[RESOLVED] Cruise performance not realistic

[Tango]

There is something funky about the reheat, because the aircraft can largely hit altitude/maximum speed as it should, but there is still a problem as the climb performance is still wrong, even in full reheat.

 

Best regards,

Tango.

[Corrigan]

Thanks, but that is not it. Also, the flaps retract due to air pressure upon them.

 

Yeah, wasn't implying that that was the entire issue, just that it's something that everyone might not think of ahead of every test. Also, you can go quite fast with flaps in TO.

 

It seems weird to me that the flight model should be this off. Has it been tuned using different figures? If so, maybe Dolphin could share some of them?

Edited September 20, 2014 by Corrigan

[TurboHog]

With three external fuel tanks a was able to reach 13 000 m in 13 minutes. I activated afterburner in 6000 m and after reaching 13 000 m i still had 400l in external tanks. Well it is really not efficient but possible even from the ground.

 

We're talking about climbing without afb.

 

Based on Tango's climb test, I would say that the DCS Mig's performance is way outside any reasonable margin of error.

 

Of course these charts are only guidelines and maybe some of them are calculated results instead of tested results. However, the results differ significantly from the charts and to such an extent that I can safely say that the flight performance is unrealistic.

 

I may sound a little rough sometimes, arguing about what I think is wrong with the FM. But I really appreciate the work that got into this module and I hope that this is seen as help and not as my way of expressing frustrations about the FM.

Edited September 20, 2014 by TurboHog

[aaron886]

I like that you guys are doing serious tests, just keep in mind that you too are making an assumption when you say that these charts do not require the use of afterburner. If they don't say, I don't think you can speak so surely.

[TurboHog]

I have consolidated all posts that contain tested data in the first post in this thread to make it easier for the devs to retrieve the information.

 

I will update the first post if new test results are posted.

[TurboHog]

I like that you guys are doing serious tests, just keep in mind that you too are making an assumption when you say that these charts do not require the use of afterburner. If they don't say, I don't think you can speak so surely.

 

I am quite sure that the chart assumes non-afb use

 

• It is SOP to turn off the afb after reaching 600km/h
  
• Fuel consumption for the climb-out is ~425L in clean configuration. With use of the afterburner you will consume much more.
  

 

I will try to find more evidence for this. I am quite sure - not sure.

Edited September 20, 2014 by TurboHog

[Tango]

I like that you guys are doing serious tests, just keep in mind that you too are making an assumption when you say that these charts do not require the use of afterburner. If they don't say, I don't think you can speak so surely.

 

The manual states that climb is conducted at 870 kph TAS, at FULL POWER, which in manual-speak, means MIL, or without reheat.

 

Where reheat is to be used, it either states FULL REHEAT or FULL REHEAT AND SECOND REHEAT (e.g. in the case of zoom climb, for example).

 

It states this quite early on, and either references this condition later on (it will say something like "climbing as per paragraph xyz", otherwise it will state exactly the condition under which the aircraft is to be flown for a particular flight phase or maneuver.

 

The only thing missing is some statement about power settings, but it largely talks about maximum performance, so it is either maximum altitude, maximum range, or maximum speed, so it is either "full power" or "full reheat" that it references most of the time. It does mention expected fuel consumption however (it always states this somewhere), so I guess the % RPM is considered pointless.

 

The only time it talks about other power settings is when it is referring to maintaining a specific airspeed in cruise or descent, but then it is either "adjust power to maintain" or "idle".

 

Given the aircraft and its role, I guess it doesn't need to be more specific than that, anyway.

 

Best regards,

Tango.

Edited September 20, 2014 by Tango

[aaron886]

If it is very clear about it being one or the other, I will tentatively agree

[Tango]

I can only suggest you download it and read it. It's rather informative when you get digging. I think I linked it further up this thread.

 

EDIT: Here it is: http://forums.eagle.ru/showpost.php?p=1470696&postcount=852

 

Best regards,

Tango.

[TurboHog]

Wait a minute. We're making a real mess for the devs to make any sense out of this.

 

Tango, can you share the track in which it took 12 mins 20 sec to reach 7200m?

 

I just did my own climb-out test and I was pretty amazed.

 

It took 3 mins 50 sec to reach 7000m (that's 20 seconds faster!), burning almost excatly the amount of fuel as in the chart. No burner except on take-off. Everything is within what I call 'the reasonable margin of error'

 

See attached file.

 

However, the high-altitude cruising issue remains. I think we should focus on that issue.

SARPP_DATA_2014_08_21_00_14.txt

[Corrigan]

One suggestion is separate Flight performance tests: Results and Flight performance tests: Discussion threads. The former could be just one or a few posts, and we could bounce ideas in the latter.

[Tango]

One suggestion is separate Flight performance tests: Results and Flight performance tests: Discussion threads. The former could be just one or a few posts, and we could bounce ideas in the latter.

