Kurfürst
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Some additional gun dispersion data, via Olivier Lefebrve / AAW:
Here are the results of a lenghty research into dispersion data, which is quite hard to come by...
The data is based on 100% diameter dispersion with 1 mil = 1/1000th of rad, the kind of mount is precised next to the weapon. 75% dispersion diameter is supposed to be half the 100% diameter which seems quite true for most weapons, this value is provided when quoted in the source (M2 data for instance).
We can clearly see the impact of the wing mounting compared to engine mounting, the later seems to have absorbed recoil and vibration much better... indeed dispersion is at least 2 times greater with wing mounted weapons.
Engine mount are the most efficient but nose mounting or cowling mounting does not provide the same amount of precision the mount being much more prone to vibration it seems.
Note that US data on the M2 is confusing since the reference data comes from a P-38 nose mounted M2, but the US manuals use the same dispersion data for wing mounted weapons. Either the P-38 mounts are really up to no good or the manuals make a wrong assumption when it comes to wing dispersion. I tend to believe the later, i think the wing mounted M2 would have had a dispersion of at least 12mils and probably more.
If you quote this data on other sites/bbs please precise the source being AAW. TIA
H means Height (or max dispersion diameter) as i previously used vertical and lateral dispersion values.
D means distance.
Units are metric.
German Weapons
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MG-17 Cowling mounted (Bf 109F-2 / Bf 109F-1 actual tests)
H = 0.60 / 0.8 m
D = 100 m
R/D = 60/10000 80/10000
= 6 mils / 8 mils
MG-131 Cowling mounted (Fw 190A - theorical max)
H = 1m
D = 100m
H/D = 100/10000
= 10 mils
MG-151/15 Engine mounted (Bf 109F-2 actual test)
H = 0,35 m
D = 100 m
H/D = 35/10000
= 3.5 mils
MG-FF Engine mounted (Bf 109F-1 actual test)
H = 0,2 m
D = 100m
H/D = 20/10000
= 2 mils (very tight patern)
MG-FF Wing mounted (Bf 109E-3 actual test)
H = 0,35 m
D = 100m
H/D = 35/10000
= 3.5 mils
MG 151/20 Engine mounted (Bf 109G-6 - theorical max)
H = 0.3m
D = 100m
H/D = 30/10000
= 3 mils
MG 151/20 Wing mounted - inner (Fw 190A - theorical max)
H = 0.7m
D = 100m
H/D = 70/10000
= 7 mils
MG 151/20 Wing mounted - outer (Fw 190A - theorical max)
H = 0.8m
D = 100m
H/D = 80/10000
= 8 mils
MK 108 Engine mounted (Ta 152 - therorical max)
H = 0.35
D = 100m
H/D = 35/10000
= 3.5 mils
Allied Weapons
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M2 Nose mounted P-38 (USAAF 1944 Gunnery manual)
H = 1.88 m
D = 229 m
H/D = 188/22900
= 8.2 mils (75% = 4.1 mils)
Hispano 20mm Nose mounted P-38 (USAAF 1944 Gunnery manual)
3 mils 75%
6 mils 100% assumed
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Also one of the rare occasions I actually agree with Holz.
this might prove interesting.
http://forums.eagle.ru/attachment.php?attachmentid=107361&stc=1&d=1415955237
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That's only 3.5 mils at 100 meters for the Mk108... which, incidentally, probably opens up to well beyond 5 mils at 1000 meters, given that they would go transonic well before then.
The MG151/20 wing mount is a whopping 10 mils at a mere 100 meters, if your data is correct.
Huh, guess that means my comment about the GAU-8 being more accuratate was... oh, man, what's the word... the antonym of "wrong"...? Gee, it's at the tip of my tongue!
Gauss. You are looking for Gauss.
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The GAU 8 may be well one of the most accurate large caliber Gatling guns, and as close to perfect for the job it was meant to do, but its pointless to compare it to the others, be it small caliber, single shot bolt action rifles or 120mm APFSDS tank guns. You build a Gatling for Rate of Fire, not for accuracy.
In any case, the GAU 8 has nothing to do with the K-4.
