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APC Propeller Technical Advisories

* 21X14E Replaced by 21X13E Propeller.

The 21X13E propeller has replaced the 21X14E. The original 21X14E propeller was mislabeled and was actually a 21X13E. We have corrected this labeling error and there should be no change in performance. We appologize for any inconvenience. (LP21013E).


* Safety Issue Regarding 15.5X12 - 4 Blade Propeller.

Please discontinue use of the 15.5X12 4 blade propeller on the YS170 engine. This propeller was designed for a 140 and is not sutible for larger, more powerful motors. Several failures have been reported. (LP415512).

** Propeller Size Recomendations.

Landing Products does not make specific recommendations for propeller sizes. 

Large variations exist in engine/motor performance characteristics and in model aircraft applications.  Therefore, Landing Products is unable to reliably offer propeller size recommendations for specific combinations of motor type, size and application.

Please rely on written instructions/recommendations that are provided with most motors.  If propeller size recommendations are not provided with the motor, please contact the motor manufacturer for suggestions.

** Engine Shaft Hole Alignment.
The prop hub aft surface and aft hole are precisely defined during molding.  However, post-molding shaft hole drilling may induce minor angular mis-alignment of the prop with the engine shaft.  This hole mis-alignment is avoided by use of a tapered reamer to slightly enlarge the prop hole forward of the aft surface.  This causes the prop to precisely register with the engine shaft at the aft surface and hole.

** 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.


  1. Do not continue use of the propeller if any vibration is heard during flight.
  2. Discontinue use of the propeller if any stress marks are evident on the blades after use.


Propeller Advisories

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