Airdrop Systems

"Aerial delivery" is a military phrase that refers to products used to airdrop personnel, ammunition, vehicles, or supplies to military forces or humanitarian recipients on the ground. In major engagements and in large relief efforts, DOD can consume hundreds if not thousands of these highly engineered units. The industry consists largely of parachute manufacturers and suppliers of components used in various air delivery systems. Cargo and personnel parachutes are the main products of the aerial delivery industry, but manufacturers also produce special skids, pallets, and shock absorbing systems for delivering products to the ground intact.

The types of airdrops are free fall, aerial supply, heavy drop, and extreme low level delivery. a. A free fall airdrop is any subsystem that does not require or use a descent-control device or retardation technique to reduce the effect of gravity on the rate of descent. An aerial supply airdrop is any subsystem that utilizes a descent-control device or retardation technique but does not utilize a platform for mounting the load. A heavy drop airdrop is any subsystem that uses both a descent-control device or retardation technique and a platform for mounting the load. Normally, the term "heavy drop" is associated with heavy equipment such as wheel or track vehicles. An extreme low level delivery airdrop is any subsystem that does not use a descent control device but does utilize a retardation technique to arrest the load velocities in the horizontal plane with respect to the ground.

The aircraft that are presently used for airdrop have a large opening at the aft end of the fuselage through which the loads leave the aircraft. The standard airdrop aircraft are the C-130, the C-141, C-17 and C-5 cargo aircraft. A force is required to extract or eject a load from these airdrop aircraft. This force is supplied by ejection or extraction devices.The aircraft cargo is restrained from extraction by latches and lock settings of the cargo rail system which provides 1/2 G of aft restraint at a given gross weight of the platform. This extraction restraint is overcome by the aft directed force of the extraction parachute and an airdrop occurs. The platform detents disengage at the time of restraint release. A lockout pin keeps the detents fully retracted and locked out of position.

The design of an airdrop system is based on getting the cargo to the ground, in the least possible time without damage to the aircraft or the cargo, by applying the most economical and practical methods. The least possible drop time is desirable for maximum drop accuracy, the minimum dispersion of the drop loads, and the minimum effect of the wind drift. Theoretically, the ideal airdrop system would let the equipment free fall, without employing any type of deceleration device, but would absorb the landing shock to prevent damage to the cargo. Practically, the use of the ideal airdrop system, particularly for bulky or heavy objects, is prohibited by the size, the weight, and the cost of the shock-absorbing devices that would be required.

The shock-absorbing devices on the platforms and the containers, in conjunction with the parachutes, have great advantages. The stabilizing effect of the canopy permits the cargo to absorb impact shock in essentially only one direction. Airdrop systems are designed, in general, to achieve the best possible compromise between a system for landing-impact absorption and a rate of descent low enough to hold the design of the shock-absorbing devices to reasonable size, weight, and cost and in proportion to the fragility of a specific item.

Operation Provide Promise was the largest humanitarian airdrop operation in the history of the United States. Relief supplies to the former Republic of Yugoslavia (Bosnia-Herzegovina) started in February 1993 and officially ended near the close of 1995. More than 30,000 bundles of humanitarian aid were airdropped in support of this operation. These bundles included food, medical supplies and winterization items (such as blankets, clothes, plastic sheeting, nails, candles and tape). Because of the drop zones' dangerous locations, none of the airdrop equipment was recovered during Operation Provide Promise. This resulted in $30 million worth of air items depleted from US war reserves. Operation Provide Promise identified the need for more accurate, less labor-intensive and less costly aerial delivery equipment. The need for better delivery equipment opened the door for new technologies in the mid-1990s, taking into account three main concepts: the Low Cost Aerial Delivery System (LCADS), the Enhanced Container Delivery System (ECDS), and the Humanitarian Airdrop Container System (HACS).

Since their first major deployment in 1942, parachutes have been an important tool in the arsenal of the United States' armed forces, enabling the delivery of troops and equipment to inaccessible locations with speed and often with surprise. Following the initial use of parachutes in World War II for large-scale troop deployments, the technology evolved rapidly to support a broad range of "aerial delivery systems" for cargo and other payloads. The technological and manufacturing base of the air delivery systems used by the armed forces is now many decades old and is well established. The US military relies on these systems not only in times of conflict, but also for assisting in humanitarian relief operations around the globe.

Accuracy is the capability of an airdrop system to deposit the load at a predetermined spot on the ground in the drop zone from an aircraft over the drop zone. Accuracy does not include the problems associated with getting to a particular drop zone or identifying a drop zone as the correct drop zone. The most important element that detracts from accuracy is the effect of wind drift during descent. A computed air release point (CARP) method is utilized in determining the point at which the airdrop loads should be released in order to impact on the desired area. Wind velocity and direction at the drop zone are determined, relayed to the delivery aircraft, and used to compute the proper release point. A shortcoming of this method is that it does not consider wind velocity and direction changes with altitude. This shortcoming can seriously affect the accuracy of high altitude drops because of the possibility of changing wind conditions.

