Improve the P-47

[Stoney74]

Originally posted by bozon
The point HoHun is making and a few missed is that replacing mg with cannons is not a way to increase firepower but to save weight (while keeping about equivalent firepower).

I tend to agree with this, assuming the reliability of 20mm was sufficient. 684 lbs weight reduction? I'd take that anytime.

His original argument was that the change in armament would create the reduction in weight, which would allow for enough extra internal fuel to escort U.S. bombers all the way to their target and back.  Therefore, you keep the weight, you just trade armament for range.  The only problem is that, aside from his turbo to super exchange, he still hasn't explained how the change in armament frees up enough room for the extra gas.  Only the turbo/supercharger change would create space, so really, the armament question is moot without room in the airframe for the required volume of fuel.  So really, his argument should be an analysis of how much worse the high altitude performance would be and how the 2X20mm armament would compensate for it.

[HoHun]

Hi Krusty,

>In an plane as heavy as the P47, saving 600lbs wouldn't help.

It would, especially at high altitude where induced drag, which is increases with weight, plays an important role. At high altitude, you'd get a 25% climb rate increase from saving 684 lbs.

>well the M had a different engine or rating than the D which is the real reason it was such a performer.

They cut the weight to improve performance, no way around that :-) If all the goodies do no harm, why give up some of the goodies?

>Take out 2 of the 50 cals. And their ammo. How much weight does that save? Take out half the ammo on the remaining guns. Now how much have you saved.

Before: 8x ,50 Browning M2 - 375 rpg - 562 kg - 100% firepower

After: 6x ,50 Browning M2 - 187.5 rpg - 298 kg - 75% firepower

-> 582 lbs weight savings.

>You now have the same firepower as 2x20mm (6x50cal) at nearly the same weight savings.

Well, but you have only half the ammunition, too :-) You could make this change instead:

Before: 8x ,50 Browning M2 - 375 rpg - 562 kg - 100% firepower

After: 2x Hispano II - 115 rpg - 157 kg - 94% firepower

-> 893 lbs weight savings.

(Note that I doubt the accuracy of the Navy's factor of "3" between the two gun types. The Luftwaffe used a factor of 3.34 between the MG151/15 and the MG151/20, and the MG151/15 was much more potent than the 12.7 mm Browning.)

>Putting 2x20mm in a plane and nothing else was just begging for complaints.

Well, the Navy planned to replace the 12.7 mm gun with the Hispano cannon because the 12.7 mm jammed in long bursts, and the Hispano didn't. The Hispano was quite reliable in British service, and if the USAAF would have placed more management attention on the gun, it could have been available in reliable form for them, too.

>You couldn't really add more fuel. You couldn't really do much without a major redesign (like the 47N's wing).

Oh, we're talking about just 110 gallons here. As described way up in this thread, you can simply extend the engine mount a bit more to shift the centre of gravity forward and mount a small tank in the rear fuselage. The rest can be stored in the space saved in the gun bays and perhaps in small wing tanks outboards. I'm not quite sure how much fuel the P-47N could take, but I'd bet the increase was by much larger than 110 gallons.

Regards,

Henning (HoHun)

[humble]

Originally posted by AquaShrimp
The P-47 was relegated to ground attack work because of its short-commings.

But would it have really be neutered?  Cannons were far superior to machine guns in ground atttack work.  In one Korean War test, twenty 50 caliber rounds and twenty 20mm rounds were each fired into a seperate truck.  The 50 caliber rounds merely broke the drivers seat, while the 20mm rounds exploded the vehicle.

Stressed skin has been mentioned a few times to be more fragile than non-stressed, but I've never seen any confirmation of this.

This thread is long so i'm sure this has been covered but your somewhat clueless. The P-47 was an outstanding interceptor and very capable in that role. In fact it was every bit the equal of the P-51. What it didnt have was the P-51's range so as the pony was deployed the P-47 (and P-38) were redelpoyed in support of the tactical airwar.

