Mounting Switch Bands into the Payload Bay

[MidOH]

I have a couple medium power rockets where I simply glued it in.

On the 4" I'm building, I'm using some wood inside the payload bay coupler, and some 4-40 blind nuts from an airplane. Only because everyone else is bolting payload sections together. Monkey see, monkey do. I'd rather still just glue it in.

Remove the boosters shock cord, unscrew the lower bulkhead, pull on the chute, and the sled and everything comes right out the top of the rocket.

 

[AlexBruccoleri]

For rail buttons, on 5 inch diameter and lower, I install 8-32 Rotaloc nuts and switch between 1010 airfoils and regular 1515 buttons (most of which have a hole for 8-32 screws).

For 6" diameter and above, I install 1/4"-20 Rotalocs to switch between 1515 airfoils and Unistrut buttons.

Scott over at SCP is the only one I am aware of making airfoils right now: https://scpconcepts.com/airfoil-rail-guides/. The ones you buy from Apogee, Onbadhawk, Giant Leap, etc are all made by him.

You can take a look at the booster section of my Darkstar Ultimate build to see what I mean: http://www.mountainmanrockets.com/i...uilds/6-inch-wildman-ultimate-darkstar-build/

Nice build on the Darkstar! Couple other questions...Are the 1515 airfoil buttons stronger/bigger than the Aero Pack ones? Do you think the Aero Pack buttons are an issue on large rockets? My understanding is the rail is the main issue and even a 1010 button/rail would be fine if it was on a truss, though I am not sure.

Also regarding the Rotalocs. Did you need to machine the inner part of the button to fit around the part sticking through the airframe?

 

[mtnmanak]

Nice build on the Darkstar! Couple other questions...Are the 1515 airfoil buttons stronger/bigger than the Aero Pack ones? Do you think the Aero Pack buttons are an issue on large rockets? My understanding is the rail is the main issue and even a 1010 button/rail would be fine if it was on a truss, though I am not sure.

Also regarding the Rotalocs. Did you need to machine the inner part of the button to fit around the part sticking through the airframe?

I don't think the airfoils are any bigger or stronger - in this use-case, I wanted to be able to switch between Unistrut and 1515 buttons. The Unistrut buttons require a 1/4"-20 screw. Most of the 1515 buttons I found (including the Aeropack ones, I believe) have a hole sized for 8-32. I tried boring the hole out on some of the regular 1515 buttons with a drill press, but despite some success, the hole usually was a little off center. Then I realized the 1515 airfoils were already sized for 1/4"-20 screws - problem solved!

I think 1010 buttons work all the way up to some pretty big rockets, but that 6" Darkstar will almost always be on the away cell, so those rails are pretty much always 1515 or Unistrut. Loaded with an N motor, this rocket is about 70 pounds on the pad - I wouldn't want to trust 1010 buttons to something that heavy.

For the smaller rockets with the 8-32 Rotalocs, the same issue presented itself. The 1515 buttons worked fine, but all the 1010 buttons I found were holed for 6-32 or smaller. The 1010 airfoils are already set up for 8-32, so perfect!

I did not machine the Rotalocs - I just gently bent them out to match the curvature of the rocket tube and then JB welded them on.

 

[mtnmanak]

Alex - Next time we are at a launch (maybe URRG or Metra in the Spring?) - come on by and we'll take a look at some of these installs in person! I will be flying at MDRA this winter and plan to put both the Darkstar and the AGM-33 up on N motors at Red Glare if the weather is good. May also do the same at URRG before the corn and soy beans get too high!

 

[AlexBruccoleri]

I don't think the airfoils are any bigger or stronger - in this use-case, I wanted to be able to switch between Unistrut and 1515 buttons. The Unistrut buttons require a 1/4"-20 screw. Most of the 1515 buttons I found (including the Aeropack ones, I believe) have a hole sized for 8-32. I tried boring the hole out on some of the regular 1515 buttons with a drill press, but despite some success, the hole usually was a little off center. Then I realized the 1515 airfoils were already sized for 1/4"-20 screws - problem solved!

I think 1010 buttons work all the way up to some pretty big rockets, but that 6" Darkstar will almost always be on the away cell, so those rails are pretty much always 1515 or Unistrut. Loaded with an N motor, this rocket is about 70 pounds on the pad - I wouldn't want to trust 1010 buttons to something that heavy.

For the smaller rockets with the 8-32 Rotalocs, the same issue presented itself. The 1515 buttons worked fine, but all the 1010 buttons I found were holed for 6-32 or smaller. The 1010 airfoils are already set up for 8-32, so perfect!

I did not machine the Rotalocs - I just gently bent them out to match the curvature of the rocket tube and then JB welded them on.

It would be great to chat in person. You have some slick building techniques. Maybe this will be near the end of the button chat online. The Rotalocs looks like they have a piece that sticks out. Hexagonal in cross section. Does that just act like a standoff or does the Unistrut button contact the airframe?

 

[rharshberger]

Was just looking at Rotalocs, looks like the maker of PEM Nuts (self clinching nuts) Penn Engineering also makes a version called VariMount in nut, stud, and t-nut styles among others.

https://www.pemnet.com/fastening-products/pem-varimount-fastening-system/

 

[mtnmanak]

It would be great to chat in person. You have some slick building techniques. Maybe this will be near the end of the button chat online. The Rotalocs looks like they have a piece that sticks out. Hexagonal in cross section. Does that just act like a standoff or does the Unistrut button contact the airframe?

