Diamond Eclipse Propellers: Wood Prop Nuancesby Dylan Gingerich
Everyone would agree that the propeller is an extremely important part of the airplane. Wooden propellers are installed on the Diamond DA-20-C1 aircraft, and they are actually subject to some unique operating characteristics.
The Diamond Eclipse DA-20 is equipped from the factory with a W69EK7 Series Sensenich propeller. This particular prop is economical to produce and is constructed of wooden laminations. To help increase its durability, a synthetic erosion strip is built into the leading edge of the prop. This propeller is listed in the Diamond AFM (pilot’s manual), and it’s what all of the takeoff, climb, and cruise performance charts reference.
Another option is the German-built MT propeller. A Supplemental Type Certificate (STC) authorizes the use of this propeller on the DA-20. It sports a metal leading edge, which makes it far more durable than the Sensenich design. As another plus, this prop has a much more efficient airfoil, adding 5-7 knots to the top cruise speed of the DA-20. Because of the improved performance characteristics of the MT prop, a Flight Manual Supplement is required. This document contains updated cruise charts that reflect the improved performance. The document number is Doc. E-1342, and it can be found in the AFM or you can download it from our site here. N660DC and N476DC, two of Sweet Aviation’s DA-20s, are equipped with the more modern MT propeller. N212DX is equipped with the original Sensenich propeller, which will be updated to the more expensive and improved MT propeller at the appropriate replacement time.
A maintenance item particular to either type of wooden propeller is the requirement to frequently inspect the connecting bolt torque. Changes in temperature and humidity cause the wooden propeller hub to expand and contract. These fluctuations require frequent checks to ensure the correct bolt torque is maintained. This check only takes about five minutes, and it’s required to be done every 50 hours of flight time for the Sensenich propeller, and every 100 hours of flight time for the MT propeller.
Another nuance of a wooden propeller stems from how it is stored. Because the wood retains a small amount of moisture, the propeller should be stored horizontally after engine shutdown. This becomes more important the longer it sits. If the prop is stored vertically, the moisture can work its way to the lower blade. This will cause an unbalanced condition, which will become noticeable in the form of vibration. This whole problem is largely avoided, however, because paint and fiberglass covering are used on both of the wooden propeller models installed on the Diamond Eclipse.
Sweet Aviation recently purchased a dynamic propeller balancer to help correct unbalanced propeller conditions, aiding in vibration elimination. The balancer is a small handheld computer that includes a photo tachometer and a vibration sensor. These sensors are mounted on the engine while the engine is run at a low cruise RPM. The computer measures the amount of vibration in inches per second, or IPS. It then calculates a solution to the imbalance and informs the mechanic where weight should be added to the spinner back plate, similar to adding weights to a vehicle’s wheel in order to balance it.
Though wooden propellers come with the challenge of a little extra maintenance and attention, their light weight and relative inexpensiveness help to make them a very efficient and practical option for smaller aircraft, such as the Diamond Eclipse.