Flightradar Q
 

I saw lights of a helicopter in night sky yesterday after dark, believe at least from sharp turns it apparently made it was helicopter,
opened Flightradar out of interest to see if it was more police activity but saw nothing in this area moving.
would the aircraft not appear like the military flights we see (Chinooks) that pass over here quite often?

When a police heli is flying over the city here, I can't see it on FR24 so I assume it's the same as military aircraft.

Good, not just me then.

Just been on FR and viewed a couple of lights from local helicentre so I know the normal aircraft are visible at least,
expect last night was just chasing the usual suspects hereabouts

Can't speak to the situation in the UK, but in the US all the big sites, such as FlightRadar, FlightAware, etc. rely on both a paid-for FAA radar data feed as well as host of independent, primarily amateur, ADS-B receiver sites. Thus you will get both ADS-B and non-ADS-B equipped traffic.

Obviously, if the traffic is not within a radar or amateur ADS-B coverage area, and helicopters are often low enough for that to happen, it won't be seen.

The FAA also has a program where you can opt your aircraft out of the publicly accessible FAA feed. It need not be a military or public safety aircraft to opt out. However, such aircraft, if ADS-B equipped, cannot hide from the amateur ADS-B receiver network. Even more interestingly, there are now networks of amateur MLAT stations that can geo-locate regular Mode C and older, non-ADS-B Mode S transponder emissions, not that such equipment will remain relevant for very much longer in the US given the US ADS-B mandate.

One thing that is not clear is whether or not the big websites like FlightRadar are given a "do not publish" list by the FAA. They can't stop a local ADS-B receiver operator from seeing everything that is around them, but they don't have to forward that information when it is uploaded to FlightRadar from one of the amateur receiver sites.

I've dabbled in this arena, and have built a dual frequency (978 and 1090MHz) ADS-B receiver unit. I can easily see all ADS-B equipped aircraft for many miles around, depending on altitude, of course. So when the Black Helicopters are coming to get me I'll be able to see them coming ;)

You can buy your own, commercially made, ADS-B receiver, or construct your own if you are handy with a PC, and not be subject to big website filtering, nor the multi-minute delay they put into their feed for "security theater" purposes.

Hmm, I shall have to have laptop to hand when I next hear it's (Police) drone as it very distinct, see if it shows up or not.
interesting FR doesn't show 'everything' as an amateur I'd not considered their coverage till now so that's worth remembering,
for the record I'd imagine at least that local forces of Law & Order would have use of fairly new equipment and a quick search on net reveal aircraft in use over this region; G-EMID

at least I think that's the current machine

aa777888, there's no primary radar feed into FR24 in the UK. I think it might be unique to the US. However there is a slight delay with the displayed data, supposedly for safety (terrorist) reasons.

Bravo73 is closest, as FR24's main source of data is from ADS-B equipped aircraft. However they also will show an aircraft location if they can get a fix based on Multilateration from multiple receivers. However, tactical military aircraft are also filtered out whether they are ADS-B equipped or not.

FR24 have an FAQ and "How it Works" sections on their website if more info is needed.

So back to the OP, I would think that it is highly likely you were seeing a military aircraft.

Hopefully this reply will be approved and posted (last one still hasn't mods)
The Police helicopter for here has a very recognizable engine tone so I'll have laptop ready I hear it hovering over town shortly
and try FR to track it.

The military that fly past here, (Chinooks usually) normally have a set heading, the one last night wasn't apparently and made a turn too,
which made me think what with its lack of record on FR it might have been Police

If you are equipped with Mode S Extended Squitter, then the ground receivers (hosted by enthusiasts) will pick you up.
You need to be in range of 3 for triangulation, so accuracy can vary.
If you don't want to be seen, you can write to them with proof of ownership and request to be invisible or anonymous, something that must be repeated with the other sites like planefinder.

For the US at least, ADS-B Out is now mandatory (as of Jan 1, 2020) for most aircraft flying in or near controlled airspace.

Here in the US, there is a new wrinkle that was added back in July of 2019
So some can turn off the ADS-B out.

Government and an other aircraft owners can ask FR24 and similar sites to have their aircraft removed from display...

Police/military a/c are often filtered out from FR24. Google 'global ADSB exchange' and you'll find a site that displays a lot more unfiltered air traffic.

"nor the multi-minute delay they put into their feed for "security theater" purposes."

speaking of this, I was at the YVR airport tracking the g/f's flight in and watching the flights land and I thought it was all pretty accurate...

until I was watching her "flight" come in from the distance when she texted me she was at the gate.

I was like whoa...I expected a delay, but not so much her flight was already landed and i was watching a different one come on matched to the FR map.