B-29 high altitude accuracy

[wiking85]

I can't seem to find an answer to this online, perhaps you can help; how accurate was high altitude (over 30k feet) B-29 bombing? I've read that they were forced to come back down to medium altitudes to bomb accurately over Japan, yet I still see some people claim that the B-29 would have been able to use its higher ceiling to bomb Germany to dust if the war in europe lasted longer. What is the truth on this, was the B-29 capable of reasonable accuracy in area bombing over 30k feet?

 

[Balljoint]

The Jetstream is particularly strong over Japan and seriously compromised high altitude bombing accuracy. There are probably weaker upper winds over Germany and Germany had better area bombing targets. But accuracy from 30,000+ would certainly be less than from 20,000 and change.

B-29s . Victory in the Pacific . WGBH American Experience | PBS

 

[Shortround6]

The trouble with bombing from 30,000ft is the air (wind) below 30,000ft.

The Bomb sights were supposed to figure in the airplane's drift ( difference in true speed over ground vs indicated airspeed and any side component/s) by measuring (tracking) a fixed point on the ground. However the bomber had no way of knowing if the wind was constant in direction and velocity all the way from ground level to the bombers altitude. Observing smoke plumes from fires/smoke stacks might give an idea of ground conditions. Wind can reverse direction let alone change velocity several times between 0 ft and 30,000ft.
The Problem with Japan was that the jet stream was more pronounced in it's effect than over Germany. Please note that the Jet stream/s move around from month to month and year to year.
Another consideration is that while the B-29 carried a lot more bombs than the B-17/B-24 many of the early B-29 raids on Japan were conducted by relatively small numbers of aircraft. Around 100-200 aircraft for starting raids which meant they were trying for "point" targets (aircraft factories, etc) rather than just trying to bomb cities. They later changed to bombing the entire city from medium altitude ( medium altitude also allowed much larger bomb loads)

Assuming you can find the center of a city ( a big assumption at times) it actually takes a lot to miss a sizable city even from 30,000ft. IF the bomb is dropped over the center of a city 4 miles in diameter the bomb would have to move 1 foot sideways (forward, left, right, backwards) for every 2.84 feet it dropped to miss the city (19.4 degrees). That is a lot of wind

 

[stona]

Whilst the comments about the jet stream are appropriate the USAAF, whilst aware that something was going on, had no idea exactly how these high speed winds operated. Nobody did, it was a little understood phenomenon in the 1940s.

The problem with bombing accuracy when undertaking area bombing raids of this type isn't so much hitting a target the size of a city which is hard to miss, as argued above. The problem is achieving a concentration of bombing, both in space and time, which will cause the desired level of destruction. This is what led to the evermore sophisticated attack profiles used by the RAF late in the war. The 'Sector Bombing' technique developed by 5 Group is a good illustration of this.

Cheers

Steve

 

[GregP]

The bombing accuracy from 30,000 feet was off by enough to warrant dropping the attack altitude of the B-29's down to 18,000 - 20,000 feet for more hits, so the accuracy from 30k wasn't anything to write home about.

 

[Juha]

IIRC Japanese scientists were aware on jetstreams. That wasn't a big surprise because the phenomenon was so strong above Japan and Northern Pacific. And IIRC this knowledge was behind the idea of using balloons to bomb USA.

Juha

 

[Shortround6]

This may have had something to do with the bombing altitude;

"A load of 5000 pounds of bombs could be carried over a 1600-mile radius at high altitude. A load of 12,000 pounds of bombs could be carried over a 1600-mile radius at medium altitude."

A 140% increase in bomb load?

The night incendiary raids were hardly an example of precision bombing even if very effective.

 

[davebender]

All level bombers using Norden bombsight would have similar accuracy. What sight did B-29 employ?

 

[stona]

IIRC Japanese scientists were aware on jetstreams. That wasn't a big surprise because the phenomenon was so strong above Japan and Northern Pacific. And IIRC this knowledge was behind the idea of using balloons to bomb USA.

Juha

A Japanese scientist whose name evades me at the moment had done some work, tracking balloons at high altitude, and was aware of some high velocity winds at high altitudes. He published his findings in Japanese which is one reason why his research was little known outside of Japan. To suggest that the Japanese understood the jet stream and how it operated, even over their country would not be true.
Cheers
Steve

 

[Deleted member 63714]

IIRC Japanese scientists were aware on jetstreams. That wasn't a big surprise because the phenomenon was so strong above Japan and Northern Pacific. And IIRC this knowledge was behind the idea of using balloons to bomb USA.

Juha

Yes, I think you are right about that. They DID realize something about the stream of air above. I know, and most on here also know, that the Japanese made hundreds of balloon bombs that reached into the American plains and caused damage (relatively minor though it was). Many average U.S. citizens are unaware that this occurred even today. I've told many people the story of Japan's balloon attacks to gaped surprise.

 

[FLYBOYJ]

All level bombers using Norden bombsight would have similar accuracy. What sight did B-29 employ?

Most of them used Nordens.

 

[GrauGeist]

The bulk of the balloons landed west of the Rockies.

