Author Topic: Improve the P-47 (Read 12547 times)

Charge · « **Reply #120 on:** October 10, 2006, 03:24:35 AM »

"Personally, I believe the effectiveness of the Brownings is much greater than just two Hispanos. "

Certainly in Aces High the Brownings are very accurate. But are they correctly modelled? Four guns stacked per wing (a large wing) and fired at the same time for three seconds are not likely to produce such concentrated pattern. The .50s in P38 could do that but the nose of the a/c is not subject to flexing in flight.

Of course for three seconds firing time the .50 start to produce a concentrated statisitical pattern but I find it hard to believe that wing mounted guns could produce that kind of pattern to 1000 yds -especially in flight.

Just my opinion.

Well, this is not the first time this matter has been discussed...

-C+

HoHun · « **Reply #121 on:** October 10, 2006, 04:02:52 AM »

Hi Widewing,

>I don't think it takes more than a glance to determine which gun set-up is most likely to score hits.

The question is, which setup is going to score more kills? A 20 mm Hispano projectile has 4.9 times the energy of a 12.7 mm API round. That's at the muzzle, at least - and due to the higher chemical energy of the 20 mm round that is not affected by drag, the balance shifts further in favour of the Hispano the farther you go downrange.

You'd have to draw at least five or six dots on the Hispano chart for each dot that is actually there to give a true impression of the comparative firepower (or hold the trigger down for at least five times as long) to give a true impression of relative firepower.

It's often overlooked that the probability for destruction of the target is Pd = Sum (Ph * Nh * Pk). When the probability of a hit is the same, the number of hits Nh has the same influence as the probability of kill for each hit Pk.

States at this, it becomes obvious that there is no inherent advantage in batteries with a high rate of fire unless "everything else is equal" - which in the case of machine guns and cannon does not apply.

Regards,

Henning (HoHun)

gripen · « **Reply #122 on:** October 10, 2006, 04:47:03 AM »

Quote

Originally posted by HoHun

The question is, which setup is going to score more kills? A 20 mm Hispano projectile has 4.9 times the energy of a 12.7 mm API round.

Hm... the right question is, does supposed 4,9 times more energy mean same kind of ratio in the effectiveness of the round.

Not according to US Navy because they rated 1 Hispano equal to 3 M2s.

Quote

Originally posted by HoHun

You'd have to draw at least five or six dots on the Hispano chart for each dot that is actually there to give a true impression of the comparative firepower (or hold the trigger down for at least five times as long) to give a true impression of relative firepower.

Well, this part is (again) misunderstanding of probability; generally the M2 had roughly 20% higher ROF than the Hispano so per time unit the probability of the hit is better than assumed per projectile (assuming everything else equal). In addition the differences in ballistics might cause notable differences.

As an interesting sidenote there was a 1000-1100 rpm version of the M2 in production as early as 1939.

gripen

Charge · « **Reply #123 on:** October 10, 2006, 06:01:07 AM »

"Not according to US Navy because they rated 1 Hispano equal to 3 M2s."

How did they figure that out?

I don't think HoHun is talking about the hit probability but firepower, which means hits yes, but also the effect of those hits.

The distance and HE performace makes it difficult to compare. At close range the 6x.50Cal may be as effective as two Hissos, but from a distance the better kinetic energy and HE content of 20mm requires the addition of one .50Cal to achieve the same effect with ROF effect added than the 2xHisso. If I had any math skills I'd calculate it...

Also remember that from extreme ranges the German Mine ammo is still almost as lethal than from point blank due to HE performance.

From shooter point of view the speed and flatness of bullet path is an asset of course.

-C+

HoHun · « **Reply #124 on:** October 10, 2006, 07:07:28 AM »

Hi Charge,

>"Not according to US Navy because they rated 1 Hispano equal to 3 M2s."

Note that I am talking about projectiles when I'm quoting a factor of 5.9 in favour of the Hispano. Using muzzle power, 1 Hispano equals 3.74 Brownings. (I'm not sure the US Navy used anything better than a rule of fist - arriving at an integer number is such a comparison doesn't look overly accurate.)

>I don't think HoHun is talking about the hit probability but firepower, which means hits yes, but also the effect of those hits.

