Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Wilbus on October 15, 2002, 07:49:53 AM
-
Not a whine, so all you whine police dweebs might aswell leave now.
Hazed posted a nice interesting chart a while ago, comparing US aircraft weapons with eachother.
Thought I'd throw in the MG151 in the test and calculate the way they have.
Weight of fire is equal to "number of rounds fired per minute".
Lethality is equal to "weight of fire * Velocity^2 (raised to 2) * 10^-8.
MG 151 rate of fire: cirka 700 rounds per minute. I'll calculate with 700/min.
(The 650 rounds/min is when equiped on a Ta152 with prop spinning.)
Muzzle Velocity: 805 m/s (2641,1 feet/s)
Weight of bullet (M-Geschoss = High explosive, used against airplanes) 197,2 g (0,4348 lbs).
My calculations may be wrong but I don't think so. Think I've calculated it right.
Weight of fire (lbs/min) Weight: 0,4348 * 700 = 304,36 lbs/min.
Lethality: Weight of fire * Muzzle Velocity^2 * 10^-8
304,36 * 2641,1^2 * 10^-8 = 21,23
So acording to these calculations, the Mg151 has greater lethality then both the 1941 M2 20mm, and the 1944 M3 20mm.
-
This is the chart Hazed posted.
-
Wilbus, you are calculating the lethality of M-Geschoss projectiles based on its weight and muzzle vel like if they were normal AP shells. This is wrong. The mine projectiles are going to explode upon impact, so, even at much slower muzzle velocities they are going to cause similar damage. This is (should be) just the big advantage of the mines, no matter the range, no matter the energy, just hit the enemy and they explode like small hand grenades.
Your formula may be good for normal AP projectiles, very dependant on its weight and muzzle vel.
And two questions about AH modeling:
Do we have M-Geschoss in AH?
Do mines lose destructive power with the range?
-
I calculated it to go with the US test, meaning, that without the HE (as has been left out of lethality on the US guns aswell) the Mg151 should be more leathal. Add HE to this and it would probarly be more leathal as it contained more HE.
But the test is calculated acording to no HE, lethality is no HE just impact and destructive power. I've calculated the same way for the Mg151.
-
To put it short, explosive power isn't in the test at all, not for the US nor for the MG151.
-
Wilbus, I think you may have underestimated the 151. A HE round is typically lighter than an AP round (steel or tungsten is heavier than the explosive compound). If the US chart submitted calculate with the weight of 20 mike-mike AP shells you should look for the weight of a German AP shell (if they used one). I think you would see a significant increase in 151 lethality.
Another note: Had the M-Geschoss a proximity fuse, or a delayed detonation fuse? The latter would be more effective against heavy-bombers as they explode inside the aircraft.
-
I am not an expert but I thought this would help... just what I did a long time ago when I was flying Air Warrior...
Please take a look at this table:
(http://member.nifty.ne.jp/flying_dutchman/reference/table1.jpg)
Data for this table was borrowed from:
Emmanuel Gustin's Extensive Military Aircraft Database
Vermillion's Website
R. Shaw, Fighter Combat, ISBN 0-87021-059-9
J. Horikoshi and M. Okumiya, Reisen, A small history of the Japanese Naval Aviation, ISBN4-257-79028-8
Magazine Maru Editorial Department, Shiden, Shidenkai, and Type94 Float Plane, ISBN4-7698-0631-0
I took the data from Emmanuel Gustin's Extensive Military Aircraft Database first and then filled the missing parts from Vermillion's Website like the information on explosives and the projectile weight for the Ho-5 cannon. I also used the information on TNT as Vermillion presented which stated that the amount of TNT is proportional to the weight of the projectile. However, I notice that Vermillion's website has moved elsewhere.
Well, depending on the type of projectile it is, the proportion would vary I suppose, together with the type of explosive. But assuming that each of these guns had similar projectiles for the sake of comparison, this table might be of benefit.
