# B-29 Modifications



## Zipper730 (Jun 22, 2020)

I remember seeing different figures in the post-war periods for range & payload for the B-29. It would also appear that the altitude seemed to have gone up. I'm curious what changes were made on the B-29 during and after the war?

Particularly variables that affected speed.



 Airframes
, 
M
 MIflyer
, 

 MiTasol


----------



## FLYBOYJ (Jun 23, 2020)

Well aside from the Silverplate modifications, this is where the B-29 ultimately went







Boeing B-50 Superfortress - Wikipedia


----------



## Zipper730 (Jun 24, 2020)

FLYBOYJ said:


> Well aside from the Silverplate modifications, this is where the B-29 ultimately went


No, I know the B-50 was the ultimate result of the B-29. What I was talking about was the various modifications made to the B-29's during operational use (which include Silverplate), and into the post war (not including B-50's).

I remember seeing a video which involved the RAF discussing interceptor attacks which involved jet-fighters flying at bombers from the sides and from behind, then curving into and then coming head-on against them. For this test, a series of B-29's were used for the test. The B-29's were given speed figures that seemed higher than the ones cited in WWII.

I'm curious if changes were made to the cowlings, the engines, the turbochargers, and stuff?


----------



## FLYBOYJ (Jun 24, 2020)

Zipper730 said:


> No, I know the B-50 was the ultimate result of the B-29. What I was talking about was the various modifications made to the B-29's during operational use (which include Silverplate), and into the post war (not including B-50's).
> 
> I remember seeing a video which involved the RAF discussing interceptor attacks which involved jet-fighters flying at bombers from the sides and from behind, then curving into and then coming head-on against them. For this test, a series of B-29's were used for the test. The B-29's were given speed figures that seemed higher than the ones cited in WWII.
> 
> I'm curious if changes were made to the cowlings, the engines, the turbochargers, and stuff?



There were some mods done to the B-29 in the post war (I believe they were relatively minor) but ultimately the "goal" was the "B-29D" which eventually became the B-50. The re-designation was done to get money appropriated to new aircraft programs.

Reactions: Like Like:
1 | Informative Informative:
1 | Like List reactions


----------



## GrauGeist (Jun 24, 2020)

The post-war B-29D, which led to the B-50, had the Pratt & Whitney R-4360 engines (rated at 3,500hp each), as opposed to the Wright R-3350 engines (rated at 2,200hp each).
Perhaps this is the B-29 you're thinking of?

Reactions: Like Like:
1 | Like List reactions


----------



## FLYBOYJ (Jun 24, 2020)

There were operational mods done to late production B-29 that were more role related too.


----------



## Graeme (Jun 25, 2020)

Zipper730 said:


> RAF discussing interceptor attacks which involved jet-fighters flying at bombers from the sides and from behind, then curving into and then coming head-on against them. For this test, a series of B-29's were used for the test.



That sounds like the Meteor interception trials with 616 Squadron - but they were against B-24s...

Reactions: Informative Informative:
1 | Like List reactions


----------



## Zipper730 (Jun 25, 2020)

FLYBOYJ said:


> There were some mods done to the B-29 in the post war (I believe they were relatively minor)


Such as?


> There were operational mods done to late production B-29 that were more role related too.


Like the 300 that were built without the gun-computer for fire-bombing missions?


----------



## MIflyer (Jun 25, 2020)

Some of the B-29's had most of their guns removed for the nighttime fire raids. By Korea the guns were back, but maybe they used some of the ones with only tail guns for those tests.


----------



## Skyediamonds (Jun 25, 2020)

I heard about “Silverplate” but never knew what exactly was involved. Can anyone briefly describe?
Gary

Reactions: Agree Agree:
1 | Like List reactions


----------



## GrauGeist (Jun 25, 2020)

"Silverplate" was the delivery program for the Atom bombs destined for Japan.

The size and weight of the bombs (there were four - one was tested state-side and two if the three remaining were deployed on Japan) dictated airframe modifications as well as additional instrumentation installed on all the bombers in the B-29 composite group.

Reactions: Informative Informative:
1 | Like List reactions


----------



## manta22 (Jun 25, 2020)

Skyediamonds said:


> I heard about “Silverplate” but never knew what exactly was involved. Can anyone briefly describe?
> Gary



In the '70s a forward section of a B29 fuselage arrived in a local Tucson salvage yard. Nose art identified it as "The Dutchess" and the salvage yard owner maintained that it had been one of the planes involved in the A-bomb program. If this were true it should have been placed in the Pima Air Museum or some other place to preserve it. I undertook to try to trace The Dutchess' history and talked to Paul Tibbets on the phone for 45 minutes about it. Tibbets was friendly and quite helpful and gave me some things to check to see if it had been one of the 509th Composite Group's planes. The most significant feature was the single bomb-bay rather than two shorter bomb bays on a standard production B29. He also related that many other changes were also made to the Wichita production run of these special versions. He gave me Chuck Sweeney's phone number and I talked to him as well. He did not know of a B29 named The Dutchess but said that it might have been one of the Los Alamos research planes.