Over time, the knowledge and history of the balloons has been lost...there was a time when just about any native of the west coast or pacific northwest knew about them. I live just a few miles from where one came down intact (it landed in a small town called "Hayfork" in Trinity County) and is the most complete example ever recovered. Several others landed in this area as well.

The one truly interesting story about the balloons, is that one nearly screwed up the nuclear test facilities in Washington state!

 

[Koopernic]

I can't seem to find an answer to this online, perhaps you can help; how accurate was high altitude (over 30k feet) B-29 bombing? I've read that they were forced to come back down to medium altitudes to bomb accurately over Japan, yet I still see some people claim that the B-29 would have been able to use its higher ceiling to bomb Germany to dust if the war in europe lasted longer. What is the truth on this, was the B-29 capable of reasonable accuracy in area bombing over 30k feet?

The problem with bombing from 30,000ft over much of asia and japan was 100 mph stratospheric winds called the jet stream.

The Norden used the same technology as Naval gun fire or an AAA predictor, probably considerably less if truth be told, but it was miniaturized.

The bomb aimer tracked an object on the ground by adjusting the speed of electrical variable speed motors which tilted the mirror in the bomb-sight. Trigonometric and other camshafts converted to linear coordinates. Once the tracking speed was set right the object remained steady in the reticule.

The speed setting of the variable speed drives then gave the true ground speed of the aircraft. By mechanically subtracting this with the TAS (True Air Speed) and heading the wind drift could be calculated. Tables or a ballistics cam then gave bomb fall time, bomb trail error in consideration of altitude, air density, bomb type etc and with the wind drift could calculate the offset required which in the case of the Norden could be fed directly as a heading to the auto pilot.

Of course the jetstream was uncooperative by not being steady and consistent at different altitudes. One can find photographs of smoke trail bombs dropped to try and estimate this; they were quite squiggly. Maybe a doppler weather radar might have helped.

Hap Arnold was very unhappy with Hansel's results and replaced him with LeMay who implemented RAF style firestorm city burning tactics with the B-29's coming in at 8000ft. This greatly increased bomb load and spared the engines at a time the R-3350 was still teething a little. LeMay has nothing but nice things to say about Hansel. One argument for this was that Japanese industry was dispersed in many small workshops.

It killed a million, the atomic bombs were nothing compared to this. Neither Arthur Harris or Curtiss Lemay ever minced words about what they were doing and had in fact been ordered to do. One is left with a strange respect for their honesty. There was a motion to prosecute Walter Dornberger for war crimes, he was the the engineer and Army artillery officer who had helped von Braun to build the V2 and fire it against various cities. Of course in the cold light of day coming up with a legal precedent or mechanism to prosecute Dornberger would have been a kind of hypocrisy and a somewhat a case of scoring an own goal, especially in the future. Dornberger emigrated to the USA where he worked on Dyna Soar.

As to how accurate the Norden was at high altitude, I don't know the figures. It may have been quite accurate but other considerations such as bomb load and desire for area bombardment tactics having driven the strategy and statements such as 'the norden is inaccurate at high altitudes due to the jet stream were not factual. There doesn't seem to have been any critical examination of this by historians.

The USAAF eventually had a very accurate ground mapping radar called the eagle, which had a large external antena. It was much better than H2S or H2X and allowed fairly accurate night bombardment.

In terms of using the B-29 against Germany it should be noted that this would reduce the B-29's available over Japan, leaving essentially nothing. It would be possible to convert B-17 production lines over to B-29 but only with some delay.

Also the Luftwaffe was much better positioned to intercept the B-29. Even without specific high altitude engines their existing engines were better than most, they had GM-1, cryogenic nitrous oxide which gave stunning performance at high altitude (hundreds were produced as retrofits) and had in fact delayed the introducion of high altitude fighter.

With the fall from influence of Goering and latter Milch Fritz Saukel took over and he preferred to pump out quantity rather than quality. The appearance of the B-29 would have forced the production lines to change over to quality.

 

[tyrodtom]

Haven't you ever looked up at the clouds and noticed they're going in a different direction than the ground level winds ?

Also occasionally you'll notice the high altitude cirrus, or cirro-stratus clouds going in a different direction than the cumulus clouds at lower altitude.

Any bomb dropped through those different wind directions and speeds is going to be affected by them, and no bomb sight could be programed with all the possible varibles.

Like old computer programmers used to say, " crap in, crap out". That's not really exactly what they said, but I'm sure you know what they meant.

 

[FLYBOYJ]

In terms of using the B-29 against Germany it should be noted that this would reduce the B-29's available over Japan, leaving essentially nothing. It would be possible to convert B-17 production lines over to B-29 but only with some delay.

The plan was to replace B-17s and B-24s with B-32s.

 

[Deleted member 63714]

The bulk of the balloons landed west of the Rockies.

Over time, the knowledge and history of the balloons has been lost...there was a time when just about any native of the west coast or pacific northwest knew about them. I live just a few miles from where one came down intact (it landed in a small town called "Hayfork" in Trinity County) and is the most complete example ever recovered. Several others landed in this area as well.

