies only by RPM so that at 2800rpm it sounds the same whether you are at 0% throttle or 110% throttle. It should have the speed of the engine sound controlled by RPM and the volume of the engine sound controlled by MP. This would add an incredible amount to the immersion IMHO & would totally eliminate the "My engine won't idle down" or "throttle completely porked" threads.

Now for the Kommandogerat. I'll start with the one in the Bf-109. The fact that it sets the RPM too low at all throttle settings has been covered very well already (& may already be fixed if patch reports are accurate) so I'll skip over that part. First of all the Bf-109 has a variable pitch prop not a constant speed prop like the Fw-190. However in "Auto" it is modeled like a CSP. This is incorrect. The second problem is with the throttle response. While it is true that the Kommandogerat did not respond instantly to changes in throttle position & the one in the Bf-109 was slower to respond than the one in the Fw-190, the throttle was still directly connected to the lever in the cockpit. And so the pilot had to be smooth & deliberate with his throttle to avoid overboosting or overrevving his engine. The way it's modeled in the game leads one to suspect that the developer believes that the Kommandogerat somehow made the engine "foolproof". In other words that the pilot could ram & jam the throttle any way he liked with out any concern for his engine. This is incorrect as well. Also much of the delay that the Kommandogerat had was the response time of the prop pitch regulator itself. This delay would have been present in manual mode as well. However in the game it responds instantly. & lastly the prop pitch should stay in whatever position the Kommandogerat had it in when "auto" mode was switched off. & it should stay in this position until the pilot moves the manual control to this position or past it. In other words if the Kommandogerat has the prop pitch at 70% for example and your control slider is at 50% you should move your slider up to 70% then the manual PP should engage. If you have it mapped to buttons of course it would just move from 70%

Finally the Fw-190, Since the Fw-190 had a CSP, the way it's modeled in "auto" is Ok. The problem is in manual mode. Switching off "auto" mode should leave you with a fully functioning CSP. However in the game it only works partly like a CSP. For example if you set the RPM to 2200 it will maintain that RPM if you alter your airspeed. But it will make no attempt to maintain the set RPM if you move your throttle. This is incorrect. & of course the throttle response problem is the same as that of the Bf-109.

I don't know how much of this stuff has been fixed in the upcoming patch or how much of it is posible to model in the sim with the existing computers of today but these are some of my dreams for the game.

Well if you've stuck with me through this a Big SALUTE! to you! /i/smilies/16x16_smiley-happy.gif

Cheers.....Smokin256

Edited to make the chart look right



Message Edited on 10/04/0308:47PM by Smokin256

XyZspineZyX
10-05-2003, 04:11 AM
There has been some discussion & some confusion regarding manifold pressure on the boards lately. So I thought I'd chime in with some thoughts & suggestions.

First, manifold pressure.

At sea level sitting on the runway with the engine not running we should see approx. 30 in/hg in the American planes, 1.0ATA in the German planes, 100kPa in the Russian planes & 0psi boost in the Hurricane. On the runway at idle we should see approx. 13in/hg in the American planes, .45ATA in the German planes, 45kPa in the Russian planes & -8psi boost in the Hurricane. At this time only the German planes are close. They should be pegged low off the gauge though. Normal cruise settings for most of the planes in the game are around 27-30in/hg for American, 1.0-1.1ATA for German & I haven't seen any charts for Russian planes but it can be assumed they're similar. Max manifold pressure such as it is seems to be ok for most planes in the game. The other thing that is incorrect about the way it's modeled is that at a given Throttle setting decreasing RPM should cause MP to increase. And increasing RPM should cause MP to decrease.

In the original IL2 Sturmovik game the MP gauge was directly connected to your throttle. This would be a good starting point for modeling MP in Forgotten Battles. The MP gauge reading should be modeled primarily on Throttle position & modified by RPM. Something like this;

Throttle position.....10% @ 1000rpm = .47ATA
Throttle position.....20% @ 1560 " = .72 "
Throttle position.....30% @ 1810 " = .87 "
Throttle position.....40% @ 1990 " = .97 "
Throttle position.....50% @ 2150 " = 1.06"
Throttle position.....60% @ 2260 " = 1.12"
Throttle position.....70% @ 2380 " = 1.17"
Throttle position.....80% @ 2500 " = 1.25"
Throttle position.....90% @ 2600 " = 1.30"
Throttle position....100% @ 2710 " = 1.37"
Throttle position....110% @ 2800 " = 1.42"

Now if you are at 80% throttle & you have the prop pitch or CSP set so that your RPM is 20% below the RPM on this chart. Then your MP would read 20% higher, Like this;

Throttle position...80% @ 2000rpm = 1.5ATA

Or the other way around, RPM 10% higher, MP 10% lower, like this;

Throttle position...80% @ 2750rpm = 1.12ATA

This is a chart I made up for a generic German aircraft. The ranges & numbers would have to be changed for each specific model based on historic figures & settings for cruise, Max. continuous & military power. But the basic formula is very simple & would work for every plane in the game.

I don't know how Difficult this would be to impliment but in addition to adding realism it would give the developers a parameter on which to base two things. One is overboost damage, something that is currently not modeled. & the other is a "minor" change to the engine sound. Currently the engine sound varies only by RPM so that at 2800rpm it sounds the same whether you are at 0% throttle or 110% throttle. It should have the speed of the engine sound controlled by RPM and the volume of the engine sound controlled by MP. This would add an incredible amount to the immersion IMHO & would totally eliminate the "My engine won't idle down" or "throttle completely porked" threads.

Now for the Kommandogerat. I'll start with the one in the Bf-109. The fact that it sets the RPM too low at all throttle settings has been covered very well already (& may already be fixed if patch reports are accurate) so I'll skip over that part. First of all the Bf-109 has a variable pitch prop not a constant speed prop like the Fw-190. However in "Auto" it is modeled like a CSP. This is incorrect. The second problem is with the throttle response. While it is true that the Kommandogerat did not respond instantly to changes in throttle position & the one in the Bf-109 was slower to respond than the one in the Fw-190, the throttle was still directly connected to the lever in the cockpit. And so the pilot had to be smooth & deliberate with his throttle to avoid overboosting or overrevving his engine. The way it's modeled in the game leads one to suspect that the developer believes that the Kommandogerat somehow made the engine "foolproof". In other words that the pilot could ram & jam the throttle any way he liked with out any concern for his engine. This is incorrect as well. Also much of the delay that the Kommandogerat had was the response time of the prop pitch regulator itself. This delay would have been present in manual mode as well. However in the game it responds instantly. & lastly the prop pitch should stay in whatever position the Kommandogerat had it in when "auto" mode was switched off. & it should stay in this position until the pilot moves the manual control to this position or past it. In other words if the Kommandogerat has the prop pitch at 70% for example and your control slider is at 50% you should move your slider up to 70% then the manual PP should engage. If you have it mapped to buttons of course it would just move from 70%

Finally the Fw-190, Since the Fw-190 had a CSP, the way it's modeled in "auto" is Ok. The problem is in manual mode. Switching off "auto" mode should leave you with a fully functioning CSP. However in the game it only works partly like a CSP. For example if you set the RPM to 2200 it will maintain that RPM if you alter your airspeed. But it will make no attempt to maintain the set RPM if you move your throttle. This is incorrect. & of course the throttle response problem is the same as that of the Bf-109.

