Northrop’s TAB for All Seasons
By Tony Chong
Perhaps one of the most unusual designs proposed by the heritage Northrop Corporation was the Truck, Airplane, Boat (TAB) Vericraft triphibian, an ungainly looking vehicle that attempted to be the all-in-one answer to the U.S. Army’s looming tactical needs.
TAB was developed in the mid-1960s in an attempt to secure participation in an Advanced Research Projects Agency (ARPA) program called Project AGILE. One of the issues under investigation was the problem of mobility and logistical supply to remote bases and outposts in inaccessible environments. With the U.S. increasingly involved in the Vietnam conflict this was a major concern for military planners.
Northrop envisioned a rugged, easy to build, low-cost aircraft that had the ability to operate effectively not just in the air, but on the water and on land as well. While primarily designed for the short-range utility cargo mission, it was to be easily adaptable for use as a troop transport, weapons carrier, mobile command post or medical evacuation vehicle.
The proposed craft featured a rectangular box of a fuselage outfitted with a catamaran hull, retractable wheels and rotatable wings and tail. Twin Pratt & Whitney PT6-B15 turboprop engines, mounted in a single pod nacelle, provided power to a 7.5 foot shrouded propeller. Engineered with a constant-chord wing with a span of 60 feet, the TAB was to be 40 feet long, with a folded wing width of 9.5 feet and a height of 13.5 feet. The cargo compartment was to be 6 feet high, 6 feet wide and 15 feet long. Gross weight, complete with up to 4,000 lbs of cargo, was projected at 12,000 lbs.
Conversion to any operational mode was anticipated to take approximately 10 minutes. Additionally, all mode conversions could be done onboard the TAB during water operations. The vehicle was also scaled to fit into the cargo hold of a Lockheed C-130 Hercules transport for long, overseas deployments.
Northrop expended considerable time and effort in this design. A multi-volume proposal brochure was developed that included cost and operations comparisons to other proposed Army vehicles, including the fixed-wing de Havilland of Canada CV-2 (later C-7) Caribou and the rotary-wing Boeing-Vertol CH-47 Chinook and Bell UH-1 Iroquois (Huey).
Performance was projected to be modest. The 130 mph air speed would be slightly faster than the Huey but much slower than the Caribou or Chinook. Truck speed would top out at 50 mph. Ironically the boat mode would provide the best performance with calm water speeds up to 35 kts.
A detailed scale model was built toward this effort, along with a larger scale radio controlled model of the basic TAB design. Interestingly enough, no formal N-number was attached to the program. While a Preliminary Design (PD) number was likely given to the TAB, its identity has proved elusive thus far.
In any event, the program did not go forward. ARPA declined to offer funding, perhaps in part because the newly implemented 1966 agreement between the Army and U.S. Air Force mandated that the Army give up all fixed-wing tactical airlift capabilities in exchange for unrestricted development and acquisition of rotary-wing assets. TAB’s primary customer was now obliged to go with the UH-1 and CH-47. The end result was the coming of age of the helicopter-borne air-mobile Army during combat operations in the Vietnam War.
Kristi Harding contributed to this article.
For further reading on Project AGILE, go to: http://en.wikipedia.org/wiki/Project_AGILE
A look into the scope of Project AGILE can be found in this July to December 1963 semiannual report by ARPA, including Subproject III to which TAB was tailored: http://www.nal.usda.gov/speccoll/findaids/agentorange/text/00340.pdf
A review of the Army/Air Force 1966 agreement can be found here: http://en.wikipedia.org/wiki/Johnson-McConnell_agreement_of_1966