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Yes, provided that the said accuracy would change much with maximal distances up to and around 1000 m.. or that flight simulations would bother with calculations for each round, based on complex ballistic tables detailing data for 100 meter intervals, including corrections for humidity, temperature etc. :doh:
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At what ranges did the MK 108 achieve a theoretical 1.5 mil, and under what conditions?
http://en.wikipedia.org/wiki/Angular_mil#Metric_Mil-dot_formula
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The GAU 8 is not really comparable to the MK 108, as its a radically different setup (multiple barrels, extremely powerful round and obscene rate of fire) which greatly contributes to that its accuracy (dispersion) is much worse at 5+ mils, as given by the report. Of course the GAU just literally obliterates any target with the sheer amount of rounds fired - it very much works like a huge shotgun firing #000 DU shots.
The MK 108 is, in contrast, a rather accurate weapons system (with dispersion ca. 1,5 mils IIRC) that fires fewer shells with much lower muzzle velocity and is meant for air targets. I suppose there is not much of a point firing its HE and Incendiary rounds at anything else than similarly flimsily built unarmored ground targets, though hitting a truck, an open topped half-track or gun position with the equivalent of 10 hand grenades per second sounds effective.
For everything else, there is MasterCard and/or the MK 103, a very different beast meant for the K-10 variant, despite the comparable ballistics performance GAU 8, with a dispersion of 2 mils but only about 1/10th of the rate of fire.
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Remember that your targets move with speed as well...so that factor goes out of the window :P
Relative to the target, yes, but ballistics of the shell - no. A shell fired at 500 m/sec from a plane travelling at 200 m/sec will have a velocity of 700 m/sec, or so.
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Ballistics table for MK 108 Minengeschoss, Type A. I believe there were other developments for the same ammo, with more pointed noses than the blunt nosed Ausf. A, which retained muzzle velocity much better, however I am not sure if these were developments only or were used in regular service as well.
Note that velocity will also effected by air density (altitude!) and aircraft speed (100-200 m/s is added to the speed of the projectile) as well.
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Well, not exactly.
1st - Imagine you are shooting an actual M2 .50 on the ground, trying to hit something at some hundreds of meters;
2nd - Have a light barrel on that HMG which will decrease your accuracy but lighten the recoil (I think?);
3rd - Get you and the gun in movement;
4th - Get your target also moving;
5th - Add thick glass just infront you;
6th - Add the turbulence factor;
7th - Add a general slight shaking everywhere (engines, uneven air, etc.);
8th - Remember you are instructed to only shoot small bursts of 10-15 rounds per gun and have a certain cooldown time (it's stated in various manuals of the time, I'll try to find them);
9th - Even if one bullet hits, it's possible it wouldn't do that much damage, they are just HMG bullets after all, not cannons;
10th - Maybe more stuff I missed?
If it was that easy, they wouldn't really need escorts. :thumbup:
11th - if you manage shred that 109/190 despite all this, it won't bring back flashy gun camera footage back to base to be shown weekly on Hitler Channel... the dead tell no tales, same thing with victory reports, only those guys make those who suceeded and survived to tell about it.
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This video get posted on every discussion about the 108, but it does show the destructive power quite well.
Wouldn't want to be the tailgunner.
Posted this before, but here's a Spitfire shot down with Mk 108:
Quite a recoil!
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in a Rockwell commander flown by Bob Hoover yes.
So whats the difference between a Rockwell Commander and a Heinkel 111?
Because curiously, the two can have rather similar wingloading and powerloading. That and of course the RC is quite a bit slower.
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Which one is what? present me with a contradiction.
You say that a virtual pilot shouldn't be able to do something a real life pilot won't be willing to do. But there is no logical or physical connection between the two whatsoever.
Ok, lets try to use a picture then to illustrate it...
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what I am actually saying is that if the sim in question is making a low level full aerobatic routine in a medium bomber so easy that an internet pilot can do it any time they like yet real world test pilots wouldn't attempt it because the odds are almost certain death then the FM is wrong.I'm not aware of any manouvers that work on an 8 out of 10 basis, they either work or they don't, the success of which is determined by the execution, no pilot should attempt it unless confident of complete success.
So which one is it?
