Boeing C-17 Globemaster III

Boeing · United States · first flew 1991 · transport aircraft

The Boeing C-17 Globemaster III is a large strategic and tactical airlifter capable of carrying outsize cargo directly into austere short airstrips, combining the payload of a strategic transport with the airfield flexibility of a tactical one. It has become the backbone of US and allied heavy airlift.

Recognition (WEFT)

W — Wings	High-mounted, swept
E — Engines	4 × turbofan, wing-mounted
F — Fuselage	53 m fuselage
T — Tail	T-tail

WEFT is AircraftIQ's four-point recognition method — how it works.

Spot it by:

Four high-bypass turbofans with thrust reversers operable on the ground
T-tail with large horizontal stabiliser
High-wing with winglets and supercritical aerofoil

The high-set swept wing with four large turbofan engines, T-tail, and blunt upswept rear fuselage with a rear ramp are defining. Winglets on a military transport are unusual and help confirm the type.

Specifications

The Boeing C-17 Globemaster III has a length of 53 m (174 ft).
It has a wingspan of 52 m (171 ft).
Its maximum speed is 833 km/h (518 mph).
Typical crew: 3.

Figures are for the representative variant described above; marks differ. See how AircraftIQ sources figures.

History

Developed by McDonnell Douglas (later absorbed by Boeing) to replace the C-141 Starlifter, the C-17 entered USAF service in 1993 after a troubled development. It has since logged millions of flight hours in operations across the Gulf War, Afghanistan, Iraq, and numerous humanitarian missions.

Variants

The airframe has been essentially unchanged across production; export variants differ by customer avionics suites. Boeing produced 279 aircraft before the line closed in 2015.

Where you'll see it

Operated by the USAF, Royal Air Force, Royal Australian Air Force, Royal Canadian Air Force, UAE, Qatar, Kuwait, and India among others; the RAF fleet is based at Brize Norton and is central to UK strategic airlift.

In depth

Much of what looks awkward about the C-17 is aerodynamic sophistication solving the contradictions of the strategic-tactical airlifter. The wing uses a supercritical aerofoil, a flattened-top, more sharply cambered section that delays the formation of shockwaves and lets the aircraft cruise efficiently at high subsonic speed without an excessively thin or sharply swept wing. Marrying that high, thick wing to four large high-bypass turbofans creates a ground-clearance problem — big-diameter fans hung under a high wing sit uncomfortably close to the runway — and the designers accepted a deliberate compromise: the engine pylons let the nacelles droop below and ahead of the wing, angling the thrust line and complicating the exhaust path, in exchange for keeping the fans clear of the ground and, crucially, positioning that exhaust where it can be put to work by the flaps.

That exhaust is the heart of the aircraft's short-field trick. The C-17 uses an externally blown flap system: at low speed the engines are angled so their exhaust washes directly over and through large, slotted Fowler flaps that deploy across most of the trailing edge. The flaps redirect and entrain the jet efflux downward, turning engine thrust into additional lift and letting the aircraft fly a steep, slow, controlled approach. The result is that a machine grossing well over 250 tonnes can operate from runways under a thousand metres long — around 3,000 feet — landing steeply, stopping with powerful thrust reversers that can be run on the ground, and then reversing under its own power to back out of a confined strip, something no other aircraft of its size can do.

The cargo system matches that access to austere fields. The C-17 delivers by the Container Delivery System, in which bundled loads on rollerised pallets are extracted by drogue parachutes out of the open rear ramp in a rapid sequence; by low-altitude parachute extraction, where a heavy load is dragged out by parachute a few feet above the ground so it lands without a long descent; and by mass personnel drops, with paratroopers exiting from side doors and the ramp. In practice these look dramatic — the aircraft flying low and slow with the ramp down, pallets tumbling out on canopies in a string, or lines of parachutists streaming from both sides — and each mode exists to put cargo or troops onto ground the aircraft itself may not be able to land on.

Telling it apart from its stablemates is mostly a matter of size and engine type. Against the Airbus A400M, the clearest cue is the powerplant: the C-17 has four podded turbofans with no propellers, where the A400M has four turboprops with large scimitar-bladed propellers; the C-17 is also visibly the larger aircraft and carries prominent winglets, unusual on a military transport. Against the Lockheed C-130J Hercules the gap is even wider — the Hercules is a much smaller four-turboprop machine with a straight wing and a conventional low-set tailplane, while the C-17 towers over it with a swept wing, a tall T-tail, and jet engines. In all three the high wing, rear ramp, and upswept tail are shared family traits; it is engine type, sheer size, and the T-tail-plus-winglets combination that fix the C-17.

For the spotter, the C-17 is one of the more reliably encountered heavy military types. In the UK the RAF fleet works from Brize Norton, and its arrivals and departures over Oxfordshire are a regular sight, with the Royal International Air Tattoo at nearby Fairford a near-certain annual opportunity to see one on the ground and often flying a display. Worldwide the type transits and stages through large civil and military hubs on strategic runs, was a fixture of operations through Gulf bases such as Al Udeid in Qatar and historically Kandahar in Afghanistan, and turns up at international airports wherever heavy or humanitarian lift is needed — its size and four-engine, winglet-tipped silhouette making it hard to mistake on a crowded ramp.

Related aircraft

AircraftIQ — the aircraft field guide: 5,024 recognition guides, live overhead identification, works offline.