Luton and District Association for the Control of Aircraft Noise
Helicopters - frequently asked questions (FAQs)
The author of this note lives under a low level flight path which crosses the main runway of a major Airport. Prior to about 2004, there was limited noise nuisance from helicopters, and the noise from a small number of Cessna or similar light aircraft was not an issue. Subequently much more noise nuisance has been caused by commercial and recreational Helicopters using this route.
What are the main parts of a Helicopter?
These are the fuselage (or body), the main rotor blades, the tail rotor blades, the gearbox(s), and the engines(s). The engines may be of the piston engined type for small Helicopters such as the Robinson R22, and either one or two gas turbines* for larger helicopters. (* A gas turbine is related to the familiar jet engine - see Wikipedia under `gas turbine’)
What is the `mechanical’ and exhaust noise from a Helicopter?
Mechanical noise can arise from the gearbox(s) on the Helicopter – remember the whine from an original Mini car reversing up a road ? Exhaust noise from a piston engine is much the same as a car engine, except there is a minimal exhaust system ! For the gas turbine engine, the noise is a muted `jet engine like’ noise, caused by the hot exhaust gases from the turbine. Again there is no silencer.
What is `blade noise’ from a helicopter?
The main low frequency noise, the `thwap-thwap’ sound, originates from the main rotor, and is caused by `blade vortex interaction’. (Each blade causes a vortex of air, and the next blade along `chops’ this vortex). This low frequency noise travels rather too well, and can sometimes be heard 20-25 seconds before the helicopter passes overhead.
Higher frequency noise – right in the middle of the most sensitive part of the human hearing range – orginates from the tail rotor.
From a psycho-acoustic (human perception) viewpoint, Helicopter noise is not generally percived as a `pleasant’ noise, and has been rated as 10-15 decibels more annoying than other aircraft noise, for the same reading on a noise meter. (see references - DEFRA nan xxxx, GLA report + web links)
How close can a helicopter be to me? – the 500 foot rule
In uncongested areas the minimum distance is 500 feet from persons or structures. For congested areas this distance is 1000 feet. Considering a powerful helicopter may be over 1500 horspower, and a Super Puma `heavy’ helicopter over 3000 horsepower, these rules need urgent revision. (Even the most powerful lorries are circa 450 horsepower, and they are of course silenced and subject to noise regulation)
What are Air Traffic Control Height limit maxima?
In our area, because of the proximity of a major airport, and the general trend to `squash’ ever more aircraft into the airspace, helicopters are not permitted to fly at a height greater than 1500 feet above sea level. If you already live on a hill – for example some parts of our County are 350 feet above sea level – then in our region the maximum height above your chimney is only 1150 feet.
What is the carbon footprint of a Helicopter?
High! The types of engines used in helicopters, either piston engines or gas turbine, are unlikely to have a thermal efficiency of much over 25%. In other words 75% of the heat energy of the fuel is wasted. Compare this with the Government orginated edicts to fit condensing boilers to homes, where a thermal efficiency of over 90% is expected. In addition to carbon dioxide, the other usual combustion pollutants are emitted, namely VOCs, Particulates, NOx and CO. Many helicopters only do 1 to 2 miles per gallon.
What are `Emergency Services’ Helicopters?
Mainly the Police and the Air Ambulance. Whilst the vast majority of people support the use of Helicopters where life is at risk, there is increasing nuisance from Police Helicopters being used on `routine’ matters – for example the Norfolk Police are reported to have dispatched a helicopter to police a `rave’, and Essex police to look for cannabis houses. It is suggested that policing of this sort could be accomplished just as readily by normal ground based policing methods.
What are Visual Flight Rules (VFR)?
Most Helicopters fly by visual reference to the ground. If a helicopter is to be flown in cloud, then the machine must have two engines and the Pilot must be `Instrument Rated’. However, obtaining an Instrument Rating is costly exercise and it is thought that only a minority of Helicopter pilots have this qualification.
What happens if there a mechanical failure of the Helicopter?
If the main rotor system is intact then is is possible for a Helicopter to `autorotate’ – like a sycamore seed – to a safe landing. It is a CAA requirement that Helicopters must be able to alight safely if there is a total engine failure. However, it is unlikely that a Helicopter can achieve a `glide angle’ of much over 4 to 1. In other words a helicopter at 500 feet above ground can only probably travel about 2000 feet. If there is main rotor blade or main gearbox failure, then the consequences are usually fatal. (ie the recent North Sea helicopter crash which claimed 15 lives was caused by gearbox failure)
Who can I complain to?
The local Airport Operator, Department for Transport (DfT), the Civil Aviation Authority (CAA), your MP, and the Chief Constable of your region for Police Helicopters.