We transmitted emergency because we started with a burning smell on the take off roll. Called emergency at about 300 ft. As the aircraft was just out of maintenance we were unsure whether this was a transitory phenomenon due to some form of burnoff of residue or what?
By 500 ft we were turning downwind to land ASAP. Calling mayday was superfluous as we were in the circuit and in constant contact with a most helpful and encouraging ATC/ tower who cleared the way for us.
We stopped on a taxiway and fuel off, master off, mags off and @@@@ off. The firies put it out. Damage about $12000.
If we had been out of the circuit and more than say, two minutes away when smoke started, it would have been a mayday call.
We were @#$%ing lucky.