Mark Wegmet wrote: >I acquired a project (KR2S) that is about 40 - 50% complete; boat, spars, > tail feathers etc. that was originally built to the plan's wing > configuration. I would like to use the "new" airfoil and know that the > spars > need to be "taller". > What do you think is the best approach to doing this? The spars I have are > extraordinarily well built... they are complete, including the "weep" > holes > for vacuum relief in the mahogany. Should I "cap" them fully, in other > words > over the mahogany facings on the spars, or should I just cap the main > spruce > spar material?
The AS5046 airfoil was designed specifically to fit the stock KR2x spars, so it will fit your airplane. If the spars are already tapered (front to back) you might need to add some material to the top and/or bottom of the spar, which is easily done by lamininating a thin strip of spruce (whatever it takes) to it with T-88 and then retapering the spar to perfectly match the new airfoil. Just make sure there are no abrubt discontinuities in the spar where it enters the fuselage (or anywhere else), as that's a stress riser point. The template for that particular situation is at http://www.krnet.org/as504x/as5046_00_600.pdf , and there's more info on the different versions at http://www.krnet.org/as504x/templates.html . If you are considering going all the way to the AS5048 airfoil, which is way thicker, you can do that, but you'll be adding several pounds of dead weight to your spars, and the discontinuity at the fuselage becomes even more severe, so I'd remove the spars, cut them up, reconfigure into taller ones, and reinstall. That's way more trouble than it's worth, less than optimal in several ways, and the hassle/benefit ratio would be huge. I wouldn't even consider it. There's certainly nothing wrong with having a longer horizontal stabilizer, regardless of the airfoil shape it's in. If it's built and glued in place, I'd just leave it. If it's bare wood, you could scab on some more height and use the new tail airfoils also. As for the mahogany spar facing, there's no reason to touch that at all, since you may only be adding material to the top and bottom caps, so your equalization holes should be safe. That feature is in the plans, so I don't know that they're that extraordinary. I thought I sent this last night, so if it shows up again, it's a glitch in the system, not me losing my mind completely... Mark Langford n5...@hiwaay.net website www.n56ml.com
