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off center vent band

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Idunno

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I bought a missileworks 54mm ebay sled where the switch mount is at the end of the sled. For my 7 inch ebay this means my vent band will be off center with something like 1.5 inches of space on one side and a 4.5 inches on the other side. I can't really think of any reason why this would be a problem but before I glue is there anything inherently bad about an off center vent band? Thanks!
 

MikeyDSlagle

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Yes and no. Make sure the 1.5" side is the side you will be holding in place with rivets/pins/screws etc. It may be prone to binding if used as the loose end.

I try to have at least a caliber on each side, which would be 2" or so.

You do know a switch band isn't necessary?
 

AdAstraPerAspera

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You do know a switch band isn't necessary?
I've flown dual deploy without a switch band plenty of times, works great. I'm not sure I would trust the plastic rivets in this setup, but with screws and a t-nut backing you'll be fine. If your rocket is fiberglass or the MAC canvas phenolic you can probably get away with no backing for at least a few flights. I've had the holes start to open up after a number of flights doing this with PML quantum tube. If it's nut backed this doesn't really matter, though. I would put the switch/vent hole on the screwed together side, not the separating side, that way you can be sure the hole in the airframe stays lined up with the hole in the coupler.
 

MikeyDSlagle

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I've flown dual deploy without a switch band plenty of times, works great. I'm not sure I would trust the plastic rivets in this setup, but with screws and a t-nut backing you'll be fine. If your rocket is fiberglass or the MAC canvas phenolic you can probably get away with no backing for at least a few flights. I've had the holes start to open up after a number of flights doing this with PML quantum tube. If it's nut backed this doesn't really matter, though. I would put the switch/vent hole on the screwed together side, not the separating side, that way you can be sure the hole in the airframe stays lined up with the hole in the coupler.
Yep well said. If I got room I often use wood blocks and threaded inserts. That surely holds. Not sure the OPs 54mm will have room for that though. I don't much trust a threaded connection if it doesn't have some sort backing backing, in which case I'll use rivets.

So...in this particular situation I would probably ditch the switch band.
 

Chris_H

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The least invasive compromise is to modify or abandon that sled to adjust the switch placement. The 1.5 seems a little short, and the 4.5 is slightly long for a 54mm.
 

AdAstraPerAspera

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You could also use the switch band, centered on the coupler, but put switch access holes through the non-separating section of airframe, same as if you didn't have the switch band. That will take the stress off of the rivets or screws, but leave plenty of coupler in both airframe sections.
 

MikeyDSlagle

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But then what would be the point of the switch band? Well ... sampling ports I suppose.
 

GaryT

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I have never used a switch band, 1 I don't like them and 2 with the way I set up my Av-Bays I have no use for them. If your setting up some type of switch you'll activate from the outside? remember you don't have to use one of the static port holes to activate the switch, just make a separate hole for the switch all by itself.
 

AdAstraPerAspera

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But then what would be the point of the switch band? Well ... sampling ports I suppose.
It would transfer the stress better than a couple holes with bolts through them (assuming there switch band is glued to the coupler), and preserve the length on the rocket.
 

Idunno

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For those who don't use a switch band, is it just the rivets to the top section holding the ebay in place? I'm new to high power so not sure how that works.
Drilling an extra hole on the side held together with rivets and keeping the band in the middle sounds like a better idea than an off center vent band. I guess then I would have 4 vent holes instead of 3 in the ebay section.
 

Flyfalcons

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Yes I have two rockets without a vent band, six holes total alternating between sampling port and screw. I use bolts with T-nuts inside, not plastic rivets. Very strong connection, and I like having only one break point mid-tube instead of two.
 

GaryT

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This is my SBR Fusion Kit, I have 3 vent holes around the Av-Bay and 3 screws and nuts around the Av-Bay. I use a heavy duty push button switch for turning on the altimeter. I have a T Allen wrench that fits the small hole for turning the unit on and off. Been using this set up for over 10 years from G motors up to O motors.





 

manixFan

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For those who don't use a switch band, is it just the rivets to the top section holding the ebay in place? I'm new to high power so not sure how that works.
Drilling an extra hole on the side held together with rivets and keeping the band in the middle sounds like a better idea than an off center vent band. I guess then I would have 4 vent holes instead of 3 in the ebay section.
Yes, you can use plastic rivets. I've used them on everything from 29mm to 7.5" 50lb+ rockets flown on N motors. You have to do a bit of math to calculate the load on the rivets but they are very strong in shear. While I have used them on 'cardboard' rockets, they work much better with phenolic or any kind of fiberglassed tubing. There are many sizes available and you need to make sure you get the right length so you can fully seat the head of the rivet. Too short and the fingers can't expand properly. I consider them to be single use. Several years ago I bought a variety of sizes in packages of 100 each and have yet to run out.

Every time plastic rivets come up there is always some pushback on using them for large rockets. But they are no better or worse than any other system.


Tony
 
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David Schwantz

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the nice thing about rockets is there are many ways to do the same thing. I have done both switch band and no switch band. If You do not use one you can put the pull pin right in the joint between the two tubes. This way you get the full length of the coupler on both sides. With a switch band you can put the switch just about anywhere you'd like. I do not use plastic rivets myself, although I know they work well. I like to use steel 2-56 screws with a ply plate and blind nut on the inside. I also use this setup for the shear pin mounts. Will work with all kinds of tubes. Also makes getting the broken shear pin part out really easy.
 

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