I noticed that the energy given off by the explosive is quite high in comparison to the kinetic energy of the projectile itself. Given the distance the projectile has to travel (and the loss of kinetic energy), the energy of the explosive will become more pronounced, I think.
Lastly, if anyone could enlighten me... I believe the table that Hazed posted comes from Mr. R. Shaw's book, Fighter Combat. There, I notice that the lethality is not calculated in the form of kinetic energy, but a formula something close to it. Is this an accepted method of calculating lethality or are there other methods for this?
Just wondering and my two cents on this issue...
-
Fdutchman, the chart you posted shows the velocity of the Panzergranate (AP) and Brandsprenggrante (Fire high-explosive shell). Velocity of those is 705 m/s. M-Geschoss had 805 m/s.
Calculations for AP and Fire Grenade shells.
Velocity: 705 m/s (2313 ft/s).
Weight of bullet: 223 g (0,4916 lbs)
Weight of fire (lbs/min) 0,4916 * 700 = 344,12 lbs/min.
Lethality: 344,12 * 2313^2 * 10^-8 = 18,41.
18,41 using AP shells.
-
Wilbus, I think perhaps your chart has the MG151 cartridge weight, rather than the projectile weight. The M2/Hispano Mk2 projectile was considerably more massive than that of the MG151/20 (whether M-Geschoss or AP/HE).
(edit)
Regardless of this, I think the 'weight of fire' theory is barely adequate as any measure of a gun package's effectiveness. It disregards not only HE component, which became ubiquitous as the war progressed, but penetration considerations too.
-
What Bombjack said. Those figures are for the weight of the entire round. The projectile weights you're looking for are 92 g and 115 g respectively.
-
Discussing the "lethality" thing Bombjack.
You may very well be right on the weight thing though, it's probarly the complete shell.
I wounder a thing though, is the MG151 modelled with 705 m/s or 805 M/s???????
-
Thanks Pyro, my misstake, wrote my above message right as you wrote yours I think.
May I ask what velocity our have? Don't matter to me if it is 705 or 805, just interesting to know.
Please don't think I am trying to say anything is wrong or that I am whining cause I am not, just asking :)
-
Wilbus, obviously I don't know what velocity the shells have in AH, but it would be realistic for them to travel at different speeds if they were M-Geschoss vs AP. The Mine shells weighed less like Mandoble says, so with the same cartridge (same amount of propellent) as the AP/HE shell, they actually gained a higher muzzle velocity.
However this lack of density (as well as a slightly less aerodynamic shape) counts against the Mine shell in range, since it slows more quickly.
A quick digression on the subject of "Mine shells are unaffected by low velocity, they are effective even at extreme range": imagine you hold a firecracker in your open palm and it goes off, what happens? You burn your hand. Now close your fist around that same firecracker... your wife's going to be opening your mail for you for the rest of your life.*
Same deal with an explosive shell. We're not looking at grenades here, if they go off outside the skin of the aircraft their effectiveness is going to be low - they need to have enough velocity left to penetrate before they explode. Mine shells slow down very quickly, that is why their effective range is low.
(edit, so people don't think I'm down on the MG151)
Of course, if that shell gets through into an enclosed space where the blast is contained... then you're looking at serious damage. Swings and roundabouts, you gain in one area, you lose in another.
* crap film, but I like the quote :)
-
Same deal with an explosive shell. We're not looking at grenades here, if they go off outside the skin of the aircraft their effectiveness is going to be low - they need to have enough velocity left to penetrate before they explode. Mine shells slow down very quickly, that is why their effective range is low.
Yup I knew that, who said anything else?
(edit, so people don't think I'm down on the MG151)
Really sucks to always have to protect yer self from flames by saying such things don't tou think? :(
-
Re. the Dutchman's table: there were considerable differences in the percentage weight of HE in the shells used by different nations.
The Germans focused on blast effect initially, with the 20mm M-Geschoss clocking 19-20g HE in a 92g shell (20%). Other types of shell generally managed no more than 10%; e.g. the Hispano loaded around 10-11g in a 130g shell. The Soviet shells were typically only around 6-8%. The Japanese varied quite a bit.
