Luftwaffe desynchronised aero engines.

[malladyne]

One common thread to the accounts given by many survivors of the German aero attacks on the UK during WW2, is that they recalled the sound of the attacking aircraft engines as being de-synchronised or "off beat". Does anyone know what this means and how it differs from those engines of Allied aircraft which were, presumably, synchronised ?

[Graham Boak]

This is a matter of adjusting the revolutions of the engines so that the propellors are revolving at the same speed - in synchrony. When propellors rotate at different speeds there will be time when they coincide and times when they don't, producing a beat in the noise, a regular rise and fall. This is generally considered annoying and tiring to the crew, but was thought to confuse sound detectors.

[George Hopp]

Thanks for that explanation, Graham, because I also had heard of the de-synchronized German engines. And, yet, Allied pilots were always fiddling with the rpm to synchronize the aircraft engines.

[Nick Beale]

I think that pretty much anyone who experienced air raids on Britain will tell you that German engines made a throbbing noise. Everyone believed it, although there may be an element of folk wisdom in that of course.

[Brian Bines]

Some late war raids were referred to in the newspapers as being by 'scalded cats' raiders i.e engines at higher revs attacking in shallow dives, so I suppose by this time de-synching the engines was redundant.

[Graham Boak]

The British had put a lot of effort into sound location. Although it had proven inadequate, the Luftwaffe did have good reason for attempting countermeasures. I know of no equivalent German effort (although I am sure there will have been some) so the RAF chose to put crew comfort first.

I also suspect that it was considered the Proper Way of doing things, rather like three-point touchdowns, and not applying power on the approach. Not the Done Thing, old boy. Ideas that went out of the window in mass wartime use, although synchronising the engines did have a genuine value in crew comfort, and hence efficiency.

[PeterVerney]

I understand the Germans were ordered to desynchronise their engines when approaching UK because they knew of our efforts to use sound location, one of the concrete mirrors can still be seen on top of the inland cliff overlooking Romney Marsh.
But threepointers were the mark of a polished pilot, my man loved to show off his Mosquito landings! but ran the risk of the dreaded swing.
Going well off the point, your bit about a bit of power on the approach, reminded me of an incident at Wattisham in the middle '50's. The proper fighter pilot break and landing is to approach the runway at high speed, close the throttle and zoom turn onto the downwind leg, lower u'cart and flaps , turn finals and land, all without again touching the throttle.
A Wattisham Hunter pilot attempted this one day and discovered late on the approach that he did need that little extra bit of urge. When he went for it the engine had flamed out and he touched down in the undershoot. When he reached the end of the runway the undercarriage was wiped off and he finished up sliding sideways along the ORP (a concrete layby where fighters were marshalled to scramble on exercises).
At the end of that stood the runway controllers caravan, the occupant of which had watched the whole exercise. He decided to bale out but was too late and found the Hunters wingtip stopping a few feet away from the steps out of the caravan.

[Graham Boak]

Remaining off the point for a moment, I was thinking of the troubles experienced with the Hudson, which apparently bounced dramatically, until they gave up and accepted "wheelers" as approved technique.

[Juha]

Hello
IIRC early in the war also at least some BC pilots desynhcronised their engines before entering enemy airspace. Motive was also to confuse sound detectors.

Juha