Fw-190 and compressor stage change...

[Guest deleted@50488]

Sometime ago users complained about the altitude at which the compressor stage transition in the Fw190 A-3 happens - was too low ( Winter Maps )...

 

I don't know if this has also been addressed ( never tested it again ) but Han refuted those claims with a valid argument - by that time we only had Winter maps and weather ( cold weather ), and indeed cold Winter days are prone to bring the various pressure levels to lower true altitudes ( heights ) than ISA or Summer days.

 

- Problem is, since it's an aneroid that it's used to measure that pressure, we should see the same altiude in the altimeter, no matter if it's Winter or Summer, provided we have it set for QNH and make our experiments with the same QNH setting of the underlaying mission.

 

I guess Han acknowledged there was a problem with this, and was going to ask, internally, for a fix, but I really don't know if it got fixed ?

 

Meanwhile we got key combinations to set the altimeter scale to QNH or QFE, and Spring and Summer Maps were released, and I never tried again to check at what indicated altitude the change occurs for scenarios where the same QNH is defined in the mission, and we test between a cold Winter day and a hot Summer day ...

 

Will try to check that again...

 

BTW: How can we edit missions that can be set in the QMB so that we can set the proper weather parameters ( wind, turbulence, pressure and temperature...) for testing ? 

Edited March 12, 2016 by The-UNINSTALLER

[coconut]

How can we edit missions that can be set in the QMB so that we can set the proper weather parameters ( wind, turbulence, pressure and temperature...) for testing ? 

Try this: Start QMB, save a track, go to your track folder, go to the subfolder that corresponds to the track you saved. There should be an msnbin file in there that you can open with the mission editor.

To open it, click Open in the File menu, then enter the name of the msnbin file. The filter does not show msnbin files, but you can open them anyway by typing in the name directly. You will have to change the mission type to single-player, or whatever it's called, then save it to you data/Missions folder.

Edited March 12, 2016 by coconut

[Ala13_ManOWar]

I don't know if this has also been addressed ( never tested it again ) but Han refuted those claims with a valid argument - by that time we only had Winter maps and weather ( cold weather ), and indeed cold Winter days are prone to bring the various pressure levels to lower true altitudes ( heights ) than ISA or Summer days.

 

The thing is in winter, so high pressure atmosphere (low DA), stage change should happen later, not earlier while in summer (so low pressure, high DA) should appear earlier than later.

 

S!

[Guest deleted@50488]

Well, just tested and it looks ok for me...

 

Thx coconut for your suggestion...

 

Thing is, is aneroid-based systems are used, then it is working OK as it is right now.

 

I used the Stalingrad map. Set the altimeter to QNH, and in Winter I got the change at about 2244m with the altimeter reading something like 2,6 km, while in Summer I got the change at 2592m ( HUD ) with - as it was supposed to be - the altimeter reading the same 2,6 km.

 

This is perfect !

 

If the system measures pressure ( and this is affected by density of course ) than the change should happen lower in Winter.

 

I believe most people don't really understand what the temperature ( geopotential height ) side of the "from high to low" saying means - the whole pressure levels are "compressed" in denser / cold weather, so, for a same QNH, if it is, say 760 mm on both situations, for instance the 650mm level will be lower in Winter than it is in Summer, and if pressure is what is used by the system to operate the change, then it must occur lower in Winter than in Summer, for the same QNH!

 

IL-2 is, as far as I can tell, doing it correctly :-)

[II./JG77_Manu*]

IRL you could set the altitude where the gear change would happen at any temperature. It was always adjusted to temperature, so that the gear change happens at the best possible altitude for any temp. This could be done in very short time, before a sortie (not while flying though)

Edited March 12, 2016 by II./JG77_Manu*

[Guest deleted@50488]

IRL you could set the altitude where the gear change would happen at any temperature. It was always adjusted to temperature, so that the gear change happens at the best possible altitude for any temp. This could be done in very short time, before a sortie (not while flying though)

 

Great piece of info Manu!  Thx! I didn't know it was possible - I know very few details about this great ww2 birds  :-), but it makes sense. If such was also possible in BoS, then it could happen also at the best possible pressure alt., but that would require a bit more of complexity and an additional item in the menus for such aircraft types.

Edited March 12, 2016 by The-UNINSTALLER

[Ala13_ManOWar]

If the system measures pressure ( and this is affected by density of course ) than the change should happen lower in Winter.

