Structural weight of early U.S. fighters compared to Spitfire Mk1 and Bf-109,

[to_change22]

As I've been reading through various resources on pursuit fighter development in WW2, I've noticed a weird trend that I'd love to get some advice on. Simply put, the structural weight of 1935-1940 era U.S. pursuit fighters (single-engined) was larger than the Bf-109E or the Spitfire Mk1. This was partly responsible for their poor climbing performance (given than climbing performance is proportional to P/W ratio).

Here's some data with sources:

Curtiss P-40A (without armor or self-sealing fuel tanks): Gross weight = 6782 lbs
- Source: http://www.wwiiaircraftperformance.org/P-40/P-40_Official_Summary_of_Characteristics.pdf
Curtiss P-40B (with armor, self-sealing fuel tanks, and 2 additional machine guns): Gross weight = 7326 lbs
Bell YP-39 & P-39C (with armor and self-sealing tanks): Gross weight = 7000 lbs
- Source: Bell YP-39 Airacobra

Spitfire Mk1 Gross Weight: 5,935 lbs.
Bf-109 Gross Weight: 5,875 lbs (sources vary).

What accounts for this drastic difference in weight? References and people with aero-engineering experiences would be greatly appreciated

 

[BarnOwlLover]

USAAF/USN load standards were different than the European or Japanese standards of the time. This lead to US fighters being overbuilt in some areas. I'd do a quick read up on the development of the lightweight P-51 Mustangs (XP-51F/G, P-51H) for a quick introduction to how this changed during World War II. There's also other members here who can provide a more detailed explanation than I can.

 

[pbehn]

The P-36 was contemporary with late 30s European designs empty weight 4,567 pounds gross weight 5,650 lb/

 

[Shortround6]

To some extent the US aircraft were bigger, at least compared to the 109.
When you build 40-60 extra sq ft of wing it has to weigh something.
Now if you want that extra 40-60 sq ft of wing to survive an 8 G turn or pull out maybe it has to weigh a little more?
P-36 to P-40 gained around 250lbs of weight in the wing structure as the powerplant went up in weight, protection was added and more guns and ammo were added.
I will bet they were not using the same tires on a P-40N that they were using on a P-36. They may have been the same size but the later tires may have used more plies and more rubber to handle the greater loads.

Compare the war loads. Like the weight of armament.
Everybody was going to use a pilot, most everybody was going to use about 100-130US gallons of fuel (for early fighters) for combat. US fighters carried more fuel for ferrying.
Most everybody was going to use a radio and so on.

The US did use stronger construction but some Italian machines were built even stronger but be careful.
The were the simple straight line G loadings (banked turn or dive pull out) and there were negative G loadings and there were Loads imposed yawing or spinning and there were loads imposed by landing (bouncing off the ground). Unless you have a list of such loads it is hard to say. And different classes of aircraft were built to different standards even in the same country. You don't want to try to pull 4 Gs in a loaded DC-3.

 

[tomo pauk]

What accounts for this drastic difference in weight? References and people with aero-engineering experiences would be greatly appreciated

Until the people with experience in aero-enginering chime in, here is the 'IMO'.
A lot of weight difference vs. Euro fighters was due to the much greater fuel load, talk 70-80% more for the P-39C, or a P-40 from 1940. Extra 70 US gals of fuel = extra 420 lbs. Bigger fuel system weight more even without the fuel itself. Heavier fuel system dictates stronger airframe to support it for the same G load, and stronger airframes are bound to be heavier than less strong airframes.
P-39 also carried a far more substantial weight of armament and ammo than European fighters, so again the weight spiral goes up. Early P-40 saw the weight increase of the wing sub-assembly, due to the 'old' wing from P-36 experiencing wrinkles under high G-loads.
Heavier aircraft will require heavier undercarriage.

Bf 109 have had the advantage of starting out as a small and light fighter, so, by the time the DB 601 was installed in it, the weight increase was mostly 'localized' on the powerplant (includes propeller and cooling systems) and fuel systems.

Real jump in the weight happened with US aircraft when they switched to protected fuel system (with P-39D for the Bell fighter, while in Curtiss fighter the increase was gradual), with introduction of protection for pilot (again the pre-mid 1941 versions were mostly lacking that), as well as when P-40 went to 6 HMG battery (with P-40E).

