Level Bombing Chart

I flew again the "smuggling ships" mission and wanted to try straight and level bombing of a ship but I have very bad accuracy and no real experience in this mode. So I brought up an old chart I saved once and tried to use it but missed horribly. So I looked at it again harder and I understand it. I went into editor and made a simple mission with unlimited bombs and tried it over and over. It works!

The table is in German but I can repeat it here.

[TABLE=head]Abwurfhöhe (m)|||Abwurfgeschwindigkeit (km/h)|||Visierwinkel X, der am Visier eingestellt wird||Verzögerungszeit für den Abwurf von Bomben mit T (s)|||

|Hw|Hg||Vw|Vg||||21,10|21,25|21,39

|300|300||800|790||6°30' (113T)||5,3|5,4|5,5

|300|328||900|890||6°30' (113T)||3,6|3,7|3,9

|300|250||1000|990||6°30' (113T)||2,2|2,4|2,6[/TABLE]

I assume "w" and "g" refer to true and indicated or something similar. It makes sense that airspeed reads about 10km/h less than true at 0.3km altitude and showing 50m too low as a result of high airspeed is also roughly consistent with charts. Since DCS module doesn't seem to model these instrument effects I use the true values in practice.

Repeat in English:

[TABLE=head]Bombing height (m)|||Velocity (km/h)|||Sight Angle||Drop delay time (s)|||

|Ht|Hi||Vt|Vi||||21,10|21,25|21,39

|300|300||800|790||6°30' (113T)||5,3|5,4|5,5

|300|328||900|890||6°30' (113T)||3,6|3,7|3,9

|300|250||1000|990||6°30' (113T)||2,2|2,4|2,6[/TABLE]

In practice the sight is set to a high angle of 6.5 degrees and the radio altimeter warning set to 300m (personal invention). The target is overflown level as near as possible to to the given airspeed 800, 900, or 1000 km/h and near level at 300m height. As soon as the central pipper dot passes the target the pilot begins counting "one-one-thousand, two-one-thousand" and so on. When the indicated time is reached the bombs are released.

The times are given for 21,X where 21 means MiG-21 and 10, 25, 39 refer to to 100kg, 250kg, 390kg (fire bomb, not in DCS but use for 500kg) payloads. It is surprising that heavier bombs should be released closer to the target (you would think they have more slick ballistic coefficient). But testing with FAB-100 and 21,10 times agreement was very good.

Probably you will not destroy tanks with this but large buildings are very possible to hit. I think a ship especially along its length would be a practical target. I encourage you to try it yourself and see how it works.

So far I've only been practicing with 100kg bombs at 800kph. Results are promising, but I definitely need to work on my flying skills.

Do you know of any dive bombing charts?

Yeah. I've tried it but it's really hard without the sight allowing a pre-calculated range. With L-39 you can do this and just wait for the pipper to flex to know your slant range.

[TABLE=head]30°|Velocity km/h W (G)|Height m W (G)|Distance m|Angle 10 25 39

Entry|750 (670)| 2600 (2550)

Release|970 (920)|1100 (1050)|1860|6°00', 6°15', 6°30'

Recovery|970 (930)|600 (570)[/TABLE]

[TABLE=head]40°|Velocity km/h W (G)|Height m W (G)|Distance m|Angle 10 25 39

Entry|800 (700)| 3100 (3050)

Release|880 (850)|1300 (1270)|1525|6°00', 6°15', 6°30'

Recovery|900 (875)|600 (570)[/TABLE]

[TABLE=head]40°|Velocity km/h W (G)|Height m W (G)|Distance m|Angle 10 25 39

Entry|900 (770)| 3500 (3450)

Release|950 (900)|1500 (1460)|1520|6°00', 6°15', 6°30'

Recovery|970 (930)|600 (570)[/TABLE]

For the first one I did several runs with FAB-100x2 50% fuel until I got a rhythm. I pressed a 3-count of forward trim from level entry to help with the dive. I entered 2600/670 with a 4G pull through about 70 degrees heading (right) at 90% RPM. At entry the target just graced the top-aft corner of the radio channel placard with my head at a height where I could just barely put the top of the fixed reticle line within the sight. Target was placed about 70 mil on the fixed reticle and followed in to 1100m height for release.

After release was a 5G recovery through level at which point I added dry thrust and climbed at about 20 degrees to go again. Accuracy was 50% of bombs within about 25-30m.

I guess the () speeds are airspeeds indicated. The () heights are I think due to altimeter lag and other effects that don't really happen so I used the true heights. In my practice case the target elevation added ~200m to all values.

Is there a table for other types of bombs? Like the m54 TU or for the RBK family and BL755? These types will be the most useful on level bombing.

I have no such table.

I've discovered that active pause is an excellent resource for trajectory discovery. You can release bombs in active pause and they fly out according to your velocity at time of pause even though you are stationary. By this method all that is required to evaluate trajectories is to set up release conditions and then dispense bombs as needed watching where they go.

