Re: Prop Hub Interference?
Posted: Wed Mar 15, 2017 2:44 pm
Michael - I agree. My problems seem to consistently stem from vendor-supplied parts. I feel for the Sonex/AeroConversions team. But I also am beginning to question their QC process and vendor-management. Its tough to do as a small business, but these are things that can have an impact on safety and brand reputation.. :(
I got a Dial Indicator and took several measurements today. I remain concerned about my Prop Hub. Here's an excerpt from my email to Sonex:
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I have performed additional measurements of the crankshaft and prop hub this morning and can confirm that while the crankshaft shows less than 0.001" of variance during a rotational test (see photos near the bottom of this album), the prop hub shows 13 thousandths variance in both major dimensions, throughout a 360 revolution. Here is a video of the measurements. Note that its tough to hold the camera and all parts properly in the recording; but I verified these measurements without the camera running. I also made sure that the crankshaft was pushed to the rear during all rotation tests, to ensure that run-out was not causing errors.
This is not a matter of the engine case being machined a bit offset or not enough; the prop hub is *clearly* not concentric to the crankshaft. A 13-thousandths error at the prop flange, multiplied out over the length of a Sonex propeller, is over 1/16" for each blade (assuming a 50" prop). That's over 1/8" of propeller track error due to the prop hub alone (leaving no tolerance left to deal with anything not perfect with the prop itself)!
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--Noel
I got a Dial Indicator and took several measurements today. I remain concerned about my Prop Hub. Here's an excerpt from my email to Sonex:
----------
I have performed additional measurements of the crankshaft and prop hub this morning and can confirm that while the crankshaft shows less than 0.001" of variance during a rotational test (see photos near the bottom of this album), the prop hub shows 13 thousandths variance in both major dimensions, throughout a 360 revolution. Here is a video of the measurements. Note that its tough to hold the camera and all parts properly in the recording; but I verified these measurements without the camera running. I also made sure that the crankshaft was pushed to the rear during all rotation tests, to ensure that run-out was not causing errors.
This is not a matter of the engine case being machined a bit offset or not enough; the prop hub is *clearly* not concentric to the crankshaft. A 13-thousandths error at the prop flange, multiplied out over the length of a Sonex propeller, is over 1/16" for each blade (assuming a 50" prop). That's over 1/8" of propeller track error due to the prop hub alone (leaving no tolerance left to deal with anything not perfect with the prop itself)!
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--Noel