SA-3 Goa Semi-Scale 2 Stage with Cluster Booster

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rharshberger

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Note: I probably should have put this in the Scratch Build section, but its is LPR too.

Not long ago I discovered OpenRocket and then its neat scaling function. Using one of the STA technical drawings most likely from Peter Alway, I built the rocket full scale in OpenRocket then scaled it to a BT-60 for the sustainer. The SA-3 Goa SAM (Soviet S-125 Neva/Pechora) was fielded in 1961 making it a contemporary of the Nike Ajax, Nike Hercules among others.

The Booster is a 24mm with 2x18mm cluster, the two additional tubes seen in the pictures are for the recovery system and looks (symmetry), the booster was constructed in the in-flight configuration since on the original the fins fold forwards 90 degrees along the booster. A little liberty was taken with the fins to help with stability. The sustainer is a BT-60 with a BT-50 inner tube extending to the nose cone under 13 inches of shrouds. The nose cone is a derelict from a Commanche III that failed the Uhaul Impact Resistance Test (got crushed when moving homes). The nose requires 1.1 ozs of epoxy and lead shot for nose weight.

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24mm and 2 of the recovery tubes fitted, the Centering Rings are 1/8 inch Midwest Birch Plywood cut on my scroll saw with a homemade circle jig and then sanded to final size on another jig mounted to my Delta belt/disc sander. A 3/4 inch and 1 inch Forstner bit work perfectly for making the holes for the BT-50 and BT-20 tubes.

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Booster guts assembly with all tubes in place, centering ring on table is for the rear shroud

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Two views of booster with recovery shock cords in place, due to the fact that upper shock cord mounts will not be accessible once rockets assembled I used 12 inch stainless steel fishing leaders
to protect them from the heat of the ejection charges.

More to follow in a bit.
 
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rharshberger

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Okay here comes some more.

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Booster Outer tube added 3 inch BT from Balsa Machining Service (who has awesome customer service btw), also notice the pressure relief ports for the AirGap staging (Passport style sort of). The third picture shows the 1/2 inch thick balsa ring used as part of the interstage transition. Picture four shows the inner and outer pressure relief holes.
 

rharshberger

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Lots more to follow.

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Okay Booster fins are now attached, as is conical transition with elliptical cut outs. Conical Transition is cardstock with 4 sections of 1/16 inch balsa glued to back, which makes it fairly tough and light weight. The third photo is sustainer with out fins but tranistions in place (not seen are the BT50 to BT60 centering rings in the approximate 4 inch section of the bottom, BT50 is like 16 or so inches long with 13 inches of shroud covering it. If I build this again I will use shorter shrouds but more of them to better simulate the true shape of the Goa a centering ring is used under the joint between shrouds. The cardstock has been soaked with CA to toughen.
 

rharshberger

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Getting closer to finished.

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Assembly complete. Sustainer fins are 1/8 balsa and booster fins are 1/8 basswood, another change for a future version would be basswood fins on the upper, since one of the large balsa fins broke on the first flight (because I got the grain running parallel to the root not parallel to the leading edge :y:). Shroud around Booster motor tubes are 1/16 inch Balsa.
 

rharshberger

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Here she is sitting on the pad loaded with a D12-0 and two C6-3s in the Booster, and D12-7 in the upper stage. Recovery is dual 12 inch Mylar parachutes, and the upper stage recovers on a 12 inch Mylar chute with a 3 inch spill hole. The first flight was beautiful. She boosted straight and fast, separation is really cool because the booster is stable by itself it sort of veers off to the side trailing the tracking smoke before deploying both chutes. This picture is from the second flight after the broken fin got repaired. My next post will show some unforseen internal damage that had to be fixed.

The white paint is Duplicolor sandable light fill automotive primer. The launch site is the Tri-City Rocketeers Launch Facility near Pasco, Washington. There are no trees within almost a mile of our site and we have a 10k altitude waiver.


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rharshberger

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Now it gets ugly, after two beautiful perfect flights.....

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Center picture is where it all started, the standard BT-50 tube is not strong enough and the dual C6-3 ejection charges ruptured it on the second flight between the upper and middle centering rings (only area exposed to ejection charge pressure). It was necessary to cut the Booster apart and remove the bad section of tube. I probably will use a C6-3 and C6-5 instead of dual C6-3s in the future that way only one charge is going off at a time. Notice the burn marks on the upper centering ring, the wood underneath is not damaged beyond being sooted up. The two closed tubes in the center photo are the dummy motors that protect the parachutes from the exhaust.