For 900 TS, 300m height level release

[Table="head]Weapon|Range|TOF

FAB-100|1788|8.25

FAB-250|1865|8.13

BetAB-500|1909|8.30

BetAB-500ShP|787|11.38

RBK-250 (unarmed)|1885|8.04

RBK-250 (armed)|1831|8.13

FAB-250 M54 TU|534|14.63

FAB-100x4|1771 (first bomb)|8.26

BL-755 (unarmed)|1850|8.00

BL-755 (armed)|1802|8.85

RBK-500 (unarmed)|1866|8.16

RBK-500 (armed)|1839|8.21

FAB-500|1920|8.09[/Table]

This matches well the describe waiting 0.2s for 500kg vs 250kg bombs. At 900km/h 0.2s is 50m. If you compare FAB-500 and FAB-250 ranges they are about 50m different.

It suggests for this release condition to consider BL-755 as FAB-100 and RBK to either be FAB-250 or between FAB-100 and FAB-250. Final position was only done once per bomb so there is no accounting for random dispersion (although in a qualitative test FAB-500 was consistent to <3m). Most bombs impacted with 15-20° angle so each meter of height error equals 2.74m of longitudinal error. A significant ~187ms delay was found between button press and bomb release.

Some more charts. Again, only german.

https://forums.eagle.ru/showpost.php?p=2789917&postcount=4

Excellent, thanks.

Some more charts. Again, only german.

I ran the first one through Google Translate, this is what I came up with:

Column 3 is correct, 4 is (weapon-)launch speed, 5 launch height, 6 launch distance.

Annotation 1 basically says to take target altitude difference to airport into account, due to QFE being used. I cannot do any good translation of that.

Annotation 3: When ending the dive, use at least 4g.

Well, expected QFE in target area should be set before flight. Settings knob is hidden in front avionics bay, but we don't have modeled this.

QFE avionics bay only applies to slant range unit and RSBN letdown. Right now ASP sight only does slant range in narrow conditions which do not include manually set angles. Is this correct? I don't know. I would think that it would be very helpful in the design to use reticle growing as a way to recognize release height.

Anyway we are looking at just the cockpit altimeter which is only based on adjustment knob in the cabin. In any case the note simply reminds the pilot that the table is about heights not altitudes. The pilot should add the correction to his altitudes or set altimeter (or other systems if using slant-range unit) such that target is at 0m datum.

I think you might just use the artificial Horizon to get an idea on what degree from the ground the aircraft is pointing. The radar altimeter in dive-bombing would be quite useless.

QFE avionics bay only applies to slant range unit and RSBN letdown. Right now ASP sight only does slant range in narrow conditions which do not include manually set angles. Is this correct? I don't know. I would think that it would be very helpful in the design to use reticle growing as a way to recognize release height.

QFE setting device called ZDW-30 is integral part of ASP-PFD-21 set, and exist in every variant of MiG-21 equipped with this gunsight, and what interesting in earlier variants this thing was inside cockpit. Honestly I don't know how this working with gunsight because I don't have detailed technical description. From papers I have is clear that ZDW-30 is automaticaly connecting with gunsight ( together with altitude device DW-30 and AGD-1 pitch channel ) when pilot switching to "Ground" mode, whatever what kind of weapon is chosen.

From MiG-21MF cockpit.

Yep in "Ground" mode and "Manual" we should have possibility to set angles from 1,15 deg to 7deg down, and yes, according papers, reticle should start growing after cross max distance value ( setted by pilot ), but only in dive I think. Generally all pilot's manuals not recomending level bombing due low accuracy ( and that's why others aircrafts with this gunsight ( like Su-7, early Su-17 ) had separate aiming device for level bombing ).

RSBN-5 had it's own QFE settings device.

OK, flight manual said warning when using RSBN (6S?) that Air-Ground switch should be in air setting (not ground) for cross country flight. I thought it was related to let down baro setting.

It makes sense that slant range unit kicks in at some dive angle (20°?) to calculate range. Maybe it is for AUTO and B set? I wonder if you must set a calculated span setting so that 22mil = angular size of span at calculated slant range. But "CC" position says that knob only sets reticle ring radius directly. I don't understand the sight in detail.

Yes, I have the same problem like you, without detailed description is really hard understand differences between some gunsight's modes. But I hope soon will able get detailed manual for ASP-PFM-7 which was a variant of ASP-PFD for fighters-bombers, and maybe then everything will light up.

Anyone remember what the max depression in manual mode was on the old ASP? Was it 7°? Then new ASP goes to 11.

11 / 7 = 1.57

Level bombing was 6.5°, now 6.5 * 1.57 = 10.2°

On 11/6/2018 at 11:48 PM, Frischi234 said:

Some more charts. Again, only german.

 

 

https://forums.eagle.ru/showpost.php?p=2789917&postcount=4

 

 

 

 

This is great! Let me guess, you have an original copy lying around...