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Maybe in your world it means that, but what I am actually saying is that if the sim in question is making a low level full aerobatic routine in a medium bomber so easy that an internet pilot can do it any time they like yet real world test pilots wouldn't attempt it because the odds are almost certain death then the FM is wrong.
Low probability of success and the lack of any chance of success are not the same things. And how many real world pilots would like to risk a manouver that works perfectly well, say 8 out of 10 times..?
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Well if you can have both... ;)
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Thanks for the quick aero lesson BitMaster! :)
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Thanks YoYo!
Out of curiousity, what defines max roll rate? I understand what assists it, but what gives the limit, i.e. what stops the airplane from rolling even faster when it reaches to max rolling angular speed? Air resistance of wings themselves that is from the wings moving perpendicular to the rolling plane, or some lift equilibrium (since roll is from changed lift, negative and positive of the two wings from aileron displacement as I understan) I cannot seem to figure out...
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If Bob Hoover made it in his plane it is not mean that he would be able to do in He111 right after take off.
He-111 has different size, weight and P/W ratio.
Cant imagine how such plane like He-111 could do near straight roll after take off or loop at such low speeds.
Ah, the He 111 issue. The roll may be off, but lacking data, I can't tell.
Size however nothing to do with it, except inertial moments and structural load limits. Apart from that, its all relative to the other numbers.
But aside from these, I think what many people miss in those hotly discusses BOS videos is how ridiculusly low the He 111 wing loading can get, especially with lighter load. Go check it out. One would need to crunch numbers, of course, but such low wingloading should assist looping ability. Its not all about power loading - yes, power loading can be used to overcome aerodynamic limits, and even a brick will fly with enough thrust. A low wing loading plane will however require less thrust to manouvre, including in loops, at lower speeds. If you can build up enough speed, I don't see problem. And by decreasing weight - this varies a lot more on a bomber than on a fighter - even thrust-to-weight ratio isn't all that poor either.
IRL use of course pointless to the extent of being dangerous, but theoretically, doing loops in a 111 does not seem to be impossible.
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Fantastic video DB605, thank you very much for sharing! Its great to see Rote 7 is back in business again.
Also the quality of the video is fantastic, especially the audio recording. Its head and shoulders above anything else, and the sound of the DB engine is a blast, as always.
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I am almost certain that it reads "Klappen-Ausshlag auf 220 m/m begrenzt", m/m being for milimeters and meaning that the radiator flap opening is limited to 220mm wide. That's roughly 2/3s of the max opening (350 mm) of the 109G
As to cause of this note or solution, I can only guess this was to limit drag.
I have seen the 220mm max opening on some original drawings for 109K, and I can guess that perhaps the original 350 mm radiator opening was excessive and found unneccesary. Perhaps it means that this note refers to the implementation/installation of an improved radiator with optimized flow ("verbesserter Kühlerdurchlauf"), that mentioned in 1945 January performance calculation for improved propellers.
http://kurfurst.org/Performance_tests/109K_PBLeistungen/files/5026-17_conditions.jpg
Another possibility is that IIRC the 605D engines fitted to the 109K-4/G-10 had increased temperature limits, which the radiator could maintain at 220 mm max opening.
The K-4 may have sported a new radiator type of 36 sq. decimeters area, though there are some who doubt this and maintain that it used the same as 109G series.
Opening the radiator fully came with considerable drag, so limiting their maximum opening would also limit drag rise. See this drag chart for January 1944 for 109G
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Original documentation showing WerkNummer blocks of K-4 aircraft fitted with the 20 mm cannon are even better.
Sounds interesting, I was somewhat sceptical about these 2cm K-4s, even from the venerable dr. Prien. If that is true, I would be surprised if there would be more than a handful. While technically it must have possible, I have seen no trace of it in original documentation. Even the K-2 sheets I have show MK 108.
So any chance of seeing these Werknummer blocks?
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It could mount 20mm gondolas though. It would need be checked if the firing scheme could be altered during flight, iirc it could be but I would not say it for sure before checking the manuals.
In any case there were two fire triggers and iirc the default setup was fuselage (108+131s) guns mapped for the MG muttons and and wing guns (2cm cannon) on the cannon button.
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Getting a bit 'clutch at straws', who on earth is going to try and get max turn performance with power at idle, bombs and tanks attached?
