Some thoughts on "combat effectiveness/performance" factors that are often hidden.

[Shortround6]

I got to thinking about some of the hidden (not often thought about ) things that affect both effectiveness and performance. This was in regards to the idea that the US could have used cheaper, lighter planes and gotten about the same effectiveness in combat. Maybe they could but I am not interested in going into the claims/losses rabbit hole. I am thinking about a quite different rabbit hole that has even less documentation.
I am going to use the US as the example as the US is rightly or wrongly considered to have the heaviest/most rugged aircraft and actual combat performance (climb and turn) suffered.
In the early part of the war with France vs Germany there was one sort of war going on. Apologies to the Poles but that part of the war was too short for engine life and airframe life or accident rate to have much effect. It did have an effect even during the Phony war over the winter of 1939/40.
Amount of spare parts for both engines (and accessories) and airframes became more important. For France and Germany the front lines were only a few hundred Kilometers from the factories except for the purchased American planes (Hawk 75s). In some cases there are reports of the French squadrons not being able to repair/maintain aircraft due to lack of spare parts because a high percentage of the parts were going to new construction. We don't (in English sources) have much good information about the reliability/durability of French engines, except it was not what was wanted once they got passed the Hispano-Suiza radials which seem to have been really horrible. Now against this is the fact that distances and flight times were short, often 2-3 hours? or less?
The Hawk 75s have had a little written about them about this. The US got two reports in 1939, one Oct 1939 and one id Dec about things like fuel tank protection, fuel management (tank switches), landing gear operation, ammo capacity and rear seat armor. One French commander reported that 3 of his Hawks had been damaged due to bullets penetrating the hydraulic system for the landing gear. Others had been damaged due the electric landing gear position indicator failing to function. His own mechanics came up with a visual indicator, white paint on part of the landing gear that was only visible when the landing gear was down, red paint on the part when it was not down. In Early Jan 1940 the head of the French Air Mission in the US was trying very hard to purchase 30 extra wing sets for the Hawk 75s already delivered. The French had ordered the equivalent of 25% spares in monetary value for the first 200 planes (equivalent to 50 airframes) but they were running out of spare wings a lot faster than expected. They had 30 Hawks grounded due to damaged wings in jam 1940. The US Army with a very vested interest in problems with the P-36 as the US P-36s were interspersed with the French Hawk 75s on production line and the US Army and over 500 P-40s with a very closely related airframe on order. The US Army had the Military Intelligence Division revue the French reports and give their assessment.
US Report was that the major causes as a high rate of landing accidents (but no cause/s?) and lack of sufficient spares.
The Hawks seem to have done quite well in combat in both the Phony war and after the actual invasion.
French fighter fields were often not very good. Many of them were old (WW I or just after) and not maintained well during the years of peace. Some were very good if they had been regular fields in the 1930s.
Many countries wound operating from poor airfields after the BoF. In the BoB both sides operated from a variety or airfields and both sides, while transport distances were short, often prioritized new construction over spare parts.
Both the Spitfire and 109 are often criticized for weak landing gear and/or landing/ground handling problems. What is rarely/never mentioned is what else gets damaged in landing/taxiing accident that caused by the landing gear? Can they just bolt a new landing gear leg onto the original mounts or does the wing (Spitfire) or fuselage (109) need parts or replacements. Sometimes on the Hawks the landing gear leg punched it's way up through the wing.
What is known on the Hawks is that the wings on the P-40s (the ones with four .303/.30 cal guns) gained about 150lbs over the P-36/Hawk 75 wings.
Some of the French Hawks had four 7.5mm mgs.
The P-40 was heavier and needed stronger wings handle the US required G loadings. Now despite the Hawk 75s being built to handle 11.5-12 Gs ultimate (breaking, bending could be at a lower G load) in flight they had a problem with landing. US P-36s also had problems with landing gear attachments and wing skin buckling around the landing gear.
How much of the weight increase was to handle the flight load/s and how much was to fix the landing gear problem/s I don't know. P-40E and up gained about another 100lbs in the wings, higher gross weight.
When the US went to war it did so in areas thousands of Kilometers from the factories. Spare aircraft or spare parts were going to take a lot longer to get to where they were needed and cost a lot more (fuel and manpower) to get them there.
The US had started testing their engines (commercial and military) to a 150 hr endurance test instead of the 100 hours most of the rest of world used in 1936 (?) which meant that US engines were a little heavier than other engines during the 1930s and early 40s.
Now once you get to a crappy airfield in the North African dessert or some of the Jungle airfields or coral Islands US endurance testing is sort of useless but only sort of. An engine that limped though a European test (there were different standards on how many full power hours and how many parts could be replace) trying to operate in the same environment as a US 150 hour engine (with a few allowances) might show a similar life span, roughly 2/3rds ???
British had problem. Flying out of England, close to the Factories, had the best conditions (on average) for engine life compared to flying out of North Africa or the Far East and with the Med shut down sending spare aircraft/parts/engines around Africa was real logistics problem.
Japan had a problem also but is about 2800-2900 miles from Japan to Rabaul and around 6000 miles from San Francisco to Henderson Field.
Not saying that either county designed aircraft with those specific transport distances in mind but the US was more mindful than most that logistics was going to be a major factor in any war the US got involved with.

Some things just sort of happened. The US was figuring out how to make protected tanks and fit armor/BP glass during much of 1940. Sometimes it didn't make it into some the planes until 1941 and while the US figured it would have to fight Japan at some point they didn't know when or what planes they would have and they didn't know that the Japanese would fail to follow the world trend and not fit protection to many of their aircraft for 2-3 years after most other nations did. US pilots sometimes took guns/ammo and fuel out to increase performance. I don't think they ever took out armor/BP glass.
Perhaps the US overbuilt considering the amount of time a fighter or it's engine or it's guns would last on average in combat. But if you go too light you are loosing more equipment to mechanical attrition than to combat and accidents.

Every air force and point to planes that were lost to a single 7.5-7.9mm bullet (the Golden BB) and to planes that came home with several hundred holes and/or major pieces missing. Both are the exceptions and trying to figure out 'average' damage that was survivable takes a lot more time, information and computer power than I have.

I will note the Odyssey of the US 1st Pursuit Group in Dec 1941 to June/July 1942.

Dec 7th the Group is at Selfridge Field Michigan and is ordered to San Diego to guard against the Japanese.
Dec 8th the first aircraft arrive in San Diego, about 2000 miles straight line. Entire group (including ground elements) arrives Dec 22nd.
At least one squadron had been in El Paso Texas.
The 2st stays at San Diego until April 15th when it is decided to send the 1st to England and for them to fly across the Atlantic. The 1st is to get brand new P-38Fs from the factory prepared for the trip. The Group heads east to New England. and then is told to fly west after Midway. They are stopped in North Carolina and then sent sent north to Bangor Maine. By June 18th the 1st Pursuit group has it's full compliment of P-38s at Bangor. June 23 sees the first P-38s fly out of Presque Isle Maine to Goose Bay Labrador.
The US was sort of used to deployments that covered several thousand miles.
By the late 30s they were operating trans-continental air services several departures per day. It took about 15-17 hours and took 3 refueling stops.
The US Airlines were demanding reliable, long lived engines.

 

[GregP]

Quite interesting things to bring up, Shortround ...

We had some experience with Allison V-1710s when I was working with Joe Yancey, and we had several running fine after 1,000 hours. Of course, these hours were not combat hours, they were civilian hours and these engines rarely got to full rated power except at takeoff, and even then, the power was slightly decreased since they were running 100LL fuel.

I don't know of any Merlins that have made 1,000 hours in civil operations, but that doesn't mean they haven't ... it just means I can't verify it at this time from personal knowledge. The way they run, it could easily happen. They sound great and ARE a great engine.

I DO know you have to do valve seats every so often in Merlins and they require you to tighten the head bolts every 25 hours or so by design. You don't have to do that in an Allison, and Allison maintenance in general seems to be less than Merlin maintenance.

All that means is that different engines require different maintenance. Airframes are the same way. Each has it's strong and weak points.

I know the Planes of Fame F8F Bearcat's R-2800 that we have only gets operated to about 1,600 hp due to fuel limitations ... 100LL instead of 100/130 PN fuel. It gets less stress than an engine operated by the military services in WWII.

None of the above speaks to combat usage. The TBO (time between overhauls) in WWII was NOT set by how the engine power degraded over time or operating characteristics at the time. It was set so that 99.5% of the engines that came in for overhaul were in good enough shape to BE overhauled and not sccrapped due to out of limits wear in some area. That is, an engine ready for overhaul in WWII was likely running well at the time it was exchanged for a new or overhauled engine. They needed most engines to be able to be overhauled because very few engine blocks were made as replacements. Almost all went for new engines.

I can say the Spitfires we used to have on loan were much easier to damage around the hangar than the U.S. airplanes. That is airframes, not engines. It's not that they seemed lighter, they WERE lighter. A Spitfire IX came in at 5,610 - 5,816 lbs empty and 7,500 - 9,500 lbs at takeoff. A P-51B came in at 6,985 lbs empty and 11,800 gross weight. Both had essentially the same engine. So, even when empty, the Spitfire IX was 1,100 - 1,300 lbs lighter. That translates into a bit more delicate around the hangar and in use. Fewer stringers and bulkheads or thinner metal, one or the other. I believe the skins were the same thickness (mostly 0.040" Aluminum), so the real answer is more internal structure in the P-51B. More = heavier and likely, stiffer.

We had a local P-51D a few years back have a landing accident. The tailwheel downlock failed in flight. When the aircratf landed, the tailwheel folded up and the rudder was dragging on the runway. I spoke to the pilot and he said words to the effect that NOBODY practices landing a P-51 with only brakes. That is, they touch down and stay straight with rudder, and transition to brakes when the aircraft has slowed considerably. It took this pilot some time, a few seconds anyway, to understand what had happened because he was first trying to use the rudder to steer normally and he found it wasn't working. Hence, he transitioned to brakes. Since the rudder was dragging on the runway, it wasn't moving left and right to stay straight. As a result, the aircraft was off-line by the time he DID use brakes and it groundpooped in the grass off the runway at Chino. The stress bent they landing gear attach point in one wing. Easy to tell by looking at it! It took more than a year to fix that at Fighter Rebuilders shop. Granted, the time is not indicative of the effort ... it had more to do with the Insurance Company than the maintainers fixing anything. But, it wasn't simple. So, as you state above and as experience shows, fixing things like basic internal structure in a WWII fighter wing are NOT simple or quick. Fixing minor EXTERNAL damage is MUCH quciker and easier.

Good topic. I'm pretty sure you have just scratched the surface of the subject, but you made a very good start to it. I'm not too sure where one would find out the types things you discuss historically (what documents could be analyzed, that is), but we all know these things cropped up. You cannot use an airplane very long without working on it, and normal use creates some damage, even if is just stripping screws and rounding bolt heads when removing and replacing panels for maintenance.

Cheers, Shortround.

 

[Geoffrey Sinclair]

Forecasting wartime spare parts levels is sort of like forecasting your requirements for rally driving unknown distances based on your regular work commute travel on good roads. The easiest way to up production numbers was to reduce the number of components set aside for spares.

The general rule was everyone was caught short the first times they encountered heavy combat and some made deliberate choices, the US had more warning time but had some trouble believing the numbers required (So did Churchill). Not only spare parts but the personnel to do the repairs, including moving the damaged aircraft as required. Going into largely unknown environments was another factor, like the tropics and flying at greater heights. The US published the two volume official history Global Logistics and Strategy looking at things from higher levels, it had more distances to cover during internal movements but the USN versus IJN plans aside not a lot about major expeditionary forces, the islands the navies were going to fight over did not have a lot of room and no one was forecasting how good you could make a wartime construction system. The merchant ships needed were not being built. The US had a much bigger civil than military aviation industry, which had different objectives and requirements, like reliability and economy versus absolute performance.

If anyone was building long range aircraft as standard requirement it was the IJN.

The US was heavier idea needs the usual qualifications, the B-17/24 ended up around the same weights as the Halifax/Lancaster, the US mediums were built on the assumption they would be intercepted and so went for survivability, the heavyweight P-47 started out about 600 pounds heavier than the Typhoon. Some of the extra weight is due to when the aircraft was designed, the later the more powerful the engines available, amongst other things those engines needed more airframe strength to stay attached, some early Merlin Mustangs did not have the engine bearer strength of the Spitfires, add more fuel as well. The Hellcat had a 2,000 HP engine but on specifications did not have much performance over the Zero with half the power, the weight went into other features, including pilot safety and good carrier landing characteristics.