Towards the end of the war, the Luftwaffe moved away from blast effect in favour of incendiaries, as fire was the big bomber-killer. They developed more strongly-built and heavier M-Geschoss (so they would penetrate more deeply) loaded mostly with incendiary material, and with hydrostatic fuzes which detonated only when they hit a fuel tank. Nasty - but very effective.
Tony Williams
Military gun and ammunition website: http://www.quarry.nildram.co.uk
Discussion forum at: http://forums.delphiforums.com/autogun/messages/
-
Originally posted by Tony Williams
Re. the Dutchman's table: there were considerable differences in the percentage weight of HE in the shells used by different nations.
ahh thank you for the clarification :)
-
Yes, the percentage of explosive to the weight of the projectile was an assumption I had to make in my early work, because there was not any good data available for most of the shells we were comparing. Since then, I've found alot better data (I have it for most all countries now from original source documentation) and Tony wrote his book which contains that data as well.
Luftwaffe guys. Please realize that mine shells were not used exclusively. Even at the height of the bomber offensive in the West (where they used a larger percentage of mine shells) mine shells were only 1 in 3 or 1 in 4, in a standard ammunition belt. So to do the calculation correctly, you must account for ammunition mixes.
I don't have a copy of it handy, but I did this once on a spreadsheet with all the correct data, and accounting for ammunition mixes, and it still comes out the same. The Hispano is more effect in damage and ability to hit than the MG151.
FD my webpages are gone, lost to the great HD crash ghost of the internet. My webhosting company switched servers and lost all my webpages, and almost simultanesouly I had a HD failure on my computer at home and lost all the copies of it there.
-
Indeed, it was more of an attempt to show the difference in lethality between those with explosive rounds and those without. I think it did show that there was quite a bit of difference which was dependent on the amount of explosives in the shells.
-
Verm,
is this your site?
http://web.archive.org/web/*/http://www.vermin.net/
-
Are you talking about this?:D :D
Btw this guy is LLv34 Blauk with MG151;)
(http://www.muodos.fi/LLv34/h_BK_mg151.jpg)
-
Looks like Blauk is ready for the bird hunt.
-
Yes Mitsu !! :)
Thank you. I didn't know that existed.
-
Luftwaffe guys. Please realize that mine shells were not used exclusively. Even at the height of the bomber offensive in the West (where they used a larger percentage of mine shells) mine shells were only 1 in 3 or 1 in 4, in a standard ammunition belt.
Don't believe that at all, however, mixing ammuntion was standard in all airforces, almost no planes used one shell only but they mixed incendary with HE and more.
-
Originally posted by Wilbus
Don't believe that at all, however, mixing ammuntion was standard in all airforces, almost no planes used one shell only but they mixed incendary with HE and more.
I have a copy of an original German document, dated 1944, which gives the following data for loading 2cm ammo belts:
Fighters: 2x M-Geschoss, 2x HEI-T, 1x API or APHE
Nightfighters: as above but with dim trace in the HEI-T
"Kampf-Schlachtflieger und Jaeger": 10x HEI-T, 10x M-Geschoss, 1x API, 1x APHE.
Tony Williams
Military gun and ammunition website: http://www.quarry.nildram.co.uk
Discussion forum at: http://forums.delphiforums.com/autogun/messages/
-
Originally posted by Vermillion
Yes, the percentage of explosive to the weight of the projectile was an assumption I had to make in my early work, because there was not any good data available for most of the shells we were comparing. Since then, I've found alot better data (I have it for most all countries now from original source documentation) and Tony wrote his book which contains that data as well.
Just wait for the next one :)
Tony Williams
Military gun and ammunition website: http://www.quarry.nildram.co.uk
Discussion forum at: http://forums.delphiforums.com/autogun/messages/
-
Hi Tony,
>"Kampf-Schlachtflieger und Jaeger":
Are you sure? "Kampf-Schlachtflieger" is not an established technical term as far as I know.
