Low Altitude P-47D Razorbacks vs Gustav

[Shortround6]

The difference in time of flight for the two weapons tested by the USN is 0.13 seconds to 500 yards. By the figures above an aircraft flying at 300 mph travels 57 feet in that time, close to two Bf 109 lengths and that would be the adjustment needed compared to the .50 calibre machine gun at maximum deflection i.e. 90 degrees angle off. There were very few, if any, pilots who could hit anything at maximum deflection in any case.
The adjustment of lead, to compensate that 57 feet, at 500 yards, is less than two degrees
The adjustment is much less at lower angles off. Too much is being made of the total time in flight rather than the difference in time in flight, which is relevant in the comparison, for the two systems.
Cheers
Steve

Trouble is we are falling back into the Hispano vs .50 cal pit. The difference in flight time is much greater between the .50 and the German guns.

I would note that there are several charts in "Flying Guns of World War II" that show the proper aiming points for a Spitfire vs an HE 111 that show various ranges and dead astern, 3 degree angle off and 7 degree angle off. and at 7 degrees off and at either 300 or 350 yds (Book is in storage after the move) if I remember right the Spitfires proper aiming point to hit the fuselage was just about the wing tip of the inside wing. Or about 35ft from the center of the fuselage. On a 109 the proper aiming point would be around one extra 1/2 wing span beyond the end of the wing tip.
Judging a 2 percent difference is hard enough on the ground. that is not a total of 2 percent but a difference in the total lead needed for either gun.
The difference is much, much less at 300yds or meters. But it goes back to the fuselage mounted guns argument. By the time the range gets long enough for the fuselage mounted guns to show any advantage so many other things are coming into play that the whole firing solution resembles a "Hail Mary" pass in American football ( throw the ball as far down field as you can and pray one of your receivers catches it).

 

[stona]

Most pilots just couldn't estimate range and angle off with any accuracy at all. I've done the exercises in the RAF's 'Bag The Hun' manual and was depressed at how badly I did! It is not easy at all. This would be a far greater impediment to accurate shooting than a tenth or quarter second difference to the time in flight of the ordnance used. The best chance most had, at least until the arrival of proper gyro gun sights, was zero or very near zero angle off. All they had to do then was not open fire out of range, yet another frequent and serious problem.

Fun for the family if you haven't already seen it

http://www.pdf-archive.com/2014/02/...ery-manual/bag-the-hun-raf-gunnery-manual.pdf

Cheers

Steve

 

[drgondog]

The USAF finally broke the code of 50 Cal vs 20mm during Korea - due to the fact that the 50 calibers, centrally located, were hitting MiGs with authority but at 35000 feet jet fuel was not explosive when a fuel tank was hammered with API. The GUNVAL experiment with 20mm equipped F-86s finally was convincing.

One anecdote - Bill Whisner told me of a Mig that he centered with the last 50+ rounds per gun at 40,000 feet, saw pieces fly off and it went into an evasive dive - and blew up at 30,000 feet. It was dead but didn't know that it was dead until sufficient air density brought the fact to its attention.

 

[Shortround6]

Took me a while to find it but here are the times of flight for most German guns;

Time of flight for German rounds to 300 and 600 meters.

7.92mm AP 10 g............0.453..........1.159
13mm HEI 34 g.............0.49............1.22
15mm HEI 57.5g...........0.357...........0.816
20mm HEI 92g..............0.551..........1.428 (from a MG/FFM)
20mm HET 117g...........0.477...........1.101 (from a MG 151)
30mm HEI 330g............0.696...........1.66 (MK 108 )

And

From a different source: time of flight to 600 yds for US .50 cal. 0.72 sec and for the 20mm Hispano 0.84 sec. Granted it is a 10% shorter distance.

At 300 meters and under except for the 15mm and the 30mm there isn't enough difference to get exited about between the German guns. going over 300 meters and the closer you get to 600 meters the more difference you get.

 

[parsifal]

what would be the typical or median engagement distance in 1944? I would think 150-200m though you get your freaky exceptions like Hartman.

The biggest advantage of the 50 over the 20mm is the velocity of its projectile, and of course that reduces the margins for error when trying to predict or give lead for the target. But how much really. im afraid im unconvinced that at 200m it makes that much difference to the accuracy issue if you are firing a 20mm cannon or a 50cal

 

[stona]

what would be the typical or median engagement distance in 1944? I would think 150-200m though you get your freaky exceptions like Hartman.

