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kiershar

Bf109 Overreving when flying at high altitude

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When flying level at ~600 km/h+ at 4000m+ alt the bf109 f4 overrev and the RPM doesn't stabilize. Also somehow my engine shut down by itself and restarted multiple times in a row when diving from 6k alt, never had that happen before.

 

Is that normal? Something definately changed with the automatic RPM recently but I don't think i saw patch notes about that.

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Its simply because the whole Throttle-Kommandogerät-Stuff is plain wrong modeled. But hey, according to the dev's it works as it should... ;)

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Just start a QMB free flight and start at 6k alt. Accelerate to 600, watch the RPM meter and you'll instantly see what i'm talking about.

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You have to pull the throttle back to the white stripe on the throttle quadrant. That's the throttle setting for steep dives.

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There's a difficulty setting that manages your engine and prevents overstressing the engine. Don't know what it's called. It is switching off, because you're nearing the maximum rpm stated in the pilot handbook. The guys in Moscow are probably using the standard DB maximum of max. rpm + 2%, i.e. about 2750, however, the 109 manual states to keep it below 3000. At any rate, the engine was supposed to be send back to the factory for inspection if limiting rpm were exceeded. In game, it will probably blow sooner or later, same thing as with the weird boost time limits.

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The problem as I see it is that they (the developers) are using % percentage of throttle opening versus ata.  As you climb the ata will tail off as it should at higher altitudes but if you increase the throttle to maintain ata you will blow your engine (if you exceed % of throttle) even though the ata is no where near max 1.42.  This is not realistic.

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That's actually perfectly realistic. Assuming you mean the drop of manifold pressure above critical altitude of the supercharger. Then the RPM will become the sole limiting factor.

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He probably meant that the engine blows without obtaining full ata just as if it was. 2700 rpm weren't as critical as the 1.42 ata that went with it.

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From what I understand the kommandogerat should lower the prop pitch automatically to bring it at 2500 rpm, which it is not doing. And as far as i know there's no supercharger on bf109 f4 but i could be wrong.

 

I'll make a video to show the problem.

Edited by kiershar

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Kommandogerät, 109? Flip that 0 and 9 around. ;)

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There I made a video for it :

 

https://www.youtube.com/watch?v=_MxRaWo9IXo

 

In the first part, you can see when I reach 560 the prop pitch dial stops and the RPM starts rising. Around 600 the engine enters emergency mode by itself. I nudge the throttle a little bit to make the 80% appear as proof. Basically the automatic RPM stops working and stays above 2500 rpm, slowly damaging the engine. After that I start to throttle down to bring the RPM at 2500 manually, you can see the engine entering combat mode at ~50% throttle. As the plane gets around ~2700m alt I throttle back up to 80% and the automatic RPM is able to keep it at roughly 2500 rpm.

 

Second part (1:35) is where the engine switch off and on by itself multiple times in a row, probably a consequence of the automatic RPM not adjusting the prop pitch properly. In that scene I only touch control surface, no throttle input at all. The engine shuts down 3 times in a row and the throttle goes wild.

Edited by kiershar

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So what is the expected behavior?

 

Some observations from flying an aircraft that does not have any kommandogerat (Bonanza with constant speed prop):

  • Entry: level flight, 25 in Hg, 2,500 RPM
  • Set up: reduce power to 21 in Hg
  • Set up: reduce RPM to 2,000 RPM
  • Result: pressure is up to ~23 in HG, need to manually reduce it back to 21 in Hg

Conclusion: Forcefully reducing RPM will result in increased pressure.

 

Not exactly the same as what you are observing, but I think the same principle is at work.

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When flying level at ~600 km/h+ at 4000m+ alt the bf109 f4 overrev and the RPM doesn't stabilize.

 

Is that normal?

 

I don't know, how it did react exactly at this altitude, but it makes sense. There was no "RPM limiting computer" at work. Use manual pitch at this altitude.

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From my understanding the engine shouldn't have the power to overrev at that altitude with the pitch at 8:30.

That is the maximum pitch available here.

But then, there was the ability to feather the prop in RL, so maybe a even higher pitch was possible.

Edited by I./ZG15_robtek

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S!

 

 Just test how well the planes keep their manifold pressure. Bf109G-2 with DB605A-1 should still have 1.3ata at 5.7km and after that gradually decreasing so that at 10km would be 0.65ata.

 

 

post-539-0-94281900-1416920336_thumb.jpg

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So altitude pressure affects directly the engine inside pressure through increased propeller revolutions  due to thinner air ?

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Kommandogerät, 109? Flip that 0 and 9 around. ;)

The DB 601 and DB 605 had also an Kommandogerät... nothing to flip.

 

 

And to make one thing clear the RPM was maintained by this complex device. It was an automatic pitch control always setting the rpm according to the manifold pressure you set with the throttle.

 

 

 

So altitude pressure affects directly the engine inside pressure through increased propeller revolutions  due to thinner air ?

