Fall Away Strap on Boosters

Hey,

I've just finished my retro Estes Canadian Arrow and fancy something a bit different to the usual, so I am intending to custom build a 24mm rocket with four strap on 18mm boosters that will fall away on burnout and be recovered separately from the main sustainer.

Here are some rocksim pictures of the rough design, I intend to call it Riders on the Storm;



My question though, is what is the best method to attach the boosters for separation? I have seen a few threads on a similar matter and read an article from apogee but still unsure. The best way I have seen so far is with dowel and launch lug, however I am still puzzled as to how the booster stays safely attached to the sustainer and how it separates at burnout. Any picture examples would be fantastic. Thanks!

Since the fins are on the sustainer and not the boosters, you could make better use the "trick" that Carl Campbell used on his Delta IV Heavy model. Attach launch lugs to the sustainer and dowels to each booster so that the boosters stay attached when the rocket is upside-down and fall away when you turn the rocket right side up. Use shorter-duration, higher-thrust motors in the boosters. The boosters will push against the hooks until the thrust of their motors falls below that of the main motor then they'll fall away.

Carl's rocket had fins on the boosters, so if all the motors failed to light or some came up to power late, the rocket usually got stuck on the launch rod. In your case, the rest of the rocket should fly okay as long as the main motor ignites. So, it'll probably work a little better than the method worked for Carl.

Carl recommended using all black-powder motors and Quest Q2G2 igniters with a good 12V launch system. That should allow all of the motors to ignite at the same time.

-- Roger

I've considered this with a custom design before and unfortunately I had not came up with another alternative from those you have discussed. In the end I just ran with my initial three 24mm core and four 18mm outboards. After that one worked, I designed another based on a single 24mm and seven 18mm outboards. I hope that you can come-up with something on this, because I really like your design and whatever you come up with I could incorporate into my eight motor design. And besides, yours dropping those boosters would look seriously cool. There are some accomplished cluster builders here and I suspect someone out there has a technique that will work for you. Good luck! I look forward to seeing this fleshed-out.

Steve

Give me a little bit and I'll post some pics of the way I do it. The booster remains fixed to the rocket even with a missfire or prefire----downside--the boosters come off in two tethered pieces--not as cool as a single unit but it works and is safe.

Thanks for the reply guys. Roger I have seen this method most commonly and I worry about a booster being left on the pad or late firing and being a serious danger. Steve thanks for the encouragement, hopefully we can figure something out. Hornet Driver, i've heard of your method where the booster remains fixed but separates in two pieces, but I couldn't really picture it to figure out how exactly it does this, would be interested to see!

Ideally I want the boosters to be finless, separating in one piece, SAFE! Obviously we don't always get what we want, but there has to be a way here!

I remember seeing a couple of good threads on this topic. I'll do some research and let you know what I find.

Here's a rocket whose sustainer has a 24mm mount and whose four parallel boosters have 18mm mounts. It doesn't look much like yours but the attachment system may be useful to you. It's my Thunderbird missile.

Basically, I don't like the idea of having the boosters simply drop off as described by an earlier post; if one booster lights a bit late, the rest of the rocket will take off leaving it behind, then it will ignite and go unstable. So the boosters have their own detaching nose cones and streamers. On each booster, one pair of lugs mounted near the back mate with dowels on the sustainer which point backwards, so that this part will just drop off. Except that there's another pair of lugs mounted on the booster nose which mate with lugs on the sustainer that point forwards. So long as the booster's nose is attached, the booster is held in place forwards and backwards and can't fall off until the booster motor has burned out. A C6-0 (or B6-0) has no delay or ejection charge, but when the propellant grain burns through it generates enough forward pressure to kick out a (relatively loose) nose cone and streamer. This is the result:

adrian said:

Here's a rocket whose sustainer has a 24mm mount and whose four parallel boosters have 18mm mounts. It doesn't look much like yours but the attachment system may be useful to you. It's my Thunderbird missile.

Basically, I don't like the idea of having the boosters simply drop off as described by an earlier post; if one booster lights a bit late, the rest of the rocket will take off leaving it behind, then it will ignite and go unstable. So the boosters have their own detaching nose cones and streamers. On each booster, one pair of lugs mounted near the back mate with dowels on the sustainer which point backwards, so that this part will just drop off. Except that there's another pair of lugs mounted on the booster nose which mate with lugs on the sustainer that point forwards. So long as the booster's nose is attached, the booster is held in place forwards and backwards and can't fall off until the booster motor has burned out. A C6-0 (or B6-0) has no delay or ejection charge, but when the propellant grain burns through it generates enough forward pressure to kick out a (relatively loose) nose cone and streamer. This is the result:

View attachment 133633

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That's a great set up you've come up with.

Do you have more pictures that show where the collors are attached on the two boosters and clearly show how they interlock and disengauge with each other by the nose cone being blow off?

Close ups of how the cone is holding everything in place and launch ready would be excellent.

bradycros said:

That's a great set up you've come up with.

Do you have more pictures that show where the collors are attached on the two boosters and clearly show how they interlock and disengauge with each other by the nose cone being blow off?

Close ups of how the cone is holding everything in place and launch ready would be excellent.

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The underlined words Thunderbird missile indicate a link to my page about the model. Anything you find there which is underlined is also a link - at the time when I wrote that page I didn't know how to do embedded images.

adrian said:

The underlined words Thunderbird missile indicate a link to my page about the model. Anything you find there which is underlined is also a link - at the time when I wrote that page I didn't know how to do embedded images.

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Thank you for a fast reply. I understand about the links. What I can't visualize how the nose cone blowing off ( unless the collers and posts are attached directly to the cone) causes the coller assembly to disengauge.

I thought pictures of the whole set up assembled and disasembled would clear up the confusion on my part and allow me to visualize how these doo-dads work together.

bradycros said:

Thank you for a fast reply. I understand about the links. What I can't visualize how the nose cone blowing off ( unless the collers and posts are attached directly to the cone) causes the coller assembly to disengauge.

I thought pictures of the whole set up assembled and disasembled would clear up the confusion on my part and allow me to visualize how these doo-dads work together.

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Going round the rocket, number the boosters 1 to 4. Then boosters 1 and 3 have the lugs on the detaching nose cone; boosters 2 and 4 each have half of the collar with a forward-pointing dowel at each end of the half-collar. The collars are attached to the booster main bodies. So the left lug on booster 1 and the right lug on booster 3 mate with the collar on booster 4; the right lug on booster 1 and left lug on booster 3 mate with the collar on booster 2. The nose cones on boosters 2 and 4 play no part in the locking system.

When the boosters are attached and all nose cones are in place, then, booster 1's lugs lock booster 2's and booster 4's half-collars together on one side, while booster 3's lugs lock them on the other side. When either of booster 2 or 4 blows its nose cone, the collar is effectively broken and all the boosters can slide off backwards.

adrian said:

Going round the rocket, number the boosters 1 to 4. Then boosters 1 and 3 have the lugs on the detaching nose cone; boosters 2 and 4 each have half of the collar with a forward-pointing dowel at each end of the half-collar. The collars are attached to the booster main bodies. So the left lug on booster 1 and the right lug on booster 3 mate with the collar on booster 4; the right lug on booster 1 and left lug on booster 3 mate with the collar on booster 2. The nose cones on boosters 2 and 4 play no part in the locking system.

When the boosters are attached and all nose cones are in place, then, booster 1's lugs lock booster 2's and booster 4's half-collars together on one side, while booster 3's lugs lock them on the other side. When either of booster 2 or 4 blows its nose cone, the collar is effectively broken and all the boosters can slide off backwards.

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Well, there ya have it. I was thinking the collers disengauged because they were attached to the nose cone some how. Thank you for the information and clearing that up for me.

Luke said:

Thanks for the reply guys. Roger I have seen this method most commonly and I worry about a booster being left on the pad or late firing and being a serious danger.

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If you use Q2G2s as were suggested, and a good 12volt controller, this will not be an issue. I use the Pratt controller hooked up to my pickup's battery and was able to launch this:


I just wire all ignigters into two connections like this:

It seems sort of sloppy, but it's effective.

Some interesting solutions, i'll take a closer look this afternoon.

Think I have solved the issue myself though, and actually in a way that should make the whole rocket more interesting. Off to buy some graph paper! Pics to follow

bradycros said:

I remember seeing a couple of good threads on this topic. I'll do some research and let you know what I find.

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The Thunderbird SAM artical shows a good solution. Another good solution can be found at www.rocketryforum.com/showthread.php?20838-AstroG-Scratch-Build-Clister-2-stage-side-mount

Some drawing...starting to realise a few issues with the design. So my fix for the strap on booster design is that using the usual method, some kind of male connector on the booster will slide up and into a female connector on the main sustainer, allowing the boosters to push up on the sustainer whilst they're ignited and slide out and fall away at burnout.

BUT, the safety fix I have thought of so far is to add a second stage to the main sustainer, this will friction fit at the bottom and will have connectors for the boosters to sit on. Therefore as long as the lower stage is lit, it will thrust upwards and hold safely in place any unlit or late firing booster pods, if the stage fails to ignite but the boosters do, I'm hoping it will stay sitting on the pad rather than making an underpowered launch with no way of ejecting the main chute.

Planning on using 4 x C6 for the boosters, a D12 for the second stage that will stage into a small B6 at separation. Whole design is currently around 40" high, BT60 to BT80, with 18" BT55 boosters.

Would appreciate some feedback. Questions are, do you think the attachment method is safe and will work? Worried that the C6 motors thrust faster than the D12 and will leave it behind. Is the overall design too big for the power? Does staging a D12 into a small 18mm motor make sense? And confusing me most at present, how the hell do I launch this thing?! Rails would be preferable but obviously there's nowhere to put the buttons or get the rail close to the sustainer!

Luke said:

And confusing me most at present, how the hell do I launch this thing?! Rails would be preferable but obviously there's nowhere to put the buttons or get the rail close to the sustainer!

View attachment 134073

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1 Put a standoff on the series booster (1st stage) for a button
2 Lose the BT80 payload section and stay with BT60 all the way up
3 Use a rod and put the lugs on the payload section and the side of a fin

Mike

Awesome. The engineering in functional, fall off boosters have some creative solutions. Subscribed!

There is also the interlocking tab method of the ARC 18/24. Has always worked on my kit, three launches on 4 A8-3 fall away boosters and a D12-5 in the core. A bit of work to build but it is said to work on even a misfire, and you don't have to worry about the boosters falling off at the pad before the launch.

Struggling with the stability of this thing, so many motors at the back means a lot of nose weight required, which is bringing down the altitude drastically. argh.

Luke said:

bringing down the altitude drastically. argh.

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Which is? And what are your expectations?

Luke said:

Struggling with the stability of this thing, so many motors at the back means a lot of nose weight required, which is bringing down the altitude drastically. argh.

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The parallel staged rocket pictured in Stine's Handbook of Model Rocketry has the strap ons at the nose which would help with the CG issue.

I am aiming for 1000' area, currently it's coming up on rocksim at about 12-1500', obviously once the boosters separate and the final C6 kicks in it's taking it most of that distance.

Problems are that the take off weight is quite high for the motors and so it's maybe too slow off the pad. The stability margin is quite low also. I think i'm getting there now though, may shrink the design a little which I guess would help with these issues? Then start building the mark 1.

Will.......strap on boosters on top are nowhere near as cool.