Mihaly, with regard to your "newbie" questions let me attempt to give you answers to what I'm familiar with.
1. The FAA will only award an "Homebuilt" an airworthiness certificate in the "Amateur" built category. The "Light Sport" designation is only used for "factory" built aircraft that have been proven to meet the ASTM guidelines. Now any aircraft that meets the LSA criteria for gross weight, stall speed and top speed, etc. can be operated by anyone exercising the LSA privileges. (Think Cubs, Champs, etc.) While some will scoff at an LSA KR-2, IMHO it can be done. Yes, keep the empty weight as low as possible, use the same span as the "Diehl" wings (24ft) and the original RAF airfoil in the plans. You may also need to use vortex generators to meet the stall speed. I don't think by going "small" on the engine output is necessary as you limit the top speed by the propeller selection. (That's exactly what the Sonex folks do even with the 120hp Jabirus'). 3. There are substitutions for spruce that have been successfully used in the past, douglas fir being the most popular, stronger but heavier. I would certainly check around your area for spruce availability, but spruce needs to meet some pretty stringent criteria (including the way it's harvested comes to mind) to be graded "aircraft". As you suggest you could use Aircraft spruce in the spars and longerons and something else in the less loaded areas. Do your research! Good luck Rick Human KR-2 N202RH (LSA compliant)
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