About aiming targets

[mcoffee]

Not always and not in this case. The "train of boxes " was not the rule( the longer the train, the happier the FLAK ). In the "6 air front formation" the position of boxes could be the same in cruising and bombing. In the sheet to which my original question referred is clearly said "bombing formation".


Yes, of course. I told that only one PFF leaded the Group and aimed during the bombing run. The spares were inactive unless malfuctions or alternate targets needed their intervention.

The 'train of boxes' was used when attacking a point target such as a bridge. You should find the 465th attack sheet in the mission folder and see what it says.

When bombing by PFF, the Mickey Ship leading each attack unit sighted independently. Again, a review of the mission folders will confirm this.

 

[mentuhotp]

This topic is very stimulating. But I'll try to focus again on the question that pushed me to start it.

To reorder my ideas I have partially modified the picture below.

1st problem : Plane in wind. In absence of wind the aircraft could theoretically fly with the nose pointing the target, but in presence of wind it had to contrast the drift which the wind would have impressed to it. So it had to fly with the nose upwind to keep its course straight to the target ( this was called "kill the drift" ).

2nd problem : Bombs in wind : at the moment of the release the bombs were taken by the wind and carried downwind ( to the right in the picture ). The Bombardier had to compensate this by flying a course on the left of the target ( COURSE OF PLANE ) and not over the target ( COLLISION COURSE ) to place the bombs on the ACTUAL TRAJECTORY which actually leaded them on the target. This compensation was called "sight for deflection".

So, while sight for "both range and deflection" meant fly on the pink course in the picture and hit the target, sight " only for range " meant fly on the blue course in the picture, avoiding to consider the influence of the wind on the bombs which would fall ( red trajectory in the picture ) right of the target.

Now, substitute the two planes in the picture with two boxes of 7 - 8 planes. In the specific case that I consider, the Box further upwind in the picture sighted for range and deflection, so it had high chances to hit the target. The other sighted only for range. Apart every feature of the bombs that could interfere with their fall and which may have dispersed them, the bombs of the second Box, by effect of the wind, had to impact on the right of the target.

My question is : what was the underlying logic in this ?

 

[buffnut453]

This topic is very stimulating. But I'll try to focus again on the question that pushed me to start it.

To reorder my ideas I have partially modified the picture below.

View attachment 720471

1st problem : Plane in wind. In absence of wind the aircraft could theoretically fly with the nose pointing the target, but in presence of wind it had to contrast the drift which the wind would have impressed to it. So it had to fly with the nose upwind to keep its course straight to the target ( this was called "kill the drift" ).

2nd problem : Bombs in wind : at the moment of the release the bombs were taken by the wind and carried downwind ( to the right in the picture ). The Bombardier had to compensate this by flying a course on the left of the target ( COURSE OF PLANE ) and not over the target ( COLLISION COURSE ) to place the bombs on the ACTUAL TRAJECTORY which actually leaded them on the target. This compensation was called "sight for deflection".

So, while sight for "both range and deflection" meant fly on the pink course in the picture and hit the target, sight " only for range " meant fly on the blue course in the picture, avoiding to consider the influence of the wind on the bombs which would fall ( red trajectory in the picture ) right of the target.

Now, substitute the two planes in the picture with two boxes of 7 - 8 planes. In the specific case that I consider, the Box further upwind in the picture sighted for range and deflection, so it had high chances to hit the target. The other sighted only for range. Apart every feature of the bombs that could interfere with their fall and which may have dispersed them, the bombs of the second Box, by effect of the wind, had to impact on the right of the target.

My question is : what was the underlying logic in this ?

You're missing the 3rd problem - random dispersion of bombs laterally across track due to differences in aerodynamic performance. The diagram shows a nice neat condition where all bombs follow the same general path, A bomb dropped in any of the 3 aircraft positions shown in the diagram had an equal probability of hitting the actual target due to the dispersion mentioned.

 

[mentuhotp]

You're missing the 3rd problem - random dispersion of bombs laterally across track due to differences in aerodynamic performance. The diagram shows a nice neat condition where all bombs follow the same general path, A bomb dropped in any of the 3 aircraft positions shown in the diagram had an equal probability of hitting the actual target due to the dispersion mentioned.

Even if they dispersed in many directions I don't think they fell upwind .... And in any case, if everything was so random, why then aim ?

 

[buffnut453]

Even if they dispersed in many directions I don't think they dropped upwind ....

