Boosted Arcas as a two stage project

mikebpd221

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I'm looking at trying my first two stage project and selected the first boosted Arcas as a model to emulate. Lots of good kit models of the HV sustainer although I found what appears to be an odd artifact in the first boosted version. I've seen photos of the first boosted version that have the extended fin profile common to all of the HV variants but it retains the boat tail rear end of the single stage version. I've added my project inspiration photo below. I'm curious as to how the interstage coupling was accomplished with the pictured arrangement and how best to incorporate it into a one half scale model. I'm using the 2.2" MAC Performance kit as a base for the HV ARCAS and I had an extra boat tail in the parts bin that fits that body tube and a 29mm motor mount. The museum displays I've seen of the single stage Arcas also have a flare at the end of the boat tail, a detail the Semroc version includes in their model. I'm at something of a loss as how that seats in the interstage on the booster. I'm thinking a flat ring at the top of the interstage of the same external diameter as the body, with a stepped inner diameter, the outer part for the boattail flare, and an inner diameter just larger than the motor retainer. I'm planning on using a slimline retainer to keep the outside of the retainer as small as possible. I figure this would allow for a seating ring that measures 1/2" thick ring with the same height divided into the two steps. Small pins set into the flare or raised notches at the fin roots would prevent rotation between the two stages prior to drag separation. I'm going to prototype the interstage before I go anywhere else on the build since that's the challenge I don't have worked out yet. This group definitely has members more experienced than me at this and I wanted to get some input to aspects I may not have considered. I've seen the NASA report on their sounding rockets that's cited in a number or ARCAS threads and that really falls short on design specifics. I'm surprised to see that no one seems to have done the build I'm contemplating, unless the early two stage design was abandoned after limited launches because it just didn't work very well. At any rate, input is appreciated.
 

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mikebpd221

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I managed to find a single historical photo of the booster for the first generation Arcas. Definitely not a simple, bayonet style connection. The picture shows friction fitted clips that extend up the fin roots. The approach clearly worked, but I don't think I can duplicate that structure for my project. I also found the original booster was designed to fire in conjunction with the sustainer. That's not something I'd like to see in mine. I've opted for the Boosted Arcas II design instead which is far simpler of a build and more flexible. Both stages can be made for motor or electronic deployment and it sims stable with almost every 38mm to 29mm motor combination. I got started on the construction this weekend and the sustainer is coming along nicely. I'll see about getting some build photos posted I will say that I love the MAC Performance phenolic canvas. Machines very cleanly, sands easy and is not far behind fiberglass for strength. I can see that stuff becoming a new favorite for future builds.
 

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mikebpd221

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Finally making some progress on this as a build instead of just a concept. Construction on the internal components for the sustainer is moving along and I got the interstage coupler fitted. The fit is a touch snug still but I'll do the final adjustment for that when I have the booster section finished. I'm really happy with how it turned out. Now I'm on to setting the location for the internal electronics in the mid body bay. I went with a Raven to handle the sustainer ignition and back up ejection charge. The booster electronics have simpler demands so my Missileworks RRC2 will handle that. Here are a few photos of the build as it moves along.

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mikebpd221

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Moved on to the booster section this weekend. Similar construction methods, just with LOC plywood and tubes. I did a fiberglass lamination on the tubes to cover up spirals and to add some rigidity. Fins got edges beveled and a layer of fiberglass as well. Everything fit up nicely and is rock solid. I used an Additive Aerospace sled for the AV bay. Still on working on mounting charge wells, but in a happy accident, the banana plug jacks I had left over from my launch controller work perfectly for the electrical connections. Getting close to where this turns into a rocket instead of a bench project.
 

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PeterAlway

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I've been doing some fix-up work on my scale drawings this month, trying to get them all in shape for an eventual RotW V, and I stumbled into a subject that I had forgotten I'd drawn. I remember someone asking about the Boosted Arcas some weeks ago, and I see this thread is revised, so I hope this is of some interest. Boosted Arcas 16.GIF
 

mikebpd221

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That was exactly what I was looking for at the start of this project but couldn’t find. Thanks for putting it out there. If I ever consider a new version (read bigger) I may have to try this configuration.
 

Ez2cDave

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I've been doing some fix-up work on my scale drawings this month, trying to get them all in shape for an eventual RotW V, and I stumbled into a subject that I had forgotten I'd drawn.

Peter,

The upcoming ROTW V is great news . . . Will all of the Supplements be included in it ?


QUESTIONS about the Interstage on your drawing :

( 1 ) Do you have dimensions for this section ?

( 2 ) Do you have any photo's of that particular Interstage, as it looks very different from others I have seen ?

Thanks !

Dave F.