One way to overcome the resultant inaccuracies from wind conditions is to increase the rates of descent for the supplies and the equipment being dropped. This increased rate of descent tends to reduce the effect of various wind conditions that can exist in a particular area. This theory should hold true, and the same degree of accuracy should exist, at any given altitude provided the pilot has the proper sighting instruments for determining his release point. The increased rate of descent requires more stringent energy absorption at impact. Recently, newer methods are being developed to allow real-time measurement of winds at different altitudes along the trajectory to allow a more accurate CARP calculation.

Accuracy is not dependent on rate of descent alone. The means of extracting or ejecting aerial supply equipment or bundles from the aircraft must be positive so that a firm basis from which to compute exit time will be established. The deployment time of the retarding device must be constant. Finally, before the entire system can be effectively utilized, an accurate aerial supply drop sight must be provided for the pilot.

Today, airdrop is an operational task of AMC's airlift mission area, applicable to the force enhancement role projecting power by transporting people and material to potential airdrop locations throughout the world. Yet, enhancements to airdrop technology and techniques are essentially unchanged from those of 40 years ago, despite dramatic advances in sensors, computing technology, and guidance, navigation, and control (GN&C). The delivery accuracy of precision guided munitions (PGM) permits us to drop a bomb down an airshaft to destroy an underground bunker, yet it remains difficult to airdrop cargo repeatably within 1,000 feet.

Since precision airdrop was identified as a key technology opportunity in the SAB Global Reach Global Power report in 1992, a better picture of the application of technology to enhance airdrop operations has emerged. This research highlights the importance of airdrop as an integral and important airlift capability. The 1992 SAB study set the goal of achieving today's precision from much higher release altitudes. That is, precision airdrop from 25,000 to 40,000 feet will be as accurate as current airdrop from 300 to 1,200 feet, about 100 feet. If this goal is maintained, accuracy at any given altitude will need to be improved by as much as an order of magnitude.

One principal mission of airlift aircraft is to deploy, resupply, and redeploy combat forces and material during wartime and contingencies. In addition, airlift aircraft are called upon to support humanitarian efforts during emergency situations. Based on the threat, available airfields, and delivery area/target requirements, airdrop (from any altitude) may be the only delivery means available. These missions must be conducted in weather ranging from day visual flight to night weather conditions. As a supporting force under many operations plans, transport aircraft commanders must be capable of quickly deploying and conducting airlift and airdrop operations anywhere in the world. Current and future airlift aircraft will play an ever-increasing role across the spectrum of conflict.

Airlift aircraft are constrained in the airdrop process by the demands of reasonably accurate positioning relative to the drop zone. Once the parachute is deployed, the person or cargo is subjected to deviation from the target by several factors which add up to an "error budget."

The application of precision airdrop technology means much more than devising one or two new devices. The most effective airdrop system will include a family of delivery solutions, all integrated with a core support system on board the aircraft. Broadly, the precision airdrop system can be divided into two components: aircraft equipment and the aerial delivery system (ADS). Examples of aircraft equipment include navigation and targeting systems, sensors, computers, and cargo compartment mechanisms. The ADS is that part of the precision airdrop system that comprises the payload, the extraction system, and the recovery system that safely carries the payload to the ground impact point. The ADS may be guided or unguided.

Improved airdrop capabilities, for all altitudes, in all weather, will provide aerial delivery alternatives that enhance mission flexibility, increase safe areas of operation, and complement the rapid forced entry tactics required to counter anticipated threat environments. Precision delivery will reduce drop zone size requirements and assembly times, thereby decreasing ground forces' exposure time to hostile fire and detection. Individual units, and the supplies and specific items of equipment associated with them, can be delivered to preplanned locations within the drop zone, effectively multiplying the number of drop zones available.

The equipment to be sustained, the theaters of operation, and the time periods for which the force will be sustained are identified in the Defense Planning Guidance (DPG). The HQDA Guidance Letter defines the location and duration of each MCO, contingency, or other operation and the force structure to be used to build equipment density. Consistent with current aerial delivery doctrine (capability of forced-entry of brigade-sized forces and increased cargo airdrop demand (Army Transformation studies)) and based on input from SMEs, a draft aerial delivery equipment (ADE) enclosure to the Guidance Letter was developed and submitted to HQAMC in late March 2004. Based on planning factors in this Enclosure, personnel parachute requirements should drop by about 70%. This requirement was based on satisfying current mobility requirements for brigade-sized airdrops on the order of a few thousand troops. The 1999 ADE cargo air delivery requirement, in terms of short tons per day, was retained. This planning factor (short tons/day) contains the most uncertainty. However, based upon discussions with SMEs, the mix of cargo delivery methods was markedly reversed to reflect more of a reliance on Containerized Delivery System (CDS) (a fraction being the Low Cost Airdrop System). Because these requirements were last calculated in 1999, it is important that these requirements be updated to reflect the proper amount and mix of ADE.