BF 109 G-6/14 too slow

[the_emperor]

I did some testing and compared those two models in IL-2 with the most recent data sheets I could find for those two models.

Testing in IL-2:

Engine and Radiators set on automatic

Map: Rheinland Autumn

Indicated Air Speed converted to True Airspeed rounded down (since we ufnortunately dont have TAS Indicator we can enable in the game) via http://www.hochwarth.com/misc/AviationCalculator.html

 

 

The Curves (or better the line) for the models from the datasheet are very simply extraploated since only the top speeds at sea level and at full throttle hight are known.

If any one has the time, please falsify or verify  my findings. If needed I can also provide the flown figures for the indicated air speed for comparison.

 

Cheers

 

 

[CountZero]

When i tested last time i got this speeds:

 

G6 is blue, G14 is red (lest is combat, right lines are emergancy)

 

also i used this converter:

https://aerotoolbox.com/airspeed-conversions/

placed IAS speeds values from game in Equivalent Airspeed

 

 

 

Edited October 13, 2020 by CountZero

[HR_Zunzun]

That is interesting because I have just posted some similar regarding p-47 speeds. Essentially 25kph slower at altitude but very similar at SL. Then I saw your post. 109 G6 and G14 Devs speeds are similar to what you have as real values. It is your test that diverged (like mine).

Then I made a couple of quick-dirty tests on Fw190D9 and La5FN and found similar results. Slowers by a good margin (only test them at FTH).

I wonder if we are having some kind of problem all across the board.

[CountZero]

They could just add TAS in game as suggested to them many times, like any other serious flying game has , it would slove lot of mistery with speeds they give in specs.

[the_emperor]

13 minutes ago, CountZero said:

When i tested last time i got this speeds:

 

G6 is blue, G14 is red (lest is combat, right lines are emergancy)

 

also i used this converter:

https://aerotoolbox.com/airspeed-conversions/

placed IAS speeds values from game in Equivalent Airspeed

 

 

 

your values for the G-6 seem to bee a bit higher. Would you mind sharing your indicatedAirspeed Data, maybe I made a mistake there (mine is down below)

Many Thanks

[CountZero]

I dont have them i run tests on G6 long time ago.

 

EDIT:

just for example i pick your value of 446kmh IAS for 6500m and used converter on my link and get 625kmh as TAS for it, similar as on pictures of my test chart. 

Edited October 13, 2020 by CountZero

[HR_Zunzun]

I use the same converter (was one of the two link in my p-47 tests). Applying to 446kph at 6500m and I still get 612kph as TAS

[CountZero]

Like i said before i place IAS from game in Equivalent Airspeed section, this is where i place all my IAS from game and get most accurate speeds for all airplanes i test to what is said in specs.

 

Edit:

if i dont use equivalent section, and use calibrated like you then for all airplanes in game i get slow speeds to what in game specs say they should be doing at alt. So either all airplanes are to slow to what specs say as they go higher or convertion method is wrong, and thats why i settled for equivalent field for my ias speeds for game, as it give me most plousable speeds compared to what game says they should be for all airplanes.

 

But again if devs add TAS indicator like any other flying game has, we would not have this problems, as i doubt they have big errors in airplane speeds in this flying game.

Edited October 13, 2020 by CountZero

[the_emperor]

29 minutes ago, CountZero said:

But again if devs add TAS indicator like any other flying game has, we would not have this problems, as i doubt they have big errors in airplane speeds in this flying game.

 

I second that, all we are doing right now is a litte bit of guesswork. I did make that in the suggestion section a some time ago...

[the_emperor]

3 hours ago, CountZero said:

i place IAS from game in Equivalent Airspeed section, this is where i place all my IAS from game and get most accurate speeds for all airplanes i test to what is said in specs.