I have just picked 6 P-47 encounter reports, at random, from about 300. I have ignored the surprising number which don't mention the range at which the enemy aircraft was engaged.

1. 300 yards closing to 100 yards
2. 400 yards (also mentions 20 degrees deflection)
3. 400 yards closing rapidly to 150 yards
4. 200 yards closing to 'about' 75 yards
5. 300 yards
6. 300 yards closing to 150 yards.

Not very scientific but it tends to confirm that the engagement typically stared at 300 yards to 400 yards. The average of those six is a fraction over 300 yards.

Cheers

Steve

I've done the same for 6 P-51 encounter reports and got the following.

1. 300 yards closing to 200
2. 150 yards
3. 300 yards
4. 300 yards
5. 250 yards
6. 300 yards

Again, around 300 yards seems to be the range of initial engagement, though this time the average is slightly under 300, likely skewed in such a small sample by the one much lower than average number.

 

[Shortround6]

But how much really. im afraid im unconvinced that at 200m it makes that much difference to the accuracy issue if you are firing a 20mm cannon or a 50cal

At 200 meters it makes little or no practical difference but again, not all 20mm are equal. .50 cal vs Hispano and the practical difference doesn't show up until 400 meters if then, they have almost identical muzzle velocities and the Hispano shells greater sectional density (weight vs frontal area) almost makes up for the better shape of the .50 cal bullet.
.50 cal vs a 20mm MG/FFM is a whole different story. The Mine shell left the muzzle at 700m/s vs the 850-890 M/S of the .50 cal and was the equivalent of throwing a ping pong ball. The Heavier AP and tracer rounds (and combinations) left the muzzle at around 585M/S
The MG 151/20 is in-between. About 805M/S with the mine shell and about 705-720MS with the AP and tracer rounds.

Please note;

20mm HEI 92g..............0.551..........1.428 (from a MG/FFM)
20mm HET 117g...........0.477...........1.101 (from a MG 151)

Because of the different guns these two projectiles have almost the same MV (within 5-20M/S out of 700M/S) Which strongly suggests there is a cross over point when they are fired out of the same gun. Under a certain range the mine shells will have a lower time of flight which equals out at the cross over range and then the HET (and AP) rounds having shorter times of flight beyond that.

Now at short ranges (300 meters or under?) it may make little "practical" difference as to which German shells have the lowest times of flight compared to each other, compared to the .50 cal rounds they are going to need 12-15% more lead at common ranges.
How important is this?
US Army did some studies (mostly theoretical) and estimated that a 25% increase in muzzle velocity (assuming similar projectiles) would increase hit chances by 50%. This was the impetus for most, if not all, of the American high velocity gun projects during WW II.
The projects all came to nothing (too ambitious) and the original theory was never really proven (or disproved).

This differences are too small to modeled in the type of game Kettbo is talking about but the "bonus" for the fuselage mounted guns on the 109 can be done away with. (unless needed to get the German fans to play

 

[tomo pauk]

SR6,
Do you have time of flight for the Mine shell (ie. 92 g) fired from MG 151/20?

 

[Shortround6]

No, I don't, I will note that the rounds slow down less (or retain velocity better) at higher altitudes where the air is thinner, just like aircraft, less drag.

Germans figured the "practical" range of most of their guns at 400 meters against bombers, max range showed more variation. But the below average and above average guns would be the usual suspects. 7.9mm being below average, MG 151/15, MK 103 and BK 5 being above average (but hardly common guns). I can't remember if the MK 108 was listed or what its ranges were.

 

[stona]

Given that the average range at which engagements started seems to be around 300 yards, I see 300 metres a lot in Luftwaffe accounts too, I think there is a risk of overstating the potential disadvantages of time in flight for cannon armament, including the German 20mm cannon.
It proved itself in practice to be a very effective armament and whichever way we turn the figures, far more devastating on target air frames than any calibre of machine gun.

The .50 calibre machine gun obviously largely out ranged any contemporary cannon, but that's not the point. The limiting factor for effective range in air to air combat was the sighting system, not the weapon itself. The reason both sides were engaging at somewhere around the 300m mark is because that was the range at which they could reasonably expect to score some hits on the target. With a 20mm canon you might only need one or two hits on a typical fighter. With a machine gun you would usually need many more, the point made by Commander Monroe at that conference in 1944.

Cheers

Steve

 

[tomo pauk]

The reason I ask is that there should be a definitive advantage in the time-to-distance for the Mine shell when fired from the MG 151/20, against the heavier 'Sprenggranante', due to higher MV, if only for shorter distances involved in air combat. Even the 10% improvement will give 1 second to 600 m (vs. 1.1something for the heavier shell), that compared to ~0.92 sec for the Hispano II does not look so bad.

edit: it is that bad. I've just checked out the LW ammo manual, the Mine shell fired from MG 151/20 will have MV of 775 m/s (the manual gives a bit lower MVs than usually encountered, for all of German guns), needing 1.276 sec to reach 600 m. Muzzle energy is 2817 mkg for the M-shell round, vs. 3092 mkg for the 'usual', heavier HE shell - the propellant weight/volume/content being lower for the M-shell?

edit2: hmm - propellant weight is 18.5 - 19 g for any MG 151/20 cartridge

 

[stona]

If the USAAF's fighters had been engaged in trying to shoot down bombers, like the Luftwaffe was and the RAF had been, then the impetus to sort out and fit cannon armament would have come at least two or three years earlier than it did historically. By 1944/5 all US fighters would have been armed with cannon, like their German and British equivalents.
Cheers
Steve

 

[tomo pauk]

Hmm - the P-38 with two M9 cannons, 37 mm, 608 g HE shell @ 800 m/s? The P-63 with M10 cannon + V-1650-5 (yep, Packard Merlin, 2-stage, with extension shaft & intercooler)?

 

[Shortround6]

I am not trying to say that the .50 was better than a 20mm on a one to one basis or a two to one basis or even a three to one basis.
However it seems to me that bit too much is made of the US (and British) comparisons of the .50 to the 20mm Hispano when what we are trying to compare is the .50 vs the MG 151/20.

And in the case of a "standard" 109G-6 vs P-47 we are comparing ONE 20mm gun to SIX .50 cal guns. This is assuming that we think one 13mm MG 131 is equal to one .50 cal Browning which is a large gift to the 109.

Most people figure the MG 151/20 as being roughly equal to the Hispano but that is because they are trading off different attributes.
The higher rate of fire of MG 151 (until the MK V Hispano shows up but that is rather late) tending to cancel out the lighter ammo (115-117gram projectiles not including mine shells vs 128 gram shells.) and lower velocity compared to the Hispano. AS a weapon system the MG 151 was lighter, more compact and used lighter ammo so had advantages there also.

MG 151 vs the .50 cal the rate of fire advantage disappears or reverses slightly. The kinetic energy difference is much closer between the .50 and MG 151 leaving the MG 151 more dependent on it's HE (and good fuses) and the majority of German 20mm shells except for the mine shell carried between 3.6 and 7.3 grams of "chemical" (incendiary or HE) or roughly 1/2 what a Hispano shell carried. Granted even a 40% mix of mine shells bring the HE load way up.

The higher velocity of the .50 (essentially the same at practical distances for the Hispano) is going to counter act whatever mysterious advantage the center line gun/s had by making deflection shooting easier, and yes not ALL engagements involved defection shooting.

 

[Milosh]

Unless the shoot was from dead ahead or dead astern it was deflection shooting.

 

[stona]

Unless the shoot was from dead ahead or dead astern it was deflection shooting.

Take a look at Luftwaffe gun camera footage. Ignore the attacks on fighters which usually end up in a turning fight (kurvenkampf) in which unsuccessful and usually high deflection shots are taken. Most of the successful attacks on bombers are made from close to directly astern or head on, ie close to or in fact zero deflection.
It's the only way most pilots could hit anything before the advent of gyro gun sights and even those (particularly German ones) were not always easy to use (I read a 1944 Rechlin report on the EZ 42 a few days ago which said 'shooting with the EZ 42 is not easy and requires much practice.')
Cheers
Steve

 

[kettbo]

kettbo, how are you going to factor in the manoeuvrability penalty of the gun pod armed Gustav?

Those pods caused a considerable negative penalty to the planes handling.

