Sunday, July 1, 2007
The Sierra Stallion
It’s not your father’s Citation!
How do older airplanes keep up with the new hotrods? It’s a simple formula: Anytime there’s a significant base of aircraft, there are people who will make improvements to the basic design. Mark Huffstutler is an example of this rule.
In 1980, Mark opened an FBO and, thus, embarked on a career in the aviation business. Soon afterward, he acquired Sierra Industries and bought the Robertson STOL operation. With Robertson and a few other acquisitions came several STC’d Citation modifications, chief among them the Eagle wing fuel modification. He didn’t stop there. “Today we hold over 80 STC modifications for Citation aircraft alone, from locks to motors,” he says. “More than one third of the Citation fleet has a Sierra modification. We have 90 Eagle modifications flying and have done over 120 long-wing aircraft.”
Not satisfied with wider passenger doors, camera and baggage doors or radome covers, Mark wanted to find a permanent solution to the underpowered, expensive-to-operate Pratt & Whitney engines. “We started working with Williams in the mid-’90s,” he explains. “First we looked at re-engining Learjets, but abandoned that project due to thrust issues. When Williams introduced the FJ44-2 motor in 1999, we really began working on the Citation application, achieving approval in March 2002. Combined, the wing and the engine modification result in a range increase of 65% to 1,650 nm, a speed increase of 50 knots and reduced time to climb to FL430, beating the older airplanes’ climb performance by almost an hour. A fantastic improvement.”
The true test of payload, range and climb capability is performance at high-density altitudes. In the United States bizjet world, the benchmark is the Aspen Two departure from Sardy Field Aspen, Colo. A climb rate of 950 feet per mile is required for just over four miles—few business jets can achieve these results. According to Mark, “We can do Aspen. Every other jet in this weight class must off-load people or fuel, or wait for cooler temperatures to meet the climb requirement out of Aspen. We can take off in the middle of summer at gross weight and climb straight to cruise altitude. There’s no combination of weight, temperature or field elevation at which we cannot do that.”
The Williams engine used by Sierra is smaller and lighter and produces significantly more thrust than the Pratt & Whitney JT15D it replaces. Climb rates are up across the board; twin-engine climb by 73% and, most importantly, the single-engine climb at gross weight is improved by 69%. Power in reserve contributes to safe operations at any airfield. The FJ44-2 generates 32% more thrust, and fuel consumption is reduced 25% from the legacy engines. All in all, the Williams is an ideal match for the venerable Citation airframe.
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