The British could put forward the Stirling as a much more rugged design than the US heavies based on empty weights, how much of the P-40 weight is Curtiss or the way it is an update of an older design instead of then current US practice? The Empire State Building is over strength compared with later designs.

Always remembering there were people on the other side putting holes in your equipment. The Luftwaffe thought it took around 20x20mm or 2 to 3x30mm. hits to bring down a heavy bomber if no fire was started.

Given the USAAF reports its aircraft losses as 1/3 in USA, 1/3 non combat/war weary and 1/3 combat it is clear accident rates had a big impact on the maintenance system and those rates went up as average crew experience went down. RAF, end August 1939 75 out of 475 delivered Hurricanes had been Struck Off Charge, 27 out of 305 Spitfires, 38 out of 210 Gladiator I. The site Martin's Aviation Pages lists British non training unit all causes aircraft casualties September 1939 to March 1940 as 584 losses and 897 damaged, by end August 1940 that was up to 2,794 lost and 3,585 damaged plus 233 abandoned.

The Narrow Margin by Wood and Dempster have a cumulative battle casualties table fr the RAF at home presumably for the war, to 1 July 1940 82 bombers category 2, 358 lost, 56 fighters category 2, 517 lost, other types 16 category 2, 104 lost, as of 31 October 1940 it was bombers 198/725, fighters 766/1,657, others 66/200.

According to the Ministry of Aircraft Production aircraft awaiting spares as a percentage of all aircraft within the RAF, end of month June 1941 to February 1942 was 8.5%, 9.7%, 10.2%, 9.9%, 9.4%, 8.2%, 8.4%, 8.0%, 7.0%. End June 1941 RAF Home Commands had 932 aircraft awaiting spares of which 611 were trainers, end February 1942 1,090 aircraft, 602 trainers. October 1941 to March 1942 spares requested in the month, around to over a third there was no stock and a similar number had over 10 month's stocks. Drill down and Hurricane spares were more plentiful than Spitfire, engine spares had under 15% no stock, propeller generally over 40% no stock, airframes varied between 13 and 48%, usually closer to the lower figure. We know any functioning repair system at a given date is going to have under repair and not under repair for <reason>, the question being what is an acceptable level of not under repair.

March 1942, aircraft storages, front line combat types, 212 aircraft needing engines (all but 2 Merlins), 479 needing propellers, 346 needing constant speed units, 193 (all Blenheim) needing turret, total 1,240, though some needed more than 1 component. January 1945, of the 8,949 aircraft and 512 airframes in storage units 1,292 had equipment deficiencies. (Top 5 were 121 Oxford I, 76 Anson, 71 Beaufighter TF.X, 60 Stirling IV and 45 Martinet.)

When introduced into RAF service the Merlin had an engine failure rate of 1 per 500 hours of flying, as of the December 1941 to May 1942 period it was 1 per 1,000 hours, the Sabre was 1 per 340 hours.

Some of the 15th Air Force 1945 monthly reports have Engine Change Reports, graphs of average running time per aircraft engine changed. generally speaking the R-1830 radials in the B-24 and the R-1820 radials in the B-17 had at least an average of 300 hours running when changed, few had 400, with the R-1820 ahead, most having 350 or more hours. Overhauled engines usually had around half the average hours of new engines. The V-1650 Merlins and the V-1710 Allisons usually averaged over 200 hours, few made it to 300 until March/April. Overhauled Allisons were around half the new engine hours, overhauled Merlins more like a quarter. In civil service the radials lasted several times longer between overhauls.

You find WWII history in some interesting places. Journal of the American Statistical Association, V 41 no. 234, June 1946, pages 190 to 203. "Actuarial Analysis of the operating life of B-29 aircraft engines", by O L Altman and C G Goor. Lots of obvious and not so obvious points.

1) R-3350's were in critical supply in 1944 and the first half of 1945. This is despite usually the number of R-3350 built to date being twice the number needed for B-29 built to date. Supply problems were easing around the end of the war.
2) Air transportation was used to fly R-3350's to the US for overhaul, at best 2 R-3350's would fit in a cargo plane.
3) Overhauled engines had around 10% lower "life" before the next overhaul.
4) The -23 was the carburettor and the -57 the fuel injected versions. The -23 was modified to improve reliability.
5) The statisticians noted the standard USAAF methodology for forecasting engine life was only suitable for a reasonably static population. Not where there was a steady arrival of more strength with new aircraft.

In terms of engine life, operations in India were the worst, since each combat sortie required three reasonably rapid climbs, India to China, China to Japan, China to India. Next came training in the US, finally the best were the units in the Marianas.

Expected life prior to first overhaul, early operations from India, 163 hours, -23 engines. Using modified -23 engines this had risen to 280 hours by February/March 1945 for aircraft operating from India and 304 hours from the Marianas. The figures for B-29s used in training were 221 hours and 310 hours versus the 163 and 280 hours figures above.

Operating from India a comparison between the modified and unmodified -23 engines showed 80% of the unmodified and 95.3% of the modified engines survived to over 100 hours, 33.9 of the unmodified and 81.5% of the modified engines survived to over 200 hours, 0.2% of the unmodified and 47.3% of the modified engines survived to over 300 hours.

In the Marianas, as of 20 November 1944 the average hours on each -23 engine removed was 91, by 20 January 1945 it was 151, as of 30 April it was 234. These figures include removals for engine model changes, modifications, accidents and battle damage. They are also under estimates of the normal engine lifetime because so many of the engines were new. The figures include new and overhauled engines, so it is either the number of hours since the engine was built for new engines or since overhaul for the overhauled engines.

Engine hours before removal as of 31 May was 259 hours, and 31 July 272 hours. These figures are for engines removed because of mechanical problems only. Even in July the steady number of new B-29s arriving drove down the average engine hours per removed engine.

A study as of 31 July 1945 noted in the Marianas the -23 engines 96.8% of new and 92.5% of overhauled logged more than 100 hours before replacement, 87.5% and 75.7% respectively logged over 200 hours, 62.7% and 43.4% logged over 300 hours, 19% and 8% logged over 400 hours, none logged over 500 hours.

