Helicopter vibration

More of an FYI than any sort of tech support request…

This morning, the house began to shake, things started to rattle, and I wondered … just for a second … then it became obvious that it was a very low flying twin rotor helicopter. It didn’t appear on Flightradar24, so I assume it was military rather than the more usual forestry helicopters (that might explain it’s altitude too).

I wondered about the signals picked up by the shake/boom:

I had thought that it was just the house shaking, but no, the ground was too, and quite a lot by the look of it. Looking at the trace in more detail, it is clear that it came close to saturating the geophone. The average “counts” value from mine is ~16,600:

Just a bit more and it would have been clipping.

The infrasound channel looks quite similar:

I am guessing that the dynamic range of the infrasound is somewhat higher, but don’t know for certan. I suppose I should look at that.

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Good eye spotting this Philip!

I have noticed the same between my Shake sensors and my Boom sensor. If an helicopter (especially big ones like the one you captured) transits very close or directly over my house, perceptible vibrations can be heard (and seen) over the house frame itself. And, naturally, the air displacement is also captured by the infrasound sensor.

If it wasn’t on FR24 then yes, there is high possibility of being a military craft. You can check, if you don’t already know it, with https://globe.adsbexchange.com/ which is used worldwide to track military movements.

I have been using Flightradar24 mostly because it has a limited version of the history replay available on the free version, but I am thinking of getting a subscription to adsbexchange, because not only are military flights (mostly) missing on Flightradar24 but they allow (presumably for a fee) civilian aircraft to block any information about them.

Side story: I live at the top end of a large valley on the side of an old lava flow. It forms a relatively steep escarpment, about 1,000’ high (we are 550’) the local town is at the foot of this escarpment. There is a flight training school further down the valley and they do helicopter training. They like bringing the students up to our location because wind conditions are much more challenging than over the flat valley.

The flights became more and more frequent and extended into the nighttime, and the altitudes seemed to get lower and lower … the local FaceBook group was full of people complaining about their houses rattling and shaking and the noise waking up children etc. I mentioned that they could see who it was by looking at Flightradar24 … well, seem that quite a few people did, then called the flight school that owned the helicopters and complained. The flights became much less frequent, but their aircraft all show as “Blocked” on Flightradar24. Can’t even tell if they are fixed-wing or rotary…

ADSBExchange should be able to show even these “blocked” aircrafts, unless there are some stronger restrinctions that do not allow data to be displayed from their id feeds.

Oh, that’s an interesting situation indeed. I remember when I was a child and still living in Italy, my area was used for Panavia Tornado dogfight and simulated target practice… yes, they were loud and our windows rattled, but they were so cool to see at low altitude!

Looks like the “Blocked” aircraft do indeed show.

There is a valley in Wales where the RAF practice low level flying. The road runs down the valley high along one side. If you are not expecting it, a fighter plane streaking past you, level with you, can be a bit disconcerting.

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I am under the flight path of helicopters from Marine Corps Air Station Miramar (formerly “Top Gun”) and get signals multiple times per day from the helicopters. No surprise, since they fly low enough to rattle all our windows, too.