Amateur/Home Built/Experimental
Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor
Flight Crew Last 90 Days 80; Flight Crew Total 4100; Flight Crew Type 20
Training / Qualification
Aircraft Equipment Problem Less Severe; Ground Event / Encounter Ground Strike - Aircraft; Ground Event / Encounter Loss Of Aircraft Control; Ground Excursion Runway; Inflight Event / Encounter Loss Of Aircraft Control
Aircraft Aircraft Damaged
Aircraft; Manuals; Weather
I was instructing a student pilot for his Sport Pilot certificate in his CC-11 homebuilt. We were doing stop-and-go landings on Runway 17.  The wind was from 220 degrees at 8 knots; with occasional gusts and direction shifts of 15-20 degrees.  On rollout after a normal touchdown at approximately 20 MPH; the aircraft swung suddenly into the wind; then swung back in a groundloop to the left. Pilot inputs from the student and myself were ineffective; the left main gear left the ground and the right wingtip struck the ground causing damage to the tip.The aircraft had been equipped with oversize 'tundra' tires; inflated to a pressure of 10 PSI per the manufacturer's recommendation. The aircraft actually rolled over on the outboard edge of the right tire allowing the wingtip to strike the ground. I believe this occurred due to a combination of factors. First; a gusty crosswind which apparently was within the operating limits of the aircraft. Second; the oversize tires changed the 3-point pitch attitude of the aircraft which may have decreased rudder effectiveness due to blanking of the tail by the wing. Third; the increased width of the tire on the ground prevented the aircraft from sliding sideways; instead acting as a pivot point on the asphalt runway. Finally; the low pressure allowed the tire to roll over; there were actually scuff marks on the entire side of the tire all the way to the hub cap.I believe there are several lessons here. Caution should be exercised when operating tundra tires from a paved surface; they grip over a wide area and are susceptible to this type of rollover when side loaded. Operating on grass whenever possible would be preferable. A wheel landing may be helpful in this scenario but at some point the tailwheel has to come down and the ability to resist a crosswind is compromised. The high deck angle induced by the larger tires is also a factor. Crosswind limits should be reduced with this combination of circumstances. The aircraft could probably have been landed almost directly into wind by landing at an angle across the runway. This should be considered a valid option for this type of slow-landing aircraft.
While doing stop and go landings in a tundra tire equipped CC-11 homebuilt; the owner Student Pilot and the Reporter; providing instruction; lost control of the aircraft and groundlooped in a moderate gusty cross wind.  The right tire was scuffed to the wheel rim and the right wingtip sustained some damage when it struck the ground.