Bf 109-G DB605A (and AM) engine full throttle height (Volldruckhöhe)

[the_emperor]

Hey there,
according to manuals, climb- and engine charts the critical height (Volldruckhöhe) for the 109's DB605A engine is rated at approx. 5.4 - 5.7km in climb (at 350kph TAS so ~280kph IAS?) and 6.4-6.6km in level flight for Steig-und Kampfleistung (1.3ata/2600rpm).
Unfortunately my engines in the 109Gs with DB605A start to loose boost in climb at around 3000m with the DB605A at 1.3ata/2600rpm.
And I seem to have the same issue with the DB605AM. Its critical height in climb is ratet at approx. 4000m with Notleistung (1.7ata/2800rpm) and approx. 5000m in level flight, but boost pressure starts to drop at around 1000m in climb.
So my questions: is there a special engine setting I am missing except pushing the throttle to the desired ata/rpm setting or did I missread the technical manuals and charts for this plane?  I am not that familiar with the 109 models and just getting used to them since I mostly fly Spitfires.
So far only tested on summer maps (should there be a difference between summer and winter for the engines critical height?).
Thanks for your help.
Cheers

Edited April 19, 2020 by the_emperor

[Raven109]

Check your realism settings. I think there was one that automates the engine more than you'd like. Perhaps "Engine auto-control" or "Simplified controls".

Edited April 18, 2020 by Raven109

[6./ZG26_Klaus_Mann]

You are correct, this is the Document to back you up. It is a Comparison between the DB605A and AS, with the Value in Parenthesis giving the Values for the DB605A. It clearly states the FTH in a Climb is 5.7km for the A and 7.3km for the AS, and in Level Flight is 6.6km for the A and 8.3 for the AS.  This is for 1.3ata and 2600 RPM http://www.wwiiaircraftperformance.org/me109/VB-109-20-L-43.pdf

Edited April 18, 2020 by 6./ZG26_Klaus_Mann

[the_emperor]

Here are two further document which give us the the boost in climb  for the DB 605 A Engine:
http://www.wwiiaircraftperformance.org/me109/me109g-14026-page6-1200.jpg
http://www.wwiiaircraftperformance.org/me109/me-109g6-16476-pg7-1400.jpg

and here are those I found who give us the 4km full throttle hight for the DB605AM at Notleistung in climb.
http://kurfurst.org/Performance_tests/109G14_PBLeistungen/files/PBG14_ROC_SNplusMW50.jpg
http://kurfurst.org/Engine/DB60x/DB605_datasheets_AM.html

Edited April 18, 2020 by the_emperor

[41Sqn_Skipper]

Game specification gives the 5800m as Volldruckhöhe of DB605A and DB605AM. 

 

In a test flight with Bf 109 G-14 I achieved 1.3 ata at 5.8km. Above that altitude manifold pressure dropped. 

 

 

Edited April 18, 2020 by 41Sqn_Banks

[Raven109]

@the_emperor, the charts you've posted show for the AM version, a Volldruckhoehe of 5800m:

 

g6 db605A climb power setting @ ~4k:

 

g6 db605A climb power setting @ ~5.5k:

 

g6 db605A climb power setting @ ~6k:

 

Edited April 18, 2020 by Raven109

[the_emperor]

1 hour ago, 41Sqn_Banks said:

Game specification gives the 5800m as Volldruckhöhe of DB605A and DB605AM. 

 

In a test flight with Bf 109 G-14 I achieved 1.3 ata at 5.8km. Above that altitude manifold pressure dropped. 

 

 

You are going 450kph IAS. The charts give~350kph TAS (~280kph IAS) in climb. that could be a reason for the difference.
At 450 IAS the boost should drop at 6.4-6.6km height
Also there seems to be a difference for summer und winter maps  (should there be one for the critical height of the engine?).
On winter maps the engine seems to keep boost in climb up to 5.7km height, on summer maps the boost starts to drop at 3km height.

