Aircraft System Design Success Story - Hydraulic Pump and Power Systems Division | Parker US

Aerospace

In Aerospace System Design and Development, It Takes a Village to Succeed

Aircraft

 

Challenge

A general rule in aircraft system design and development is that it takes at least five years to go from concepts to design, testing, and FAA (Federal Aviation Administration) certification. Bringing a new system to market requires a broad range of engineering skills and excellent project management.

A job that involved multiple divisions of Parker Hannifin Corporation illustrates the staggering complexity of design and development projects of this type. Parker was approached by a well-known maker of commercial and executive jets for assistance in developing a new flap control system, including the flap power drive unit (PDU), for its new business jet. From the project start, various divisions were responsible for everything between the flap select lever in the pilot’s hand to the actuators that actually move the flaps, including the flex shafts, positionsensing devices, and control electronics. Any change to other system components had to be evaluated and tested for how it would affect the performance of the motor under development.

Solution

At the heart of the new system was a custom resolver-commutated, inverter-driven brushless DC motor with an integral solenoid-operated power-off parking brake. The system included two of these motors to power the main wing trailing-edge flaps through a speed summing differential. Parker drew on a large pool of engineering talent to design and verify the new flap control system, including three engineers just for the motor, a power transmission specialist, three engineers for the balance of the flap power drive unit, a quality engineering team, and a separate verification team to design test equipment and handle testing.

After evaluating the customer’s operating requirements, Parker’s magnetic design engineers performed a Finite Element Analysis to customize the size, shape, and materials used in the motor’s magnets. Other things were also looked at, including the gauge of the copper wire used, the number of turns of wire, and the lamination material. Although in some ways it could be considered a standard servo motor, it was optimized for this precise application.

Designing and building the new motor to meet the aircraft manufacturer’s requirements presented Parker’s Hydraulic Pump and Power Systems Division several engineering challenges. It had to provide the required torque at a very high speed to deliver sufficient power output. After many months of collaboration, including design and development, design acceptance with Parker’s and the customer’s design teams, experimentation, and “iron bird” testing. Each motor was able to provide a maximum of 17,000 rpm at 6 in-lbs. of torque. Iron bird testing is where an aircraft is loaded into an electromechanical structure that simulates the stresses an airframe would experience in flight.

Many challenges were related to the extreme environments in which the motor needed to perform flawlessly, such as in ambient temperatures ranging from -65° to +158°F and under a wide range of loads, both in flight and on the ground. It also had to meet all commercial aerospace environmental conditions related to electromagnetic interference (EMI) with other nearby components, vibration, duty cycle, etc. The team noted that at -65°F at 35,000 feet, oil turns to sludge. At the other end of the spectrum, it can be 120°F on the tarmac with the mechanic constantly operating the flaps to try to track down a source of the noise. The motor designed had to handle both ends of that—produce enough torque to keep operating at very low temperatures and not overheat during the most aggressive thermal cycles.

The high efficiency required of this motor made an inherently low cogging torque design essential. The maximum motor output torque requirement was so close to the motor starting requirement that any cogging torque would have robbed it of the torque needed to get it moving. Parker went to enormous efforts to create a motor that did not cog. Efficiency was also critical because of the relatively low level of power provided by the plane’s internal generation system. The level of power available from the aircraft to drive the motor was just 28V, 50A per RTCA DO-160, making high efficiency doubly critical.

Possibly the biggest challenge the design team faced was creating a powerful motor that could fit into the tight confines of the motor enclosure. Figure 1 below illustrates the final dimensions of the motor in its housing.

Results

For everyone involved in the PDU motor project, the final motor design represented an important learning experience that can be applied to subsequent motor design and development challenges. Most importantly, with Parker Hannifin’s depth and breadth of aeronautical, electromechanical, mechanical, magnetic, and materials engineering expertise the project was successful.

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