Bf-109s and FW190s against B17s

[Shortround6]

Greg, a P-47 with eight guns and 425rpg carried about 1335lbs worth of guns and ammo, now add the gun mounts, charging/firing systems, gun heaters and ammo boxes/feeds.
An Armament system that heavy requires a larger fighter than than a 600lb armament system, even if just 20 sq ft of wing to carry the extra weight at 40lbs per sq ft.

I did say there were two other reasons, One was, as you so nicely illustrated with the photos was the turbo system. The second reason was the 305 US gallons of fuel in fuselage between and under the cockpit and engine. roughly double the fuel of a P-40, or British Merlin powered fighter or a bit less than double what a Fw 190 carried.
Try sticking three 55 gallons drums worth of MORE fuel inside any of those air craft and see how fat their fuselages get
Again the weight may require a bigger wing than the fighter carrying 120-160 US gallons of fuel.

With the guns and ammo their wasn't a lot of room in the wing for fuel. The P-47N extended the wing and used the extra space for more fuel.

Not all of the 22 sq ft of added wing area was used for fuel but without the wing stretch fitting that amount of fuel in plane would have been very difficult.

Sorry if I made it sound like the .50 cal battery was the main cause of the size of the P-47.

 

[Shortround6]

I Would also note that the Battery of eight .50 cal guns and the amount of ammo also helped fuel the requirement for the R-2800 engine and the 305 gallons of Fuel.
If the Army had been happy with say, four .50 cal guns and 300rpg ( a weapons load of about 650lbs, not including accessories) then the required performance of 400mph at 25,000ft might well have been meet by using a smaller engine. The smaller engine would require both less fuel and a smaller/lighter wing to lift it. The smaller airplane would require smaller landing gear on so on.

With the Army asking for six guns minimum and preferring eight the need for the R-2800 and the turbo was pretty much a done deal and the rest of the airplane followed.

Please note that most other early war 2000hp class fighters with heavy armament were also big airplanes. Late war means better fuel and engines could provide the wanted power at less weight and volume. Also note that the FW 190 was planned for much less armament than it wound up with. What got shoehorned in later could be different than what the plane was planned around.

 

[pbehn]

How many hits did all that turbo tubing need to make it inoperative?

 

[stona]

Also note that the FW 190 was planned for much less armament than it wound up with. What got shoehorned in later could be different than what the plane was planned around.

True, but it was planned around a 1500 hp engine and for four rifle calibre machine guns (MG 17) and two 20mm cannon (MG FF/M) which was pretty good for a fighter of its time. It wasn't intended to be a night fighter and the fleets of US day time bombers wouldn't turn up for some time.
Cheers
Steve

 

[drgondog]

The P-47 was 'late to the dance' to introduce increased internal fuel because a.) there was no way to introduce new 'extra' 70 gallon tank under the cockpit with a kit like the 85 gallon tank in the Mustang B and P-38J leading edge 55 gallon tanks, and b.) re-design the wing was a long lead time activity (P-47N). This is why the P-47D remained in Penetration and Withdrawal escort as the P-38J and P-51B took the target escort in March 1944 through VE Day, The 56FG P-47M and late P-47D with factory 70 gallon fuselage tank COULD have gone to Berlin after July with production P-47D-25, but at that time the decision was made to convert all P-47 and P-38 FG's (except 56FG) to P-51

 

[Shortround6]

I would note that the later P-47Ds had higher powered engines, although using water injection for take-off was questionable in 1943/early 44 (if ever?) , they got the paddle bladed prop and they may have had the benefit of longer runways than the P-47 planning of 1940/41 was allowing for.
Point is that the operating conditions a plane works under could change quite a bit from those envisioned when it was still on paper.
It is those operating conditions, length of runways, take-off power, desired payload, range, performance and so on the help decide how big a plane is when designed.
As the conditions change the big plane gets more capable but it is also possible to build a smaller plane to do the original job if fuel, engines, propellers and runway conditions all change.