I never did find out the history of The Dutchess B29 and it disappeared from the salvage yard thereafter.


----------



## FLYBOYJ (Jun 25, 2020)

From wiki:

Silverplate - Wikipedia


----------



## Juanita (Jun 25, 2020)

"The most significant feature was the single bomb-bay rather than two shorter bomb bays on a standard production B29."

Very interesting to hear this remark about the bomb-bay doors. Did he go into detail? 
I have drawn several Silverplate examples and I didn't notice a change to the doors. Admittedly many of the photos are post-WW2 but they all seem to have the radar fitted (radar sits between the two bomb bays).
Would be very interested to hear more...I'll modify my artworks if they have an error.

There is a link to one of the artworks (yes, I know, the nose art is incorrect - if flew the mission with no nose art, and the full Bockscar artwork was applied soon after the mission)


Juanita

Reactions: Like Like:
2 | Like List reactions


----------



## Juanita (Jun 25, 2020)

Just for fun. Here is a size comparision between the largest Allied bomber of WW1 (Handley Page V/1500) and a B-29.
The V/1500 was designed to bomb Berlin but the war ended before the type had flown any combat missions.

Reactions: Like Like:
2 | Like List reactions


----------



## GreenKnight121 (Jun 25, 2020)

The B-29B was a lighter version, with improved performance. 311 were built. Boeing B-29B Superfortress

Six B-29s were fitted with R-3350-CA-2 fuel injection engines and the revised "Andy Gump" nacelles that were intended for late production B-29As in a program to service test these new engine installations. These aircraft were redesignated YB-29J. Some of these YB-29Js were used for photo-reconnaissance work as RB-29J. Boeing YB-29J Superfortress 

Info from Boeing B-29 Superfortress by Joe Baugher


The single bomb bay was only on the initial test Silverplate B-29 - all of the operational ones had the standard bomb bay configuration. Silverplate


> B-29-5-BW 42-6259 (referred to as the "Pullman airplane" from an internal code name assigned it by the Engineering Division of Army Air Forces Materiel Command) was delivered to the 468th Bombardment Group at Smoky Hill AAB, Kansas, on 30 November 1943, and flown to Wright Field on 2 December.
> 
> Modifications to the bomb bays of 42-6259 were extensive and time-consuming. Its four 12-foot (3.7 m) bomb bay doors and the fuselage section between the bays were removed and a single 33-foot (10 m) bomb bay configured. The length of the initial gun-type bomb shape was approximately 17 feet (5.2 m), necessitating that it be carried in the aft bomb bay, with some of its length protruding into the forward bay. The implosion-type bomb was mounted in the forward bay.[8] New bomb suspensions and bracing were attached for both shape types, and separate twin-release mechanisms were mounted in each bay, using modified glider tow-cable attach-and-release mechanisms.
> 
> ...



Second increment Silverplate B-29s were modified as follows: 


> They were fitted with British single-point bomb releases mounted on a re-designed H-frame suspension rack fitted in the forward bomb bay, so that additional fuel tanks could be carried in the aft bay. A new crew position, called the "weaponeer station", was created in the cockpit with a panel to monitor the release and detonation of the bomb during the actual combat drops.
> 
> .....
> 
> ...



Silverplate B-29 with Little Boy:

Reactions: Like Like:
2 | Like List reactions


----------



## nuuumannn (Jun 26, 2020)

There was a B-29 (42-24441) that was fitted with existing manned gun turrets instead of the production remotely operated ones, and another, YB-29 was modified with the nose turret and side blister turrets (fitted in the forward fuselage aft of the cockpit and one on the fuse side where the remote operator's blister was) for the PB4Y Privateer and B-32 Dominator.


----------



## nuuumannn (Jun 26, 2020)

Juanita said:


> Very interesting to hear this remark about the bomb-bay doors. Did he go into detail? I have drawn several Silverplate examples and I didn't notice a change to the doors. Admittedly many of the photos are post-WW2 but they all seem to have the radar fitted (radar sits between the two bomb bays). Would be very interested to hear more...



The single bomb bay Silverplate aircraft was modified to fit the Thin Man bomb, which had a length of 17 feet, so it couldn't fit within the confines of the B-29's two bays without removing the central section where the radome sits in your illustrations, Juanita. The Thin Man was the first atom bomb designed for carriage by an aircraft and was based on the gun portion's length (that fired the 'bullet' at the fissile material to create a chain reaction). Once it was realised that the uranium isotope U235 could be used instead of plutonium, the gun size and therefore the bomb was reduced in length, thus Little Boy was born and the B-29 could carry a bomb within the confines of one of its existing bays - with two inches to spare. Until then, the USA didn't have an existing aircraft to carry the Thin Man internally without modification and it was suggested that the only aircraft in 1943 that could was an Avro Lancaster.