More knowledgable members will probably chime in wrt. differences about the G limits, IIRC British have far more relaxed G limit for side loads than what what was demanded in the USA.

 

[Shortround6]

The 109 was designed for a 950-1000lb 600-700lb engine, two 7.9mm machine guns (or one 20mm cannon/no machine guns) 235-270 Liters of fuel.
Everything else was stuffed in later, they did a very, very good job of stuffing more things in.
BUT there was limit what it could do, even with beefing up.

Spitfire and Hurricane had limits too. Light plane with big wings trying to lift more guns than anybody else in the mid/late 30s. Many European planes were trying to operate out small airfields. British took too long to be convinced the variable pitch propeller was NOT a passing fad.
Some selected numbers for the Spitfire I.

Gross weight..................... 5875lbs

Load carried........................1585lb
Guns,ammo, etc...................685lb
Petrol........................................646lb


Prop hub..............................36lb
Wood prop/spinner........96lb
Radiator...............................98lb
cooling system..................56lb
Cooling fluid....................142lb


In an air cooled fighter the last 3 items don't exist. A Plane with constant speed prop (assuming about the same power) has propeller weight of 2 1/2 to 3 times the weight.
German 109 with four machine guns had about 1/2 the weight for the guns but 5/6 the weigh of ammo (500rpg (?) instead of 300rpg)
P-36 was designed for a single .50 and a single .30 (roughly the equal of 4 small machine guns in weight/ammo)
P-40 was a P-36 with a liquid cooled engine and double the guns/ammo. Then they went to four wing guns and more ammo.
P-40D/E was another story, with 6 guns and full ammo (1870 rounds) it was carrying 945lbs of just guns and ammo, no etc (gun sight, flares, and so on,)

If you are designing for 8 Gs the P-40E wing needs to hold an additional 2400lbs more than the 8 gun Spitfire wing. Now throw in the "safety factor" The US wanted a 50% safety factor, the British might have been OK with a little less (? Correction welcome)

A P-40 with four guns and 250rpg (1000 rounds total) was carrying about 400lbs less than than a P-40 with 6 guns and full ammo (there were about 15-16lbs worth of misc. equipment for each gun). Carrying too much weight of guns/ammo was at least as much of a problem as excess structural weight.
Also that the P-36/French 75s had a lot trouble with their wings. They may not have broken them in flight (or not often) but bent-broken wings when landing on poor airfields was a major concern.

 

[blueskies]

This is from various weight surveys I've collected;

Weights of wing group / wing area = weight per sqft

P-51b= 1070 / 235 = 4.55
P-38= 1813.6 / 328 = 5.53
P-47D= 1459.6 / 300 = 4.87
P-39= 934.6 / 213 = 4.39
Hawk 75= 842 / 236 = 3.57
Spit MkII= 972 / 242 = 4.02
190A3= 1113 / 197 = 5.65
109f-2= 748 / 173 = 4.32

Landing gear - gear weight / empty weight = % We
P-51b= 775 / 7015 = 11
P-38= 885.94 / 12195 = 7.3
P-47D= 1123 / 9957 = 11.3
P-39= 516.6 / 6020 = 8.6
Hawk 75= 572 / 4483 = 12.8
Spit MkII= 459 / 4517 = 10.2
190A3= 515 / 7424 = 6.9
109f-2= 264 / 5097 = 5.2

Landing gear weight is very tricky to compare without knowing the design loads, ie was it 4g @ normal gross or @ MTOW? Regardless of that the US generally had higher gear loading requirements then Europe. When the lightweight mustangs were built nearly half the structural weight savings came from the gear.

 

[PFVA63]

Blue Skies,
Thanks for sharing your data. I went aherad and populated your data ontop of some plots that I have put together for US type WWII era fighters, based primarily off tyhe book "America's 100,000" by Francis Dean, but with some additional data that I have found on the Hawk 75 on the internet.

In general, your data for the US type planes agrees very well with the data in Dean's book, and the data thaat you have for other nation's planes fall close to the trend lines for these points.

