Newmarket, New Hampshire – Controllable Pitch Propeller (CPP) blade inspection is a complex task that requires some additional considerations. The best option is to inspect the propeller in-situ while everything is mounted, synced, and set at the forward pitch setting. However, due to their size and the ability to disassemble the propeller’s blades (and spares), individual CPP blades are frequently what the repair facility receives – in other words, the blades are not always accompanied by their corresponding hub. This document serves to provide guidance for TrueProp Virtual users working on individual controllable pitch propellers.
Controllable Pitch Blades
When capturing a single CP blade, it is very important to scan the blade palm and bolt pattern. The hub mechanism interfaces with these holes, making them critical positioning references (similar to the bore in a monoblock propeller). Always scan the root and palm. Best practices should also capture the underside of the palm, since the position of this plane determines the resulting diameter of the blade.
Controllable Pitch Blades
When capturing a single CP blade, it is very important to scan the blade palm and bolt pattern. The hub mechanism interfaces with these holes, making them critical positioning references (similar to the bore in a monoblock propeller). Always scan the root and palm. Best practices should also capture the underside of the palm, since the position of this plane determines the resulting diameter of the blade.
Blade Orientation
Once the blade has been captured, it must be properly positioned in XYZ space. It is easiest to start by registering an individual blade to a coordinate system first, then assembling the blades into a full propeller for inspection.
Pay careful attention to the bolt pattern. Some key aspects:
Once the blade has been captured, it must be properly positioned in XYZ space. It is easiest to start by registering an individual blade to a coordinate system first, then assembling the blades into a full propeller for inspection.
Pay careful attention to the bolt pattern. Some key aspects:
- Keep palm/hub mechanism interfaces centered about the Y axis.
- Put the bottom of the palm plane on the XZ plane.
- Register the center of the critical bolt holes using cylindrical fits.
- Set the pitch angle orientation using the angle of the bolt holes on the palm. If there is a drawing, this angle may be explicitly defined for the design pitch.
| Assembling with a Virtual Hub The process should be repeated for all available individual blades. These blades can then be assembled virtually on a representative hub. The hub plane for each blade should be defined and the blade palm bottom mated to this plane. This moves the blade into the proper diameter for the inspection process, ensuring your inspection data is taken with cylindrical sections at their intended design orientation. |  |
Analysis in TrueProp
With the assembled data fully registered, we can import the STL mesh into TrueProp. The Virtual Plugin accepts the STL mesh and extracts the radial inspection data for each blade.
With the assembled data fully registered, we can import the STL mesh into TrueProp. The Virtual Plugin accepts the STL mesh and extracts the radial inspection data for each blade.
 |
 |
When no design data is available, TrueProp can generate a proxy design reference by averaging the profiles of the imported blades. This provides a baseline for comparing blades and determining the overall quality of the blade set (Class S, 1, 2, 3 or no class). The reference can also be saved and re-used for comparison of additional blade scans, spares, rebuilt blades, and so forth.
