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Originally Posted by zog139
(flew/fly very stably, so an F-104 PMC model should, with relatively little or possibly even no forward ballast, fly equally well.)
I respectfully disagree. I have built four F104 models and each one if them required a significant amount of ballast to get the CG where it needs to be. I used another modelers CP calculation that was derived from the cardboard cutout method. Each model flew very well. YMMV
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Depending on how many forward interior detail parts there are, especially in larger-scale (1/32 and 1/48 scale) F-104 kits (the ejection seat(s), pilot figure(s), the cockpit's/cockpits' instrument panel(s) & side panels, the radar dish and its mechanism [under a removable nose radome], etc.), the more likely forward ballast would be unnecessary, or nearly so, and:
The version of F-104 that is modeled for PMC flying can also make a difference. For example, the XF-104 and YF-104A, F-104A, and F-104C had/have shorter (from front-to-back; that is, smaller-chord), and thus somewhat lighter, vertical stabilizers than other F-104 variants (and the YF-104A also lacked the centerline ventral strake that later F-104 variants have, which would delete a bit more tail mass, in a YF-104A PMC model). Plus, some F-104 variants (the F-104B, F-104D, TF-104G, etc.) have two seats--and definitely noticeably longer cockpit canopies--which add more mass well ahead of the wings, which would benefit PMC models of these Starfighter variants. Also:
The Cox and Estes X-15 RTF models (particularly the latter) flew/fly well, and they didn't/don't need ballast. Their wings' and tail surfaces' relative sizes and locations (with respect to each other, and to their fuselages' widths, lengths, and fineness ratios) were/are similar to those of the F-104. In any event, of course I concur with the wisdom of determining the location of a PMC model's--or *any* non-kit model rocket's--CP (Center of Pressure) with respect to the model's Center of Gravity (CG), and adjusting either (or both) to ensure stability in vertical (or nearly so, for launch angles up to 30 degrees "down" from the local vertical), rocket-powered flight. But as with the RTF X-15 models, F-104 PMC models need not always require added ballast up front.