The three main things that stick out to me looking at the plots are that 1) the Gear Weight for the Me-109 fall towards the lower range of the data provided (near the points for the F4F family with their short stubby landing gear), 2) the wing size for the German planes tends to be a bit smaller than that for the US and UK planes that there is data for, and 3) the wing weight for the FW-190 seems to fall maybe a bit above what the trend line would look like if I traced it down to the lower winf areas of the German planes.

In general though, the Spitfire Mk II data appears to me to fall very well in line with the trends for the US data.

Regards

Pat

 

[marathag]

Nice visual for size

 

[Jugman]

Keep in mind some of these fighters ( F4F, P-39, P-47, BF 109) do not have wing center sections so their wing weights look comparatively better than they actually are.

 

[PFVA63]

Keep in mind some of these fighters ( F4F, P-39, P-47, BF 109) do not have wing center sections so their wing weights look comparatively better than they actually are.

Hi,
I believe that the wing weight category used by the US during this time period could included "fuselage carry-through structure" as part of the "Wing Group", as shown in the link below for the F4F-4 from the wwiiaircraftperformance.org website

http://www.wwiiaircraftperformance.org/f4f/f4f-4-detail-specification.pdf

Specifically, the 1181 lb Wing Group weight is listed as consisting of;

1030lb for the wings
38 lb for the ailerons
43 lb for the flaps
70 lb for the fuselage carry-through structure

Similarly the specifications for the F4U-1 from the same site lists a 2121.7 lb Wing Group Weight for that aircraft including;

1088 lb for the center section
872.2 lb for the outer panels
6.6 lb for the wing tips
57.6 lb for the ailerons
97.3 lb for the flaps

http://www.wwiiaircraftperformance.org/f4u/f4u-1-detail-specification.pdf

Regards

Pat

 

[Jugman]

The F4U uses a wing center section that uses the spar as the carry-through structure. This is a permanent part of the wing center group assembly and not a separate part.

The F4F is what I was thinking of.

This doesn't appear to be the case for the P-47. Dean lists the the weights of the wing and body groups of the P-47D as ~1450lbs each. For a total weight of ~2900lbs. On the other hand, McCutcheon list a wing group weight of 1950lbs and a body group weight of 740lbs for a total weight of 2690lbs. These are for the proposed XIV-2220 conversion of a P-47B. The only relevant structural difference between the two is the 8" plug in the P-47D. Interestingly the land gear group weighed only 840lbs. for the P-47B or some 300lbs lighter.

 

[Jabberwocky]

Some weights for 1936-1940 US Pursuit fighters. Source is Joe Baugher's various webpages.

	Empty	Normal loaded	Gross	Maximum
P-26A	2197​		2955​
P-26B	2302​		3062​
P-26C	2332​		3075​
P-35	4315​	5599​
P-35A	4575​	6118​
P-36A	4567​	5470​
P-36C	4620​	5734​
Hawk 75A-4	4483​		5692​
Hawk 75A-4	4541​		5750​
Hawk 75M	3975​		5305​
Hawk 75O	3975​		5172​
P-39C	5070​		7075​	7300​
P-39D	5462​		7500​	8200​
P-40	5376​	6787​		7215​
P-40B	5590​	7326​		7600​
P-43	5654​		7810​	7935​

 

[Wild_Bill_Kelso]

As I've been reading through various resources on pursuit fighter development in WW2, I've noticed a weird trend that I'd love to get some advice on. Simply put, the structural weight of 1935-1940 era U.S. pursuit fighters (single-engined) was larger than the Bf-109E or the Spitfire Mk1. This was partly responsible for their poor climbing performance (given than climbing performance is proportional to P/W ratio).

Here's some data with sources:

Curtiss P-40A (without armor or self-sealing fuel tanks): Gross weight = 6782 lbs
- Source: http://www.wwiiaircraftperformance.org/P-40/P-40_Official_Summary_of_Characteristics.pdf
Curtiss P-40B (with armor, self-sealing fuel tanks, and 2 additional machine guns): Gross weight = 7326 lbs
Bell YP-39 & P-39C (with armor and self-sealing tanks): Gross weight = 7000 lbs
- Source: Bell YP-39 Airacobra

Spitfire Mk1 Gross Weight: 5,935 lbs.
Bf-109 Gross Weight: 5,875 lbs (sources vary).