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All cleaned up, the two sticks in the left photo are to prevent recovery wadding/dog barf from being pushed into chamber.

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Hopefully my solution will fix the problem. The tube in the center picture is to replace the ruptured section, the kraft colored piece is a section of heavy walled BT-50 coupler lined with metal foil HVAC tape, and the shorter outer section is heavy walled BT-50 tube covered in the same tape then the two were glued together. The right side photo is the lower section fully assembled. The left photo is just test fitting of the piece to the upper section. The ejection chamber is now reinforced to a point that using staggered delays on the 18mm motors will hopefully not allow this to happen again.

Next flight will be at the Nov 15, 2014 launch date for the Tri-City Rocketeers https://www.tricitiesrocketeers.org/. Hopefully I will get some better pictures and video as this model is fun to fly.
 

powderburner

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Very nice work there.
Looks good. Pretty nice build if this was just for flight testing.
I am looking forward to seeing a lot more pix as you finish the design and add an exterior color scheme.

And probably a smart choice to NOT make those booster fins actually pivot.
 

rharshberger

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This was a test of multiple things. Eventually I plan to refine it a little more and possible upscale it a bit for Giant Sport Scale and improve the finish quality. The 4 motor tubes on the booster can actually be moved toward center more and that will clean up the rear shroud. This one is just for flying now, but it will most likely get what appears to be the standard Soviet Paint scheme of white/light grey, with the booster rear shroud, interstage, all fins, and a wide band around the area just ahead of the sustainer fins painted a darker grey. I also have lots of pictures that show so really good Russian lettering and the control bellcranks that run to two of the sustainer fins. Hope to get the painting done in the next two weeks, along with my beefed up Blue Bird Zero (doubled the BTs for flying on F39s or other 24mm composite motors) and modded Mean Machine, plus my 5year old daughters stretched Snipe Hunter clone from Semroc.


I will probably add pivoting fins to the GSS version, and make them the proper size, also they would be lockable/pinned in the flight position since GSS requires actually making a flight with the model. Of course for modelling competitions I got lots and lots of detail to add and make correct.
 

rharshberger

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Today was a sad day for this model, after a beautiful boost and booster recovery. The sustainer got picked up by a thermal, I followed it as about .75 miles before losing sight of the sustainer as it dropped into a potato field over a mile from the launch site. I didn't think that a sustainer weighing about 4 oz, with 18" chute that had a 5" spill hole would glide that well but it did, of course my real mistake was putting the wrong chute in it to begin with the normal chute is a 12" with a 2" spill hole. It was a good day for thermals and a bad day for rocket recovery for a few fliers, at least one parachute duration models floated away, a Cherokee-D and my Goa's Sustainer.

Good news is that the boiler plate flew so well that its time to scale it up to a 6" Booster....when I get the time and money to do it.
 

burkefj

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That was a beautiful flight, sorry you lost it.
 

rharshberger

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Agreed all, it is definitely time to go big on it, but that will have to wait for the fall as I have several Honey-Do items that have to be done first, I have put them off too long prepping for my L2 so the Nike Hercules and the SA-3 Upscale will have to wait for a couple of months.
 

rharshberger

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I am just touching back on this thread to update some design change thoughts.

1) get rid of the stainless steel leaders as shock cord attachments: the reason is they are in a non-service area and the BP residue will and did eventually damage the leaders causing one to snap off, I am unable to replace the attachment point without tearing the booster apart (again).

2)change the stainless steel leaders to kevlar, and find a way to make them replaceable: probably just put a loop on each end of the kevlar and run it through the eyelet inside, using a snap swivel to join the two loops, when the kevlar needs to be replaced I can just tie a piece of string onto one loop and fish the string through the eyelet, the string will allow me to fish a new kevlar shock cord through.

Still planning on upscaling this rocket but its looking like maybe next year (2016).
 
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rharshberger

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Wow, three years later and I still haven't gotten back to this one, its still on my list of upscale to do's once I get a bit of experience with HPR staging. The LPR booster is sitting lonely on a shelf in the shop, and I am seriously considering building a new sustainer for it, as it was such a crowd pleaser to fly.
 

Ez2cDave

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Wow, three years later and I still haven't gotten back to this one, its still on my list of upscale to do's once I get a bit of experience with HPR staging. The LPR booster is sitting lonely on a shelf in the shop, and I am seriously considering building a new sustainer for it, as it was such a crowd pleaser to fly.
Some "motivation" . . . Enjoy !

Dave F.

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