Planes were usually the size they were for reasons that made sense at the time of design.

 

[tomo pauk]

The P-47 was 'late to the dance' to introduce increased internal fuel because a.) there was no way to introduce a 70 gallon tank under the cockpit with a kit like the 85 gallon tank in the Mustang B and P-38J leading edge 55 gallon tanks, and b.) re-design the wing was a long lead time activity (P-47N). This is why the P-47D remained in Penetration and Withdrawal escort as the P-38J and P-51B took the target escort in March 1944 through VE Day, The 56FG P-47M and late P-47D with factory 70 gallon fuselage tank COULD have gone to Berlin after July with production P-47D-25, but at that time the decision was made to convert all P-47 and P-38 FG's (except 56FG) to P-51

There was never a 70 gal fuselage tank on the P-47. The type started with two fuselage tanks, main with 205 gals, and reserve (or 'auxiliary') with 100 gals, for obvious total of 305 gals. The main tank was made taller, thus gained 65 gals, for total of 370 gals per P-47. New main tank was introduced with the 'bubbletop' P-47D-25, from April '44.

There were several field mods, made by technicians of the 5th AF (CO being Gen. Kenney, who else), reportedly at August 1944. One added under-seat 42 gal fuel tank, another added the form-fitting 'slipper' tank of 'about 70 gallon'. Mods were abandoned due to aircraft becoming too heavy in take-off conditions (there was several accidents during the take off phase) with all of that plus drop tanks, plus the already increased factory tankage of 370 gals.

 

[tomo pauk]

True, but it was planned around a 1500 hp engine and for four rifle calibre machine guns (MG 17) and two 20mm cannon (MG FF/M) which was pretty good for a fighter of its time. It wasn't intended to be a night fighter and the fleets of US day time bombers wouldn't turn up for some time.
Cheers
Steve

The Fw 190 was planned for two 13mm and two 7.9mm machine guns, all in the wing roots. With bigger wing installed while in prototype phase the plans for wing-mounted armament changed. Another change in armament was due to engine change. The new BMW 801 was longer and heavier than the initial BMW 139, thus, in order to have the CoG within acceptable limits, the cockpit was 'pushed' towards rear, thus making extra space between engine compartment and cockpit. That place was used to house 7.9mm guns and their ammo.
BTW - Fw 190 initially have had 1000 HP (if even so much) at 25000 ft, vs. P-47 2000 HP. Turbo was there for a reason, and it worked as advertised.

 

[stona]

Also true, but I'm not counting anything before the A-0 as the armament developed along with the rest of the aircraft before a final production version was decided. The Spitfire wasn't planned to carry eight guns, but it too was altered at an early stage.
The V-2 did indeed get 2 x MG 17 and 2 x MG 131. The V-5 with the first 801 installation only had 4 x MG 17, but that doesn't mean it was a planned service weapon installation. The A-0 got the weapons that the A-1 would eventually carry into service.

Rodeicke gives the power of the BMW 139 as installed in the V-1 as 1500 PS Startleistung (1 min). Kurzleistung (5min) 1410 PS at 4,500m. Erhote Kurzleistung (30 min) 1270 PS, 4,900m. Dauerleistung 1150 PS, 5,400m.
I'm sure that by 7500 - 8000 m it was struggling, but I can't put my hand on a chart..

Cheers

Steve

 

[tomo pauk]

...
Rodeicke gives the power of the BMW 139 as installed in the V-1 as 1500 PS Startleistung (1 min). Kurzleistung (5min) 1410 PS at 4,500m. Erhote Kurzleistung (30 min) 1270 PS, 4,900m. Dauerleistung 1150 PS, 5,400m.
I'm sure that by 7500 - 8000 m it was struggling, but I can't put my hand on a chart..
...

I've draw the red line that starts at about 4.5 km with 1410 PS. At 25000 ft (~7.6km) it can't make 950 PS.
Original graph represents 30 min (Steig & Kampfleistung) for the BMW 801C, with different lines for different level speeds (= different level of ram effect). 'Abgas-strahlshub' is exhaust thrust, in kg obviously.

