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My La-5 is very slow - what am I doing wrong?


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#1 gnomechompsky

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Posted 11 February 2017 - 18:14

Despite looking at various guides for the La-5 I can't seem to get the correct engine settings.

 

From what I understand, I should be able to push it to ~600kph at 6,000m.  In spite of this I seem to be only getting 400!?

 

Here is what I am doing:

 

Start QMB with single plane at 6,000m (La-5 obviously) with 50% fuel.

 

Keep auto-level on.

 

Set throttle to full (100%)

Set prop RPM to 2,300 (93%)

Set mixture to 80%

Set inlet cowl fully open (100%)

Set outlet cowl fully closed (0%)

Set oil rad fully open (100%)

Set super charger to stage 2 (not really sure what this means)

Put boost on.

 

Even as I play now I am only getting 420kph at 6,300m with around 10% fuel left.  Surely this isn't right?


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#2 JtD

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Posted 11 February 2017 - 20:35

Even as I play now I am only getting 420kph at 6,300m with around 10% fuel left.  Surely this isn't right?

I'm near certain you're looking at either the cockpit gauge or the HUD, both of which show the so called indicated air speed (IAS). IAS depends on the density of the air and is only showing true air speed (TAS), if you fly in sea level standard atmosphere conditions. In all other conditions, you need to apply corrections. There are sophisticated methods, but as a start you can assume 1% increase for every 150m of altitude.

Depending on the map conditions (winter, autumns, summer) the 420kph at 6300m translate to roughly 580hph TAS. This is already pretty close to the 600kph you're expecting.

You can use the search function, google or go straight to wiki for more detailed explanations, if you like.
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#3 headwarp

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Posted 11 February 2017 - 21:21

I'm near certain you're looking at either the cockpit gauge or the HUD, both of which show the so called indicated air speed (IAS). IAS depends on the density of the air and is only showing true air speed (TAS), if you fly in sea level standard atmosphere conditions. In all other conditions, you need to apply corrections. There are sophisticated methods, but as a start you can assume 1% increase for every 150m of altitude.

Depending on the map conditions (winter, autumns, summer) the 420kph at 6300m translate to roughly 580hph TAS. This is already pretty close to the 600kph you're expecting.

You can use the search function, google or go straight to wiki for more detailed explanations, if you like.

 

I was googling like crazy trying to find something that could tell me whether the performance specs we read about speed at altitude were based on TAS or ground speed.   An old instructional video explained to me this - Indicated airspeed of 400km at high altitudes is faster than IAS 400km at lower altitudes.    without going into things I don't fully understand enough to explain correctly - altitude also has an effect on the speed of sound and the speed at which an aircraft can enter compressibility. 

 

I tried a couple flights at 6000m with different fuel loads.. at 52L i was able to push past 450km/h IAS but felt like I was constantly  fiddling with rudder/elevator/aileron trim as my airspeed changed the slightest bit.   I don't have much experience in the la-5 but it seems like there's a lot to manage, and a bit touchy. 


Edited by headwarp, 11 February 2017 - 21:29.

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#4 Matt

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Posted 12 February 2017 - 11:37

Mixture is automatic in the La-5 if you keep it at 100%. So if you're looking for best performance, leave it to 100%. You should only reduce mixture to decrease fuel consumption.

 

Boost only works with supercharger gear 1, so you can switch that off in gear 2. Also for maximum performance, you have to set RPM to 100%.


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#5 =r4t=Sshadow14

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Posted 12 February 2017 - 19:20

Its always IAS (Air speed) and generally measured @ 5,000ft
you CANNOT fly a plane with TAS (or ground speed)

As for the tests planes in IL2 are all measured using IAS and standard pressure 2992 inch/mg and at altitudes listed.

 


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#6 headwarp

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Posted 12 February 2017 - 20:11

Its always IAS (Air speed) and generally measured @ 5,000ft
you CANNOT fly a plane with TAS (or ground speed)

As for the tests planes in IL2 are all measured using IAS and standard pressure 2992 inch/mg and at altitudes listed.

 

 

https://drive.google...FRwMDJVWGc/view

 

From pg 43-61 is chuck's specs for the La-5 we get in the game.   His charts are showing 620km/h at like 6500m.  slightly slower when you start to get under 6000m.   So then the OP's question is still relevant.. what is he doing wrong?

 

I couldn't get the thing going very fast with low fuel loads myself at 6000m or above.   Which seems to emulate my experiences with modern jets even that at high altitudes it's harder to reach indicated air speed.    My air speeds at that height in the Ilvl match up with chuck's numbers if we're measuring TAS or Ground speed, which I understand to be utilized mostly for navigation and time purposes.

 

 

If the charts on pg 61 of chuck's il-2 guide are indicating IAS then I too am suddnely curious how to obtain such speeds.   I'll try using max power myself next time I take a flight in it..  

 

 

But looking at those charts.. I can't help but feel that's very fast for level flight at 6km altitude. So maybe I'm misinterpreting it.   

 

If that is IAS at level flight..I don't feel as confident in my ability to generate speed in the Bf-109f-4 using slip and stabilizers at those altitudes where chuck's guide reports it punching in at 700km/h at 6000m. 

 

But I'm also wondering if myself, (and possibly the OP) misinterpreted those charts and how to apply them. 

 

 

I'm going to play around.. and if IAS is the measure and indeed at level flight, then perhaps we need an expert on the La-5 to chime in for the OP.  Or perhaps it was simply the suggestion of running at max rpm above. 

 

 

*Edit* - flying at 6200m level in the bf-109 with emergency power I seem to hit max of around 500km/h doing my best to manage stabilizer to avoid climbing and keeping the slip center (which at this speed seems about right).  Restating chucks guide lists it as capable of 700km at this altitude.  But again.. I could be missing details as to what his charts actually mean.. and I'm wondering if the OP is also using Chuck's guide.   Maybe it's a measure IAS in regard to the structural limitations of the plane and nothing to do with level flight..but as far as my inexperienced self knows it could be TAS/GS.  WHich yes.. you use IAS when thinking about stall speeds and plane limitations.. but there are formulas pilots have used to calculate CAS/TAS/Ground speed based on IAS that weren't computerized back in this time period afaik. 

 

 

Or maybe my noobness is showing.. and most of you guys could fly circles around me up high. ;) Which is very possible. 


Edited by headwarp, 12 February 2017 - 20:43.

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#7 =r4t=Sshadow14

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Posted 12 February 2017 - 20:18

it probably much like Stuka Max speed.

Very hard to reach 390kph with max bombload on deck.

But climb to 1K then dive to 450kph and it will slow to 390kph and hold this for almost ever.

i had a car like this (old crap) was so slow in 5th gear it could only reach 110km/h on flat motorway but if i down shifted to 4th gear accelerated to 140 then put it in 5th it would slow to about 130kph and hold this speed.

IAS is the measure..
There is no gauge in a ww2 plane that measures ground speed they are all based on air speed


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#8 headwarp

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Posted 12 February 2017 - 20:58

it probably much like Stuka Max speed.

Very hard to reach 390kph with max bombload on deck.

But climb to 1K then dive to 450kph and it will slow to 390kph and hold this for almost ever.

i had a car like this (old crap) was so slow in 5th gear it could only reach 110km/h on flat motorway but if i down shifted to 4th gear accelerated to 140 then put it in 5th it would slow to about 130kph and hold this speed.

IAS is the measure..
There is no gauge in a ww2 plane that measures ground speed they are all based on air speed

 

 

Ok.. I just read something stating Airspeed=Groundpseed on day with no wind. so Im editing my previous statement.  But also stated AIrspeed = groundspeed minus windspeed.

 

https://www.grc.nasa...plane/move.html

 

I glanced over it but I didn't even see mention of the effect of air density with altitude. But I have read other things that describe forumlas to calculate their effect. 

 

So, perhaps chucks guide is on a day with no wind.  But with a bunch of math im not very familiar with,ias becomes slower than groundspeed with lower air density @ altitude and given windspeeds.

