Getting Started

Current draw also determines the number of starts you will get from the battery. For a given charge condition, the battery is capable of delivering a given number of starts and that number is directly related to the amount of current the starter draws while cranking. A starter drawing twice the current will only give you half the number of starts before battery depletion.

Operational duty cycle

A final performance factor that should be considered is the starter’s operational duty cycle. This characteristic is important as it reflects how well the starter can tolerate repeated starting attempts and overcranking abuse. Duty cycle is a ratio that measures how long a device may be operated to how long it must rest. This ratio is usually represented as a percentage of operational time to rest time. In the case of a starter it reflects how long you can engage the starter and how long you must allow the starter to rest before the next starter engagement. Most starters on the market today have duty cycle ratings of around 4 to 6 percent, but some can exceed 10 percent duty cycle ratings.

So why is duty cycle so important? Warranty data from starter manufacturers indicates that the principle cause of in-service starter motor failures is overcranking abuse. A starter with a higher duty cycle will be able to deliver a higher number of starts within a given window of time without overheating. This is an important performance indicator when considering a starter as it will have a direct impact on starter longevity.

Fit, weight, performance, and any additional features available are all considerations you should keep in mind when evaluating aircraft starters. The tips in this article should help you make a more educated purchasing decision the next time you consider a replacement starter.

Rick Quave is director of engineering at Kelly Aerospace Power Systems, makers of E-drive starters. Rick can be reached at rquave@kellyaerospace.com.