Since people seem to get confused by different "probabilities", I'll just call it lethality so that we know what we are talking about:

L = Nf * Ph * Pk

Firepower would be:

FP = ROF * Pk

Note that this does not include hit probability, which depends on the situation and is not directly determined by the weapon.

Regards,

Henning (HoHun)

Captain Virgil Hilts · « **Reply #125 on:** October 10, 2006, 07:24:39 AM »

Hit probability IS determined by the weapon. The last time we fooled with them the Ma Duece 50 BMG was more accurate and ballistically superior to the 20mm cannon. The 50 BMG shoots a much flatter trajectory, and, loaded with ammo NOT designed to create dispersion, shot a tighter group. When shooting over a RANGE of distances, especially where the distance is not a given, but instead must be judged by the shooter by an educated guess, the round with the flatter trajectory will score the greater number of hits PER ROUND FIRED. Further, when you factor in the variables in rate of closure, convergence factors over the distances involved, and the various factors introduced by deflection shooting, flatter trajectory makes a HUGE difference.

Yes, it is true that the 20mm in a number of forms has become the round of choice on U.S. fighters. However, they are now fired from the various GE electric "Galting Gun" type cannons with a rate of fire far beyond what was possible in World War II. Further, the average modern fighter pilot has more hours in training than the average fighter pilot in World War II had in total flying time. Also, the modern fighter pilot has all sorts of true computer aided sights. Comparing even Vietnam era fighters to World War II fighters is far more useless than comparing apples and oranges.

HoHun · « **Reply #126 on:** October 10, 2006, 07:47:55 AM »

Hi Hilts,

>Hit probability IS determined by the weapon.

It's determined by multiple factors, including the weapon. That's the reason it's not part of the firepower definition as above.

Think of a sniper rifle - it does not have much raw firepower, but it can be highly effective anyway.

(It only makes a difference for the point where you enter the Ph factor "per round fired", as you correctly noted, into the equation.)

>The 50 BMG shoots a much flatter trajectory, and, loaded with ammo NOT designed to create dispersion, shot a tighter group.

As a P-38 fan, I'm sure you're familiar with the Bore Sighting Chart for the type, which shows only a small difference between 20 mm and 12.7 mm trajectories? (If not, I'd offer to post it.)

Of course, the P-38 with its nose mounted armament was one of the best planes regarding long range fire, so at extreme range you'd actually notice the longer drop. The "effective boresight range" against a fighter-sized target is about 800 m for the 12.7 mm on the P-38, I haven't entered the Hispano II data yet but it should be slightly less than that.

The pattern size of course depends (among other factors) on the rigidity of the mounting, and for aircraft guns, the 12.7 mm gave a relatively wide pattern in a wing mount. Again, the P-38 is pretty ideal since nose mounts tend to be quite rigid.

>Comparing even Vietnam era fighters to World War II fighters is far more useless than comparing apples and oranges.

Did I do that? I thought I deleted that paragraph before posting :-)

But seriously, the USAF went to cannon in the Korean war, and the Gatling guns came only later.

Regards,

Henning (HoHun)

Nightshift82 · « **Reply #127 on:** October 10, 2006, 08:16:19 AM »

the P47 is the bestest plane in World War 2 period.

Angus · « **Reply #128 on:** October 10, 2006, 09:38:36 AM »

Nonono. It's teh Fairey Swordfish:D

gripen · « **Reply #129 on:** October 10, 2006, 10:20:00 AM »

Quote

Originally posted by Charge

I don't think HoHun is talking about the hit probability but firepower, which means hits yes, but also the effect of those hits.

The correct way to present this is just claim that each hit is more effective - at arguable multiplier. Presenting this as longer shooting time gives wrong impression of hitting probability, which is in the case of Hispano roughly 20% lower for each gun due to ROF at given time frame assuming everything else equal.

The effect of the round naturally depends on target - historically the M2 did well against German fighters.

Quote

Originally posted by HoHun

Note that I am talking about projectiles when I'm quoting a factor of 5.9 in favour of the Hispano. Using muzzle power, 1 Hispano equals 3.74 Brownings. (I'm not sure the US Navy used anything better than a rule of fist - arriving at an integer number is such a comparison doesn't look overly accurate.)

Well, notable thing is that there is no reason to believe that US Navy rating - despite what ever way it's created - is some how biased. They choosed Hispano after war; 4 x 20mm, not 2 x 20mm.

gripen

gripen · « **Reply #130 on:** October 10, 2006, 01:33:12 PM »

Quote

Originally posted by gripen
... wrong impression of hitting probability, which is in the case of Hispano roughly 20% lower for each gun due to ROF at given time frame.