I don't know how much of this stuff has been fixed in the upcoming patch or how much of it is posible to model in the sim with the existing computers of today but these are some of my dreams for the game.

Well if you've stuck with me through this a Big SALUTE! to you! /i/smilies/16x16_smiley-happy.gif

Cheers.....Smokin256

Edited to make the chart look right



Message Edited on 10/04/0308:47PM by Smokin256

XyZspineZyX
10-05-2003, 05:02 AM
I'll give this a big salute. S!

--AKD

http://www.flyingpug.com/pugline2.jpg

XyZspineZyX
10-05-2003, 05:08 AM
bump

Nice idea, will give a reference to those MP/rpm's relationships /i/smilies/16x16_smiley-wink.gif problems.

XyZspineZyX
10-05-2003, 06:17 AM
Its being worked on http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

Ps=V(T-D)/W
III/JG11_IvanK

XyZspineZyX
10-05-2003, 06:27 AM
As a matter of refrence the 109 system is perhaps better described Variable datum constant speed unit, though this description is also a little loose.

Many people communicate directly with Oleg, One is an expert on the DB engine series and probably has more DB605 runing time in the cockpit of a 109 than most people. He comes from an engineering background and has been directly involved in DB605 re builds, and is a very experienced pilot at that.

What you see in FB is not perfect but pretty close. As to other MAP display anomiles with throttle movement I think you can expect some fixes here too.

Ps=V(T-D)/W
III/JG11_IvanK

Ps=V(T-D)/W
III/JG11_IvanK

XyZspineZyX
10-05-2003, 08:42 AM
Smokin256 wrote:
-Currently the engine sound varies only by RPM so that at 2800rpm it
- sounds the same whether you are at 0% throttle or
- 110% throttle. It should have the speed of the
- engine sound controlled by RPM and the volume of the
- engine sound controlled by MP. This would add an
- incredible amount to the immersion IMHO & would
- totally eliminate the "My engine won't idle down" or
- "throttle completely porked" threads.


This will be a huge immersion bosster I believe.I have posted about this before and said that the next sim should model loaded and unloaded engine sounds.Your idea of using engine speed for rpm's and engine volume for MP is great and I hope they implement it.

XyZspineZyX
10-05-2003, 10:33 AM
Ivank wrote:
- Its being worked on /i/smilies/16x16_smiley-happy.gif
-

Great to hear that.

Good work there Smokin and great idea for the engine sound. It is odd now at min throttle and max rpm.

Kernow
249 IAP

XyZspineZyX
10-06-2003, 01:47 AM
Ivank wrote:
- As a matter of refrence the 109 system is perhaps
- better described Variable datum constant speed unit,
- though this description is also a little loose.

I'll respectfully reserve judgment on that for now. Everything I've seen or read mentions a change from the two blade fixed pitch wood propeller to a three blade variable pitch metal prop early on, sometime around the B-D model. & then a change to a slightly larger propeller with a slightly different blade shape around the late E or early F model. & a change from the DB-601 to the DB-605 engine around the mid to late G model. But nowhere has anyone ever mentioned a change from the variable pitch prop to a constant speed prop. However I wouldn't be the least bit surprised to find holes in my research! /i/smilies/16x16_smiley-happy.gif In the end it doesn't really matter to me. As long as it remains a constant speed prop or a variable pitch prop when switched to manual mode.

- What you see in FB is not perfect but pretty close.

Here I must disagree. Looking at the engine management system in the 109 as a whole, there really isn't much that is right. regardless of the variable pitch vs. constant speed debate. Still I'm hopeful that they'll get it sorted out.

- As to other MAP display anomiles with throttle
- movement I think you can expect some fixes here too.

Really good news about the patch fixes. Keeping my fingers crossed & looking forward to it. /i/smilies/16x16_smiley-happy.gif

Cheers........Smokin256

XyZspineZyX
10-06-2003, 07:20 AM
Smokin.

Perhaps I should have qualified things a little. I agree with you on the B,C,D series. As to when the Constant Speed came to the 109 that is a good debate. My refrences indicate that prior to the F it was a straight out Variable pitch unit. However people with better refrences than me indicate that the CSU "type" operation actually arrived in the late E series. By CSU type operation I am refering to what we see in AUTO in FB.

"Here I must disagree. Looking at the engine management system in the 109 as a whole, there really isn't much that is right."

So what exactly are you refering to as not being right?

If you prefer Email me at: ttail@zip.com.au


Ps=V(T-D)/W
III/JG11_IvanK

XyZspineZyX
10-07-2003, 08:10 AM
Aw hell, I don't mind talking about it here. /i/smilies/16x16_smiley-happy.gif Maybe we can drum up some interest. Whenever a techie topic like this comes up around here I see everyones eyes glaze over! /i/smilies/16x16_smiley-happy.gif

Ivank wrote:
" - Perhaps I should have qualified things a little. I
- agree with you on the B,C,D series. As to when the
- Constant Speed came to the 109 that is a good
- debate. My refrences indicate that prior to the F it
- was a straight out Variable pitch unit. However
- people with better refrences than me indicate that
- the CSU "type" operation actually arrived in the
- late E series. By CSU type operation I am refering
- to what we see in AUTO in FB."

I have some questions about this stuff but it's late & I'm too tired to think straight. Can you take a look at the English translation of the Finnish G2 manual over at bf109.com & see what you think? Especialy the prop pitch controls on page 13 & Diving & descending on page 15. Some of that stuff has me really confused now.


"- So what exactly are you refering to as not being
- right?"

Well first of all the throttle position/rpm settings that the Kommandogerat uses are too low. As an example an F4 on manual at 5000 meters cruises comfortably at 400kph w/ 65% throttle & 2200rpm. On Auto 65% throttle gives you only 380kph. 400kph in auto requires 87% throttle. In auto 100% throttle gives you 2400rpm. (But this has already been well covered & sounds like its already been fixed.)
Second is the slow throttle response. It responds with the same delay as the prop pitch. (Although I'll grant you this might be more related to the MP gauge response Wierdness than actual engine power.)
Third is when you switch to manual the prop pitch should stay where it is until you change it. Not jump to 100% or wherever it was the last time it was used.
Fourth is the response time of manual prop pitch control itself. It's too fast. It shouldn't respond all that much faster than Auto. At least it shouldn't be instantanious like it is now. I don't think any prop pitch control can move that fast.