Depends on which direction the wind is blowing. If the wind is bang on the nose at 10kts then a bomb dropped at 120kts will still land upwind, albeit at shorter along-track distance from the drop point compared to a bomb dropped with a 10kt tailwind.

I was specifically talking about cross-track dispersion which isn't mentioned in the diagram but was a very real factor given post-release bomb "wobble" and aerodynamic imperfections affecting trajectory.

 

[mentuhotp]

Even if they dispersed in many directions I don't think they dropped upwind ....
Sorry I meant fell no dropped

 

[buffnut453]

Even if they dispersed in many directions I don't think they dropped upwind ....
Sorry I meant fell no dropped

Depends what you mean by "upwind"....upwind from where? The drop point? The estimated impact point in still conditions? Relative to other bombs dropped at the same time?

 

[mentuhotp]

Depends what you mean by "upwind"....upwind from where? The drop point? The estimated impact point in still conditions? Relative to other bombs dropped at the same time?

From the moment they leave the aircraft the bombs are carried by the wind in the direction of the wind, so downwind from the point of release. They cannot be carried in the opposite direction ( upwind ). If you toss a handful of ping pong balls in a river, they might touch the water in a disperse manner but they will follow the stream, they will not go up the river . . .

 

[buffnut453]

From the moment they leave the aircraft the bombs are carried by the wind in the direction of the wind, so downwind from the point of release. They cannot be carried in the opposite direction ( upwind ). If you toss a handful of ping pong balls in a river, they might touch the water in a disperse manner but they will follow the stream, they will not go up the river . . .

Firstly, a 500lb bomb is not a ping pong ball. Secondly, it all depends on the direction and speed of the wind. A bomb dropped at 120mph into a 10mph headwind will NOT get blown backwards. Period.

 

[mentuhotp]

Firstly, a 500lb bomb is not a ping pong ball. Secondly, it all depends on the direction and speed of the wind. A bomb dropped at 120mph into a 10mph headwind will NOT get blown backwards. Period.

But it will fall shorter of the target. And this was considered by the Bombardier, who entered the value of the wind in the bombsight before releasing.

 

[buffnut453]

But it will fall shorter of the target. And this was considered by the Bombardier, who entered the value of the wind in the bombsight before releasing.

Agreed. But that's not what you said. You said a bomb couldn't land upwind when, clearly, it could. Yes, it won't travel as far as a bomb dropped under still conditions but it will still travel forward into the wind.

The other thing to bear in mind is that windspeed and direction can change drastically at different altitudes.

None of this changes the fact that bombs did not fall in even remotely predictable ways...indeed, they still don't today, which is why we developed laser designation and GPS-aided INS kits for bombs to improve precision and accuracy.

 

[mentuhotp]

Agreed. But that's not what you said. You said a bomb couldn't land upwind when, clearly, it could. Yes, it won't travel as far as a bomb dropped under still conditions but it will still travel forward into the wind.

The other thing to bear in mind is that windspeed and direction can change drastically at different altitudes.

None of this changes the fact that bombs did not fall in even remotely predictable ways...indeed, they still don't today, which is why we developed laser designation and GPS-aided INS kits for bombs to improve precision and accuracy.

Sighting for deflection implies consider the crosswinds. The variables could be many but the bomb will always fall in wind direction ( downwind ). If the direction of the wind reverses, just like you said, the bomb will take the new direction of the wind and it will fall downwind in the new direction. As you can see in the picture from the " Bombardiers' Information file " the bomb will be deviated in the actual direction of wind. There's no physical law that can bring it on the opposite direction, towards the wind (upwind). Turbolence, updrafts and downdrafts could influence the fall of the bomb, which would land short, long, to the right or to the left of the target, but the cross - trail ( CT ) cannot be negative, that means, in the picture below, that the bomb will not fall to the right of the aircraft course, unless the direction of the wind reverses.

 

[buffnut453]

Sighting for deflection implies consider the crosswinds. The variables could be many but the bomb will always fall in wind direction ( downwind ). If the direction of the wind reverses, just like you said, the bomb will take the new direction of the wind and it will fall downwind in the new direction. As you can see in the picture from the " Bombardiers' Information file " the bomb will be deviated in the actual direction of wind. There's no physical law that can bring it on the opposite direction, towards the wind (upwind). Turbolence, updrafts and downdrafts could influence the fall of the bomb, which would land short, long, to the right or to the left of the target, but the cross - trail ( CT ) cannot be negative, that means, in the picture below, that the bomb will not fall to the right of the aircraft course, unless the direction of the wind reverses.