 

[Shortround6]

We are back to designed for and developed to. The German MG 17 may have been a bit heavier than the .30/.303 Browning but the ammo is close enough ignore the difference. The MG 131 was about 12kg lighter than a US .50 cal and the ammo was around 4kg per hundred rounds lighter (not including links/belt on either). The MG 131 apparently took a longer time to develop than planed forcing the substitution of other guns. The MG/FF cannon is actually about 1kg lighter than the .50 cal Browning although that may vary depending on accessories, the MG/FF does need the drum.
An FW 190 with either four MG 17s and two MG/FFs or two MG17s, two Mg 131s and two MG/FFs is carrying little more, if as much, as a P-40C, in part because the P-40 was carrying 380rpg for the .50 cal guns, probably around 40kg too much.

It is not until the FW gets the wing root cannon that it is carrying a really substantial load of weapons (referring to weight, not getting into an argument about effectiveness here). I would note that the FW 190 got a bigger wing after the first few prototypes in order to handle in the increase in Military load (or perhaps the 801 engine was heavier than 139?).

 

[stona]

It is not until the FW gets the cannon that it is carrying a really substantial load of weapons (referring to weight, not getting into an argument about effectiveness here). I would note that the FW 190 got a bigger wing after the first few prototypes in order to handle in the increase in Military load (or perhaps the 801 engine was heavier than 139?).

The Fw 190 did get the cannon with the A-0, a '0' series being difficult to find a British equivalent for, a sort of prototype of the series production standard, certainly not a test or prototype machine like the V series. As a result the A-1 also had the wing root cannon. The Fw 190 was cannon armed from its earliest service incarnation.

The wing loading of the V-5 machine with the 801 series engine was 228 Kg/m2 compared with 187 Kg/m2 for the V-1 and this led to the larger wing being developed. Where the extra weight came from I don't know.

Cheers

Steve

Edited 'wing root cannon' to 'cannon'

 

[tomo pauk]

...
It is not until the FW gets the wing root cannon that it is carrying a really substantial load of weapons (referring to weight, not getting into an argument about effectiveness here). I would note that the FW 190 got a bigger wing after the first few prototypes in order to handle in the increase in Military load (or perhaps the 801 engine was heavier than 139?).

801 was 160 kg/~350 lbs heavier than the 139.

The Fw 190 did get the wing root cannon with the A-0, a '0' series being difficult to find a British equivalent for, a sort of prototype of the series production standard, certainly not a test or prototype machine like the V series. As a result the A-1 also had the wing root cannon. The Fw 190 was cannon armed from its earliest service incarnation.

The wing loading of the V-5 machine with the 801 series engine was 228 Kg/m2 compared with 187 Kg/m2 for the V-1 and this led to the larger wing being developed. Where the extra weight came from I don't know.

Cheers

Steve

The Fw 190A-1 was with 4 MGs and two MG FFM cannons. A-2 got the wing root MG 151/20E cannons.
Item 7 lists ammo for the wing (root) MG-17s, item 8 lists ammo for the wing MG FF(M)s:

 

[bobbysocks]

this is a chicken or the egg question....did they put 8 50s in the bolt because they had a plane with the size that could accommodate them or did they have the 8 guns as a requirement from the very beginning and have to build around that??

 

[Shortround6]

It's an egg, Nobody designs a fighter plane to be about 80-95% complete and THEN tries to decide what guns to put in it.
That is what the last part of this thread is about.
If you don't know what the payload will be (weight and volume of guns) it is mighty hard to design the airplane.

Please remember that the P-38 and P-39 started with two requirements, both wanted the same armament, the same speed, the same altitude. the Difference was that the requirement that lead to the P-38 required twice the endurance than the requirement that lead to the P-39. Just providing the extra fuel wound up leading to the two engines instead of one and all the rest. The P-38 and P-39 diverged form the initial requirements before they flew but that is where they started.

