police helicopter, how fast
Discussion
Saw a pusuit documentary on sky (yeah i know)
where despite flying in a straight line, and the motorways slightly winding course, some low-life in a Porker, he'd nicked from a showroom in Bristol, actually picked up enough speed through traffic, by weaving about/hard shoulder. To evade a single chopper, being spotted further down the road, by a neighbouring counties machine, which filmed him trying to hide in a farmyard, from where bib picked him up by guidance from the air.
Was he just lucky that day, or can a helicopter
(american?) easilly fly faster
what does a Knot translate as to mph?
where despite flying in a straight line, and the motorways slightly winding course, some low-life in a Porker, he'd nicked from a showroom in Bristol, actually picked up enough speed through traffic, by weaving about/hard shoulder. To evade a single chopper, being spotted further down the road, by a neighbouring counties machine, which filmed him trying to hide in a farmyard, from where bib picked him up by guidance from the air.
Was he just lucky that day, or can a helicopter
(american?) easilly fly faster
what does a Knot translate as to mph?
You're surprised at 120mph?
I don't think it's a bad speed at all considering....straight line flying...no bends, traffic, camber etc to deal with....
Very difficult to outrun a police helicopter..I mean..if you out run it for a mile on a very long stetch of motorway, it would be up with you again at the first real sets of curves....
In addition, the Zoom on the camera would mean very little in evidence is lost...
I don't think it's a bad speed at all considering....straight line flying...no bends, traffic, camber etc to deal with....
Very difficult to outrun a police helicopter..I mean..if you out run it for a mile on a very long stetch of motorway, it would be up with you again at the first real sets of curves....
In addition, the Zoom on the camera would mean very little in evidence is lost...
I don't doubt the effectiveness of using these machines, but I was suprised at the overall speed they fly at, always imagined as a fixed wing aircraft of about the same physical size is (i think) capable of double that (ground speed) that choppers, being more modern and advanced than a cessna, would somehow have been capable of higher speed.
As you point out, 120+ camera/nightsun light and infra-red on board would outweigh the slight slowness
Perhaps a max-power chopper is needed
Mc donnel chav-opter
As you point out, 120+ camera/nightsun light and infra-red on board would outweigh the slight slowness
Perhaps a max-power chopper is needed
Mc donnel chav-opter
Helicopters are pretty slow, but the road looks pretty different from up there.
The limiting factor in helicopter speed, is the speed of the forward going rotor tip. You'll find that even on the very fastest helicopters, by the time you get to about 160mph forward speed (for the helicopter), the forward going rotor tip is just marginally subsonic.
If the tip goes supersonic the resulting shockwave defeats the centrifugal action that keeps the rotor blade taught.
If you get a motorway style "big curve", they can cut the corner at full tilt, where the car would be lucky to achieve walking speed.
You can't get away from a helicopter. Which is why I don't understand the need for whizzy police cars.
>> Edited by dilbert on Saturday 19th February 13:48
The limiting factor in helicopter speed, is the speed of the forward going rotor tip. You'll find that even on the very fastest helicopters, by the time you get to about 160mph forward speed (for the helicopter), the forward going rotor tip is just marginally subsonic.
If the tip goes supersonic the resulting shockwave defeats the centrifugal action that keeps the rotor blade taught.
If you get a motorway style "big curve", they can cut the corner at full tilt, where the car would be lucky to achieve walking speed.
You can't get away from a helicopter. Which is why I don't understand the need for whizzy police cars.
>> Edited by dilbert on Saturday 19th February 13:48
Dilbert is spot on with the reasons for the helo top speed, but there are also other factors. The Twin Squirrel that a lot of forces use claims a top speed of around 130 mph, but that will thrash itself to bits if it has to maintain it. Most larger helos are capable of maintaining the 90-120 mph mark. (Just as food for thought, the Sea King, operated by the RAF and Navy and several other private companies, can only do around 90 kts. So don't fall off a cliff a long way from a SAR unit!)
Oh, and don't try and do the Keanu Reeves 'Speed' trick of driving into an airport, they just get a special clearance to follow you. However, extremely built up areas, multi storey carparks and such, would be a winning choice!
Oh, and don't try and do the Keanu Reeves 'Speed' trick of driving into an airport, they just get a special clearance to follow you. However, extremely built up areas, multi storey carparks and such, would be a winning choice!
Some examples:
Humberside: MD 902 - 143mph
W.Yorks: Same, poss. different engine
N.Mids: EC135 - 150mph
Met: AS355N - 135mph?
Hants police used to have an Optica Scout, fantastic looking thing and that had a top speed of 135mph, although I don't think it was equipped with video, and FLIR was a military only thing at the time.
Gareth
Humberside: MD 902 - 143mph
W.Yorks: Same, poss. different engine
N.Mids: EC135 - 150mph
Met: AS355N - 135mph?
Hants police used to have an Optica Scout, fantastic looking thing and that had a top speed of 135mph, although I don't think it was equipped with video, and FLIR was a military only thing at the time.
Gareth
Well, having now done some research!!!!......
I think the stalling retreating blade is as much of a problem as the supersonic advancing one.
It seems my guess about maximum speed was quite wide of the mark, the record is held by the Lynx at 250mph.
I think the thing to bear in mind however is that there is considerable advantage in normal circumstances to having a higher rotor speed. It may sound odd, but when you fly a helicopter you are really flying the rotor.
It wouldn't surprise me in the slightest if the helicopter that holds the speed record was modified, and pretty difficult to fly as a result. Predicted modifications;
1) Adjustments to the section of the rotor to give greater lift at lower speeds.
2) Slower overall rotor speed.
The problem with running the rotor at a lower speed is that you run far closer to the point where it collapses.
I'm certainly not an expert in helicopter design. It would be nice if one could comment.
I think the stalling retreating blade is as much of a problem as the supersonic advancing one.
It seems my guess about maximum speed was quite wide of the mark, the record is held by the Lynx at 250mph.
I think the thing to bear in mind however is that there is considerable advantage in normal circumstances to having a higher rotor speed. It may sound odd, but when you fly a helicopter you are really flying the rotor.
It wouldn't surprise me in the slightest if the helicopter that holds the speed record was modified, and pretty difficult to fly as a result. Predicted modifications;
1) Adjustments to the section of the rotor to give greater lift at lower speeds.
2) Slower overall rotor speed.
The problem with running the rotor at a lower speed is that you run far closer to the point where it collapses.
I'm certainly not an expert in helicopter design. It would be nice if one could comment.
g_attrill said:
Hants police used to have an Optica Scout, fantastic looking thing and that had a top speed of 135mph, although I don't think it was equipped with video, and FLIR was a military only thing at the time.
It was the first production model as well, before it was involved in a crash which unfortunately killed the two police officers on board.
www.hants.gov.uk/hchs/optica.html
Dwight VanDriver said:
... and don't forget the wind factor. Head on into a 30 mph wind will knock that speed off. More effect, I understand, than at ground level.
DVD
Ps 5 kts = 5.8 mph
www.lerc.nasa.gov/WWW/K-12/WindTunnel/Activities/knots_vs_mph.html
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