Cheers.......Smokin256

XyZspineZyX
10-07-2003, 02:11 PM
As a pilot with good RL piston/prop/supercharged time (>1200hrs), I totally agree on the original post for rpm/manifold pressure relationship. It is how it works and It is great news that it is being worked on.
And by all means, great work Oleg! I havn't been playing anything else for months!


"See, Decide, Attack, Reverse or Coffee Break" E.H.

XyZspineZyX
10-07-2003, 09:36 PM
Smokin, Ivank, thanks for shedding light on this subject. I had suspected the prop governor delay was intentional, and the engine volume issue makes those idle decents make more sense.

Glad to hear a guy with DB time is on the team and I look forward to the results. One request for the 1C team: if this is changed in an upcoming patch, please include a sentence or two in the ReadMe to let us separate the features from the bugs. It might cut down a bit on the whining and bug reports, too (hey, I can dream.)

Blotto

"Only the spirit of attack, born in a brave heart, will bring success to any fighter craft, no matter how technically advanced." - A. Galland

"Look, do you want the jets, or would you rather I slap the props back on?" - W. Messerschmitt

http://home.mindspring.com/~blottogg/sitebuildercontent/sitebuilderpictures/14fsPatch.gif

XyZspineZyX
10-08-2003, 08:05 AM
After some more studying I've come to the conclusion that Ivank is right. It does appear that it was a CSU "type" system.
From the Finnish G2 manual;
3) While descending,the engine idling and your speed is less than 200kph, you must set the blade pitch control to manual or closely monitor that the airscrew pitch does not get too low (over 12 o'clock).
Sounds like a constant speed prop to me! And here;
4) Manual setting must be used;
When flying with 0 airscrew pitch (descent setting), or if the governor fails. This also sounds like a CSP.

Looking at #3 above I found this very interesting; "or closely monitor that the airscrew pitch does not get too low (over 12 o'clock)".
12 o'clock! that's about 90% prop pitch!
And this;
J. Landing
1) Slow down to 220kph.
2) set pitch control to automatic if you have flown with manual setting so far.
If you must use the manual setting, set the airscrew pitch to the 11:30 position.
That's about 85% prop pitch.
And here;
C. Take-off.
1) set flaps to 20.
2) Set pitch control to "automatic". If you are going to take off with the manual setting, you must drive the airscrew pitch to the 12 o'clock position. Again, about 90% prop pitch.

What I think all this means is that the Kommandogerat set the CSP to a higher rpm at low throttle settings for take-off, descent & landing. Lower rpm settings through the middle for cruise & high rpms again at the high throttle settings for climb & combat power. The curve as I envision it would have looked like this;
0% throttle = 2800 rpm
10% throttle = 2520 rpm
20% throttle = 2350 rpm
30% throttle = 2420 rpm
40% throttle = 2340 rpm
50% throttle = 2280 rpm
60% throttle = 2260 rpm
70% throttle = 2280 rpm
80% throttle = 2350 rpm
90% throttle = 2440 rpm
100% throttle = 2620 rpm
110% throttle = 2800 rpm

The more I think about it the more sense it makes to me. Look at the procedures from the P-51 manual;

Take-off 40"hg @ 3000rpm

Climb 35"hg @ 2600rpm

cruise 26-28"hg @ 2300-2400rpm

7. BEFORE LANDING
A. Mixture AUTO RICH.
B. Oil and coolant shutters AUTOMATIC.
C. Fuel selector to fullest tank. NOTE: Never land on droppable wing tanks.
D. Booster pump switch to NORMAL position.
E. RPM increased to 2600.
F. Normal gear procedure:
a. ****** throttle to check landing gear warning light (17"-22" M.P.).
b. IAS 170 or below. Put landing gear handle in DOWN position.
c. Allow time for gear to extend.
d. ****** throttle to check warning lights. If light does NOT come ON at previously noted position of throttle, gear is DOWN and LOCKED.

Think about it, What is the whole purpose of the Kommandogerat system in the first place. To lighten the pilots workload right? Basically to do automatically what the P-51 pilot must do manually.

Look at this from the Finnish G2 manual;
1. Diving
The pitch control must be set to "Automatic" if you have flown with the manual setting so far.
Adjust the throttle to the white line.
Maximum RPM in dive - 2800
Maximum speed in dive - 750 kph.

I'll bet you anything that this "white line" they're talking about is the spot on the throttle levers travel where the RPM is the lowest.
What do you guys think?

Cheers........Smokin256

XyZspineZyX
10-08-2003, 05:13 PM
Smokin256,

If you start a topic for discussion with statements made as if what you are saying is factual; example:

"First of all the Bf-109 has a variable pitch prop not a constant speed prop like the Fw-190."

and

"Throttle setting decreasing RPM should cause MP to increase. And increasing RPM should cause MP to decrease."

Then it seems important to me that such statements should either be factual or should include references to back up the statements just in case they might not be true. In this manner a reader who is sceptical can check the sources which lead to the conclusions.

You have disinformed the readers here with your first post regarding the 109 prop governor and have retracted this earlier statement. Thanks for the diligent maintenance on that subject.

I have a copy of a few pages in a German service manual describing the 109G2 Auto pitch device which included a wiring diagram. (Thanks to a reader on this board)
If such evidence and my ability to interpret the diagram is accurate than your first statement concerning the 109 Prop is definitely false.

The 109s used a governor in Automatic mode to switch on and off an electric motor that adjusted the prop pitch. In manual mode the pilot switched the electric motor manually.

In Automatic mode the 109 Governor, as far as my understanding goes, is controled by a prop lever, meaning that the desired power output or RPM is selected by the pilot with this lever. The odd thing about the 109 constant speed prop system when compared to the more common constant speed prop systems used by the Allies and used in modern planes is that this prop lever was linked to the throttle lever. In effect the pilot then controlled both the throttle and the prop lever with the same handle when the system was configured for Automatic prop control.

Moving onto the second statement that appears to be at odds with the facts and please illuminate this misunderstanding; manifold pressure on planes with boost systems such as hydraulic driven superchargers or even exhaust driven turbochargers will go up as RPM increases, True or False?

Your work is appreciated, but please be accurate.



JG14_Josf

XyZspineZyX
10-08-2003, 08:59 PM
JG14_Josf wrote:
- Smokin256,
-
- If you start a topic for discussion with statements
- made as if what you are saying is factual; example:
-
- "First of all the Bf-109 has a variable pitch prop
- not a constant speed prop like the Fw-190."
-
- and
-
- "Throttle setting decreasing RPM should cause MP to
- increase. And increasing RPM should cause MP to
- decrease."
-
- Then it seems important to me that such statements
- should either be factual or should include
- references to back up the statements just in case
- they might not be true. In this manner a reader who
- is sceptical can check the sources which lead to the
- conclusions.
-
- You have disinformed the readers here with your
- first post regarding the 109 prop governor and have
- retracted this earlier statement. Thanks for the
- diligent maintenance on that subject.