----------



## GrauGeist (Jun 26, 2020)

nuuumannn said:


> Until then, the USA didn't have an existing aircraft to carry the Thin Man internally without modification and it was suggested that the only aircraft in 1943 that could was an Avro Lancaste


But the USAAF command, being what it was, would have used the B-19 before using anything British.

Reactions: Funny Funny:
1 | Like List reactions


----------



## nuuumannn (Jun 26, 2020)

GrauGeist said:


> But the USAAF command, being what it was, would have used the B-19 before using anything British.




Now, we've been over this subject before....

Reactions: Funny Funny:
1 | Like List reactions


----------



## manta22 (Jun 26, 2020)

Jaunita;

Paul Tibbits went into great detail about the differences in his B29s but that phone call was almost 50 years ago so I don't remember much. I should have recorded that phone call.


----------



## SaparotRob (Jun 26, 2020)

So the B-29 evolves from the pinnacle of the “armed bomber will get through” theory to the Mosquito style “fly high, fly fast” plan. 
Kind of settles that pre war debate.


----------



## SaparotRob (Jun 26, 2020)

Yes, I know that the bulk of B-29 missions in WW2 were at relatively low altitude. I think the Korean conflict had it up high.


----------



## chipieal (Jun 26, 2020)

Skyediamonds said:


> I heard about “Silverplate” but never knew what exactly was involved. Can anyone briefly describe?
> Gary


Silver plate was the password that General Groves was given in developing the Atomic Bomb. Anything he needed he just used Silver plate. I am assuming that since the B - 29 was the delivery vehicle, it made sense that Silver plate may have been used in this context

Reactions: Informative Informative:
1 | Like List reactions


----------



## GrauGeist (Jun 26, 2020)

SaparotRob said:


> Yes, I know that the bulk of B-29 missions in WW2 were at relatively low altitude. I think the Korean conflict had it up high.


It was intended to conduct higher altitude bombing missions but the Jet Stream over Japan made that impossible, so lower altitude missions were conducted instead.
The bombing missions conducted at higher altitudes in Korea were along the lines of the B-29's original design.


----------



## SaparotRob (Jun 26, 2020)

Wasn’t the slipstream one of the reasons why daylight bombing wasn’t so effective in Europe?


----------



## GrauGeist (Jun 27, 2020)

SaparotRob said:


> Wasn’t the slipstream one of the reasons why daylight bombing wasn’t so effective in Europe?


No, the prevailing high altitude currents over Europe changed seasonally and were not as critical as the Jet Stream over Japan.

The high altitude bombing accuracy over Europe is an entirely different matter and has been discussed in great length in several threads in the forums here.

Reactions: Like Like:
1 | Like List reactions


----------



## soaringtractor (Jul 2, 2020)

FLYBOYJ said:


> There were operational mods done to late production B-29 that were more role related too.


There were mods done to the cowlings to allow more airflow, the cause of the engine fires, and to the supercharger/turbochargers on the engines !!! the silverplate planes were built with the mods to carry the atomic bombs !!! Some B29s had most of the defensive guns removed especially for the low level fire bombingd, more bombs carried and less jap fighters around and more P51's to defend !!!


----------



## soaringtractor (Jul 2, 2020)

SaparotRob said:


> Wasn’t the slipstream one of the reasons why daylight bombing wasn’t so effective in Europe?


Did you mean Jet stream ??? The winds at altitude that raised hell with accuracy of bombing ???? The winds at various altitudes blow in different directions making any bombing run sketchy !!!! The bomb sight made no difference in accuracy, only IF there was NO wind at all and that is rare !!!! Why low level bombing was employed !!!


----------



## soaringtractor (Jul 2, 2020)

GrauGeist said:


> No, the prevailing high altitude currents over Europe changed seasonally and were not as critical as the Jet Stream over Japan.
> 
> The high altitude bombing accuracy over Europe is an entirely different matter and has been discussed in great length in several threads in the forums here.


The winds at altitude still played hell with bombing accuracy in Europe !!


----------



## BobB (Jul 2, 2020)

There were many mods made during WWII. People who worked for Bell-Atlanta told me that an airplane would come off the production line in Marietta and immediately be flown to Wichita for mod work at the same time that airplanes were being flown into Marietta from other plants for mod work that was only done at Marietta. It all sounds crazy but it worked.

Reactions: Informative Informative:
1 | Like List reactions


----------



## SaparotRob (Jul 2, 2020)

soaringtractor said:


> Did you mean Jet stream ??? The winds at altitude that raised hell with accuracy of bombing ???? The winds at various altitudes blow in different directions making any bombing run sketchy !!!! The bomb sight made no difference in accuracy, only IF there was NO wind at all and that is rare !!!! Why low level bombing was employed !!!


