The German proximity fuse.

"Eunometic" wrote in message
oups.com...



The Germans were only just begining to introduce to troop testing
ground mapping microwave radars.


Whereas the RAF and USAF were using them in service
by the thousand

snip




Several accoustic homers for aircraft and missiles were under
development.

1 "Baldrin" by Messerscmitt and Telefunken. Used 16 valves and 4
microphones. Range was 350m when flown on piston engined aircraft and
several kilometers when flown on an Me 262. It had a wide 180 degree
view.

2 Parrallel development at ELAC with an estimated range of 2km but
never named or tested.

3 "Pudel" single microphone homer for the axially spining X-4 missile.


Which was of course never deployed

4 A Dr Trage of "Reichs Post" had a 4 microphone system under
development.

Baldrin was the only one tested.

I estimate that a 3 or 4 bladed propeller at 1500 rpm will produce 75
to 100 hertz and that a 12 to 18 cylinder exhaust will produced 150 to
225 hertz.



Take a sound meter to an airshow, you'll get a broader band
of frequencies than that

A 9000 rpm 60 bladed jet starts at about 4000 hertz.


The germans on their sub sonars used electro-accoustic crystals to
phase shift to use constructive interferience to determin direction and
I expect the same technique in sonic aircraft trackers.


Submarines suffer from somewhat less flow noise than an aircraft


Don't forget that sound was used to aim and range FLAK and that even in
WW1 in britain huge granit parabolic sound dishes would detect and
triangulate gotha bombers and zepplins out to 20-25 knautical miles.


No the sound dishes were built in the late 1920's and early 1930's

Sound can locate artillery fire and can even track bullets and shells.


Lots of luck trying to track a supersonic projectile with a medium
that travels less than half as fast.

It can tell you where it WAS and perhaps even where it was fired
from but not where its now.

Its a little slow but it is apparently a concern for stealth aircraft.


Indeed but the inbuilt limitations make it almost useless for targetting.

Keith



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