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[RESOLVED] Cruise performance not realistic


TurboHog

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Sure, but I dare say Novak could add to this discussion. He probably knows if there is such a tendency in DCS, and he obviously knows much more than we about how he's tuned the MiG high-alt performance, if it behaves as he's set it, etc etc.

 

I'm not sure how we can proceed by our selves; we've found that there are problems with the cruising ability and service ceiling, but I don't know how we can investigate further.

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I'm not sure how we can proceed by our selves; we've found that there are problems with the cruising ability and service ceiling, but I don't know how we can investigate further.

 

I, together with other testers, are talking with Novak in the process of getting the bug report resolved. As soon as I know something substantive I'll let you know. In the interim there is nothing further to do - let the matter run it's course.

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Good news! Thanks Viper.

 

Some complementary info from original MIG-21 Bis English manual (pg. 129):

 

"156. The service ceiling for an aircraft carrying two missiles and climbing at

FULL THROTTLE at a true airspeed o! 870 km/h, is 12,000 m (under the standard atmosphere

conditions, at an average weight of the aircraft) and 11,000 m with four missiles.

The service ceiling for an aircraft carrying two missiles and climbing at FULL REHEAT (under the standard temperature conditions) is 17,500 m, the fuel remainder at the ceiling altitude amounting to 700 L.

15?. When flying for the service ceiling with four missiles attached, the aircraft can reach the ceiling only when it carries a drop tank, owing to higher rates of fUel consumption; the tank should be dropped when empty."

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Hello guys,

 

apologies for I did not post anything recently here. We are very busy...

 

Nothing much to say, engine was initially tuned to curves without external stores, in level flight, on altitudes, in restrictive manner, with SAU engaged. It turned out that engine power will be insufficient in gaming environment (more subjective aircraft handling) and with weapons/stores (which are another story but must be taken into account here). This is especially noticeable with altitude, when air density fall significantly (lift properties) and engine power starts suffering (dm drops for same M). It is re-tuned; unfortunately this latest FM won't be in following DCS update (possible today or tomorrow) since the repo was locked several days ago for preparation purposes. "Intermediate" FM that will be available with mentioned update should contain number of small improvements, not noticeable for most of players, but you might notice some.

 

When it comes to high-altitude/high-speed aircraft handling, things are "touchy" - patience is the word. There is no playing superman at high altitude; there is no air there guys, and 21 wings are small. To achieve highest altitudes you need to accelerate in level to at least 1.8M then climb. You will be around M limit as your IAS drops. For cruising at 15+ -17km with externals you need to get to 10km with reasonable amount of fuel first. Otherwise, the game will be short.

 

Best regards.

Power through superb knowledge, training and teamwork.

 

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Hello guys,

 

apologies for I did not post anything recently here. We are very busy...

 

Nothing much to say, engine was initially tuned to curves without external stores, in level flight, on altitudes, in restrictive manner, with SAU engaged. It turned out that engine power will be insufficient in gaming environment (more subjective aircraft handling) and with weapons/stores (which are another story but must be taken into account here). This is especially noticeable with altitude, when air density fall significantly (lift properties) and engine power starts suffering (dm drops for same M). It is re-tuned; unfortunately this latest FM won't be in following DCS update (possible today or tomorrow) since the repo was locked several days ago for preparation purposes. "Intermediate" FM that will be available with mentioned update should contain number of small improvements, not noticeable for most of players, but you might notice some.

 

When it comes to high-altitude/high-speed aircraft handling, things are "touchy" - patience is the word. There is no playing superman at high altitude; there is no air there guys, and 21 wings are small. To achieve highest altitudes you need to accelerate in level to at least 1.8M then climb. You will be around M limit as your IAS drops. For cruising at 15+ -17km with externals you need to get to 10km with reasonable amount of fuel first. Otherwise, the game will be short.

 

Best regards.

 

 

I've noticed the poor engine performance at low altitude as well. The Mig-21bis has suffered a serious nerf in it current configuration. But Im sure thats not political, just like the campaign that accompanied it ... :lol:

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Hi,

 

When it comes to high-altitude/high-speed aircraft handling, things are "touchy" - patience is the word. There is no playing superman at high altitude; there is no air there guys, and 21 wings are small. To achieve highest altitudes you need to accelerate in level to at least 1.8M then climb. You will be around M limit as your IAS drops. For cruising at 15+ -17km with externals you need to get to 10km with reasonable amount of fuel first. Otherwise, the game will be short.

 

Thanks for the explanation. Whilst it is understood that high altitude and small wings are a bad combination, we can't escape the fact the manual states climb profiles, time and distance to altitude, that we can't match (we end up with climb distances over double the stated values).

 

There can be only one of two possibilities:

 

* Either the FM needs tweaking

or

* The manuals are wrong

 

I also checked glide performance from a modest 7000 m, and far from matching 70 km, I managed only 20 km. This strongly suggests a problem with the drag of the FM.

 

Best regards,

Tango.


Edited by Tango
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Except the climb distances in that manual don't make sense.

 

Why not?