There is a famous quote regarding the P-51 that goes something like this.

It's not the P-51's capabilities that make it special, its that it has those capabilities over Berlin....

[gripen]

Originally posted by HoHun

(Note that I doubt the accuracy of the Navy's factor of "3" between the two gun types. The Luftwaffe used a factor of 3.34 between the MG151/15 and the MG151/20, and the MG151/15 was much more potent than the 12.7 mm Browning.)

The German rating for the destruction factor in the case of the "minen" typen projectiles was based on assumption that about 400g of HE content was required to down one four engined bomber. The kinetic energy was not accounted at all because the type of the large target. Because there apparently was no "minen" type projectile for the MG151/15, this rating favors heavily MG151/20. Based on total energy (including kinetic) the difference is much smaller.

Generally the rating of German air weapons were driven by the need to destroy extremely large targets like four engined bombers. The US Navy rating was probably based on targets they usually assumed to meet in combat.

Originally posted by HoHun

Well, the Navy planned to replace the 12.7 mm gun with the Hispano cannon because the 12.7 mm jammed in long bursts, and the Hispano didn't. The Hispano was quite reliable in British service, and if the USAAF would have placed more management attention on the gun, it could have been available in reliable form for them, too.

Hm... at least according to Tony's site, the reliability problems seem to have been mostly in American version of the Hispano side delaying the Navy's move to the cannon armament, the British version being more reliable.

gripen

[Charge]

AFAIK the barrel length does not itself provide more accuracy, only better muzzle velocity and thus flatter trajectory. Thus I wouldn't be surprised if MK108 was more accurate than either Browning or Hispano if scatter was concerned. But MK108's shortcoming is bad trajectory. Imagine trying to hit a bomber at long range by "dropping" a 30mm round on it...

I'm not sure if I read somewhere that Hispano II was prone of jamming because of drum feed. Was the H II never made as belt fed?

Hisso V was belt fed with shorter barrel and better RPM, anybody knows if it was more accurate than H II?

-C+

[gripen]

The the belt fed mechanism for the Hispano 404 was originally designed in France (by Chattellerault ??) and IIRC the first plane to utilize it was the MB.155. The Brits made their own version of this system and it replaced the drum fed mechanism around late 1941/early 1942.

Regarding the accuracy, the high velocity and flat trajectory are advantages as well as some amount of dispersion because vast majority of the error comes from the shooter (error being practically allways systematical). I've posted some German data here.

gripen

[Charge]

"The Brits made their own version of this system and it replaced the drum fed mechanism around late 1941/early 1942."

So the Hisso II was already modified for belt feed.

I have to disgree with you to some extent Gripen. If you look at the dispersion patterns presented previously and consider the size of the a/c then I'd say that the smaller dispersion will give you higher probability of hits at extreme ranges.

But when you are maneuvering and shooting at the same time the pilot's accuracy plays a huge role, of course. At some ranges the disperison can have good effects, too, but getting scattered hits with weapon which has ammo that does not have much effect will not do you much good.

Anybody have the disperison pattern for P38's Hispano?

-C+

[gripen]

Well, the problem of the Hispano patterns posted by Widewing is that the concentration of the bullets is not in the target area (notable drop at 1000 yards if compared to to patterns of the P-47). Disperion itself is not particularly different based on just looking the patterns; density of the pattern of the P-47 is greater due to more guns and higher ROF.

According the data I posted (linked above), even a good shooter itself cause dispersion which is far greater than dispersion caused by the guns (steady target). Note also that usually 400 yards is considered as the limit of practical shooting range (more in the case of the large bombers).

gripen

[Charge]

"Well, the problem of the Hispano patterns posted by Widewing is that the concentration of the bullets is not in the target area"

That is what troubles me. IIRC the patterns should look pretty much the same for Hisso and 50Cal. It would be intersting to see the actual patterns.

