In my last article, I discussed the failure and replacement of the starter adapter on the aircraft. The adapter connects the starter motor to the internal gears of the engine, providing a “clutch” of sorts to engage the starter motor during starting and disengage it once the engine is running on its own power. Anytime that a component is removed from the aircraft, such as the starter motor in this case, good mechanics use the opportunity for inspection, repair, or upgrade. After all, aircraft maintenance is a labor-intensive endeavor. If you already have components sitting on the bench, it pays to get ahead of the curve and give them the TLC they require before putting them back on the aircraft.
In the case of starter adapter work, it’s critically important to ensure that the starter is working properly because a faulty starter could quickly destroy the investment made in a new adapter. The starter/adapter relationship is critical in Continental engines, and there are many starters to choose from. I met with the experts at Quality Aircraft Accessories (QAA) and Hartzell Engine Technologies to understand how they determine the best starter for different applications. Brett Benton, president of QAA, has been at the helm of the business since 2008. During that time, the company has seen some unintended consequences of starter design changes in the industry.
In nearly every facet of aviation, creating lighter components is considered a major design goal because it directly affects the useful load of the aircraft. When lightweight starters came onto the market, they were considered perfect for this role. In versions where they were not directly connected to the engine, such as in Lycoming engines, they were extremely successful and had few major issues. However, when installed directly on engines through starter adapters, some of the designs caused problems. The Iskra starter is one example.
The Iskra lightweight starter (and some other early lightweight starters) used a system of planetary gears to generate the necessary torque to start the engine. This gearing introduced a significant “drag” on the starter shaft when the starter was not in use. In other words, if you held the starter in your hand and tried to spin the drive shaft, it would be fairly difficult to turn. An unintended side effect of this drag was eventually discovered in the fleet of in-service aircraft as some starter adapters began to fail prematurely. It turns out that the extra drag of the starter motor was not allowing the adapter to release properly, leaving the engine turning the starter rather than the other way around. The bottom line is that it was determined that all starters used on these engines must freely turn with less than 5 inch pounds of force required to spin the shaft of the starter (reference Aircraft Specialties Services Service Bulletin S-2008-01). The starters with planetary gears that don’t meet that requirement are no longer on the market, but that doesn’t mean they’re not readily available through eBay and other sources as “great deals,” so buyer beware.
Benton also referred me to Timothy Gauntt, director of product support for Hartzell Engine Technologies, to gain more information for making my starter decision. Gauntt explained that of the variety of starters on the market, each has its respective advantages for different situations. The simplest differentiator, of course, is weight. However, while losing some weight off the nose might be great for a Mooney, it’s not necessarily helpful for a tail-heavy Bonanza. Additionally, you can always take a good thing too far. Super lightweight starters are available that were designed with the aerobatic market in mind. They’re great when every ounce matters, but not necessarily the best option for flight school owners who don’t want to deal with their starters again for many years.
There are also indirect consequences of the design choices of different starters. Starters that utilize permanent magnets often are lighter, spin faster, and draw less power during engine starts. However, the nature of their operation requires that the aircraft battery be fully charged to put out the required voltage for the motor to engage. Although it may be counterintuitive, a traditional starter will still try to turn the engine over with a low battery (just not as fast), while a permanent magnet starter may not spin at all. And so, you have a trade-off: light weight and lower power draw versus higher weight and a chance at getting home with a low battery.
In my case, Benton recommended the Sky-Tec PowerLite starter. It weighs four pounds less than the high-time Prestolite starter we removed, has an advanced ball-bearing design, and will still allow us to start if we find ourselves away from home with a low battery (which is what happens when you leave the cabin door open with the dome light on…not that I’ve ever done that).
There are many considerations when choosing a starter, and I recommend getting expert advice from companies such as QAA and Hartzell to evaluate your aircraft and mission so you get the best starter possible. Until next time, I hope you and your families remain safe and healthy and wish you blue skies.