Yeah I knew it was risky wording my first post the way I did & I debated wording it more in the form of a Question. But I was afraid that if I did I would get a lot of replys like, " I think it worked this way" or "I'm not sure but didn't this plane have such 'n; such system?" I figured this way I would get replys from the Guys who had the most knowledge of the subject. So, sorry for any misinformation. /i/smilies/16x16_smiley-happy.gif BTW speaking of which, where are all the Fw-190 guys? /i/smilies/16x16_smiley-happy.gif

As far as references. I don't remember any specific sources. I can only recommend to do what I did. Google up everything I could find on "Messerschmitt Bf-109, Bf 109, Daimler Benz Db-601 DB 601 Db-605. Focke-Wulf Fw-190 BMW-801 & so forth. Then wade through all the stuff picking out the gems & throwing the rest away. Unfortunately I suspect all the best stuff is in German & I don't speak it so I'm left with only the english sites or badly translated stuff.

- I have a copy of a few pages in a German service
- manual describing the 109G2 Auto pitch device which
- included a wiring diagram. (Thanks to a reader on
- this board)

Wow very cool! I have a couple Questions for you on that subject if you don't mind. But I'm at lunch at work at the moment so I'll Get back to you on them after work.

- If such evidence and my ability to interpret the
- diagram is accurate than your first statement
- concerning the 109 Prop is definitely false.

Yes I have come to the same conclusion. /i/smilies/16x16_smiley-happy.gif

- The 109s used a governor in Automatic mode to switch
- on and off an electric motor that adjusted the prop
- pitch. In manual mode the pilot switched the
- electric motor manually.

Yes I've come to this conclusion as well & I believe because of this that it's unrealistic to be able to map PP to an axis. (At least on the G2 model.) But that is a subject for another time.
-
- In Automatic mode the 109 Governor, as far as my
- understanding goes, is controled by a prop lever,
- meaning that the desired power output or RPM is
- selected by the pilot with this lever. The odd thing
- about the 109 constant speed prop system when
- compared to the more common constant speed prop
- systems used by the Allies and used in modern planes
- is that this prop lever was linked to the throttle
- lever. In effect the pilot then controlled both the
- throttle and the prop lever with the same handle
- when the system was configured for Automatic prop
- control.

I'm out of time so I'll continue when I get home from work.
Once I can boot the kids of the computer! /i/smilies/16x16_smiley-happy.gif

Cheers......Smokin256

XyZspineZyX
10-08-2003, 09:40 PM
http://naca.larc.nasa.gov/reports/1945/naca-wr-e-192/

The above link was also offered by someone on this board.

It describes a U.S. test of the 190 automated engine control.




JG14_Josf

XyZspineZyX
10-09-2003, 03:24 AM
This 190 guy is listening closely http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif Unfortunately I don't have much to offer, except possibly that the Bf109 system was not actually a 'Kommandergerat'. As I understand it the Kommandergerat was a complex electro/hydrualic system fitted specifically for the BMW801. Semantics I know, not particularly relevant to the discussion.

As to manifold pressure (and its relation to RPM), that is a bit over my head still, it seems quite complex in actual operation. No doubt there is a bit wrong with what we have now. Your explanation looks even closer to the real thing, but unless I miss my guess, it is even more complex than that. As it is now, the FB Kommandergerat (FW190) behaves reasonably correct imho (no doubt it can be done even better).

XyZspineZyX
10-09-2003, 08:11 AM
JG14 Josf Thanks for the link to the FW-190 report. Great stuff.

JG14_Josf Wrote;
- Moving onto the second statement that appears to be
- at odds with the facts and please illuminate this
- misunderstanding; manifold pressure on planes with
- boost systems such as hydraulic driven superchargers
- or even exhaust driven turbochargers will go up as
- RPM increases, True or False?

Keeping in mind the key words from my original post "at a given throttle position", False. As I understand the Hydraulicly driven system in the 109, they had a secondary throttle blade between the supercharger & the primary throttle blade (the one connected to the pilots throttle lever). This secondary throttle blade was controlled by an automatic regulator that kept the pressure available at the primary throttle blade constant regardless of the actual pressure that the supercharger was putting out. So if you have a constant pressure available at the primary throttle blade. & the throttle blade isn't moved then an increase in RPM (and a proportionate increase in airflow) must cause a drop in pressure in the manifold downstream of the obstruction (primary throttle blade).

The turbocharger system in the P-47 uses a single speed supercharger to provide the actual boost in manifold pressure (except at take-off where the turbo helps). The job of the turbocharger was basically to maintain normal atmospheric pressure at the carburator inlet at high altitudes so that the supercharger could continue to do it's job. So basically the fact that it had a turbocharger makes no difference.

I hope that was clear enough. It's getting late.

Cheers......Smokin256

XyZspineZyX
10-09-2003, 05:17 PM
http://www.avweb.com/news/columns/182146-1.html

http://www.avweb.com/news/columns/182102-1.html

In general, these gear-driven supercharger systems will produce much higher manifold pressures (and greater power) than the equivalent normally-aspirated engine. Some will produce up to 60 inches instead of the usual 29 inches at sea level in a normally-aspirated engine, and some of the Reno racers jack the MP up to as much as 120 inches! Most of these installations will produce far more than maximum power at full throttle, so it is usually necessary for the pilot to stop the throttle at some point well before reaching the mechanical stop, to avoid over-boosting the engine. If you're in the habit of simply pushing the throttle forward to the stop, you're in for a rude surprise with one of these.


Smokin256,

The above is a source of information. It is a reference for anyone interested in the subject of engine management, and other Airplane related stuff. It does not include any specific references to the Me109 or FW engines.

My interpretation of your original post generated my question which read:
"...manifold pressure on planes with
boost systems such as hydraulic driven superchargers
or even exhaust driven turbochargers will go up as
RPM increases, True or False?"

to which your response is:

""at a given throttle position", False."

Your answer goes on to explain how the Diamler engine managed manifold pressure changes relative to changes in RPM. You included a note about the P-47.

I did miss the point about "at a given Throttle setting" in your initial post but it is still not clear enough for me to be able to understand how increases in RPM do not increase manifold pressure on an engine with mechanical boost.

Do you know what is used on the Diamler engine to regulate the secondary throttle blade (Plate?), is this regulator an RPM or a manifold pressure sensing device or something else? Can you refer to any sources?

In a hypothetical plane with the throttle at 50% in a hard enough climb to cause a decrease in RPM, where this example plane has a consant speed type prop but the prop is at the fine pitch stop and in the climb the blade pitch will not go any finer so the engine is dropping RPM, what happens to Manifold pressure as the plane RPM slows down in a hard climb with constant 50% throttle? What happens to the manifold pressure if the plane goes from 2000 rpm down to 1500 rpm in the climb?

Now what happens to manifold pressure if the same plane at the same 1500 rpm in a hard climb at 50% throttle goes nose low into a dive? What happens to the manifold pressure if the plane at 50% throttle overcomes the prop pitch coarse range, hits the stop and over revs to 2500 rpm?