Yup, meant jet stream. That’s what happens when I stay up past my bedtime.


----------



## FLYBOYJ (Jul 2, 2020)

soaringtractor said:


> There were mods done to the cowlings to allow more airflow, the cause of the engine fires, and to the supercharger/turbochargers on the engines !!! the silverplate planes were built with the mods to carry the atomic bombs !!! Some B29s had most of the defensive guns removed especially for the low level fire bombingd, more bombs carried and less jap fighters around and more P51's to defend !!!


All mentioed earlier in this thread including Silverplate


----------



## GrauGeist (Jul 2, 2020)

soaringtractor said:


> The winds at altitude still played hell with bombing accuracy in Europe !!


Not like over the home islands of Japan where the Jet Stream typically exists at 30 to 39 thousand feet ASL and travels westerly at 110mph.

And the B-29s involved in the fire-bombing missions had all MGs removed but the tail-gun position in order to reduce fuel consumption and increase speed. They were not escorted as the missions were flown from either China or later from the Marianas and the Japanese did not have an effective night-fighter at the time.

Reactions: Like Like:
1 | Agree Agree:
1 | Like List reactions


----------



## Zipper730 (Jul 4, 2020)

MIflyer said:


> Some of the B-29's had most of their guns removed for the nighttime fire raids.


From what I recall, the turrets remained, but the guns and ammo were removed with the exception of the tail-gun. If not all the time, sometimes the crews were retained to operate as lookouts.

For these raids, I'm curious if they removed the gun-computer, or kept that. From what I remember, 300 B-29's were built without the gun-computer installed.



GrauGeist said:


> "Silverplate" was the delivery program for the Atom bombs destined for Japan. . . . The size and weight of the bombs (there were four - one was tested state-side and two if the three remaining were deployed on Japan) dictated airframe modifications as well as additional instrumentation installed on all the bombers in the B-29 composite group.


What instrumentation was installed?


> It was intended to conduct higher altitude bombing missions but the Jet Stream over Japan made that impossible, so lower altitude missions were conducted instead.


I thought the fact that the amount of energy to climb to high altitude made it more practical to cruise lower. From what I remember, the raids carried out over Tokyo were done at something like 5000-10000' or less. What typical altitudes were seen during daytime raids after March, 1945?



GreenKnight121 said:


> The B-29B was a lighter version, with improved performance. 311 were built.


So, those are the versions without the gun-computer?


> Six B-29s were fitted with R-3350-CA-2 fuel injection engines and the revised "Andy Gump" nacelles that were intended for late production B-29As in a program to service test these new engine installations.


I guess the implementation of the new nacelles was due to the end of the war?


> The single bomb bay was only on the initial test Silverplate B-29 - all of the operational ones had the standard bomb bay configuration.


Do you have any pictures of that one?



soaringtractor said:


> There were mods done to the cowlings to allow more airflow, the cause of the engine fires, and to the supercharger/turbochargers on the engines


I assume they loosened the cowling up? As for the turbochargers, provided I didn't misunderstand, what modifications were made there?


----------



## GrauGeist (Jul 4, 2020)

Zipper730 said:


> What instrumentation was installed?


All the B-29s in the 509th composite group were able to deliver the A-bomb or monitor the drop. When Enola Gay made her run, she was accompanied by other B-29s who were acting as monitors.
When Bock's Car made their drop, Enola Gay was one of the monitors.
The instruments included weather gathering, radiation monitoring, additional radio equipment and so on.
Also, each Silverplate B-29 had an additional crew station up in the cockpit for monitoring the bomb while in the bomb bay as well as monitoring the release and detonation, called the "weaponeer station".



Zipper730 said:


> I thought the fact that the amount of energy to climb to high altitude made it more practical to cruise lower. From what I remember, the raids carried out over Tokyo were done at something like 5000-10000' or less. What typical altitudes were seen during daytime raids after March, 1945?


The effort to get to altitude is rewarded by more efficient cruise at those higher altitudes.
The later daytime raids were at varying altitudes (well below 30,000 feet) but the fire-bombing raids were made at roughly 5,000 feet.


----------



## MIflyer (Jul 5, 2020)

When I was at Tinker AFB in the 70's I talked to some people there who had actually worked on the 509th BG aircraft.

It seems that it was normal procedure for B-29's coming off the production line at Wichita to go straight to Tinker Field for modifications and other tasks. One common task was to remove the fuel flow meters from the aircraft and calibrate them. But in the case of the aircraft going to the 509 BG they insisted that the fuel flow meters be calibrated while in the aircraft. This was much more difficult to accomplish but gave better accuracy.

