Rocket 305 Blade Length Discrepancy - FYI

[SpamPilot]

I'm in the middle of a prop overhaul right now on my Rocket 305, which uses the McCauley 3AF32C505 hub.  The shop wanted to trim the blade tips down because they thought they were too long.  So I did some research, and found none of the official sources agree on this.

McCauley propeller application guide: blade is an 82NEA-5.5, maximum diameter 76", minimum 74"
Rocket POH: blade is an 82NEA-5.5, diameter 76.5" (no minimum or maximum specified)
STC SA5691NM: blade is an 82NEA-6.5, maximum diameter 76", minimum 74"
Rocket engineering drawing number 305.14.500 rev B page 1: blade is an 82NEA-6.5, no diameter specified

The measured blade length (diameter) on my prop is 76.6".  That agrees with the installation record that shows that -5.5 blades were on the prop that was installed when the TSIO-520-NB was dropped in.  It does not agree with the engineering drawing.

A -5.5 means the initial blade length should be (82"-5.5")=76.5".  A -6.5 means the initial blade length should be 75.5".  So it appears the McCauley guide and the STC, which both list 76" as the maximum diameter, are both wrong (they are not self-consistent).

The McCauley guide lists 37 applications of the C505 prop on a TSIO-520-N or -NB.  None of them, except for the Rocket, list a minimum diameter less than 75".

The only one of these that is legally authoritative, AFAIK, is the engineering drawing (the text of an STC does not supersede the approved data that was the basis for the STC; some STCs do have errors).

In an attempt to clear this up, the shop owner spoke with Darwin Conrad at Rocket.  I'm told Mr. Conrad seemed to be in a grumpy mood, perhaps understandable for a Monday morning.  Mr. Conrad said that this was the first time that anyone had found such a discrepancy in the history of the STC.  He said (this is secondhand, as I did not speak to him directly) that the prop has always just been a prop for a Cessna 340A.  Pressed on the topic, he said if he looked into it, it would probably take a week or more to come up with an answer.  The shop owner said Mr. Conrad didn't sound too keen on doing this.

Unfortunately, the information about the 340A doesn't clear this up.  The McCauley application guide lists both the -5.5 and the -6.5 as OEM for the 340A with the TSIO-520-NB, and the -6 via an STC.  None of them have a minimum length specification of 74", so the application information for the 340A is both ambiguous and at odds with the STC (and the STC is at odds with the POH).

Wish I had been able to dig up a definitive answer on this.  Not sure what the legally correct thing to do is.  Figured I'd at least put this out in the public record for comment.