HiTech, you may check real MG-FF dispersion here

[straffo]

Originally posted by hitech

Did I miss somthing?


HiTech

The focal used ?
The field of view is perhaps not the one for a 50 mm lens.

[GODO]

Originally posted by moot
Mandoble, you made that test standing still, right?

Flying at 5000 feet and about 350 mph.

[GScholz]

I recant my previous estimate. I'd say it is 200 meters.

[GODO]

Originally posted by hitech
Did I miss somthing?

At 100 yards the P47D40 wingspan covers all the horizontal yellow line (extreme to extreme) of the default gunsight.

in the 109 gunshight image, dispersion is 38x39 pixels, the lenght of the P47 wingspan at 100 yards would be about 300 pixels.

In the HoHun 100 yards image, the P47 wingspan covers 440 pixels and the dispersion yellow circle is 15x13 pixels. Translating that into the 109 gunsight picture, mk108 dispersion would be 10x9 instead of the current 38x39. This is four times the dispersion calculated by HoHun.

What did I miss?

[Pyro]

Mand, I thought your position has always been that there isn't enough dispersion?

In the model, I can set dispersion figures individually for each gun.  As it is, I don't have figures for all guns and have just used a generic figure for each caliber of weapon.  I'd be interested in knowing more about Hohun's figures, I don't recall seeing those before.

[niklas]

About the range:

Did the top MG shoot straight on a 109? then you should be able to know the width  of the inner circles in the target. This will give you a hint about the width of the outer circles where they shot at.
Then you have to know the width of the mounted guns and you probably will be able to calculate  the shooting distance with some simple geometric formulas, counting pixels in the first picture for target and wing guns width

niklas

[Krusty]

I truly and honestly can NOT believe how bad 30mm dispersion is!!

What the heck!??! It disperses at 100d more than most planes span!! It's got a large, round, cone of 10 yards across, and that's NOT taking into account how SLOW the round is, nor how BADLY it drops in flight.. Deflection shots are almost impossible, as it is, and you add this humungous "cone-o-bullets" into the mess and I have to ask.. WHY was the 30mm nerfed like this?


I know for a fact in AH1 you could get hits with it, but in AH1's super-simplistic over-size hit bubble world, it could get away with it. In AH2's hyper-accurate aiming and hitting system, such an overblown random cone is unacceptable. I believe somebody in HTC said that 30mm hasn't changed since AH1.

Well there's your proof. It *hasn't changed*, but all other gunnery aspects have. I think 30mm *needs a change*, because as of now it is a throwback to the older engine, and ONLY worked in the older engine, with huge-arse hit bubbles that spanned 10 yards around every plane. Now we don't have those, but the bullets still fly like we do. The result? 5% of those bullets may hit now, in reality, where about 70%+ may have hit in AH1.

[butch2k]

on a P-38 the M2 100% dispersion pattern was 8 mil (official value).

I agree with Hohun's values on the MG-FF (mine from actual tests being 1.2-1.3) but the the nose mounted MG-151/20 seems a tad too precise. Indeed from tests i have the MG 151 (15mm) was in the 3-3.5 mils for a centerline mounting.
The MG-17 values were around 6-7mils for cowling mounted weapons.

Hohun could you tell where you got those values from ?

[HoHun]

Hi Pyro,

The distance of the range test in the pictures is pretty accurately 100 m. The 109 Lair had a Me 109C-3 sighting data sheet up from which you can tell that the bare crosses are for the reference sighting points while the ringed crosses (OK, that was obvious :-) are the impact points. The Luftwaffe used either 50 m or 100 m test firing distances, and the position of the impacts slightly inboard of the reference points rule out the 50 m distance. In fact, they fit the 100 m distance for the 200 m harmonization suggested by the C-3 manual very well.

The second set of ringed crosses is a bit puzzling because they could only be hit at about 280 m, which seems excessive. As I only have a few pages from the manual and the appendix with the exact target layout is missing, I can't provide an explanation :-(

(The C-3 was a planned variant that was replaced by the E-3 before it entered production. Apparently, the manuals were already printed.)

>In the model, I can set dispersion figures individually for each gun.  As it is, I don't have figures for all guns and have just used a generic figure for each caliber of weapon.  

From what I've read, the difference between the usually very rigid nose/wingroot mounting and the more flexible wing mounting was far more important than the weapon type.

>I'd be interested in knowing more about Hohun's figures, I don't recall seeing those before.

The nose-mount figures are from a German memorandum on anti-bomber guns.

The wing-mount MG151/20 figures are from the Ju 87 harmonization procedure. (Only the D-5 was produced with 20 mm cannon, but the cannon armament also was shipped as Rüstsatz to retrofit exisiting Stukas.)

The wing-mount M2 figures were posted by someone else on some board. Maybe someone else has more details?

The bomber gun figures (B-17 and B-24) were posted by someone as scans from a USAAF bomber training manual respectively a modern compilation of interesting pages from one.

Note the difference in dispersion between the 1.0 mil for a nose-mounted MG FF/M and the roughly 2 - 3 mil for the wing-mounted MG FF/M in the photograph.

I've got to admit that there is a slight ambiguity in the German document about whether the 1.0 mil is dispersion radius or diameter - while the text says radius, the table uses the diameter symbol.

The Ju 87D-5 manual actually is clear in specifiying a 2.5 mil dispersion radius, though the calibration on the ground is considered OK with a 3.5 mil radius.

