Nightengale
Recruit
- 1
- Dec 28, 2022
The B24 had a substantially lower ceiling than the B17. Why? Was it the Davis wing? The different engines?
B24 ceiling vs. B17 ceiling
- Thread starter Nightengale
- Start date
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SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
The angels didn't want anything that ugly any closer.
SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
I'm gonna' catch some flak for that.
ThomasP
Senior Master Sergeant
With the B-17 and B-24 it would have been primarily a matter of wing loading.
40 lb/ft2 for the B-17 at 57,000 lbs (1420 ft2 gross wing area)
vs
54 lb/ft2 for the B-24 at 57,000 lbs (1048 ft2 gross wing area)
Everything else being equal, the aircraft with the higher wing loading will have a lower ceiling.
Wing planform and Aspect Ratio come into play also, as does power.
In theory, a higher aspect ratio wing (with the same area) will have lower drag and hence allow a higher ceiling. But in this case the B-24 wing has a significantly lower area and the resulting higher wing loading is too great for the effect of a higher aspect ratio to make up the difference.
Higher engine power will allow a higher ceiling due the the higher speed achievable (higher speed = higher lift at the some AOA). In practice both aircraft (B-17F vs the B-24D) had about the same Vmax at 25,000 ft with the same Military power (1200 BHP) - the critical altitude for the turbo-superchargers. Their respective engines had similar power at higher altitude also (I think) - or at least not enough difference to make up for the effect of the B-24's higher wing loading.
40 lb/ft2 for the B-17 at 57,000 lbs (1420 ft2 gross wing area)
vs
54 lb/ft2 for the B-24 at 57,000 lbs (1048 ft2 gross wing area)
Everything else being equal, the aircraft with the higher wing loading will have a lower ceiling.
Wing planform and Aspect Ratio come into play also, as does power.
In theory, a higher aspect ratio wing (with the same area) will have lower drag and hence allow a higher ceiling. But in this case the B-24 wing has a significantly lower area and the resulting higher wing loading is too great for the effect of a higher aspect ratio to make up the difference.
Higher engine power will allow a higher ceiling due the the higher speed achievable (higher speed = higher lift at the some AOA). In practice both aircraft (B-17F vs the B-24D) had about the same Vmax at 25,000 ft with the same Military power (1200 BHP) - the critical altitude for the turbo-superchargers. Their respective engines had similar power at higher altitude also (I think) - or at least not enough difference to make up for the effect of the B-24's higher wing loading.
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Shortround6
Major General
So did the B-24 formations.
Interesting article here The Boeing B-17 Flying Fortress, or the Consolidated B-24 Liberator?
Geoffrey Sinclair
Staff Sergeant
- 904
- Sep 30, 2021
I mainly agree with the critic of the article. The statistical approach. 8th Air Force for war, heavy bombers.
343 airborne bomber sorties were at night, 745 tons of bombs. SortieL are airborne less diversions, recalls, unused spares etc. Special is 482 BG missions testing H2X etc. Bombing sorties are those by the bomber units, unless explicitly reported otherwise excluding leaflets, special units and trucking operations, but do include 1,404.9 tons of supplies dropped by parachute June to August 1944, 598 tons dropped in March 1945 (costing around 18 B-24 and most of their crews out of 240 on the low level operation), total such supply sorties unknown, plus the 2,276 / 2,275 / 78 / 2,254 / 1 sorties in May 1945 dropping 4,184.1 tons of supplies in the Netherlands. Over and above the dedicated leaflets unit, the bombers dropped 2,086.6 tons of leaflets.
Trucking operations were done August 1944 to April 1945, total 9,880.2 tons or which 9,623.8 tons were in September 1944. They are not counted as bomber sorties.
Figures also exclude the three deployments to North Africa, 1,453 sorties, 1,288 effective, 3,365 tons of bombs, 69 aircraft MIA. (Including 30 in the Ploesti raid)
Losses for war
Missing unknown is aircraft believed to have landed in friendly territory on the continent, unlocated and/or unheard of during the month of loss or 30 days thereafter. The B-17/24 attrition table says 5,930 MIA/Cat E/Missing the Aircraft Loss Rate table says 5,857. Implying about half the missing were total losses. Note 4,172 MIA in the sortie table and 4,192 in the attrition table.
The December 1944 report says in 1944: B-17 1,879 MIA, 506 Category E, 83 missing unknown, B-24 842, 363 and 18. B-17 250 tons of supplies by parachute in September 1944, B-24 510 tons Losses on ground considered non operational.
Statistical summary of 8th Air Force Operations says in 1944: B-17 1,881 MIA, 503 Category E, 78 missing unknown, B-24 883, 348 and 17. While the official figures tend to agree on sortie totals losses have their differences.
