Most Overrated aircraft of WWII.....? (1 Viewer)

[Shortround6]

The P-36 with better R-1830 in that light does not sound bad. The P-66 with that engine sounds even better.
While a thing or two can be pointed out to the pinsong's proposal (I do it often, not just to him ), even the over-weight F4F-4 was good for service ceiling of 33000 ft, and the F4F-3 was supposedly good for more than 37000 ft.

and this is where the comparison or usefulness of the service ceiling comes in. The Wildcats didn't really fight at 30,000ft and up over Guadalcanal, but they could fight at 20-30,000ft much better than the P-40s and P-39s could at those altitudes.
I would also note that the "book" figures for ceilings apply to a 'standard' 59 degree F day at sea level and the corresponding temperature at altitude.
Go to the tropics and/or North African dessert and the temperature (and thus air density) at even 30,000ft is quite a bit warmer. Warmer/less dense air means less lift from wing and less power from the engine and a propeller with less bite so you can have a several thousand foot reduction in "practical" ceiling vrs the book numbers. For the Wildcat with a "book" number of 33-37K being reduced to 30-33K means you can still fight at 25-26K, If your "book" number was 29.5K then you are in deep crap trying to fight at over 20,000ft.

 

[Shortround6]

I'm with Smokey. But I go a little further. Boeing products have been victims of overhype from Alpha to Omega. As befits the biggest planemaker in the land that brought you Madison Avenue.
But it doesn't start with the B-17. With the notable exception of the 747 and possibly the 727, practically everything they've built has fallen short of its advertising. From the post WW1 biplane fighters, the B-9, the 247, and on through the Stratocruiser, B-47 (a slippery, treacherous machine), B-52 (a sitting duck: Hanoi 12/'72), right on up to the 787(lithium battery fires), each has left a lot to be desired. In many cases, they were immediately followed by another manufacturer's product which was more developed but didn't beat them to market. (DC-3, B-10, B-24, DC-6/7)
I make exceptions for the 747, which was/is an outstanding achievement and deserves the hype, and the 727, which nailed the S-duct issue that had stood in the way of trijet design for several years.
My girlfriend, who spent the last couple years of her career flying 737-800s, likened it to " a Model A Ford retrofitted with a drive by wire system and an awesome stereo". A nice flying airframe, but not a fully integrated high tech airplane like the Embraers and Canadairs she'd been flying. 21st century electronics shoehorned into a 20th century airframe.
The one place where Smokey and I part ways is the P-51. Fantastic airplane, but one in a cluster of fantastic airplanes, and not the be-all and end-all the hype would have you believe.
Cheers,
Wes
PS: I know you guys SY, SR, DR, TP, BillR, Greg, and Biff, are going to pick me apart on this, but to quote MacBeth, "Lay on, MacDuff!"

I might have less trouble with the position if different arguments were used. However many of Smokey's arguments/facts were either not true or don't really apply.
Plenty of good aircraft had the first prototype crash and a lot of them for something that was actually wrong with the aircraft and not a pilot/crew error.

You also have to lay some of the blame on the customers at times. Or the users, In the case of the B-52 not quite the same thing, the customers were the guys who ordered the thing in the late 1940s and early 50s, The users who sent it over Hanoi in 1972 had been lieutenants or captains when it was purchased.
Misapplication isn't quite Boeing's fault.
While the Stratocruiser (307) wasn't really one of the worlds greats neither was the DC-4E.

1 built, sold to Japan just before WW II
Had next to nothing to do with the DC-4 except the 4 engines and the DC-4 designation.

 

[XBe02Drvr]

The users who sent it over Hanoi in 1972 had been lieutenants or captains when it was purchased.

And the users who flew it were in diapers!

 

[XBe02Drvr]

Friend of mine talked with a young AF pilot who delivered a BUFF to the boneyard and was looking through old logs to discover it was commanded on its first operational mission by his grandfather!
Cheers,
Wes

 

[Shortround6]

We are getting a bit far of the track but on the B-52, is it a great plane because it has lasted as long as it has or Congress is too cheap to buy replacements?

I don't think when it was designed they ever thought it would last this long. Granted all the ones in service have been rebuilt/overhauled a number of times but it was originally designed to attack at high altitudes and when that mode of attack became non-viable (due to AA missiles) they adopted a low altitude, ground hugging attack profile which, by pure chance, the B-52 with it's long flexible wings could actual do. trouble was every hour spent at low altitude was worth 5-10 hours of high altitude flight in stress life for the airframe. Then you get to Vietnam and some genius/s decide to attack North Vietnam at similar altitudes and speeds to the attack profile deemed useless back in the late 50s due to...... wait for it.............the same AA missiles and AA guns the Russians had in the late 50s. which North Vietnam now had in abundance.
Granted the B-52s in 1972 had better electronic jammers but come on!

