La-5 Critical Altitude at 6300m for me / a bit too high?

[6./ZG26_Klaus_Mann]

Testing the La-5 I found the critical altitude to be around the 6200-6300m. Even in Winter time this seems a bit optimistic for a simple single stage supercharger.

[SKG51_robtek]

That is not the only questionable part of the FM's.

[Finkeren]

I seldom take the La-5 that high up, but if what you're saying is accurate, then that does seem too high. I'd expect something like 4,000m which seems to be where the Klimov 105PF starts needing leaning.

That is not the only questionable part of the FM's.

Not really FM as much as CEM. Please don't make another FM discussion out of this.

[SCG_Space_Ghost]

I seldom take the La-5 that high up, but if what you're saying is accurate, then that does seem too high. I'd expect something like 4,000m which seems to be where the Klimov 105PF starts needing leaning.

 

Not really FM as much as CEM. Please don't make another FM discussion out of this.

 

CEM is a gameplay element. FM's are the dynamics of how the aircraft performs under certain conditions.

 

Please don't get dismissive about things.

[6./ZG26_Emil]

La-5 can get way way way above 6000m! 

[Matt]

Testing the La-5 I found the critical altitude to be around the 6200-6300m. Even in Winter time this seems a bit optimistic for a simple single stage supercharger.

What is the critical altitude of the M-82 according to your data and what influence does the single stage type supercharger have on the critical altitude overall?

 

For instance, the AM-35A of the Mig-3 had a single stage supercharger and did pretty well at high altitude.

Edited June 5, 2015 by Matt

[Urra]

There was a discussion about 6 months ago regarding proper in-flight settings for radiators etc in expert setting for la5...but it's impossible to locate in forum since la5 is only 3 characters. If anyone can post a link I would be greatful.

[StG2_Manfred]

For instance, the AM-35A of the Mig-3 had a single stage supercharger and did pretty well at high altitude.

...and performed therefore worse at lower altitudes,right?

[dkoor]

If old Il-2 1946 is anything good regarding MiG's FM, that thing was true beast for its time.

It performed really well at all operational alts. Don't know about technical side etc. but when you face it in combat on axis side you couldn't do much if the MiG guy wanted to disengage... he would just point nose down and escape. That would be the case vs Fockes but then again they weren't exactly their contemporaries...

 

MiG cons were somewhat inferior maneuverability vs Bf-109 and relatively weak weaponry, vs experienced guys you really needed to be a sharpshooter to cripple and down something.

2x7,62 and 12,7mm weren't exactly enough in Il-2 1946.
Luckily that doesn't seem to be the case now. Rightfully

[Wulf]

What is the critical altitude of the M-82 according to your data and what influence does the single stage type supercharger have on the critical altitude overall?

 

For instance, the AM-35A of the Mig-3 had a single stage supercharger and did pretty well at high altitude.

 

 

Typically, at least in the real world, you can't have it both ways.  A single stage supercharger can't give you optimal performance at both low and high altitudes - it just can't.  My experience of the La-5 is that is does very well down in the weeds so ... if it's also good up high, well...yeah - bit odd m8 I'd have thought.  

[StG2_Manfred]

If old Il-2 1946 is anything good regarding MiG's FM, that thing was true beast for its time.

It performed really well at all operational alts. Don't know about technical side etc. but when you face it in combat on axis side you couldn't do much if the MiG guy wanted to disengage... he would just point nose down and escape. That would be the case vs Fockes but then again they weren't exactly their contemporaries...

 

MiG cons were somewhat inferior maneuverability vs Bf-109 and relatively weak weaponry, vs experienced guys you really needed to be a sharpshooter to cripple and down something.

2x7,62 and 12,7mm weren't exactly enough in Il-2 1946.

Luckily that doesn't seem to be the case now. Rightfully

https://en.wikipedia.org/wiki/Mikoyan-Gurevich_MiG-3

[Finkeren]

La-5 can get way way way above 6000m!

Critical altitude is not the same as service ceiling.

 

It is the altitude at which a supercharged engine can no longer keep up with the lower air pressure and you have to start leaning the mixture.

CEM is a gameplay element. FM's are the dynamics of how the aircraft performs under certain conditions.

Semantics, but let's just say you're right.

 

Please don't get dismissive about things.

Sorry, but that post added nothing to the discussion of the topic at hand and just threatened to drag this thread off track and into yet another discussion about real or percieved flaws in BoS flight physics. Edited June 6, 2015 by Finkeren

[JtD]

I hope you guys are aware that the La-5 is powered by an Ash-82 engine with a two speed single stage supercharger. This in theory allows an engine to deliver great performance at sea level and in the stratosphere, even though in case of the Ash-82 as on the La-5 the critical altitudes at full throttle are about 2km for first gear and about 5km for second gear, depending on the source you take. Keep in mind that during flight these altitudes will increase due to ram pressure.

