The launch of the PW500 series completes a turbofan product range for Pratt & Whitney Canada.
Graham Warwick/MONTREAL
In a single month in 1994, Cessna launched two business jets and gave Pratt & Whitney Canada the first two applications for its new PW500 small turbofan. The Citation Bravo and Excel are, respectively, powered by the 11.6kN (2,600lb)-thrust PW530A and 17.2kN PW545A, all-new engines which share a common core.
The 13-20kN PW500 family bridges the gap between P&WC's 10-15kN JT15D and the 22-31kN PW300, explains Anthony Cristofaro, marketing manager, corporate aircraft, at the Canadian engine manufacturer. P&WC considered improving the JT15D, but a feasibility study showed the strengths of a "clean-sheet" design, he says.
The PW500 programme is the first at P&WC to make full use of integrated product development, where all disciplines from design to support are involved from the outset. Cessna's involvement was vital in achieving a good long-term relationship with the customer, says Cristofaro.
The engine has its roots in a turbine-technology integration demonstrator (TTID) which P&WC used to test new concepts such as the integrally bladed rotor (IBR) fan. Design was begun in February 1992, and the 18kN-class TTID was run for the first time in November 1992.
The engine selected by Cessna initially was smaller than the TTID, but the aircraft manufacturer required P&WC to guarantee 25% growth capability. Eventually, Cessna needed 50% growth to meet the Excel power requirement, Cristofaro reveals, and the PW545 is similar in size to the TTID.
The baseline PW530 has an IBR fan with abradable case (introduced on the JT15D-5D); one centrifugal and two axial compressor stages; a reverse-flow combustor; a single-stage high-pressure (HP) and two-stage low-pressure (LP) turbines; and a forced exhaust mixer, introduced on the PW300 and which reduces specific fuel consumption by 1%. Control is hydro-mechanical.
The growth PW545 has the same core, married to a new low-pressure system. The diameter of the IBR fan is increased from 584mm to 693mm, and an IBR boost stage is added. A third LP turbine stage is added, to drive the larger fan and boost stage, and single-crystal HP-turbine blades are introduced, to allow higher core temperatures. Fan-case acoustic treatment is introduced to counter the increased noise from the larger fan. Control is by single-channel full-authority digital engine-control (FADEC). The target-type thrust reversers for the PW530A and PW545A are being designed and manufactured by Nordam.
The PW500 FADEC is based on that developed by United Technologies sister company Hamilton Standard for P&WC's PW200 helicopter turbo-shaft. Whereas as a dual-channel FADEC will automatically retard the engine to idle in the event of a failure, the single-channel FADEC will freeze the engine at its last throttle setting awaiting pilot action, Cristofaro explains.
While the Citation Bravo is an upgrade of the JT15D-powered Citation II, the Excel is a new aircraft, which combines the performance of the Citation V Ultra with the cabin cross-section of the larger Citation X, creating a new class of "wide-body" light business-jet.
Cristofaro says that Cessna's customer-driven decision to increase cabin diameter on the Excel drove up the engine size needed and led P&WC to resize the PW500 core. The bigger core had to be built within the already agreed price, he says, adding that P&WC is meeting its cost targets.
It has been a challenge to meet the 275kg dry-weight target for the PW530, he admits. Aggressive weight-reduction efforts at P&WC and development partner MTU (which is responsible for the LP-turbine module) have maintained the specification weight, Cristofaro says.
An "ecology system" captures the unused fuel, which drains from the engine at shutdown, and would otherwise drain overboard, and feeds it back into the combustion chamber at start-up. This avoids the need for a cumbersome collector tank in the aircraft and saves weight overall, he says.
ENGINES FLYING
P&WC has delivered three experimental PW530s to Cessna, the first of which is being flown on the aircraft manufacturer's T-47 Citation engine testbed, replacing the left-side JT15D. The remaining two engines powered the Bravo prototype on its first flight in April.
The Canadian engine-manufacturer has been flight-testing the PW530 on its Boeing 720 engine-testbed since May 1994, and was scheduled to begin flying the PW545 in April. Cessna will flight-test the engine on its Citation III testbed in June, and the Excel prototype is scheduled to be flown in March 1996.
There are seven engines in the PW530 development programme. The engine, first run in November 1993, is performing "better than specification", says Cristofaro. Certification is planned for December 1995.
The first PW545 was run in December 1994 and met its sea-level performance targets, he says. The engine is being torn down for inspection after 30h of running. Certification is scheduled for December 1996, a year after that of the PW530.
Looking ahead, Cristofaro says that there is still growth potential in the PW545, although the present engine represents the limit of the common-core approach. A cooled HP turbine and "major changes" to the low-pressure spool will be required to develop the engine further. Advanced design of a growth PW500 has begun, and a demonstrator is planned.
Source: Flight International
