The C-17 is the U.S. Air Force
's newest heavy transport
aircraft. It is intended to replace the aging C-141B Starlifter
fleet, and to augment the KC-10 Extender
and KC-135 Stratotanker
, both of which can be used for cargo transport. It does not have the gross
carrying capacity and size of the C-5 Galaxy
transport; however, it is designed more for reliability, availability and flexibility than sheer capacity.
This is not to say that the thing is a panacea. On the contrary, the development and procurement of the C-17 has been beset with problems, not least of which is the perfectly plausible proposal that the same lift requirements could be met for much less money by simply purchasing a fleet of proven aircraft with world-wide maintenance and support - the Boeing 747 Cargo freighter. Compared to the unit cost of $236 million for the C-17, the unit cost of the 747-400 Cargo is roughly $168 million1. Before evaluating that possibility, let's have a look at what the C-17 is intended to do - what makes it special?
While the air force is eager to trumpet the availability and low maintenance requirements of the C-17, it must be remembered that they are bragging in the context of other military aircraft - notable maintenance and sometimes availability problems. In many cases, military aircraft are designed for burst performance, not constant service. The United States, with its perhaps unenviable position as one of the few (if not the only) nations with both the desire to poke its nose in all over the world and the pocketbook to do it, tends to need to use transports all the time. This is in fairly sharp contrast to other nations, which not only may not use their aircraft regularly save for training, but usually are concerned with much shorter distances and much lighter loads.
The C-141 fleet began becoming dangerously aged even before the Gulf War. Cracks had begun to proliferate in the wing roots of the jets; since replacing the mainspar of an airplane is nigh on impossible without completely rebuilding the entire airframe (and because that tends to be so expensive) the Air Force naturally went looking for a replacement. The C-17 design was the military answer. Of course, it wasn't the only answer! Let's compare it to its nearest civilian rival, made by the same company in fact.
The C-17's capacity is less than that of this civilian rival, the 747 Cargo, at a maximum payload of 170,900 lbs. for the Globemaster versus 244,500 lbs for the 747. The 747 flies faster (0.85 Mach vs. 0.74 Mach), and has a longer range (4,450 nm vs. 2,400 nm) as well. It cruises roughly 8,000 feet higher than the C-17. Furthermore, the 747 offered several unique advantages. For one, it 'came with' a global maintenance and support organization, including personnel familiar with it and parts & consumables available in nearly every country that supports commercial heavy aviation. For another, it represented a tried and true design, iterated many times (the current version is the 747-400, roughly the fourth major design change in the airframe's history). Why, then, would one ever choose an unbuilt, untested, expensive alternative? Good question. Let's see.
The C-17, as a purpose-built military transport, includes many options the 747 cannot match. For example, it is designed to operate in environments that its civilian cousin cannot; notably, short, rough airfields with significant debris present, on uncertain surfaces. The C-17 can (claims the Air Force) take off from a runway as short as 3,000 feet, and perhaps 90 feet in width. The 747 requires the 8,000 to 12,000-foot altars found in most modern commercial airports; more, these huge edifices must be in good condition. The C-17, in addition, can operate strictly from the strip; that is, it has thrust reversers and steering that allow it to be turned around on a 90-foot-wide strip using the good ol' (if you ever took a driving test) K-turn, or three-point turn, since it can back up.
Although relatively sturdy, the 747 is no different from other modern jets in its vulnerability to FOD and breakage, although not nearly as sensitive as some. Finally, and this is probably the difference hyped the most: the C-17 allows RO/RO operation. That is to say, it is a 'low deck' airplane, and with its built in ramps can load cargo (people, items, vehicles, etc.) straight off the ground. In order to load a 747 Cargo, you need a specialized device called a 'K-lift' which you have probably seen in airports. The K-lift is the 'scissors' lift which elevates a platform in order to match heights with a freight container (or loose load) and the cargo hatches, some ten to twenty feet from the ground (higher in the case of the upper holds).
The 747 does have its own bells and whistles; it operates with a two-person crew and has its own powered cargo management system. It has been iterated since the previous freighter version, the 747-200F, to provide more efficient operation and durability.
Moving on, however, the Air Force stuck to its guns on the notion of having an airplane which didn't require logistical support at the far end (cargo loading equipment) in order to be useful. Although this doesn't prevent the U.S. from purchasing *some* C-17s and some of the much cheaper 747-400Fs, a case can be made that not having to maintain two different support structures makes things easier. In addition, some analysts note that in the case of large-scale need, the U.S. Government already has access to a fleet of 747-400F freighters, through the implementation of the CRAF.
1: The 747 cost figure is derived (roughly) from a deal done between Boeing and ILFC, for delivery beginning in 2002, of 5 747-400 Long Range variants. This model is newer than the base 747-400 available when the C-17 procurement was being debated. Five aircraft, along with options on five more, was estimated at $1 billion. Subtracting a deposit on the options of five percent, along with fifteen percent (SWAG) for volume discount for a large government purchase of, say, fifty aircraft, leaves $800 million for five planes. Dividing, we get $160 million per aircraft. Note that even with none of these deductions, the $200 million per plane figure would be $36 million-plus cheaper per aircraft than the C-17.
So, on to some stats!
From its Air Force fact sheet:
- Primary Function: Cargo and troop transport
- Prime Contractor: Boeing Company
- Power Plant: Four Pratt & Whitney F117-PW-100 turbofan engines
- Thrust: 40,440 pounds, each engine
- Wingspan: 169 feet 10 inches (to winglet tips) (51.75 meters)
- Length: 174 feet (53 meters)
- Height: 55 feet 1 inch (16.79 meters)
- Cargo Compartment: length, 88 feet (26.82 meters); width, 18 feet (5.48 meters); height, 12 feet 4 inches (3.76 meters)
- Speed: 450 knots at 28,000 feet (8,534 meters) (Mach .74)
- Service Ceiling: 45,000 feet at cruising speed (13,716 meters)
- Range: Global with in-flight refueling
- Crew: Three (two pilots and one loadmaster)
- Maximum Peacetime Takeoff Weight: 585,000 pounds (265,352 kilograms)
- Load: 102 troops/paratroops; 36 litter and 54 ambulatory patients and attendants; 170,900 pounds (77,519 kilograms) of cargo (18 pallet positions)
- Unit Cost: $236.7 million (FY98 constant dollars)
- Date Deployed: June 1993
- Inventory: Active duty, 58; Air National Guard, 6; Air Force Reserve, 0