View attachment 720518

But the degree to which each individual bomb is affected by the wind will vary depending on each bomb's heading. Your diagram shows the bomb on exactly the same heading as the aircraft. Many bombs didn't fall like that. They wobbled after release or an imprecisely-fitted or damaged tail assembly would alter the bomb's heading. Thus the wind would affect each bomb differently, resulting in lateral spread, just as I keep trying to explain. Some of the bombs would fall "less downwind" and some might fall "more downwind" but you still end up with lateral spread.

Again, look at this image of bombs coming out of a B-24. How many of them are perfectly aligned with the aircraft's heading, do you think?

 

[mentuhotp]

But the degree to which each individual bomb is affected by the wind will vary depending on each bomb's heading. Your diagram shows the bomb on exactly the same heading as the aircraft. Many bombs didn't fall like that. They wobbled after release or an imprecisely-fitted or damaged tail assembly would alter the bomb's heading. Thus the wind would affect each bomb differently, resulting in lateral spread, just as I keep trying to explain. Some of the bombs would fall "less downwind" and some might fall "more downwind" but you still end up with lateral spread.

Again, look at this image of bombs coming out of a B-24. How many of them are perfectly aligned with the aircraft's heading, do you think?

View attachment 720521

They are perfectly aligned till they are in the bomb bay. In the precise moment they leave the aircraft every one of them is taken by the wind, each in its personal way. But even if they will touch earth the much scattered as possible, as a whole they will be deflected in the same direction, to the left of the aircraft if the crosswind comes form right, to the right of it if the crosswind comes from left.

 

[buffnut453]

They are perfectly aligned till they are in the bomb bay. In the precise moment they leave the aircraft every one of them is taken by the wind, each in its personal way. But even if they will touch earth the much scattered as possible, as a whole they will be deflected in the same direction, to the left of the aircraft if the crosswind comes form right, to the right of it if the crosswind comes from left.

Again, it depends on the wind direction. You're using a very extreme example of a 90 degree crosswind. Wind that's coming from 10 degrees off the left side of the aircraft may have more unpredictable results as one bomb may align perfectly into wind (i.e. align 10 degrees left) while another may align 10 degrees to the right of the aircraft's nose (i.e. 20 degrees to the right of wind direction). The effect of the wind on those two bombs will be very different. The first bomb will likely land to the left of aircraft track (i.e. upwind) while the second will definitely land to the right of track (i.e. downwind).

It is incredibly situation dependent. And none of this seemingly endless argument gets around the simple fact that there was bomb dispersion both along and across track...which was the entire point I was making in the first place.

 

[JDCAVE]

A lot of arm waving here guys. i might suggest that someone finds some literature on the physics of the ballistics of bombs and the effects of wind direction on bombing. I'm certain there is some out there.

I don't know about practice in the USAAF, but I do know that during the latter stages of the war there was an inordinate amount of effort in RAF Bomber Command on the topic of Wind Finding". Select experienced crews were tasked as "wind finders" and transmitted their "found winds" back to Bomber Command HQ. These were examined by "quant" types and meteorologists and a sequence of "broadcast winds" were transmitted back to crews at regular intervals as they traveled to and from the target.

Wind was a setting on the RAF Mk XIV bombsight and also the SABS bombsight. I gotta believe it was also a setting on the Norden bombsight.

Jim

 

[JDCAVE]

I posted the following on RAF Commands Forum and I'm reposting it here:

I have been reviewing the Form 441's (Navigator Logs) by my father's navigator for Dresden, February 13/14, 1945. I had been wrestling with what is meant by the notation during the flight over Germany. On page one the Flight Plan is detailed, together with the Forecast W/V's and air Temps. I understand these to be "Forecasts", provided by Bomber Command Meteorologists. Along the route there was a procedure for updating these, whereby "wind-finders" broadcast wind direction and velocities back to Bomber Command. Presumably these individuals compared their positions from the "Air Plots" (from "Dead Reconning" headings and air speeds) or alternatively with the "Air Position Indicator" (API) with those from the "Fixes" obtained from GEE. I understand that there was a process of calculation. Bomber Command then evaluated the information that was passed to them and then broadcast new winds to crews that were recorded by the Wireless Operation and passed on to the navigator.

