** Slo Fly and Electric Props off center holes:
The paper insert lists the pilot hole as the precision hole which can be used to precisely drill the non-precision hole. Our preference is to use a tapered reamer from the front side of the prop to avoid contact with the precision hole entirely.

Unfortunately, we are forced to gate the material in through the center of all axis's which necessitates a second operation of drilling out the sprue. For this reason the precision locating rings were adopted for electric propeller production.

It is our experience that most of the time some customers fail to read the instructions for properly mounting the propellers.

** Q40 pylon racing propellers are now available again.
However, a new warning concerning their use is now posted below.
This warning is particularly important when using higher performance Q40 engines now entering the market.

** Pylon Racing Propellers Warning

A previously unobserved failure mode potentially exists when the resonant lateral frequency of the fuselage is excited by the engine rotational frequency.  The failures are causing the outer portion of the tip (typically last ¾ inch) to fail during flight.

This failure mode has been observed only with very limited combinations of Q40 engine, propeller, and fuselage design. We suspect that fuselage resonance, in combination with higher performance engines now entering the market, is the most probable cause for the propeller tip failures. 

The initial symptoms of the failure mode are audible vibration noise in flight.  The postulated mechanism has not been observed on the ground, due to the Q40 engines operating at reduced RPM until airborne.

This failure mode has, to our knowledge, has not yet caused catastrophic failure.  However, the potential for more serious consequences is a concern. 

Changing propeller characteristics very mildly (pitch change or diameter reduction) effectively mitigates the resonance effects.   This rather strong sensitivity to propeller design clearly indicates the presence of a highly tuned resonance condition. 

The observance of this new failure mode suggests that this same mechanism could occur with other combinations of fuselage stiffness (natural frequency) and engine characteristics. This might be especially true given the continuous improvements in engine performance.   Therefore, the following cautions are particularly emphasized when operating higher performance pylon racing model aircraft.

CAUTIONS: