I am hoping to sell an old YA A4 DF that's been in mothballs since '93.
It's never flown off grass, but I need to set it up to be able to fly off a small grass field for the buyer.

The A4 has the sport wing, OS91/Dynamax w/Performance Specialty AAC liner/piston, Boca ceramic bearings,
weight=14lbs wet. The power and rpms are there, just doesn't seem to have the thrust for grass.

Currently the thrust tube exit diameter is 4 inches. I would like to change it to 3.5 or 3" to increase the static thrust. Has one done this? What is the optimal diameter for the thrust tube outlet?

Thanks,
Keith