On F/O Marvin Seale's Form 441, at regular times, he records the following, for example at 0035 hrs, page two of the document:

"P 250/60 250/75 245/95"

And…

"F 250/60 255/75 255/85"

And at 0110, 25 minutes before bombing, he records the following:

"P 250/60 255/75 255/85"

And…

"F 250/55 260/75 265/85"

And…

"X 260/55 260/75 265/85"

"Air Positions" at turning points are denoted as boxes and "Fixes" from "GEE" or "H2S" as "+" signs.
I understood these to be 3 different directions (i.e. from the WSW), and velocity for winds. I had thought that "P" stood for "Predicted" or "Passed" (as in passed to Bomber Command), "F" to denote "Found" or "Forecast". But what did "X" refer to? Target? Wind data to be used at the Target? And three different winds: Were these for different heights, that might be inputs for the bomb sight? I had reviewed Peter Hoare's paper and could not find any insight.
I found the answer from the 6-Group Navigation summary, (6-Group ORB appendices) February 1945 and specifically on Wind Finding and titled BOMBER COMMAND WIND FINDING:

"P" refers to "Past" and "F" refers to "Future"

"…At specified times, depending on the "Force" to which they are applicable, winds are broadcast from Command to the Main Force. These broadcast winds, numbering six per message are divided into two Groups-Past and Future. The message broadcast will consist of a "P" followed by three winds, being the winds applicable for the past half hour at 10, 15 and 20,000 feet and an "F" followed by three winds which are a forecast for the next half hour. These messages are broadcast every half hour from the time at which W/T silence may be broken through H hour to a specified time on the return journey. A bombing wind for each of the three wind heights may also be passed a short time before H hour."

I think we can safely assume that that third set of winds, prefaced with an "X" is a "bombing wind".

The following links from Library and Archives Canada, 6-Group Royal Canadian Air Force operations record books – LAC Reel: 12420

6-Group navigation summary for February, 1945:

https://heritage.canadiana.ca/view/o...0/1021?r=0&s=1

Group Wind Finding:

https://heritage.canadiana.ca/view/o...0/1024?r=0&s=1

Bomber Command Wind Finding:

https://heritage.canadiana.ca/view/o...0/1025?r=0&s=1

Period for Wireless Transmission and WOp's listening duties:

https://heritage.canadiana.ca/view/o...0/1027?r=0&s=1

All of the above, notwithstanding, I asked F/O Marvin Seale about Broadcast winds and he said he was aware of these, but "Can't recall doing too much with them." His Form 441, reveals that was in fact the case. Even though he recorded these winds in his log, at the S/C Turning Points, he still seemed to follow the Forecast Winds in the Flying Plan.

Jim

 

[33k in the air]

A lot of arm waving here guys. i might suggest that someone finds some literature on the physics of the ballistics of bombs and the effects of wind direction on bombing. I'm certain there is some out there.

The following might be of assistance: Terminal Ballistic Data — Volume I: Bombing from the Office of the Chief of Ordnance (Aug. 1944). It contains charts showing range vs. altitude of release, differential effects on range from headwinds, striking velocity and angle of fall vs. altitude of release, trail vs. drop, earth displacement of bombs, and damage effects of bombs. It also includes tables showing bomb performance against concrete and fragmentation damage from bombs.

It can be downloaded from the Ike Skelton Combined Arms Research Library. This site hosts a wealth of documents and publications from the era.

 

[Shortround6]

Heck, the manual on the A-26 gives information on the effective at ground level of flying 100 ft too high or too low and the difference of being off a small amount in speed. I forget the amount but it was something like 5 or 10 mph?

 

[elbmc1969]

More wind considerations:

Each aircraft will be in different wind conditions. There are always variations, even over small distances.

Wind is not constant with altitude. You might be able to measure the wind around your aircraft, but the wind might be in the opposite direction 5,000 feet below you.

Turbulence, air pockets, updraft, and downdraft. Wanna see bombs move in random directions for a while?

Saying, "bombs don't move upwind" may be literally true of you mean that for every small fraction of flight, the bomb is moving with the wind. However if you get down to really small units of time, you'll have a bomb moving north that enters wind blowing to the south and does just the opposite, if we want to be incredibly pedantic.

In any case, a group of bombers aiming to create a pattern instead of all separately aiming at the same point may give better practical results because it counters systemic errors.

Apologies that I haven't read this from the beginning, so I may be rehashing things or missing something.