In order for the locking basswood strip to work, the positioning of the centering rings is critical.
Here's step nine from the Semroc instructions.
The rear ring is glued 3/8" from the rear of the tube. The upper ring is 2 1/4" from the rear.
The lower ring has the larger notches for movement of the engine hooks.
The upper ring has the larger rectangle notch for the locking basswood strip that glues inside the body tube.
The Centuri style mount uses the appropriate ST-7 tubes. The fit was tight so I enlarged the holes slightly by wrapping sandpaper around an used engine.
The basswood locking strip was used to double check the spacing between the centering rings before glue fillets were added.
Notice the large notch in the upper ring. The notch slides over the basswood strip. The (no notch) lower ring stops the mount from going any further up into the tube. A quarter turn of the mount locks it in place inside the body tube.
GOTCHA: The thin "points" on the centering ring crescents can break off. Carefully slide the assembly together.
Kudos to the genius of Semroc's late Carl McLawhorn. He designed a similar system for the SLS series (Hustler, Aero Dart, Explorer) as well as the SLS Laser X et al. Instead of a single basswood strip there were notches in the fore centering ring for the TTW fins and notches in the fins to twist-lock the centering ring/motor mounts. But you have to carefully assemble the motor mounts precisely so everything fits right. Brilliant.
ReplyDeleteHi BAR,
DeleteI had a Semroc Explorer with the TTW, engine mount locking fins. I thought that was a great idea.
This one has surface mounted fins, Carl found a great way to adapt!