Using credit sorties and ignoring the missing unknown the 1944 report says B-17 MIA rate 1.54%, overall loss rate 1.96%, B-24 1.33% and 1.86%. Using the summary B-17 MIA rate 1.54%, overall loss rate 1.96%, B-24 1.27% and 1.82%. A third set of figures B-17 1,957 MIA, 502 Cat E, 1.61%, 2.02%, B-24 858 MIA, 346 Cat E, 1.30% and 1.82%. Overall the B-24 has a lower loss rate but more chance of being written off in crash landings.
For 1944/45 the B-17 operational accident rate per 100 take offs was 0.22, non operational accidents per 1,000 hours were 0.97, the B-24 0.3 and 1.01. Result total accidents were 931 B-17 and 558 B-24. When it came to fatal accidents 150 B-17 with 1,092 deaths, 148 B-24 with 1,049 deaths.
For the 8th Air Force for the war B-17s were 68.5% of the heavy bombers sent on missions, 69.2% of credit and 70.2% of effective sorties. B-17 were 62% of mechanical, 58.7% of weather and 61.5% of other cause aborts. B-17 MIA rate of 1.6% of credit sorties and a total loss rate of 2.1% of credit sorties dropping an average of 5,140 pounds of bombs. B-24 MIA rate was 1.2%, total loss rate 1.8% average bomb load of 5,321 pounds.
From a near complete list of B-17 losses but missing some B-24 ones.
Deaths when shot down by fighters, for the B-17 about 37% of an average 9.74 man crew were KIA when lost to fighters, 32.1% of an average 9.2 man crew were KIA when lost to flak. For the B-24, after taking out the low level mission flak losses, something like 49.4% of an average 9.4 man crew were KIA when lost to fighters. 37.1% of an average 8.9 man crew when lost to flak.
The Luftwaffe kill claims against 8th and 15th AF B-17s are remarkably consistent, over claiming by about 2 to 1 month after month for the entire campaign. Assuming all the B-17s listed as lost to battle damage, unknown causes or a combination of flak and fighters were in fact lost to fighter attack means the monthly figures move around a lot more and the over claim ratio for the entire campaign drops from 2.1 to 1.7 to 1. The figures for the 8th AF B-24 losses indicate Luftwaffe over claims were under 2 to 1, if all the unknown etc. losses were to fighters it would be as low as 1.5 to 1, and the upper bound around 1.95 to 1. This seems to indicate the B-24 was easier for a fighter to shoot down.
| HB sorties | Airborne | SortieL | credit | effective | MIA |
| Bombing | 330866 | 318793 | 293919 | 266872 | 4139 |
| Carpetbag | 2844 | 2844 | 2750 | 1847 | 24 |
| Trucking | 2434 | 2434 | n/a | 2323 | 2 |
| Leaflet | 2428 | 2428 | 2302 | 2298 | 3 |
| RCM | 1159 | 1152 | n/a | 1110 | 2 |
| Special | 202 | 202 | 180 | 173 | |
| ASR | 16 | 16 | n/a | 16 | |
| Scout | 207 | 207 | n/a | 197 | |
| Aphrodite | 35 | 35 | 35 | 35 | |
| Weather | 1553 | 1553 | 1493 | 1485 | 2 |
| Total | 341744 | 329664 | 300679 | 276356 | 4172 |
Trucking operations were done August 1944 to April 1945, total 9,880.2 tons or which 9,623.8 tons were in September 1944. They are not counted as bomber sorties.
Figures also exclude the three deployments to North Africa, 1,453 sorties, 1,288 effective, 3,365 tons of bombs, 69 aircraft MIA. (Including 30 in the Ploesti raid)
Losses for war
| MIA | Cat E | Missing unknown | Type |
3093 | 1025 | 126 | B-17 |
1099 | 551 | 36 | B-24 |
The December 1944 report says in 1944: B-17 1,879 MIA, 506 Category E, 83 missing unknown, B-24 842, 363 and 18. B-17 250 tons of supplies by parachute in September 1944, B-24 510 tons Losses on ground considered non operational.
Statistical summary of 8th Air Force Operations says in 1944: B-17 1,881 MIA, 503 Category E, 78 missing unknown, B-24 883, 348 and 17. While the official figures tend to agree on sortie totals losses have their differences.
Using credit sorties and ignoring the missing unknown the 1944 report says B-17 MIA rate 1.54%, overall loss rate 1.96%, B-24 1.33% and 1.86%. Using the summary B-17 MIA rate 1.54%, overall loss rate 1.96%, B-24 1.27% and 1.82%. A third set of figures B-17 1,957 MIA, 502 Cat E, 1.61%, 2.02%, B-24 858 MIA, 346 Cat E, 1.30% and 1.82%. Overall the B-24 has a lower loss rate but more chance of being written off in crash landings.