I have no idea if Boeing was selling the Air Force the new jammers or not

 

[pbehn]

Sea Hornet was 15-30 mph faster than Tigercat (despite 15% less power) , difference being greater as altitude is increased. Sea Hornet climbed better and was with greater range, while RAF's Hornet was still a better performer.

I would say they were pretty comparable given the extra seat and armament of the Tigercat. My point was that through all the theorising and experimentation at the end of the propeller era two planes with completely different engines turned in just about the same, If the Hornet was superior then that shows that any previous bias towards water cooled V12s had some merit. Personally I don't think there was any bias and just as a jet engine isn't simple because it has only one moving part, air cooled radials were in no way simple or even cheap because they didn't have a water jacket. Their need for heat resistant and thermo conductive alloys and to be able to operate across a big temperature range made them just as complex.

 

[XBe02Drvr]

Their need for heat resistant and thermo conductive alloys and to be able to operate across a big temperature range made them just as complex.

Not to mention the lubrication issues that go with that temperature and BMEP.
CHEERS,
Wes

 

[pbehn]

The British "test" was flawed for a bunch of reasons. Despite being told that the B-17Cs they got weren't really ready for combat the British used them anyway, in the typical British "penny packet" numbers, rarely more than 3 aircraft per mission, which is hardly enough to set up the defensive formation quantity of fire the 'theory' depended on. The as fitted armament consisted of a single manually operated .50 cal out each waist window, one, 50 cal out the back of a ventral tub and the fourth out the top of the radio compartment, however field of fire and indeed field of view for the dorsal gunner were best described as restricted..

The British only ever received a penny packet number of B-17Cs, twenty in total. I have read precisely the opposite comments from the British side. That is the Americans said they were fit for service and the British said they weren't, The Americans concluding that the British didn't want it to work and so they didn't make it. From what I read there were lots of niggling problems with things icing up, not only guns but also oxygen systems and instruments. The idea of protective covering fire with the defence of a B-17C (fortress I) was a complete myth, a major problem was vapour trails as I remember.

 

[XBe02Drvr]

The idea of protective covering fire with the defence of a B-17C (fortress I) was a complete myth, a major problem was vapour trails as I remember.

The USAAC hadn't experienced any actual combat since WW1, and their thinking encompassed P-26 class opposition. When the B-17 came out, it was nearly as fast as fighters then in service, and thus amenable to the "lightly armed fast bomber" concept. When fighter performance and armament "took off", bomber think didn't keep up on this side of the pond.
Cheers,
Wes

 

[parsifal]

The figures I have seen is over a 1000 LW a/c claimed by all the French flown fighters, not just by the H 75 units; while the likely actual number shot down by French flown fighters is 355.
Secret Défense - Mai-Juin 40 : le mythe des "1000 victoires" aériennes définitivement explosé - Libération.fr

No the initial claims for LW losses to h-75 units was more than 1000 LW a/c. it is coincidental that this number coincides with total loss claims made by the FAF

In fact, if FAF were claiming to have shot down only 1000 LW aircraft, they would be seriously under claiming LW losses, as Overy clearly explains.

LW losses were substantially higher than that.

In May and June 1940 the Luftwaffe lost 1,482 aircraft destroyed in the air and a further 488 written off on landing. A further 219 were written off after being returned to the factories. Calculated losses inflicted by the RAF and the minors amounted to no more than 650 LW a/c. By deduction that means the FAF caused the loss of over 1500 LW aircraft, either as direct shoot downs or subsequent write offs. Because the campaign was so short, relatively few of the LW machines were lost in non-combat related incidents. Ive read somewhere it was in the order 200 a/c. French flak was negligible, perhaps 50 LW a/c in total. The lions share of LW losses were at the hands of the French fighter forces, which tore into the LW causing it damage from which it never recovered fully.

The FAF destroyed more LW a/c than they (the French) had on strength at the beginning of the campaign The LW lost nearly half their total strength at the start of the battle, and well above the replacement rate from the factories. As the battle continued, the lack of large air reserves began to tell and French fighter aircraft began to inflict some severe losses on the LW. Allied air tactics, learned in the harsh school of battle, started to improve. Over the evacuation beaches at Dunkirk the Luftwaffe lost 240 aircraft in three days of fighting and von Kleist was forced to report "enemy air superiority (FC is believed to have been responsible for the loss of about 100 LW a/c, nearly all of the rest were at the hands of the FAF.

