Colin writes: "Build them right and light and build in the correct empty C of G position and there are no issues with the plane at all. Only issues you want to dream up."
Larry responds: "Builders and fliers on the net would be better served if you would use your knowledge and expertise to educate builders and fliers on how to avoid the problem rather then belittle them for their mistakes." "Where is your CG located, in respect to MAC, with you and a passenger and how much does it change from full to empty fuel." Good points. I have no experience flying the KR2. I do have experience in airworthiness certification test flying and have test flown a number of amateur built aeroplanes also. Therefore I ask how the "correct empty C of G position" is readily established in a modified aeroplane? Generally speaking, the aft CG limit is driven by static stability requirements - such as stall/spin recovery - and the forward limit by pitch authority considerations, such as the landing flare. The Rand Robinson plans I presume specified a CG range for the MAUW KR2 (900lb). Convention would dictate that this was likely established by an initial analysis then refined by flight test measurements. But exactly what iteration in the aeroplane's evolution did this occur at? What engine was Rand using at the time - it would have been a VW derivative and not an 0200/Corvair/Jabiru? Modification of the forward fuselage for an alternative powerplant (propeller, spinner, cowling and so forth) are all destabilizing and without analysis and testing you cannot know their effect on the static margin. And of course, all KR-2 aircraft are flown within the specified 900lb MAUW! It is clear that the KR2 is resilient to builder modification in many respects. In absence of current and relevant quantitative data, the only guidance regarding CG range would be from that specified in the original plans, and that is the best guess starting point. In absence of a further analysis, it would be necessary for the builder to establish an empirical CG range by flight test - which seems to be what is happening - sort of. It would be a good investment in time researching the matter of safely and sensibly investigating the operating CG limits of any given version of the aeroplane and then religiously adhering to them. Nga mihi Kiwi
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