Telling aircraft apart

You don't need to memorise a catalogue. Almost every identification narrows quickly if you check four things in order: how many engines and where they are, the nacelle shape, the wingtip, and the nose and tail profile.

Airliners

Variant by variant — 737 generations, widebodies, regionals, freighters.

Light aircraft

Training types, fast singles, twins and light-sport.

Business jets

Citation, Gulfstream, Bombardier, Embraer, Falcon and the turboprops.

Military

Fighters, transports, tankers and trainers.

Narrowbodies — the two you'll see most

Boeing 737 — flat-bottomed engine nacelle, a pointed nose, and an eyebrow-free flight deck on newer builds. The MAX adds tall split-tip winglets and a serrated engine cowl edge.
Airbus A320 family — circular nacelle, blunter nose, and on modern examples the tall curved sharklet. The A319, A320 and A321 differ mainly in fuselage length and door count.

Both engines need the same clearance over the runway, but the 737's airframe sits much lower on its gear, so the bottom of the nacelle was flattened to fit — the dashed line is the circle that isn't there. The A320 sits higher and kept a round nacelle.

Widebodies

Boeing 787 — raked wingtips with no winglet at all, and a serrated (chevron) trailing edge on the engine nacelles. The wings flex noticeably in the climb.
Airbus A350 — curved blended wingtip and a distinctive dark "mask" around the flight-deck windows.
Boeing 777 — large, long, no winglets on most variants, and a main gear with six wheels per leg rather than four.
Airbus A330 — similar size to a 777 but with a smaller wing, plain winglets and four wheels per main leg.

Seen end-on, outboard wing at the right. A raked tip adds span and sweep with nothing vertical at all (787, late 777s); a fence is a short blade above and below (early A320s); blended winglets curve up (737NG, A330ceo); a sharklet is taller and more curved (A320neo); a split tip points up and down at once (737 MAX).

The wing of an Airbus A321 seen from a passenger window at sunset, ending in a tall curved sharklet — An A321's sharklet, photographed from the cabin. The best wingtip views are from a window seat behind the wing, and the tip device dates the aircraft better than the livery does.Photo: Asurnipal · CC BY-SA 4.0 · source

Regional jets and turboprops

This is where most people stop, and it's mostly a tail question. An Embraer E-Jet has a conventional tail with engines under the wing. A CRJ has a T-tail with engines mounted on the rear fuselage. An ATR 42/72 is a high-wing turboprop with a T-tail; a Dash 8 / Q400 is a high-wing turboprop too but noticeably faster-looking, with a longer nacelle and a distinctive whine.

Where the tailplane sits, in orange. Low on the fuselage is conventional — almost every modern airliner and most light aircraft. On top of the fin is a T-tail, which is what you see on rear-engined types (CRJ, ERJ, MD-80, business jets) because the engines are in the way. Part-way up the fin is cruciform, the compromise.

Light and general aviation

High wing versus low wing does most of the work. Cessna 172 and 182 are high-wing with a strut; Piper PA-28s are low-wing; Cirrus SR20 and SR22 are low-wing composite aircraft with a distinctive swept tail and no separate cabin door frame. If it's a low-wing composite single with a parachute placard on the fuselage, it's a Cirrus.

Registrations are the shortcut: an aircraft's tail number tells you the type, age and operator through any public registry or tracking site. See watch live.

Photographs and references

For photographs of the real thing, Wikimedia Commons' aircraft category is freely licensed and very large, and planespotters.net pairs its photos with each individual airframe's build date, operator history and fate.