What I mean was during winter cold air density is higher indeed while in summer warm air density is lower. So change should be the opposite you say, lower in summer, higher in winter.

 

S!

[Guest deleted@50488]

No Ala13.. the whole geopotential "collapses" in Winter cold times, so, if you have a situation with the same QNH at an aerodrome, in hot Summer vs cold Winter, the pressure level corresponding, for instance to 850 hector Pascal (hPa), roughly 1500m in ISA conditions will actually be bellow 1500m "true" altitude ( height ) in Winter, and above in Summer.

 

See for instance fig. 11 on page 15, of  "Aviation Weather for Pilots and Flight Operations Personnel"

 

And Ala13, since you're also a DCS user, I just wanted to point out it is exactly modelled the same way there :-) - so, correctly modelled on both sims :-)

 

Unless the system worked based on other than barometric pressure, it'll kick in lower in Winter and higher in Summer

Edited March 13, 2016 by Von-Queca

[Ala13_ManOWar]

All right mate, will check it. But still I think it's all about DA (Density Altitude), doesn't matter winter or Summer but usually during winters with lower temperatures density is higher (usually, not always) so makes sense you don't need a supercharger change so soon (nor sooner mixture setting for instance, and you're plenty of manifold pressure for higher altitudes, etc), and the opposite for summer (usually, not always, of course). I'm not even saying it's well or wrong modelled as I don't own 190A3.

 

S!

Edited March 13, 2016 by Ala13_ManOWar

[GridiroN]

What practical difference does it make if the compressor changes at the wrong place, other than satisfying pedants (albeit, it's always better to be accurate in a sim game) 

 

Why would you ever want to change the altimeter scale to accommodate the compressor change if it affects nothing at all and is automatic anyway?

[unreasonable]

All right mate, will check it. But still I think it's all about DA (Density Altitude), doesn't matter winter or Summer but usually during winters with lower temperatures density is higher (usually, not always) so makes sense you don't need a supercharger change so soon (nor sooner mixture setting for instance, and you're plenty of manifold pressure for higher altitudes, etc), and the opposite for summer (usually, not always, of course). I'm not even saying it's well or wrong modelled as I don't own 190A3.

 

S!

 

The actual mechanism that changes the gear is triggered by static pressure - (atmospheric pressure, near enough), with a link to the position of the control lever - rpm, in effect. This has been confirmed by people who have the manual and by a NASA report that reverse engineered the control system. Long thread about it a while ago. 

 

You can read all about it here:   

naca BMW Bench Test.pdf

[Guest deleted@50488]

What practical difference does it make if the compressor changes at the wrong place, other than satisfying pedants (albeit, it's always better to be accurate in a sim game) 

 

Why would you ever want to change the altimeter scale to accommodate the compressor change if it affects nothing at all and is automatic anyway?

 

Me ? I don't get your point ? I think it actually is changing at the correct place, hence my OP...

[GridiroN]

Me ? I don't get your point ? I think it actually is changing at the correct place, hence my OP...

 

I'm asking what difference the compressor makes. The engine in the FW is pretty much totally automatic and unless I'm mistaken (which is why I'm asking) this doesn't affect it's performance. So are people bothered by the compressor because it's not realistic, or because it's hurting the FW190's actual engine performance?

[Guest deleted@50488]

I'm asking what difference the compressor makes. The engine in the FW is pretty much totally automatic and unless I'm mistaken (which is why I'm asking) this doesn't affect it's performance. So are people bothered by the compressor because it's not realistic, or because it's hurting the FW190's actual engine performance?

 

I agree with you, but since this subject was debated a couple of months ago, and I have since then made some tests with this and other sim, and found they're actually doing it exactly the same way, and because they DO model the effect of temperature in the pressure gradient ( with altitude ), I thought I should point it out - because it's a positive, rather than a negative aspect of the simulation.

 

Also as comparisons with civil flight simulators I have used for many years, bot il2 BoS and that other combat flightsim end up doing a better job in modelling this details.  That was the idea behind my post :-)

[Yogiflight]

Not completely the topic, but does someone know, why, when I increase power, at about 70%, the needle of the ata-gauge jumps back from, I think it was 1.0 to about 0.95 and then goes on climbing and when decreasing power the same vice versa?

[JtD]

Change between lean and rich mixture. It also has a small effect on boost.

[Yogiflight]

Thanks for the answer, JtD, I didn`t know that.