For 1944/45 the B-17 operational accident rate per 100 take offs was 0.22, non operational accidents per 1,000 hours were 0.97, the B-24 0.3 and 1.01. Result total accidents were 931 B-17 and 558 B-24. When it came to fatal accidents 150 B-17 with 1,092 deaths, 148 B-24 with 1,049 deaths.
For the 8th Air Force for the war B-17s were 68.5% of the heavy bombers sent on missions, 69.2% of credit and 70.2% of effective sorties. B-17 were 62% of mechanical, 58.7% of weather and 61.5% of other cause aborts. B-17 MIA rate of 1.6% of credit sorties and a total loss rate of 2.1% of credit sorties dropping an average of 5,140 pounds of bombs. B-24 MIA rate was 1.2%, total loss rate 1.8% average bomb load of 5,321 pounds.
From a near complete list of B-17 losses but missing some B-24 ones.
Deaths when shot down by fighters, for the B-17 about 37% of an average 9.74 man crew were KIA when lost to fighters, 32.1% of an average 9.2 man crew were KIA when lost to flak. For the B-24, after taking out the low level mission flak losses, something like 49.4% of an average 9.4 man crew were KIA when lost to fighters. 37.1% of an average 8.9 man crew when lost to flak.
The Luftwaffe kill claims against 8th and 15th AF B-17s are remarkably consistent, over claiming by about 2 to 1 month after month for the entire campaign. Assuming all the B-17s listed as lost to battle damage, unknown causes or a combination of flak and fighters were in fact lost to fighter attack means the monthly figures move around a lot more and the over claim ratio for the entire campaign drops from 2.1 to 1.7 to 1. The figures for the 8th AF B-24 losses indicate Luftwaffe over claims were under 2 to 1, if all the unknown etc. losses were to fighters it would be as low as 1.5 to 1, and the upper bound around 1.95 to 1. This seems to indicate the B-24 was easier for a fighter to shoot down.
GregP
Major
The truth walrus hurts.
GregP
Major
What a lot of people don't think about when it comes to statistics is that the MIA rate and overall loss rates depend largely on what targets the aircraft were assigned to hit. Now, we can't perform the experiment, but what do you think the rates would be if we exchanged B-17s with B-24s and each hit the other's targets?
The statistics tell us what happened, not why it happened, the way it happened, or even how hairy the missions were.
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33k in the air
Staff Sergeant
- 1,335
- Jan 31, 2021
With a large enough sample size, variations due to target difficulty should average out.
Geoffrey Sinclair
Staff Sergeant
- 904
- Sep 30, 2021
I thought my note about agreeing with the critic was enough to avoid needing to point out the limits of statistics.
Loss rates go up with distance and bad weather before the bad guys do anything and the longer the distance the less reliable the weather forecast is. Rates go up with time spent in hostile airspace. It is easy enough to count the AA guns around targets to compute that risk but the real killers of bombers are fighters and that means working out the chances of interception, starting with how many fighters are in range of the route and how good the interception control is.
Against the bad weather loss bias idea is the RAF seems to have preferred cloudy days when bombing the Ruhr by day, using the more accurate ground based bombing aids in exchange for decreased flak accuracy, the Luftwaffe's decision to discontinue instrument training for day fighters also made bad weather safer for the allies.
The statistics do tell us what happened, the actual performance of the aircraft in the real life situation, and it does point why some decisions were made, like converting the mixed bomb division to all B-17 instead of all B-24. Also the way it happened, the altitudes, speeds, bomb loads etc. The statistics show the B-24 had a higher ratio of Category E to MIA on operations buy that is at least partly due to the B-24 taking more damage on average in a crash.
As for hairy mission, statistics work best for large numbers of missions where all the different factors tend to head towards their average. Missions with above average losses are the hairy ones. As an aside WWI had things like Bloody April but looking at the loss statistics as a percentage of sorties flown, those losses would be well within the acceptable range in WWII.
Loss rates go up with distance and bad weather before the bad guys do anything and the longer the distance the less reliable the weather forecast is. Rates go up with time spent in hostile airspace. It is easy enough to count the AA guns around targets to compute that risk but the real killers of bombers are fighters and that means working out the chances of interception, starting with how many fighters are in range of the route and how good the interception control is.
Against the bad weather loss bias idea is the RAF seems to have preferred cloudy days when bombing the Ruhr by day, using the more accurate ground based bombing aids in exchange for decreased flak accuracy, the Luftwaffe's decision to discontinue instrument training for day fighters also made bad weather safer for the allies.
The statistics do tell us what happened, the actual performance of the aircraft in the real life situation, and it does point why some decisions were made, like converting the mixed bomb division to all B-17 instead of all B-24. Also the way it happened, the altitudes, speeds, bomb loads etc. The statistics show the B-24 had a higher ratio of Category E to MIA on operations buy that is at least partly due to the B-24 taking more damage on average in a crash.
