Filling the Gap In Slots Behind Fins

[LMazza]

Hey, I've searched the forum and I couldn't find anything on this subject. My question is, how do you fill the gap behind fins in rockets in which the MMT and fins have been inserted after assembly?

I have already seen somewhere that you can take some of the removed BT and glue that in the gap but does anyone have their own method? Thanks in advance.

 

[eugenefl]

Greetings! Interesting you bring this up. I suppose you are referring to the empty slots behind the fins after the fin can has been inserted into the airframe... if so, I basically take a piece of the cut out fin slot and trim it to length. Typically, the aft centering ring is exposed which makes for a nice gluing point. I usually just coat the exposed edges of tubing, exposed CR, and bottom of fin with CyA and press the little excess piece of tubing in place. Once it's dry, use some FnF to fill the grooves. Sand a bit and it's ready to prime over. I know this is basically reiterating the method you stated previously, but I don't know how much easier this can get.

 

[Stymye]

you never mentioned
how big is this rocket? bt-60 , 6" ?

 

[Ray Dunakin]

Originally posted by LMazza
Hey, I've searched the forum and I couldn't find anything on this subject. My question is, how do you fill the gap behind fins in rockets in which the MMT and fins have been inserted after assembly?

I have already seen somewhere that you can take some of the removed BT and glue that in the gap but does anyone have their own method? Thanks in advance.

There are various solutions, depending on the design of the rocket. For some rockets, you can simply have the fins extend all the way to the aft end of the rocket. Or have the aft centering ring in position there, so that it supports whatever you use to fill the gap.

On most of my rockets, the aft centering ring is recessed quite a ways into the rocket to allow a stage coupler to fit. (The forward end of the stage coupler is slotted to fit around the fins.) I usually cut a 1/2" ring of airframe tube, slit it so it can expand, and fit it over the outside of the airframe, covering the fin slot gaps. I glue it in place and make a smooth "fillet" along the forward edge to reduce drag a little. This method does result in a bit more drag (basically it widens a short section of the airframe) but it also makes the aft end of the airframe very sturdy.

 

[Silverleaf]

1) Measure from the point right below the fins to the end of the rocket/tube.

2) Take a piece of card stock and cut a piece to wrap around the rocket.

3) Attach with Wood or white glue, then fill in the cut with wood filler, sand smooth and paint

4) Smooth transition, with little drag results.

 

[LMazza]

All great ideas. I'm still not sure which method I'll use yet but it's looking like I will glue in some scrap BT. (In the slots.) I am lucky in this regard because I kept the excess that I cut out.

Stymye, it's a 3" BT.

Thanks again guys!