[RESOLVED] Cruise performance not realistic

[Andrei]

Well, without bringing any numbers into the thread and just subjective feeling I find it hard to believe that MiG-21 is unable to sustain non-AB cruise flight @ 9000m with ground base temperature @ 22* centigrade. Load was above average: 3x drop tanks, no gun ammo. Even after most of the fuel from the external tanks was depleted, aircraft would still slow down to critical AoA with non AB throttle setting.

[Philipp2]

I think EGT cames from cone. It controls the air for the engine depending on speed, height, elevator movement and pressure difference. So when airflow is changing the volume of air is different and then the Temperature will rise or get lower due to rich or leaner "mixture".

[TurboHog]

I think EGT cames from cone. It controls the air for the engine depending on speed, height, elevator movement and pressure difference. So when airflow is changing the volume of air is different and then the Temperature will rise or get lower due to rich or leaner "mixture".

 

Exhaust Gas Temperature.

 

Does your mig-21 fly backward?

 

;)

[Corrigan]

Could we maybe get some developer feedback? Some pointers? I don't mind doing tests myself but if Dolphin maybe could tell us if he has any suspicions we could test more efficiently.

 

I have another suggestion: I think we should make a standardized .miz for testing high-alt. cruising. Maybe starting at 6000 m at 800 km/h TAS or something, with the correct atmospheric conditions and aircraft load etc, since it seems we should focus only on what happens above this altitude anyway. Just so that it's easier to standardize, people who want to do tests can download it. I'll do this when I get home unless someone does it before.

[TurboHog]

Could we maybe get some developer feedback? Some pointers? I don't mind doing tests myself but if Dolphin maybe could tell us if he has any suspicions we could test more efficiently.

 

I have another suggestion: I think we should make a standardized .miz for testing high-alt. cruising. Maybe starting at 6000 m at 800 km/h TAS or something, with the correct atmospheric conditions and aircraft load etc, since it seems we should focus only on what happens above this altitude anyway. Just so that it's easier to standardize, people who want to do tests can download it. I'll do this when I get home unless someone does it before.

 

Me and Tango's tests (All in post # 1) were conducted under ISA conditions (International Standard Atmosphere). We only took loadouts that we could find in the cruise/climb charts.

 

Would like to see feedback from the devs indeed.

[theGozr]

With out FFB I cannot even tell anything .. but at first view it does have an interesting sinking feeling I'm in doubt.

Edited September 21, 2014 by theGozr

[Philipp2]

Post 2

From ex Mig pilot

Without AB:

After takeoff best climb speed is 850-900kmh. You'll get about 60 m/s climb rate. This will decrease.

After reaching tropopause engine power will increase a bit.

When reaching 10000m you'll turn on AB if you want continue climb. This will be with Mach 1.8 .

Then climb to max ceiling alt should be possible.

 

With AB

After AB 2 cutoff continue with about 150m/s. Same acceleration to Mach 1.8.

Max alt for Mig is mostly 58400 feet. But I think this is a dynamic gained altitude.

[Philipp2]

@turbohog

No but EGT depends on airflow and fuel flow. Fuel is a fix component, air is changing continuously.

[Corrigan]

Post 2

From ex Mig pilot

Without AB:

After takeoff best climb speed is 850-900kmh. You'll get about 60 m/s climb rate. This will decrease.

After reaching tropopause engine power will increase a bit.

When reaching 10000m you'll turn on AB if you want continue climb. This will be with Mach 1.8 .

Then climb to max ceiling alt should be possible.

 

With AB

After AB 2 cutoff continue with about 150m/s. Same acceleration to Mach 1.8.

Max alt for Mig is mostly 58400 feet. But I think this is a dynamic gained altitude.

 

 

OK, do you have a source for this? Which version 21 did he fly?

[TurboHog]

Post 2

From ex Mig pilot

Without AB:

After takeoff best climb speed is 850-900kmh. You'll get about 60 m/s climb rate. This will decrease.

After reaching tropopause engine power will increase a bit.

When reaching 10000m you'll turn on AB if you want continue climb. This will be with Mach 1.8 .

Then climb to max ceiling alt should be possible.

 

With AB

After AB 2 cutoff continue with about 150m/s. Same acceleration to Mach 1.8.

Max alt for Mig is mostly 58400 feet. But I think this is a dynamic gained altitude.

 

Could you try to reproduce that in DCS? We may also need a better confirmation of the source.

 

I don't think the FM handles like this.

 

Please set 15 degrees celsius and fly clean configuration to keep test conditions identical. Please post your SARPP record afterwards.

 

@turbohog

No but EGT depends on airflow and fuel flow. Fuel is a fix component, air is changing continuously.

 

I thought that you thought this is where EGT was measured. My bad for misunderstanding.

Edited September 21, 2014 by TurboHog

[159th_Viper]

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?

 

Here's a track:

 

MiG-21 Climb Clean 10000 m.trk

 

I take off from Krasnodar with 86% fuel and zoom-climb to 10 500 feet. Once at altitude I level off, Mil-Power and cruise. All the while I sustain altitude, with IAS of 550km/h, increasing to 580km/h IAS (950km/h TAS), increase in IAS as a result of decreased weight due to fuel consumption.

 

Arrive at Tuapse at altitude 10 500 AGL, IAS 580km/h, said altitude maintained from Gelendzhik via coast.

[TurboHog]

Here's a track:

 

[ATTACH]104823[/ATTACH]

 

I take off from Krasnodar with 86% fuel and zoom-climb to 10 500 feet. Once at altitude I level off, Mil-Power and cruise. All the while I sustain altitude, with IAS of 550km/h, increasing to 580km/h IAS (950km/h TAS), increase in IAS as a result of decreased weight due to fuel consumption.

