The aircraft would replace the 450-aircraft C-130 fleet, but the USAF may buy no more than 250. Even after at least five years of discussion, the USAF still does not know whether it wants a fixed-wing, tiltrotor, rotorcraft or airship. . . . the next C-130 may have to carry up to 190% more payload and assume a new mission — mounted vertical maneuver. Taking on the MVM mission means dropping off medium-weight armored vehicles — think Bradleys, not Abrams — in places the enemy does not expect. Long, concrete runways? Not any more. Fifteen hundred feet of level, hard-packed surface? That might work. Perhaps better: a clearing big enough to land a really big tiltrotor or helicopter.
It's asked the defense industry for input.
One fo the main reasons that the Air Force is so unclear about what a short range cargo aircraft should do, is that it isn't the real customer. Logistics is something that the Air Force does as a service to the Army (and to a lesser extent that Marines). But, they and not the Army, get to decide what the Army should receive to meet its needs.
Here, as in the area of close air support, the Air Force simply doesn't have the bureacratic incentives to do the job optimally for the people who will need that job done well.
How Big Does It Need To Be? Should The Cargo Designers Have A Say?
The truth of the matter is that airlift is not a decision that should be made in a vacuum. The capacity of the C-130 and its big sister aircraft, the C-17 and C-5, are major design criterion for everything that they carry. If something can't be transported by air, it won't be available for soldiers until several weeks after it begins. There may be some need for larger aircraft, and some need for smaller vehicles and systems for it to transport.
The Stryker, a lightweight version of the U.S. multiple rocket launcher system, and a variety of other recent major Army projects have been driven by what the C-130 can carry, a decision that has left some in the Army concerned that underweight vehicles and weapons are being fielded simply because the C-130 is too small, the C-17 is too scarce, and the C-5 can't land in anyplace more primative than a half decent airport. Logistics considerations have also been a major design factor in the Marine Expeditionary Fighting Vehicle.
The Army's main battle tanks (at 70 tons each) and Bradley Infantry Fighting Vehicles (at 35 tons each) are to big to transport by C-130 (which can carry 20 tons), and that has limited their usefulness. The C-17 can carry one tank, or two Bradleys. In the past, the Army has usually preferred to Bradleys to one tank when push comes to shove and the choice must be made.
One option for a C-130 replacement would be to make a next generation C-130 that could carry 35-40 tons, while being smaller and less expensive and more numerous than the C-17, and to keep new military vehicles under those size constraints.
The Trouble With Airships, Helicopters and Jets
Airships (e.g. lighter than air aircraft such as blimps) have a potential place in the logistics system. They can cross any terrain on land or sea without having to transfer cargo, don't depend on existing infrastructure, can land vertically, and have a speed and fuel efficiency similar to a truck. But, they aren't appropriate for situations where there is hostile fire is possible, or where speed and surprise are necessary, so they are more of a substitute for rail, transport truck convoys, and ships, than for the C-130 or other traditional airlift options. They can carry large loads relative to those of fixed wing aircraft. Concept airships have been designed to carry loads of up to 160 tons (compared to about 122 tons for a C-5 Galaxy transport aircraft, the largest in the U.S. military fleet). Major military contractors have developed drone airships as military concept systems as recently as 2006 with a one ton payload for intelligence applications. "In 2010, the U.S. Army awarded a $517 million (£350.6 million) contract to Northrop Grumman, to develop Long Endurance Multi-Intelligence Vehicle (LEMV) systems." DARPA considered projects up to 450 tons of payload capacity and a 12,000 mile range in its WALRUS program discontinued in 2006. Top speed for an airship, due to drag considerations, is 80-100 miles per hour. The top alititude for an airship is 3,000-8,000 feet. For comparison purposes, research into high speed military sealift ships has focused on payloads of 500 to 5,000 tons.
Helicopters are slower than fixed wing aircraft, harder to maintain in the field, and use more fuel. The Air Force is also loathe to consider big transport helicopters because helicopters are generally under the jurisdiction of the Army. The C-47 Chinook, the largest Army transport helicopter, can carry a load of about 12 tons, a load similar to that of the C-27J, a fixed wing cargo aircraft that is bascially a "mini-C-130" that has recently entered military service. The Sikorsky CH-53E Super Stallion used by the U.S. Marine Corps can carry up to a 16 ton external load.
The Soviet Union created four different models of very large transport helicopters that could carry from 11 to 40 tons during the Cold War, but the only one to carry more than a 20 ton load "was considered a failure by its manufacturer and Soviet authorities. The V-12 was simply too big and difficult to maneuver to be a practical machine." It was cancelled after two prototypes. The 20 ton payload capacity Russian Mil Mi-26 is the largest transport helicopter in service today.
Conventional wisdom is that helicopters don't scale well and aren't good heavy transport vehicles.
Fuel efficiency and low speed manuverability has also been one of the main attactions associated with the C-130's propeller, rather than jet engine design.
The Trouble With Tiltrotors
The military's MV-22 Osprey tiltrotor aircraft has a 5 ton payload capacity (it can't even carry a Humvee), which is small relative to other air transports, was extremely expensive to develop, and has still had maintainance issues in the field. It isn't at obvious that there is a huge gap in military need that needs to be filled by a tiltrotor aircraft between proven designs for short takeoff and landing fixed wing aircraft, and helicopters, with comparable payloads. It is an expensive and fussy alternative to buy in large numbers to fill a gap if there is one.
The C-130 is also already very large for an aircraft that might deploy from ships at sea (aircraft carrier landings with C-130s have been done once or twice on an experimental basis to test the concept), even ships as big as American supercarriers. Yet, one of the main motivations for the tiltrotor capability of the MV-22 was the ability to deploy from ships, which required greater vertical landing capabilities.
Possibilities: Seaplanes, Drones, And Short Drops
A seaplane version of a C-130 successor could be easily developed (there used to be a similar seaplane in service in the Air Force) could serve a similar need for deployment from the sea. A C-130 successor seaplane could also land any place with a decent lake or coast, without having to have any runway preparation. This wouldn't be as much of a technological breakthough as a vertical landing tilt-rotor plane, but would still open up many landing options that are not available in the status quo.
One approach to the "Mounted Vertical Manuever" goal would be to have an aircraft outfitted for very low altitude, low speed airdrops, essentially dangling its cargo just above the ground, at a low speed, and dropping it tens of feet instead of tens of thousands of feet in an airdrop to a destination. While a hover would be nice for this kind of manuver, a plane that could briefly slow itself to 80-90 miles per hour at a low altitude over a field or highway for a cargo drop might be able to meet this objective, and a somewhat higher speed might be workable with "batman-like" rear parachutes to slow down the dropped cargo as it falls a short distance to the ground. There have been efforts to design high lift, low speed drone aircraft, for example the "FanWing" with a circular fan that runs the length of the aircraft.
Another question is whether there is room for an unmanned cargo aircraft in the U.S. fleet. When the cargo isn't soldiers, the need for a perfect safety and reliability record isn't as great, and it costs a great deal to extract the last little bit of reliability out of an aircraft. Unmanned aircraft can carry a greater percentage of their weight in cargo with the same performance. They can be sent to places where the fear of being shot down would be too great for manned aircraft. Drone technology is already in place to deal with many of the key technology barriers to this kind of project. A drone cargo aircraft probably wouldn't make sense as a reaplcement for the entire C-130 fleet, but it could take on many of its jobs.