Based on my experience with HP parts, parts lists, and blueprints, here's the convention that seems to prevail in the standard HP/RS-series parts numbers:
All standard HP part numbers include a prefix and a body number. The part number may also include a suffix and a side.
The Prefix is a two-digit number followed by a dash (-), and designates the aircraft type for which the part applies, or for which it originally applied. 11- parts are for HP-11, 14- parts are for HP-14, and so on.
You can tell that that many parts are common between the RS-15 and the HP-18 wing spars by the 15- prefix part numbers in the HP-18 parts lists. You can also tell that a lot of the bearing parts, such as the 11-160 and the 11-161, are the same as originally used in the HP-11. However, the prefix can be a little bit confusing for some of us, since parts for both the HP-15 and the RS-15 use the 15- prefix. However, this is not a great concern, since there are only two or so HP-15s in the field (both of them finished as HP-16s), and about 40 RS-15s. Unless otherwise noted, the 15- series prefix designates RS-15 parts.
The Body designates where the part applies, and what part it is. The part number body generally follows this convention:
100 to 199: Wings
200 to 299: Aft fuselage
300 to 399: Tail surfaces
400 to 499: Forward fuselage
500 to 599: Undercarriage
600 to 699: Brakes?
For many HP parts, the body number is common among several HP types. For example, the -455-1R is the tow hitch right side bulkhead regardless of whether you are talking about an HP-11 (the 11-455-1R), an HP-18 (the 18-455-1R), or any HP. These parts all look a bit different, because they fit into different aircraft, but the function is the same.
Also, for some parts the body number also includes a letter. This usually occurs for parts that are late additions to the parts list, added after all the nearby numbers have been assigned. Good examples are the 18-117A splice plates and the 18-117B shims.
The Suffix is an optional number that is used to designate any of several trivial elements about the part. For later HPs, the suffix idicates that the part is part of a larger assembly. For HP-11 through HP-14, the suffix indicates that the part is part of a weldment assembly.
The Side is an optional text string that designates that the part is one of two mirror images that apply respectively to the right (starboard) or left (port) side of the aircraft. The side can be any of the following:
In the future, we are adding the following extensions to the part numbering system implemented by Bryan Aircraft:
18B- and 15B- Prefix Part numbers that use the prefix 18B- and 15B-, such as 15B-120 R&L apply to the B-wing project, which is basically a version of the HP-18/RS-15 wing that uses a tweaked FX airfoil over the stock wing spar. Preliminary drawings are in progress, and CNC-cut wing rib sets are already available.
700 Body Part numbers that have body numbers in the range 700 through 701, such as 18-704-1, apply to the add-on center stick kit for the HP-18. Basically, I'm treating the 700 range as "supplemental" parts for HP Aircraft, LLC kits.
24- Prefix Part numbers that use the prefix 24- are for the HP-24, a future-generation ship similar to the HP-18, but with a roomier cockpit, a forward-hinged canopy, a carbon-rod-based wing spar, and other relatively modern features. Details TBD, look for this one in mid-2004.