Edited April 18, 2020 by the_emperor

[41Sqn_Skipper]

4 minutes ago, the_emperor said:

You are going 450kph IAS. The charts give~350kph TAS (~280kph IAS) in climb. that could be a reason for the difference.
At 450 IAS the boost should drop at 6.4-6.6km height
Also there seems to be a difference for summer und winter maps  (should there be one for the critical height of the engine?).

 

I was flying level to take the sceenshot, boost was 1.28-1.29 ata during the whole climb from 1500m and above 5800m is started to drop below 1.28 ata. 

 

How much boost do you loose above 3000m?

[Raven109]

11 minutes ago, the_emperor said:

Also there seems to be a difference for summer und winter maps  (should there be one for the critical height of the engine?).

 

Yes, temperature has an impact on pressure.

[the_emperor]

6 minutes ago, 41Sqn_Banks said:

 

I was flying level to take the sceenshot, boost was 1.28-1.29 ata during the whole climb from 1500m and above 5800m is started to drop below 1.28 ata. 

 

How much boost do you loose above 3000m?

The Boost starts to drop from 1.3 at 3000m to 1.24 at 5700m. Tested on summer maps, as the engine seems to keep boost pressure on winter maps.
 

[-=PHX=-SuperEtendard]

In the Autumn map which is the standard temperature and pressure conditions where the planes should be tested I get around 6000 meters for critical altitude with 1.3 ata with the Bf 109 G-2 in max speed level flight.

Edited April 18, 2020 by -=PHX=-SuperEtendard

[41Sqn_Skipper]

The Volldruckhöhe in the german documents is corrected to "Normaltemperature", there are for sure differences in winter/summer maps.

In the original IL-2 one had to use the Kuban map to performance tests as it had the standard day condition. I have no idea what the Luftwaffe considered as a standard temperature/pressure and which map has it in IL-2 GB.

[sevenless]

1 hour ago, 41Sqn_Banks said:

The Volldruckhöhe in the german documents is corrected to "Normaltemperature", there are for sure differences in winter/summer maps.

In the original IL-2 one had to use the Kuban map to performance tests as it had the standard day condition. I have no idea what the Luftwaffe considered as a standard temperature/pressure and which map has it in IL-2 GB.

 

Something like this?

 

The International Standard Atmosphere

In the ISA Troposphere, sea level temperature is +15C and the temperature reduces by 6.5C per 1,000 metres (about 2C per 1,000 ft). The pressure at sea level is 1,013 mBar and the acceleration due to gravity is 9.81 m/sec².

 

 

Parameter	metrisches Maßsystem	imperiales Maßsystem
Feuchtigkeit /H2O	0 rel. %	0
Druck p0	1013,25 hPa	29,92 inHg
Dichte ρ0	1,225 kg/m3	0,002378 slug/ft3
Temperatur T0	15 °C / 288,15 K	59 °F / 518,67 °R
Schallgeschwindigkeit a0	340 m/s	1116,4 ft/s
Gravitation	9,80665 m/s2	32,174 ft/s2

 

 

https://www.flightdatacommunity.com/the-international-standard-atmosphere/

Edited April 18, 2020 by sevenless

[LukeFF]

3 hours ago, 41Sqn_Banks said:

I have no idea what the Luftwaffe considered as a standard temperature/pressure and which map has it in IL-2 GB.

 

All of the autumn maps in quick mission mode are set to ISA.

[the_emperor]

10 hours ago, -=PHX=-SuperEtendard said:

In the Autumn map which is the standard temperature and pressure conditions where the planes should be tested I get around 6000 meters for critical altitude with 1.3 ata with the Bf 109 G-2 in max speed level flight.

 

6 hours ago, LukeFF said:

 

All of the autumn maps in quick mission mode are set to ISA.

Thank you very much now my instrument readings correlate with the charts.
I did not expect full throttle height effected that  much by seasonal change since I never noticed any difference  in my Spitfire in different seasons.
 