As for hairy mission, statistics work best for large numbers of missions where all the different factors tend to head towards their average. Missions with above average losses are the hairy ones. As an aside WWI had things like Bloody April but looking at the loss statistics as a percentage of sorties flown, those losses would be well within the acceptable range in WWII.
GregP
Major
Not too sure that is correct if the B-17s (for example) hit Schweinfurt all the time and the B-24s (for example) hit much less well-defended targets all the time. I'm NOT saying B-24s hit less well-defended targets all the time ... I'm saying their target packages were not randomly spread around among the heavies.
Some targets, like ball bearing factories, aircraft production, armament production, shipyards, etc. were military necessities and were well-defended. Some targets were civil or less-needed and were less well-defended. Now, I'd believe your contention if the targets were chosen randomly for both B-24s and B-17s, but I think they weren't. Whatever groups were responsible for Schweinfurt were hitting Schweinfurt to the exclusion of other aircraft groups, and they didn't switch aircraft around just for the heck of it. It well might be the case that the hard targets were switched around, but I'd have to look at that before accepting that the losses "balanced out."
GregP
Major
Have to disagree with your premise about losses and the "real killer of bombers."
If you look at the US Navy, let's take just the Hellcat.There were one-third more losses to AAA than to enemy fighters and about the same losses to enemy fighters as operational losses. The biggest single hit was AAA.
Look at the Statistical Digest of World War Two, Table 159: Airplane Losses on Combat Missions in the ETO (since we are in the ETO).
Enemy aircraft and AAA had almost the same number of losses (2,452 for enemy aircraft and 2,439 for AAA) for heavy bombers; 131 for enemy aircraft and 4,92 for AAA for medium bombers (who operated inside the flak envelope almost exclusively); and 1,691 to enemy aircraft and 2,449 to AAA for fighters (with 1,184 to operational losses).
From the above, flak was the best killer of airplanes and was equal to fighters as a bomber killer for heavy bombers and the best at it for everything else.
I flat disagree with "loss rates go up with time spent in hostile airspace." This was WWII, not modern warfare. The loss rates went up if they got attacked, sure, but time spent in hostile airspace didn't mean you would get attacked. If depended largely on here you were and what you were doing. If you were in a Mosquito on a PR run at altitude 30,000+ feet) and at speed (300+ mph), you were likely not going to get attacked. If you were in an A-20 at 15,000 feet by yourself and not headed for a well-defended target, you were unlikely to be attacked unless someone chanced across you. But, if you were in a large bombers stream headed for a well-defended target, you were very unlikely NOT to be attacked.
I disagree with "loss rates went up with distance" and "loss rates went up with weather." I have spent about 20 years around WWII warbirds. Their engines are reliable to the point of being almost laughably reliable. I worked the Planes of Fame Airshow for 10+ years. We ran 50+ sorties a day for 3 days once a year. That's 1,500+ sorties. We had a grand total of 5 aborts during those 10+ years. One was a Corsair who couldn't get one wing to unfold (hydraulic issue) and one was a flat tire. The other 3 were engine-related before takeoff. That's a total of 0.2% or less engine-related issues. Note, once running, we had one precautionary landing due to engine. That's 0.067% airborne engine issues. We also had one Curtiss-Electric prop get stuck in cruise pitch due to a failed electric brush setup. It was easily fixed once the parts were located. And that's for 70-year old engines. Imagine how much better they were when they were relatively new engines.
Weather is a factor only when it is extreme. Flying in clouds won't make you crash unless you have a midair, which is unlikely in formation but more likely in combat. Flying in a thunderstorm might well get you killed, but there is almost no excuse for flying into a thunderstorm. Only idiots do that and they generally don't survive to continue being idiots.
GregP
Major
However, because we disagree doesn't mean we have an issue between us; we don't. I just think the real killer was flak and loss rates weren't rising just because we were flying over Axis airspace.
Cheers!
33k in the air
Staff Sergeant
- 1,335
- Jan 31, 2021
But that didn't happen all the time, which is the point. You'd have to show in the bombing missions a substantive difference in targets assigned; I highly doubt going through something like Roger Freeman's Mighty Eighth War Diary would show any such meaningful difference in the aggregate.
It should be noted the aggregate does not reflect the change which occurred over time. Flak became more of a threat as the enemy fighter force was reduced in number and capability.
Are these warbirds being operated at anywhere near their typical combat gross weights? Are these warbirds being operated regularly at their typical combat altitudes? Are these warbirds being regularly operated in mediocre to deteriorating weather combat missions often were? Are these warbirds being operated routinely for the lengths of time that a single mission during the war required? Are these warbirds being operated at anywhere near the frequency at which wartime aircraft were operated for sustained periods of time?
