Mk 82 and Snakeye depression tables

[Manuel_108]

And what altitude would be too low?

[MBot]

The CBU-52 in DCS disperses after 4 seconds of flight. The weapons manual suggest that the CBU-52 can be fuzed for a height of burst between 900 ft and 3000 ft. Though I am not sure if this is AGL or pressure altitude (probably the latter). Can anyone confirm?

[Eddie]

The CBU-52 (and all the SUU-30 based CBUs) can be equipped with the FMU-56 air burst fuse, so yes it does have air burst functionality. The FMU-56 is a Doppler radar based fuse like the FZU-39 used on the SW-65 canister (CBU-87/97) so altitudes are AGL

[Erk104]

I am certain about 2000 Alt figures but at 1500 for 30 degree is a 7g pull out and I haven't got too much experience with 3000 feet yet. But I think the 2000 foot drops are really close.

Edited July 29, 2016 by Erk104

[Erk104]

I am certain about 2000 Alt figures but at 1500 for 30 degree is a 7g pull out and I haven't got too much experience with 3000 feet yet. But I think the 2000 foot drops are really close.

 

forgot to include the table:

[diditopgun]

Mhmm.... Far from the 80mils from Belsimtek manual so....

[MBot]

I am trying to figure out ZSL AoA corrections but I can't get it right. Lets have a look at the following dive:

 

 

KIAS 480

3000 ft MSL

30° dive

5 Mk-82, 17'000 lb

 

 

Now let's try to calculate ZSL AoA correction:

 

 

A: 26 MILS

B: 16 MILS

C: n/a

 

ZSL AoA = A + B - 35 = -3 MILS

 

 

But now let's look at the in game AoA directly. External view status bar says AoA is 0.8°, which equals 14 MILS. This is flight path to fuselage reference line. Since zero sight line is 35 MILS from FRL, ZSL AoA correction = 14 - 35 = -21 MILS

 

Why the big difference? Interestingly with the chart method all my bombs seem to fall long, while adjusting pipper depression by measuring in-game AoA gets a lot better results. Where is my mistake?

[IvanK]

As I see It Chart B gives 19mills, Chart A gives you 26mils. Then since I figure you re in Flaps Auto you need the Flap correction from chart C which gives you around -22 mils so all up (19+26) - 22 = 23mils

 

Like you I find I get far better bombs just using the Depression straight from the Ballistic tables without any AOA correction and then taking in to account the Huge (300-400') Alt lag.

[MBot]

As I see It Chart B gives 19mills, Chart A gives you 26mils.

 

Sorry but I can't see it. Could you give me the dummy approach and draw me the lines?

 

Then since I figure you re in Flaps Auto you need the Flap correction from chart C which gives you around -22 mils so all up (19+26) - 22 = 23mils

 

Since auto flaps at these speeds keeps flaps up (also compare with external view status bar 0% flaps and visually confirming flaps are in), should we not omit C?

 

Cheers for helping me figuring this out!

Edited July 30, 2016 by MBot

[IvanK]

I can live with 16mils from Chart B :) WRT AOA due Flap I guess if you are in AUTO and they are up then agree dont correct for AOA for flap influence.

I presume these charts where made for Non Auto aeroplanes with Flap in Manvr position ?

 

Any way as I said I get more consistent bombs calculating for the release altitude/TAS using straight ballistic table depression values then ignoring any AOA. Also then drop +300 to +400' on the Altimeter based on your planned relase height.

 

For 20 Deg passes I use +300ft worth of Altimeter lag. for 45 deg pass I use 400ft worth of Altimeter lag.

[MBot]

Actually my experience so far is that AOA correction with game data makes things even better. Usual attack configurations seem to yield an AOA of more or less 0.8°, which is 14 MILS from FRL or -21 MILS from ZSL. So as a rule of thumb taking the MILS from the ballistic tables and subtracting 20 MILS gets pretty good results (in the rare occasions that I hit all other parameters).

 

 

To get back to the AOA table from the weapons manual again, can someone explain to me why there is a correction for configuration (B)? What influence do external stores have on AOA? I get that they cause drag, which is countered by thrust. But shouldn't AOA in level flight simply be a function of weight an IAS? And stores weight is already being accounted in gross weight for under A.

[diditopgun]

I am trying to figure out ZSL AoA corrections but I can't get it right. Lets have a look at the following dive:

 

KIAS 480

3000 ft MSL

30° dive

5 Mk-82, 17'000 lb

 

 

Now let's try to calculate ZSL AoA correction:

 

A: 26 MILS

B: 16 MILS

C: n/a

 

ZSL AoA = A + B - 35 = -3 MILS

 

 

But now let's look at the in game AoA directly. External view status bar says AoA is 0.8°, which equals 14 MILS. This is flight path to fuselage reference line. Since zero sight line is 35 MILS from FRL, ZSL AoA correction = 14 - 35 = -21 MILS

 

Why the big difference? Interestingly with the chart method all my bombs seem to fall long, while adjusting pipper depression by measuring in-game AoA gets a lot better results. Where is my mistake?

