Andy,

Attached are 3 photos of the Nelson adapter for the TD 0.020. It is made on a lathe, no way around that. There is very little material between the ID and OD of the adapter requiring that it be made from steel. I made one from aluminum a while back and it broke after a few uses. I was hoping that someone worked out the best combustion chamber geometry for the TD preferably running on about 65% nitro with lots of proplyene oxide for the turbo plug

With a turbo plug one could make the adapter from aluminum and have sufficient wall thickness.Given a lathe and a bottoming tap the part is relatively easy to make with only the external thread being a bit of a pain to cut on the lathe. Even with a quick change gearbox I am not a fan of cutting fine threads especially in steel.

Cutting the female thread for the turbo plug can easily be done using a tap available from Enco or MSC for about $4.00. They only have plug taps in the required size but they can be easily ground to serve as a bottoming tap.

By the way I make lots of heads for nostalgia and modern engines for the Neslon plug for fellow free flighters. In general the Nelson plug properly setup on an old nostalgia engine will add about 400 rpm and on a modern engine one can often get another 1000+ rpm.

Bob