Comparing the one extreme, the 1500 rpm 50% throttle condition climb and the other extreme the 2500 rpm 50% throttle dive; what will the difference be, if any, in manifold pressure? What happens to manifold pressure in the rpm ranges between the two extremes?

It is difficult for me to understand how an engine with a compressor will not increase manifold pressure as the engine speeds up from 1500 rpm to 2500 rpm with a constant 50% throttle. A compressor will be able to boost more pressure at higher RPM and this confuses the issue. The factor of load on the engine further confuses the issue. My point being that although someone who understands how these things work and therefore are able to make statements that appear to be simple facts, the actual process of understanding the situation is not so simple and with the many variations in engine systems it is difficult to nail down just how these WWII planes did work and if IL2/FB is modeling them accurately.








JG14_Josf

XyZspineZyX
10-09-2003, 06:42 PM
MP is related more to the power and does not go hand in hand with rpm. In FB if you put Bf on manual put let's say 50% throttle and play with pitch - what do you see. RPM going hand in hand with MP, this is wrong. What would be the use of an additional instrument telling essentially the same?

If you have driven a car with turbo you might know that if you floor the gas pedal, MP will go up and stay up already at medium revs. Now, if you reach the highest revs and lift your foot, what happens? Yes, MP vanishes in an instant, revs stay longer, engine starts braking.

MP (charged or free-breathing engine) indicates airflow in the manifold (one has under-pressure/suction, the other has overpressure). Airflow goes along with correct mixture and mixture goes together with power (you can't charge without fuel or there will be trouble). This said the MP should _roughly_ follow the throttle lever and rpm the prop control.


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http://people.freenet.de/hausberg/schimpf.gif

XyZspineZyX
10-09-2003, 09:25 PM
JG14_Josf;
Great Questions! I have almost no time right now since I'm at lunch.


JG14_Josf wrote;
- It is difficult for me to understand how an engine
- with a compressor will not increase manifold
- pressure as the engine speeds up from 1500 rpm to
- 2500 rpm with a constant 50% throttle. A compressor
- will be able to boost more pressure at higher RPM
- and this confuses the issue. The factor of load on
- the engine further confuses the issue. My point
- being that although someone who understands how
- these things work and therefore are able to make
- statements that appear to be simple facts, the
- actual process of understanding the situation is not
- so simple and with the many variations in engine
- systems it is difficult to nail down just how these
- WWII planes did work and if IL2/FB is modeling them
- accurately.

The main thing to keep in mind concerning superchargers is that through out the normal range of operation if you increase the engine & therefor superchargers RPM by 20% for example, you increase supercharger output by 20%. But you also increase the engines airflow by 20%. So the engine uses all the additional air from the supercharger & the net pressure change is zero.

Maybe EFG_Zeb would be good enough to pop in with some real world examples. /i/smilies/16x16_smiley-happy.gif

Damn! out of time.

Cheers.....Smokin256

XyZspineZyX
10-10-2003, 07:03 AM
JG14_Josf wrote;

"Do you know what is used on the Diamler engine to regulate the secondary throttle blade (Plate?), is this regulator an RPM or a manifold pressure sensing device or something else? Can you refer to any sources?"

Here's a page on the DB-605
http://www.aviation-history.com/engines/db605.htm
It's not all that detailed but it's pretty good. It explanes the inner workings of the secondary throttle blade better than I could. I wish I could find a detailed diagram like the one in the NACA report on the Fw-190.

"In a hypothetical plane with the throttle at 50% in a hard enough climb to cause a decrease in RPM, where this example plane has a consant speed type prop but the prop is at the fine pitch stop and in the climb the blade pitch will not go any finer so the engine is dropping RPM, what happens to Manifold pressure as the plane RPM slows down in a hard climb with constant 50% throttle? What happens to the manifold pressure if the plane goes from 2000 rpm down to 1500 rpm in the climb?"

Well using the generic chart from my first post. We'll say 50% throttle, 2,000RPM @ we'll say 1.0ATA. As the RPM begins to decrease the MP would begin to increase and when the RPM gets down to 1500RPM the MP would be about 1.25ATA

" Now what happens to manifold pressure if the same plane at the same 1500 rpm in a hard climb at 50% throttle goes nose low into a dive? What happens to the manifold pressure if the plane at 50% throttle overcomes the prop pitch coarse range, hits the stop and over revs to 2500 rpm?"

As the RPM starts to increase back towards 2000 RPM The manifold pressure will decrease back to the original 1.0 ATA. The MP will remain at 1.0ATA while the RPM stays at 2000RPM then when the RPM starts to rise the MP will begin to drop. And when the RPM gets to 2500 the MP will be about .75ATA.

Ugly Kid wrote;

-"MP is related more to the power and does not go hand in hand with rpm. In FB if you put Bf on manual put let's say 50% throttle and play with pitch - what do you see. RPM going hand in hand with MP, this is wrong. What would be the use of an additional instrument telling essentially the same?"

"If you have driven a car with turbo you might know that if you floor the gas pedal, MP will go up and stay up already at medium revs. Now, if you reach the highest revs and lift your foot, what happens? Yes, MP vanishes in an instant, revs stay longer, engine starts braking."

In a turbocharged car when you floor the gas pedal the boost will rise quite quickly to the point where the waste-gate opens. After this the boost pressure will stay the same regardless of the RPM.

"MP (charged or free-breathing engine) indicates airflow in the manifold (one has under-pressure/suction, the other has overpressure). Airflow goes along with correct mixture and mixture goes together with power (you can't charge without fuel or there will be trouble). This said the MP should _roughly_ follow the throttle lever and rpm the prop control."


Ugly_Kid I agree with You. This brings up a couple of interesting points. Do you have a turbocharged car handy? One with a manual trans. & a boost gauge? (or does anybody?) If so, take it out on a straight stretch of road with a pretty steep hill that goes up & then down. Choose a gear & a speed that gives you a small amount of positive boost. Then without moving the throttle climb the hill & go down the other side & see what happens to the boost pressure.

In a turbocharged car under hard acceleration you can have a situation where you have RPM & manifold pressure or boost increasing at the same time. This is due to turbo lag. & this may be the source of some confusion. This happens because the car engine can accelerate so fast that the turbo impeller just can't physicaly spool up Quick enough to keep up. A gear driven supercharger doesn't suffer from lag & a turbocharger in an aircraft such as the P-47 or P-38 is a completely different animal.


Well I think I've bored you all long enough for tonight.

Cheers......Smokin256

XyZspineZyX
10-10-2003, 02:22 PM
- The main thing to keep in mind concerning
- superchargers is that through out the normal range
- of operation if you increase the engine & therefor
- superchargers RPM by 20% for example, you increase
- supercharger output by 20%. But you also increase
- the engines airflow by 20%. So the engine uses all
- the additional air from the supercharger & the net
- pressure change is zero.

you got it but your conlution is wrong. You have to take into account that the charger is able to pump more air than the engine sucks.

the same example with volume of air

engine 100l charger 120l => 20l difference

now increasing the rpm 20%

engine 120l charger 144l => 24l difference

and the 4l Air will result in a higher MP

-In FB if you put Bf on manual put let's say 50% throttle and play with pitch - what do you see. RPM going hand in hand with MP, this is wrong.