 

Arrive at Tuapse at altitude 10 500 AGL, IAS 580km/h, said altitude maintained from Gelendzhik via coast.

 

Part of the track may be broken as it stopped right before reaching 10000m.

 

Some remarks:

 

It took you 9.1 minutes while travelling 130km to reach 9000m

It should take 5 minutes and 50 seconds while travelling 65km

 

Your track confirms the other reports of underpower and bad performance at altitude. I have attached your SARPP track to this post.

 

Could it be that you have an updated version of the FM, since you are a tester? Your description of the track did not quite match what I saw during the play back. You can check by comparing your SARPP with the one I have attached. Should be the same.

SARPP_DATA_2014_08_21_21_42.txt

[Philipp2]

It's the Mig 21 MF I guess. So BIS should do it better. There's good German page about Mig 21. I could translate this with some interesting diagrams.

[159th_Viper]

Say what?

 

Your post # 1 specifically states that you cannot maintain cruise speed at 10 000m. I maintained and increased cruise speed at 10 500 metres and yet you state that there is underpower and bad performance?

 

I cannot seem to reconcile your argument, sorry.

 

Ps: Same version you have.

[TurboHog]

Say what?

 

Your post # 1 specifically states that you cannot maintain cruise speed at 10 000m. I maintained and increased cruise speed at 10 500 metres and yet you state that there is underpower and bad performance?

 

I cannot seem to reconcile your argument, sorry.

 

Ps: Same version you have.

 

Please read carefully. Only with 2 x R3R and a 490L in the center. With this loadout 10000m is an allowed cruise altitude.

 

Try cruising clean at, say, 45000ft.

 

And please post your version of the SARPP record. I want to compare it to the one I got from the track.

 

10000m

 

(5) No stores, average weight during measuring phase: 17000lbs --- 200L/7min -> 1714L/hr

(6) 2 x R3R, average weight during measuring phase: 17500lbs --- 200L/6.8min -> 1765L/hr

(7) 2 x R3R, 490L drop tank, average weight during measuring phase: 18500lbs --- Unable to maintain cruise speed w/o afterburner

 

And you do not find it strange that it took you over 9 minutes to reach 9000m?

[159th_Viper]

My apologies - wrong track: I inadvertently posted Tango's track previously downloaded. Here's the correct track:

 

Mig cruise 10 500m.trk

[Tango]

Even if you're able to maintain altitude/speed (MIL power? No reheat?) your climb performance is dire, compared to what it should be doing.

 

Simply put: MiG-21bis is a ROCKET. If you zoom-climb from sea level at 1200 kph she should attain 42000 ft/min rate of climb (213 m/s).

 

Best regards,

Tango.

Edited September 21, 2014 by Tango

[159th_Viper]

Even if you're able to maintain altitude/speed (MIL power? No reheat?) your climb performance is dire, compared to what it should be doing.

 

Simply put: MiG-21bis is a ROCKET.

 

Best regards,

Tango.

 

Lol it was your track - see above post.

 

Please read carefully.

 

I did:

 

 

SARPP_DATA_Climboutclean_10000m+cruise.txt: Climb-out to 10000m......(unable to maintain good cruise speed at 10000m)

 

[TurboHog]

 

 

I did:

 

Cool. I will analyze your track.

 

Is it within a reasonable margin of error from the climb chart? (~6 minute climb)

 

Isn't it stange by the way that the SARPP reports 90% RPM, while we have almost 100% indicated (needle 1) at full power?

[Tango]

Isn't it stange by the way that the SARPP reports 90% RPM, while we have almost 100% indicated (needle 1) at full power?

 

Yes... 10% (at the top end) of any turbine is *significant*. It doesn't explain everything (see my idle glide test - 20 km from 7000 m when it should be 70 km!) but it will affect performance nonetheless.

 

Best regards,

Tango.

[Corrigan]

Isn't it stange by the way that the SARPP reports 90% RPM, while we have almost 100% indicated (needle 1) at full power?

 

When we talked about that earlier I just assumed that the SARPP uses another scale, not "physical" RPM but rather power output normalized to unity. Then again, is it reasonable that reheat adds ~10% power on top of military? I dunno.

[Tango]

Then again, is it reasonable that reheat adds ~10% power on top of military? I dunno.

Reheat can add 50% or more thrust, depending on the situation (it can add drag as well, but that is extremely specific as to when/if that occurs).

 

P25-300 engine:

 

Static thrust (kgf): 4100

Full static reheat (kgf): 6850 (60% increase).

Full reheat, near Mach 1.0, sea level (kgf): 9900

 

Best regards,

Tango.

Edited September 21, 2014 by Tango

[Corrigan]

Well, whatever scale SARPP uses I don't think we can read too much into it.

[159th_Viper]

 

Is it within a reasonable margin of error from the climb chart? (~6 minute climb)

 

The climb commenced at 12:01:35 and I got to 10 000 metres at 12:03:08, so approximately 93 seconds or thereabouts for the zoom-climb. Was more concerned with the Cruise performance at 10 000 metres as alluded to.

[Corrigan]

I think maybe we should talk about this table. First of all, does anyone have an alternate flight manual? I think this is a good time to try to look at a second trustworthy source.

 

Also, doesn't anyone else see a problem with this chart?

 

http://i.imgur.com/WsJ8TBf.jpg

 

Take the 7000 m clean climb as an example. I'll quote myself:

 

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?