Three's company - 3F3NC scratch MP capable slightly-odd roc

[Y3kankerous]

Been mulling an idea over for a while and thought it might as well see the light of day. Maybe its an interesting idea, maybe its a terrible idea, maybe its been done many time before!!
This could naturally fit as an odd-roc, but part of the aim is to make something capable of big acceleration with dual/multiple deployment so decided to put it here in MP and fingers crossed get some advice!
The concept is basically a bit like the LOC viper 3, but without a forward section. Or looking at it the other way, like an Estes sidekick but with another airframe. So it is going to be three joined minimum diameter airframes, each with its own nosecone, but with common fins. The first version will be three times 18 mm, but who knows maybe a three x 24mm could be a future project if anything good came of the prototype version.
The things I like with this are....
i. the potential to use anything from (possibly) a single A motor, up to low E impulse with three Cs... or even Klima D motors for F impulse (lets shelve this one for now tho...) or indeed any combination of the above. So it should be flyable in almost any venue.
ii. using different motors with different delays to deploy different recoveries... most usefully... a drogue on a short delay, then a chute (and either a second chute or drogue in whatever order) so as to ensure good recovery while limiting drift, particularly for the higher impulses.
I fully realise this is not going to be a high efficiency design!
Here is a very rough mock up with rubber bands and cardboard fins to show the approx idea...

 

[Y3kankerous]

Here is a very rough, first iteration OR SIM, the NC is nothing like what I have in mind and i realise that OR will probably not simulate much of the highly unconventional airframe... possible nothing at all in which case its just giving me a vague idea of stability for a given lenght and fin dimension, which would still be a good place to start.
first on three A8s which looks OK

Here is the same rocket on three D9s, which I already definitely firmly shelved and not sure why I'm even doing the SIM...

The stability would need to be much higher esp if it was actually going to attempt to go anywhere near that velocity range (firmly shelved like I said), but something to work on. This doesn't include any chute mass as yet

 

[Y3kankerous]

There are clearly a number of challenges to work on, particularly to get it MP capable.

NC design - definitely the big one, as it needs to be aerodynamically sensible as well as functional for ejection. I am favouring individual NCs rather than a compound one because I think they will eject more cleanly (can even be ejected without retention on their own streamer). Possibly off-centred tips so they create a better aero. Or could do something wacky like rotated to make it spin/corkscrew/rip to shreds. Maybe the body tubes are cut at an angle to help throw the NCs out when the eject. Probably a 3D printing job to get them symmetrical.
Joining the fins very robustly - seems like there is plenty of surface area to work with so is achievable but needs some thought, maybe some small inserts. Epoxy will help but need to be careful with more aft mass.
The body tube transition - the SIM confirms my guess that the aft mass loading will need the airframe to be quite long, so assuming I use standard BT, then its two lengths. The join is an obvious weak spot... one solution could be to stagger this (can be seen in the rubber band mock up), which would bring the total length down a little but I think would be much stronger). Plus maybe another 3D printed insert to help with alignment, like an internal rod to get the separation spot on and help with an epoxy bead.
Thrust steer - because the axial separation is small, and the fin area is large my guess is this will not be a big problem. Plus I can easily test at low power by just flying it on e.g. a single C. It would make sense to impart a very slight motor cant by having a larger separation at the aft (ie from the fin insertion between the tubes) than at the fore.
The motor mounts don't seem too difficult although there could be some nice detail for the retainer.
Lots of design decisions to be made about the size and placement of the fins, to be iterated in the SIM, plus mateial etc. Currently thinking a pretty standard but large MP type shape made of ply with a small aft overhang, not far off the SIM above.

Thats were I'm up to for now. Will try and make some sketches of some of the ideas for details as above. Very open to feedback and ideas!

Also the name is a working title... so far its either that or "three's a crowd". was also thinking of trio like the old school choc bar. Prob some better ideas out there tho

 

[techrat]

I would name it "Tri-Poli" - and see if Tripoli notices.

 

[lakeroadster]

Why not 3 nose cones?
You should be able to simulate this pretty easily in OR just by using pod's.
The Estes Side Kick is similar to what you're building here.

Looking forward to watching this build.

 

[Y3kankerous]

The sidekick is definitely one of my starting reference points (also LOC viper) altho my guess is it will need much stronger bonding between the airframes than side kick if it is going to MP.
With the OR SIM I couldn't find a way to put on three NCs... Sounds like I need to spend longer fiddling. Good to know it's possible!
My thinking with needing a more complicated NC set up than three standard-ish NCs is that to make the airframe bond strong enough (as above altho accepting I may be over doing this) it will need to basically be beaded directly between body tubes at the fore. This would then not leave clearance for each NC to pop off separately. Particularly if there was a small cant in the body tubes.
That's not too say that the NCs would actually have to be massively different. Even just removing the shoulder on the points closest the other NCs so they don't bind might be enough (altho id be worried until id tried it). One for a static ejection test maybe.
I did another very basic rubber band mock up on this to show the idea about a simple outward angled NC (see picture) and this gave me another idea. This is to go without any NCs at all, since the angled cut off is probably moderately aero. With a bit of luck they might even hum!! And the ejection charges would just chuck the recovery out the front.
This would then be 3F0NC...
I'm thinking of just giving it a go like this because it simplifies the whole thing so much I could just get on and glue it together to see what happens...