The one truly interesting story about the balloons, is that one nearly screwed up the nuclear test facilities in Washington state!

I know I've read somewhere that the only fatalities by the balloons occurred in Oregon? I believe... ? I think there is some sort of monument where they were killed. A few of the balloons managed to make it to the Dakotas, Kansas, Iowa, and Michigan. The Japanese also hoped the balloons would start forest fires. It seems a might silly now, but it actually worked just as they thought... They predicted about 10% would reach North America. That's pretty much what happened but they didn't do the damage they hoped they would. More probably landed in the forests of the northwest and in the high Rockies.

 

[stona]

"Hap Arnold was very unhappy with Hansel's results and replaced him with LeMay who implemented RAF style firestorm city burning tactics with the B-29's coming in at 8000ft. This greatly increased bomb load and spared the engines at a time the R-3350 was still teething a little."

What bombing from 8,000 ft did was increase the concentration of the bombing as I mentioned above. Without this concentration it is not possible to establish the conditions for a fire storm. Scattering bombs over a city will NOT do it. It's why the RAF so rarely, even late in the war, achieved the desired result.
When it did (most famously at Dresden) the result was devastating. An area raid is exactly that, an attempt to utterly destroy a designated area of the target city. Using 'Sector Bombing' this area should look like a slice of cake with a 32 degree angle at the 'sharp end'.
Cheers
Steve

 

[Juha]

A Japanese scientist whose name evades me at the moment had done some work, tracking balloons at high altitude, and was aware of some high velocity winds at high altitudes. He published his findings in Japanese which is one reason why his research was little known outside of Japan. To suggest that the Japanese understood the jet stream and how it operated, even over their country would not be true.
Cheers
Steve

I'm not claiming that they fully understood the jet stream but they knew enough of them to allow them to excecute a "strategic bombing campaign" based on them. Now the operation wasn't a great success, only some 3% (300) of the launched balloons arrived to the North-America killing 6 and produced some minor material damage. But that the tried that type of intercontinental attack shows that they had at least some understanding on how the jet streams worked.

Juha

 

[Reegor]

To amplify this answer:
The jet stream was unknown and initially not believed, and it led to fuel exhaustion problems among other things. But Norden bombsights were intended to cope with high altitude winds. One difficulty with them was that if the AC was going with the (jet stream) wind, it was too fast for the Norden - literally it was not able to track that quickly. If the AC went against these winds, it had a long time over the target, giving more chance to be shot down by ground fire. Add to that the changing winds as the bombs descended.

For this and other reasons, the attempts to bomb military targets such as specific AC factories were essentially complete failures. LeMay switched strategies out of necessity, which included:

• Going below 10,000 feet
• Night instead of day
• Incendiaries instead of high explosive, and trying for secondary damage from fires, rather than blast
• Targeting cities instead of specific military installations

Surprisingly, much of the brass' concern with ineffective bombing was due to (military) politics. The B-29 program had been very expensive (more than the Manhattan Project) and they could not afford to let it be seen as a failure.

I can dig out some references on this if it is important. Many of the relevant books are, unfortunately, too old to be available online.

The problem with bombing from 30,000ft over much of asia and japan was 100 mph stratospheric winds called the jet stream.

The Norden used the same technology as Naval gun fire or an AAA predictor, probably considerably less if truth be told, but it was miniaturized.

The bomb aimer tracked an object on the ground by adjusting the speed of electrical variable speed motors which tilted the mirror in the bomb-sight. Trigonometric and other camshafts converted to linear coordinates. Once the tracking speed was set right the object remained steady in the reticule.

The speed setting of the variable speed drives then gave the true ground speed of the aircraft. By mechanically subtracting this with the TAS (True Air Speed) and heading the wind drift could be calculated. Tables or a ballistics cam then gave bomb fall time, bomb trail error in consideration of altitude, air density, bomb type etc and with the wind drift could calculate the offset required which in the case of the Norden could be fed directly as a heading to the auto pilot.

Of course the jetstream was uncooperative by not being steady and consistent at different altitudes. One can find photographs of smoke trail bombs dropped to try and estimate this; they were quite squiggly. Maybe a doppler weather radar might have helped.

 

[GrauGeist]

Unfortunately, the Norden wasn't able to anticipate the Jet Stream's current and counter-currents that are a result of the high-speed wind.

As most people know, especially those that fly, is that there are different wind conditions at varying altitudes. In the case with the Jet Stream, there are "back" winds that are an eddy of the stream's course, much like in a waterway. The Norden would have to be able to know the Jet Stream's course and velocity, then predict the counter-flow in the elevations below the Jet Stream and then add in the varying wind currents found in the successive layers at descending elevations. Add to that any meteorological events, such as thermals or thermal related wind currents brought about by pressure differentials such as warming inland drawing in cooler marine moisture, etc.

Japan's geographic location created a very unpredictable condition, much different than bombing solutions over continental Europe. The only upside to this ill-fated high-altitude bombing campaign, was a huge learning curve in upper atmospheric meteorology and how the Jet Stream works.