Wrong Russian fighters performance at high alts again

[Brano]

In the book from mister Stepanec http://www.airpages.ru/dc/doc112.shtml

1) изменение положения рычага высотного корректора приводит к увеличению максимальной скорости: на высоте 600 м — на 2 км/час на высоте 3500 м— на 11 км/час, на высоте 8 000 м — на 70 км/час;

 

Which says that when vysotnyi korrektor is used as recommanded (between 1/3 and 2/3 open position of lever) you can raise max speed at alt of 8km up to 70km/h.Which more/less corresponds with Kwiateks measurements.

 

Only problem is,that it is not represented visualy in game.It looks like vysotnyi korrektor is working "automaticly" instead of being purely manualy adjustable.

[VBF-12_Stick-95]

In the book from mister Stepanec http://www.airpages.ru/dc/doc112.shtml

1) изменение положения рычага высотного корректора приводит к увеличению максимальной скорости: на высоте 600 м — на 2 км/час на высоте 3500 м— на 11 км/час, на высоте 8 000 м — на 70 км/час;

 

Which says that when vysotnyi korrektor is used as recommanded (between 1/3 and 2/3 open position of lever) you can raise max speed at alt of 8km up to 70km/h.Which more/less corresponds with Kwiateks measurements.

 

Only problem is,that it is not represented visualy in game.It looks like vysotnyi korrektor is working "automaticly" instead of being purely manualy adjustable.

 

Interesting.  Couple of questions.

 

Is a specific plane being discussed?

 

What is the vysotnyi korrektor?

 

I always thought level flight "max speed" was just that, balls to the wall, with all settings at maximum performance.  What this points out is that certain adjustments may increase speed even above that?

Edited February 17, 2015 by VR_Stick

[Crump]

Only problem is,that it is not represented visualy in game.It looks like vysotnyi korrektor is working "automaticly" instead of being purely manualy adjustable.

 

Very interesting!

 

It look like this system does not "add power" or "increase performance".  As I understand it, the automatic mixture control only maintains best power ratio 18:1 for the engine up to 4000 meters.  With this system, the pilot then has to adjust his own mixture the old fashion way.

 

He uses feel of rough and smooth operation of the motor as well as the visual clues of the exhaust flame to keep the mixture properly adjusted.  It is manual mixture control.

 

They give the range of speeds that can be found if the pilot does not properly adjust the system.   It is not going to add performance, it will detract from performance if not properly adjusted.

 

I can see why the devs made it automatic.  Can you image the screams if they did not?

 

The VVS would be hopelessly outclassed above 4000 meters for many players.

Edited February 17, 2015 by Crump

[Brano]

It is book about Yaks equipped with M(VK)105PF engine.I did not read it in very details to check which particular type he is reffering to.It is general reference to all Yaks used during Great patriotic war equipped with this particular engine.

Vysotnyi korrektor is nothing else then adjustment of fuel mixture - manual.

Above 4km,where supercharger is not able to sustain same air volume as on the ground,you need to start using it,to lean fuel amount in mixture.Otherwise it will be too rich with all consequences to the engine.

[CaK_Rumcajs]

In the book from mister Stepanec http://www.airpages.ru/dc/doc112.shtml

1) изменение положения рычага высотного корректора приводит к увеличению максимальной скорости: на высоте 600 м — на 2 км/час на высоте 3500 м— на 11 км/час, на высоте 8 000 м — на 70 км/час;

 

Which says that when vysotnyi korrektor is used as recommanded (between 1/3 and 2/3 open position of lever) you can raise max speed at alt of 8km up to 70km/h.Which more/less corresponds with Kwiateks measurements.

 

Only problem is,that it is not represented visualy in game.It looks like vysotnyi korrektor is working "automaticly" instead of being purely manualy adjustable.

I'm certainly not an expert on soviet planes. But i can't imagine that max speed graphs would be ever produced for the incorrect engine setup. There is no lever that would give an aircraft magical +70km/h speed. There is a lever that when used totally improperly slows down the plane by that much. There is no way the test pilots couldn't use the lever to its optimal performance. So what we shall see in game is this drop in max performance if the mixture lever is used poorly. I'm not buying any increase above documented values.