I have too the "Lentoampumaoppi" but the actual firing test did not have the luxury of steady target at set distance and autopilot to keep the plane still while shooting as we have in AH.

IRL the effect of pilot ability was certainly a major factor when accuracy was measured at reasonable firing distances, not to 1000yds.

-C+

[Knegel]

Originally posted by HoHun
Hi Krusty,

Before: 8x ,50 Browning M2 - 375 rpg - 562 kg - 100% firepower

After: 6x ,50 Browning M2 - 187.5 rpg - 298 kg - 75% firepower

-> 582 lbs weight savings.

>You now have the same firepower as 2x20mm (6x50cal) at nearly the same weight savings.

Well, but you have only half the ammunition, too :-) You could make this change instead:

Before: 8x ,50 Browning M2 - 375 rpg - 562 kg - 100% firepower

After: 2x Hispano II - 115 rpg - 157 kg - 94% firepower

-> 893 lbs weight savings.


Regards,

Henning (HoHun)

Hi,

again he dont see the pretty important factor of time to shoot!!

8x .50 Browning M2 - 375 rpg = 29sec time to shoot.

6x .50 Browning M2 - 187 rpg = 14,4 sec time to shoot.

2 x Hispanno II - 115rpg = 11,5sec time to shoot.

Afaik the P47 already was one of the best high alt performer in WWII, probably the best build in high numbers, so a weight advantage wasnt realy needed.

Imho the damage power of 20mm´s in relation to .50cals while fightercombat get overvalued anyway.

A fighter hand much more vital areas than a Bomber and a good hitprobability the pilots only could gain on distances where even the .50cal was likely to cause damages. Therefor every .50calround  had a not to bad probability to cause vital damages, while also the tracerrounds of the 20mm´s dont was as effective and also the 20mm´s 1st had to get through the surface to cause real bad damages and i guess this also wasnt always the case.

Specialy while escort missions its better to damage a enemy than to miss him at all and the probability to at least damage a enemy increase with fireratio and time to shoot and reliability of the guns.

The .50cal may have tend to jam at long bursts, the 20mms simply dont had enough ammo to make long bursts. Let jam 2 out of 8 .50cal, the pilot still had the same time to shoot still with the firepower of 2 x 20mm.

I personally dont would like to be some hundret miles behind the frontline, trying to keep enemy fightes away from my bombers with only 115rounds per gun in 2 guns. I would better choose 4 x .50cal with 475 rounds per gun for this task to safe weight.  
 
Greetings,

[Charge]

From another board by Butch2k:

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
H/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
------------------
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

Notice that the 151/20 dispersion is much bigger in wing installation even in FW190 which has a rigid wing. So if the same percentage for added dispersion would be added to wing mounted Browning it would have dispersion of what? Roughly 13 mils?

-C+

PS. Knegel, your attitude troubles me. If you have an issue with somebody throw him a PM and sort it out.

[gripen]

Originally posted by Charge

I have too the "Lentoampumaoppi" but the actual firing test did not have the luxury of steady target at set distance and autopilot to keep the plane still while shooting as we have in AH.

While some what simplified, it's a good book, giving good view to the complexity of the aerial shooting.

Non steady target and other factors would generally cause increasing error which is mostly systematical, therefore also some amount of dispersion will help.  

gripen

[Krusty]

I made an interesting find on the Inter-web-a-majiggy today, when looking for something else.



So if you took the SC and put it behind the engine, like the hellcat (for example) you wouldn't need all that ducting and piping and you'd have room for almost another full "main" tank. -- probably could double the internal tankage. However, the SC takes up nearly all of it (certainly not enough room left for even a small tank.

[Krusty]

Charge:

I don't buy those theoretical max numbers. Those "theoretical max" numbers seem VERY high, especially considering the same gun in the same central position (tested in nose vs theoretical in wing root) has more than double the dispersion. Doesn't add up. At least to me.

[Krusty]

Going back to the cutaway view: