Also in MPR

[rsbhunter]

 

[rsbhunter]

As further explanation, the bt fin slots are pre slotted (Super DX-3) , so all I'd do is cut through one side of tab on bottom, fold tab out, creating a open ended slot that the fins will slide into/ out of. Here is a link to a video of it, it's in the first couple mins.
Thanks,rsbhunter

 

[loopy]

Not really a lot of negatives to this methodology, but it's also not always needed. The only rocket I've built with this method is my L3. Everything else I've done just leaving the aft centering ring off and doing the internal fillets through the back end. I don't really push boundaries, so doing internal fillets that way along with good external fillets has always been fine for me.

That being said, I do have some where it might have been better to do it the way you're talking about here. Rockets where the motor mount doesn't leave much room between the motor tube and the body tube. Honestly, I just don't see many negatives to doing it this way.

 

[cls]

There's a good argument to not overdoing the fin attachment. because when they do eventually break, it can't be fixed so the entire bottom section is scrap.

Butt joints and external fillets are usually enough.

Properly done, those rarely come apart in flight. Most damage is on landing, and road rash, bouncing around in the car, crushed by folding chairs and water jugs.

 

[4regt4]

There's a video of LOC's assembly of a 4" Iris using this technique. It's on their catalog page. For brevity, you can skip to about 3:20.

Hans.

https://locprecision.com/collections/rockets-4-00-diameter/products/yiris4

 

[dr wogz]

Not a fan of this method. If the fins are slightly off, they won't go back into the slots.. [the slots in the tube is your guide as to where & how the fins go. building outside, you assume you know..) also, cutting the slots removes the 'hoop strength on the tube end..

this is something LOC started doing..

 

[terryg]

I had to do this to repair a rocket that broke just in front of the fin can during a landing. It was very difficult to cut the fin slots on the repacement tube with no support on the end of the slot. It worked but it was a real pain.

 

[Art Upton]

Not a fan of this method. If the fins are slightly off, they won't go back into the slots.. [the slots in the tube is your guide as to where & how the fins go. building outside, you assume you know..) also, cutting the slots removes the 'hoop strength on the tube end..

this is something LOC started doing..

It was being done long before LOC started doing it

 

[loopy]

Not a fan of this method. If the fins are slightly off, they won't go back into the slots.. [the slots in the tube is your guide as to where & how the fins go. building outside, you assume you know..) also, cutting the slots removes the 'hoop strength on the tube end..

this is something LOC started doing..

I put the motor mount in the booster and use the slots to line up the fins while doing the initial bond. Then I remove the motor mount with the fins installed, do the internal fillets/FG reinforcement where the fins hit the motor tube, then install the motor mount assembly as I typically would. After installing the motor mount, secure the aft end of the tube to the aft centering ring. Several techniques for doing this, including putting a strip of FG cloth around the aft end to strengthen it.