"Kampf-/Schlachtflieger" (bomber/attack aircraft) would make more sense, but in combination with "Jäger" it really could be read as "all combat aircraft", which I'd say is somewhat surprising.
>10x HEI-T, 10x M-Geschoss, 1x API, 1x APHE.
Is there any instruction on the actual order within the belt as well? (I assume that 10/10/1/1 isn't the actual order :-)
Do the German documents provide any background on why any specific mix is chosen?
Regards,
Henning (HoHun)
-
Originally posted by HoHun
Hi Tony,
>"Kampf-Schlachtflieger und Jaeger":
Are you sure? "Kampf-Schlachtflieger" is not an established technical term as far as I know.
"Kampf-/Schlachtflieger" (bomber/attack aircraft) would make more sense, but in combination with "Jäger" it really could be read as "all combat aircraft", which I'd say is somewhat surprising.
>10x HEI-T, 10x M-Geschoss, 1x API, 1x APHE.
Is there any instruction on the actual order within the belt as well? (I assume that 10/10/1/1 isn't the actual order :-)
Do the German documents provide any background on why any specific mix is chosen?
Regards,
Henning (HoHun)
I can't provide any more help, Henning - the information in the document is exactly as I have presented it, and that's all there is.
Tony Williams
Military gun and ammunition website: http://www.quarry.nildram.co.uk
Military gun and ammunition discussion forum: http://forums.delphiforums.com/autogun/messages/
-
Edited, was delyric.
-
Im interested of the ballistics here, meaning how much drop did the ammo have, say, in 500 meters of flightpath?
The destruction power has not yet concerned me (YET) in AH but the ability to hit targets within 100 - 500 meters in various G-loadings.
Lazer-Hispano vs. Sling-shot 151/20?
To those with data and ability: How much drop do these two cannons ammo have in 300 meters? Or what is their flight time for this distance?
(Depends of course of the grenade being used...)
This would pretty much tell something about their usefullness in deflection shooting.
I also think there is difference whether a M-geshoss enters the fuselage or the wing as the blast would have a different expansion room and thus different blast-effect (Making the wing hit more lethal). Am I on wrong tracks here?
-Charge+
:confused:
-
The 117g API shell in the MG 151/20 took 0.898 secs to reach 500m, by which time it slowed from 720 to 430 m/s and dropped 3.37m from the line of sight. Figures for the 92g M-Geschoss are 0.952 secs, 790 to 363 m/s and 3.5m.
I don't have comparable figures for the Hispano. However, according to German sources the rate of velocity loss was similar to the 117g HEI, which would have meant a velocity loss from around 860 to 520 m/s, with obviously a shorter flight time and smaller drop than the German shells.
Tony Williams
Military gun and ammunition website: http://www.quarry.nildram.co.uk
Discussion forum at: http://forums.delphiforums.com/autogun/messages/
-
Hi Charge,
>To those with data and ability: How much drop do these two cannons ammo have in 300 meters? Or what is their flight time for this distance?
Here's the flight time table for the MG151/20 mine shell compared to the 20 mm AP M75 round:
d (m) - MG151/20: t (s) - 20 mm AP M75: t (s)
100 - 0.13 - 0.13
200 - 0.29
300 - 0.47 - 0.43
400 - 0.69
500 - 0.94 - 0.77
The MG151/20 data is from the official Geran ballistic table (805 m/s muzzle velocity). The M75 data is based on a 800 m/s muzzle velocity, but the flight times are rough estimates from the speed graph and might be slightly inaccurate.
