Why combat crews wanted to know the speed of flak

[b17sam]

An often discussed topic of conversation among WW2 combat crews in their off time was that we all had our own personal flak shell destined to meet up with us or miss. As it took a certain amount of time for the shell to reach our altitude, we had that interval of time to move a foot or so in any direction to avoid the fickle finger of fate. Conversely, any movement, or no movement at all might cause the flak shell to go straight up our gluteus maximus, and we'd become nothing but another statistic. This conversation was quickly followed by more important questions that we could deal with, such as girls, sex, and what we did on our last pass.

 

[lesofprimus]

Interesting to know Sam.... What was the general feelings of the crews in late 44??? Pesimistic or motivated???

 

[HoHun]

Hi B17sam,

>As it took a certain amount of time for the shell to reach our altitude, we had that interval of time to move a foot or so in any direction to avoid the fickle finger of fate. Conversely, any movement, or no movement at all might cause the flak shell to go straight up our gluteus maximus, and we'd become nothing but another statistic.

Hm, for an individual crewman, moving about would make no difference.

However, for the entire aircraft, evasive action actually made sense.

I have tried to calculate just how much sense, using a simple approximation, based on the information that 1 in 16000 shells shoots down the aircraft, and that the lethal radius of the 8.8 cm shell is 4.5 m. (I had to assume the gunnery errors are of equal magnitude in azimuth, elevation and range, and to pretend that the target is a dimensionless dot, so it's not terribly accurate

Both bits from information are from the same book I quoted in the original thread:

http://www.ww2aircraft.net/forum/aviation/60-year-old-problem-10466.html

Choose a distance you have moved from the aim point on the horizontal axis, then read the relative "probability of kill" from the vertical axis.

For example, moving from the aim point by 30 m (ca. 100 ft) would reduce the chances of the Flak to down the aircraft to 50% of what it would be if the aircraft stayed on the aim point.

However, the Flak directors were capable of "following" climbs and turns, so any evasive manoeuvres would have to be unpredictable, random, and probably somewhat violent.

(By the way, prior to the war the lethal radius of the 8.8 cm Flak was thought to be 15 m instead of just 4.5 m, so heavy Flak turned out to be just 2.7% as effective as expected. However, the effect of bombing attacks had been expected to be much greater, too ... probably an indication that in times of peace, weapon effectiveness tends to be exaggerated.)

Regards,

Henning (HoHun)

 

[b17sam]

==Hm, for an individual crewman, moving about would make no difference.==
The above statement from the previous post fails to recognize the numerous statements of crew member reports of penetrating flak and bullets inches away from where they had been seconds ago. The sheet metal repair guys would work all through the might patching holes to prepare the ships for the next morning's mission.
Our crew picture clearly shows a square 20 inch patch too darn close to the navigator position on Mah Ideel.

 

[Matt308]

Yeah but your question is more one of philosophy, than physics. It smacks of the proverbial tree falling in the woods, does it make any noise. Or perhaps the "butterfly effect". Your question is an ancient question of philosophy much analyzed by Descartes. If each action based upon free will results in a branching of reality...can the crewmember "move" to avoid the branch that seals his fate?

You don't really expect an answer do you.

 

[HoHun]

Hi B17sam,

>>==Hm, for an individual crewman, moving about would make no difference.==

>The above statement from the previous post fails to recognize the numerous statements of crew member reports of penetrating flak and bullets inches away from where they had been seconds ago.

I admit that my statement was not precise - of course, moving about could make all the difference you describe

Moving about after the shot left the barrel would not change the statistical chances of being hit though - and that's what I meant to say.

There might be one safe and one lethal position - but there is no way to tell which will be safe and which will be lethal until after the impact.

Regards,

Henning (HoHun)