Accidents, battlefield attrition, and Allied attacks on airfields all took their toll. Pilot losses were high, and by the end of the battle exhaustion and frayed nerves reduced Luftwaffe effectiveness even more. Their sortie rate fell from around 4 per airframe at the start of the campaign, to just under two per day at finish, whilst FAF moved in reverse, starting at 0.9 per day per a/c to about 2.1 sorties per day at the end.

 

[swampyankee]

I'm with Smokey. But I go a little further. Boeing products have been victims of overhype from Alpha to Omega. As befits the biggest planemaker in the land that brought you Madison Avenue.
But it doesn't start with the B-17. With the notable exception of the 747 and possibly the 727, practically everything they've built has fallen short of its advertising. From the post WW1 biplane fighters, the Pshooter, the B-9, the 247, and on through the Stratocruiser, B-47 (a slippery, treacherous machine), B-52 (a sitting duck: Hanoi 12/'72), right on up to the 787(lithium battery fires), each has left a lot to be desired. In many cases, they were immediately followed by another manufacturer's product which was more developed but didn't beat them to market. (DC-3, B-10, B-24, DC-6/7)
I make exceptions for the 747, which was/is an outstanding achievement and deserves the hype, and the 727, which nailed the S-duct issue that had stood in the way of trijet design for several years.
My girlfriend, who spent the last couple years of her career flying 737-800s, likened it to " a Model A Ford retrofitted with a drive by wire system and an awesome stereo". A nice flying airframe, but not a fully integrated high tech airplane like the Embraers and Canadairs she'd been flying. 21st century electronics shoehorned into a 20th century airframe.
The one place where Smokey and I part ways is the P-51. Fantastic airplane, but one in a cluster of fantastic airplanes, and not the be-all and end-all the hype would have you believe.
Cheers,
Wes
PS: I know you guys SY, SR, DR, TP, BillR, Greg, and Biff, are going to pick me apart on this, but to quote MacBeth, "Lay on, MacDuff!". Burnham Wood is not yet come to Dunsinane.

Actually, I never worked for Boeing, so I've no axe to grind, either way. Until the 707, Boeing was largely kept afloat by its military contracts; only when they were able to steal a march on Douglas, and get the 707 into service before the DC-8 did they really become a significant player in the commercial airline market. Boeing has survived its US competition -- Lockheed gave up commercial aviation and Douglas was having financial issues when it was merged with McDonnell, and McD/D's MD-11 follow-on to the DC-10 never met its guarantees, didn't sell, and probably put McD/D's finances into a tail spin.

The DC-2 and DC-3 pretty much killed the 247 in the market; probably about 120 times more DC-4s were built than 307s, Boeing built 56 377s; Douglas built over 700 DC-6s and over 300 DC-7s. Lockheed built about 400 commercial Constellations. Of course, Lockheed built the L-188 Electra, which promptly developed a rather bad reputation due to a sub-synchronous whirl mode. Convair tried, and failed, with the 880/990.

 

[Stig1207]

No the initial claims for LW losses to h-75 units was more than 1000 LW a/c. it is coincidental that this number coincides with total loss claims made by the FAF

In fact, if FAF were claiming to have shot down only 1000 LW aircraft, they would be seriously under claiming LW losses, as Overy clearly explains.

LW losses were substantially higher than that.

In May and June 1940 the Luftwaffe lost 1,482 aircraft destroyed in the air and a further 488 written off on landing. A further 219 were written off after being returned to the factories. Calculated losses inflicted by the RAF and the minors amounted to no more than 650 LW a/c. By deduction that means the FAF caused the loss of over 1500 LW aircraft, either as direct shoot downs or subsequent write offs. Because the campaign was so short, relatively few of the LW machines were lost in non-combat related incidents. Ive read somewhere it was in the order 200 a/c. French flak was negligible, perhaps 50 LW a/c in total. The lions share of LW losses were at the hands of the French fighter forces, which tore into the LW causing it damage from which it never recovered fully.