I'm not sure why the AP projectile's muzzle velocity is below the Hispano-typical 850 m/s, but I think the numbers cast an interesting light on the topic nevertheless :-)
Regards,
Henning (HoHun)
-
Hi again,
It just occurred to me that I mistook yards for meters with the M75 AP projectile. Please ignore my results for now :-)
Regards,
Henning (HoHun)
-
Hi yet again,
Here's the corrected flight time table for the MG151/20 mine shell compared to the 20 mm AP M75 round:
d (m) - MG151/20: t (s) - 20 mm AP M75: t (s)
100 - 0.13 - 0.13
200 - 0.29
300 - 0.47 - 0.44
400 - 0.69
500 - 0.94 - 0.79
Regards,
Henning (HoHun)
-
In the case of a fighter aircraft in a tailchase, ballistically things are worse because the shooter and target are both moving. If the shooter and target are both travelling at say... 150m/s, then a projectile with a nominal muzzle velocity of 800 m/s would actually be going 950 m/s when fired. The higher speed means higher drag and the deceleration of the round relative to the still moving target will be more pronounced. A projectile fired at a target 500m distant might actually have to travel 650m or 700m before it catches the target. This results in significantly more drop than would be experienced firing at a static target, and slower rounds will suffer greater penalties.
Hooligan
-
Hi Hooligan,
>In the case of a fighter aircraft in a tailchase, ballistically things are worse because the shooter and target are both moving.
Of course, you're right. That's why I provided data for up to 500 m range though Charge specifically asked for 300 m :-)
But actually, drop isn't a big issue since the sightline is depressed to compensate for that. From the trajectory diagram for the Fw 190A-7/A-8, at 650 m was about 1.2 m below the sight line, which is not quite 2 mil. (A typical WW2 gunsight circle would have 70 mil diameter.) From the P-38 boresighting chart which only runs to 500 yards, I'd say its 20 mm cannon was about as far below the sight line as the Fw 190's at 650 m.
(The flatter trajetory meant that the P-38's cannon arched to only 15 cm above the sight line compared to the Fw 190's 80 cm.)
It's interesting to have a look at shooting accuracies the Luftwaffe considered to be realistic against heavy bombers under combat conditions:
d (m) - Ph MG151/20 - Ph MK103 - Ph MK214
500 - 9.1% - 10.0% - 10.5%
1000 - 3.3% - 3.8% - 3.8%
1500 - 0.8% - 1.3% - 1.5%
The 50 mm MK214 as a large-caliber high-velocity weapon of course had a significantly flatter trajectory than the MG151/20, but that only paid off beyond effective range.
I think that reinforces my belief that drop is less interesting than flight time, and in fact, Charge had originally asked for deflection shots :-)
The necessity to account for deflection of course greatly reduces the sensible engagement range, so it certainly makes sense that Charge wanted to look at ranges of up to 500 m. Judging from the typical convergence settings used by the USAAF, they did indeed expect to fire at ranges of 250 to 300 yards only :-)
Regards,
Henning (HoHun)
-
Originally posted by HoHun
I'm not sure why the AP projectile's muzzle velocity is below the Hispano-typical 850 m/s, but I think the numbers cast an interesting light on the topic nevertheless :-)
It was heavier, weighing in at 165g rather than 130g, and in fact the US stats I have give an MV of only 775 m/s. I'm not sure how much use this saw; I would expect it to have been used against ground targets, as it contained no HE or incendiary material as you would expect for use against aircraft.
Tony Williams
Military gun and ammunition website: http://www.quarry.nildram.co.uk
Military gun and ammunition discussion forum: http://forums.delphiforums.com/autogun/messages/
-
Originally posted by Tony Williams
The 117g API shell in the MG 151/20 took 0.898 secs to reach 500m, by which time it slowed from 720 to 430 m/s and dropped 3.37m from the line of sight. Figures for the 92g M-Geschoss are 0.952 secs, 790 to 363 m/s and 3.5m.
On reflection, these drop figures I quoted have to be wrong, since gravity causes objects to drop nearly 10m in the first second. I took them from an original German data table but I probably misinterpreted the symbol at the top of the column; these figures may refer to the maximum trajectory height above the sight line.
Tony Williams
Military gun and ammunition website: http://www.quarry.nildram.co.uk
Military gun and ammunition discussion forum: http://forums.delphiforums.com/autogun/messages/
-
Tony,
drop 10 meters in the first second? The final velocity might be ~10m/s ( 9.81m/s ) but the distance travelled ain't. Unless I am completely off the mark I get ~3.96 m drop for the first MG 151 round using those values.
