[RESOLVED] Cruise performance not realistic

[Corrigan]

And as I mentioned, just after you start the climb, Viper, you're doing 930 TAS. Again, not to be a dick, but I think you would have done much worse if you had stuck to the manual's prescription.

[TurboHog]

 

Interesting that no-one commented on my track yet. See my post here: http://forums.eagle.ru/showpost.php?p=2185785&postcount=42

 

I have added this info to the 1st post, along with my 10000m (2 missiles + tank) cruise test.

[Tango]

Thanks!

 

Best regards,

Tango.

[Corrigan]

So, Viper, can I ask your impression? Do you think there's something wrong with the flight model? Or are you not convinced? Or do you think there's a slight problem but it's being exaggerated?

[159th_Viper]

I cruise at 10000m with two missiles and a center 490L fuel tank. I lose speed and eventually the SAU can't hold it anymore and allows the aircraft to descent. This is not supposed to be like this.

 

Here's my track:

 

Mig cruise 10 500m drop-tank and two missiles.trk

 

Ignore the climb.

 

I cruise at 10 500m AGL with a centre drop-tank and 2 missiles (R3-S) at a speed of 520km IAS. I then drop down to 10 000m AGL and cruise at 520km/h IAS until I get bored 12 minutes into the flight.

 

Noted, there is a 10km/h difference slower than what the manual states. Not sure whether that is enough to establish a bug report. I'll request a second opinion.

[159th_Viper]

So, Viper, can I ask your impression? Do you think there's something wrong with the flight model? Or are you not convinced? Or do you think there's a slight problem but it's being exaggerated?

 

That's what I am trying to ascertain here - I always presume that there is indeed something wrong (why else would someone bother to report it?) even though it does not necessarily accord with my findings, which is why I try to replicate member findings and post my own results. Doing so highlights my failures and possible those of others and helps me better understand exactly what the issue is and how to report it.

 

In this specific instance there is as of yet too many unknowns, test aircraft parameters being but one. I definitely feel as if the service ceiling is way too low at present but then again that's just a feeling. Have not tested specifically - still hung up on the cruise speed at altitude allegation at present :)

[JorgeIII]

Thanks Tango to pointing this out and doing the tests. Keep this going.

 

I found by myself there was something very wrong trying to climb at military power following the data from MIG-21 BIS export version manual (impossible to maintain IAS and a climb rate much over 7000 m).

 

For those asking or confused (and confusing) there is real, specific and clear data available.

 

Its hard to understand how LN took so long and made this incredible flying physics and didn't get this right. Otherwise the Mig-21 has an excellent flying feeling.

 

I hope its no to hard for them (and don't take to long) to bring the module physics close to acceptable values.

[Corrigan]

That's what I am trying to ascertain here - I always presume that there is indeed something wrong (why else would someone bother to report it?) even though it does not necessarily accord with my findings, which is why I try to replicate member findings and post my own results. Doing so highlights my failures and possible those of others and helps me better understand exactly what the issue is and how to report it.

 

In this specific instance there is as of yet too many unknowns, test aircraft parameters being but one. I definitely feel as if the service ceiling is way too low at present but then again that's just a feeling. Have not tested specifically - still hung up on the cruise speed at altitude allegation at present :)

 

Well, like I said before, I think we all appreciate the time.

 

Getting back to your 10500 m cruising track: again, I worry about your fuel load. You're at 800 L even before you drop to 10000 m. The aircraft isn't tactically useful. I worry that it's an unrealistic scenario.

[Corrigan]

Here's a track which I find problematic:

 

I have 60% internal fuel, the small centreline tank and 2 R3Rs. I start at about 10000 m, immediately go into Recovery mode, and use reheat up to about 500 km/s IAS. I then come out of reheat and just wait. After like 3-4 mins I'm down to 410 IAS, 12 deg AoA. Shortly after I start to lose altitude.

 

The track ends about 7 mins after I started with me doing 370 km/h IAS, at 9500 m and falling, still in recovery mode.

 

Clearly, it's not possible to cruise in this configuration at this altitude. The question then is, should it be? I'd that everything I've read indicates yes.

10kcruising.trk

Edited September 21, 2014 by Corrigan

[ff4life4]

I really appreciate all of your testing everyone. I'm sure at some point the aircraft will preform as advertised.

 

I have always felt it was sluggish at altitude for a Mach 2 fighter. Hell, a fully loaded 747 can climb to FL320, and even the Sabre can get to 35k reasonably easily and perform well.