What was the typical serviceability rate for USAAF bombers and fighters in the ETO?
I wish I had the puff pieces on the use of statistics by the AAF in WW2. They were both aimed at highschoolers to get them interested statistics. One of them was an interview with of the many hundreds of statisticians that served with the 8th AF. The other was an interview with an 8th AF General. I believe it was Doolittle but don't hold me to that. In both articles they offhandedly cite keeping the loss rate between the the B-17 and B-24 equal -to maintain unit moral- as an example of the use of statistics by the 8th AF.
Then there is this:
Then there is this:
Transcript of the following lecture has been posed on this site before. There's no doubt in the author's mind as to which aircraft he deemed the superior aircraft and which he relegated to deservedly a substitute standard design, despite its being produced in far greater numbers.
THE FORTY-FOURTH HARMON MEMORIAL LECTURE IN MILITARY HISTORY, The Aircraft that Decided World War II: Aeronautical Engineering and Grand Strategy, 1933-1945, The American Dimension John F. Guilmartin, Jr. United States Air Force Academy 2001
B-17 (pp.17-20 of 44)
The Boeing B-17 Flying Fortress was the anvil against which the USAAF fighter force hammered the Luftwaffe fighter arm to destruction in the skies over Germany. That was of immense strategic importance above and beyond the destruction that B-17s visited on military and industrial targets, threatening a level of damage to key industries that the Third Reich's leaders could not tolerate. The B-17 was a singular design for which there would have been no viable substitute until the B-29 became available in quantity… if Boeing could have designed the B-29 without the experience gained from the B-17. Even before long range fighters were available to escort deep penetrations, massed formations of B-17s took a significant toll of the Luftwaffe fighter arm, both physically and psychologically, helping to make subsequent the German air arm's recovery impossible.
The B-17 was an uncompromising 1934 design intended to produce the fastest, highest-flying heavy bombardment aircraft extant. Boeing's design team adopted those objectives in response to stated Army Air Corps requirements, but pushed them to the limit as a conscious high risk, high gain strategy to deliver blows against an industrial enemy. For a variety of reasons involving internal Army politics and blind luck—the loss of the first prototype to a pilot error accident—that strategy nearly failed and most of the initial Army bomber contract went to the mediocre twin-engine B-18, a derivative of the DC 3 civilian transport. That having been said, Boeing's boldness reaped huge strategic dividends in range, bomb load and ability to absorb battle damage.
The excellent Wright R-1820 nine-cylinder engine, re-engineered at Air Corps insistence to burn 100-octane gasoline, was an essential cornerstone of the B-17's success.26 Another was the development of the turbo supercharger by General Electric on an Air Corps contract, the only discrete Army research and development program to receive funding through the Great Depression. The importance of the turbo supercharger lies in the fact that the War and Navy departments stopped subsidizing the development of military aero engines during the Great Depression. American military aircraft would henceforth be powered by engines designed for civilian use, and while high altitude performance had obvious military importance it had little civilian value. The European solution, gear-driven superchargers designed as an integral part of the engine, was an obvious non-starter for economic reasons.27 The military market was simply too small. American superchargers therefore would be add- on accessories and the only evident way to power such a supercharger was a turbine driven by engine exhaust gasses. The extremely high temperatures and rotational speeds to which the turbines were subjected posed obvious problems. A further complicating factor was the lack of full-sized high altitude wind tunnels: turbo superchargers could only be tested in actual flight with the obvious risks that entailed. Beginning work in 1919, General Electric eventually surmounted these problems and by the mid-1930s was fielding increasingly reliable turbo superchargers.28 The B-17 was slated for them from the beginning.
The result was a bomber capable of delivering a two-ton bomb load over a thousand miles from its base—the figures are approximate, based on data from missions flown over Germany in 1943-44—penetrating enemy air defenses in formation at altitudes of 25,000 to 29,000 feet.29 The emphasis in the preceding sentence is warranted since a formation's speed and ceiling are dictated by its most poorly performing aircraft. Such performance, unprecedented in the mid- to late 1930s, speaks volumes both for the soundness of the B17's design and for the excellence of Wright, General Electric, and Boeing production line quality control. The excellence of the B-17's design is highlighted by comparing it to that of the Consolidated B-24 Liberator, the closest thing to an available substitute. A newer design by five years and similarly powered,30 the B-24 was nonetheless inferior to the B-17 in every critical performance parameter that counted in the European theater of operations save maximum range.
