What was the strange aircraft I heard at the dock?

The other day I was down at the dock and I heard an aircraft coming up from behind. I didn't look up right away but it caught my ear because commercial jets don't fly that way (westward, from the small island airport).

I looked up as it passed over, a thousand feet up or so, expecting a 707 or 737, when what do my wondering eyes perceive but a tiny Cessna-like or Piper Cub-like 2-seater prop craft. Same size and silhouette. Straight wings, blunt tips, etc. Indistinguishable from every other two seater that buzzes the city.

But this craft did not drone like a prop plane; it roared like commercial jet.

I'm familiar with turbo props - the island airport flies hundreds of Dash-8s past my house every day. This was not that.

No unusual lumps in its silhouette either, like maybe a big rotary engine or exhaust.

It sounded like a jet from the moment it was audible till it was out of earshot. It did not change its tune appreciably like the big copters do, that sound like a jet from afar but gradually change to the beating of rotors as they pass. Get those here daily too. What did I hear/see??

Start with; https://flightaware.com/live/
Find your local airport, look for arrivals or departures, go back to the date and event.
Next time, look immediately for the plane's live track.

You might also consider; https://www.flightradar24.com/

Thanks.

So, during the two hour window, after I filter out all the Dash-8s , there are only four craft left. And only two of them are single engine:

Cessna 210 Centurion

"... six-seat, high-performance, retractable-gear, single-engined, high-wing general-aviation light aircraft." Pilatus PC-12

Ah!

"... a pressurized, single-engined, turboprop aircraft...

Mystery solved!
Thanks!

But the Pilatus is a turbo-propeller, engine which sound you are familiar with.

It's an uncommon configuration, is the point; single engine turboprop, so he wasn't expecting to hear a turbine. Popular plane though.

Lnewqban said:

But the Pilatus is a turbo-propeller, engine which sound you are familiar with.

Yeah that second video def captures it. All jet-roary, no prop-droney.

It's not what the Dash-8s I'm used to sound like.
.

Since in another thread is a discussion of old commercials:

The night before last I was hearing a plane, likely a jet, makihng a very UFO-like "wow wow" noise at about 2 Hz. There was definite;y something going on in the atmosphere - a few minutes later thunderstorms rolled in.

The lesson I learned is that things don't always sound like they are supposed to.

Baluncore said:

Start with; https://flightaware.com/live/
Find your local airport, look for arrivals or departures, go back to the date and event.
Next time, look immediately for the plane's live track.

You might also consider; https://www.flightradar24.com/

@Astranut is an aircraft nut. You recognise this Astra?

Vanadium 50 said:

Since in another thread is a discussion of old commercials:

The night before last I was hearing a plane, likely a jet, makihng a very UFO-like "wow wow" noise at about 2 Hz. There was definite;y something going on in the atmosphere - a few minutes later thunderstorms rolled in.

The lesson I learned is that things don't always sound like they are supposed to.

Could be a mismatch between engine RPM on a twin. You get a definite beat frequency relative to the degree of mismatch. That mismatch is rather dangerous, though, especially with larger aircraft and engines, and they have propeller synchronizers and even syncrophasing systems to line up all the propellers on the plane to rotate in unison. That's why you often see photos of, say, a P-3 Orion or a C-130H Hercules with all four props in unison.

Other factors can impact sounds as well. If you look at, say, a Cessna 172 and a 182, they seem quite similar, but they sound very different once you go full throttle. Part of that is the increase in horsepower, the larger engines, etc, but also propeller blade count and propeller diameter. You get a ton more noise out of a prop at takeoff power by adding as little as an inch or two to the blade length. It adds up quick at 2700 rpm.

With atmospheric variation, that could be the sum of two paths, one reflected with Doppler, the other path direct.

Some helicopter rotors produce a distinct beat as the blades pass over the tail assembly.

During WW2, allied aircraft over Britain synchronised their engines. Axis aircraft turned off the engine synchronisation, to generate a deliberate beat, to make acoustic direction finding more difficult. IFF was not essential when an aircraft could be heard.