[Finkeren]

I hope you guys are aware that the La-5 is powered by an Ash-82 engine with a two speed single stage supercharger. This in theory allows an engine to deliver great performance at sea level and in the stratosphere, even though in case of the Ash-82 as on the La-5 the critical altitudes at full throttle are about 2km for first gear and about 5km for second gear, depending on the source you take. Keep in mind that during flight these altitudes will increase due to ram pressure.

And that precisely is the reason for making two-stage superchargers like in the Spit Mk. IX and P-51: To get as close to optimal performance as posible at both low and high altitudes. No matter the gearing a single stage supercharger like on the La-5 just won't be able to keep up too far outside the pressure range it is optimised for. And since the Ash-82s supercharger was optimised for low level performance (AFAIK) I think 6300m sounds like too high a critical altitude for the second gear even accounting for the winter conditions.

[6./ZG26_Custard]

After a fair few hours of time spent in MP from what I have seen, the La-5 it is probably the best kept secret in the soviet arsenal. I  know little of the real world data regarding this aircraft but in this sim there are a fair few folk that will climb up to 8k plus and proceed to bounce 109's with relative ease.  I have been shot down twice by La-5's who where way higher (because I didn't think they would be) and I was at 6k. 

[=FI=Rambo]

After a fair few hours of time spent in MP from what I have seen, the La-5 it is probably the best kept secret in the soviet arsenal. I  know little of the real world data regarding this aircraft but in this sim there are a fair few folk that will climb up to 8k plus and proceed to bounce 109's with relative ease.  I have been shot down twice by La-5's who where way higher (because I didn't think they would be) and I was at 6k. 

 

I usually fly all the Russian planes well above 6k for that reason

[6./ZG26_Klaus_Mann]

The 109 has a semi-two-stage infinite ratio  supercharger an manages only a modest 5500-5800m. The Fw190 which has a very similar engine nd supercharger to the ash-82 manages only around 4500m.

[JtD]

And that precisely is the reason for making two-stage superchargers like in the Spit Mk. IX and P-51: To get as close to optimal performance as posible at both low and high altitudes. No matter the gearing a single stage supercharger like on the La-5 just won't be able to keep up too far outside the pressure range it is optimised for. And since the Ash-82s supercharger was optimised for low level performance (AFAIK) I think 6300m sounds like too high a critical altitude for the second gear even accounting for the winter conditions.

Overall, nothing the two stage supercharger as in the Spitfire IX or P-51 managed could not have been done by a two speed supercharger.

 

The 109 has a semi-two-stage infinite ratio  supercharger an manages only a modest 5500-5800m. The Fw190 which has a very similar engine nd supercharger to the ash-82 manages only around 4500m.

The DB601 and DB605 have a single stage variable speed supercharger.

[Finkeren]

Overall, nothing the two stage supercharger as in the Spitfire IX or P-51 managed could not have been done by a two speed supercharger.

In theory maybe. In the reality of WW2 aircraft technology? Hardly.

[=362nd_FS=Hiromachi]

I hope you guys are aware that the La-5 is powered by an Ash-82 engine with a two speed single stage supercharger. This in theory allows an engine to deliver great performance at sea level and in the stratosphere, even though in case of the Ash-82 as on the La-5 the critical altitudes at full throttle are about 2km for first gear and about 5km for second gear, depending on the source you take. Keep in mind that during flight these altitudes will increase due to ram pressure.

Exactly, and about the sources ... I have only the graph for Ash-82FN which is a bit later model,  and it has a second critical altitude at about 5400 meters. Dont think it was different for Ash-82.  

[6./ZG26_Klaus_Mann]

The DB601 and DB605 have a single stage variable speed supercharger.

It's a single speed supercharger with an hydraulically driven, barometrically controlled High Altitude charger, which I would qualify, since it is also driven by the engine's power, as a kind of a two-stager.

[JtD]

In theory maybe. In the reality of WW2 aircraft technology? Hardly.

DB605AS - 1200hp @ 8000m. Higher compression engine, larger diameter impeller, similar net result. Of course there are technological boundaries that cannot be overcome, and late war high altitude engines certainly required two stages or a turbo. But Merlin 6x performance was achievable without.

 

Exactly, and about the sources ... I have only the graph for Ash-82FN which is a bit later model,  and it has a second critical altitude at about 5400 meters. Dont think it was different for Ash-82.

I think 5400 is the handbook figure for the Ash-82F, with 950mm boost. Assuming you have the same graph I just looked at, the Ash-82FN is shown with 4650m with 1000mm boost. Afaik, Ash-82F and the plain 82 are pretty much the same, the 82-FN slightly different not just for different boost in second gear..

 

It's a single speed supercharger with an hydraulically driven, barometrically controlled High Altitude charger, which I would qualify, since it is also driven by the engine's power, as a kind of a two-stager.

