Aerial utility has traditionally concerned artistic options to deal with distinctive challenges. Whether the duty at hand is crop spraying, pest management, or hearth preventing, a large number of capabilities are required to do the job safely and effectively. Accordingly, the plane varieties utilized for these duties have advanced and tailored in another way from most different classes of aviation.
The “Twin Cat” of the late Seventies and early ’80s was one such instance. A growth of the Fifties-era, purpose-built Grumman Super Ag Cat biplane, it changed the Ag Cat’s single 600 hp Pratt & Whitney R-1340 radial engine with two 310 hp Lycoming TIO-540 flat-6 engines.
Rather than being provided as an entire, factory-built plane, the Twin Cat was a modification provided within the type of a supplemental sort certificates (STC). The Twin Cat Corporation focused Ag Cat operators wishing for extra simply serviceable engines with elevated overhaul intervals and multiengine redundancy, and the corporate provided to journey to the client for on-site modification of their Ag Cats.
The firm had some spectacular expertise on the helm. The president had overseen the event of a turboprop conversion of the Grumman Albatross and was assisted by the previous chief check pilot on the normal aviation division of Rockwell International. Most of the check flights had been flown by Herman “Fish” Salmon, retired chief engineering check pilot of Lockheed. Salmon had performed spin testing of the P-38 Lightning and had flown the primary flights of the L-188 Electra, P-3 Orion, YF-104A Starfighter, and XFV-1 turboprop VTOL fighter.
When designing the Twin Cat, one of many high priorities was to attenuate uneven thrust within the occasion of an engine failure. The crew did so by using an unconventional engine format wherein the engines had been mounted on both aspect of the nostril with solely roughly 3.5 toes between the propeller ideas. The engines had been additionally canted barely outward to additional reduce the consequences of uneven thrust throughout single-engine operations.
The firm touted advantages past the engines’ 2,000-hour TBO and higher elements availability. While the engines had been rated at 310 hp every, a gross sales supervisor mentioned in an business presentation that they derated them “with a pencil” and that the complete 350 hp was available if wanted. The Twin Cat’s whole gasoline consumption was the identical as that of the single-engine radial Ag Cat. They additionally claimed the brand new format improved ahead visibility, prop clearance, and spray dispersion.
When the time got here for flight testing, the crew acquired to see whether or not the brand new design might ship the efficiency that backed up predictions. While the Twin Cat’s empty weight was the identical because the Ag Cat’s, at 3,500 kilos, the utmost takeoff weight was 2,000 kilos greater, at 6,500 kilos. A load jettison operate enabled the pilot to dump 2,000 kilos of payload if wanted.
The new engine format labored. With each engines working, the Twin Cat’s takeoff distances had been roughly 20 % shorter than the Ag Cat. Asymmetric thrust was so successfully minimized {that a} gross sales supervisor claimed the Twin Cat might even take off with one engine shut down after which climb at 400 toes per minute at sea degree. The firm marketed this function as a helpful answer to ferry an plane with an inoperative engine to a location the place upkeep may very well be carried out.
In the air, the utmost cruising velocity was 130 knots. By canting the engines barely downward, the stall velocity was remarkably low, at a claimed 49 knots for power-off stalls and 43 knots for power-on. A brochure claimed that the Twin Cat had “no VMC,” which might have enabled flight all the way in which right down to stall velocity with out controllability considerations.
One account of the airplane’s flight traits means that it wanted extra refinement, nonetheless. It reportedly lacked any type of rudder trim, and with an engine shut down, a pilot claimed he ran out of rudder and needed to cut back energy on the great engine to take care of management. It’s unclear whether or not the corporate deliberate to introduce rudder trim in future plane.
In the top, solely three examples of the Twin Cat had been rumored to have been accomplished and flown, and few images exist. One reportedly crashed, and the others presumably returned to their unique single-engine configuration when the corporate determined towards pursuing the idea any additional.