Sure, thats why they have compressor or supercharger's. They concentrate the air which gets into your engine so you have a better reaction.

Edited by Auva

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Thanks.

Whow after I reread your question maybe I got it wrong but:

Your engine will loose power when it comes above the Maximum Pressure Level (In German Volldruckhöhe). Until that altitude the engine gives full power. Above that altitude the engine will loose power because the air is too thin and the air compression is not strong enough. To higher that altitude engines are using mainly two concepts. The compressor/supercharger is driven directly from the engine and compresses the air. The other device is the turbocharger. This device is driven from the exhaust fumes. Both systems have their pro and cons but they are doing essentially the same. Compressing Air to allow a better Oxygen - Fuel mixture in greater altitudes.

Now when the engine goes beyond its maximum pressure height the manifold pressure drops because the engine gets not enough oxygen from the air and you encounter a power loss. The power loss leads to a lower RPM. But this can be countered by changing the propeller pitch. So if you lower the pitch of the propeller blades you can still have your engine RPM at 2.400 rpm while flying with 0.9 ata manifold pressure (example).

 

Now to get to an end, the German Fighters Bf109 and Fw190 didn't used constant speed propellers like the Allies. They had special devices which would change the pitch of the propellers according to the wanted rpm or you could manually change the pitch. Afaik those devices hold the rpm even if the manifold pressure dropped above the maximum pressure level.

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Okay, clear enough. Basically you have a minimum and a maximum pressure.  So technically you can have such high rotation and such low pressure that the engine simply breaks, no matter if it is constant speed or a auto adjusted system. Similar to driving a car at low gear but full pedal.

 

Let's see if I got it, at low air pressure altitude I must increase throttle so atmosphere gets higher inside the engine, therefore increasingly augmenting the RPM. So is the 109 auto system synchronized by lever attitude OR by real pressure inside the chamber ?

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The DB 601 and DB 605 had also an Kommandogerät... nothing to flip.

 

 

Not correct.

 

While the DB series in the Bf-109 had some automatic functions and on the surface might appear the same as the Kommandogerät produced by Bendix for the BMW801 series, it was not.

 

The DB series simply kept the propeller and manifold pressure in sync to a calibration table.   It was not interconnected with other engine functions.

 

The Kommandogerät controlled multiple functions interacting with each other.  Fuel metering, spark advance, manifold pressure, rpm, and supercharger function were all linked into one controlling unit to function as a complete system.

 

Here is the KG on the BMW801 system functions:

 

From an RAE investigation

 

post-1354-0-48013400-1416934894_thumb.jpg

 

From BMW

 

post-1354-0-35156700-1416935015_thumb.jpg

 

post-1354-0-18492000-1416935065_thumb.jpg

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Now to get to an end, the German Fighters Bf109 and Fw190 didn't used constant speed propellers like the Allies.

 

 

Correct and why they might on the surface appear to have the same automatic functions of the engine.  It would be easy to mistake the operations of the VDM hydraulic-electric propeller system with an "automatic engine control".

 

The VDM propeller in automatic operation used a pressure solenoid switch to read the engine oil pressure to vary the amount of current sent to an electric pitch change mechanism.  In other words, if you mounted a VDM hydraulic-electric propeller, it would change pitch IAW throttle settings by design.

 

Nothing to do with the DB series having a Kommandogerät.

Edited by Crump

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In the first part, you can see when I reach 560 the prop pitch dial stops and the RPM starts rising. Around 600 the engine enters emergency mode by itself. I nudge the throttle a little bit to make the 80% appear as proof. Basically the automatic RPM stops working and stays above 2500 rpm, slowly damaging the engine. After that I start to throttle down to bring the RPM at 2500 manually, you can see the engine entering combat mode at ~50% throttle. As the plane gets around ~2700m alt I throttle back up to 80% and the automatic RPM is able to keep it at roughly 2500 rpm.

 

I suppose prop pitch reaches coarse limit (8:30 in pitch meter) by power-dive, thus automatic RPM can't keep 2500 rpm and become overrev.

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There I made a video for it :

 

https://www.youtube.com/watch?v=_MxRaWo9IXo

 

In the first part, you can see when I reach 560 the prop pitch dial stops and the RPM starts rising. Around 600 the engine enters emergency mode by itself. I nudge the throttle a little bit to make the 80% appear as proof. Basically the automatic RPM stops working and stays above 2500 rpm, slowly damaging the engine. After that I start to throttle down to bring the RPM at 2500 manually, you can see the engine entering combat mode at ~50% throttle. As the plane gets around ~2700m alt I throttle back up to 80% and the automatic RPM is able to keep it at roughly 2500 rpm.

 

Second part (1:35) is where the engine switch off and on by itself multiple times in a row, probably a consequence of the automatic RPM not adjusting the prop pitch properly. In that scene I only touch control surface, no throttle input at all. The engine shuts down 3 times in a row and the throttle goes wild.