 

+1

 

We are compiling some flight test data now.

 

My previous test is bogus - seems something happened to the mission.

 

Best regards,

Tango.

[TurboHog]

We are compiling some flight test data now.

 

After talking things over on TS while performing multiple tests, we came up with some new results that combine climb-out and cruise performance.

 

I have added these results at the end of the first post, including the relevant SARPP tracks.

 

Conclusion:

 

There is something wrong with performance at altitudes above ~6000m. However, we can not really put our finger on it.

Edited September 21, 2014 by TurboHog

[iFoxRomeo]

I managed to get to Mach 2.05 the way it is described in the "real" manual @~11300m. Well I didn´t reach the 10km/530IAS without reheat, only ~8500m.

 

Emergency-Afterburner is only available up to 4000m. At higher altitudes it is switched off automatically.

 

Fox

[Corrigan]

Cool stuff, thanks for your efforts.

 

I also tried a climb test at your atmospheric settings, of a clean aircraft with 100% internal fuel, burning to 600 km/h and then climbing at 870 km/h TAS to 7000 m.

 

It took me about 4:10 (good), I spent 425 L of fuel (good), but I ended up 55 km from where I took off, and not 40 km as in the chart. Did you measure that, travelled distance?

 

EDIT

Wait, I guess I should have flown level until reaching 870 TAS, then started climbing. I kept climbing after TO and got up to 870 TAS more slowly. I'll do it again!

 

I tried again, and that took me even further away. So it seems the fuel consumption and time is spot on, but the distance taken is off by 50%.

 

EDIT 2

What am I missing with that table? How can they possibly get 40 km? If you fly 870 km/h TRUE AIRSPEED for about 4 mins you'll have moved 870*4/60 km = 58 km through the airmass. Since you're only 7 km up at the end, you have basically the same distance across the ground too. I don't understand how they've found 40 km. Is there some definitional matter I'm missing or a term I'm misunderstanding?

Edited September 21, 2014 by Corrigan

[Eldur]

Just throwing in a track of my third flight in which I tried to reach the top, M2 and climbing up keeping that speed. Ended up at ~14000m. Drop tank thrown at ~9000m, climb speed was just a wild guess, no AB until like 10000m. Popped out my air brakes by accident near the end approaching the air field and didn't really get it for a while... Maybe this is of some help investigating the problems found :)

[Tango]

Hi,

 

Here is a climb, clean, to 10000 m. I only made 9000 m.

 

Best regards,

Tango.

MiG-21 Climb Clean 10000 m.trk

MiG-21 Climb Clean 10000 m.txt

[Corrigan]

I think we should try to brainstorm aircraft configurations which would lead to the observed loss of power at altitude.

 

Maybe the nose cone logic isn't working, for example. Could we try checking that it opens properly even when the automatic system is on? Do we have charts regarding what it should do? If so, we could set it manually during the climb.

 

I'm not sure at all that the nose cone could produce the observed loss of thrust, but it's just a first example. What other things would lead to degraded performance while still showing 100% thrust?

[159th_Viper]

Hi,

 

Here is a climb, clean, to 10000 m. I only made 9000 m.

 

Strange. I tried earlier and got to 43000 feet comfortably. Here's a screenie I took on the way up:

 

 

I'll have a look at your track.

[TurboHog]

Strange. I tried earlier and got to 43000 feet comfortably. Here's a screenie I took on the way up:

 

I'll have a look at your track.

 

Check out the first post. It contains all info, including SARPP records.

 

Were you able to cruise at 43000ft without the afterburner without losing speed?

[Corrigan]

Hi,

 

Here is a climb, clean, to 10000 m. I only made 9000 m.

 

Best regards,

Tango.

 

When you move out of reheat, your RPM in that .txt goes down to about "90%" -- is that normal MIL power? Worth double-checking perhaps. We have to be careful to have the throttle as close to reheat as possible. I usually start at reheat and then inch it back until the AB stops.

[TurboHog]

When you move out of reheat, your RPM in that .txt goes down to about "90%" -- is that normal MIL power? Worth double-checking perhaps. We have to be careful to have the throttle as close to reheat as possible. I usually start at reheat and then inch it back until the AB stops.

 

90.5% is the closest to reheat you can get. Anything above 89% is about full throttle.

[Corrigan]

90.5% is the closest to reheat you can get. Anything above 89% is about full throttle.

 

Cool, just wanted to make sure.

Is it worth exploring the difference the last percent makes? Maybe performance is different in an important way between 89.5% and 90.5%. Did you check, by any chance?

[ff4life4]

I have made that mistake earlier. The detent on the X52 isnt actually full power. Full Mil power is a little past the detent.

 

It has made a slight difference in crusing performace.

 

One thing i noticed is that the EGT gauge seemed to act a little funny at the millpower/ab edge, but it could just be me

[Tango]

I think the EGT behavior is the result of the nozzle.

 

Best regards,

Tango.