Hi david,

I'm sorry - I don't know the particular airframe you mention but...

In order to get the best performance, you do need to close that gap in the intake. My advice is to NOT simply glue a ply/balsa ring in the intake as it will make a step causing turbulence. I think the smoother the airflow in the intake all the way to the fan, the better the performance.

What I would do is take some poly-ply / FG sheet / Mylar and make a cone that will glue flush inside the intake and gradually come down to the diameter of the Turbax fan. In other words, like a funnel.

Hope this helps.

Adil