Page 32 - Mar17ABS

Violating the duty cycle just a
couple of times will do irreparable damage to the starter, and in extreme cases, it can render the starter inoperable.
Starter: The starter is the actual unit that converts the electrical power to mechanical energy in the form of torque, which is used to physically rotate the engine to initiate the starting process.
“No matter what the cause or reason, if any of the system’s components are not working properly, the results can run from poor starter performance to outright damage to the starter itself,” Gauntt said.
Starter System Troubleshooting 101
As Gauntt explained, the starter is at the end of a chain of components. In its simplified form, the starter converts the battery’s electrical power to mechanical energy in the form of torque, which is used to crank the engine.
Cranking requires a significant amount of current (typically ~400A in-rush, ~70A cranking). Voltage at the battery equals the potential or push in the system, but if the system has too much resistance along the path, the battery can’t f low enough current to the starter to do its job.
That resistance comes in the form of corroded terminals, dirty or worn contactors and old wiring. And, since they suffer from lower potential already, older aircraft with original 12-volt systems are especially prone to problems.
Also, take time to check the other components of the system to ensure good current flow including the aircraft’s
30 • TWIN & TURBINE
switches, relays, and even the aircraft’s key or push-button starter device.
Age-related and moisture-induced corrosion can attack the connecting terminals and erode the internal contacts slowing the flow of power. Even the smallest bit of corrosion on a wire or connection point could be the source of a problem.
Gauntt said that a commonly overlooked point of corrosion is the engine-bonding strap. The ground system should be checked for electrical ground integrity using a VOM. A maximum of 0.2-ohms of resistance at any bonding/ ground connection is the borderline limit.
While you’ve got the cowls off, check the condition of the electrical conductors and insulation around the wires for chafing damage. Gaps in the insulation will allow moisture to corrode the wiring, increasing its resistance.
A weak battery will make even the cleanest system struggle. Low voltage will require the starter to turn slowly and remain engaged for a longer period of time. Extended engagement periods will lead to heat build-up in the starter motor and reduce its service life.
And always, when it comes to battery troubleshooting, follow the manufacturer’s guidelines for ongoing inspections, real-charge capacity testing and maintenance including checking the terminals for corrosion. Even a well- maintained battery could lose 2.5 percent of its charge in a week.
A Quick Word about Kickbacks
The dreaded kickback occurs when, during the starting process, the engine’s crankshaft abruptly changes rotational direction. A significant kickback can displace the crank as much as 90 degrees in 33 milliseconds and cause significant damage to the starter’s drive and gear engagement system. In extreme instances, kickback can actually break the starter’s mounting pad away from the engine.
Gauntt explained that kickback issues can often be resolved by adjustments to the engine’s ignition and fuel systems or through the pilot’s ‘modification’ of engine starting techniques. Always follow the engine OEM’s instructions when making changes to the system’s settings or starting procedures.
(Hartzell Engine Technologies has introduced a new family of starters that eliminates kickback damage, but that’s another story.)
New-Generation Starters
While the functionality of starters hasn’t change in decades, Hartzell Engine Technologies (HET) and Sky-Tec currently offer an array of new-generation lightweight and legacy starters designed to deliver optimum performance even in the harshest environments.
or www.skytecair.com. T&T •
For more information about Hartzell Engine Technologies’ complete selection of starters, please visit www.hartzell.aero
March 2017