The Wrights knew it. So does every aeronautical engineer, aircraft manufacturer and pilot. More than anything else, the engine defines the performance of the airplane.
Calvin Burgess, a successful real estate developer and owner and president of Spirit Wing Aviation in Guthrie, Okla., told AIN in November 1999, “I always wanted a Learjet, but the [General Electric] CJ610 in the 20 series is an antiquated engine.” A 4,300-hour, commercial-rated pilot then, he already owned a Piper Cheyenne IIA, a P-51 Mustang, a Douglas A-26 Invader and a Waco YMF5. “When I found out about the Williams FJ44-2C engine just before the 1999 NBAA Convention in Atlanta, I became seriously interested in retrofitting the new turbofan on a Learjet,” he said.
On January 9 this year, Burgess saw his dream literally take flight. At 10 a.m., test pilots Ed “Moose” Skowron and Paul O’Donnel (employees of Flight Test Associates, Tucson, Ariz., contracted to Spirit Wing) took off from Guthrie Municipal Airport in the first FJ44-powered Learjet 25D modified by Spirit Wing. That one-hour flight was quickly followed by a 1.4-hour flight after lunch, and two more flights the following day with flight-test engineer George Hillman also on board, for a total of 6.4 hours. Landings were made at Guthrie, Wiley Post and Burns Flat Airports.
Airwork in the production-conforming Spirit Wing Learjet 25D included multiple in-flight engine shutdowns and relights, single-engine flight, stall tests and system checkouts. Initial flight-test limits of 31,000 feet and Mach 0.74 were attained. Describing the Spirit Wing airplane (N17AH), Skowron, a former Bombardier test pilot with some 25,000 hours in Learjets, said, “At takeoff, the acceleration and climb felt just like the original Lear. It flew with the snappiness of the 20 series on less fuel than a 30 series.”
The flights were a long time coming.
In late 1999, before Burgess had purchased his first pre-owned Learjet (he now has five) or even received engineering mockup engines from Williams International, he estimated that first flight of a Spirit Wing FJ44-powered Learjet would take place in November 2000 and that an STC for the modification would be received by the first quarter of 2001. That obviously did not happen. Numerous engineering difficulties– the design of the nacelles being a major one–manifested themselves over the last two years. The point was to do it right. In December, when first flight was imminent, Spirit Wing director of operations Mike Pinwell told AIN, “We’re very, very close, but not rushing. Time does not supersede safety.”
But now the hard research, engineering and design work is behind them and Burgess last month said he expects flight testing for certification, estimated to need about 250 hours, will go smoothly. “The FAA has been great,” he said, estimating Spirit Wing would receive the STC in the third quarter of this year.
So confident is Burgess in the demand for the retrofit that he has already ordered 24 more FJ44s from Williams. The first two will be delivered in the summer, for the second airplane. Work on this airplane will help determine how long it takes to do the retrofit, which Burgess estimates at about 90 days, and the price. He has funded the entire project himself (“for a whale of a lot of money”) and has yet to accept deposits, although he said he has “lists of interested people.” He hopes to keep the cost of the modification, which includes two new FJ44-2C engines and several other changes, to $1.7 million.
Spirit Wing is also working on an RVSM package for the early Learjets that would cost about $100,000. If a customer takes both the engine retrofit and RVSM package, Burgess said he plans to give $25,000 back on the cost of the FJ44s. “With the price of a used Lear 25D now between $350,000 and $900,000 and our mods,” Burgesss claimed, “you could end up with an RVSM-qualified Learjet with new Williams engines for $2.1 million.”
Now a 5,200-hour pilot, Burgess plans to keep N17AH, which was grounded after its two days of flight for installation of flight-data-gathering equipment and computers. The airplane is expected to be back in the air early next month to begin its certification work. Flight testing by Flight Test Associates, is expected to take five to six months.
Aircraft Design Services of San Antonio did the engineering and design work, except for the nacelles, which were done by Nordam Nacelles/ThrustReverser Systems Division in Tulsa, Okla. In addition to new Williams engines, modifications to the airplane include airframe drag reductions and upgrades of the nacelles, pylons, hydraulic pumps, fuel system, generators, environmental controls and engine gauges. The FJ44-2C incorporates a fuel controller, modified specifically for the Spirit Wing retrofit.
The primary benefits of the Spirit Wing modification, Burgess told AIN, are Stage 3 noise compliance, an average fuel burn (800 pph total) roughly half that of the original engines, much lower operating costs and the in-the-works RVSM package. The 25D’s center tank had to be removed (decreasing fuel load by 1,300 pounds) to comply with new FAR Part 25 engine rotor-burst requirements, but with the reduced burn, NBAA IFR range with four passengers actually increases to 1,700 nm compared with the original 1,014 nm. Mtow will probably end up close to the same as the original, but other performance numbers vary, due in part to the differences in performance characteristics of turbofan (FJ44) and turbojet (CJ610) engines.
Takeoff thrust of the FJ44-2Cs, at 2,400 pounds, is actually about 450 pounds less than that of the airplane’s original GE CJ610-8As. Burgess explained that several design changes make up this difference by reducing thrust required. For takeoff, 260 pounds of thrust are gained because the CJ610s are rated at standard temperature (59 degrees F), while the FJ44s are rated at 72 degrees F. More thrust is accounted for because the older engines were mounted with a slight upward cant (more drag, equivalent to 56 pounds of thrust), the FJ44s operate with bleed air on all the time (40 pounds) and finally, at 100 knots the turbofan FJ44s do not lose as much thrust as the turbojet CJ610s due to ram air, the equivalent of 100 pounds of thrust.
According to Burgess, at 72 degrees F and 100 knots the FJ44-2C and the CJ610-8A produce nearly equivalent available thrust, when these adjustments for the installation are figured in. In cruise, drag equivalent to 150 pounds of thrust was removed by mounting the FJ44s farther out (four inches), up (eight inches) and back (16 inches).