Incorrect mach reading since last patch?

[DarkFire]

I've been trying my hand at speed & altitude attempts recently with the Su-27. Attached is the track.

 

There appears to be a problem with the reading of the Mach meter in the cockpit. At the 10:35 mark I start at ~3g pull up to >50* pitch and zoom climb. The altitude reached (just over 31,100 m) is consistent with the in-cockpit reading. What was drastically different was the reading of the Mach meter at the point of pull-up.

 

According to Tacview at the point of pull-up I was doing 2,530 Kmh which again according to Tacview equates to 2.38 - 2.40 Mach. The in-cockpit Mach meter was barely showing over 1.5 Mach.

 

I've tried this a couple of times with different meteorological conditions e.g. temperature and in each case the Mach meter in-cockpit consistently and drastically under-reads. Has anyone else seen this?

 

Edited to add ziped .acmi file.

Edited May 3, 2015 by DarkFire

[Weta43]

If you zip it first, you can.

[DarkFire]

If you zip it first, you can.

 

Thanks, edited and added.

[combatace]

My mach meter shows that my fully loaded Su-27 can super cruise (mach 1.1 at mil power)

[karambiatos]

The mach reading has to do with air pressure now, so it can show wrong readings.

[DarkFire]

The mach reading has to do with air pressure now, so it can show wrong readings.

 

Interesting. Further experimentation is called for...

 

Edited to add: I don't think that pressure variation could possibly account for all the variation between actual and instrument-given Mach numbers.

 

The test I just did was as follows:

 

1) Standard DCS day, i.e. default ME settings.

 

2) On take-off from Anapa, QFE was exactly 760.

 

3) Linear track out over the sea towards Batumi.

 

4) Maximum speed was achieved at roughly 8:17 in to the flight, out over the sea. Tacview gives altitude as having been 12,663 m which agrees with in-cockpit altimeter and HUD.

 

5) Tacview thinks my true speed at that time was 2,611 Kmh or Mach 2.46, whereas the cockpit reading was barely Mach 1.6.

 

5) At exactly 2000 kg of fuel remaining I began a 3g pull up to 60* pitch, at maximum thrust. Maximum altitude achieved was 32,640 m at only about 10Km distance from being directly over Batumi airfield.

 

6) On landing at Batumi I was informed that QFE was 759.25 - that equates to ~0.001% pressure difference across the entire 650Km flight.

 

The in-cockpit Mach reading can't be accurate :huh:

 

Attached are the .track file, the zipped .acmi and a screen shot showing the speed profile from Tacview

Edited May 4, 2015 by DarkFire

[combatace]

Interesting. Further experimentation is called for...

 

Edited to add: I don't think that pressure variation could possibly account for all the variation between actual and instrument-given Mach numbers.

 

The test I just did was as follows:

 

1) Standard DCS day, i.e. default ME settings.

 

2) On take-off from Anapa, QFE was exactly 760.

 

3) Linear track out over the sea towards Batumi.

 

4) Maximum speed was achieved at roughly 8:17 in to the flight, out over the sea. Tacview gives altitude as having been 12,663 m which agrees with in-cockpit altimeter and HUD.

 

5) Tacview thinks my true speed at that time was 2,611 Kmh or Mach 2.46, whereas the cockpit reading was barely Mach 1.6.

 

5) At exactly 2000 kg of fuel remaining I began a 3g pull up to 60* pitch, at maximum thrust. Maximum altitude achieved was 32,640 m at only about 10Km distance from being directly over Batumi airfield.

 

6) On landing at Batumi I was informed that QFE was 759.25 - that equates to ~0.001% pressure difference across the entire 650Km flight.

 

The in-cockpit Mach reading can't be accurate :huh:

 

Attached are the .track file, the zipped .acmi and a screen shot showing the speed profile from Tacview

 

I see your cockpit reading was showing Mach 2.45 and tacview was also showing Mach 2.45.

[mvsgas]

I see the same as combatace. Using the clock on the to left ( after pressing right control at pause) you reached mach 2.40 at 974 seconds. 12:16 and 15 seconds on the cockpit clock.

 

It is funny, you help me realize I have been reading the altimeter wrong all this years in SU-27 :doh:

Edited May 6, 2015 by mvsgas

[Ironhand]

I've been trying my hand at speed & altitude attempts recently with the Su-27. Attached is the track.

 

There appears to be a problem with the reading of the Mach meter in the cockpit. At the 10:35 mark I start at ~3g pull up to >50* pitch and zoom climb. The altitude reached (just over 31,100 m) is consistent with the in-cockpit reading. What was drastically different was the reading of the Mach meter at the point of pull-up.