As noted above the training schools in the US went through R-3350 engines quicker than the combat units in the Marianas, for example 57.9% (new) and 36.4% (overhauled) logged over 300 hours, but once this mark was passed the engines in the US held up more, so 24.6% and 10.4% logged over 400 hours, and 1.2% and 0.2% managed over 500 hours.

The fuel injected -57 engine had a higher time between overhauls, so in the above study 31.2% used in training logged over 400 hours, and 4.9% logged over 500 hours.

The USAAF Statistical Digest has the 20th Air Force flying between 10 and over 14 hour missions per the monthly averages, 621,975 hours of which 479,113 were on combat missions, at 200 hours per engine that is around 12,500 engines.

The US statistics on spares production indicate says airframe plants might not be making any, which makes some sense if they were assembly plants, or some plants were more dedicated to spares, it clearly varied, an example, Consolidated, San Diego in 1943, 25,656,000 hours making B-24, 3,185,000 making B-24 spares, Fort Worth no spares made for knock downs assembled, for other B-24 18,949,000 hours for assembly, 907,000 for spares.

The Spitfire and Bf109 undercarriage attached to the fuselage.

 

[Shortround6]

A few expansions and or quibbles.

The Hellcat had a 2,000 HP engine but on specifications did not have much performance over the Zero with half the power, the weight went into other features, including pilot safety and good carrier landing characteristics.

A lot of it went into armament.
plane.............Spitfire 1...........................Spitfire VB........................................A6M2....................................F5F3
Guns..................80kg.....................................150kg.............................................82kg......................................196kg
ammo*.............71kg.......................................93kg..............................................67kg......................................327kg
total.................151kg......................................243kg...........................................149kg.....................................523kg

Ammo includes the drums. The types of plane were built to different load standards. US figured 8 G service load with a 50% safety factor, British a bit less and the Japanese a bit l ower than the British. Building your plane to hold over 3 times the weight of guns and ammo and then not have it break while pulling a slightly lower than 12 G load? (bending was probably OK). And back to carrier landing, the F5F-3 was supposed to be able to land on the carrier with that 523kg load of guns and ammo without breaking the wings/landing gear/arrestor attachment points. Stronger structure adds weight fast. The "new" heavier structure has to be able to meet the 12G load goal

how much of the P-40 weight is Curtiss or the way it is an update of an older design instead of then current US practice?

A bit of both, again see US load limits (G loads). Adding guns, ammo, armor and self sealing tanks means you either make the structure heavier or you accept a lower G limit. I am guessing they did both. Major change from the P-36 to the P-40, another change from the early P-40s to the P-40D/E and perhaps just minor slippage of the G limits in later models?

The Spitfire and Bf109 undercarriage attached to the fuselage.

Sort of on the Spitfire?

Open to correction.
Spitfire used a 'stub' wing that was part of the fuselage structure?
Landing was fastened to this 'center' spar that was part of the fuselage structure and the main parts of the wing were fastened to the stub wing?
109s fastened the landing gear to

P-40s had a 'though' wing. There were left and right halves but normally the entire wing would be shipped in one box (with landing gear) and the Fuselage (and engine) shipped in a 2nd box and then they would bolt/fasten the fuselage on top of the wing.

Zero used a combined wing and fuselage structure somewhat like the Spitfire (?) but I don't know where they 'broke' it for shipment/repairs. Outer wings attached just outside of the landing? or somewhere else? Display examples in museums may not have been disassembled according to factory joints? Japanese may have detached the rear fuselage and engine for shipment and kept Cockpit and wing together?

 

[special ed]

Forecasting wartime spare parts levels is sort of like forecasting your requirements for rally driving unknown distances based on your regular work commute travel on good roads. The easiest way to up production numbers was to reduce the number of components set aside for spares.

The general rule was everyone was caught short the first times they encountered heavy combat and some made deliberate choices, the US had more warning time but had some trouble believing the numbers required (So did Churchill). Not only spare parts but the personnel to do the repairs, including moving the damaged aircraft as required. Going into largely unknown environments was another factor, like the tropics and flying at greater heights. The US published the two volume official history Global Logistics and Strategy looking at things from higher levels, it had more distances to cover during internal movements but the USN versus IJN plans aside not a lot about major expeditionary forces, the islands the navies were going to fight over did not have a lot of room and no one was forecasting how good you could make a wartime construction system. The merchant ships needed were not being built. The US had a much bigger civil than military aviation industry, which had different objectives and requirements, like reliability and economy versus absolute performance.

If anyone was building long range aircraft as standard requirement it was the IJN.

The US was heavier idea needs the usual qualifications, the B-17/24 ended up around the same weights as the Halifax/Lancaster, the US mediums were built on the assumption they would be intercepted and so went for survivability, the heavyweight P-47 started out about 600 pounds heavier than the Typhoon. Some of the extra weight is due to when the aircraft was designed, the later the more powerful the engines available, amongst other things those engines needed more airframe strength to stay attached, some early Merlin Mustangs did not have the engine bearer strength of the Spitfires, add more fuel as well. The Hellcat had a 2,000 HP engine but on specifications did not have much performance over the Zero with half the power, the weight went into other features, including pilot safety and good carrier landing characteristics.

The British could put forward the Stirling as a much more rugged design than the US heavies based on empty weights, how much of the P-40 weight is Curtiss or the way it is an update of an older design instead of then current US practice? The Empire State Building is over strength compared with later designs.

Always remembering there were people on the other side putting holes in your equipment. The Luftwaffe thought it took around 20x20mm or 2 to 3x30mm. hits to bring down a heavy bomber if no fire was started.

Given the USAAF reports its aircraft losses as 1/3 in USA, 1/3 non combat/war weary and 1/3 combat it is clear accident rates had a big impact on the maintenance system and those rates went up as average crew experience went down. RAF, end August 1939 75 out of 475 delivered Hurricanes had been Struck Off Charge, 27 out of 305 Spitfires, 38 out of 210 Gladiator I. The site Martin's Aviation Pages lists British non training unit all causes aircraft casualties September 1939 to March 1940 as 584 losses and 897 damaged, by end August 1940 that was up to 2,794 lost and 3,585 damaged plus 233 abandoned.

