It was not steady it rose and fell
Because the Luftwaffe did not feel it necessary to synchronize their engines-in the technology of the 1930s (which is when nearly all Luftwaffe bombers were designed)-that required the services of a Flight Engineer-ie another crew member. It was a design trade-off-save the weight of accommodating another crew member vice using that weight savings for more speed, fuel or payload.
That’s it. Nothing strange or “tactical” about it.
The Luftwaffe relied primarily on several different planes during the Battle of Britain: –ME/bf 109 (a fine air supremacy fighter that lacked the range to have much fighting time over Britain) –ME110 (originally assumed to be a fighter but quickly proven to be a disaster in that capacity, evolved into a light bomber role in this campaign) –JU87 (ie: Stuka) which played a negligible role in this campaign. The primary German bombers for the Battle of Britain were the JU-88 (a versatile aircraft that was deployed in smaller numbers than the HE-111 or Do-17 yet experienced higher losses), HE-111 (nearly obsolete by the time this campaign occurred) and Do-17 (The Flying Pencil), and the Do-217(perhaps Germany’s best bomber).,
It was a characteristic sound of the engines fitted to the three main types of manned bombers which operated against the Uk,namely the Dornier 17,Heinkel 111 and Junkers 88.By the same token,the Merlin engines of the Spitfire,Hurricane and Defiant fighters had a distinct whistling sound.The V1 flying bomb had a pulse jet,which resembled the sound of a two stroke motorbike,whereas the V2 was a rocket,the forerunner of space travel.
The Germans did not synchronize the engines on their multi-engined aircraft, like the British and the Americans did. So a German bomber had a kind of roooooAAAAAAoooooooAAAAAAooooorrrrr sound.
It may not have been the engine note that changed, but the sound echoing off nearby buildings giving a ‘Doppler’ effect. I do believe that certain Dornier aircraft were actually Diesel powered, & the engines that were subsequently siezed after the end of the war went on to power the first Diesel powered locomotives in the UK. I may be wrong but me dad told me that years ago & being a good son I believed him.
In the early days of ww2 the defence forces used to use what amounted to “mechanical ears” ! They were large cones attached to microphones, to detect the noise of approaching aircraft. By “de-synchronising” the engines it was thought that it made it harder to determine the height, direction etc of approaching aircraft. Radar rendered the method obsolete.
You can still see on Romney Marsh, in East Kent, the remains of “Sound Mirrors”, this was another way of using sound to detect aircraft. The strange thing is , IT WORKS !!!
they certainly did have a desynchronised sound. i was told that unlike our constant speed propellors they had two speed ones. constant speed props are easy to synchronise , easy way in a DC4 was to stand a cup of tea on the throttle console. you could judge it from the ripples. of course we did have a synchroscope if it worked ! alan
They deliberately desynchronised the engines on multiple engine bombers to make the weird sound scary. Throttling back a little on one engine was enough to create the sound.
Are you getting mixed up the the Doodlebug. That was a simple unmanned pulse jet which made a distinctive noise.
The Stuka dive bomber had sirens and also had a distinctive sound.