I made these "temporary jack points" out of 2" x 2" x .25 angle. I hooked the outer edge with a regular floor jack, and it made jacking up the plane very easy for weighing purposes. One the plane was on the scales, I found that rolling the tire around a little alleviated side stresses and gave a more accurate reading. I used a 400 pound Pelouze 4040 scale that cost about $130 at Office Max. That works great up to 400 pounds per wheel, but after that, you're out of scale! It has a couple of features that make it perfect if your plane isn't too heavy...the display is constant, and once zeroed it continues to read until it's turned off, and it has a remote display, so you can both weigh and sit in the plane as "pilot" at the same time.

I did my "final" weight and balance, but didn't quite have "everything" on it yet, including the spinner, so I put "surrogates" in place to make sure they were all accounted for. Total empty weight is 732 pounds, but paint will probably add 12 pounds or so. The CG range with pilot and empty to full fuel is 16.4% to 19.8%, out of the 15% to 30% of chord range that is generally considered safe for the KR.

Add a 227 lb passenger to get to the 1200lb gross and I'm at 26% chord. Total CG range from skinny pilot with no fuel to full gross is 4.5", or less than 10% chord. At gross weight, fuel shift is only 1" full to empty, moving forward as fuel is burned. See final weight and balance spreadsheet for more details. If you don't have Excel, you can view the "dumb" pdf file at final weight and balance pdf file. Locations for fuel and passengers is calculated from actual fuel and pilot/passenger weights, so these station numbers are accurate, not just "guestimates". My datum was the back of my prop hub, which is two inches longer than William Wynne's, and is located 28.5" from the firewall. The wing leading edge is 16.5" from the front face of the firewall, but this is unlike most "normal" KR2S's, so be careful with using these spreadsheets for your own use. Use your own measurements, not mine! But this means for most "normal" KR2S's that are built per plans and use a Corvair engine, CG should be just about right in the middle of the range, assuming you don't use a forward fuselage mounted header tank, and you balance your elevators with about 4 pounds of lead like I did.

I didn't just get lucky that it's "right", I've been checking weight and balance forever. I'm really a little further forward than where I want to end up, because the closer to neutral, the faster I'll go. But on the other hand, for somebody just starting out in the KR world, forward is just fine. I still haven't installed my backup battery, so it will go back in the fuselage somewhere, with some pretty small (maybe 16 ga) wires running to it. After all, it's not there to start the engine, just to keep me aloft during an emergency, and that doesn't take much current at all. It will be isolated from the rest of the system (except during charging) by a $3 Radio Shack diode. The 5 pound UPS "backup" battery will get me pretty close to the center of the range.

Where did I get a 1200 pound gross weight from? Well, my spars ARE a little beefier than most, but I'm not really counting those, as the wing attach fittings are really the limit, and they are per the KR2S plans. I'm not planning on any high G aerobatics, and my load rating will have to be kept down in the 5g range to stay under "design limits", but that's fine with me.

Return to Mark Langford's KR2S N56ML.