The book "Friendly Monster" describes the work a B-29 crew had to do to get their aircraft all tuned up and everything calibrated to make it fly properly. A B-29 straight out of the factory needed a lot of work and the crew had to fly it many hours to figure out what the airplane liked and what adjustments were required.

I read of one B-29 that had the after fuselage made by a different company than the forward fuselage. I think the two companies involved were Bell and Martin. They found the aft fuselage was a slightly larger diameter than the forward fuselage and the aft section had to be crimped down to fit the forward part. And for some reason that B-29 was the fastest one in the squadron.

Reactions: Like Like:
2 | Like List reactions


----------



## Zipper730 (Jul 5, 2020)

GrauGeist said:


> All the B-29s in the 509th composite group were able to deliver the A-bomb or monitor the drop. When Enola Gay made her run, she was accompanied by other B-29s who were acting as monitors.
> When Bock's Car made their drop, Enola Gay was one of the monitors.
> The instruments included weather gathering, radiation monitoring, additional radio equipment and so on.
> Also, each Silverplate B-29 had an additional crew station up in the cockpit for monitoring the bomb while in the bomb bay as well as monitoring the release and detonation, called the "weaponeer station".


Fascinating


> The effort to get to altitude is rewarded by more efficient cruise at those higher altitudes.


Theoretically: In practice, it _appears_ to be affected by rate of climb and available range. If I recall correctly, the B-29 would break even by flying at 35000' if it could only fly 5500 miles (something that might have been beyond the capability of the plane with any payload). Though some sources list climb-rate figures that compare with the B-17, I'm not sure if that covered the fact that climb-speed was more limited due to engine cooling over other aircraft, and I'm not sure what weight it applied at.


> The later daytime raids were at varying altitudes (well below 30,000 feet) but the fire-bombing raids were made at roughly 5,000 feet.


Did they fly 5000' from Tinian to Tokyo and back? Or did they cruise higher?

I remember hearing after the raids on Tokyo, they sometimes flew day raids at altitude, but lower than earlier flights, and I'm not sure what altitudes were typically employed.


----------



## MIflyer (Jul 5, 2020)

The B-29's used for monitoring the atomic attacks dropped instrumented packages that transmitted data back. Just after the Hiroshima mission a group of students found one of the instrumentation packages and opened it. Inside they found a letter addressed to Japan's top physicist, explaining that the US had developed the atomic bomb. They read the letter and burst into tears, knowing that the war was lost.

When he heard of the attack the leader of the A6M design team, Jiro Horikoshi, called that same physicist and asked him what he thought it could be. The Phd replied, "We will have to find out more but it sounds like an atomic bomb." Horikoshi was thunderstruck. Before WWII he and other top experts gathered to discuss what possible weapons the USA could come up with. The atomic bomb was brought up but they concluded that was at least 100 years away. Imagine finding out suddenly that your adversary was 100 years more advanced than you had thought.

Reactions: Like Like:
3 | Like List reactions


----------



## Zipper730 (Dec 23, 2020)

This is one source where I heard differences in speed: 360 knots @ 30000' which calculates to 414 mph. That said, there could be errors here, as the ability to carry 3400 nm with 20000 pounds of bombs seems to be erroneous unless they made some amazing changes to the plane.


----------



## Joe Broady (Dec 26, 2020)

Zipper730 said:


> For these raids, I'm curious if they removed the gun-computer, or kept that. From what I remember, 300 B-29's were built without the gun-computer installed.



Computers, plural. There were five sighting stations (nose, tail, top, left, right) and each had its own computer. The last three had "double parallax" computers because they could control two turrets simultaneously. These computers weighed 130 lb each. The single parallax computers for the nose and tail stations were 25 lb lighter. Four of the five computers were in a well under the gunner compartment floor. The nose computer was above the navigator instrument panel.

"When you are operating in high temperatures give the computer a break. Pull up the floor boards over the computer well for better ventilation." Then as now, computers didn't like to get hot.

B-29 Gunner's Information File (no date)
T. O. No. 11-70A-1, The Central Fire Control System, Handbook of Operation and Service Instructions, 5 December 1944

I think I found that first manual online, maybe at the Army Air Forces Collection. The second one I paid for and it's a monster at 620 MB.

Reactions: Like Like:
1 | Like List reactions


----------



## GrauGeist (Dec 26, 2020)

Zipper730 said:


> Did they fly 5000' from Tinian to Tokyo and back? Or did they cruise higher?


They would typically climb to about 19 - 20 thousand feet and cruise, once they hit a waypoint offshore that turned them towards Tokyo, they'd start their descent and level off at 5 thousand before target.
This helped both with fuel consumption and maintaining speed for their egress and climb back to altitude for the trip home without burning excessive fuel.


----------



## Zipper730 (Dec 27, 2020)

Joe Broady said:


> Computers, plural.