Doubling the guns from four to eight could mean adding 300kg or more to an aircraft, not to mention trying to fit in the gun bays. The P-47s landing gear shortened up 9in as it retracted to help leave room for the guns. See middle picture in post #61. Also see photo of original XP-47 with Allison.

Also Seversky/Republic had orders for the XP-44 which was pretty much an XP-43 Lancer with the R-1830 taken out and a Turbo-ed
R-2180 of about 1400hp put in. Army may have wanted six guns on that one. P & W didn't want to fool around with the 14 cylinder R-2180 so that engine source dried up.

Please note that the US Army requested some very heavy armaments in a number of proposals/prototypes that essentially doomed them. The whole Curtiss P-53/P-60 saga ( and even cutting the number of guns after the initial design/construction couldn't save them. Another eight .50cal fighter to start with.
Multiple 37mm cannon in the XP-54 is another one.

 

[wuzak]

Multiple 37mm cannon in the XP-54 is another one.

I believe it was two, having started with only 0.50" or 0.50" and 20mm.

This change, along with the tilting mechanism for compensating the different trajectories between the 37mm and 0.50" guns installed, the pressure cabin, turbos, etc resulted in the empty weight of the XP-54 more than doubling.

The XP-67 was to have 6 37mm.

 

[stona]

The Fw 190A-1 was with 4 MGs and two MG FFM cannons. A-2 got the wing root MG 151/20E cannons.
Item 7 lists ammo for the wing (root) MG-17s, item 8 lists ammo for the wing MG FF(M)s:

As I said, the type was cannon armed from its earliest service version. The cannon were initially in the outer wing position (outside the propeller arc for obvious reasons), not the wing root as I erroneously typed above (now corrected).

The armament varied through the V/A-0 aircraft.

Whatever the original intention, the armament clearly developed along with the rest of the aircraft.

Cheers

Steve

 

[stona]

It's an egg, Nobody designs a fighter plane to be about 80-95% complete and THEN tries to decide what guns to put in it.

But they certainly alter the weapons requirement after the aircraft comes off the drawing board. Both the Spitfire and Hurricane were designed around four guns. The eight gun requirement was part of the conflation of various specifications. Both Hawker and Supermarine said they could fit eight guns ("without trouble or delay" in Mitchell's words for what would become the Spitfire) but they were NOT part of the original specification about which both fighters were designed and amounted to a doubling of the armament. The original Hawker monoplane, which became the Hurricane was designed with two wing guns and 'two interrupter guns in the fuselage', eight wing guns is very different.
So whilst the Supermarine fighter was still at the mock up stage (not 80-95% complete) the Hawker fighter was more avanced, and required a completely new set of wings for the new armament. Fortunately the nature of the design made this more easy than it might otherwise have been. The initial idea was to build the eight gun wings as a back up plan, holding them "in reserve", but this was soon abandoned and we all know the Hurricane in its eight gun form.
To compensate for the increased armament the requirement to carry 4 x 20lb bombs was dropped and the endurance, i.e. fuel capacity/load, reduced.
Cheers
Steve

 

[Shortround6]

But they certainly alter the weapons requirement after the aircraft comes off the drawing board. Both the Spitfire and Hurricane were designed around four guns. The eight gun requirement was part of the conflation of various specifications. Both Hawker and Supermarine said they could fit eight guns ("without trouble or delay" in Mitchell's words for what would become the Spitfire) but they were NOT part of the original specification about which both fighters were designed and amounted to a doubling of the armament. The original Hawker monoplane, which became the Hurricane was designed with two wing guns and 'two interrupter guns in the fuselage', eight wing guns is very different.
So whilst the Supermarine fighter was still at the mock up stage (not 80-95% complete) the Hawker fighter was more avanced, and required a completely new set of wings for the new armament. Fortunately the nature of the design made this more easy than it might otherwise have been. The initial idea was to build the eight gun wings as a back up plan, holding them "in reserve", but this was soon abandoned and we all know the Hurricane in its eight gun form.
To compensate for the increased armament the requirement to carry 4 x 20lb bombs was dropped and the endurance, i.e. fuel capacity/load, reduced.
Cheers
Steve