 

Perhaps try a fighter in quick mission starting at 6000m  prior to the introduction of BoM/BoK and fill us in on your experience at sustainable max speed in level flight at 6000m? The stuka has no such speed chart in Chuck's guide >.< And I've only seen charts for planes from BoS

 

And while true we have no visual gauge in a ww2 fighter for CAS/TAS/Groundpseed,  if I read correctly it was around this time that we began to get a better understanding of the effects of speed and airflow at altitude and began to develop formulas for calculating CAS/TAS/Groundspeed using just math alone.. which just requires a brain, or the ability to communicate with someone who has access to measurements of windspeed who might have a piece of paper and a pen.. or a calculator.  I at least get that groundspeed is used mostly for drafting flight plans. 

 

Not knowing the math... my experience with altitude and flying = being in an su-27 or f-15c in DCS world contrailing at 30 thousand feet (around 9144m) struggling to keep above 350-450knots (been awhile..i'd have to check) IAS without burners. If I remember correctly there was a way to display TAS as opposed to IAS.  Kicking on the burners and beginning a shallow dive, you also notice how you break the sound barrier at lower IAS and higher altitudes (lower temperatures)

http://www.fighter-p...om/jetmach1.htm  (not going to try to say I'm smart enough to determine how accurate that webpage is, however -  it does show the effect I'm discussing) 

 

Different era of plane..different sim tho.  So I'm just as confused as the OP.. still wondering if he's found any answers for himself. 

 

Just fyi Shadow I am by no means trying to argue with you or expect you to go thru this extra work..but I'm still feeling uncertain and the OP has peaked my interest in obtaining clarity.  I'm going to do as you suggested and climb higher and try to dive into speed and see how long i can maintain it. 

 

At lower altitudes I personally don't feel a struggle trying to obtain higher IAS. 


Edited by headwarp, 12 February 2017 - 22:15.

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#9 =r4t=Sshadow14

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Posted 12 February 2017 - 21:59

There is no need for chucks guides..(no offense to him or his work, just saying the devs have provided what seems to be the EXACT info not based on user tests)
The planes specs are listed ingame on the mission screen. 


Thats because the speed of sound changes with altitude so you can over stress a plane and hit mach 1 @ only 500mph if you high enough but Mach 1 @ sea level is around 740mph.
Here these might help

rfo4mwY.jpg

Regardless of where you are in the world day or night summer or winter.
Above a certain altitude its the same Temperature Everywhere.



 


Edited by =WFPK=Sshadow14, 12 February 2017 - 22:01.

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#10 headwarp

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Posted 12 February 2017 - 22:33

Well, you did say one thing that completely cleared this up for me, and should for the OP.  Looking at the La-5 Ser.8 

 

 

9 lines into the specifications at mission startup.

 

Maximum true air speed at 6500 m, engine mode - Nominal - 603km/h

 

So the first response to the OP is correct, your indicated air speed will NOT be 603km/h at 6500m.

 

It will more likely be between 420km-450km  IAS.  But you'll really be doing more like 580-600km/h TAS. (just going off of what the first response stated) Neither is wrong.. just different measurements.  (IAS measuring has to do with airflow if i'm not mistaken, where TAS and ground speed have more to do with surface travel - again if I'm not mistaken) 

 

Flying a mission and trying to reach said indicated speed would have saved us some wordiness.. but thanks very much for pointing out to me info on the mission startup screen. 

 

I'm going to assume Chuck's guides fall more along the lines of True Air speed or even Ground speed as well. 

 

FYI OP - Trim it perfectly to obtain 450km/h IAS at 6000m+  Fly in normal mode so you dont have to deal with engine management if you're not already used to trimming..once you've got trimming down add CEM to see its effect on speed, which I used your settings in expert.. normal mode keeps the rpm at 2400 to achieve speed with full throttle. 

 

Also tested diving into speed.. at about 8000m i was struggling to get above 360km/h IAS at level flight.. I dove to about 570km/h IAS by the time I leveled out at 6000m and the speed immediately began dropping in La-5.   Working as intended imo.   I'll leave verification of accuracy to some really talented mathematicians. 

 

Sorry for hijacking the OP's thread - but thanks shadow for leading us to a definitive (while maybe not 100% accurate..close enough for me) answer. 


Edited by headwarp, 12 February 2017 - 23:04.

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#11 gnomechompsky

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Posted 13 February 2017 - 20:27

All, thanks for the responses.


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