A final factor contributing to the B-17's success was the decision by the Air Corps during the 1920s to adopt the .50 caliber machine gun as its standard aircraft weapon. Designed toward the end of World War I as a heavy infantry machine gun, the Browning .50 caliber was an uncompromising design with exceptional ballistic performance.31 Not only was its projectile nearly four times as massive as that of .30 caliber weapons, its superior ballistic coefficient and streamlined shape gave it the best velocity over distance characteristics of any commonly used aerial machine gun of World War II.32 As a result, the Fortress's effective defensive fire ranged well beyond the practical hitting distance of any Axis air-to-air gun. While unescorted B-17 formations proved unable to sustain deep penetrations of German airspace without incurring prohibitively heavy losses, they inflicted serious losses on the German fighter arm in the process. To be sure, the Air Corps initially underestimated the need for defensive armament and Boeing engineers resisted the addition of turrets that spoiled the aircraft's aerodynamic shape. Ultimately, however, tactical logic and superior engineering prevailed and from early 1942 on B-17s were well provided with heavy defensive armament, much of it mounted in power-operated turrets.
Facilitated by intercom and radio connections, the Fortress' aircrew arrangement throughout the cockpit, crew compartment and fuselage ensured that the dispersed crewmen retained their group cohesion in air to air combat. Compartmentalized responsibilities and specialized training demanded aircrew discipline in coordinating defensive fire and fighting battle damage to the airframe, engines and subsystems. This dispersed crew arrangement provided for more defensive armament that could protect the bomber from all flight attitudes of fighter attack, especially with the B-17G modified "chin" turret model giving frontal attack defense. The size of the airframe and engineering capacity enabled the Fortress to grow in defensive firepower from ten .50 caliber machine guns aboard the "E" model to the "G" model with thirteen machine guns providing all around defense. The porcupine firepower gave large formations of B-17s overlapping fields of fire that enabled adjacent elements and squadrons to cover one another. The result was the fifty-four aircraft combat box formation that dealt severe blows against the industrial strength Nazi Germany.
The final analysis, bombers exist to drop bombs, and a late war USAAF study showed that the B-17 was the most accurate Army bomber (the second most accurate being the B-29), enjoying a small, but significant, advantage over the B-24 despite the fact that B24s bombed from lower altitudes.33 In ex post facto validation of the Air Force's preference for heavy bombers, the study showed that four engine bombers were significantly more accurate than twin engine bombers across the board.34 That the B-17, a 1934 design, was still in front line service in 1945 speaks volumes for the quality of its design.
THE FORTY-FOURTH HARMON MEMORIAL LECTURE IN MILITARY HISTORY, The Aircraft that Decided World War II: Aeronautical Engineering and Grand Strategy, 1933-1945, The American Dimension John F. Guilmartin, Jr. United States Air Force Academy 2001
B-17 (pp.17-20 of 44)
The Boeing B-17 Flying Fortress was the anvil against which the USAAF fighter force hammered the Luftwaffe fighter arm to destruction in the skies over Germany. That was of immense strategic importance above and beyond the destruction that B-17s visited on military and industrial targets, threatening a level of damage to key industries that the Third Reich's leaders could not tolerate. The B-17 was a singular design for which there would have been no viable substitute until the B-29 became available in quantity… if Boeing could have designed the B-29 without the experience gained from the B-17. Even before long range fighters were available to escort deep penetrations, massed formations of B-17s took a significant toll of the Luftwaffe fighter arm, both physically and psychologically, helping to make subsequent the German air arm's recovery impossible.
The B-17 was an uncompromising 1934 design intended to produce the fastest, highest-flying heavy bombardment aircraft extant. Boeing's design team adopted those objectives in response to stated Army Air Corps requirements, but pushed them to the limit as a conscious high risk, high gain strategy to deliver blows against an industrial enemy. For a variety of reasons involving internal Army politics and blind luck—the loss of the first prototype to a pilot error accident—that strategy nearly failed and most of the initial Army bomber contract went to the mediocre twin-engine B-18, a derivative of the DC 3 civilian transport. That having been said, Boeing's boldness reaped huge strategic dividends in range, bomb load and ability to absorb battle damage.
The excellent Wright R-1820 nine-cylinder engine, re-engineered at Air Corps insistence to burn 100-octane gasoline, was an essential cornerstone of the B-17's success.26 Another was the development of the turbo supercharger by General Electric on an Air Corps contract, the only discrete Army research and development program to receive funding through the Great Depression. The importance of the turbo supercharger lies in the fact that the War and Navy departments stopped subsidizing the development of military aero engines during the Great Depression. American military aircraft would henceforth be powered by engines designed for civilian use, and while high altitude performance had obvious military importance it had little civilian value. The European solution, gear-driven superchargers designed as an integral part of the engine, was an obvious non-starter for economic reasons.27 The military market was simply too small. American superchargers therefore would be add- on accessories and the only evident way to power such a supercharger was a turbine driven by engine exhaust gasses. The extremely high temperatures and rotational speeds to which the turbines were subjected posed obvious problems. A further complicating factor was the lack of full-sized high altitude wind tunnels: turbo superchargers could only be tested in actual flight with the obvious risks that entailed. Beginning work in 1919, General Electric eventually surmounted these problems and by the mid-1930s was fielding increasingly reliable turbo superchargers.28 The B-17 was slated for them from the beginning.