[303_Kwiatek]

In the book from mister Stepanec http://www.airpages.ru/dc/doc112.shtml

1) изменение положения рычага высотного корректора приводит к увеличению максимальной скорости: на высоте 600 м — на 2 км/час на высоте 3500 м— на 11 км/час, на высоте 8 000 м — на 70 км/час;

 

Which says that when vysotnyi korrektor is used as recommanded (between 1/3 and 2/3 open position of lever) you can raise max speed at alt of 8km up to 70km/h.Which more/less corresponds with Kwiateks measurements.

 

Only problem is,that it is not represented visualy in game.It looks like vysotnyi korrektor is working "automaticly" instead of being purely manualy adjustable.

 

You can't increase maximum avaliable speed by changing mixture you can only prevent lost maximum speed if you will adjust mixture ratio.

 

So its mean that if you dont adjust mixture you will loose  2 kph at 600m,  11 kph at 3.5 km and 80 kph at 8 km.   So if Yak-1 IRL reached 520 kph at 8 km its mean that will loose  80 kph without mixture correction -  so maximum speed will be 440 kph instead 520 kph.

 

So if for example at 6 km maximum speed of Yak-1 with PF engine was 545 kph without mixture correction it would be fly maximum ab. 480-490 kph.

 

So mixture correction only prevent maximum avialiable speed lost not work as a aditional boost speed.

Edited February 17, 2015 by 303_Kwiatek

[Brano]

All datas abou max speed we have for Yak-1 with M105PF in all availabe charts are given for ~4km = max altitude for supercharger=test pilots didnt have to use vysotnyi korrektor at all.

What speed  can Yak-1 reach at 6km or 8km? I have no idea.

[303_Kwiatek]

Maximum speed will be decreasing in all prop planes above supercharger rated power.  For M-105 PF motor maximum power is avaliable at 2700M, for a plane it would give maximum speed at 3.5-3.6 km then maximum speed will be decreasing.   For Yak-1 1942 with M-105 PF motor maximum speed was 570 kph at 3.65 km then speed will fall off.

 

I think it is quite easy to understand for all.  So there is no possible that the same Yak-1 which could have maximum speed 570 kph at 3,65 km could reach 600 kph at 6 km.  Not IRL.  Only in BOS.

 

Some Yak-1 with PF engine data:

 

Russian Graph 0213: The LaGG-3 and Yak-1 fighters with the Klimov M-105PF during the period 1942-(1943).

 

Altitude/Speed

Meters/mph

S.L.---313 (330)

1,000-331 (346)

2,000-343 (351)

3,000-349.5 (358)

4,000-354 (370)

5,000-346 (362.5)

6,000-335 (351)

 

Maximum: 357.5 mph.@ 11,650 ft. (370 mph.@ 13,350 ft.)

 

Range Clean: 403 (434) mls.

 

Armament: 1 x 20mm/120 rds. + 2 x 7.62mm/750 rpg. (1 x 20mm/140 rds. + 1 x 12.7mm/240 rds.)

 

Combat Weight: 6,430 (6,358) lbs. 

 

Engine: Klimov M-105PF

 

Wing Loading: 34.83+ (34.44+) lbs./sq.ft.

 

Power Loading: 5.103+ (5.046+) lbs./hp.

 

Service Ceiling: 32,800 (32,965) ft.

[Brano]

As I pointed out earlier,vysotnyi korrektor is not working properly.In game it looks like klimov keeps his 4km power output even on higher altitudes.

[VBF-12_Stick-95]

I ran the test in the OP.  The speed was as claimed, no problem. 

 

What I did find totally amazing was was the temperatures for both water and oil.  They were through the roof with no overheating indication.  I tried tests at 4000 and 5000 meters decreasing the rad settings as I went and received overheating messages with oil and water around 90.  At 6000 meters however I can fly all day with oil at about 112 and water at about 103 without overheating.  Regardless of altitude, shouldn't the engine temperature operating parameters remain about the same?

[303_Kwiatek]

At higher alts cooling is less efficent so engines will more overheat at high alts then in lower alts.

 

Another interesting facts is that Russian Klimow M-105 PF instaled on Yak-1 and Lagg-3 in 1941-1942 overheated really badly. Pilots were instructed to level flight after climb 1-2 kms and drop RPMS from 2700 to 2200 for cooling engine  ( these is knwon fact even in BOS Russian forum).  The same about La5 overheated problems and forsah usage ( which was forbiden casue of these problems).