Indeed I did use EAS for conversion and the G14 looks reasonable, but the G6 still seems a bit slow

[CountZero]

16 hours ago, the_emperor said:

Indeed I did use EAS for conversion and the G14 looks reasonable, but the G6 still seems a bit slow

Few updates ago they fixed speed problems on G14 i would not be suprised if they didnt check other 109s so probably they need to fix 109G6 next if they go one by one.

[the_emperor]

3 hours ago, CountZero said:

Few updates ago they fixed speed problems on G14 i would not be suprised if they didnt check other 109s so probably they need to fix 109G6 next if they go one by one.

 

Yes, they should have a look at it.

It is still weird, that our speedometers show equivilant air speed (takes compressability into account ) instead of calibrated air speed (IAS) which for us seems to be more relevant when manouvering the planes?

[HR_Zunzun]

Yes. I have just discovered this and strikes me as very weird too.

[-=PHX=-SuperEtendard]

This is data taken by Der Sheriff, compared with real Bf 109 G-14 speeds by Kurfurst according to a comparative chart he made

The 50% fuel does have some effect, particularly at higher altitudes, this could explain the speed difference up there. This data is quite old though (before the G-14 was "broke" then fixed), I should retest it nowadays to see how it compares. The TAS was calculated using this page http://indoavis.co.id/main/tas.html  and I collected temperature data from the Kuban Autumn map using Bf 110 and Pe-2 with their external temperature indicators at the different altitudes, I compared it with a German report of Bf 109 G-2 showing both indicated and true air speed and we got very close numbers to the German calculated TAS, not more than 3 km/h discrepancy at the most, usually in the 1-2 km/h region.

Edited October 16, 2020 by -=PHX=-SuperEtendard

[the_emperor]

Thank you very much. Yes, when using EAS instead of CAS to calculate TAS the G-14 seems to be quite right.

 

Unfortunately the G-6 still seems to lack some speed and the full throttle height for the 1.3/2600rpm setting seems to be 6km instead of the 6.6km. 

[CountZero]

Why i think coversion method of using Eqvivalent speed to get TAS is correct is because when i look at game files for 109g6 and speeds they say there airplane ai should be doing at combat mod at 1000m alt intervals, and i do test and then convert that speeds, i get almost same line:

Blue is data from in game files for 1.3 ata 109g6

and red is my test and conversions, left is combat mode speeds and right emergancy speeds, so if something is wrong its not in conversion or test methods.

[JtD]

Because it came up - several of the historical performance figures are also derived from treating CAS as EAS, meaning they ignore compressibility and give too high speeds at altitude. For instance, all speed performance figures for the Fw190 up to the A-8 are given without taking compressibility into account (thus are too high), while figures for the A-9 and later take compressibility into account (thus are correct). Fw only changed that in 1944.

 

I don't think I have seen a similiarly definitive statement for the Bf109 anywhere, but we can be pretty sure that not everything that Messerschmitt or the Luftwaffe tested is always spot on. Best I know - there's a Messerschmitt test report from September 1942 that mentions the transition, so it shouldn't be an issue with the G-14, we just can't be 100% sure.

Edited October 18, 2020 by JtD

[the_emperor]

Yes in deed. Early germans document sometimes dont take compressability into account and it is somestimes hard to discern, whether it is the case or not.

But late war document offen give us the perfomance figures as "berechnet" or "errechnet" (calculated), which do take compressability into account.

The two docuements shown above at least say so: "Berechnung13.8.44"

 

And then there is still the "mystery" why our speedometers ingame do give us EAS instead of CAS?

Edited October 19, 2020 by the_emperor

[FTC_Karaya]

19 hours ago, JtD said:

Because it came up - several of the historical performance figures are also derived from treating CAS as EAS, meaning they ignore compressibility and give too high speeds at altitude. For instance, all speed performance figures for the Fw190 up to the A-8 are given without taking compressibility into account (thus are too high), while figures for the A-9 and later take compressibility into account (thus are correct). Fw only changed that in 1944.