The Narrow Margin by Wood and Dempster have a cumulative battle casualties table fr the RAF at home presumably for the war, to 1 July 1940 82 bombers category 2, 358 lost, 56 fighters category 2, 517 lost, other types 16 category 2, 104 lost, as of 31 October 1940 it was bombers 198/725, fighters 766/1,657, others 66/200.

According to the Ministry of Aircraft Production aircraft awaiting spares as a percentage of all aircraft within the RAF, end of month June 1941 to February 1942 was 8.5%, 9.7%, 10.2%, 9.9%, 9.4%, 8.2%, 8.4%, 8.0%, 7.0%. End June 1941 RAF Home Commands had 932 aircraft awaiting spares of which 611 were trainers, end February 1942 1,090 aircraft, 602 trainers. October 1941 to March 1942 spares requested in the month, around to over a third there was no stock and a similar number had over 10 month's stocks. Drill down and Hurricane spares were more plentiful than Spitfire, engine spares had under 15% no stock, propeller generally over 40% no stock, airframes varied between 13 and 48%, usually closer to the lower figure. We know any functioning repair system at a given date is going to have under repair and not under repair for <reason>, the question being what is an acceptable level of not under repair.

March 1942, aircraft storages, front line combat types, 212 aircraft needing engines (all but 2 Merlins), 479 needing propellers, 346 needing constant speed units, 193 (all Blenheim) needing turret, total 1,240, though some needed more than 1 component. January 1945, of the 8,949 aircraft and 512 airframes in storage units 1,292 had equipment deficiencies. (Top 5 were 121 Oxford I, 76 Anson, 71 Beaufighter TF.X, 60 Stirling IV and 45 Martinet.)

When introduced into RAF service the Merlin had an engine failure rate of 1 per 500 hours of flying, as of the December 1941 to May 1942 period it was 1 per 1,000 hours, the Sabre was 1 per 340 hours.

Some of the 15th Air Force 1945 monthly reports have Engine Change Reports, graphs of average running time per aircraft engine changed. generally speaking the R-1830 radials in the B-24 and the R-1820 radials in the B-17 had at least an average of 300 hours running when changed, few had 400, with the R-1820 ahead, most having 350 or more hours. Overhauled engines usually had around half the average hours of new engines. The V-1650 Merlins and the V-1710 Allisons usually averaged over 200 hours, few made it to 300 until March/April. Overhauled Allisons were around half the new engine hours, overhauled Merlins more like a quarter. In civil service the radials lasted several times longer between overhauls.

You find WWII history in some interesting places. Journal of the American Statistical Association, V 41 no. 234, June 1946, pages 190 to 203. "Actuarial Analysis of the operating life of B-29 aircraft engines", by O L Altman and C G Goor. Lots of obvious and not so obvious points.

1) R-3350's were in critical supply in 1944 and the first half of 1945. This is despite usually the number of R-3350 built to date being twice the number needed for B-29 built to date. Supply problems were easing around the end of the war.
2) Air transportation was used to fly R-3350's to the US for overhaul, at best 2 R-3350's would fit in a cargo plane.
3) Overhauled engines had around 10% lower "life" before the next overhaul.
4) The -23 was the carburettor and the -57 the fuel injected versions. The -23 was modified to improve reliability.
5) The statisticians noted the standard USAAF methodology for forecasting engine life was only suitable for a reasonably static population. Not where there was a steady arrival of more strength with new aircraft.

In terms of engine life, operations in India were the worst, since each combat sortie required three reasonably rapid climbs, India to China, China to Japan, China to India. Next came training in the US, finally the best were the units in the Marianas.

Expected life prior to first overhaul, early operations from India, 163 hours, -23 engines. Using modified -23 engines this had risen to 280 hours by February/March 1945 for aircraft operating from India and 304 hours from the Marianas. The figures for B-29s used in training were 221 hours and 310 hours versus the 163 and 280 hours figures above.

Operating from India a comparison between the modified and unmodified -23 engines showed 80% of the unmodified and 95.3% of the modified engines survived to over 100 hours, 33.9 of the unmodified and 81.5% of the modified engines survived to over 200 hours, 0.2% of the unmodified and 47.3% of the modified engines survived to over 300 hours.

In the Marianas, as of 20 November 1944 the average hours on each -23 engine removed was 91, by 20 January 1945 it was 151, as of 30 April it was 234. These figures include removals for engine model changes, modifications, accidents and battle damage. They are also under estimates of the normal engine lifetime because so many of the engines were new. The figures include new and overhauled engines, so it is either the number of hours since the engine was built for new engines or since overhaul for the overhauled engines.

Engine hours before removal as of 31 May was 259 hours, and 31 July 272 hours. These figures are for engines removed because of mechanical problems only. Even in July the steady number of new B-29s arriving drove down the average engine hours per removed engine.

A study as of 31 July 1945 noted in the Marianas the -23 engines 96.8% of new and 92.5% of overhauled logged more than 100 hours before replacement, 87.5% and 75.7% respectively logged over 200 hours, 62.7% and 43.4% logged over 300 hours, 19% and 8% logged over 400 hours, none logged over 500 hours.

As noted above the training schools in the US went through R-3350 engines quicker than the combat units in the Marianas, for example 57.9% (new) and 36.4% (overhauled) logged over 300 hours, but once this mark was passed the engines in the US held up more, so 24.6% and 10.4% logged over 400 hours, and 1.2% and 0.2% managed over 500 hours.

The fuel injected -57 engine had a higher time between overhauls, so in the above study 31.2% used in training logged over 400 hours, and 4.9% logged over 500 hours.

The USAAF Statistical Digest has the 20th Air Force flying between 10 and over 14 hour missions per the monthly averages, 621,975 hours of which 479,113 were on combat missions, at 200 hours per engine that is around 12,500 engines.

The US statistics on spares production indicate says airframe plants might not be making any, which makes some sense if they were assembly plants, or some plants were more dedicated to spares, it clearly varied, an example, Consolidated, San Diego in 1943, 25,656,000 hours making B-24, 3,185,000 making B-24 spares, Fort Worth no spares made for knock downs assembled, for other B-24 18,949,000 hours for assembly, 907,000 for spares.

The Spitfire and Bf109 undercarriage attached to the fuselage.

Makes one wonder how the USSR did with their engines on the three B-29s they had, as well as the Tu-4s to follow. Their pilots' habit of using full throttle in flight may have changed for these engines.

