Cris Fir, pine and mahogany will work just fine in place of spruce on most of the construction. I personally used all three of these woods on different aircraft except the main spar. On the main spar I used good quality straight grained spruce on my first two KR's, on the third KR, I used locally grown clear spruce with slightly uneven grain but compensated for this by laminating the spruce to offset the grain runout. On a forth aircraft (still in progress), I am using mahogany for the spars and local spruce for the boat. On the Horizon II that I have just completed, The entire plane is made of clear pine, which is what was provided by the company that provided the plans and materials. This plane is fabric covered, geodectic construction. In summary you can use a variety of wood and the weight penalty is miniscule. I never weighed individual pieces of the aircraft as I felt it was unimportant....I doubt there is a penalty of more than twenty pounds. You have plenty of areas to make up for CG variences like moving the battery to the rear or adding a heavier and more robust tailwheel and spring. On my last KR I did all of these things while moving my type 4 vw engine 3 inches forward to give it a more aesthetic appearence. Type of wood to use comes up very often and our archives are probably full of interesting articles. When I start my forth KR I will use pine thru-out except for the main spar. I have not played with other materials for the main simply because I do not want to get involved with structural testing there. TRUST YOUR GOOD JUDGEMENT Pat ----- Original Message ----- From: "Cris." <flyi...@gmail.com> To: "KRnet" <kr...@mylist.net> Sent: Saturday, October 29, 2005 10:14 AM Subject: KR> Wood replacing
> As some of you already know, I still have some months to wait before > starting to build. > My first step, after the "zero step" consisting in preparing the shop, > will > be the "boat". > I have some contacts to buy Spruce, here in Italy, but I'm reading lots of > stuff about construction techniques and in one of EAA publications I found > an interesting article about replacing Douglas Fir for Spruce. > > In a few words, accepting a 29% more weight I could gain 26% in resistence > (in general, simply replacing without redesigning the structure) and this > could allow me to avoid big trouble in getting the wood (also $$$ > related!). > > > My questions: > > 1. In your opinion/experience, what is the weight of spruce wood you guys > used building your KR2S? Obviously that 29% should refer to the wooden > part, > not to the total weight. > > 2. I'll install a Rotax 912 (80HP), sensibly lighter than usual > installations. Since the weight will increase mainly behind the firewall, > will I face problems with the CG position? > > 3. Some publications report that Douglas Fir is more critical using > Epoxies. > Is that a known issue? > > Thank you so much. > > Cristiano. > >