 

At least LA5 overheat problems was simulated in BOS.

Edited February 17, 2015 by 303_Kwiatek

[VBF-12_Stick-95]

At higher alts cooling is less efficent so engines will more overheat at high alts then in lower alts.

 

Another interesting facts is that Russian Klimow M-105 PF instaled on Yak-1 and Lagg-3 in 1941-1942 overheated really badly.

 

So if engines overheat at higher at higher altitudes more easily, why isn't it overheating?  If it overheats at higher altitude one would have to back off throttle or open rads. This is not happening.

[Brano]

I'm certainly not an expert on soviet planes. But i can't imagine that max speed graphs would be ever produced for the incorrect engine setup. There is no lever that would give an aircraft magical +70km/h speed. There is a lever that when used totally improperly slows down the plane by that much. There is no way the test pilots couldn't use the lever to its optimal performance. So what we shall see in game is this drop in max performance if the mixture lever is used poorly. I'm not buying any increase above documented values.

You are right,it is not about boosting the speed.I might wrote it in not very proper way.My point was,that you really had to use vysotnyi korrektor at altitudes above 4km to get max output from the engine.It is not the situation we have now in game, I am affraid.It would be nice to hear a word from devs where the truth is.

[303_Kwiatek]

So if engines overheat at higher at higher altitudes more easily, why isn't it overheating? If it overheats at higher altitude one would have to back off throttle or open rads. This is not happening.

 

These is question for devs

 

Example of avaliable power between Russian Klimow M-105 PF and example BMW 801 D

 

Russian  M-105 PF could keep 1180 HP only to 2700 m then power rapidly drop.  At 6 km it got only about 770 HP power.

 

 

For comparison BMW 801 D at 2 gear of supercharger could keep 1440 PS to 5.7 km. 

 

 

These could give some picture how fight at higher alts could end for Yak-1 pilot

Edited February 17, 2015 by 303_Kwiatek

[VBF-12_Stick-95]

Thanks Kwiatek.  I guess the more precise question is:

 

If you are able to fly at higher temperatures than the engine permitted without overheating, wouldn't that contribute to the increase in speed that you observed?

[303_Kwiatek]

I think problem with overheating or absense of it is another thing.

 

Here is rather problem of engine power at high alts.  Even if engine will be overheat more quickly still you will be able to achive maximum speed until it will broken.

 

In these case it is power problem.  Overheating is aditional thing casue it will be limit your time at maximum power settings ( it is good simulated with BOS LA5 for example)

Edited February 17, 2015 by 303_Kwiatek

[Brano]

I guess that if you fly in Yak at 4km with given max speed and game does not take into account different engine conditions at 6km=power output is the same as at 4km,your TAS will be higher (10-12%?).

[303_Kwiatek]

If power drop by altitude is wrong modeled and engine will produce more power then should at higher alts e.x. at 6 km surly it will casue speed increase ( but also climb rate)

 

BTW mixture in M-105 PF engine was need to adjust from 3 km not 4 km.  From 4 km mixture adjust was need in 105 PA engine.  It is surly also wrong modeled in BOS actually. It was better simulated in old IL2. ( when you not adjust mixture your overich it and lose power was noticed combined with black smoke from exauhst)

 

 

6 min about mixture.

Edited February 17, 2015 by 303_Kwiatek

[Crump]

 

 

You can't increase maximum avaliable speed by changing mixture you can only prevent lost maximum speed if you will adjust mixture ratio.

 

Exactly.

 

For the readers.. 

 

Power is directly tied to specific fuel consumption.  There is only one fuel to air ratio for an engine to achieve best power, one for peak EGT, and only one for best economy.

 

Changing that specific fuel consumption will change the power but not above the best power fuel to air ratio which is the rated power for the engine.  It is not like Methanol Water or Nitrous Oxide which will greatly increase indicated power at the same manifold pressure. 

 

In this case,  with pure manual control, the pilot is adjusting for Peak EGT and not even best power.  Without an EGT gauge, he would have no way to find it.  If you lean to rough and push forward to smooth, you will find the vicinity of the peak EGT point.

 

 

BTW mixture in M-105 PF engine was need to adjust from 3 km not 4 km.  From 4 km mixture adjust was need in 105 PA engine.  It is surly also wrong modeled in BOS actually. It was better simulated in old IL2. ( when you not adjust mixture your overich it and lose power was noticed combined with black smoke from exauhst)

 

 

Depends on.......Density altitude not the indicated altitude.  