Depending on the airframe thickness, some of the actual threaded nut will stand proud of the outside airframe surface. The Composite Warehouse/Madcow tubes are a little thicker, so the nut is almost flush. The Wildman tubes are thinner and more of the nut rises above the surface. I just use a washer to fill the gap. In the photo below, the washer is 5/64" thick and works perfectly for the 6" Darkstar.

A couple other nice things about "modular" button mounts: First, you can transport the rocket without anything sticking out. I have broken off a few rail buttons/lugs while transporting my rockets in the past. Second, you just need a small amount of kit to accommodate all your rockets. The little bag of button parts shown below covers all my HPRs at a launch.

 

[mtnmanak]

Was just looking at Rotalocs, looks like the maker of PEM Nuts (self clinching nuts) Penn Engineering also makes a version called VariMount in nut, stud, and t-nut styles among others.

https://www.pemnet.com/fastening-products/pem-varimount-fastening-system/

I saw these too and would love to try them! If anyone knows of a vendor that sells them (in less than industrial quantities), that would be cool. I don't think McMaster-Carr carries them.

 

[AlexBruccoleri]

Depending on the airframe thickness, some of the actual threaded nut will stand proud of the outside airframe surface. The Composite Warehouse/Madcow tubes are a little thicker, so the nut is almost flush. The Wildman tubes are thinner and more of the nut rises above the surface. I just use a washer to fill the gap. In the photo below, the washer is 5/64" thick and works perfectly for the 6" Darkstar.

A couple other nice things about "modular" button mounts: First, you can transport the rocket without anything sticking out. I have broken off a few rail buttons/lugs while transporting my rockets in the past. Second, you just need a small amount of kit to accommodate all your rockets. The little bag of button parts shown below covers all my HPRs at a launch.

View attachment 500974
View attachment 500976

Got it and looks very slick. The Aero Pack design is similar and a flange nut is left in the rocket and buttons can be swapped out easily.

 

[MidOH]

Great Planes 4-40 blind nuts is what I'm goin to try on my Loc 4.

 

[Banzai88]

NM

 

[kramer714]

I use floating nutplates (day job stuff) MS21075-06 or -04 These are designed to be mounted to thin fiberglass and hold VERY well. You can install them without a jig, but the jig makes it easier. Two small countersunk rivets (nut plate rivets) hold the nut plate in place. We use THOUSANDS of these at the 'day job'

top picture - nutplate used to mount a rail button
middle picture - a screwed in place coupler coupler with nutplates on top, bodytube screwed into a couple on the bottom
Bottom Picture - nutplates attached to the inside of the coupler.


Mike (actual aerospace engineer) K

 

[krislhull]

I use floating nutplates (day job stuff) MS21075-06 or -04 These are designed to be mounted to thin fiberglass and hold VERY well. You can install them without a jig, but the jig makes it easier. Two small countersunk rivets (nut plate rivets) hold the nut plate in place. We use THOUSANDS of these at the 'day job'

top picture - nutplate used to mount a rail button
middle picture - a screwed in place coupler coupler with nutplates on top, bodytube screwed into a couple on the bottom
Bottom Picture - nutplates attached to the inside of the coupler.


Mike (actual aerospace engineer) K

View attachment 501791View attachment 501792View attachment 501793

I never thought about using nut plates… I have a bunch at home, and can easily get them at work as well.

 

[mtnmanak]

Thanks for looking into that. I looked at McMaster and they have a huge selection. Do you have specific nut and washer suggestions for common tube sizes?

Also the cost of LumaDyne's is high when compared to McMaster. If they are a custom part they are priced fine. Also they seem worth the money if they are easy to use and reliable. Compared to motors, most building supplies are cheap....so it is best to get high quality parts in my opinion.

Lumadynes are back in stock - more expensive than ever, about 10% more than they used to be:

https://www.apogeerockets.com/Building-Supplies/Misc-Hardware/Aluminum-4-40-Tube-Fasteners-3-pk

 

[AlexBruccoleri]

Thanks! I ordered a few, though I came up with something nice too. I combined the PEM nuts on the inside with aircraft finishing washers. The result looks nice so far. See link below. Anyway I like trying slick solutions out and happy to use Lumadynes,

https://spenceraircraft.com/hardwar...490-hole-dia-0-193-0-223-alt-part-603-10.html

 

[mtnmanak]

Thanks! I ordered a few, though I came up with something nice too. I combined the PEM nuts on the inside with aircraft finishing washers. The result looks nice so far. See link below. Anyway I like trying slick solutions out and happy to use Lumadynes,

https://spenceraircraft.com/hardwar...490-hole-dia-0-193-0-223-alt-part-603-10.html

Nice! Do you have any pictures of using the finishing washers in practice? Would love to see how they turned out - so much cheaper than the lumadynes!

 

[FredA]

I use nut plates (t-nuts) for rail buttons....but use them reversed from the usual usage.
I get the short version where the length of the threaded part pretty much matches the thickness of the rocket wall.
I'll drill a tight clearance hole for the threaded part and put a dab of epoxy on the plate and push into the hole.
I use a screw and oversized nut to pull them to the body and hold them tight and square while the epoxy sets.

This method "lines the hole" with threaded metal and, more importantly, presents a pretty flat, snag-free surface on the inside.

 

[AlexBruccoleri]

Nice! Do you have any pictures of using the finishing washers in practice? Would love to see how they turned out - so much cheaper than the lumadynes!

I will post some pictures. I used this on a LOC LaserLoc 313. Even though buying all the pieces is cheaper, I prefer to give business to rocket people when possible. Unfortunately they were not available.

 

[AlexBruccoleri]

Here are two pics of the finishing washers. Hope this helps!

 

[mtnmanak]

Here are two pics of the finishing washers. Hope this helps!

Nicely done!