The FAF destroyed more LW a/c than they (the French) had on strength at the beginning of the campaign The LW lost nearly half their total strength at the start of the battle, and well above the replacement rate from the factories. As the battle continued, the lack of large air reserves began to tell and French fighter aircraft began to inflict some severe losses on the LW. Allied air tactics, learned in the harsh school of battle, started to improve. Over the evacuation beaches at Dunkirk the Luftwaffe lost 240 aircraft in three days of fighting and von Kleist was forced to report "enemy air superiority (FC is believed to have been responsible for the loss of about 100 LW a/c, nearly all of the rest were at the hands of the FAF.

Accidents, battlefield attrition, and Allied attacks on airfields all took their toll. Pilot losses were high, and by the end of the battle exhaustion and frayed nerves reduced Luftwaffe effectiveness even more. Their sortie rate fell from around 4 per airframe at the start of the campaign, to just under two per day at finish, whilst FAF moved in reverse, starting at 0.9 per day per a/c to about 2.1 sorties per day at the end.

Total LW operational losses, destroyed and written off were in the 1400-1500 range, but to all causes, not destroyed in the air.

 

[parsifal]

you will have to take that up with overy and murray, who tell a different story

 

[Stig1207]

Perhaps take it up with the French?
La contribution des données chiffrées à la construction d'un mythe....
I don't read the language, but with a bit of Google translating, it shows that even the French don't support your assessment.

 

[Smokey Stover]

Them thar is fighting words Smokey

When making claims like that it is best to have all your ducks in a row and unfortunately your ducks are different breeds in different ponds.

Crash of prototype had nothing to do with the qualities of the aircraft, good or bad. They tried to take off without unlocking the control surfaces. Gust locks had been installed to keep the large control surfaces from flapping around in the wind and getting damaged. One thing that came of this accident was take-off check lists. Douglas got the contract, in large part, because a twin engine bomber was cheaper than a 4 engine. They could get a lot more planes for the money ( first order for B-18s was a whopping 82 aircraft)

The 4000lb bomb load is a furphy that just will not go away. It seems to have got it's start in an offhand quote from a General to a war correspondent. B-17s routinely carried 5000lb loads to Berlin and 6000lbs on occasion to Berlin and often on shorter flights. The element of truth to the 4000lb load is that while the Berlin bound B-17s carried 5000lbs of iron bombs the ones carrying incendiaries carried a bit over 3000lbs so the average was 4000lbs.
A B-17, with the external bomb racks (seldom used) could get 17,000lbs off the ground, it just couldn't go very far with it.
External racks would hold a pair of 4000lb bombs (or smaller) and did not block the bomb bay.
Mosquitoes could not carry the 4000lb cookie until 1944 so what they could or could not carry makes little difference to B-17s in action in 1942/43. Mosquitoes carried four 500lbs inside and two outside at best for the first year or more of operation. And they very rarely carried incendiaries except for target marking.

The British "test" was flawed for a bunch of reasons. Despite being told that the B-17Cs they got weren't really ready for combat the British used them anyway, in the typical British "penny packet" numbers, rarely more than 3 aircraft per mission, which is hardly enough to set up the defensive formation quantity of fire the 'theory' depended on. The as fitted armament consisted of a single manually operated .50 cal out each waist window, one, 50 cal out the back of a ventral tub and the fourth out the top of the radio compartment, however field of fire and indeed field of view for the dorsal gunner were best described as restricted.
View attachment 483890
There was one additional .30 cal or .50 cal in the nose. British were using either two or three power turrets in most of their bombers at this point and why they thought that a handful of manually aimed .50 cal guns was such a big improvement as to allow daylight operation is beyond me.

The B-17E was already on order when the RAF got their 20 Fortress MK Is and with double the number of guns and twin dorsal and ventral power turrets the firepower was significantly higher. Still not enough as it turned out but there was reason to discount earlier experience.

BTW you might want to check on that just a few more bombs a little bit further for the B-29 comparison also.

Ok i admit i was a little unfair. And some of my facts where on the lamb. But there is little doubt that without the P-51 there is no way the airwar over europe would have ended so quickly. And if the 17 really was such a great aircraft why did they replace/build so many B-24's. Im not saying it was a bad aircraft. I just think its looks and fond memories of the lucky crews that made it back have overshadowed its capabilities. But i concede to some of your points. Just one last thing, the bombload was not increased until the B-17F came online and that was still only 8,000lbs. But at a cost. By using a stronger undercarriage, the maximum bomb capacity was increased from 4,200 lb (1,900 kg) to 8,000 lb (3,600 kg). Though this modification reduced cruise speed by 70 mph (And it was never what one would call fast to begin with) (110 km/h), the increase in bomb capacity was a decided advantage. But a number of other modifications were made, including re-integrating external bomb racks, but because of its negative impact on both rate-of-climb and high-altitude flight the configuration was rarely used and the racks were removed.