 

There's also a compressibility corrected level speed chart for the 190A-5 from Oct-43:

http://www.wwiiaircraftperformance.org/fw190/190a5-level-20-10-43.jpg

 

So these corrections happened earlier than 1944.

 

Not sure about Messerschmitt AG but Rechlin started correcting for compressibility from at least mid 1942 onwards. There was a flown performance trial for the Bf109F-4 which was later corrected for compressibility. Kurfürst's site gives a brief summary of this:

http://kurfurst.org/Performance_tests/109F4_Datenblatts/109F4_dblatt_calculated.html

Edited October 19, 2020 by Karaya

[the_emperor]

27 minutes ago, Karaya said:

Not sure about Messerschmitt AG but Rechlin started correcting for compressibility from at least mid 1942 onwards. There was a flown performance trial for the Bf109F-4 which was later corrected for compressibility. Kurfürst's site gives a brief summary of this:

 

Yes,  If somewhere is noted that the figures are calculated ("berrechnet") it is a strong indication, that compressibility is accounted for.

[JtD]

2 hours ago, the_emperor said:

Yes,  If somewhere is noted that the figures are calculated ("berrechnet") it is a strong indication, that compressibility is accounted for.

 

No, it is not. All true air speeds (TAS) are being calculated from indicated air speeds and other properties. The calculation is just different (more complex) if you want to correct for compressibility. You can see both formulas on the sheet Karaya linked.

 

The basic procedure was to calibrate the speed indicator at low altitude over a test course marked and measured over ground. You measure time on the ground (or/and in the air) between start and end point, you'd record indicated speed, temperature and pressure (and maybe other quantities if you needed to be more accurate). Knowing true air speed from the ground measurements and indicated air speed as well as atmospheric conditions, you'd use that to calculate position error of the speed indicator, giving you a chance to arrive at calibrated air speeds for the indicator used. You could then go on to measure indicated speeds at different altitudes and test scenarios, while still recording pressure and temperature, so you could calculate your true air speeds at altitude from converting the IAS to CAS using the position error determined earlier and from that you would calculate TAS using the recorded atmospheric properties. Either with correction for compressibility, or not. But you'd always calculate. You'd then would also calculate additional corrections to arrive at a defined standard condition of the aircraft, say full take off weight, which you don't actually have in the flight test. Weight, for instance, is constantly changing.

 

Outside of this, performance figures marked as "berechnet" (calculated) often refer to figures not (yet) backed up (sufficiently) by flight testing. They did calculate a lot back then, even without computers. It would look like this (part of a climb calculation for the A-9). You could arrive at best climb speeds and certain climb performances, but until they were tested and confirmed, they'd be marked as "berechnet", in particular when compared to flight test confimred data (of say previous models).

 

2 hours ago, Karaya said:

So these corrections happened earlier than 1944.

 

Yes, they certainly did. Otherwise they wouldn't know what difference it makes and would never arrive at the conclusion to use the more accurate calculation.

Interestingly enough, the 656 from the A-5 in this calculation also found their way into some official performance figures, even though it was stated that figures for A-8 and earlier all come without correction. OTOH, the A-5 aircraft data sheet for instance gives 680 km/h, without correction. Even there it's not as binary as I remembered it to be.

[the_emperor]

12 minutes ago, JtD said:

No, it is not. All true air speeds (TAS) are being calculated from indicated air speeds and other properties. The calculation is just different (more complex) if you want to correct for compressibility. You can see both formulas on the sheet Karaya linked.

True you always have to calculate

But in the German documents there seems to bee a difference in terminology as early charts for TAS often say "Messung"/"gemessen" (measured), or "erflogen" (dont realy know how to translate that) as opposed to "errechnet"/Berechnung" in later document which seem to account for compressability.

I would not say it is a proof, rather a hint

 

I guess a true air speed indicator for our virtual instruments would be really nice to have by now.

Edited October 19, 2020 by the_emperor