Since that mystery is solved may I ask why the DB605AM at Notleistung (1.7/2800rpm) does not give me its critical hight in climb at 4000m? or did I misread the documents?
Cheers


 

[Raven109]

I think you might be confusing full pressure height, with the maximum power height for a certain throttle setting.

 

Full pressure height is the height at which the compressor cannot ensure the boost anymore for a certain power setting. So, for the emergency power setting, the compressor fitted to the AM engine cannot hold 1.7 ATA after 5.8km. This can be seen in-game as well (full pressure height at around 5.5km at 500km/h IAS). One thing that is interesting to me is that ram-pressure has a large impact on the ATA indication, more so in the G-14 than the G-6 for example, according to some limited tests that I've run.

 

Maximum power height is the height at which the engine produces the most power (according to how it's been tweaked to perform, since fighter engines were usually configured to cover certain needs relevant to the current tactical situation: high altitude interceptor, low altitude dogfighter, etc, and other factors), for a given throttle setting. For example, according to the table you linked, the AM will produce 1700PS at 4000m, when the throttle setting is set to Emergency power (aka 2800RPM /1.7 ATA). However, the compressor will still provide maximum ATA above this height up to 5.8km.

 

One discrepancy between the docs and the game is the maximum available power. The linked table seems to state 1700PS @ 4000m (which doesn't seem to exactly match the chart below it, which is missing the X axis), the G-14 spec in game says 1700HP @ 5600m. Can this be put down to any conversion between measurement units, or test conditions? Or can it be because different docs were used by the dev team?

Edited April 19, 2020 by Raven109

[the_emperor]

1 hour ago, Raven109 said:

I think you might be confusing full pressure height, with the maximum power height for a certain throttle setting.

No I hope not. I mean the boost pressure provided by the supercharger in climb and its critical height

 

1 hour ago, Raven109 said:

according to the table you linked, the AM will produce 1700PS at 4000m

yes that is correct. That chart also gives us the critical height of the engine, at which the the supercharger is not able to compensate for the height and the boost pressure starts to drop (the engines produced HPs start to drop off drastically, too)

at around 4000m which correlates with the climb charts.
As far as I know the engine charts for the german engines all give us power und full throttle height in climb ("die Höhenleistungen sind abgestellt auf den Gesamtdruck: statisch + dynamisch und ergeben sich ohne die Berücksichtigung der Rückstoßenergie")
http://kurfurst.org/Engine/DB60x/DB605_datasheets_A1.html
and if (and again that is a big if, I might be completely wrong here) the DB 605 AM Engine should produce full boost of 1.7ata/2800 in Climb up to 4000 meters and 5000m in level flight, due to ram pressure

Iam just talking about the boost not the acual power produced by the engine.

And again if I completly missread the documents or got something else wrong, big sorry and many thanks for your patience.
Cheers
 

Edited April 19, 2020 by the_emperor

[Raven109]

2 hours ago, the_emperor said:

That chart also gives us the critical height of the engine, at which the the supercharger is not able to compensate for the height and the boost pressure starts

to drop

at around 4000m which correlates with the climb charts.

 

 

The only chart for the AM engine that I see is the one pasted above. This shows power curves at different throttle settings. I.e PS(Y axis) with regards to height(X axis) (if we assume that the missing X axis is height), for different throttle settings (those are the RPM and ATA pairs). It doesn't show ATA vs height.

 

The table for AM is giving a pressure max height (Volldruckhoehe) of 5800m, not 4000m. I'm assuming that this is for the 1.42 ATA setting, while the VH = 5.5km at the top is the height at which the compressor cannot maintain 1.7 ATA anymore. 

 

The AM is just an A with C3 fuel and MW50 injection added. It doesn't use a different compressor, thus the max altitude for the compressor will be the same as the A.

 

In-game at 4000m the 1.7 boost can only be achieved in level flight, at high speed.