 

[Smokey Stover]

I'm with Smokey. But I go a little further. Boeing products have been victims of overhype from Alpha to Omega. As befits the biggest planemaker in the land that brought you Madison Avenue.
But it doesn't start with the B-17. With the notable exception of the 747 and possibly the 727, practically everything they've built has fallen short of its advertising. From the post WW1 biplane fighters, the Pshooter, the B-9, the 247, and on through the Stratocruiser, B-47 (a slippery, treacherous machine), B-52 (a sitting duck: Hanoi 12/'72), right on up to the 787(lithium battery fires), each has left a lot to be desired. In many cases, they were immediately followed by another manufacturer's product which was more developed but didn't beat them to market. (DC-3, B-10, B-24, DC-6/7)
I make exceptions for the 747, which was/is an outstanding achievement and deserves the hype, and the 727, which nailed the S-duct issue that had stood in the way of trijet design for several years.
My girlfriend, who spent the last couple years of her career flying 737-800s, likened it to " a Model A Ford retrofitted with a drive by wire system and an awesome stereo". A nice flying airframe, but not a fully integrated high tech airplane like the Embraers and Canadairs she'd been flying. 21st century electronics shoehorned into a 20th century airframe.
The one place where Smokey and I part ways is the P-51. Fantastic airplane, but one in a cluster of fantastic airplanes, and not the be-all and end-all the hype would have you believe.
Cheers,
Wes
PS: I know you guys SY, SR, DR, TP, BillR, Greg, and Biff, are going to pick me apart on this, but to quote MacBeth, "Lay on, MacDuff!". Burnham Wood is not yet come to Dunsinane.

Im a big supporter of the P-51 as i said below. How anyone could say that fighter was overrated is beyond me. Had it not been for that fighter the loss rate of 17's would have been so bad daylight raids would have surely been halted. Infact after the disaster at Ragensberg & Schweinfurt the US top brass were ready to switch to night bombing along with the British.

 

[parsifal]

Perhaps take it up with the French?
La contribution des données chiffrées à la construction d'un mythe....
I don't read the language, but with a bit of Google translating, it shows that even the French don't support your assessment.

I suggest you get another translator. I do speak a little French and it is saying that essentially the question of losses is controversial and hard to conform, but at least 1000 Luftwaffe aircraft were destroyed in the air by the FAF, A/c destroyed in the air don't include aircraft that landed and were then written off. If you do include those numbers, losses inflicted on the LW by the French begin to climb toward the 1500 mark. What makes it difficult are that LW records are incomplete and we cant be sure who shot down what.

if you are going to use a foreign language source, it pays to have some idea of what you are posting.


This source does appear to be pretty good, though it is not properly referenced. It is possible that it has partisan positions to promote. There are some notoriously right wing French sources these days.....but it seems okay, thats about all i can say in its favour. But even if it is fairly balanced the centrepiece of its positioning is that it wants to challenge the established and accepted numbers. That's interesting and it is certainly not impossible but it is a far cry from proving anything, other than the author believes the numbers are contentious.


According to Peter Cornwell's "The battle of France then and now": between Sep 1939 to June 10th 1940 Luftwaffe lost 2168 aircrafts and about 3710 air crews killed or missing in the west, of which over 1800 were lost after 10 May. These losses do not include losses in Norway.

 

[drgondog]

Im a big supporter of the P-51 as i said below. How anyone could say that fighter was overrated is beyond me. Had it not been for that fighter the loss rate of 17's would have been so bad daylight raids would have surely been halted. Infact after the disaster at Ragensberg & Schweinfurt the US top brass were ready to switch to night bombing along with the British.

It is true that there was significant discussion regarding 'joining RAF' in night bombing in October, 1943. A B-17 BG for training in night operations with H2X was established and Navigators, Bombardiers and Pilots were in fact trained in radar guided attacks.

That said, the issues far outweighed the possible benefits. First the training in the States and supply chain of both bombers (B-17 and B-24) all needed to be modified but only limited kits, and depots, were available with capacity to modify for night opertions - the lead time to 'get operational' was contemplated near mid 1944 to get same bomber force over targets. Second, there was legitimate skepticism that POINTBLANK objectives targeting destruction of aircraft manufacturing centers, Or degrading the LW in time for Overlord, could be achieved with RAF tactics. Third, there was not enough time or airspace to assemble both 8th AF and RAF BC over England without suffering horrendous attrition to accidents. Fourth, the P-51B-1 was arriving in a steady stream in October, 1943 as well as early arrivals of the P-38J, pointing to enough Long Range Escort (with Hoped for capability vs LW Day Fighter arm) to execute ARGUMENT/Big Week as planned for February, 1944. Last, the horrible daylight bombing environment due to northern Europe weather pointed to a 'stand down' for late fall 1943 - time to recover both aircraft and crews while continuing to bomb targets within range of P-47D escort with external pressurized combat tanks,

Simply stated - at no time was an actual 'switch' to join RAF at night ever seriously planned.

 

[SuperFire]

We are getting a bit far of the track but on the B-52, is it a great plane because it has lasted as long as it has or Congress is too cheap to buy replacements?

...

Is this a bad time to bring up space-based weapon systems including lasers and the fact that all conventional warfare is out-moded depending upon reliability and scalablity of the ultimate high-ground? But, black projects have no public proof to back them up; still, why buy new conventional bombers when an invisible beam can zap anything in a micro-second. At least food for thought. Of course the answer might be horrifically sobering about governance and the human races need for conflict.

 

[Shortround6]

Ok i admit i was a little unfair. And some of my facts where on the lamb. But there is little doubt that without the P-51 there is no way the airwar over europe would have ended so quickly. And if the 17 really was such a great aircraft why did they replace/build so many B-24's. Im not saying it was a bad aircraft. I just think its looks and fond memories of the lucky crews that made it back have overshadowed its capabilities. But i concede to some of your points. Just one last thing, the bombload was not increased until the B-17F came online and that was still only 8,000lbs. But at a cost. By using a stronger undercarriage, the maximum bomb capacity was increased from 4,200 lb (1,900 kg) to 8,000 lb (3,600 kg). Though this modification reduced cruise speed by 70 mph (And it was never what one would call fast to begin with) (110 km/h), the increase in bomb capacity was a decided advantage. But a number of other modifications were made, including re-integrating external bomb racks, but because of its negative impact on both rate-of-climb and high-altitude flight the configuration was rarely used and the racks were removed.

The B-17 may have been over hyped, both at the time and in popular writing since then. But I like to do analysis based on facts.
The B-24 had several advantages over the B-17, unfortunately it also had a few disadvantages which did not come out until it had bee in service for a while.
as to one aircraft replacing another, that gets very difficult some times.
For the B-17 the big change from the early planes came with the "E" model, This was ordered Aug 30 1940, well before the British had flown a Fortress I let alone used one in combat. It was in production in Sept of 1941 and by Dec 7th over 40 had been built (some were at Pearl harbor) and plans were made to produce it at two additional factories. The Vega plant ( a division of Lockheed ) and at a new factory run by Douglas, it takes time to build,equipe and staff factories and by the time these extra factories came on line they wound up building B-17Fs only 512 "E"s were built which is a small number compared to the overall total.
Now simultaneously the B-24 was going into production at Consolidated/San Diego and at Consolidated/Fort Worth and at Douglas/Tulsa. Ford/Detroit and North American/Dallas were brought in By Jan of 1942. First roll out of planes from these factories were months away.
Trying to swap which factory produced which aircraft could lead to months of lost production not to mention hundreds of tons of parts in the supply chain from subcontractors. B-17 and B-24 used different engines so you either came up with a new model to use up the existing engine manufacturing capability or you changed one or more factories over to make the other engine. IN 1943 alone Chevrolet made over 23,000 P & W R-1830s under licence and Buick made over 24,000 more. Studebaker built over 23,000 Wright R-1820s that year (and almost 50% more in spare parts).
Changing such programs in mid stream takes some awfully good reasons.

I would really like to see some evidence that the B-17E or F cruised 70mph slower than the early ones because of changes to the airplane. SO you have to compare at the same altitude and using the same power settings (RPM and Boost) or close to it. Yes they were slower But the 70mph figure is a bit dubious.
Speeds for large formations were often quite a bit lower than what the aircraft could do when flying alone or with only a few companions.
I would note that weight can play a large part also. And some of the early B-17s the weights they measured the performance at were absurdly low.

I Know the racks were removed but claiming the B-17 was over rated because the Lancaster could (as modified by 2-3 squadrons worth of aircraft) carry a 22,000lb load is not a very good argument.