 

[Shortround6]

there was a reason that the US 4 engine bombers used a "flight engineer"

B-29 flight engineer's panel.

 

[bf109xxl]

Makes one wonder how the USSR did with their engines on the three B-29s they had, as well as the Tu-4s to follow. Their pilots' habit of using full throttle in flight may have changed for these engines.

Could you please cite a source on the Soviet pilots' habit of flying at full throttle? I have other information - for example, pilots kept the airspeed too low in thunderstorm clouds causing crashes, so they were instructed to increase the airspeed in such conditions.
The service life of the ASh-73TK was relatively low and reliability of the early series was abysmal, but the situation was gradually improved. Interestingly, the problems with the ASh-73 (without turbochargers), which were installed on Be-6 flying boats, were much less - they are not mentioned much at all.

 

[GregP]

A few expansions and or quibbles.


A lot of it went into armament.
plane.............Spitfire 1...........................Spitfire VB........................................A6M2....................................F5F3
Guns..................80kg.....................................150kg.............................................82kg......................................196kg
ammo*.............71kg.......................................93kg..............................................67kg......................................327kg
total.................151kg......................................243kg...........................................149kg.....................................523kg

Ammo includes the drums. The types of plane were built to different load standards. US figured 8 G service load with a 50% safety factor, British a bit less and the Japanese a bit l ower than the British. Building your plane to hold over 3 times the weight of guns and ammo and then not have it break while pulling a slightly lower than 12 G load? (bending was probably OK). And back to carrier landing, the F5F-3 was supposed to be able to land on the carrier with that 523kg load of guns and ammo without breaking the wings/landing gear/arrestor attachment points. Stronger structure adds weight fast. The "new" heavier structure has to be able to meet the 12G load goal


A bit of both, again see US load limits (G loads). Adding guns, ammo, armor and self sealing tanks means you either make the structure heavier or you accept a lower G limit. I am guessing they did both. Major change from the P-36 to the P-40, another change from the early P-40s to the P-40D/E and perhaps just minor slippage of the G limits in later models?

Sort of on the Spitfire?
View attachment 850642
Open to correction.
Spitfire used a 'stub' wing that was part of the fuselage structure?
Landing was fastened to this 'center' spar that was part of the fuselage structure and the main parts of the wing were fastened to the stub wing?
109s fastened the landing gear to
View attachment 850643
P-40s had a 'though' wing. There were left and right halves but normally the entire wing would be shipped in one box (with landing gear) and the Fuselage (and engine) shipped in a 2nd box and then they would bolt/fasten the fuselage on top of the wing.
View attachment 850644
Zero used a combined wing and fuselage structure somewhat like the Spitfire (?) but I don't know where they 'broke' it for shipment/repairs. Outer wings attached just outside of the landing? or somewhere else? Display examples in museums may not have been disassembled according to factory joints? Japanese may have detached the rear fuselage and engine for shipment and kept Cockpit and wing together?

Back about 18 years ago, we had an Ha.1112 on a cart (we still have it) that had been groundlooped. Another volunteer and I asked to put new landing gear on it and start the repair process. The two landing gear mounts attached to the firewall and the engine mount. The forward mount has an adjustment screw for length to set the gear tracking for toe-in.

Each wing panel attached with 3 bolts to the fuselage points. So, if someone shot out a lower mount bolt, the wing would fold up and the pilot had to find a way to bail out. Likewise, if someone shot out an upper wing mount bolt, the wing would stay on just fine unless you rolled it over or put negative g on it. Then it would fold down and the pilot had to find a way to bail out. If someone shout out the single bolt away from the upper and lower, the wing would fail and depart the aircraft and it was nylon letdown time.

We repaired the groundloop damages and here we are, 17 years later, and it STILL hasn't flown ... but it HAS moved up on the priority list and is slated to be flying within a few years now.

No point here, just FYI. Cheers.

 

[GregP]

there was a reason that the US 4 engine bombers used a "flight engineer"
View attachment 850655
B-29 flight engineer's panel.

Isn't that an early video game with poor graphics?

 

[Dimlee]

Isn't that an early video game with poor graphics?

Nope, it's quite a modern game, note the VR glasses on his head.

 

[don4331]

Sort of on the Spitfire?
View attachment 850642
Open to correction.
Spitfire used a 'stub' wing that was part of the fuselage structure?

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Spitfire is worst/best of both worlds. Fuselage doesn't have the landing gear/the 2 wings are separate and include landing gear

 

[GregP]

Nope, it's quite a modern game, note the VR glasses on his head.

My mistake! I thought they were beer goggles.

 

[PAT303]

I personally think a major part of combat effectiveness is having total confidence in your aircraft. If you read pilot reports on the Spitfire and Hurricane as examples you will notice time and again how pilots talk fondly on how forgiving they are to fly and how they ''talk'' to the pilot when pushed to their limits, for me having that feeling would greatly increase my confidence in engaging in combat. Armor, self sealing fuel tanks, a good radio, survival gear and good vision are all points that increase the effectiveness of fighters.

 

[Steamed_Banana]

I think a lot of it was actually just knowing the aircraft. Early in the war a lot of Allied pilots in particular went into combat with almost zero hours 'on type'. That often proved to be a big problem. Part of the reason the Hawk 75 did well in the BoF was they had more time to learn to fly it, 'how it talked' etc., whereas with some of the French made types like the D.520 they had days or hours to figure all that out.

 

[Steamed_Banana]

I got to thinking about some of the hidden (not often thought about ) things that affect both effectiveness and performance. This was in regards to the idea that the US could have used cheaper, lighter planes and gotten about the same effectiveness in combat. Maybe they could but I am not interested in going into the claims/losses rabbit hole. I am thinking about a quite different rabbit hole that has even less documentation.

The real losses are really not anywhere near the kind of mystery some people around here seem to want to think.

 

[GregP]

The real losses are really not anywhere near the kind of mystery some people around here seem to want to think.