This fits well with a statement in the Baade report prepared for the Soviets after WW2 that dispersion as observed on the ground was worse than in the air. (I figure a three-point suspension allowed worse oscillations of the airframe structure than a continous suspension by aerodynamic lift did.)

Regards,

Henning (HoHun)

[HoHun]

Hi Butch,

>on a P-38 the M2 100% dispersion pattern was 8 mil (official value).

For which distance? It seems so high that I assume more than 100 m, so we might see the trumpet effect in action here ;-)

>I agree with Hohun's values on the MG-FF (mine from actual tests being 1.2-1.3) but the the nose mounted MG-151/20 seems a tad too precise. Indeed from tests i have the MG 151 (15mm) was in the 3-3.5 mils for a centerline mounting.
The MG-17 values were around 6-7mils for cowling mounted weapons.

Hm, could that be a question of radius vs. diameter?

Regards,

Henning (HoHun)

[butch2k]

Mine are calculated as diameters using the standard 1 mil = 1/1000th of rad and measured at 100m for German data and 228m for the M2. And those are the 100% dispersion cones.

Note that actual dispersion is ALWAYS considered as a CONE (see reasons below), and not an hyperbolic one . This could be seen for instance on USAAF dispersion charts for various vintage fighters.
Indeed it's the 75% dispersion cone (75% of the bullet go through this cone) which is generaly used because it prevents the weird magic bullet effect which could have an adverse effect on the 100% dispersion.

For M2 the 75% dispersion cone is 4 mils and 100% dispersion 8 mils, underlining the extreme dispersions of some bullets.

[GODO]

Originally posted by Pyro
Mand, I thought your position has always been that there isn't enough dispersion?

In the model, I can set dispersion figures individually for each gun.  As it is, I don't have figures for all guns and have just used a generic figure for each caliber of weapon.  I'd be interested in knowing more about Hohun's figures, I don't recall seeing those before.

Just the correct dispersion per weapon and its mounting. Using generic dispersions for each caliber without considering mounting and specific weapon dispersion is like using generic ROF,  muzzle vel or punch power for every weapon depending on caliber. The dispersion inducted by the weapon and the corresponding mounting (not the ballistics of the round) is the primary factor to measure the accuracy at medium and short ranges, where the round is still full of energy and external factors will still have little effect on the round trajectory.

Take a look at the common Spit or Typh real gunsights, just a generic circle oriented to spray enough to score some hits at short range. Now take a look at the 109 revis, carefully marked. 109s cant just press the trigger and hope to score hits with a single gun and small ammo clip, 109s depend much more on gunsight and accuracy of the gun. This is even more evident with 109K series with a single mk108.

Applying a generic high dispersion to multigunned planes may ensure to score some hits even being a poor aimer, but for single gunned planes like 109s with Mk108, the effect is probably the opposite, being unable to score a single hit after spending all the rounds.

IMO, every gun should have its correct dispersion depending also on the mounting placement, this is as important as any other gunnery factor already present.

[HoHun]

Hi Butch,

>Mine are calculated as diameters using the standard 1 mil = 1/1000th of rad and measured at 100m for German data and 228m for the M2. And those are the 100% dispersion cones.

Are they radius or diameter?

The Luftwaffe memo I've got my numbers from is for 100% dispersion, too.

>Note that actual dispersion is ALWAYS considered as a CONE (see reasons below), and not an hyperbolic one .

Hm, what are the reasons?

As far as I know, it's generally accepted that off-centre bullets actually fly a turn because they're a lifting body with an angle of attack that's sustained by the stability due to its spin. That would support the trumpet idea qualitatively, though I have no idea how much it is quantitatively.

>This could be seen for instance on USAAF dispersion charts for various vintage fighters.

I've never seen such a chart :-( I've got one for the Ju 87D-5, though.

>For M2 the 75% dispersion cone is 4 mils and 100% dispersion 8 mils, underlining the extreme dispersions of some bullets.

Thanks, that's about what I'd have suspected from a sort-of-Gauss dispersion!

Regards,

Henning (HoHun)

[Karnak]

Krusty,

15ft is more than most plane's spans?  Wow.  I've been reading some really wacked stats on these aircraft.  All my sources put wingspans over 30ft for nearly every fighter.


Yes, 15ft is too much, way too much, but decending into hyperbole doesn't help.


I did a test last night using the MK108 at 100 yards while sitting on the ground.  It did not look substantially different than MANDOBLE's image.

[Pyro]

Originally posted by GODO
Using generic dispersions for each caliber without considering mounting and specific weapon dispersion is like using generic ROF,  muzzle vel or punch power for every weapon depending on caliber. The dispersion inducted by the weapon and the corresponding mounting (not the ballistics of the round) is the primary factor to measure the accuracy at medium and short ranges, where the round is still full of energy and external factors will still have little effect on the round trajectory.

No, it's not like that at all.  First of all, things like velocity and mv is readily available information.  Dispersion is not.  

Second, you attach way too much importance to it.  It would have to get extremely large before it could anywhere close to the other factors you put it in company with.  

But having said that, I'm all for getting it more accurate.  I don't remember if I have the fuselage guns set differently than wings, but I would prefer to redoing everything on an individual basis all at once.  It would only take me about 15 minutes if I had all the numbers in front of me.  So how about you gather all the numbers and post them for hashing out and then I'll stick them in.  Sound good?

-edited for typo