What a fascinating thread! And that presentation by SXS is fascinating - even if a lot of it was beyond my skills of understanding!
I am going to put a 'leading question'!
When I worked on 721MSU (very many years ago), our principle job was scoring simulated bomb runs using a very accurate tracking radar. The aim was to track an aircraft doing this 'bombing run' and plot it in great detail on a large electronic table driving a pen over a huge sheet of paper. We had all sorts of tables and whizzy other things to project where any of various bomb types would hit after release. We would know the exact release point, height and track from the (quite precise) radar info.
But... (don't you hate that word?)...
We also had to build in an offset for DCA (Drift Correction Angle) which was, basically, the difference between aircraft calculated heading and track - given to us by r/t - along with their calculated DCA; (i.e. the aircraft might be 'pointed' at the target - but it might be flying slightly 'sideways' if you get what I mean). OK, from the aircraft point of view, virtually everything was done, usually electronically, using NBS; though 'reversionary bomb runs' could be interesting!
So... going back to 'visual' bomb sights, would there be a need to have a DCA correction?
When I worked on Song Song range in Malaya, visiting V Bombers occasionally used the High Level target at night. We were told that they put in a deliberate offset to avoid actually hitting the target and causing damage (100 pound practice bomb) The offset distance and bearing was kniwn only to the crew wbo applied it as a correction to the plot provided by us for each bomb.
They still hit it though so that must have must have been a miss! Pix on the Song Song range thread.
What a fascinating thread! And that presentation by SXS is fascinating - even if a lot of it was beyond my skills of understanding!
I am going to put a 'leading question'!
When I worked on 721MSU (very many years ago), our principle job was scoring simulated bomb runs using a very accurate tracking radar. The aim was to track an aircraft doing this 'bombing run' and plot it in great detail on a large electronic table driving a pen over a huge sheet of paper. We had all sorts of tables and whizzy other things to project where any of various bomb types would hit after release. We would know the exact release point, height and track from the (quite precise) radar info.
But... (don't you hate that word?)...
We also had to build in an offset for DCA (Drift Correction Angle) which was, basically, the difference between aircraft calculated heading and track - given to us by r/t - along with their calculated DCA; (i.e. the aircraft might be 'pointed' at the target - but it might be flying slightly 'sideways' if you get what I mean). OK, from the aircraft point of view, virtually everything was done, usually electronically, using NBS; though 'reversionary bomb runs' could be interesting!
So... going back to 'visual' bomb sights, would there be a need to have a DCA correction?
Chris, the second part of my Norden bombsight presentation deals with "Cross Trail"; which results from "Drift". Drift is caused by cross-winds, where the aircraft "drifts" downwind of its track towards the target. Cross-winds also cause the bomb to drift downwind of the target when it's released.
The Norden was able to calculate the drift angle from the difference between the direction the aircraft's nose was initially pointing, and its direction after drift had been nullified (or "killed" in bombardier parlance). Drift causes the Norden sight optics to tilt downwind, causing the bombardier to fly a track which is parallel and upwind of the original track towards the target.
Hopefully, the presentation should explain these concepts better.
As I said, I found the presentation fascinating; however, some bits failed to register in my decaying brain cells... or I missed them as I read through. I blame it on old age, alcohol, smoking and any other pathetic (or reasonable) excuse I can offer. What we had to do on the MSU was quite simple in comparison with what a bomb aimer had to do!
I shall try to re-read that presentation and take more notice this time as it is an interesting one.
As a slight aside, I find it interesting how the 'old-time' bomb aimers' instructions were used for clarity over the intercom such as "R-i-i-i-ght"; "Left-left" and "Steady" to avoid confusion and are now (mis)used by people as just the same word repeated such as "left left" and "right right" by such denizens of proprietary as the police! To me, the 'old time' instructions were much more obvious! And they call it "progress"?
Whilst sitting out in the garden watching the clouds one strange thing was that the higher clouds moved one way whilst the lower ones move another. Although only a small angle it was difficult to judge without looking up vertically. If wind finding was taken at one height only the lower wind would be missed and this may have affected the input drift.
No Amount Of Evidence Will Ever Persuade An Idiot (probably not Mark Twain)
Whilst sitting out in the garden watching the clouds one strange thing was that the higher clouds moved one way whilst the lower ones move another. Although only a small angle it was difficult to judge without looking up vertically. If wind finding was taken at one height only the lower wind would be missed and this may have affected the input drift.
Peter, you're absolutely right; wind direction and speed can vary with altitude. As I understand it, the atmosphere can fragment into layers; and these layers can be moving at different directions and speeds. Consequently, although the aircraft's heading could be adjusted to maintain a desired track (allowing for the wind speed and direction at its altitude), the differing wind forces below it can adversely affect the distance the falling bomb travels downwind of the aircraft's track (known as "cross trail").
Furthermore, due to drag, a bomb will hit the ground some way behind the aircraft. This distance is called "trail". The amount of trail normally set into the Norden bombsight depends on the bomb's shape, size, and initial air speed. However, if a falling bomb enters a layer of air travelling in a different direction and speed, this will affect its air speed (the speed of the air flowing over the bomb), which in turn alters the trail. As an extreme example, it's obvious what the effect will be on a bomb travelling into a headwind, which then picks up a tailwind.
In the USAAF during WW2, I believe that trail and cross trail were sometimes calculated by lead bombardiers before a mission using the latest meteorology reports for the target area in order to take account of the varying wind speeds and directions. However, if there's one thing we can't rely on, it's the weather
PS I really enjoyed your article "Simulated Bombing Using Infrared Targets" in the latest "Airfield Review". Thank you.
Agreed the article was most informative and I've been interested in both navel and air drop items.
I remember reading that during the WW1 battleship exchange on the dogger bank the top side sailors reported seeing the shells tumbling through the air ?
Apparently fire bombs were reported as fluttering down ?
The senior scientific officer who worked out the distance between release and landing of the bomb discussed in the Astley Walk thread tried to explain the subject to me in the similar terms as used by SXS.
My best recollection of tutorial discussion from fifty years ago was that the tumbling navel shells were not applicable to WW2 due to the between war improvements in navel guns & shells while the fluttering fire bombs were due to a combination of low mass and increased air density at lower levels.
Naval engagements in WW1 such as Jutland and Dogger would open at extreme range. Shells fired through the rifled gun tube were imparted spin at high RPM resulting in axial stability but at end of flight the spin rate would have decayed resulting in the shell yawing then tumbling. Being large diameter and, by then, relatively slow moving they were visible to the intended recipients. The design of some shells was such that the centre of gravity was behind the ideal point the designer accepting that they would be spin stabilised. Design improvements by WW2 resulted in better shell stability at lower rates of spin and forward velocity.
But tell that to the deck sailors on HMS Hood!
Naval battles with considerable loss of seamen versus navel battles with considerable loss of semen as the old joke says.
The old naval jokes are the best ~ thanks for bringing them back to life.
My aunts boy friend was on the Hoods final sailing and after the war she was in contact with one of the few survivors ( 3 ? ) He had been standing on one of Hoods rear open decks taking air when the next thing he remembered was coming too in the water.
He told her that they had removed a lot of the Hoods deck armor because at the time in the late 1940's early 1950's they were still blaming the gun crews for repositioning the flash curtains to the magazine.
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