Issue 13: Gulfstream III

One of the most impressive assets the Gill boasts is its range and the ability to operate consistently at high altitudes, an essential requirement in the photo recce role. In a typical mission profile, a Gill recently flew non-stop from Hawaii to Washington DC in a 14-passenger configuration and landed with more than 2200 pounds of fuel remaining. Other notable non-stop flights have been between Savannah, Georgia and Hanover, West Germany and, Geneva to Washington DC. This translates to a range of 4155nm at an economical cruise speed of Mach 0. 775 or a shade under 500 mph including full IFR reserves. In the altitude spectrum, the Gill regularly operates around the mid-forties ascending as fuel is burned off to a maximum operational altitude approaching 50,000 ft. Test aircraft have actually been taken to 52,000 ft, which is an altitude many fighter aircraft have trouble reaching. One of the major secrets to attaining this level of performance is the choice of Rolls Royce Spey turbofans. The Spey is not a young engine, though it does benefit by maturity (some 20,000,000 flight hours, actually)! The constant thrust of a low by-pass turbofan at high altitude is what is required to actually maintain performance at altitude. Gulfstream thoroughly investigated the newer advanced technology high by-pass turbofans available, but none had sufficient power to sustain operations above the 45,000 ft ceiling. Canadair, having to cease development of their “E” model, extended-fuselage Challenger powered by just such an engine is a classic example of the fact that pure thrust is required to satisfy performance demands at high altitudes and airspeeds.

The Spey Mk511-8 (RB163-25) provides 11,400 lb thrust and, above 40,000 ft, provides SFC figures comparable to any new engine. Much of the performance gain for the Gill comes from the new wing and the addition of drag-reducing winglets. In fact, these three specific design factors (modified Spey, new wing, winglets) provide an increase in fuel efficiency in the order of 13 per cent over the Gulfstream II.

An example of the longevity of the structure of this aircraft is that NASA uses the Gil to train astronauts in extreme manoeuvres requiring controlling the aircraft while simulating weightlessness for minutes at a time. In this role, the crews of Columbia have been trained for the past three years aboard their Gulfstreams performing a descent profile that has the aircraft dropping 16,000 ft per minute, around six times that of a regular commercial airliner descent! To maintain control, the crew use 90 per cent power in reverse thrust with the main gear down and is aided by a special underbelly air brake. The aircraft also routinely undergo 50-degree bank turns pulling in excess of 2G and yet operate over 500 hours a year in this exceptionally demanding environment.

More than 140 Gulfstream Ills are on order or option and the current monthly production rate stands at three aircraft, this rising to five per month in 1983. Testimony, in fact, to the design excellence of Gulfstream’s newest offering