INTERSTAGE - CROP.JPG

1618411524422.png



arcbooostedarcas1 - LARGE.jpg


BOOSTED ARCAS - Large.jpg


1618411640368.png


1618411683315.png


1618411811715.png
 
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PeterAlway

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Honestly, I drew that a couple of years ago--I didn't remember drawing it, let along the process of sorting it out. I may re-examine it later.
 

mikebpd221

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Sorry for letting this thread go dormant for a bit. After Mr Alway added his drawings, I revisited the original booster configuration for my build. I ran a couple prototype configurations past my prefect's RSO's and more experienced club members to get some input as well. It was definitely worth the second look and I have a much more solid build going on now. The interstage coupler was rebuilt as the prototype was just a little wobbly. Instead of building up layers of cardboard tube, I went with a phenolic centering ring to go from the 38mm tube at the center to the 54mm airframe. This nested on top of a 3" G10 ring with 38mm center. The G10 got slots for holding the forward vanes as well as some holes for supplemental reinforcing screws. I drew from Jon Coker's ARCAS booster and used a similar method for adding the open truss section. Threaded inserts on both ends terminating in plywood rings mounted in the same jig as the G10 ring. Alignment stayed spot on through drilling the holes and mounting the inserts. The truss detail was made out of 1/2" aluminum tube and 1/4" plastic tube. The aluminum got threaded inserts on both ends to keep everything centered for the stainless #10 threaded rod. The whole assembly went through several test fits to make sure it was solid and everything stayed straight and true. Final assembly of the interstage was done with epoxy in all of the threaded connections. I added the vanes to the top of the interstage using the sustainer as an assembly guide. The vanes are 54mm thin wall fiberglass with a G10 rib down the center that also fit into mounting slots in the top ring. These got epoxied into place with fillets added at the base. Once that cured, I extended the screw holes into the epoxy and added the screws as a final reinforcement for the connection. After everything was assembled, it got gap filled, sanded, refilled, and resanded. I'm thinking a 3d printer is definitely the way to go instead of all that. At any rate, everything fits nicely and the booster joins with no lateral movement. It slides off cleanly and should have no problem with drag separation. Dimensions are not exact to any of the source drawings or photos as my interpretation of the design ran up against making a flying model out of what parts I had available. I'm still pretty happy with the result and am hoping for a few good days to get some paint on this thing.
 

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PeterAlway

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Since I last checked in here, I had the opportunity to get my hands on an actual booster to measure. I don't have a drawing done yet. but I can shed some light on this. The doodads you have to hold the sustainer are essentially correct with a T cross section like you built, though the real ones are a bit simpler. The support struts are siimple cylinders, and the wider parts are actually plastic doodads that slip over the struts. That's why you see the simple struts in some images, and the struts that are thicker near the bottom in some. Unfortunately, I need to get some booklets ready to sell NARAM before I can take the time to draw up my measurements.
 

mikebpd221

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I appreciate your attention to detail in finding solid examples of the rockets you're documenting. I'd noticed the same differences in some of the source photos I've found and just chalked it up to the engineers trying different approaches during the program.
Personally, I'm just glad to take on the challenge of making the flight part work, with a nod to what came before as inspiration. So much more of a teaching tool for my son and I than just building from a kit. The challenges for the model maker are obviously different that that of the historical mission makers, and the solutions are going to be as well. I'm just glad to be able to keep a little bit of both in what I bring to the range. Please keep the inputs coming. This project was intended to be a conversation starter as much as a flight model.
 
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Ez2cDave

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Since I last checked in here, I had the opportunity to get my hands on an actual booster to measure. I don't have a drawing done yet. but I can shed some light on this. The doodads you have to hold the sustainer are essentially correct with a T cross section like you built, though the real ones are a bit simpler. The support struts are simple cylinders, and the wider parts are actually plastic doodads that slip over the struts. That's why you see the simple struts in some images, and the struts that are thicker near the bottom in some. Unfortunately, I need to get some booklets ready to sell NARAM before I can take the time to draw up my measurements.

Peter,

Very cool . . . Looking forward to seeing your drawing(s) and, hopefully, some nice pics !

Dave F.
 

mikebpd221

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Very cool. I can see a lot of details with mine that I got wrong, but if I ever fail to recover the booster, I'll be able to make a Mark II version more faithful to the original.
 

mikebpd221

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Good news to report from the field. After two flights of the sustainer stage things are looking good. All of the electronics have tested out and now it's just a matter of selecting the right booster/sustainer motor combination to fly. The only real disappointment was that the original camera system I had built into the sustainer turned out to be garbage, so I need to try something else. Ground video just isn't going to cut it for a two-stage flight.
 

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