No thats correct. It is not correct that it is not possible to change the MP with the thottle.

Greatings
Merlin /i/smilies/16x16_smiley-happy.gif

JG301_Merlin
Kapit√¬§n 3. Staffel
Jagdgeschwader 301 "Wilde Sau"
http://www.jagdgeschwader301.de
http://www.jagdgeschwader301.de/images/wappen-t1.gif

XyZspineZyX
10-10-2003, 09:06 PM
Merlin_VFA34 wrote:
-- The main thing to keep in mind concerning
-- superchargers is that through out the normal range
-- of operation if you increase the engine & therefor
-- superchargers RPM by 20% for example, you increase
-- supercharger output by 20%. But you also increase
-- the engines airflow by 20%. So the engine uses all
-- the additional air from the supercharger & the net
-- pressure change is zero.
-
- you got it but your conlution is wrong. You have to
- take into account that the charger is able to pump
- more air than the engine sucks.
-
- the same example with volume of air
-
- engine 100l charger 120l => 20l difference
-
- now increasing the rpm 20%
-
- engine 120l charger 144l => 24l difference
-
- and the 4l Air will result in a higher MP

Greetings Merlin!
Yes you are absolutely correct but I suspect that you missed the keywords earlier, " At a given throttle position". The post you are refering to above is a simplified example used to illistrate a particular point. Your example above would be correct if the engine had unimpeded airflow. But what we're talking about at the moment is the engines behavior regarding RPM changes at a particular throttle setting. Damn! Out of time again. The bottom line is. We're trying to figure out & illistrate a way for Oleg & Co. to model MP realisticly without requiring a second procsessor to do it.
-
--In FB if you put Bf on manual put let's say 50% throttle and play with pitch - what do you see. RPM going hand in hand with MP, this is wrong.
-
- No thats correct. It is not correct that it is not
- possible to change the MP with the thottle.

Forgive me if this question is intended for Ugly_Kid but I don't remember anyone saying it was not or should not be posible to change the MP with the throttle.

??? Sorry I'm confused!

Cheers,,,,,Smokin256



Message Edited on 10/10/03‚ 01:21PM by Smokin256

Message Edited on 10/10/0301:22PM by Smokin256

XyZspineZyX
10-11-2003, 03:33 AM
There remains some confusion on this subject.

Here is another source:

http://www.virtualpilots.fi/en/hist/WW2History-KyostiKarhilaInterview.html

________________________________
I seem to remember that the Messerschmitt reacted faster, having fuel injection. The Messerschmitt engine control has been praised in general and not in vain.

What about the boost pressure, it could be adjusted to above the allowed level even by accident?

Yes, there was no limiter and in different altitudes the boost pressure is different.

The Messerschmitt supercharger was powered over a liquid clutch which maintained even boost pressure.


If the airscrew governor breaks down, then the too high speed of rotation causes increase in boost pressure. Then the engine is very soon worn out.
____________________________________





JG14_Josf

XyZspineZyX
10-11-2003, 02:54 PM
- Greetings Merlin!
- Yes you are absolutely correct but I suspect that
- you missed the keywords earlier, " At a given
- throttle position". The post you are refering to
- above is a simplified example used to illistrate a
- particular point. Your example above would be
- correct if the engine had unimpeded airflow. But
- what we're talking about at the moment is the
- engines behavior regarding RPM changes at a
- particular throttle setting. Damn! Out of time
- again. The bottom line is. We're trying to figure
- out & illistrate a way for Oleg & Co. to model MP
- realisticly without requiring a second procsessor to
- do it.

no I saw your keywords and I was not talking abbout throttle full open. I was talking about a throttle setting where the engine is able to increase RPM.

I don‚¬īt think that Oleg need our help. I think someone has talked to him about the MP gauge and he said that the fightmodel is not able to model it correct but they will try to model it in the future.

---In FB if you put Bf on manual put let's say 50% throttle and play with pitch - what do you see. RPM going hand in hand with MP, this is wrong.
--
-- No thats correct. It is not correct that it is not
-- possible to change the MP with the thottle.
-
- Forgive me if this question is intended for Ugly_Kid
- but I don't remember anyone saying it was not or
- should not be posible to change the MP with the
- throttle.
-
- ??? Sorry I'm confused!

I‚¬īam also confused now.

Greatings
Merlin /i/smilies/16x16_smiley-happy.gif

JG301_Merlin
Kapit√¬§n 3. Staffel
Jagdgeschwader 301 "Wilde Sau"
http://www.jagdgeschwader301.de
http://www.jagdgeschwader301.de/images/wappen-t1.gif

XyZspineZyX
10-11-2003, 04:04 PM
If the engine is running with 50% throttle position and you go manual and increase the rpm you effectively unload the engine, you decrease the torque and thus you need less power. Why on earth should MP go up? Take a car with charger and push the gas pedal with the gear on neutral not much activity on the MP, is there?

MP is an indication of power output. You effectively order power with throttle setting, it is not logical to say I want to have only half the power and expect the charger to charge.

Yes, if the charger is connected to crankshaft it needs the revs i.o to charge, same for turbo it needs exhaust gas flow in order to charge but there is no need to charge if you don't need the power.

Dive in an aircraft pull throttle on the idle and put fine pitch. Soon the prop is windmilling and rpm goes up but the prop is turning the engine not vice versa so there is no need to charge, no need for power -> MP stays down.

Opposite example give full throttle but put a overtly coarse pitch. Charger can't charge because the charger is not running fast enough MP will stay low and engine is coughing. There is a rpm dependency on MP but mainly it is a matter of throttle position and engine torque.

At high rpm your charger may be running fast but the throttle position regulates the wastegate and if you don't give the throttle it will blast all the air out of the wastegate (no MP then).

This is how I understand it with my limited knowledge I think there are couple of guys who knows it better, so please fill in the gaps.http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

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XyZspineZyX
10-12-2003, 04:15 PM
Ugly_Kid wrote:

"If the engine is running with 50% throttle position
and you go manual and increase the rpm you
effectively unload the engine, you decrease the
torque and thus you need less power. Why on earth
should MP go up?"



The Finnish veteran pilot Ky√¬∂sti "K√¬∂ssi" Karhila was interviewed:

"If the airscrew governor breaks down, then the too high speed of rotation causes increase in boost pressure. Then the engine is very soon worn out."



I cannot answer the question "Why on earth should the MP go up?" with anything other than specualtion.


Here is more from the Finnish pilot interview:

"What about the boost pressure, it could be adjusted to above the allowed level even by accident?

"Yes, there was no limiter and in different altitudes the boost pressure is different."

