At their May 2025 meeting, members and guests of the Grampaw Pettibone Squadron were privileged to hear a presentation from Major Hammond (Hamm) McKie Salley (US Army Infantry, Ret.), about the design considerations for combat support airlift using the C-17 and the Advanced Theater Transport concept aircraft. Hamm noted that he was not an aviator. However, he did have a background in analysis and research and worked at McDonnell Douglas.
Hamm spoke about early requirements for design of a military transport aircraft, which led to the creation of a generic list of mission needs with design impacts. The following is a brief list of those early needs.
The first requirement was the cargo compartment size and cargo weight. This requirement would set the design parameters for the rest of the aircraft: Dimensions of the plane, gross take off weight, engine power, center of gravity, landing gear capability, etc.
The maximum payload of the C-17 is 172,000 pounds flying into a 3,000 foot strip. Maximum hinge payload is 130,000 pounds and will support an M1 Abrams tank. The maximum ramp payload is 40,000 pounds, equivalent to 4,463-Cargo Pallets.
To determine the cargo compartment design, it was necessary to create an equipment database that identified a world-wide military vehicles list. This database would include physical features, such as length, width, height and weight. Supporting modeling and layout simulations required icon figures be created representing each vehicle within the database list. A combination of mix and match vehicle and equipment could then be modeled by icon figure(avatar) and mission need.
Once the list of vehicles was identified, multiple layout models were created to determine the optimum mix of equipment loaded in the modeled aircraft simulations by military need. The loadmaster would have to be familiar with all possible combinations of vehicles and cargo to insure compatibility with loading and consistency with maximum load. The following groupings represent the modeling;
- Heavy Division – Tank Battalion, Mechanized Battalion, Engineering.
- Light Infantry Division – Air Defense, Field Artillery
- Typical Helicopter Loads
- Outsize Marine Corps Firepower
In addition to equipment load configuration, the combination of equipment and personnel loads were configured.
- Fighting Vehicle and Troops
- Tanks and Troops
- 155mm Howitzer and Troops
- 1-1 ¼ Ton Trucks, 5 Ton Van and Troops
- 1-1 ¼ Ton Trucks and Troops
Hamm summarized the development and use of the C-17. It can transport all Army / Marine Corps Combat Equipment bigger than 463-L Pallet (88 inches wide, 108 inches long, and 21⁄4 inches high) with a useful payload of 172,000 pounds. Oversize cargo will fit on the C-17 and the aircraft is capable of accessing; a semi-prepared surface, with combat offload function and able to backup with a 180-Deg turn on an 80 Ft. surface. The engine exhaust is directed up and away.
Hamm concluded his talk on the C-17 with focus on the future needs for replacement of the C-130 aircraft, also known as the Advance Theater Transport (ATT). The aircraft proposed was to be a SSTOL (Super Short Take-off and Landing) with Tilt-rotor capability. The aircraft features were presented to contain information and compare the ATT concept to existing aircraft. The comparison focused on combat delivery metrics, mobility capability, airlift capability in support of rapid decisive operations, load carrying comparison of existing aircraft and payload radius comparison. The proposed aircraft design was presented to different branches of the U.S. military. A final brief was rejected by the Air Force because it was not jet powered.
A-400M
The ATT was presented as a co-development with Airbus. Upon rejection by the U.S. military, Airbus continued the program independently. They developed an aircraft known as the A-400 and based design on many of the ATT capabilities. Total sales value of the 178 aircraft sold to nine countries is in excess of $22 billion.
Grampaw Pettibone thanks Hamm Salley for his informative presentation.
(L-R) GPS Ops O Cindy Macha, XO Vince van den Brink, CO Tim Brown, Speaker-Hammond Salley
Photo by Bruce Guberman
