Date: 202003
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: J3 Cub
Operator: Personal
Operating under: Part 91
Flight plan: None
Mission: Personal
Flight phase: Cruise
Airspace: Class E ZZZ
ATC / advisory: CTAF ZZZ
Reporter organization: Personal
Reporter function: Captain; Single Pilot
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Distraction
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Object
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Diverted; Flight Crew Landed As Precaution
Contributing factors: Procedure
Primary problem: Procedure

Narrative: Beautiful day about an hour before sunset; time to go flying. I pushed the Cub out of hangar; hooked the tail to the tiedown and asked my wife; in front seat; to hold the brakes. I had done the preflight in the hangar but didn't turn on the nav lights until out on the ramp. After priming the engine the Continental 65 hp started on the first blade; as usual. Then I remembered I hadn't checked the nav lights and decided to walk around the airplane; giving it a wide birth since the engine was idling. Right wing; left wing; and tail lights were all operational so I boarded the aircraft; checked instruments; turned on radio and taxied to RWY 8.  After the run up we took off. On crosswind a neighbor called and informed me he saw something dragging from my tail wheel. That's when I immediately remembered I had failed to disconnect the tail wheel tie down.  I assumed the rope had broken and that's what he had seen. I also recalled a slight bump when I turned 180 degrees to align with the RWY. It occurred to me there may be something more than just the rope attached to the tail wheel. I turned east over an open field and considered what I should do. I decided I should land on a grass runway about 15 miles away with a sparsely populated route from our airport. It seemed to take forever since I made several deviations to avoid over flying any houses.  The airplane was flying normally; I did not feel any indication of more than just a rope trailing the aircraft but thought it prudent to stay away form buildings on the ground. I made a straight in approach; observed no other traffic.  When I flared for the touch down I felt a distinct bump; it happened twice then stopped as I touched down. After stopping and shutting the engine off I left the Cub on the runway and checked the tailwheel. Nothing was attached; but about 500 feet behind me I noticed a large object on the runway.  I walked to it and picked up the rope; still attached to an 8 inch ball of concrete. What amazed me the most was how could I not notice any change in the aircraft performance with that concrete attached. I checked the tail wheel and did not see any damage so I left the concrete in the trash and flew home. After several hours of going over how this could have happened I developed the chain of events.1. The ramp had been plowed from a 6 inch snow fall a few days earlier. The snow had melted and I saw where the plow had struck the tiedown I used and loosened the concrete holding the metal hook.2. The melted snow had soaked the area around the concrete softening the soil holding the tiedown.3. I usually tiedown the tail; start the engine then immediately disconnect the tiedown from the tail wheel.  This time; however; I decided to check the nav lights before releasing the tail wheel. By the time I walked around the aircraft; I completely missed the tail wheel.I did not get a chance to weigh the piece of concrete that broke out of the ground but it was fairly heavy. What strikes me most odd is I felt absolutely nothing while taxiing; taking off; and en-route that this was attached. (Aside from a slight bump when when doing a 180 on the runway.) I am going to repair the tie-down and bury the stake in the concrete below the level of the dirt so the snowplow will not be able to knock it loose in the future.  I am also going to double check; then check again the tail wheel tie down before each flight.




Synopsis: Pilot reported failure to detach tail tiedown and taxied and departed with the tiedown rope and pad eye still attached to the aircraft; requiring a diversion and precautionary emergency landing.