Helicopters you'll actually see

Civil helicopter identification is easier than fixed-wing, because the fleet is smaller and the tail is usually decisive.

Light singles

• Robinson R22 / R44 / R66 — the world's training and private helicopters. Thin two-blade main rotor, very slim tail boom, and a distinctive slapping rotor noise.
• Airbus H125 (AS350 Écureuil) — the workhorse for utility, tourism and firefighting. Three-blade main rotor, sleek nose, often seen with a cargo hook.
• Bell 206 JetRanger / 407 — the classic news and charter helicopter; the 206's narrow cabin and tapered tail boom are instantly recognisable.

Twins

• Airbus H135 / H145 — the standard air-ambulance and police machines across much of Europe. The H135's fenestron — a shrouded tail rotor set inside the fin — is the giveaway, and it's the reason they sound so much quieter than a conventional tail rotor.
• Leonardo AW139 — bigger, used offshore and for VIP transport; five-blade main rotor and a deep fuselage.
• Sikorsky S-76 — retractable gear, which almost nothing else in this class has.

Why they sound different

Blade count and tip speed set the character of the noise. Two-blade heads slap; four- and five-blade heads produce a smoother, lower beat. A fenestron or a shrouded tail rotor cuts the high-frequency whine that a conventional tail rotor throws sideways, which is why hospital helipads in cities so often operate the types that have one.