Thanks for all the suggestions and insights regarding moving the main gear on my tri-gear KR-2. I understand that my particular KR-2 may not be typical concerning tipping on the tail during boarding and de-boarding. The why part is fairly obvious after a bit of on the airplane experimenting. With half fuel and otherwise empty, I placed two 50-pound sand bags on the front of the baggage compartment shelf: Tips over right now. I can do the same thing without the sand bags by hanging on to the front of the turtle deck in a climb aboard stance. If I jump on or off quickly, I can avoid the tipping. The arm of the sand bags is 50 inches. Going back to my weight and balance spread sheet, I played with the numbers to see where the cg would be during the loading sequence. My wheels are currently at 17 inches from datum. CG for the sand bag test was 17.1 inches. Not a violent tip back but it goes over. This is the same math Mr. Pazmany presents in his design book. So, how did this come about? When I was attaching the Diehl gear to the spars, I was cautioned not to get the wheels to far aft because the elevator may not have enough authority to rotate the aircraft for take off at minimum take off speed. Don't know what the moment for the elevator would be at 55 knots, but now I am somewhat sure there is plenty of authority at that tail. At the time I could have easily set the main wheels another 2 inches aft by choosing where to drill the holes in the gear leg. No where was there any direction as to exactly what the number should be. I went conservative regarding the elevator authority consideration. Further playing with the weight and balance numbers for worse case situations with fuel and heavy passenger, shows the tipping cg to be at 19 inches from datum. The cg would move forward to 14.6 inches when all are seated, still only 2.4 inches margin for tipping and not desirable for flying. Going back and drilling new holes in the gear leg is not prudent. Would need to get another set of gear legs to start over. Also the bottom of the stub wing would have to be reworked to get aileron push rod clearance. This approach is looking like another year of down time for me. Mark Langford suggested adding an extension plate at each axel. That would enable moving the wheels 2 inches aft and not generate any toe in or out issues. Would have to re-work the wheel fairings and extend the brake lines. I do have some 1/4 inch 4130 plate that might work. So, the plan is to put 30 pounds temporarily in the nose for better ground handling and continue the flight testing. When the extension plates are ready, stand down the aircraft for installation and remove the ballast. Then continue the flight testing. Further plan on limiting passenger weight to about 100 pounds; that will be viable for Young Eagles rides. Not what I wanted, but that is reality.
Sid Wood Tri-gear KR-2 N6242 Mechanicsville, MD, USA ...This morning with just myself onboard and half fuel, the cg is at 12.6 inches. I tried raising the nose on a fast taxi down the runway. With an estimated steady ground speed of 25 knots, I can easily raise the nose wheel off the pavement with back stick about two inches... Sid Wood --------------------------------------------------------------------------------------------------------- Can't you simply bolt an appropriate sized adapter plate to your current lower gear attach bracket that extends rearward just enough to keep the thing off it's tail? Assuming it's thick enough, I would not expect any toe/camber geometry changes, although if you have wheel pants, they would need some reworking to meet up with the gear legs. That's essentially what I did to make my gear longer, except I went down instead of aft. Really, I just made a new lower bracket that was longer, but essentially the same concept. It worked, but I didn't like the view over the cowling. You could also take that approach...redesigned bottom gear brackets that relocate the wheels further aft. Mark Langford -------------------------------------------------------- ...I also flew quite a bit in Terry Chezik's KR2 trigear as well getting trained up - I do not recall an issue with his... Rob Schmitt