// fats
-
Originally posted by fats
Tony,
drop 10 meters in the first second? The final velocity might be ~10m/s ( 9.81m/s ) but the distance travelled ain't. Unless I am completely off the mark I get ~3.96 m drop for the first MG 151 round using those values.
You could well be right; physics was never my strong point :)
Tony Williams
Military gun and ammunition website: http://www.quarry.nildram.co.uk
Discussion forum at: http://forums.delphiforums.com/autogun/messages/
-
Hi Tony,
>You could well be right; physics was never my strong point :)
s = 1/2 * a * t^2
t = 1 s, a = 9.81 m/s^2 => s = 9.81/2 m/s = 4.905 m
If the projectile dropped less, it must have been due to its aerodynamic properties. The MG151/20 mine shell table I have indicates an tranjectory apex point at 287 m, 1.1 m which seems to match your drop value (I'm shooting from the hip here ;-)
Regards,
Henning (HoHun)
-
Tony also realize when you see balistic tables refering to line of sight that most guns are not shot paralle to the line of sight, but first travel up threw it then back down. Any way 1 sec = 16.1 foot drop if the bullet is fired level with the ground.
-
Hi Tony,
>It was heavier, weighing in at 165g rather than 130g, and in fact the US stats I have give an MV of only 775 m/s. I'm not sure how much use this saw; I would expect it to have been used against ground targets, as it contained no HE or incendiary material as you would expect for use against aircraft.
So the M75 was a special round not normally used in air combat?
Anyway, here's the comparison again with 180 fps added on top of the AP round's speed at any distance.
d (m) - MG151/20: t (s) - 20 mm AP (2800 fps): t (s)
100 - 0.13 - 0.12
200 - 0.29
300 - 0.47 - 0.42
400 - 0.69
500 - 0.94 - 0.73
As of course a lighter, faster bullet will lose speed more quickly than a heavier, slower one, this is a rather generous estimate for the upper limit of the Hispano's advantage over the MG151/20.
Regards,
Henning (HoHun)
-
Hi Charge,
>The destruction power has not yet concerned me (YET) in AH but the ability to hit targets within 100 - 500 meters in various G-loadings.
Here's a comparison of what target speeds are the limit for each type of gun for a 90° crossing shot, based on the assumption that the sight from each cockpit is 100 mil below the sight line (as in the P-51D).
d (m) - MG151/20: v (km/h) - 20 mm AP M75: v (km/h) - Hispano advantage (%)
100 - 277 - 277 - 0%
300 - 230 - 245 - 7%
500 - 191 - 228 - 19%
According to this, the advantage given by the Hispano's higher speed could be compared to having a slightly better view over the nose when it comes to deflection shooting.
(For perspective: The difference of the forward visibility of the P-47D and the P-51D is about 25 mil, which is slightly larger than the difference between MG151/20 and Hispano lead requirement at 500 m. Of course, the P-47D's sighting advantage is indepenend of range, while the flight time advantage is less pronounced at shorter ranges.)
Regards,
Henning (HoHun)
-
Originally posted by Vermillion
Luftwaffe guys. Please realize that mine shells were not used exclusively. Even at the height of the bomber offensive in the West (where they used a larger percentage of mine shells) mine shells were only 1 in 3 or 1 in 4, in a standard ammunition belt. So to do the calculation correctly, you must account for ammunition mixes.
More than 1/3 or 1/4 actually. But mostly it was about pilot preferences.
The recommended use of ammunition in the MG151/20 was the same as with the MG FF, as follows:
- 2 Minengeschoß m. Zerl.
- 2 Brandsprenggranatpatronen L'spur m. Zerl oder Brandgranatpatronen
- 1 Panzersprenggranatpatrone o. Zerl oder Panzerbrandgranatpatrone (Phospor) .......o. Zerl