 

According to Tacview at the point of pull-up I was doing 2,530 Kmh which again according to Tacview equates to 2.38 - 2.40 Mach. The in-cockpit Mach meter was barely showing over 1.5 Mach.

 

I've tried this a couple of times with different meteorological conditions e.g. temperature and in each case the Mach meter in-cockpit consistently and drastically under-reads. Has anyone else seen this?

 

Edited to add ziped .acmi file.

Are you by any chance using the English cockpit mod? I believe that's the mod that screws up the cockpit's mach reading.

[combatace]

Just off topic, which pressure does the pressure gauge in altimeter display?

[Ironhand]

Just off topic, which pressure does the pressure gauge in altimeter display?

You mean the barometric altimeter? Barometric pressure which, in this cockpit, you can't reset to the local pressure. It's fixed at whatever the default pressure is.

[combatace]

You mean the barometric altimeter? Barometric pressure which, in this cockpit, you can't reset to the local pressure. It's fixed at whatever the default pressure is.

 

Thought so but had a second thought that it might be external atmospheric pressure. But whats the point in displaying cockpit pressure in altimeter, shouldn't it be outside pressure?

[DarkFire]

Are you by any chance using the English cockpit mod? I believe that's the mod that screws up the cockpit's mach reading.

 

Ah. And there's the answer :)

 

Ah well, at least all that flying has improved my Flanker handling :)

Edited May 6, 2015 by DarkFire

[Ironhand]

Thought so but had a second thought that it might be external atmospheric pressure. But whats the point in displaying cockpit pressure in altimeter, shouldn't it be outside pressure?

It is outside pressure. It's being used to determine your altitude. And the altitude on that analogue instrument should read the same as what you see on the HUD.

 

 

Ah. And there's the answer :)

 

Ah well, at least all that flying has improved my Flanker handling :)

I like it when the solutions are easy... :)

[combatace]

It is outside pressure. It's being used to determine your altitude. And the altitude on that analogue instrument should read the same as what you see on the HUD.

 

It shows the readings in mmHg(millimeter of Mercury) and 760mm is at sea level but it should drop as the pressure drops with the increase in altitude but it seems to remain at 760 all the time.

[Robin_Hood]

The barometric pressure (which is tunable, by the way, key commands have been added to that effect) shows the pressure at see level. It is not derived from a sensor, it is manually set. You input the QNH (pressure at sea level) or QFE (pressure at airfield elevation) and then the altimeter uses that to compute your altitude above sea level or above ground level, respectively.

 

On a side note, above a certain transition altitude, the altimeter is normally set to the QNE, which is the standard pressure (760 mmHg, 1013 mbar or 22.92 inHg depending on your preferred units) - this is so that aircraft coming from different locations can have their altimeter readings matching (otherwise, if you come from somewhere with a higher pressure, you will read a lower altitude than other people).

 

Again, it is not a sensor. It only helps the altimeter deduce your current altitude (by comparing outside pressure - measured, but not indicated anywhere in the cockpit - and the ground or sea level pressure).

Edited May 7, 2015 by Robin_Hood

[combatace]

The barometric pressure (which is tunable, by the way, key commands have been added to that effect) shows the pressure at see level. It is not derived from a sensor, it is manually set. You input the QNH (pressure at sea level) or QFE (pressure at airfield elevation) and then the altimeter uses that to compute your altitude above sea level or above ground level, respectively.

 

On a side note, above a certain transition altitude, the altimeter is normally set to the QNE, which is the standard pressure (760 mmHg, 1013 mbar or 22.92 inHg depending on your preferred units) - this is so that aircraft coming from different locations can have their altimeter readings matching (otherwise, if you come from somewhere with a higher pressure, you will read a lower altitude than other people).

 

Again, it is not a sensor. It only helps the altimeter deduce your current altitude (by comparing outside pressure - measured, but not indicated anywhere in the cockpit - and the ground or sea level pressure).

 

Thanks man, so its not a gauge rather a preset.

[Ironhand]

The barometric pressure (which is tunable, by the way, key commands have been added to that effect)...

Damn...How have I missed it all this time? RShift + - and RShift + =. Or is that a recent addition?

[mvsgas]

Damn...How have I missed it all this time? RShift + - and RShift + =. Or is that a recent addition?

IIRC for a long time on the 25 and 25T. Su-27 since the new flight model was introduce AFAIK.

[Ironhand]

IIRC for a long time on the 25 and 25T. Su-27 since the new flight model was introduce AFAIK.

 

I knew about the -25 and -25T having it. IIRC, the -25T (at least) had it back in FC1.x. I never noticed that they'd added it to the -27 as well. Now I'll have to pay attention to it. :)