 

I just find it hard to believe that this thing has such a difficult time, especially when loaded. I would have expected this thing could cruise at 40k feet loaded with 4 missiles at military power before I actually flew it.

 

Thanks for the testing.

[Cyb0rg]

Try cruising at 15km altitude, clean. Will it work? You can barely keep your speed with reheat at that altitude.

 

Out of curiosity, seems that 15km is the f-16 service ceiling. Go figure!

[Corrigan]

Out of curiosity, seems that 15km is the f-16 service ceiling. Go figure!

 

Are you saying the MiG shouldn't be able to fly there?

Table 3, p. 12 in this manual has descent data from 18 km.

 

Or am I misunderstanding you? :)

Edited September 22, 2014 by Corrigan

[Corrigan]

Even the DCS manual speaks of "altitudes above 18000 m" on p. 33. So I tried getting there.

 

My setup: clean aircraft, starting with as little fuel I dared (25%), no gun ammo. Default mission editor atmospherics.

 

I used reheat literally all the time, trying to zoom climb. I got to 15 000 m, but here I couldn't get past 450 km/h IAS in full afterburner in even flight, so I had nothing with which to zoom. Now I had only 350 L or so left, so I made a valiant attempt to convert the last of my airspeed and fuel to altitude.

Flying on fumes, I finally stalled at about 16 600 m.

 

Something is clearly very wrong with the service ceiling as well.

 

Track is attached.

 

 

EDIT: I also tried a quick test with the "Simplified engine management" option checked: no difference.

ceiling.trk

Edited September 22, 2014 by Corrigan

[159th_Viper]

Reported.

 

I'll update periodically as necessary with progress on the report.

[Prophet]

Hasn't this always been an issue since LOMAC? I recall the F15C never being able to cruise as high or as fast as it should have.

[159th_Viper]

Hasn't this always been an issue since LOMAC? I recall the F15C never being able to cruise as high or as fast as it should have.

 

Seriously?

 

 

1 - Mig performance cannot possibly be compared to the F-15. It's not even the same Development team......

 

2 - F-15C of LOMAC era is not the same as the current F-15C (SFM vs PFM).......A HUGE difference.

[Justin Case]

I don't think he compared anything to the MiG-21.

[Corrigan]

I think he means that DCS has a systematic mis-modelling of high altitude performance? If that was the case, I can imagine how it would be hard to get low- and high-alt. characteristics simultaneously correct, regardless of aircraft.

[159th_Viper]

I don't think he compared anything to the MiG-21.

 

He compared the current state of affairs, ie Mig under-performance with the apparent same state of affairs as it related to the F-15 of LOMAC era, possibly inferring that a singular cause could be a factor in explaining both airframes' lack of cruise performance.

 

Cannot possibly do so if one has regard to the two factors mentioned, ie different Dev team coding and different Flight Model.

Edited September 22, 2014 by 159th_Viper

[Cyb0rg]

Besides, F-15 had 2 engines and MIG-21 only one... you can not compare both.

[MBot]

He compared the current state of affairs, ie Mig under-performance with the apparent same state of affairs as it related to the F-15 of LOMAC era, possibly inferring that a singular cause could be a factor in explaining both airframes' lack of cruise performance.

 

Cannot possibly do so if one has regard to the two factors mentioned, ie different Dev team coding and different Flight Model.

 

It could also be a global issue by the simulation engine (early Il-2 for example was famous for difficulties with high-altitude performance). Whether it is or not I cannot judge, but that is the question Prophet raised.

[Tango]

There is one commonality between them all (don't forget A-10C has the same problem with high altitude flight): physics integrator of DCS.

 

It also explains a rather intriguing behavior with our very own L-39.

 

Best regards,

Tango.

[SilentEagle]

There is one commonality between them all (don't forget A-10C has the same problem with high altitude flight): physics integrator of DCS.

 

It also explains a rather intriguing behavior with our very own L-39.

 

Best regards,

Tango.

 

While I never examined the high altitude properties of the air within DCS, I have faith that the properties are correct. Any issues our L-39 had at high altitude was most likely due to engine performance or long period longitudinal stability.

[Corrigan]

Honestly, I think the most useful thing right now would be for the MiG devs to chime in. Some inside info would make much of this speculation obsolete and we could concentrate on more constructive things.

[Tango]

@Corrigan: as interesting as that would be, it doesn't explain why 3 AFM aircraft by 3 different developers, written years apart, all have the same basic problem with high altitude flight.

 

The common element is DCS itself.

 

Best regards,

Tango.