The U.S. Navy tracked:

• Own Losses
  • On Action Sorties (tracked all sorties)
    • Losses to enemy aircraft: Shot down by enemy aircraft.
    • Losses to AAA (flak): Lost to AAA.
    • Operational Losses: Losses to mechanical, out of fuel, any losses not accounted for above, including accidents.
  • On Other Flights: Repositioning, maintenance flights, in-transit flights, etc.
  • On Ship or Ground: Lost when ship sank or on ground during an attack.
  • Enemy Aircraft Destroyed
    • Fighter: Any armed, single or twin-engine aircraft participating in a dogfight or recognized to be a fighter, floatplanes, trainers, and for 1944 only, transports. Approximately 90% of all aircraft identified as fighters were actual fighters.
    • Bomber: Any other aircraft recognized to not be a fighter aircraft, flying boats, and for 1942, 1943 and 1945 only, transports. Approximately 90% of all aircraft identified as bombers were actual bombers.

• The USAAF tracked:
  • Combat sorties (all tracked, including non-combat sorties, in all theaters, including USA) For:
    • Theaters versus Germany: Airborne and Effective Sorties for:
      • ETO
        • Heavy Bomber
        • Medium and Light Bomber
        • Fighter
      • MTO
        • Heavy Bomber
        • Medium and Light Bomber
        • Fighter
    • Theaters versus Japan: Airborne and Effective Sorties for:
      • POA
        • Heavy Bomber
        • Medium and Light Bomber
        • Fighter
      • FEAF
        • Heavy Bomber
        • Medium and Light Bomber
        • Fighter
      • CBI
        • Heavy Bomber
        • Medium and Light Bomber
        • Fighter
      • Alaska
        • Heavy Bomber
        • Medium and Light Bomber
        • Fighter
      • 20th AF
        • Heavy Bomber
        • Medium and Light Bomber
        • Fighter
    • Individual Crossings of Enemy Lines for above.
    • Combat sorties broken out by:
      • Escort
      • Bombing and Strafing
      • Reconnaissance
    • Non-Effective Combat Sorties for Above
    • Tons and Number of Bombs Dropped by Type for Above
    • Losses on Combat Missions
      • Theaters versus Germany: ETO, MTO
        • Total Aircraft Lost
          • Losses to Enemy Aircraft
          • Losses to AAA
          • Other Causes
      • Theaters versus Japan
        • Total Aircraft Lost: POA, FEAF, CBI, Alaska, 20th​ AF
          • Losses to Enemy Aircraft
          • Losses to AAA
          • Other Causes

It is difficult to compare U.S. Navy data with USAAF data, and the U.S.A. did studies AFTER WWII to take a dispassionate look at the process of victors, losses, and things that were tough to call at the time. No other nation has published summaries with reviews of the war for their aerial forces, and our own are hard to compare between Navy and Air Force. The categories are NOT the same from USAAF to USN/MC.

The Japanese didn't track individual aerial victories. The totals we have today were taken from individual diaries saved through the war by individual pilots. Their records are even less well-defined than the rest of the Air Forces and Navies.

The British didn't seem to compile the war's statistics as a whole. Rather, they have several accounts of the Battle of Britian, Coastal Command, Fighter Command, Bomber Command, etc, but many of these documents are not complete war documents. They cover a time period and/or an operation(s). Getting the "big picture" is difficult at best without wartime totals. Also, definitions are in short supply.

Soviet records are very suspect. This is mainly due to the fact that Stalin was well-known for "shooting the messenger." That is, he sometimes killed the person who brought him bad news. So, people were quite reluctant to write down bad news and were even more reluctant to take it to superior commands. As a result, the accuracy of wartime records is quite suspect. Never saw a definition from a Soviet translated record of a loss or a victory.

Over the years we have several people who have tried to compile totals for everyone, and I'm sure their records are about as good as we're ever going to get. We know who they are in here: Magnus Family website and Jan Stefarik's site, to name a couple. But they are mostly not so well-documented that you can verify the totals without years of research. If you DO the years of research (I have), the totals are close but not exactly completely verified. Perhaps we are doomed to use the best data we can get at this time and let it go at that.

But, if anyone thinks it is simple, then perhaps they would share their data and sources? Hopefully sources that get back to primary sources ...

And this doesn't even scratch the definitions of a victory or a loss, which vary from source to source. That discussion is even longer than this one.

 

[Steamed_Banana]

I do think it's simple today, due to the internet and all the books which have been compiled and published now. I don't need to share sources, I already have mentioned most of the books and authors doing this. More and more of them are being published every month or two, for multiple different Theaters. I have also shared (and pointed out) the locations and names of some of the primary sources they used already.

There is a limit to how fine of a point you can put on it. We may not be able to every be certain which exact unit or pilot got which actual victory.

However, we do in most cases know the number of claims, and we do know the losses in a given Theater for a given period of time.

So if for example in Nov-Dec 1942 in the Guadalcanal area in the South Pacific, US fighter pilots claimed 480 enemy aircraft, and the Japanese claimed 590 enemy aircraft, but actual Japanese losses were 86 aircraft and actual US losses were 108 aircraft, that indeed tells us a big part of what we actually need to know. It's really not that complicated.

We may not know precisely which of those 86 Japanese aircraft were shot down by Wildcats, but we can see that they made 70% of the claims (just making this number up off the top of my head, but it can be calculated). So that can give us at least a ballpark idea of what damage was actually done, and for what loss (since we know that 35 Wildcats were lost in the same period).

We also can't always tell for certain which were 'operational losses' and which were lost due to enemy activity, and which of those were lost to flak vs defensive fire from bombers vs combat with fighters. But we can get pretty close to which was which in this case too. There were many operational losses on days when the enemy wasn't even flying, for example. There were days in which aircraft were lost and only one particular unit on the other side made claims. Also very common.

Before we knew the enemy losses, then yes. It was VERY complicated, in fact there was really no way to know. But those days are over now.

 

[GregP]

I do think it's simple today, due to the internet and all the books which have been compiled and published now. I don't need to share sources, I already have mentioned most of the books and authors doing this. More and more of them are being published every month or two, for multiple different Theaters. I have also shared (and pointed out) the locations and names of some of the primary sources they used already.

There is a limit to how fine of a point you can put on it. We may not be able to every be certain which exact unit or pilot got which actual victory.

However, we do in most cases know the number of claims, and we do know the losses in a given Theater for a given period of time.

So if for example in Nov-Dec 1942 in the Guadalcanal area in the South Pacific, US fighter pilots claimed 480 enemy aircraft, and the Japanese claimed 590 enemy aircraft, but actual Japanese losses were 86 aircraft and actual US losses were 108 aircraft, that indeed tells us a big part of what we actually need to know. It's really not that complicated.