The result was a bomber capable of delivering a two-ton bomb load over a thousand miles from its base—the figures are approximate, based on data from missions flown over Germany in 1943-44—penetrating enemy air defenses in formation at altitudes of 25,000 to 29,000 feet.29 The emphasis in the preceding sentence is warranted since a formation's speed and ceiling are dictated by its most poorly performing aircraft. Such performance, unprecedented in the mid- to late 1930s, speaks volumes both for the soundness of the B17's design and for the excellence of Wright, General Electric, and Boeing production line quality control. The excellence of the B-17's design is highlighted by comparing it to that of the Consolidated B-24 Liberator, the closest thing to an available substitute. A newer design by five years and similarly powered,30 the B-24 was nonetheless inferior to the B-17 in every critical performance parameter that counted in the European theater of operations save maximum range.
A final factor contributing to the B-17's success was the decision by the Air Corps during the 1920s to adopt the .50 caliber machine gun as its standard aircraft weapon. Designed toward the end of World War I as a heavy infantry machine gun, the Browning .50 caliber was an uncompromising design with exceptional ballistic performance.31 Not only was its projectile nearly four times as massive as that of .30 caliber weapons, its superior ballistic coefficient and streamlined shape gave it the best velocity over distance characteristics of any commonly used aerial machine gun of World War II.32 As a result, the Fortress's effective defensive fire ranged well beyond the practical hitting distance of any Axis air-to-air gun. While unescorted B-17 formations proved unable to sustain deep penetrations of German airspace without incurring prohibitively heavy losses, they inflicted serious losses on the German fighter arm in the process. To be sure, the Air Corps initially underestimated the need for defensive armament and Boeing engineers resisted the addition of turrets that spoiled the aircraft's aerodynamic shape. Ultimately, however, tactical logic and superior engineering prevailed and from early 1942 on B-17s were well provided with heavy defensive armament, much of it mounted in power-operated turrets.
Facilitated by intercom and radio connections, the Fortress' aircrew arrangement throughout the cockpit, crew compartment and fuselage ensured that the dispersed crewmen retained their group cohesion in air to air combat. Compartmentalized responsibilities and specialized training demanded aircrew discipline in coordinating defensive fire and fighting battle damage to the airframe, engines and subsystems. This dispersed crew arrangement provided for more defensive armament that could protect the bomber from all flight attitudes of fighter attack, especially with the B-17G modified "chin" turret model giving frontal attack defense. The size of the airframe and engineering capacity enabled the Fortress to grow in defensive firepower from ten .50 caliber machine guns aboard the "E" model to the "G" model with thirteen machine guns providing all around defense. The porcupine firepower gave large formations of B-17s overlapping fields of fire that enabled adjacent elements and squadrons to cover one another. The result was the fifty-four aircraft combat box formation that dealt severe blows against the industrial strength Nazi Germany.
The final analysis, bombers exist to drop bombs, and a late war USAAF study showed that the B-17 was the most accurate Army bomber (the second most accurate being the B-29), enjoying a small, but significant, advantage over the B-24 despite the fact that B24s bombed from lower altitudes.33 In ex post facto validation of the Air Force's preference for heavy bombers, the study showed that four engine bombers were significantly more accurate than twin engine bombers across the board.34 That the B-17, a 1934 design, was still in front line service in 1945 speaks volumes for the quality of its design.
33k in the air
Staff Sergeant
- 1,335
- Jan 31, 2021
Regarding the B-17 versus B-24 debate, I'll offer these quotes from the book The B-24 Liberator — A Pictorial History by Allan G. Blue:
There were certain other contrasts between the two aircraft which were becoming apparent to men who were acquainted with both. For example the overall impression one got from the Fortress interior was that it was, like its exterior, round and smooth — with its equipment built-in rather than added-on. Each B-17 crew member had a place to sit down and strap himself in — a small point, perhaps, but psychologically important. On the other hand the Liberator fuselage, while of larger dimensions than the Fortress, offered little in the way of comfort for the crew. There seemed to be draughts everywhere, and of such magnitude that they were far more than the troublesome spot heaters could contend with. Movement throughout the ship was awkward and difficult in full flight gear, and more often than not resulted in jarring collisions with various sharp-edged and unyielding structural members and/or installed equipment. Idle gunners sat on the floor — if they sat — and likely as not pondered possible fates for the design engineer who was responsible for a fuel-transfer system that required any prudent B-24 pilot to crack open the bomb bay doors in flight to disperse the petrol fumes. Or perhaps the ball and tail gunners thought about the greater speed with which their B-17 counterparts could exit their stations in a emergency. (p.184)
Inevitably the Liberator continued to be compared with the Flying Fortress and, as far as the later versions of the two bombers were concerned, suffered by the comparison. This was due not so much to short-comings of the Liberator — although it certainly had them — as to the fact the B-17 was in many respects an exceptional aircraft, with many of its merits having particular — and personal — appeal to the men who flew it and flew in it. From the beginning the Fortress was an honest aircraft, easy to fly in formation, with a low landing speed and with no major vices. 'A four-engined Piper Cub' was the popular and rather apt description. Most important, the Fortress retained its original characteristics throughout its development, while the Liberator did not. (p.186)
Actually the Liberator never did lose its performance edge over the B-17, as a series of tests run at Elgin Field demonstrated conclusively late in the war. Rather, the areas in which the B-24 excelled became less important in the European and Mediterranean theatres. The range of the Fortress was adequate for Europe, and individual aircraft speed became academic because of formation requirements. Altitude, however, became paramount and here, literally, the B-17 remained on top. In addition, with over 70% of Eighth Air Force mission failures being attributed to navigational errors, the superior accommodations of the B-17 nose were highly desirable. General Doolittle, in fact, considered poor visibility the number one fault of the B-24.