[Brano]

More simple for casual pilot = you have to adjust mixture according visual signs = rpm oscilation,engine running not smoothly,smoke from unburned fuel when mixture too rich.That is also written in book from mister Stepanec  (btw same guy who participated in creation of that video kwiatek posted).3 or 4km is just recommanded altitude.Of course pilot cant see density altitude.Smokin'n'shakin engine will show him.

[Matt]

Strange. I just redid the test (at standard atmosphere conditions, 15 °C outside temperature) and there's definately something wrong with the speed of the Yak-1 at 6000 meters. It's about as fast as 6000 meters as it is at 4000 mters (433 km/h IAS vs. 480 km/h IAS). Last time i did that test (which i believe was last year still), it was alright and the Yak totally lost speed above 4000 meters and the La-5 was much faster than the Yak-1 at 6000 meters (about 35 km/h TAS). The devs should definately look into that and it's definately not correct as it is.

[Crump]

 

 

More simple for casual pilot = you have to adjust mixture according visual signs = rpm oscilation,engine running not smoothly,smoke from unburned fuel when mixture too rich.That is also written in book from mister Stepanec  (btw same guy who participated in creation of that video kwiatek posted).3 or 4km is just recommanded altitude.Of course pilot cant see density altitude.Smokin'n'shakin engine will show him.

 

Exactly.  The engine will find density altitude for him!! 

[303_Kwiatek]

Strange. I just redid the test (at standard atmosphere conditions, 15 °C outside temperature) and there's definately something wrong with the speed of the Yak-1 at 6000 meters. It's about as fast as 6000 meters as it is at 4000 mters (433 km/h IAS vs. 480 km/h IAS). Last time i did that test (which i believe was last year still), it was alright and the Yak totally lost speed above 4000 meters and the La-5 was much faster than the Yak-1 at 6000 meters (about 35 km/h TAS). The devs should definately look into that and it's definately not correct as it is.

 

Well if you belive devs everything is all right

[II./JG77_Manu*]

You've not a chance of being taken seriously with comments like that.

 

Why? The Yak in game is very close to Yak3 performance at 6.000m altitude. A lot closer then to the Yak1 series 67 at least. The only thing which really can't be taken serious is the Devs (Zak's) answer to this issue.

[II./JG77_Manu*]

Just made another test. 

Yak1 again, fully closed radiators, full throttle altitude (3650m), and i reached a whopping 515 IAS (!!!), which is around 639kph TAS. So instead of flying 571kph, it flies 639. That is "just" 68kph to fast. At an altitude, which is the most common in game. This is becoming more and more ridiculous, seriously...

 

Edit:

same Test with 190 at Combat Rating. 498 IAS, which is around 617 TAS. It is supposed to fly 580kph in this conditions, so it overspeeds with 37kph. So let's assume the cold air boost, and the density in the air make the 190 fly 37 kph faster at this altitude, why does the Yak overspeed 68? That is 31kph more overspeed then the 190.

IRL the 190 under combat rating was 9 kph faster then the Yak (full throttle and closed rads) at this altitude, in game it is 22kph slower...

Edited February 17, 2015 by Celestiale

[NobbyNobbs]

BTW mixture in M-105 PF engine was need to adjust from 3 km not 4 km.  From 4 km mixture adjust was need in 105 PA engine.  It is surly also wrong modeled in BOS actually.

 

 

Yeah... Good video. But you don't understand what is Russia. Do you think that old video it's good argument? LOL. What about real docs? 

 

Flying manual for LaGG-3:

Are they kidding?

Let's check in flying manual for Yak-1

 

Ok. And at last clarify it in another book about Yak-1 with M-105 PF (printed in 1947)

 

Not bad, right? What altitude is correct?

[SOLIDKREATE]

Just made another test. 

Yak1 again, fully closed radiators, full throttle altitude (3650m), and i reached a whopping 515 IAS (!!!), which is around 639kph TAS. So instead of flying 571kph, it flies 639. That is "just" 68kph to fast. At an altitude, which is the most common in game. This is becoming more and more ridiculous, seriously...

 

You may have had a tailwind....ever think about that .

[II./JG77_Manu*]

You may have had a tailwind....ever think about that .