 

The only mistake I see is: ZSL AoA= (26 + 16)* - 35** = 7 MILS (and not -3 MILS), so ZSL AoA=0.4° and FRL AoA=2.36°

 

* 42 MILS = 2.36° FRL AoA

** 35 MILS = 1.96°

 

In game FRL AoA= 0.8° = 14.22 MILS

In game ZSL AoA= 14.22 - 35 = -20.78 MILS

 

Delta FRL AoA = 2.36 - 0.8 = 1.56° = 27.7 MILS

Delta ZSL AoA = 20.78 + 7 = 27.7 MILS

 

So in this case the manual's bomb table for 5x Mk82 ripple release 140ms 30° 3000ft 500KTAS gives 97.5 MILS

With ZSL AoA correction: 97.5 + 7 = 104.5 MILS

But with in game Delta it give: 104.5 - 27.7 = 76.8 MILS

 

So those little Delta AoA (is it proportional ? That's the question, but I presume not, just to make things more complicated lol) send our sweet Mk-82 far away....:joystick:

 

An interesting FM tweak to do for Belsimtek to reach perfection ! :D

Edited July 31, 2016 by diditopgun

[IvanK]

Actually my experience so far is that AOA correction with game data makes things even better. Usual attack configurations seem to yield an AOA of more or less 0.8°, which is 14 MILS from FRL or -21 MILS from ZSL. So as a rule of thumb taking the MILS from the ballistic tables and subtracting 20 MILS gets pretty good results (in the rare occasions that I hit all other parameters).

 

 

To get back to the AOA table from the weapons manual again, can someone explain to me why there is a correction for configuration (B)? What influence do external stores have on AOA? I get that they cause drag, which is countered by thrust. But shouldn't AOA in level flight simply be a function of weight an IAS? And stores weight is already being accounted in gross weight for under A.

 

I think its C of G influence

[MBot]

The only mistake I see is: ZSL AoA= (26 + 16)* - 35** = 7 MILS (and not -3 MILS)

 

Doh, good catch :) So that makes the discrepancy even worse.

[IvanK]

I guess its an Assumption that the displayed Status bar is FRL AOA ?

[IvanK]

My head is hurting ! .... Re reading the Weapons manual and looking once again at the reference lines etc maybe we are doing something wrong.

 

If you read the text of the manual (highlighted in Red in the graphic) they say you use the Air To Ground AOA chart you THEN subtract 35mils from that value this result is then added to the Ballistic table mill to become the Sight depression.

 

 

So according to the above procedure (and just using the output of the AOA chart directly) I have been 35mills out.

[IvanK]

Ok now getting consistent bombs 50-100ft from the target. 20 Deg LD pass releasing at 2800' ind (using 300ft Alt lag that we know the sim is presently exhibiting). So same Calc as shown earlier in the post but correcting for -35mils and not applying any correction for flap gives a Sight Dep of 98mills.

 

Param:

Roll in 7300' From Measured Base Dist out to achieve 20 deg Dive angle,400Kias

ISP 3Rads Low

Rel 500Kias 2800' Pipper On (assumes 300' alt Lag)

 

Noodle:

In prev life all our AOA figures were simpler (non US type) since our ZSL and FRL were the same. Sample worksheet in F5E manual is a bit confusing as I would have thought there would have been a step to take the 35mils off.

[MBot]

Edit to add: Counterintuitively, any time aircraft AoA is less than 2 degrees, you're actually SUBTRACTING mils from SDFP to arrive at TSS.

 

Yes, since most of the time your flight path is above the ZSL, removing something from the chart mils number is the norm.

 

Doing a little measuring and calculating, I came up with the following:

 

3.5 units AOA (cockpit instrument) equals 0° AOA. Delta 1 unit AOA is delta 0.85 degree AOA.

 

This results in the following broad rules of thumb:

* At 6 units AOA, ZSL AOA correction is 0 MILS. For every delta 1 unit AOA, apply 15 MILS AOA correction.

* 6 units is a high AOA situation (very heavy aircraft and low speed or high altitude (Nevada)). Apply no ZSL AOA correction.

* 5 units is a medium AOA situation (a reasonable bombload, some fuel spent). Apply -15 MILS AOA correction. This is the most common situation.

* 4 units is a low AOA situation (last bomb, lots of fuel spent). Apply -30 MILS AOA correction.

 

This might not be terribly sctientific, but I get some good results so far.

[autogyro]

Are you guys adjusting the attitude pitch zeroing on the ground for these bombing run tests?

 

I.e. zero at nose hiked position such that the attitude indicator shows 0 degrees pitch at cruise?

[IvanK]

I am using 3 Deg Nose down on the AI but more importantly fly a measured track on the ground to ensure correct Base distance out to achieve the required Dive angle (allowing for turn radius at 3G). I do the numbers then place easily identified objects along the Base leg path.