"The Messerschmitt supercharger was powered over a liquid clutch which maintained even boost pressure."

"If the airscrew governor breaks down, then the too high speed of rotation causes increase in boost pressure. Then the engine is very soon worn out."



My opinon is that the Messerschmitt's Diamler engine had a supercharger driven by a fluid coupling that was in turn driven by a hydraulic pump, that was driven by the engine.
The speed of the compressor and therefore the boost pressure was dependent upon engine speed, regulated hydraulic pump pressure and regulated throttle control.

The possibility exists that the diamler egine was so designed to automatically control manifold pressure and if the pilot chose to operate the engine manually he ran the risk of overboosting the engine, or if as Ky√¬∂sti "K√¬∂ssi" Karhila points out; if the prop governor breaks down, then over boost can occur if the engine over revs.

Why does engine over rev cause overboost in the Diamler engine?

My guess is that the normal automatic controls for boost pressure depend upon the relationship of throttle possition and governed prop control. Notice the Messerschmitts have a constant speed prop but they do not have a prop lever. The prop lever is linked to the throttle lever. It is not possible to lower the throttle and at the same time rev the engine at max governed rpm in the Messerschmitt. It is possible to lower the throttle and rev the engine well over any reasonable rpm with manual control of the prop pitch.
When the engine is spinning fast regardless of throttle possition the hydraulic pump is driven fast, the hyraulic coupling is then driving the compressor fast, and the compressor is then trying to pump a lot of air into the engine. Overboost occurs. Manifold pressure exceeds a safe value at a given throttle possition due to the engine reving higher than it is designed to turn at that throttle setting.



Back to Ugly_Kids question:

Why on earth should MP go up?

Here is a possible source to answer this question:


http://www.avweb.com/news/columns/182104-1.html

"Moving the throttle does not normally affect the RPM, since we are talking mostly about constant-speed props. But the converse is not true: Changing the RPM can have a major effect on the manifold pressure (MP). Depending on the circumstances, and whether you have a supercharger or not, an RPM change can move the MP either way, and you should understand why. Changing RPM can have an effect on the mixture, too (fuel pump turns faster/slower, for one thing), as well as the effective timing."

http://www.avweb.com/news/columns/182106-1.html

"However, on engines with the gear-driven superchargers and turbochargers that produce more than about 31 or 32 inches MP, full throttle may seriously overboost the engine in some phases of flight."

The answer may not be the same for each plane.




JG14_Josf

XyZspineZyX
10-12-2003, 07:26 PM
Bf...you have to consider where your engine is running once that governor breaks, eh? If it's full throttle and the governor breaks then you eventually get quite some boost, after all the wastegate is almost closed, having throttle on idle - no sweat.

You may twist this the way you like but it won't change the fact that MP is an indication for the things that happen in manifold and it is thus an indication for the power not rpm. More MP, more stuff happening, you can't charge air alone without adding fuel, if you do, bad things happen. RPM and MP are not instruments essentially stating the same information, that is all I am trying to say.

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XyZspineZyX
10-12-2003, 07:50 PM
Ugly_Kid wrote:

"You may twist this the way you like"

I am not sure why you wrote the above but Please consider the possiblity that my motive is to learn.

For example:

Did the Diamler engine us a waste gate?



JG14_Josf

XyZspineZyX
10-12-2003, 09:08 PM
Sorry I did not mean bend or twist. I meant like a cat going around a pot of hot porridge /i/smilies/16x16_smiley-happy.gif

It was not meant in a negative sense. DB probably had not necessarily a wastegate in that sense (to limit overboost) but there must have been a charger control in order to control charger based on need...(like engine torque)

And I did not mean that I _know_ something, I am here to learn as well...For me engine is a black box, I know what it does to an aircraft but I don't know too much how it accomplishes that.

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Message Edited on 10/12/03‚ 09:15PM by Ugly_Kid

Message Edited on 10/12/0309:46PM by Ugly_Kid

XyZspineZyX
10-12-2003, 10:36 PM
JG14_Josf wrote;

- Back to Ugly_Kids question:
-
- Why on earth should MP go up?
-
- Here is a possible source to answer this question:
-
-
- <a
- href="http://www.avweb.com/news/columns/182104-1.h
- tml"
- target=_blank>http://www.avweb.com/news/columns/18
- 2104-1.html</a>
-
-
- "Moving the throttle does not normally affect the
- RPM, since we are talking mostly about
- constant-speed props. But the converse is not true:
- Changing the RPM can have a major effect on the
- manifold pressure (MP). Depending on the
- circumstances, and whether you have a supercharger
- or not, an RPM change can move the MP either way,
- and you should understand why. Changing RPM can have
- an effect on the mixture, too (fuel pump turns
- faster/slower, for one thing), as well as the
- effective timing."
-
- <a
- href="http://www.avweb.com/news/columns/182106-1.h
- tml"
- target=_blank>http://www.avweb.com/news/columns/18
- 2106-1.html</a>
-
-
- "However, on engines with the gear-driven
- superchargers and turbochargers that produce more
- than about 31 or 32 inches MP, full throttle may
- seriously overboost the engine in some phases of
- flight."
-
- The answer may not be the same for each plane.
-
-
-
-
-
-
- JG14_Josf

These articals on Avweb are excellent! In the first article Josf linked to the most important passage is this;

"I'm a little nervous writing stuff like this, because I am acutely aware that not all readers are the same. Some will read this column by itself, without reading the material in previous columns that has led up to this point. Some don't care about the dirty details, and simply want to know what to push or pull and when to do it, without any desire to understand what they're doing, and why. Some may skim the material, figuring they know most of it already, and some may use a procedure "out of context."

I can only ask you to be careful when using this material. That's true of anything in aviation (or life itself!), but a bit more so in this area. A thinking pilot is always the best safety device in any airplane, and if a thinking pilot also has the practical knowledge to go with it, so much the better. In many ways, these engines are far more rugged than many believe, but ignorance or a few moments of carelessness can easily do major damage to an engine, with potential catastrophic results to the airplane. The potential for damage is even greater with supercharged engines of any type.

Finally, this information is heavily slanted towards the engines built by Teledyne-Continental Motors (TCM). The basic principles of combustion are the same for all spark-fired, gasoline-powered, four-stroke engines, from your garden tractor to the monstrous Pratt & Whitney R-4360 of bygone days. However, some of the details differ, with some slightly different limitations. It is impossible to cover them all, and since all recent development work that I'm familiar with has been on TCM engines, those are the ones we'll talk about.

If you are not prepared to study and understand the underlying principles, I do not believe you can safely and economically operate these fire-breathers, and frankly, I wish you wouldn't read this stuff at all. I'm not trying to be elitist here, just trying to warn the unwary. As someone said, "A little knowledge is a dangerous thing."

Come to think of it, this may be one reason there is so very little material of this kind "out there." Maybe no one wants to stick his or her neck out!