 

that doesn't change anything in IAS...ever think about that 

[Brano]

Just made another test. 

Yak1 again, fully closed radiators, full throttle altitude (3650m), and i reached a whopping 515 IAS (!!!), which is around 639kph TAS. So instead of flying 571kph, it flies 639. That is "just" 68kph to fast. At an altitude, which is the most common in game. This is becoming more and more ridiculous, seriously...

I would say less then your TAS value.Care to post your calculation? How do we know that devs used 571km/h at 3650m as reference max speed for Yak-1?

We discuss here problem of high altitude performance.Over 4km up to 8km.

[303_Kwiatek]

 

Yeah... Good video. But you don't understand what is Russia. Do you think that old video it's good argument? LOL. What about real docs? 

 

Flying manual for LaGG-3:

42_43.png

Are they kidding?

Let's check in flying manual for Yak-1

як_рлэ.png

 

Ok. And at last clarify it in another book about Yak-1 with M-105 PF (printed in 1947)

степанец.png

 

Not bad, right? What altitude is correct?

 

 

It looks that even Russian got problem with mixture operations

 

I think 3 km for ISA dentisy is more correct casue supercharger of M-105 PF got peak alt at 2700m which mean that above 2700m can't keep engine pressure ( less air into curburator) which affect that above 2700 m  you need to start leaninig mixture ( fuel).  There were no automat for mixture adjusting so you need to do it manually.

[303_Kwiatek]

Just made another test. 

Yak1 again, fully closed radiators, full throttle altitude (3650m), and i reached a whopping 515 IAS (!!!), which is around 639kph TAS. So instead of flying 571kph, it flies 639. That is "just" 68kph to fast. At an altitude, which is the most common in game. This is becoming more and more ridiculous, seriously...

 

Edit:

same Test with 190 at Combat Rating. 498 IAS, which is around 617 TAS. It is supposed to fly 580kph in this conditions, so it overspeeds with 37kph. So let's assume the cold air boost, and the density in the air make the 190 fly 37 kph faster at this altitude, why does the Yak overspeed 68? That is 31kph more overspeed then the 190.

IRL the 190 under combat rating was 9 kph faster then the Yak (full throttle and closed rads) at this altitude, in game it is 22kph slower...

 

I think you wrong calculated TAS.

 

I used aviation calculator and got:

 

515 kph IAS at 3650 m  =  611 kph TAS

 

Fw 190 498 IAS at 3650 m = 591 kph TAS

[II./JG77_Manu*]

I would say less then your TAS value.Care to post your calculation? How do we know that devs used 571km/h at 3650m as reference max speed for Yak-1?

We discuss here problem of high altitude performance.Over 4km up to 8km.

 

I think you wrong calculated TAS.

 

I used aviation calculator and got:

 

515 kph IAS at 3650 m  =  611 kph TAS

 

Fw 190 498 IAS at 3650 m = 591 kph TAS

 

 

i used the 2% all 1000 feet, and 3650m is 12k feet, so i calculated speed *1,24. Might be not very accurate, but that doesn't matter anyway, cause i was talking about the difference. I don't know who much this cold air boost and density difference are changing the TAS of the planes, but i know the speed difference between the planes in normal conditions, and this should stay the same. 

 

@Brano 571kph was the absolute topspeed of the Yak 1 Series 67, reached only at an altitude of 3650. Above this altitude, the speed decreased more and more

Edited February 18, 2015 by Celestiale

[LukeFF]

 

 

Delevopers claim that their planes are with only 2 % error is obviously wrong.   Yak-1 and Lagg-3 got at least 10% error in maximum speed at high alts. Moreover planes which IRL was slowier at higher alts then La5 in game are faster one.

 

And here we go, over and over again...  

 

If you think the numbers are wrong, send Han a message with your claims supporting your argument. 

 

 

Do you know that in Russia there still also strong faith in good father "Stalin"?    Instead keeping bleed faith move your brain do some research and take your opinion then.

 

The heck does that have to do with this argument? Instead of wasting your time making these types of arguments, do like I wrote above and present your evidence to the team. 

[303_Kwiatek]

Yep 571 kph was maximum speed at 3.6 km for Yak-1 with M-105 PF engine  ( it confirmed any suorces or data i have seen).

 

 

 

I don't know who much this cold air boost and density difference are changing the TAS of the planes, but i know the speed difference between the planes in normal conditions, and this should stay the same.