No-one, of course, but its worth noting that the 1.4ish cl figures for the 109E thrown around by some refer to the exact same condition - power at idle.
Pretty pointless excercise IMO, as CLmax figures vary with g-load etc. as well, so a CLmax figure referring to "dirty" landing (ie. flaps /gears down, power off, 1g) flight regime won't get you an inch closer to estimate turn rate at multiple g-s, power max etc, ie the flight regime of turning... ;)
DCS: Spitfire Mk LF IXc Discussion
in DCS: Spitfire L.F. Mk. IX
Posted · Edited by Kurfürst
Some various Some additional gun dispersion data, via Olivier Lefebrve / AAW. This might come in handy for modelling the Hispano guns on the Spitfire IX.
Unfortunately only nose mount dispersion data available for the gun, as mounted in the P-38 nose, but given that German results for the same guns in the fuselage and wings display roughly 2-2,5x higher dispersion for wing mounted installations, it would be easy to make an educated guess for the dispersion of the Hispano, and if we get an E variant, for the .50 M2s in the flexible Spitfire wing. The .303 Brownings had a quite large spread in wing installation, iirc around 20 mils for 100%.
Here are the results of a lenghty research into dispersion data, which is quite hard to come by...
The data is based on 100% diameter dispersion with 1 mil = 1/1000th of rad, the kind of mount is precised next to the weapon. 75% dispersion diameter is supposed to be half the 100% diameter which seems quite true for most weapons, this value is provided when quoted in the source (M2 data for instance).
We can clearly see the impact of the wing mounting compared to engine mounting, the later seems to have absorbed recoil and vibration much better... indeed dispersion is at least 2 times greater with wing mounted weapons.
Engine mount are the most efficient but nose mounting or cowling mounting does not provide the same amount of precision the mount being much more prone to vibration it seems.
Note that US data on the M2 is confusing since the reference data comes from a P-38 nose mounted M2, but the US manuals use the same dispersion data for wing mounted weapons. Either the P-38 mounts are really up to no good or the manuals make a wrong assumption when it comes to wing dispersion. I tend to believe the later, i think the wing mounted M2 would have had a dispersion of at least 12mils and probably more.
If you quote this data on other sites/bbs please precise the source being AAW. TIA
H means Height (or max dispersion diameter) as i previously used vertical and lateral dispersion values.
D means distance.
Units are metric.
German Weapons
-----------------------
MG-17 Cowling mounted (Bf 109F-2 / Bf 109F-1 actual tests)
H = 0.60 / 0.8 m
D = 100 m
R/D = 60/10000 80/10000
= 6 mils / 8 mils
MG-131 Cowling mounted (Fw 190A - theorical max)
H = 1m
D = 100m
H/D = 100/10000
= 10 mils
MG-151/15 Engine mounted (Bf 109F-2 actual test)
H = 0,35 m
D = 100 m
H/D = 35/10000
= 3.5 mils
MG-FF Engine mounted (Bf 109F-1 actual test)
H = 0,2 m
D = 100m
H/D = 20/10000
= 2 mils (very tight patern)
MG-FF Wing mounted (Bf 109E-3 actual test)
H = 0,35 m
D = 100m
H/D = 35/10000
= 3.5 mils
MG 151/20 Engine mounted (Bf 109G-6 - theorical max)
H = 0.3m
D = 100m
H/D = 30/10000
= 3 mils
MG 151/20 Wing mounted - inner (Fw 190A - theorical max)
H = 0.7m
D = 100m
H/D = 70/10000
= 7 mils
MG 151/20 Wing mounted - outer (Fw 190A - theorical max)
H = 0.8m
D = 100m
H/D = 80/10000
= 8 mils
MK 108 Engine mounted (Ta 152 - therorical max)
H = 0.35
D = 100m
H/D = 35/10000
= 3.5 mils
Allied Weapons
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M2 Nose mounted P-38 (USAAF 1944 Gunnery manual)
H = 1.88 m
D = 229 m
H/D = 188/22900
= 8.2 mils (75% = 4.1 mils)
Hispano 20mm Nose mounted P-38 (USAAF 1944 Gunnery manual)
3 mils 75%
6 mils 100% assumed