What accounts for this drastic difference in weight? References and people with aero-engineering experiences would be greatly appreciated

I know in part it's the wings. P-40, at least the military versions, had a wing stressed to 10G. More spars etc. Which did have some benefits.

 

[BarnOwlLover]

It should also be noted that the P-51H Mustang was built to 7.33 g loading at approx 9500 lbs, which made it pound for pound stronger than the P-51D (aside from landing gear) at the same weight. The original Mustang was designed for 8 g at 8000 lbs, but later variants weren't re-stressed for the weight increases, so max loading dropped as weight went up.

The P-51H was basically a production version of the XP-51F and G models, but standardized on 6 .50 MGs instead of 4, had increased fuel capacity (50 gallon fuselage tank and 105 gallon wing tanks, vs only the 105 max fuel tanks of the F/G and the 92 gallon wing tanks + 85 gallon fuel tank in most P-51Ds), and was re-stressed to take on that added weight without the 7.33 g limit dropping off at combat weight, as well as carrying a 1000 lb bomb under each wing and up to 10 HVARs when no bombs or drop tanks were carried.

The design of the lightweight Mustangs also proved instrumental in the development of the P-/F-82 Twin Mustang.

 

[Wild_Bill_Kelso]

Another big thing is fuel. US was expecting to have to fight at a distance, not on home territory. P-40s and Wildcats carried a good bit more fuel than Spitfires, Hurricanes, Bf 109s or Yak-1s. Lightnings, P-51s and P-47s, Corsairs and Hellcats carried much more fuel. So that is a lot of weight right there even for the empty (but self sealing) fuel tanks, and the structural strength to carry all that gas.

 

[elbmc1969]

Another big thing is fuel. US was expecting to have to fight at a distance, not on home territory. P-40s and Wildcats carried a good bit more fuel than Spitfires, Hurricanes, Bf 109s or Yak-1s. Lightnings, P-51s and P-47s, Corsairs and Hellcats carried much more fuel. So that is a lot of weight right there even for the empty (but self sealing) fuel tanks, and the structural strength to carry all that gas.

Yeah, the P-40 had at least twice the range of the Spitfire, given roughly contemporary variants. That gave a much better ability to escort tactical bombers.

Every theater was screaming for more Lightnings because their range was so incredibly useful.

 

[Shortround6]

Another big thing is fuel. US was expecting to have to fight at a distance, not on home territory.

Not quite true.
The US did expect to fight on home territory, trouble was that the home territory was huge.
Almost 540 miles from Pensacola to Miami.
470 miles from Boston to Norfolk/Newport News
680 miles from Seattle to San Francisco.
480 miles from San Francisco to San Diego.

Just getting squadrons from one area of the country to another was a major problem.

For the British it was about 610 miles from Land's end to John o' Groats

 

[Wild_Bill_Kelso]

Not quite true.
The US did expect to fight on home territory, trouble was that the home territory was huge.
Almost 540 miles from Pensacola to Miami.
470 miles from Boston to Norfolk/Newport News
680 miles from Seattle to San Francisco.
480 miles from San Francisco to San Diego.

Just getting squadrons from one area of the country to another was a major problem.

For the British it was about 610 miles from Land's end to John o' Groats

Right but there was also territories like the Panama canal zone, and various islands in the Carribean, Hawaii, etc.

Key West to Puerto Rico is 1,000 miles. Davao to Manilla in the Philippines 921 miles.

Certainly the naval aircraft were made to fly long distances too.

 

[pbehn]

Another big thing is fuel. US was expecting to have to fight at a distance, not on home territory. P-40s and Wildcats carried a good bit more fuel than Spitfires, Hurricanes, Bf 109s or Yak-1s. Lightnings, P-51s and P-47s, Corsairs and Hellcats carried much more fuel. So that is a lot of weight right there even for the empty (but self sealing) fuel tanks, and the structural strength to carry all that gas.

The poor ole P-51 was caught up in an additional "bind". In addition to its prodigious internal fuel which was increased by a rear tank almost as big as a Hurricane and Spitfires total, it was also tasked with carrying 75 external tanks, meaning it also had to carry enough oil and oxygen for its 6 hr missions, every increase involved another increase.