Understood


> The single parallax computers for the


When you say parallax, does that mean the fact that the computer would compute lead and drop, or lead, drop, and the position of the turret relative to the plane's centerline? I figure if the turrets were pointed sideways that would make the bullets seem to curve off behind the aircraft quite a bit. On a fighter it's not as complicated as you have the guns pointing wherever you're flying...



GrauGeist said:


> They would typically climb to about 19 - 20 thousand feet and cruise, once they hit a waypoint offshore that turned them towards Tokyo, they'd start their descent and level off at 5 thousand before target.
> 
> This helped both with fuel consumption and maintaining speed for their egress and climb back to altitude for the trip home without burning excessive fuel.


Did they climb back to the same altitude (19000-20000') or to a lower altitude? I remember some profiles for the P-47N when used as an attack-plane, which would see it cruise in at altitude and egress fairly close to sea-level.


----------



## GrauGeist (Dec 27, 2020)

Zipper730 said:


> Did they climb back to the same altitude (19000-20000') or to a lower altitude? I remember some profiles for the P-47N when used as an attack-plane, which would see it cruise in at altitude and egress fairly close to sea-level.


Because of the distances involved, the B-29's pilot had to keep an eye on fuel management, so they would climb back to an altitude that provided a better cruise setting.
The air's density at sea level would mean a higher consumption of fuel, plus a disadvantage if intercepted by Japanese elements.


----------



## Zipper730 (Dec 27, 2020)

GrauGeist said:


> Because of the distances involved, the B-29's pilot had to keep an eye on fuel management, so they would climb back to an altitude that provided a better cruise setting. The air's density at sea level would mean a higher consumption of fuel, plus a disadvantage if intercepted by Japanese elements.


I wasn't trying to suggest they cruised out at sea-level -- I was just trying to determine if they climbed to the same altitude they entered at, or a lower altitude.

The P-47N's ground attack profile called for a cruise to target at 10000' followed by an egress at sea-level. So I was curious if they'd cruise home at around 10000' maybe 15000'.


----------



## Joe Broady (Jan 5, 2021)

Zipper730 said:


> Understood
> When you say parallax, does that mean the fact that the computer would compute lead and drop, or lead, drop, and the position of the turret relative to the plane's centerline?



To quote the book, "PARALLAX - To compensate for the distance along the longitudinal axis of the airplane between the turret and the sight which is controlling the turret." (Handbook of Operation and Service Instructions, The Central Fire Control System, December 1944)

A similar principle is at work when a fighter's wing guns are harmonized. They are at different distances from the gun sight, so no one adjustment will get the bullets to converge on the same point at every range. But the B-29 computer can continuously compensate for parallax due to range and direction of the attacker. For example, the two upper turrets, both under control of the upper sighting station, will "toe in" slightly so their fire converges on the attacker.

Reactions: Like Like:
1 | Like List reactions


----------



## Zipper730 (Jan 6, 2021)

J
 Joe Broady

So, if you turn the turret sideways, the reticle will not be displaced further to the side to factor in that the bullets will appear to fly sideways as well as forward?


----------



## Joe Broady (Jan 6, 2021)

Zipper730 said:


> J
> Joe Broady
> 
> So, if you turn the turret sideways, the reticle will not be displaced further to the side to factor in that the bullets will appear to fly sideways as well as forward?



Not sure what you're asking, but according to these magazine articles from early 1945 the relative wind at 30000 feet and 250 mph deflects a .50 caliber bullet 12 yards sideways at a range of 800 yards when blowing at right angles to the line of fire.

Popular Mechanics Feb 1945
Popular Science Feb 1945

The pipper of a B-29 gun sight has a fixed direction with respect to the sight. It is not displaced to compensate for ballistics and target motion. The situation is completely different when a manned turret has a computing sight. That sight has a fixed relationship with the guns, so the reticle must be displaced to effect the corrections. For instance, it lags behind the attacking fighter (compared to a ring and bead sight). To put the lagging reticle on the target therefore forces the gunner to aim ahead.

But the B-29 sight is merely a means to inform the computer of the attacker's azimuth, elevation, azimuth rate, elevation rate, and range. The computer and servos in the turret do the aiming. An exception is an emergency mode you can select when the computer fails. Then the turret is slaved directly to the sight and the gunner must "aim off" with estimated corrections in the old fashioned way.


----------



## BobB (Jan 7, 2021)

Going off on a bit of a tangent; a fellow who worked at a mod center near Denver said that he had a reputation for being good at fixing B-29 fire control computers. He said that as a last resort, he would take his shoe off and whack the computer with it. The computer was full of electro-mechanical relays and sometimes one was stuck but would get knocked loose by a whack.