No, it's not. It's got exactly one stage. If you're qualifying a "kind of second" stage, you're disqualifying yourself. Just take a look at the engine - there's one impeller, not two.

[Matt]

...and performed therefore worse at lower altitudes,right?

Not therefore, but i guess they rather went for a medium critical altitude for the first gear to get a relatively smooth performance curve, instead of chosing a low altitude for the first gear and then get a huge performance loss between the two chosen altitudes (which for instance, the La-5 has).

 

 

Typically, at least in the real world, you can't have it both ways.  A single stage supercharger can't give you optimal performance at both low and high altitudes - it just can't.  

Of course it can, as long as it has more than one gear.

 

 

In any case, i checked that under normal conditions and it does reach the critical altitude at 6000 meters in flgiht, so roughly 500-600 meters above static critical altitude (if the 5450 meters altitude is correct for the M-82). A even higher in flight critical altitude would be supported by speed figures (the La-5 usually reached top speed a good bit above 6000 meters).

 

For comparison sake, the DB 601E had a static critical altitude of 4800 meters, critical altitude in flight was around 6200 meters for the Bf 109 F-4.

 

Of course, one could perhaps further test this, by reaching zero speed at different altitudes and check the boost gauge each time. I'm not gonna do that though.

Edited June 6, 2015 by Matt

[Finkeren]

Exactly, and about the sources ... I have only the graph for Ash-82FN which is a bit later model, and it has a second critical altitude at about 5400 meters. Dont think it was different for Ash-82.

I'm not sure you can compare the two. The ASh-82FN has direct fuel injection, and while it doesn't directly affect the compression of air going into the cylinders, it does change the workings of the engine quite a bit.

[Danziger]

Wow you guys sure know a lot of [Edited] about ww2 fighter engines. I always thought two stage and two speed superchargers were the same thing lol.

[Finkeren]

Wow you guys sure know a lot of sh!t about ww2 fighter engines. I always thought two stage and two speed superchargers were the same thing lol.

In a relatively simple sim like IL-2 1946 I think there is no practical difference. But for at more advanced sim it should make a difference for high altitude performance.

 

The two-speed supercharger is a compressor with 2 gears where the two-stage is actually two individual compressors working in tandem when both are switched on.

 

Generally speaking, the 2-stage supercharger is about twice as heavy (for obvious reasons) but can better keep up with lower air pressure than a single-stage.

Edited June 6, 2015 by Finkeren

[=362nd_FS=Hiromachi]

I think 5400 is the handbook figure for the Ash-82F, with 950mm boost. Assuming you have the same graph I just looked at, the Ash-82FN is shown with 4650m with 1000mm boost. Afaik, Ash-82F and the plain 82 are pretty much the same, the 82-FN slightly different not just for different boost in second gear.

Yes, that is correct. I misunderstood some description, that is Ash-82F. 

 

 

Wow you guys sure know a lot of sh!t about ww2 fighter engines. I always thought two stage and two speed superchargers were the same thing lol.

Engines are really interesting topic, and understanding how they work is very important for discussing the aircraft performance. Although i must admit that my knowledge is far below the desired in this area

[TheElf]

After a fair few hours of time spent in MP from what I have seen, the La-5 it is probably the best kept secret in the soviet arsenal. I  know little of the real world data regarding this aircraft but in this sim there are a fair few folk that will climb up to 8k plus and proceed to bounce 109's with relative ease.  I have been shot down twice by La-5's who where way higher (because I didn't think they would be) and I was at 6k. 

 

 

Just because the VVS didn't operate at higher altitudes doesn't mean they couldn't.  VVS doctrine dictated where the the Fighter Regiments spent most of their time, not necessarily the aircraft's performance.  The Yak-1 was designed to escort the IL-2, therefore it and most Russian planes of the early war prioritized medium to low altitude performance.  Unfortunately for those who value immersion and history, no one in MP is beholden to any organizational doctrine, therefore we see VVS players at 8k and Germans that never go lower than 4k to engage targets where the Air war on the Eastern front was actually fought...at low altitude.  

[6./ZG26_Custard]

 

 

where the Air war on the Eastern front was actually fought...at low altitude.

 

In essence as the Luftwaffe became much more of a defensive force as apposed to the aggressor on the eastern front the air war was dragged down to lower altitudes but the Luftwaffe tactics when flying a 109 remained fairly standard, it is an energy fighter after all. 

 

Except from Black Cross/Red Star:

 

 The normal German fighter tactic was a high-side gunnery run against lower flying enemy formations, whereafter they could use the superior climbing performance of the Bf 109 to withdraw. In this way, the German fighter pilots frequently were in a position where they could choose to engage the enemy only when the situation was to their advantage.

 

I too value immersion and history but no 109 pilot in there right mind would sit on the deck and get involved in a turning furball with VVS aircraft where they have 80% of the advantage.

 

particularly in a DF server.