Thank you for the information, but it does help my point. It also comes back to what I call "the curse of the .50cal"

The British were willing to compromise armament (the bombs) and fuel load to get the guns/ammo they wanted in an existing design.
Without that compromise what would have been the result?
A compromise of less performance?
A delay while a new aircraft/engine was worked on to give the desired performance with the desired weapons load?
A compromise that saw, air ministry officials cringing in horror, fighters equipped with something other than fixed pitch propellers


Spitfire saw the introduction of the MK II with the Merlin XII engine which was a close match to the performance of the early MK I Spitfire. Th extra engine power was used up by the weight/drag of the operational equipment added to the Spitfire in the two years after it first entered service.
Had Mitchell been given a specification for a fighter with eight guns (350rpg) armor, self-sealing tank/s, bullet proof windscreen, rear-view mirror, IFF aerials and so on, and been limited to the Merlin II or III engine, would the plane have looked different to start with?

The P-40 saw a small, but steady, decline in speed/climb from the P-40 to the P-40B to the P-40C with the fitting of more guns and protection. This was accepted by the customers. IF the Customer/s had demanded the performance of the P-40 with the armament and protection of the P-40C it would have required a new engine or a new airframe.

The "the curse of the .50cal" is that a single .50 cal with about 265-270 rounds weighs about 20lbs less than four .30/.303 guns with 334 rounds each. Just increasing the Ammo on the P-40's fuselage guns from 200rpg to 380rpg weighed about the same as a pair of .30cal guns with 500 rounds each.

If you want large batteries of .50 cal guns (6-8) with large amounts of ammo and you want to go fast high up, you need a big airplane. At least with the technology of 1941-41.

The Mustang gained about 30% in take-off power between the early Allison model/s and the P-51D with the -7 Merlin. The gain in power at 25,000ft was near 100%. But the two-stage Merlin and 100/130 fuel were unknown to North American in 1940.

 

[tomo pauk]

this is a chicken or the egg question....did they put 8 50s in the bolt because they had a plane with the size that could accommodate them or did they have the 8 guns as a requirement from the very beginning and have to build around that??

Two 'clusters' determined the P-47B/C/D etc. as we know it.
1st was the customer's requirement. Demanding the fighter that will have enough of firepower to bring down perceived enemy bombers appearing over the USA and/or it's overseas territories. The perceived bomber threat was expected to come in at high altitudes (USAF expected hi-alt bombers since they were in development in the USA itself), 20000-30000 ft, thus the new fighter was expected to fly & fight well there.

2nd 'cluster' were techincal & georgaphic realities of the day (1940-41 in the USA), ie. what is actually available in the moment, or it is in final phase of development. Heaviest weapon available that will fit in the reasonably thin wing (14% T-t-C ratio at the root) was the .50 BMG. Heavy firepower = plenty of those, with plenty of ammo -> great weight of firepower installed. The most powerful engine of the day was the R-2800, big and heavy lump of metal. In order to make plenty of power at high altitudes, it needed turbo system. Many HP = voluminous turbo ducting, intercooler and turbocharger itself -> again weight goes up. Powerful engine needs plenty of fuel, and USA was and is a big country the new fighter to defend, thus P-47 initially carried 3 times the fuel of Bf 109, Spitfire or Hurricane. All of these weight gains and customer requirements = will need a big wing, almost twice the Bf 109, or around 50% greater than the FW 190.

Republic managed to design a fine aircraft around these requirements and available techy stuff, even if we recall that P-47B was a problem no less of a problem that it was early Typhoon or early Fw 190, the P-47B never went into combat due to airframe- and engine-related problems .