----------



## Zipper730 (Jan 8, 2021)

Joe Broady said:


> Not sure what you're asking


Basically, when I said "displaced", I meant positioned to factor in lead: As described in the first link, at a distance of 800 yards, gravity will cause the bullet to drop 4.6 yards, so the reticle would be displaced so it matches where the impact point would be.

On a WWII fighter plane that had a lead-computing gunsight: The reticle would be set by selecting an aircraft's wingspan, and using a grip on the throttle to widen and narrow it, so as to encircle the target's wings. With the target's wingspan set, widening and narrowing the reticle infers range. With the aircraft in level flight, and 800 yards computed (something that would probably be useless on most aircraft, though the P-38, P-39, Mosquito NF/FB variants had centerline mounted guns), the reticle would be displaced such that it would produce an aiming point on the reflector site that would correspond to a location 4.6 yards below the centerline of the aircraft flying in a straight line.

With the aircraft pulling g-load (say a left hand turn), the increased vertical acceleration and directional changes would result in the reticle being repositioned down and to the right a greater degree so that the impact point is corrected for, when range is computed by widening and narrowing the reticle.

What I was curious was two things: Firstly, the definition of parallax, which seems to be factoring the difference between the sighting station and the position of the turret, and; whether the turret's gunsight would correct not just for g-load, but whether the reticle would be displaced as a result of the position of the turret relative to the centerline, and correct not just for drop/g-load, but also to the degree it was turned off the centerline. With the turret aimed left of the centerline, I was curious if the reticle would be displaced to the left as well as slightly down because that's the direction the bullets would appear to fly when you're pointing the gun sideways while flying at 250 mph.


> The pipper of a B-29 gun sight has a fixed direction with respect to the sight. It is not displaced to compensate for ballistics and target motion.


So the reticle in the sighting station is pointed at the target, with the computer positioning the turret based on where the reticle is aimed?


----------



## MIflyer (Jan 30, 2021)

When the B-29's were enroute to Japan in daylight they would sight vessels and provide reports on them. Trouble was, the USAAF crews proved to be very poor at identifying ships as to type and size. So some special "slide rules" were developed to enable them to use the gunsights to measure the size of the ships.

Reactions: Informative Informative:
2 | Like List reactions


----------



## pbehn (Jan 30, 2021)

GrauGeist said:


> Because of the distances involved, the B-29's pilot had to keep an eye on fuel management, so they would climb back to an altitude that provided a better cruise setting.
> The air's density at sea level would mean a higher consumption of fuel, plus a disadvantage if intercepted by Japanese elements.


I didnt see this post when it was made maybe 'cos it was on my birthday, but as I understand it the pilot of a B-29 was aware of the issues of fuel management but it was the flight engineers job. The flight engineer on a B-29 took more training than the pilot from what I've read and most of the time he was telling the pilot what to do as far as airspeed and altitude goes.

Reactions: Like Like:
2 | Like List reactions


----------



## EAIAnalog (Mar 5, 2022)

This is for Zipper730. I would quote his post, but I can't figure out how to do that. Here is a visualization of the parallax problem in the gun turrets. Hold up both of your hands with the index fingers extended. The right hand represents the gun sight and the left hand represents the turret. The distance between the hands is the parallax distance. Now move your right hand to represent the gunsight tracking the target. Since the turret control system is designed to track the gunsight, the turret matches the gunsight exactly. However the turret is not pointing at the target. It needs a correction that depends on the distance between the gunsight and the turret. That correction rotates the turret so that its line-of-sight intersects the gunsight's line-of-sight (just rotate your left hand to see what I mean). The computer sits between the gunsight and the turret, and it makes that correction, and a host of others that have been mentioned above.

In the fighter example, the guns are fixed and the computer-assisted fixed gunsight moves the pip so the pilot can "move" his guns to shoot. In the B-29 the movable gunsight internals are fixed, and the computer-assisted turret moves to the target.

Weight reduction 1 turret installation: 2 amplidynes (30 lb each), 1 dynamotor (20 lb), 1 computer (130 lb), 1 gunsight (20 lb), 1 servoamp (10 lb), 1 turret installation (150 lb?), bullets (300 rounds per gun at .5 lb/round = 150 lb x 2). So ripping out 1 turret would knock off 690 lb. The turrets may have held 600 rounds/gun, which would make the weight 990 lb.

Modifications: I'm pretty sure that the aircraft came from the factory without the radar installation. Radar installation was done at modification centers. Because of the secrecy associated with radar, this seems reasonable. It's difficult to verify because most factory photos are from above, and the wings and hull screen the radar location. Another modification would be the installation of the electronic countermeasures equipment and the associated antennas.

Reactions: Like Like:
2 | Informative Informative:
1 | Like List reactions


----------



## mjfur (Mar 5, 2022)

https://digitalcollections.museumofflight.org/items/show/46311


----------



## MIflyer (Mar 5, 2022)

By the way, while the B-29's did use the low altitude night attacks on Japan they also continued high altitude daylight attacks. So presumably the entire force did not have the gun turrets removed.