Kryten,

This is one of those interesting issues like comparative firepower!
re pods, change in mph during German testing is on the KURFURST website. Pretty hard data.
re pods, effect on maneuverability, some disagreement! No sources to quote at the moment but my recollection varies from Little effect to a lot! Older sources were not very friendly on Bf109 performance yet the last several years here has been an education

For now, using hexes to regulate things, planes turn normally after entering a hex. Additional maneuvers like trying a tighter turn, there is a chance roll. Odds are better of success if you are a veteran pilot compared to a rookie. MUST balance the detail with playability. The desire here is to have 12 or more planes up for the US and whatever the LW can manage. I have the Bf109G-14 with a great chance of making the next higher altitude band. Was thinking to knock the gun pod armed planes down one pip.

At the GIANT used book store in downtown Tacoma I found a pam by the XIX TAF re air-ground operations supporting the Third Army. Good stuff. A GREAT FIND is planning P-47 et al vs the LW.


All you other folks, big THANK YOU to all who replied! Great info to digest! Limited a bit on fine hairs re effects and I plan various dice and combos trying to get the closest comparative results, variable damage. The 30mm mk 108, each hit 'could' kill or cripple a fighter. A bad roll yields just the one hit or several chances of a miss. A good roll could be multiple hits. Range and target size +/- experience. Possible you could get a '1' as a hit result for one round hitting, more likely you'll take average points, puts you into crippled category even before going for a critical hit roll. Again, want some details but play has to go quickly.

Fully realize that most guys never saw what got them
Dogfight kills will be very difficult if you are a low skill pilot

 

[parsifal]

Hi Kettbo

Using dice for damage calculation is a great idea. Be aware, however that if you are considering larger dice to simulate the higher potential for variance as well, unless you put some kind of dampener on it. Say, for example, you use a 1d6 for a 50cal, and a 1d20 for a 30mm. Rolling a 1 for the 50 cal has a roughly 15% whilst rolling a 1 for the 30mm has a roughly 5% chance. thats fine, but it introduces a lot of variation for the heavier weapon. I doubt that is astatistictically true thing to say via your game system. If you think of the range of damage that could be inflicted from a given weapon as a number of "slots" if you like of possible outcomes, the number of "slots" available to the heaviuer weapon ought to be the same as the number available to the lighter one, with just less damage to each "slot" of damage.

Onr way of getting around this might be to work out the number of hits in a given round and then roll a further die of a certain size depending on the weapon.....just a suggestion so you would have a hit resolution and then damage resolution

One issue I would also suggest is that in a super tactical simulation like you are considering, a pilot would not know exactly when to stop firing. He would have some idea, but not a perfect knowledge as to what his opponent was up to. Sometimes a pilot would feign being mortally hit to escape, other times an escort would waste its ammo shooting up an already dead pilot

 

[eagledad]

Kettbo,

Russian tests of a BF-109G-2 with out wing guns found it to be 15 to 20 km faster than the BF-109G-2 with the under wing guns. Turn times (360 degree turn) for the 3 gun version at 1000 meters averaged 20.7 seconds, the 5 gun averaged 22.7 seconds. Loaded weights for the 2 aircraft were 3023kg for the 3 gun and 3235kg for the 5 gun. Russian tests of a P-47D-10 gives a turn time at 1000 meters of 26 seconds at a weight of 6780kg.

Eagledad

 

[kettbo]

Parsifal,

Good points....
I was trying to not do individual guns except the 30mm and 37mm stuff but nothing has been set in concrete yet
30mm would be a d10 per hit; more chances to hit a bomber at close range than a fighter at medium range
one can do a d12 and every result has the same chance
one can do 2d6 with lots of chances for AVERAGE damage, few chances for minimal or severe results BUT lowest damage is 2 pips.

Kettbo,

Russian tests of a BF-109G-2 with out wing guns found it to be 15 to 20 km faster than the BF-109G-2 with the under wing guns. Turn times (360 degree turn) for the 3 gun version at 1000 meters averaged 20.7 seconds, the 5 gun averaged 22.7 seconds. Loaded weights for the 2 aircraft were 3023kg for the 3 gun and 3235kg for the 5 gun. Russian tests of a P-47D-10 gives a turn time at 1000 meters of 26 seconds at a weight of 6780kg.

Eagledad

noted!, thank for the info. I planned a small maneuver penalty for the P-47 compared to the Gustav. You provided info showing that the 5-gun version would also have an advantage too.