Hard Decisions Series: Props

I’m getting to the point where it is time to decide on a prop. My assumptions so far are that it will be a constant speed prop, and that low weight, low initial purchase costs, and low recurring maintenance costs are all good things. The first assumption comes from flying with Eric in his fixed-pitch Bearhawk, and Bob’s recommendations. If even minimalist Bob says that I should really use a CS prop, then I’m convinced. The next assumption, that low weight is preferred, is somewhat debatable. Since we have the smaller 360 engine, the weight and balance envelope has plenty of room for forward weight. Also, the extra flywheel effects of a heavier prop aren’t entirely without benefit. So to sum it up, I would say that the weight of the prop is a wash, not really worth making any decisions over. As for the costs, both initial and recurring costs are a priority, with a slight preference towards recurring costs, since I hope that I’ll be incurring them for some time to come. So based on those assumptions, three primary contenders still stand: the Hartzell aluminum prop, the MT, and the Whirlwind. The Hartzell and MT are both certified props, while the whirlwind is experimental.

The Hartzell has the following benefits: lower initial purchase price, easier to repair in the field, more widespread and thus easier to find qualified repair stations, proven with high numbers of hours and installations*, and lots of other Bearhawks to use as examples. The cons are the history of ADs and other problems (per asterisk above), the higher weight (especially with the required dampener), the likelihood of damage in the field to the soft aluminum blades, and the less efficient blade design. If we were using an engine that didn’t require the $1000 dampener, then the Hartzel might be more favorable, but with the dampener the initial price advantage begins to diminish. I think that the overall purchase price would be around $7500. The benefit of it being a certified prop is really not a priority for me, and if anything, I’m not impressed by the history of expensive ADs that their props have had. The maintenance interval is 6 years or some insane amount of hours that won’t apply to us. The 6 year clock ticks whether the prop spins or not. After those 6 years, the prop has to be sent in and overhauled at a cost of approximately $2000, or $333 per year.

The next contender is the MT. This prop has a wooden blade that is wrapped in layers of fiberglass. It is also certified, and has tens of thousands of examples in service. The weight is slightly less, and while it doesn’t require a dampener, it has a restricted RPM range for the same reason. The prop is more durable when considering rock nicks, since the leading edge is harder. However, since MT is a German company, any repairs that require adjustments to the wooden core require that the prop be shipped back to Germany. The initial purchase price is higher, right at $10,000. The maintenance interval is very similar to the Hartzell in duration and cost of overhaul.

The final choice is the Whirlwind 200C, which is a McCauley Hub with carbon-fiber hollow-core blades. The blade design is arguably more efficient in this prop, and the overall package weight is advertised as 47 pounds. This is somewhere around 10-20 pounds less than the Hartzell, depending on who you believe. The initial purchase price is right on par with the MT. The Whirlwind goes back to the factory every 250 hours for a $650 service that includes replacement of seals and inspection of the rest, with no additional maintenance requirements. For us, that will probably mean sending the prop off every 2 years, at a cost of approximately $325 per year. Of course this is based on flying 125 hours per year, which is just an estimate. There isn’t a calendar-specific maintenance interval for the Whirlwind. At first I thought that this maintenance interval was a big problem, but Tabitha pointed out that perhaps it isn’t. The prop is a single point of failure that has no redundancy. What’s so bad about having the factory inspect it every 2 years? Furthermore, this maintenance interval is based on aerobatic use, so there is a possibility that the interval might grow over time, either by the factory’s recommendation (as TBOs often increase for engines that have been in service for a while) or by our own decision, based on our lighter-duty use of the prop. The disadvantages of the Whirlwind are the high initial purchase price, the limited maintenance facilities, and limited distribution of the prop in service.

It’s hard to know which one really will do the best from a performance standpoint, and it is quite likely that any differences wouldn’t really be noticable in our application. I lean towards the whirlwind because of the lighter weight, reduced maintenance costs (depending on how many hours we fly per year) and a perception of better durability, efficiency, and performance.

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Hours Logged This Session:
Total Hours: 1883.75