We may not know precisely which of those 86 Japanese aircraft were shot down by Wildcats, but we can see that they made 70% of the claims (just making this number up off the top of my head, but it can be calculated). So that can give us at least a ballpark idea of what damage was actually done, and for what loss (since we know that 35 Wildcats were lost in the same period).

We also can't always tell for certain which were 'operational losses' and which were lost due to enemy activity, and which of those were lost to flak vs defensive fire from bombers vs combat with fighters. But we can get pretty close to which was which in this case too. There were many operational losses on days when the enemy wasn't even flying, for example. There were days in which aircraft were lost and only one particular unit on the other side made claims. Also very common.

Before we knew the enemy losses, then yes. It was VERY complicated, in fact there was really no way to know. But those days are over now.

Half of this forum says the losses admitted by the other side are the REAL losses and that the pilots massively overclaim. That is directly because they can't agree on the definition of a loss or a victory. Many are quite ready to be venomous about it.

I'm with the half that says a pilot who shoots an aircraft from a fight gets a victory whether or not that particular aircraft or pilot ever flies against his side again or not. Therefore, the admitted losses of one side will NEVER quite equal the awarded victories.

The argument has never been settled and likely will not be. So, it's only "easy" if you recognize only YOUR point of view, regarless of what that is. Whatever position you take, there are PLENTY of people who will disagree.

So, we have to agree to disagree that it is somehow "simple."

I have a file with the victory claims by every country that kept records in WWII for aerial claims. It may or may not be exactly accurate, especially since some records were lost due to war damage, particularly German and Soviet, but it's about as good as we're going to get.

I do NOT have a file with admitted losses by country yet, and likely will never get one because so many countries either don't have those summary records or I have no idea how to find them.

It's a LOT of things, but it ain't easy, at least to me, who has been looking at this for more than 40 years.

Again, we'll have to agree to disagree.

Cheers, Steamer, be happy. The war is over and it ain't going to get any better or worse than it actually was. At some point, we may have enough data to agree with one another.

 

[Steamed_Banana]

Half of this forum says the losses admitted by the other side are the REAL losses and that the pilots massively overclaim. That is directly because they can't agree on the definition of a loss or a victory. Many are quite ready to be venomous about it.

I'm with the half that says a pilot who shoots an aircraft from a fight gets a victory whether or not that particular aircraft or pilot ever flies against his side again or not. Therefore, the admitted losses of one side will NEVER quite equal the awarded victories.

I don't think that's actually a coherent argument buddy, sorry.

The argument has never been settled and likely will not be. So, it's only "easy" if you recognize only YOUR point of view, regarless of what that is. Whatever position you take, there are PLENTY of people whoi will disagree.

So, we have to agree to disagree that it is somehow "simple."

Some of y'all just don't want to acknowledge that the myths you grew up with about this wonderful topic of military aviation were just that - myths.

I have a file with the victory claims by every country that kept records in WWII for aerial claims. It may or may not be exactly accurate, especially since some records were lost due to war damage, particularly German and Soviet, but it's about as good as we're going to get.

I've seen your file, it's got errors which I think were pointed out to you. But it's overall good enough for counting claims. That's a completely different thing than actual losses by the other side.

I do NOT have a file with admitted losses by country yet, and likely will never get one because so many countries either don't have those summary records or I have no idea how to find them.

It's a LOT of things, but it ain't easy, at least to me, who has been looking at this for more than 40 years.

Again, we'll have to agree to disagree.

Cheers, Steamer, be happy. The war is over and it ain't going to get any better or worse than it actually was. At some point, we may have enough data to agree with one another.

The data is out there, it really only makes the whole thing more interesting. I recommend embracing it.

 

[Steamed_Banana]

Half of this forum says the losses admitted by the other side are the REAL losses and that the pilots massively overclaim. That is directly because they can't agree on the definition of a loss or a victory. Many are quite ready to be venomous about it.

I'm with the half that says a pilot who shoots an aircraft from a fight gets a victory whether or not that particular aircraft or pilot ever flies against his side again or not. Therefore, the admitted losses of one side will NEVER quite equal the awarded victories.

The argument has never been settled and likely will not be. So, it's only "easy" if you recognize only YOUR point of view, regarless of what that is. Whatever position you take, there are PLENTY of people whoi will disagree.

So, we have to agree to disagree that it is somehow "simple."

I have a file with the victory claims by every country that kept records in WWII for aerial claims. It may or may not be exactly accurate, especially since some records were lost due to war damage, particularly German and Soviet, but it's about as good as we're going to get.

I do NOT have a file with admitted losses by country yet, and likely will never get one because so many countries either don't have those summary records or I have no idea how to find them.

It's a LOT of things, but it ain't easy, at least to me, who has been looking at this for more than 40 years.

Again, we'll have to agree to disagree.

Cheers, Steamer, be happy. The war is over and it ain't going to get any better or worse than it actually was. At some point, we may have enough data to agree with one another.

I'm sorry, after re-reading your post here and my reply, I think I was too snarky.

I am just a bit frustrated at what seems like rejection of the new data.

But we may actually be talking about different things, and either way, I appreciate your interest, ongoing research and active work in keeping warbirds flying, so I don't want to let my annoyance at a different perception of the data cause me to be pointlessly rude or dismissive. I'm only dismissive of the rejection of the data, and not just by you.

May clarify things a bit to point out, knowing better what actual losses were does not invalidate combat histories, ace status, unit records etc. It just ads a new dimension to it.

We cannot in fact be certain of exact ratios of victories, and the data doesn't (at least as far as I know) invalidate the record of any particular unit, pilot, or aircraft type. It just gives us a clearer picture of what actually happened, and shows us that it was a little bit harder to shoot down warplanes than we thought. Pilots with 10 or 15 victories may have actually got more like 3 or 4. That doesn't make them any less badasses, to be honest. They clearly survived and persevered in an incredibly difficult situation. Same for the aircraft.

I'm not jumping to the conclusion that a P-38 or an F4U was a bad plane. In fact, I think the records clarify much more clearly than

In general, I think we have to be quite careful of jumping to the conclusions based on the operational history data. It's just more data. But it does tell us a lot. And that part is, to me, simple.