On March 15, 2013, at 1408 mountain daylight time, a Ryan Navion, N4276K, settled onto the runway during an initial climb and subsequently veered off the runway at Rocky Mountain Metropolitan Airport, Broomfield, Colorado. The airplane sustained substantial damage to both wings when it impacted terrain. The pilot and three passengers were uninjured. The airplane was registered to and operated by the pilot under 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed for the flight that was destined to Albuquerque International Sunport Airport, Albuquerque, New Mexico.The pilot stated that after a "normal" run up, he began a takeoff roll on runway 29R (9,000 feet by 100 feet, asphalt). The takeoff roll was "normal" and he rotated the airplane at 60 mph as per the airplane flight manual. He then established a best angle of climb (Vx) at 80 mph. Upon positive rate of climb, he retracted the landing gear so as not to exceed the 100 mph landing gear speed limitation. After gear retraction, the airspeed deteriorated quickly from 80 mph to 60 mph. The pilot said he immediately reduced pitch to regain airspeed. An excessive descent rate caused him to extend the landing gear and level the wings for an imminent ground impact. The pilot stated that he made an error in the airplane weight and balance calculation by failing to add the weight of fuel in the airplane wingtip tanks, which resulted in the airplane having a takeoff weight of 3,208 lbs. The maximum gross weight of the airplane was 3,100 lbs. The pilot stated that the airplane was equipped with a higher horsepower engine and therefore equivalent to a later model of airplane, which had a maximum gross weight of 3,300 lbs. The pilot stated that he has been an airline pilot for 15 years and received windshear training every 6 months. He said he has been through countless windshear training events. He believed that the quick recognition of the event and proper recovery techniques that he had learned enabled him to keep the airplane under as much control as possible. According to the Navion Operation Manual, Normal Takeoff, states: 4. At a speed of approximately 60 to 65 mph, raise nose wheel from ground by applying gentle back pressure to the control wheel. At 70 mph, very slight additional back pressure will cause the airplane to take off. 6. Maintain an airspeed of at least 80 mph during initial climb. All [climb] rates shown were computed at 95 mph with full throttle and 2300 rpm to give highest rate of climb and most efficient engine cooling. According to the Navion type certificate holder, Vx is 70 mph. The Flight Training Handbook, AC 61-21A, Normal Liftoff, states: During takeoffs in a strong, gusty wind it is advisable that an extra margin of speed be obtained before the airplane is allowed to leave the ground, since a takeoff at the normal takeoff speed may result in lack of positive control, or a stall, when the airplane encounters a sudden lull in strong gusty wind, or other turbulent air currents. In this case the pilot should hold the airplane on the ground longer to attain more speed, then make a smooth, positive rotation to leave the ground.