Bomb Trajectories

Just been looking through my 540 page book about the Mosquito. There is a mention of a bombsight [ Mk XIV ] being used as early as May 1942. Also a photograph of a gun-turret fitted to a Mosquito ??? never knew that either. Just never seem to get around to reading all these books.

A turret? That's a new one on me. Must have been 'trial' and looked weird. The Tsetse version with a 57mm gun was my favourite.

Taken at the Woodford Heritage Centre, yesterday.
Mk.XIV Sighting head

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Lancaster Bomb Selection gear

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Just found this very good site on the Norden sight:)

www.twinbeech.com/norden_bombsight.htm

Some time ago, I became curious about the Norden bombsight. Although I found many interesting, but disparate, pieces of information on the Norden bombsight; none of these contained a clear and comprehensive explanation of how it actually worked !

The following links are to a three-part presentation, which is the result of considerable research and analysis. It is my attempt to describe the key mechanisms of the Norden bombsight, the mathematical principles on which they rely, and how they combined to produce such a revolutionary piece of technology. All questions, comments, suggestions, criticisms, or (hopefully) compliments are very welcome.

These presentations should be viewed in order.

1. docs.google.com/presentation/d/1yiSYscRn...ggY/edit?usp=sharing
2. docs.google.com/presentation/d/16PVtklzU...dWk/edit?usp=sharing
3. docs.google.com/presentation/d/1I-LejFm2...f9Y/edit?usp=sharing

Each of these links will open the presentation in a browser window - click on the "Present" button (top right) to play full-screen with animations.

Enjoy !

Thanks Steve.

I have downloaded those as PDFs to read through off-line and digest. As with any technically complicated equipment it is very difficult to produce a summary explanation in simple terms of how it works without presupposing the reader understands the problems it is designed to overcome.

I hope to comment in due course.

Peter wrote:

I did read that the Norden was not regarded as the best bomb sight but that it had better publicity. The MkXIV (or TI) and later SABS were electro-mechanical computer bombs sights like the Norden but in the right hands were regarded as more accurate. The torpedo 'F' Director worked in a similar way but in this case it was not part of the sight but took information from the sight and unlike bombs information was sent to the torpedo to set its gyro angling.

The thing I can never get straight in my head is the behaviour of the bomb trajectory when it reaches its TV.

I'm not an expert on all the various bombsights that have been produced, so I can't comment on which was best. Under ideal conditions and operated by well-trained personnel the Norden demonstrated a remarkable degree of accuracy for the time, although I'm sure these requirements were also relevant to other bombsights.

In a vacuum, a bomb will accelerate due to to the force of gravity at 32 feet per second per second. So after 1 second, the bomb is travelling towards the earth at 32 feet per second, after 2 seconds it's travelling at 64 feet per second, after 3 seconds it's travelling at 96 feet per second, and so on. However, air resistance produces an opposing force which is directly proportional to the square of the bomb's velocity; so doubling the velocity will quadruple the opposing force. This opposing force progressively reduces the bomb's acceleration. Eventually the downward-acting force of gravity (causing acceleration) is equal to the upward-acting force caused by air resistance, and thereafter it stops accelerating and its velocity will be constant. Thereafter, its trajectory would effectively be linear (a straight line) rather than exponential (when it was accelerating).

Just to add to the fun, the force produced by air resistance is also directly proportional to the density of the air that the bomb is travelling through. As the bomb falls, the air density increases. Therefore, the upward acting force caused by air resistance increases, causing the bomb to decelerate. However, if the bomb decelerates, then its velocity is reduced, and therefore the opposing force reduces ! This causes the effects of air density to be partly reduced. Terminal velocity is defined as the highest speed that a falling object attains. It's therefore possible that a bomb's greatest velocity is attained before it hits the ground.

It's enough to make anyone's brain hurt

It's therefore possible that a bomb's greatest velocity is attained before it hits the ground.