 

INITIAL PIPPER PLACEMENT (IPP)

Playing around with use of DM mode during the roll in. This places the Pipper very close to the flight path. Have all your switches and depression with Sight Selector in manual set up before the roll in, select DM (HOTAS) Place the pipper just past the target (idea is to place the pipper on the Aim Off Point) then deselect DM mode (HOTAS). Sight reverts to MAN mode and pipper drops to set depression ... normal sight handling from there on .... works for me.

 

EDIT: Sight Cage switch on effect does the same thing and is perhaps a better way to go. Cage the sight in the roll in uncage on roll out.

Edited August 1, 2016 by IvanK

[diditopgun]

IvanK you forgot the -35 mils since the begining ? I thought you did it... :laugh:

 

Yes, since most of the time your flight path is above the ZSL, removing something from the chart mils number is the norm.

 

Doing a little measuring and calculating, I came up with the following:

 

3.5 units AOA (cockpit instrument) equals 0° AOA. Delta 1 unit AOA is delta 0.85 degree AOA.

 

This results in the following broad rules of thumb:

* At 6 units AOA, ZSL AOA correction is 0 MILS. For every delta 1 unit AOA, apply 15 MILS AOA correction.

* 6 units is a high AOA situation (very heavy aircraft and low speed or high altitude (Nevada)). Apply no ZSL AOA correction.

* 5 units is a medium AOA situation (a reasonable bombload, some fuel spent). Apply -15 MILS AOA correction. This is the most common situation.

* 4 units is a low AOA situation (last bomb, lots of fuel spent). Apply -30 MILS AOA correction.

 

This might not be terribly sctientific, but I get some good results so far.

 

So it confirm that the 21 mils we found before is correct and not 7 mils as per manual.

So it confirm the problem.

[IvanK]

The single biggest error imo is caused by Altimeter lag. In the Belsimtek F5E it is around 3 x that of the aircraft. Using Book figures from the weapons manual and adding 300' of Alt lag works for 10Deg High Drag passes, 20 degree Low Drag passes. For 45 deg Low Drag passes using 400' Alt lag works.

[MBot]

Over the past days I tried to put together a sheet for the kneeboard with a set of useful weapon delivery parameters:

 

 

Put into: USER\Saved Games\DCS\Kneeboard\F-5E-3

 

 

These are all the real numbers from the weapons delivery manual. I haven't flown every profile yet, but the ones I tried worked reasonably well.

 

The CBU-52 entry is more or less a placeholder. Those aren't particularly useful flight parameters, but it is the only combination in the weapons manual with a fuze function time of 4 seconds, which matches the hardcoded flight time of the bomb in DCS.

 

I will also try to look into some good rockets profiles.

 

This is just a draft, comments and suggestions for improvement are very welcome.

[IvanK]

Looks pretty neat.

 

? note 1 are you are saying you need to -35mills correction to the displayed value ? So in the case of the MK82 45 deg pass 7000ft release at 500KIAS your chart value is 108mils ... is this sight setting or requires further correction ... like taking 35mills off to give a setting of 73mills.

 

I recrunched all my 3 standard pass numbers. For the same 45 deg pass My Sight setting is 101mills but releasing at 7400ft as there is around 400ft alt lag at the moment.

[MBot]

? note 1 are you are saying you need to -35mills correction to the displayed value ? So in the case of the MK82 45 deg pass 7000ft release at 500KIAS your chart value is 108mils ... is this sight setting or requires further correction ... like taking 35mills off to give a setting of 73mills.

 

A correction is needed, but not necessary -35. Theoretically you would have to take "A" from the AOA chart, add "B" ("C" is ignored because flaps are retracted in auto mode), subtract 35 and add the whole thing to the MILS from the weapons chart. Since the correction you come up to is most likely a negative value, you usually end up subtracting something. But I think this method is not to be trusted in DCS because I think something with the AOAs is off. Calculated AOA do not match with AOA read directly in the game.

 

What I do as a rule of thumb is subtract 30 MILS if I feel I am very light (4 units AOA on the cockpit instrument at the moment of release), subtract 15 MILS for most normal conditions (5 units AOA) and subtract nothing if I feel I am fairly heavy and high (6 units AOA).

 

For the 45°/7000ft/5000KIAS pass with 5 Mk-82 on 5 pylons, 2/3 fuel left and the target at sea level, I would therefore take the 108 MILS from the chart, subtract a rule of thumb correction of 15 and punch in 93 MILS into the sight.

 

I am not too happy with that approach, as the corrections are fairly significant, but it works so far considering my bombing is not super accurate anyway. If anyone has a better approach I am all ears.

 

I recrunched all my 3 standard pass numbers. For the same 45 deg pass My Sight setting is 101mills but releasing at 7400ft as there is around 400ft alt lag at the moment.

 

I too apply a lag correction of a couple of hundred feet, depending on dive angle, to all release and abort altitude in my table. The 108 MILS are directly from the weapons manual, again without an AOA correction yet: