Dominant Logistics
Helicopter Self - Deployment System
A lot of folks are buying into the notion that we can have our cake and eat it too; that we can have the vertical lift capabilities of a helicopter in an aircraft with the forwards speeds and range of a conventional aircraft. While it is true that this level of functionality is theoretically possible, it is not as easy as many make it out to be. Existing hybrid designs also bring numerous problems to the table that aren't present in conventional aircraft.
Tiltrotor Aircraft
Unfortunately, the posterchild of tiltrotor aircraft today is the V-22 Osprey, arguably the worst possible iteration of the concept that could be put together. The laundry list of the V-22s problems weighs more than its payload so I'm going to focus on the specific changes in design that will make this concept work in the future.
First there is the location of the engines. These were presumably moved out to the wingtips initially to reduce some complexities associated with the engines being located in the fuselage on this type of aircraft. But the need to use cross shafts to account for battle damage eliminated any gain achieved with outboard engines. This design makes the aircraft very unstable and needs to be eliminated. Moving the engines back to the fuselage will result in lower overall weight, better stability in flight, hover, and on land, and it will also dramatically reduce the hydraulic problems associated with the Osprey.
The next issue to address is the rotor/downwash problem. Many have complained of the tremendous downwash produced by the V-22s rotors and how this makes many operations unfeasible. Most attribute this problem to the fact that the V-22s rotors are not conventional rotors, but proprotors. This is somewhat correct but the bigger issue most folks seem to ignore is the interference between the wing and the rotors when tilted. The Osprey loses a substantial portion of its vertical thrust to interference from the wing. A European design is already underway that uses a split tilt wing instead of simply tilting the rotors or engines. This eliminates the interference and allows for a smaller rotor. With this design, the aircraft can take-off and land vertically, but it can also take-off and land as a conventional aircraft with only seven degrees of tilt.
The third problem that must be addressed is the extremely poor design of the cabin. If we are wanting this aircraft to replace the CH-47 family of aircraft, then it must match up to the CH-47 in every internal dimension! Payload weight is a meaningless term - cargo has dimensions and in cargo aircraft, dimension limitations tend to come into play much before payload limitations. If you can't carry it internally, there is no point in using a tiltrotor because external carriage gives up all the speed and range benefits that the tiltrotor has.
The final major issue is the ring vortex problem. Simply put, it is highly unlikely that this problem will ever be effectively overcome and design modifications that SHOULD be made will make the problem worse. Because of this, we need to view tiltrotors as transport aircraft and not as vertical assault aircraft. Does this limit the versatility of the aircraft? Not really - it only changes the way we should be using the aircraft. The C-130 can't be used as a vertical assault aircraft either but that certainly hasn't hurt it's career. It can still be an excellent addition to the force as a VTOL aircraft that can operate from a wide variety of ships and locations that ordinary aircraft cannot.
Compound Helicopters
An alternative to the V-22 that many are backing is the use of compound helicopters. This approach takes a traditional helicopter and includes a horizontal propulsion system and wings that unload the rotor, allowing for greater speed and range. But this concept also brings some serious baggage to the table.
Helicopters are incredibly complex machines already and adding an additional propulsion system will only make them more complex. While the propulsion system enhances high speed performance and maneuverability, the wings degrade low speed and hovering performance just as the V-22s wings do - through interference with the airflow from the rotors. Plus the additional propulsion system and wings add weight that reduces our total payload and range.
Another problem with compound helicopters is that the forces induced by the enhanced forward propulsion can lead to serious problems with the rotors themselves. Modern computer designs and enhanced materials can mitigate these problems to a degree but they cannot completely eliminate them. So we get higher performance in the high speed realm but lower performance in the traditional helicopter roles combined with what will likely be higher maintenance and operating costs.
As with the tiltrotor concept, this doesn't mean that we shouldn't have the capabilities of compound helicopters - only that we need to view the concept in a realistic way. We cannot afford to convert the entire helicopter fleet to compound designs but there should be a place for compound helicopters within the force. We cannot ignore the speed and range benefits that the compound option provides.
A Convertible Helicopter
So what if we modified existing helicopters in such a way as to make the compound capability an optional feature altogether? By this I mean having the propulsion and wing assemblies be removable - we can put them on for the applications where we need it and remove them for when a conventional helicopter is a better option. I see two potential methods for doing this, both of which should be perfectly viable options.
The first option is to use a pair of custom-designed wings that would attach to the helo at mounts on the sides that are otherwise used for weapons or fuel tanks. The wings would include fuel storage within the wing and would also include a custom-designed pusher engine to give the helicopter additional forward thrust. The wing and engine combination would be tailored to function at a particular cruise speed to optimize the lift and range capabilities of the platform for long-range travel. The wings would be easily removable and maintenance could be handled by a higher echelon - you simply use the wing assembly for a given period and swap them out.
Another option would be to keep the removable wing but without the pusher engines and instead to have a removable tail with an available assembly that would be a Piasecki-designed Vectored Thrust Ducted Propeller assembly. Conventional helicopters already include a driveshaft assembly to the tail to power the tailrotor - we would simply use a coupling so the shaft could power a tailrotor or a VTDP assembly. This approach frees up the underwing area for mounting weapons, cameras, fuel tanks, etc. This version probably offers greater flexibility but it also will be a far more involved process to maintain and perform the conversion between conventional and compound.
In either design, the helo could be modified to self-deploy to a given theater of combat. I call this the Helicopter Self Deployment System. Incorporating the compound design, we then use a fuel bladder in its cargo area and a flight control computer would be added with pre-programmed flight paths to get the helo to a given location automatically. This location may be a specific forward base or to a refueling point midway such as an island or a flattop ship in the ocean. Given the fact that we already have demonstrated automatic flight at long ranges (CALCM cruise missiles) as well as automated landing of helos on ships, the technology behind this should be a non-issue.
Using this system, ranges on the order of 2000 miles+ should be achievable for most helo systems currently in use. The CH-53E would probably be able to achieve around 3500 miles with this system. The systems would be removable once in theater allowing the options of a long-range vertical take-off and landing platform or a traditional helicopter.
References
http://www.oocities.org/equipmentshop/nextchinook.htm