My mistake, wrong wording. Should be: ... wrong impression of number of hits which is in the case of Hispano roughly 20% lower for each gun due to ROF at given time frame.

gripen

Charge · « **Reply #131 on:** October 10, 2006, 01:58:13 PM »

"The effect of the round naturally depends on target - historically the M2 did well against German fighters."

I'd say that particular statistical effectiveness depended from other reasons. However, I'm not saying the Jug had bad weaponry. IIRC in Meimberg's memoirs he was shot down by a Jug a couple of times, and when the Jug did hit his 109 the plane was pretty much in pieces and it was time to bail out. I think that if the Jug had had 20mms he would have been dead.

But still the 109 was armed with only one MG151/20 for some time and I think for typical use of that aircraft it was enough. E.g. Marseille's success was indication of this. But the shooter had to be accurate to be successful with single 20mm. The 4x20mm of FW190 favored the average shooters better.

-C+

gripen · « **Reply #132 on:** October 10, 2006, 02:34:22 PM »

Charge,
As you are Finnish speaking, you probably know how extreme can be pilot's expriences on effect of the weapons on various targets. One well known extreme is Sarvanto's case; six DB-3 Bombers in 5 minutes with a Fokker D.XXI and 4 x 7,7mm MG. Another extreme can be Karhila's case after bombing of the Lappeenranta base 2.7.1944, Karhila (known as a good shooter and one of the few Finnish aces who preferred wing cannons in Bf 109) was flying the MT-461 with wing cannons and met six Il-2s, used all his ammunition from close range but could not get any of them (story can be found from SILH 2/2001).

gripen

Krusty · « **Reply #133 on:** October 10, 2006, 03:13:05 PM »

Individually, if a 20mm round hits, it can be 3-5 times stronger than any single US 50cal impact.

However, consider that 2x Hispanos firing at 600rpm does 20 rps (rounds per second). A battery of 8 50cals firing at 500rpm does 66 rps.

Going by the example of a 3 second burst (already shown) that means the Hispanos fired 60 rounds total, only a few of which would have hit. The Brownings would have fired 198 rounds total, well over half of which would have hit the target.

In my perspective, a couple scattered 20mm hits is nothing compared to over a hundred 50cal impacts (conservatively estimating half weren't scattered in the screenshot dispersion), all in the same area.

Mind you, just an opinion based on all the info already presented (rates of fire looked up on the Internet)

HoHun · « **Reply #134 on:** October 10, 2006, 03:57:12 PM »

Hi Krusty,

>Individually, if a 20mm round hits, it can be 3-5 times stronger than any single US 50cal impact.

>However, consider that 2x Hispanos firing at 600rpm does 20 rps (rounds per second). A battery of 8 50cals firing at 500rpm does 66 rps.

Good approach.

It's the same as this one: L = Nf * Ph * Pk

As you see, the difference in number of rounds fired and probabilty of kill multiply, so L (Hispano) = 60 * 4.9 * PK * Ph while L (Brownings) = 198 * 1.0 * PK * Ph. (Introducing PK of unknown size as lethality of 1 Browning projectile.)

That yields:

L (Hispano) = 294 * PK * Ph (Hispano)

L (Browning) = 198 * PK * Ph (Browning)

Note that just as Hilts already pointed out, the Ph figures for both weapons are different. Ph does of course depend on the situation.

>Going by the example of a 3 second burst (already shown) that means the Hispanos fired 60 rounds total, only a few of which would have hit. The Brownings would have fired 198 rounds total, well over half of which would have hit the target.

Hm, I don't understand how you assign hit probabilities here. If the Browning has Ph > 0.5, I can't imagine the Hispano having Ph = 0.1 or something. They both share a very flat trajectory out to 700 yards at least, with just a couple of inches deviation from the common sight line.

>In my perspective, a couple scattered 20mm hits is nothing compared to over a hundred 50cal impacts (conservatively estimating half weren't scattered in the screenshot dispersion), all in the same area.

Hm, it would be helpful to have an aircraft silhoutte in that diagram. At 1000 yards, it would probably be surprisingly small ...

Regards,

Henning (HoHun)