Various questions about MiG-21bis operating limitations

I have some questions that are all related to the MiG-21bis operating limitations. A few of these have been partially asked on these forums in the past but never received a useful response, at least according to my search. I chose to include those questions here for the sake of completeness.

1) Page 15 of the game manual states:

- The main (internal) fuel tank holds 2850 l or 2225 kg.

- The 490 l drop tank holds 490 l or 382 kg.

- The 800 l drop tank holds 800 l or 625 kg.

As stated below on the same page, this all (roughly) translates to 1,279 l/kg or 0,781 kg/l.

However, the "fuel specific of gravity" is listed as 0,775 g/cm3, i.e. 0,775 kg/l immediately below. Page 9 of the book "Mikoyan-Gurevich MiG-21 Pilot's Flight Operating Instructions" (I have the hardcopy, but there's a link to a .pdf version at http://forums.eagle.ru/showthread.php?t=138880) also lists a fuel specific gravity of 0,775 g/cm3.

Which figure is actually used for in-game calculations? Which OAT is assumed for the 0,781 kg/l and 0,775 kg/l values respectively?

2) According to the mission planner, full internal fuel equates to 2280 kg. The game manual, as stated above, says 2225 kg. Which figure is actually used for in-game calculations?

3) Page 9 of the "Mikoyan-Gurevich MiG-21 Pilot's Flight Operating Instructions" lists a fuel capacity of the inner tanks of 2750 l. The manual, as stated above, has 2850 l. When starting an aircraft with 100% internal fuel from the ramp, the fuel pointer indicates approximately 2950 l regardless of OAT (tested with -50° C and +50° C). Which is the value actually used for in-game calculations? Also, it seems that the effect of OAT on fuel volume is not modelled even though it says so on page 9 of the game manual. Can anyone comment on that?

4) The manual lists a plane empty weight of 5339 kg on page 9. The mission planner has an empty weight of 6255 kg, about 1 ton more. Which value is actually used for in-game calculations?

5) Both the game manual (page 31) and the "Mikoyan-Gurevich MiG-21 Pilot's Flight Operating Instructions" say that the speed limit when carrying 8 bombs OFAB-100 is 800 km/h when BD3-60-21D1 racks are not used, an 1000 km/h when they are used. Does the in-game MiG-21 use these racks?

6) Does the in-game MiG-21 feature model 41 or 42A tyres?

7) Does anyone happen to know the definition of a "second class aerodrome" as mentioned on page 20 of the "Mikoyan-Gurevich MiG-21 Pilot's Flight Operating Instructions"? A runway length (or TORA/TODA) of less than 2000 m seems to be implied, but that is not explicitly stated.

8) Page 31/32 of the game manual states that it is not recommended to build up a g-load in excess of 3 G in flight with certain configurations. These configurations are also mentioned on page 13 of the "Mikoyan-Gurevich MiG-21 Pilot's Flight Operating Instructions". However, immediately below on that page, we are informed that for certain other configurations, g-load instability already commences above 2 G. Contrary to the 3 G case, this is not translated into a warning in the operating limitations. Does anyone have an idea why, and is the 3 G / 2 G load instability even modelled in the game?

I can only add some insight on issue 3. As the rest needs knowledge on the inner workings of the code. The volume of the fuel changes with temperature but when you load the plane with fuel they use a flowmeter on the ground and set the needle accordingly. So you will always know the volume on the ground. With temperature dropping your fule will shrink. Suppose you had a 1000 cc of kerosene at 15 deg C and it weighed 800gm. If the coefficient of thermal expansion is 0.001 per deg C for kerosene. So taking off at 15 degrees you have 2750l (that is the exact data at 15Call the rest is mambo jumbo) and climbing to a -35 environment 2750X0.001X50 that would be at 137,5l shrinking.

Will it affect your range?

No. The range is based on weight not volume. Engines transform energy from a weight unit of fuel not volume unit that is why it is not that important to follow volume that accuratelly.

Furthermore you have additional means of checking fuel level. If you have droptanks and your lights indicate they just went empty you need to check on fuel gauge if it is set correctly (by emtying drop tanks gauge schould be 2750l) and again if your 3th tank group goes empty you have exactly 900-1000l regardless what your gauge shows.

It seems that the game (at least the MiG-21bis module) uses 0.775 kg/l as fuel density. I tested this by setting an internal fuel of exactly 775 kg, which causes the fuel pointer to indicate 1000 l very precisely, and by setting an internal fuel of 1550 kg, which causes the fuel pointer to indicate 2000 l very precisely. The indicator is slightly off the markings when using 781/1562 kg of fuel.

Also, the game really does seem to calculate with a maximum internal fuel of 2280 kg, at least the fuel pointer will indicate approximately 2942 liters (I wrote 2950 above based on guesstimation) with 2280 kg (100%) set as internal fuel.

Most of the questions remain unresolved. Does anyone have any additional input?

Also, another fuel-related issue came up:

The fuel indicator overreads. Even though neither the in-game manual nor the MiG-21 manual explicitly mentions a certain amount of unusable fuel, the aircraft flames out at around 80 liters indicated. Is this realistic? If it is, does the real fuel indicator overread and is there actually zero fuel in the jet when the indicator indicates 80 liters, or is there zero USABLE fuel in the jet in that case? When answering, consider that if you set less than 3% internal fuel (68 kg/88 l) in the mission editor, you will get an instant flame-out when entering the game.

EDIT: By directly adjusting the internal fuel mass in the mission editor, I have determined that the in-game MiG-21 has exactly 62 kg of unusable fuel. With a density of 0.775 kg/l this translates to 80 l as I had determined by guesstimation.

Hello everyone,

Just a short question! Can't you drop individual (one by one) bombs with Mig-21? Just in pairs or all? Now I'm pretty good at destroying any type of ground unit with individual iron (free-fall) bombs and I don't want to waste any of them if there's no need to. Even the MI-8MTV2 can drop a single bomb if needed so. With the A-10C I'm able to hit 12 tanks (all spread out) with 12 MK-82 bombs, so that's one bomb for each tank, so it's not impossible. Now I'm not having a 100% accuracy when I put the pipper (CCIP) on a target and release the bomb, but most of the time it's not so hard to get good accuracy from a little practice then be able to get one shot one kill with a single iron bomb, so I don't know why doesn't the MIG-21 allow to shoot each bomb in single mode. If the real MIG-21 only drops both 1-2 or 3-4 or all pylons at once, that's a waste of bombs if you missed the target anyway:smilewink:...!

Cheers!

yep only pairs of bombs, but you can stagger bombs and rockets like.. rocket bomb - rocket bomb so you get one weapon per switch...

yep only pairs of bombs, but you can stagger bombs and rockets like.. rocket bomb - rocket bomb so you get one weapon per switch...

Thx man! If it works to have a rocket pod and bomb alternatively on the pylon pairs it could do the trick. I really like to use one bomb for each target and not waste them all!

Cheers!

In response to my own question number 7, page 71 of the DCS World manual states that a second class aerodrome has a runway length of 1800 - 2400 meters.

9) Page 31 of the game manual states that at M>0.8, the G limit is 7 at a fuel state of ≤800 liters. Conversely, page 19 of the MiG-21 manual states that the threshold is 850 liters. Which figure is correct?