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Flight Performance


Tango
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Hi,

 

How are people finding the flight performance? Generally it is flying very well, but I have a query over the level flight performance.

 

With two missiles mounted, and wing tanks jettisoned at 10000 meters altitude, the aircraft won't maintain airspeed at 100% power. The speed slowly bleeds off, increasing AoA, which increases drag... so it isn't possible to cruise at 10000 meters, despite manual references making it appear that it should. Initial speed was 650 kph IAS.

 

Generally with an external load, it seems the aircraft seems to require more power than expected just to maintain speed in level flight.

 

Best regards,

Tango.

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Please attach the mentioned manual reference.

 

It's the 130mb manual that was on Beczl's site. Don't you have it in your posession already? Because the limitation section in the DCS flight manual is nearly identical to the one found in this pilot's manual. I can upload it to dropbox tomorrow.

 

For details about my experiment, follow the link I posted.

'Frett'

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Thank you.

 

Aircraft weight matters a lot.

 

I just performed 30 minutes (accelerated time) flight at 10.000m with 2xR-3S and all internal fuel (which would not be the case in reality). Hanged there until I used all O2, and things started to be blurry (bug).

During this, I spent about 1100-1200 lit (3-4 afterburners, including one for full semi-turn because I got near the map edge). Im pretty sure I could have stayed there for another 30 minutes if it was not for the O2.

 

I agree that the engine power at MAX could be greater by 1-3% at this altitude. I will perform bit more tests.

 

Thank you for commenting and analyzing this.

 

acmi - flight, image - end

end_.thumb.jpg.e2491338036b7f2f03ea16f682f3b152.jpg

Tacview-20140920-013515.txt.rar

Power through superb knowledge, training and teamwork.

 

[sIGPIC][/sIGPIC]

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Interesting result.

 

I will try the same situation tomorrow and compare it to my test.

 

So I think that with the two missiles in your experiment you were just able to cruise without afterburner. Flying with a loadout that causes a little more drag and/or is slightly heavier, you will be forced to use the afterburner in order to maintain the maximum range/endurance speed, thereby causing the large discrepancy between the chart and DCS (because the chart does not assume the use of afterburner during cruise).

 

So maybe the inaccuracy of the flight model is not as large as I think it is, merely because of the sharp transition (in terms of fuel flow) between normal throttle and afterburner range. You just need to make sure that with a loadout that [as per the recommendations in the manual] allows cruising at a certain altitude, you do not need the afterburner to achieve a good cruise speed (like max range/endurance cruise speed)

 

I have no idea how the FM works, but I would say that either:

 

  • Thrust is too low at a given throttle setting
    or
  • There is too much drag (entire airframe or due to certain attachments)

 

Because you should be able to cruise at, let say, 40000 feet with two missiles and one 490L drop tank. Or am I overestimating the Mig-21's performance? At the moment, you will be forced to use the afterburner to prevent a stall if you are trying to cruise at 40000ft with said loadout.


Edited by TurboHog

'Frett'

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It's the 130mb manual that was on Beczl's site. Don't you have it in your posession already? Because the limitation section in the DCS flight manual is nearly identical to the one found in this pilot's manual. I can upload it to dropbox tomorrow.

 

Thanks in advance... I tried to get a ~113MB manual off a MEGA.co.nz site, but it won't let me get the file. This site is crap.

 

I also have the impression that drag for ordnance might be too much. With sone UB-16 pods the crate is a very lot slower. Might not be the best comparison, but if I pack a Su-25 full with UB-32 or B-20 pods, I hardly feel any difference to a clean setup, whereas more heavier and not streamlines things like bigger missiles or the Vikhr Racks drag a lot. But the MiG-21 with rocket pods feels like the Frog with Vikhrs...

dcsdashie-hb-ed.jpg

 

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@TurboHog: Exactly my thoughts!! Nice to know I'm not the only one thinking this. :)

 

Thank you also to Dolphin887. :thumbup:

 

I just tried it yet again, 2000 L internal fuel + two missiles on inboard pylons, and I couldn't maintain even 25000 ft at MIL at max range cruise.

 

It's late here - I'll test again tomorrow with a clean jet to see what happens.

 

Anyone know the nominal power setting in clean config for max range cruise? I'm not sure if the manual states a setting.

 

Best regards,

Tango.


Edited by Tango
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Thank you for your thoughts.

 

Please bear in mind that you have beta FM, mine and your result may differ a bit. Nevertheless, the difference is not significant.

 

Note that when it comes to e.g. fuel consumption, the manual you are using states that these tables are for orientation only (few pages before the page with the table in your post). Fuel consumption is modeled according to more precise tables.

 

Your inputs are very valuable, thank you.

Power through superb knowledge, training and teamwork.

 

[sIGPIC][/sIGPIC]

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So apart from the fuel consumption differences, the current FM implies that the maximum economic cruise altitude is 10000m. Because above that altitude, any throttle setting with the exception of afterburner will make you lose speed and will let you stall eventually. Or are you supposed to cruise with the afb turned on above 10km altitude, thereby consuming all your fuel in less than an hour?

'Frett'

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@Dolphin887: It's not the fuel consumption that is the problem - it's the fact that at anything less than reheat, the aircraft will eventually stall if flying in level flight at altitudes > 5000 m.

 

It is currently not possible to match the high altitude max range cruise configuration without stalling.

 

It appears that there is either too little thrust, or too much drag.

 

I'm going to try and get more precise data.

 

Best regards,

Tango.

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See post below.

 

 

Things like this are really important IMO, I think we should try to eliminate these discrepancies.

 

I seem to be able to cruise at 10 000 m indicated, with the small centreline tank and a R3R under each wing, over the sea in the default mission editor settings for weather etc.

 

Currently at full military, 6 deg AoA, 550 km/h IAS and accelerating, in Recovery mode autopilot.

 

I started the mission at altitude, with 50% internal fuel, at 33000 ft MSL and 400 kts (note units), been flying for maybe 5-10 mins.

 


Edited by Corrigan

Win10 x64 | SSDs | i5 2500K @ 4.4 GHz | 16 GB RAM | GTX 970 | TM Warthog HOTAS | Saitek pedals | TIR5

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EDIT: never mind, using different weights. I agree that there clearly is a problem with the thrust/drag at high alts.

 

 

I did a second test, now with 70% internal fuel, otherwise same as above. I enter Recovery mode at the start of the flight, and over 10 mins or so the AoA creeps up, IAS drops and I lose about 2000 m altitude before either the loss of weight from fuel or the thicker air allow me to lower the AoA and pick up speed again.

 

 

Also, at 6000 m I can certainly cruise with this loadout and full military power; currently zipping along at a few degrees alpha and accelerating through 900 km/h.

 


Edited by Corrigan

Win10 x64 | SSDs | i5 2500K @ 4.4 GHz | 16 GB RAM | GTX 970 | TM Warthog HOTAS | Saitek pedals | TIR5

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Thank you for your thoughts.

 

Please bear in mind that you have beta FM, mine and your result may differ a bit. Nevertheless, the difference is not significant.

 

Note that when it comes to e.g. fuel consumption, the manual you are using states that these tables are for orientation only (few pages before the page with the table in your post). Fuel consumption is modeled according to more precise tables.

 

Your inputs are very valuable, thank you.

 

Hello Dolphin887, here is the russian technical description with some graphics explicit for the MiG-21bis. Maybe you need it (if you dont have it already).

 

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