I recall reading where B-29 pilot said, "I flew that great big beautiful bomber over that burning city, looked down into the flames and said, 'Who did you think you were messing with?'"

Reactions: Like Like:
2 | Like List reactions


----------



## EwenS (Mar 5, 2022)

LeMay's orders were to remove the guns, ammunition and gunners for the low level night fire raids on Japan. Note, no mention of removing the turrets, which would have been a much more onerous task. BUT it is not clear just how many Bomb Groups followed those orders in full. Many seem to have left the guns in situ. Most seem to have left the ammunition behind but 3 groups flew with ammunition in the tail turret except for their homing aircraft.

Note also from that Gunners Manual pages 19-21 just which sighting positions had primary and secondary control of the various turrets. Contrary to popular opinion, not every gunner could control each and every one of the turrets. So for example the side blister gunners had no control over the upper turrets.

The 311 lightened B-29B version was interspersed on the Bell Atlanta production line (small batches and sometimes single aircraft) with normal B-29. The normal AN/APQ-13 B-29 radar was replaced on these aircraft with the aerofoil shaped AN/APG-7 Eagle radar and the tail turret was fitted 3x0.5" guns with an AN/APG-15B radar control system. Most went to the 315th Bomb Wing which began to arrive in the Marianas at the end of May 1945, flying their first mission a month later. The Eagle radar needed a 70 mile bomb run but was very accurate. So the group flew at night or in bad weather to avoid interception. Their principal targets were oil related, refineries and storage facilities on Honshu, earning them the nickname "The Gasoline Alley Boys".

Reactions: Informative Informative:
2 | Like List reactions


----------



## SaparotRob (Mar 5, 2022)

pbehn said:


> I didnt see this post when it was made maybe 'cos it was on my birthday, but as I understand it the pilot of a B-29 was aware of the issues of fuel management but it was the flight engineers job. The flight engineer on a B-29 took more training than the pilot from what I've read and most of the time he was telling the pilot what to do as far as airspeed and altitude goes.


Happy birthday!🎉

Reactions: Funny Funny:
1 | Like List reactions


----------



## manta22 (Apr 18, 2022)

manta22 said:


> In the '70s a forward section of a B29 fuselage arrived in a local Tucson salvage yard. Nose art identified it as "The Dutchess" and the salvage yard owner maintained that it had been one of the planes involved in the A-bomb program. If this were true it should have been placed in the Pima Air Museum or some other place to preserve it. I undertook to try to trace The Dutchess' history and talked to Paul Tibbets on the phone for 45 minutes about it. Tibbets was friendly and quite helpful and gave me some things to check to see if it had been one of the 509th Composite Group's planes. The most significant feature was the single bomb-bay rather than two shorter bomb bays on a standard production B29. He also related that many other changes were also made to the Wichita production run of these special versions. He gave me Chuck Sweeney's phone number and I talked to him as well. He did not know of a B29 named The Dutchess but said that it might have been one of the Los Alamos research planes.
> 
> I never did find out the history of The Dutchess B29 and it disappeared from the salvage yard thereafter.


Update: In going through some old paperwork, I found a reply from the Air Force Museum to my inquiry about a B-29 named "The Dutchess". The penciled notes are what I wrote while I was on the phone with Paul Tibbets. I thought I would pass this along as someone may be interested.

Reactions: Like Like:
1 | Winner Winner:
2 | Like List reactions


----------



## Zipper730 (Apr 20, 2022)

First,
I'm not sure what post this was on, but I remember there being issues with the cowl-flaps causing very large amounts of drag when extended (as well as control problems). While I've heard of other aircraft having control problems with the cowl-flaps out, the B-17 seemed have less issues at high altitude as the B-29 when it came to fuel efficiency (despite a similar climb-rate).

What in particular was wrong with the cowl-flaps?

Second,


EwenS said:


> The 311 lightened B-29B version was interspersed on the Bell Atlanta production line (small batches and sometimes single aircraft) with normal B-29. The normal AN/APQ-13 B-29 radar was replaced on these aircraft with the aerofoil shaped AN/APG-7 Eagle radar and the tail turret was fitted 3x0.5" guns with an AN/APG-15B radar control system. Most went to the 315th Bomb Wing which began to arrive in the Marianas at the end of May 1945, flying their first mission a month later. The Eagle radar needed a 70 mile bomb run but was very accurate. So the group flew at night or in bad weather to avoid interception. Their principal targets were oil related, refineries and storage facilities on Honshu, earning them the nickname "The Gasoline Alley Boys".


Wait, at 300 mph that would take 14 minutes for the whole bomb run... what kind of CEP did that have compared to the traditional Norden bombsight, and the LORAN aid (I think they were used in the pacific theater).


----------

