Specifications KR-2 KR-2S KR-2XL Length 14'-6" 16' 18'-6" Wing Span 20'-8" 23' 26' Wing Area 78 sq.ft. 88 sq.ft. 100 sq.ft. Gross Weight 900 lbs. 980 lbs. 1400 lbs. Empty Weight 480 lbs. 520 lbs. 750 lbs. (est) Useful load 420 lbs. 460 lbs. 650 lbs. (est) Stall speed 52 mph 52 mph 54 mph (est) Maximum speed 200 mph 200 mph 200 mph (est) Cruise speed 180 mph 180 mph 160 mph (est)
The KR-1 and later the KR-2 were designed to be small, lightweight, and easy to build. Unfortunately, there is not enough room for really tall pilots.
As the design matured, more and more people built them larger, until the KR-2S was introduced. This added an additional two inches of leg room to between the main spar and the fire wall, as well as an extra 14 inch bay behind the rear spar. In addition, very few of the completed examples turned out as light as the prototype.
When I deceided to build a plane based on the KR, it was in large part because it is a design that is easy to modify. I am very tall (see a brief bio) and needed something large. I do not recommend that anyone make the changes that I did. It is a lot of extra work and requires careful thought and analysis. Every change affects everything else.
Starting from the basic KR-2S plans, I added an additional 5 inches in front of the main spar. This is counterbalanced by an additional 6 inches behind the rear spar (an extra inch in each of the bays). To maintain everything in balance, I am using a 3 gallon header fuel tank, supplied from two wing tanks (32 gallon total) by an electric pump. The pump will run constantly with overflow returned back to the wing tanks. I also added 3 inches to the width, and one inch to the heigth.
The extra size and weight required additional wing area and span, this in turn would mean more weight, which leads to a slightly stronger structure. I performed a comparitive stress analysis that showed the fuselage wouldn't need much changing. I did add a bottom longeron doubler that runs from the firewall to the back of the baggage area. I also added an additional doubler to the top longeron, over and above that currently called for in the plans.
The main modification for strength is in the wing. The main spar center section is solid, instead of the built-up called for in the plans. The outer section main spars are correspondingly stronger. The main gear is my own design, based on the Dan Diehl gear. I sized it for a 5G static load at the 1400 pound gross weight.
The airfoil is an NACA 747A315 instead of the RAF48. The 747A315 has laminar flow over a significant portion of the chord, very low section drag, a low pitch moment, a good section lift cofficient, and a forgiving stall.
The root chord is 52 inches and is set at 2.0 degrees angle of incidence. The tip chord is 36 inches with a 0.0 degree angle of incidence. After picking a 2 degree washout, I used the method given in Theory Of Wing Sections by Abbott and Von Doenhoff to set the angle of incidence of the root cord. My design point for level flight attitude is 160 mph, 6000 ft, 1200 pounds, and a CG at 27% of the mean aerodynamic chord.
The calculated neutral stability point is approximately 34.5 percent of the mean aerodynamic chord. The CG location that should result in the minimum trim drag is approximately 28 percent of the M.A.C.
Frise ailerons. See The Sportplane Builder, by Tony Bingelis, for a discussion of the advantages. This mod turned out to be difficult to implement. The KR or Rutan style ailerons are much easier to build.
Electric flaps. I did not want have to use electric, but cockpit space is so limited, I didn't have enough room for a manual flap actuating handle. I was able to make a flap drive unit from a satellite dish actuator that is not too heavy.
Moveable seats. I wanted other people to be able to fit in my creation, but I couldn't find any seats that I liked that would fit, so I made my own. They are 1/4 inch Last-A-Foam, covered with two plys of 6 oz glass on both sides, with a uni-directional reinforcement as needed. They are mounted on 1 inch X 1 inch square tubing tracks that are bolted between the spars. Adjustment is not quick, but then it doesn't need to be.
Adjustable rudder pedals. Three different positions for the dimensionally disadvantaged.
I am also planning on a BRS ballistic parachute. It is not that I don't trust my work, or my design, but I think that they are a cheap form of life insurance. Anyone who flys with me will get my best effort in all possible ways.