 

Example:

 

7000 m, 4 mins 10 sec, 40 km (climbing at 870 kph TAS)

 

Ground speed at sea-level: 870 kph

Ground speed at 7000 m: 870 kph

 

The reason for the same value is because in zero wind conditions at ISA, ground speed = TAS.

 

Average vertical speed: 28 m/s

Average climb angle: 9.92 degrees

 

This should be easily within the capability of an aircraft like the MiG-21.

 

Best regards,

Tango.

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I've tried raising this discussion several times. I don't understand how they've arrived at their values.

 

If you climb at 870 km/h TAS for 4 mins, you will have moved about 60 km through the airmass. According to the chart, you end up at 7 km above the ground, 40 km from where you started. This is not a triangle. The chart, as I understand it, is geometrically impossible.

 

Even as you explain it, if ground speed at sea level is 870 km/h, after 4 mins 10 s you are NOT 40 km out:

 

870 * (4+1/6)/60 km = 60 km


Edited by Corrigan

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I've tried raising this discussion several times. I don't understand how they've arrived at their values.

 

If you climb at 870 km/h TAS for 4 mins, you will have moved about 60 km through the airmass. According to the chart, you end up at 7 km above the ground, 40 km from where you started. This is not a triangle. The chart, as I understand it, is geometrically impossible.

 

Even as you explain it, if ground speed at sea level is 870 km/h, after 4 mins 10 s you are NOT 40 km out:

 

870 * (4+1/6)/60 km = 60 km

 

Oh... I see what you mean...

 

In that case, will the sim climb in 60 km distance?

 

Best regards,

Tango.

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Yes, by geometrical necessity. Me on page 4:

 

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?

 

I have to go now, but maybe you could check the numbers in the glide chart too, see if they're as muddled as this one.

If we can't make sense of those data either I don't think we can draw any conclusions about the glide performance, meaning we still don't know if it's a drag problem or a thrust problem (or both).


Edited by Corrigan

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Ok, but that's a small effect. I'll check when I sit down, walking with my phone atm.

 

EDIT: turns out that is important, thanks.


Edited by Corrigan

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OK, I can't test in the sim until tonight, so maybe someone else could.

 

I did a back-of-the-envelope calculation:

if it takes us 2 min to get to 870 km/h TAS (from a standing start), at ground level, assuming an avg of 400 km/h TAS during those 2 minutes, and then start climbing as normal, the total distance taken is 44 km. So, it seems we can massage the numbers to fit into 40 km, if the 2 mins to take off and get to 870 km/h TAS is reasonable. I suspect it might not be.

 

But, I dunno if the sim can climb as steeply as this requires. Can someone test?


Edited by Corrigan

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Got to forum again to answer one user's question - noticed glide problems debate.

Glide was bad due to wrongly set engine/fuselage drag, especially on idling engine. Fix for this should appear in planned DCS patch. "Glide" on idling engine from very high altitudes is actually a glide with some power, since the idle RPM increase with altitude (you can check this in sim with 21). However, on smaller altitudes - in denser air, finesse is around 6.2 with stopped engine (as stated in the manual, emergency procedure, landing with windmilling/stopped engine) - best finesse is 6-6.5. Have no time to dig that text, but you can easily find it.

 

Again, I hope this fix will be in the patch, although I'm not 100% sure, we will see.

 

Regards.

Power through superb knowledge, training and teamwork.

 

[sIGPIC][/sIGPIC]

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Paragraph (b) might be important here - seems that the time includes the take off as well?

 

attachment.php?attachmentid=104911&stc=1&d=1411485472

 

Yeah, I included that in my sketch calculation, or are you talking about something else?

Got to forum again to answer one user's question - noticed glide problems debate.

Glide was bad due to wrongly set engine/fuselage drag, especially on idling engine. Fix for this should appear in planned DCS patch. "Glide" on idling engine from very high altitudes is actually a glide with some power, since the idle RPM increase with altitude (you can check this in sim with 21). However, on smaller altitudes - in denser air, finesse is around 6.2 with stopped engine (as stated in the manual, emergency procedure, landing with windmilling/stopped engine) - best finesse is 6-6.5. Have no time to dig that text, but you can easily find it.

 

Again, I hope this fix will be in the patch, although I'm not 100% sure, we will see.

 

Regards.

 

Thanks Novak. Are you referring to the scheduled patch/hotfix this week (tomorrow?), or a later bugfix?


Edited by Corrigan

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Are you referring to the scheduled patch/hotfix this week (tomorrow?), or a later bugfix?
I think he means the update that is imminent. They locked the files so some changes will appear in the update after.

 

Interesting comment on distance calc.

 

if it takes us 2 min to get to 870 km/h TAS
870 kph = 470 kts. For the stated condition of clean this should be easily attained within this time period, and comfortably so with some load I would have thought.

 

With boosted afterburner, it has a power to weight ratio close to 1 at takeoff.

 

Best regards,

Tango.

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Yep, easy to attain, but maybe too easy? It's not a matter of can we make it, rather, is it realistic that they allotted this much time to that phase in the chart.

 

My first guess for that time was one minute, but as I say, I can't test it in the sim atm.

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