 

Yep you right even at 3.85 km something is not right with relative speed performacne.  At these alt A-3 should be faster even at 1.32 Ata power about 10-15 kph.

And here we go, over and over again...

 

If you think the numbers are wrong, send Han a message with your claims supporting your argument. 

 

 

 

The heck does that have to do with this argument? Instead of wasting your time making these types of arguments, do like I wrote above and present your evidence to the team. 

 

Dev know these topic and i sended raport to Zack.  You know what was his response here.

 

 

Soviet planes' max speed is tuned with the possible fault of 2% maximum. This has been checked and double checked a million times. Bacause of that, max speed of all mentioned fighters is correct and will not be changed. 303_Kwiatek, on 16 Feb 2015 - 12:41, said: From my test it is clearly show that Yak-1 and Lagg-3 got not low altitutde engine but rather high alts engines in BOS. Both are about 50-60 kph too fast at 6 km. Thats why German planes don't have in BOS their RL advetntages at higher alts. IRL German fighters ( 109 and Fw 190 A-3) was faster then Yak-1 about 80-100 kph TAS at alts above 5 km. Have you actually checked this in the game? I've just checked it myself: 6000m, QM: Yak-1, 100% throttle, radiators on auto: IAS=426, TAS=584 and FW 190: АТА 1.32: IAS=465, TAS=638

Edited February 18, 2015 by 303_Kwiatek

[303_Kwiatek]

Funny is that even not accurately done Zack test ( radiator auto?) proved that  Yak-1 is overspeed at high alts (  584 kph at 6 km )

[II./JG77_Manu*]

 

 

And here we go, over and over again...  

 

 

And here we go, over and over again... Anytime anybody points out flaws of this game, especially in the FM department, no matter how obvious and easy to check and prove those faults are, there is always some mod or "Tester" coming around, dragging those facts into doubt, making fun of it, or even worse belying them.

Propaganda of the 21st century.

[LukeFF]

And here we go, over and over again... Anytime anybody points out flaws of this game, especially in the FM department, no matter how obvious and easy to check and prove those faults are, there is always some mod or "Tester" coming around, dragging those facts into doubt, making fun of it, or even worse belying them.

Propaganda of the 21st century.

 

Try again. My point is that, instead of going on and on and on and on here about how you (and Kwiatek) think things are wrong, summarize your claims about why you think things are wrong and submit them to the team for review. That's the only way things will be changed. This doesn't feel right / the data is flawed / something is off, etc., just doesn't cut it. The team doesn't have time to analyze emotions and how one "feels" about a certain flight model. Like it or not, they deal in facts, and it's been that way since they began coding ROF. 

[SKG51_robtek]

Try again. My point is that, instead of going on and on and on and on here about how you (and Kwiatek) think things are wrong, summarize your claims about why you think things are wrong and submit them to the team for review. That's the only way things will be changed. This doesn't feel right / the data is flawed / something is off, etc., just doesn't cut it. The team doesn't have time to analyze emotions and how one "feels" about a certain flight model. Like it or not, they deal in facts, and it's been that way since they began coding ROF. 

Maybe you might try again to accept those tests instead of trying to supress valid objections.

And please dont act as if Celestiale and Kwiatek weren't speaking for all who want a realistic as possible Simulation.

It was already written, more than once, that the devs have gotten the data available.

The devs decided to ignore a obvious error, imo a proven error, without providing any facts beside saying we are right you are wrong.

Thats more than enough reason to point out the errors again and again until they are corrected.

By the way, it is another "balancing" happening when the mixture control is automatic, reducing the workload this way, when one side has real automatic control and the other manual control.

Edited February 18, 2015 by I./ZG15_robtek

[Brano]

Maybe devs used Yak 1b max speed of 591km/h at ~4km as reference speed.Then addition of 20km/h to get to 611km/h seems legit = increase of speed inbetween +15/-15°C is reffered to in Stepanec book.

[Matt]

The Yak-1 goes around 580 km/h TAS at 4000 meters at standard atmosphere (assuming that the speed on the HUD is CAS and not IAS, i'm not sure about that, but the HUD speed differs from the in cockpit gauges). Nothing wrong with that imho, well inside 2% tolerance if you use the 571 km/h or 592 km/h figures that are floating around.

 

The problems starts above that altitude.