Through the Wall Fins

Im currently undergoing a project that as through the wall fins, my question however is that does anyone has any good techniques for getting centering rings in past the through the wall fins? Any ideas?

Thanks

Generally any forward centering rings need to be installed before attaching fins.

dixontj93060 said:

Generally any forward centering rings need to be installed before attaching fins.

Click to expand...

+1. Glue on your forward ring(s), insert the partially finished motor mount assembly into the main airframe (I like to tape a centering ring on to the back of the motor mount assembly at this point. In fact, I make special centering rings that have large holes drilled into them just for this purpose; the centering ring will help hold the motor mount straight in the main airframe, but can be removed later), then glue your fins in place, (remove the taped-on centering ring if you used one), then apply internal fillets to the TTW tabs, and, finally, glue your rear centering ring on.

GrossApproximator said:

+1. Glue on your forward ring(s), insert the partially finished motor mount assembly into the main airframe (I like to tape a centering ring on to the back of the motor mount assembly at this point. In fact, I make special centering rings that have large holes drilled into them just for this purpose; the centering ring will help hold the motor mount straight in the main airframe, but can be removed later), then glue your fins in place, (remove the taped-on centering ring if you used one), then apply internal fillets to the TTW tabs, and, finally, glue your rear centering ring on.

Click to expand...

+1 This is absolutely the best way to install your mount for through the wall fins. It's important to realize that AFT ring is a crucial part in keeping the mount centered.

I re-read my post, and found it a little unclear. Sorry, my bad. Here's a better version:

Glue your forward ring(s) onto the motor mount, then put glue inside the main airframe. Be sure to put the glue at the approximate depth that the forward ring(s) will be at. Next, insert the partially finished motor mount assembly into the main airframe and into the glue. I like to tape a centering ring on to the back of the motor mount assembly at this point. In fact, I make special centering ring jigs that have large holes drilled into them just for this purpose; the centering ring jig will help hold the motor mount straight in the main airframe, but can be removed later. When the glue on the forward ring is dry, glue your fins in place (without getting any glue on your jig). Once that glue is dry, remove the taped-on jig, apply internal fillets to the TTW tabs, and, finally, glue your rear centering ring on. I've also heard of placing bamboo skewers in the internal fillets for added strength; it seems like a popular proceedure on TRF, but I've never tried it myself.

I have had great results with the "Wildman" technique - half the work, less chance for a mis-alignment, and as strong if not stronger when compared to "conventional" TTW construction.


All the best, James

Fdog said:

I have had great results with the "Wildman" technique - half the work, less chance for a mis-alignment, and as strong if not stronger when compared to "conventional" TTW construction.


All the best, James

Click to expand...

What is the wildman technique?

Briefly-

• Drill a pair of holes on each side of the fin slots
• Assemble & tack the motor mount in place w/CA
• 5 minute epoxy to bottom of fins
• Inject epoxy mixed w/ chopped carbon fiber into holes
• Fillet

The injected epoxy flows around and makes all the internal fillets, including the centering rings.


For more detail read this: Linky



All the best, James

Thanks.

Thanks guys!

I'll make sure to glue the two forward centering rings first, then the fins, and then finally the last centering ring. =]

One thing I learned, and especially on larger diameter rockets made from the "Estes" type body tubes, is that excessive yellow glue will cause a "pucker" at the centering ring. I wanted to make sure a 24mm cluster Fat Boy would hold together, and layed down a heavy fillet on the top, then the bottom CRs. It took a while for me to realize that yellow glue shrinks as it dries (of course it does - the water goes out!). Epoxy, on the other hand, cures by chemical reaction, and does not shrink.

GrossApproximator said:

Glue your forward ring(s) onto the motor mount, then put glue inside the main airframe. Be sure to put the glue at the approximate depth that the forward ring(s) will be at. Next, insert the partially finished motor mount assembly into the main airframe and into the glue. I like to tape a centering ring on to the back of the motor mount assembly at this point. In fact, I make special centering ring jigs that have large holes drilled into them just for this purpose; the centering ring jig will help hold the motor mount straight in the main airframe, but can be removed later. When the glue on the forward ring is dry, glue your fins in place (without getting any glue on your jig). Once that glue is dry, remove the taped-on jig, apply internal fillets to the TTW tabs, and, finally, glue your rear centering ring on.

Click to expand...

I've done this exact method with Estes kits that included tabs on the fins.

For rockets that I scratch built I did it differently, but the design of the rocket has to match. I glue both centering rings on the motor mount tube, then glue the fins on the motor mount tube and fillet everything. I cut slots in the body tube to match the fin locations, slide the motor mount assembly into the tube and glue the centering rings one at a time, first the front one from the front then the rear one from the rear. Then I fillet the fins.

Either method is very strong buy my method uses larger fin tabs so should be stronger.