To band or not to band

[roytyson]

So I'm building a 4" two-stage rocket and am torn on switch bands. Everything I have built has had switch bands on both staging couplers and av bays. Is there a disadvantage to not using switch bands? my thought on this build was just to go body tube to body tube from the ground up. Anything I'm missing?

 

[cls]

Many disadvantages to not using switch bands, and no real costs to having them. I regret making some rockets without them.

 

[thzero]

Many disadvantages to not using switch bands, and no real costs to having them. I regret making some rockets without them.

Ok, if there are so many... what are they?

 

[Jmhepworth]

If you use a mechanical switch or twist and tape, the band makes that easier. Without a band, you need to line up the vent holes and between the av bay and the body tube. Even if you use a wifi switch, you need to line up the vent holes. And to keep them lined up, you need to use sheer pins and screws or rivets to hold everything in place. The only pros I can think of for leaving a band off is weight and perhaps some drag. That might make sense if you are trying to squeeze out every foot of altitude. I use bands on all of mine, including my two stage rockets (although I don’t have a 4 inch—I think I need one).

 

[cls]

Ok, if there are so many... what are they?

^^^^^ as above reply from jmhepworth ^^^^^

 

[green dragon]

I've never used switch bands, even on my glass kits. glued in coupler and forward av bay bulkhead - one removable end. One less point to worry about failing, no alighnment issues, etc. Sleds slip in , usually on 1/4" all thread.

 

[Titan II]

Is there a disadvantage to not using switch bands?

No

 

[sharkbait]

No

Actually yes there is.

If you skip the band on a HED you will be loading your shear pins with thrust loads and drogue separation loads.

On conventional DD, not really a big deal either way

 

[Titan II]

Actually yes there is.

If you skip the band on a HED you will be loading your shear pins with thrust loads and drogue separation loads.

On conventional DD, not really a big deal either way

Not really. You glue pieces of coupler on the inside.

 

[bobbyg23]

I just did my first rocket without a switch band. I really like it.

 

[sharkbait]

Not really. You glue pieces of coupler on the inside.

You certainly can but that’s a lot more work than a switch band you are essentially putting a switch band on the inside instead of the outside, and providing some edges to hang up recovery gear unless you fillet the top edges well

 

[bobbyg23]

Not really. You glue pieces of coupler on the inside.

Why would you glue couplers on the inside?

 

[sharkbait]

Why would you glue couplers on the inside?

The coupler bands will take the load off your shear pins

 

[roytyson]

The coupler bands will take the load off your shear pins

not sure I follow. If I put a band in and pin them, the stress really depends on how tight I have both tubes to each side of the band when I drill the shear pin holes. Bandless, is the same principle only transferring stress from body tube to body tube, with no band in between??

 

[Titan II]

Why would you glue couplers on the inside?

What Sharkbait said. It is not the whole coupler...only about 1/2" and you taper one edge before you install it if you are concerned about the recovery gear. It is really very little work. Why do I do it? How many full scale rockets have you seen with a switch band?

 

[sharkbait]

not sure I follow. If I put a band in and pin them, the stress really depends on how tight I have both tubes to each side of the band when I drill the shear pin holes. Bandless, is the same principle only transferring stress from body tube to body tube, with no band in between??

For a (standard) DD, it doesn’t really require a switch band or an internal coupler stop band. The airframes are taking the load from one to the other, the coupler/e-bay is bolted or riveted to the upper airframe, the shear pins at the NC/ upper airframe interface do not see any thrust loading

On HED, if you don’t have a switch band or internal coupler stop band the airframe is directly on the NC and the e-bay is only connected with shear pins