 

If that airspeed is EAS or IAS.....

You are so far outside the normal operating envelope of the aircraft and have exceeded Vne.  Yes, the propeller is driving the engine and you cannot expect normal behavior.

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I routinely fly at 800 km/h for gun pass and there's never any problems with the RPM at lower altitude.

 

I tested the engine a lot a few month ago and this behavior was definately not in-game (overrevs and shutdowns), yet I never saw patch notes saying the RPM behavior changed.

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I routinely fly at 800 km/h for gun pass and there's never any problems with the RPM at lower altitude.

 

 

Is that indicated or true airspeed?  That is the question that must be answered, kiershar.  Do you know the difference?  If not I can help you or you can google it.  Airplanes have mulitple speeds and are the only vehicles in existence that the speedometer does not tell you how fast you are really going and the altimeter does not tell you the height you are at.

 

So it is important to know which speed you are talking about!   :)

 

If it is true airspeed, there is a tiny portion of the airplanes envelope where you would be at Vne or just below it.  If that 800 kph is indicated then the airplane is exceeding its envelope and the real thing is not capable of achieving that speed without incident.

 

Here is the Mtt high speed testing results.  The adverse behaviors of the aircraft define the limits on the graphs.

 

post-1354-0-43426000-1417029674_thumb.jpg

Are you playing with full realism?

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It is IAS. Did you even play the game? There is no TAS indicators you would know that if you actually played.

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Nowhere in the airplanes envelope can it achieve 800 kph Indicated airspeed safely.

 

On that chart, Va is indicated airspeed and Vw is true airspeed.

 

No I do not play this game.  I am watching and seeing to decide. Is that Ok with you?

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I find it a bit insulting how condescending you are, considering you never experienced the game physics yourself. My point is that the plane overrev now, while a few month ago it did not. And the bf109 can survive speed of up to 850 km/h with absolutely no problems in-game.

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I find it a bit insulting how condescending you are, considering you never experienced the game physics yourself. My point is that the plane overrev now, while a few month ago it did not. And the bf109 can survive speed of up to 850 km/h with absolutely no problems in-game.

 

Nobody is trying to insult or be condescending either.  I have not experienced this game...correct.  I do play other flight games including ones a few that cost about 20,000 USD for 6 hours of play, LOL!!!  They are called type ratings.  :salute:

 

I pay my bills flying airplanes and have the benefit of a college education in Aeronautical Sciences.  What is that?  It is the study of science of aircraft.  What can you do with it?  Bitch about it not doing anything for you at a Regional airline, Fly really expensive or unique airplanes (if you have the experience and rating...which I do), Manage expensive or unique airplanes for deep pocket organizations, or be a team lead at Boeing, Northrup Grumman, EADS, etc....

 

 

Aeronautical science is the science of flight, and this field relates to careers involved with the design and development of aircraft. Aeronautical engineers study how flight may be achieved within the Earth's atmosphere and use that knowledge to design airplanes. Some graduates holding degrees in aeronautical science become pilots. While not all piloting jobs require students to graduate with aeronautical science degrees, the credential is a definite advantage.

For those who do not wish to work as pilots, an aeronautical science degree can lead to a career in the design, construction or maintenance side of the industry.

 

http://education-portal.com/articles/Aeronautical_Science_Job_Information_for_Recent_Graduates_Pursuing_a_Career_in_the_Aeronautical_Science_Professions.html

 

Seriously....not trying to insult or hurt your feelings.  Just trying to be helpful and answer your question about why your airplane would do that.

 

It would do that because you are flying faster than the airplane was meant to go.  Sounds like it is a feature of the game and not a bug.   

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Ok I get it you are smarter and more educated than everyone. Good job. Do I care? No.

 

This thread is about game physics of IL2-BoS, whatever fancy things you did is not relevant here. Kinda pitiful you have to stroke your ego in front of us uneducated, ignorant peasants.

 

This video is for you :

Edited by kiershar

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It was not my issue Kieshar nor did I trumpt my education, you simply got butt hurt when I very nicely answered your question.


 

 

And the bf109 can survive speed of up to 850 km/h with absolutely no problems in-game.

 

That probably should be fixed.  It is things like this that I am looking for before I drop 100 bucks on a game..... 

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Oh of course my feelings were completely hurt. haha lol...

 

Have you looked at yourself, all you do on this forum is being condescending and informing people of how knowledgeable you are of things that does not even matter, in a game that you did not even played. Nearly 900 posts on this forum and you don't even own the game... what is your purpose here?

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@ kiershar

 

this thread is about a fault in the game physics of BoS, which should be corrected.

There are quite a few planes able to survive passing Vne!

 

Oh, and by the way, if one is out of arguments it will get personal, see your last post.

Edited by I./ZG15_robtek

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The problem here is that someone is derailing the thread because he wants to talk about his career.

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