At 10:47 AM 8/18/2006, you wrote: >I am considering adding flaps to my KR2 at a later stage, and the time is >right to make provisions for them. > I wonder which design would be more >efficient, aerodynamically speaking? > Also, considering this spans only the width of the stubwings, can >you really expect any significant change? > >Serge Vidal ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
As everyone has an opinion, I'll share mine. The stall speed for most KR's are low and in the ballpark range of the C-150 at 50 mph,+&- 5 mph. I really don't think you will lower that more than a few mph regardless of the type of flap used. What the standard KR needs for a more comfortable landing approach is DRAG and the speed brake is the simplest way to achieve that. With the 2S extension and using a reasonable size tailwheel and spring (i.e., Langford) the ground angle is too shallow to achieve a high enough angle of attack to slow the airplane down for touchdown. I'm using a 30 inch gear leg as compared to the standard 24 inch Diehl legs on my 24 inch stretched fuselage. I'm able to use a 9X30 inch "belly board" and still have plenty of ground clearance, even on grass. It extends down to nearly 90 degrees and converts my KR from a rocket to a rock for landings. I even have to carry a bit of power on approach to maintain a 500 fpm decent. The entire runway, including the touchdown point are visible over the nose in my KR right down to the flare. My KR, with the longer gear and a 3 1/2 degree incidence on the wing, still only sets at 12 degrees cord angle in a ground three point attitude. Most KR's are less than that. That is several degrees below the stall angle of the wing. You can see why a perfect 3 point landing would be hard to achieve as the wing is still flying. Any unchecked vertical decent (dropping it in) will put you right back in the air with the spring from the gear. I NEVER try to three point but attempt to make the slowest possible tail low contact with the mains and then plant it on with a bit of forward stick. Once I can no longer hold the tail up with elevator I'm below flying speed, come full back with the stick, and get on the brakes. In 240 flight hours I've always had directional control with rudder only until the tailwheel is planted. I never use brakes for directional control. My last landing yesterday evening had me shut down in approx 1500 feet on hard surface. That was at 70 mph indicated over the numbers. The only landings I've made without using the speed brake have been playing on the local 8000 foot runway , approaching at 90 mph, and then just holding it off in ground effect. I could land without the brake but it puts the approach "outside my comfort zone". I suspect that may be one reason that many KR's are built but considered to hot or too hard to fly and then seldom see the light of day. SELECTABLE DRAG is the answer. We'll see how Mark's gear extensions work for him in his quest for a slower touchdown speed. I'm convinced they will make a difference and I know he will share that info with us when it happens. As always,.........................:-) Larry Flesner