Review Material

For your information, I have listed previous related columns. If you have not read them, this would be an excellent time to do so. They are the foundation for this current column, which has a lot of "advanced material" in it."


I can whole heartedly recommend reading the whole series of articles from the very beginning. It is criticly important to read (not just skim) the entire thing Starting with "Manifold pressure sucks!".

Please take the time to read the entire series & then let's talk about it. I know that it's very long but it really is important.

As you read the articles keep in mind that with a few exceptions a gear driven supercharger only changes the upper range that the manifold pressure runs at. For example 12in/hg to 56in/hg or higher instead of 12in/hg to 30in/hg as in the naturally asperated engines in the first parts of the series. It does not change the basic Throttle/MP/RPM relationship.

I've come to the conclusion that I personally don't know enough about the German automatic supercharger controls to comment on them. I read the NACA report on the Fw-190 & I realize I was wrong about a number of things. So I appologize for any misinformation on that subject. I'll limit my discusions to the manual systems.


Cheers.....Smokin256

XyZspineZyX
10-12-2003, 10:40 PM
For God Sake man, this is only a bloody game. Lighten up !!

XyZspineZyX
10-12-2003, 11:59 PM
Bulls-eye wrote:

"For God Sake man, this is only a bloody game.
Lighten up !!"

The subject matter in this post is relevant to the simulation of WWII Air Combat.

The program IL2/FB simulates WWII Air Combat.

What is the problem?

The forum is a good place to exchange information and ideas, if that is not something desirable then why read these posts?


Smokin256 wrote:

"It does not change the basic Throttle/MP/RPM relationship."

On the one hand the normaly aspirated engine depends upon the relatively low pressure created by the engine rotation to feed or suck an air fuel mixture into the engine and on the other hand the boosted engine pumps a realatively high pressure forcing the fuel and air into the engine.
How can this differnce not effect the Throttle/MP/RPM relationship?

For example (This is a question not a statement of fact)

A hypothetical engine with boost running at 100% throttle has 1.2 ata MP
Then the hyraulic pump pressure relief valve falls off dumping all hydraulic pressure that is used to drive the compressor.
What happens to the Manifold pressure?

A compressor creates more atmosphere and doesn't engine RPM effect how much more atmosphere a compressor is able to create?

Ideally the engine compressor will create just the right amount of extra atmosphere for all conditions.
Too much air/fuel is bad and too little air/fuel is bad for any given condition.
Planes with no compressors are subjected to limitations in the Earths normal atmosphere.
Engines with compressors are limited how?
What happens when the compressor turns to fast?
What happens when the compressor turns to slow?
When the engine turns the compressor then engine RPM effects the compressors ability to provide the ideal fuel/air mixture.

One possible way to adjust the compressors ability to provide the right amount of atmosphere is to use a hydraulic driven fluid coupling and adjust the pressure of the fluid used to drive the fluid coupling which in turn drives the compressor.
Another way, described by the link posted on this board:
http://www.aviation-history.com/engines/db605.htm
Throttle both ends of the compressor. One end throttles the intake end of the compressor and the other throttles the engine itself.
What constitutes a capsule control is not specified in that desription.Capsule is a term used for a device common in refrigeration and is a temperature sensitive mechanical movement. The capsule is filled with a liquid and as the liquid heats up the liquid expands to push the mechanical linkage.
It seems possible that the Diamler engine may have a pressure sensitive capsule that regulates manifold pressure; when the pressure builds to an amount over the desired value the capsule moves the butterfly throttle plate closed and visa versa.

Here is another example from the AV website:

http://www.avweb.com/news/columns/182102-1.html

"In general aviation, there are two major variants of the turbocharger. One, like the gear-driven supercharger, will produce much greater manifold pressure at sea level than the equivalent normally aspirated engine. The pilot will generally need to be careful when setting takeoff power, as full throttle will usually "overboost" the engine. A few engines had complex devices to prevent this, and some would even automatically maintain a given MP (the Merlin V-12s in the Mustangs, for example), but they are not common today."

Ugly_Kid,

Thanks for the clarification.


P.S.

The AV website has two new articles on the Hurricane.









JG14_Josf

Message Edited on 10/12/0311:02PM by JG14_Josf

XyZspineZyX
10-13-2003, 09:38 AM
JG14_Josf wrote:
- Bulls-eye wrote:
-
- "For God Sake man, this is only a bloody game.
- Lighten up !!"
-
- The subject matter in this post is relevant to the
- simulation of WWII Air Combat.
-
- The program IL2/FB simulates WWII Air Combat.
-
- What is the problem?
-
- The forum is a good place to exchange information
- and ideas, if that is not something desirable then
- why read these posts?

Yeah what he said! Hey so we like gauges, levers, valves, Gears & stuff. Go away & leave us alone we're having fun! /i/smilies/16x16_smiley-happy.gif
BTW good find on the Hurricane articles at Avweb! Great stuff!

JG14_Josf wrote:
"- On the one hand the normaly aspirated engine depends
- upon the relatively low pressure created by the
- engine rotation to feed or suck an air fuel mixture
- into the engine and on the other hand the boosted
- engine pumps a realatively high pressure forcing the
- fuel and air into the engine.
- How can this differnce not effect the
- Throttle/MP/RPM relationship?"


using the example of a naturaly aspirated engine.The air enters the carburator that houses the throttle blade & then goes to the engine. Ambient pressure (29.9in/hg or 1.0 ATA at sea level) is always applied to the throttle blade. At 2000 RPM, 50% throttle would give you X amount of MP. If you increase RPM the engine tries to pump more air. But since the throttle position stays the same & the pressure applied at the throttle stays the same, the amount of airflow stays almost the same (see note.)& the pressure drops.

Using an example of a carburated engine with a supercharger. The air enters the carburator which houses the throttle blade. then goes to the supercharger & then to the engine. The pressure available at the throttle blade is always ambient pressure. (29.9"/hg or 1.0ATA at sea level.) So at 2000 RPM, 50% throttle would give you X amount of MP. Now if we raise the RPM the engine tries to pump more air & The supercharger tries to compress more air but they can't since the throttle position stays the same & the pressure applied at the throttle (ambient) stays the same so airflow stays almost the same (see note.)& the pressure drops.

Note!
When the pressure drops there is a slight increase in airflow but it is much much less than the engine or engine/superchargers demand.

There's too much about the Hydraulicly operated supercharger in the 109 series that I don't know for me to comment on them.


- A hypothetical engine with boost running at 100%
- throttle has 1.2 ata MP
- Then the hyraulic pump pressure relief valve falls
- off dumping all hydraulic pressure that is used to
- drive the compressor.
- What happens to the Manifold pressure?

Assuming no arcane Kommandogerat wierdness it will drop to right around or just below ambient pressure. How much below would depend on how much of a restriction to airflow the now freewheeling or stopped supercharger impeller is.

I'll continue tomorrow I Gotta hit the sack!

Cheers......Smokin256