 

I'm not sure whether these charts/tables are all showing values collected while climbing or while doing level flight. 

 

10 minutes ago, the_emperor said:

And again if I completly missread the documents or got something else wrong, big sorry and many thanks for your patience.

 

No worries.

[the_emperor]

2 hours ago, Raven109 said:

The AM is just an A with C3 fuel and MW50 injection added. It doesn't use a different compressor, thus the max altitude for the compressor will be the same as the A

Correct.
the DB605AM should give us 1.42ata/2800rpm at approx 5.7km in climb and approx. 6.4-6.6km in level fllight, just like the DB605A.
and full 1.7ata/2800rpm up to approx. 4000m in climb and approx. 5000m in level flight (due to ram effect). After that the boost pressures starts to drop till 1.42ata  at 5.7km/6.6km and from there on it delivers the same amount of boost pressure as the regular DB605A in climb and level flight as the MW50 system has to be cut off:
http://kurfurst.org/Performance_tests/109G14_PBLeistungen/files/PBG14_ROC_SNplusMW50.jpg
http://kurfurst.org/Performance_tests/109G14_PBLeistungen/files/PBG14_LS_SNplusMW50.jpg
 

Edited April 19, 2020 by the_emperor

[Raven109]

Yes, that sounds right if you assume that the chart doesn't take into account ram air pressure, but your quote in German seems to indicate that it does take into account dynamic pressure. 

 

It looks like the G14 modeled is based on the assumption that such charts depict testing conditions in level flight, at least based on the limited testing I performed.

[the_emperor]

10 hours ago, Raven109 said:

Yes, that sounds right if you assume that the chart doesn't take into account ram air pressure, but your quote in German seems to indicate that it does take into account dynamic pressure. 

The Engine charts do take rame air pressure into account, but its the ram air pressure in climb (~280kph IAS) (static + dynamic pressure) not in level flight.
The Power output of the engines do start to drop rapidely at the same hight as the climb perfomance starts to decline (~5.7 km for the DB605A at 1.3ata/2600rpm and ~4km for the DB605AM at 1.7ata/2800rpm).

[Raven109]

According to this:

Which states Ohne Stau, the power output @ 5.5km and 5.8km does match the values from the table/chart you've posted. So, the chart depicting the power curves for the AM seem, as you stated, to indicate performance without ram as a factor. Since I've only tested the ATA indicator so far, I can only say that I cannot hold 1.7 ATA in a climb above an altitude of ~1km. The maximum I can get is 1.6ATA at 280km/h IAS, at around 4.5k-5.5k on very cold maps and around ~1.54ATA on autumn Kuban at mid-day.

 

I didn't do any performance tests. 

 

Edited April 20, 2020 by Raven109

[the_emperor]

3 hours ago, Raven109 said:

According to this:

Which states Ohne Stau, the power output @ 5.5km and 5.8km does match the values from the table/chart you've posted. So, the chart depicting the power curves for the AM seem, as you stated, to indicate performance without ram as a factor. Since I've only tested the ATA indicator so far, I can only say that I cannot hold 1.7 ATA in a climb above an altitude of ~1km. The maximum I can get is 1.6ATA at 280km/h IAS, at around 4.5k-5.5k on very cold maps and around ~1.54ATA on autumn Kuban at mid-day.

 

I didn't do any performance tests. 

 

That table also gives us the critical height of the DB605AM in level flight with 665kph ram air at 5,0km height (V-max-Not in V.H. (V.H.=Volldruckhöhe=critical height): 665kph-1700hp-5,0km height)
So the engine should give us full 1.7 ata in level flight at 665kph in 5,0km height.

Edited April 20, 2020 by the_emperor

[Raven109]

You might wanna see the two threads below (seems the issue was reported two years ago and was supposed to be reviewed at a later time):

 

 

 

 

Edited April 20, 2020 by Raven109

[the_emperor]

Thank you very much