In the Pacific theatre there was no vocal contest between the two aircraft, for although B-24's were originally requested by Pacific theatre commanders because they felt there was a better chance of getting them than the more popular B-17, the Liberator's longer legs soon demonstrated that it was a natural choice for an air war conducted for the most part at extreme range. The European requirement for tight formation flying was not as severe, and the typical maximum-range mission allowed Pacific Liberators, when necessary, to approach the target at adequate altitude because of the large amount of fuel burned on the way. (p.186-187)
There were certain other contrasts between the two aircraft which were becoming apparent to men who were acquainted with both. For example the overall impression one got from the Fortress interior was that it was, like its exterior, round and smooth — with its equipment built-in rather than added-on. Each B-17 crew member had a place to sit down and strap himself in — a small point, perhaps, but psychologically important. On the other hand the Liberator fuselage, while of larger dimensions than the Fortress, offered little in the way of comfort for the crew. There seemed to be draughts everywhere, and of such magnitude that they were far more than the troublesome spot heaters could contend with. Movement throughout the ship was awkward and difficult in full flight gear, and more often than not resulted in jarring collisions with various sharp-edged and unyielding structural members and/or installed equipment. Idle gunners sat on the floor — if they sat — and likely as not pondered possible fates for the design engineer who was responsible for a fuel-transfer system that required any prudent B-24 pilot to crack open the bomb bay doors in flight to disperse the petrol fumes. Or perhaps the ball and tail gunners thought about the greater speed with which their B-17 counterparts could exit their stations in a emergency. (p.184)
Inevitably the Liberator continued to be compared with the Flying Fortress and, as far as the later versions of the two bombers were concerned, suffered by the comparison. This was due not so much to short-comings of the Liberator — although it certainly had them — as to the fact the B-17 was in many respects an exceptional aircraft, with many of its merits having particular — and personal — appeal to the men who flew it and flew in it. From the beginning the Fortress was an honest aircraft, easy to fly in formation, with a low landing speed and with no major vices. 'A four-engined Piper Cub' was the popular and rather apt description. Most important, the Fortress retained its original characteristics throughout its development, while the Liberator did not. (p.186)
Actually the Liberator never did lose its performance edge over the B-17, as a series of tests run at Elgin Field demonstrated conclusively late in the war. Rather, the areas in which the B-24 excelled became less important in the European and Mediterranean theatres. The range of the Fortress was adequate for Europe, and individual aircraft speed became academic because of formation requirements. Altitude, however, became paramount and here, literally, the B-17 remained on top. In addition, with over 70% of Eighth Air Force mission failures being attributed to navigational errors, the superior accommodations of the B-17 nose were highly desirable. General Doolittle, in fact, considered poor visibility the number one fault of the B-24.
In the Pacific theatre there was no vocal contest between the two aircraft, for although B-24's were originally requested by Pacific theatre commanders because they felt there was a better chance of getting them than the more popular B-17, the Liberator's longer legs soon demonstrated that it was a natural choice for an air war conducted for the most part at extreme range. The European requirement for tight formation flying was not as severe, and the typical maximum-range mission allowed Pacific Liberators, when necessary, to approach the target at adequate altitude because of the large amount of fuel burned on the way. (p.186-187)
Greg Boeser
1st Sergeant
Promises of dropping a bomb in a pickle barrel from 5 miles up aside, in Europe bombing was formation toggling on leader.
If a bomb should happen to land in a pickle barrel, it was because said pickle barrel was within a mile of the intended target.
If a bomb should happen to land in a pickle barrel, it was because said pickle barrel was within a mile of the intended target.
