# Sparrow-Arcas

### Help Support The Rocketry Forum:

#### daveyfire

##### Piled Higher and Deeper
For those of you that know me, you know that I've built many Arcases (Arcai?) in my rocketry career. Starting with the Aerotech kit, it's been a constant feature of my fleet, in both 2.6" and 4" versions. My AT version lost a fin to a rough lakebed landing (never to be found again), and my revamped 2.6" version with a 38mm mount shredded spectacularly on an I435T while I was trying to do a 7th grade science project (whaddya expect, it was LOC tubing!). I currently own a 4" model which has flown successfully seven times.

I've had some flexible phenolic sitting in my garage for a couple years, waiting to be made into a new 2.6" Arcas model. At long last, it is being assembled. One change, however: this one is to be staged with a 4.5" Sparrow booster. Oh, and one more: it has a 54mm motor mount.

I began construction by cutting to length the tubing, and laminating it with one layer of 6 oz. fiberglass. At 2.6" diameter, the tubing was already pretty strong. I know for a fact that 54mm cardboard tubing unreinforced can handle Mach, so phenolic laminated with glass should definitely be up to the task.

With such small clearance between the 54mm motor tube and the 2.56" ID of the body tubing, a Carbon/Kevlar laminated tube coupler is used as the stage coupler. Since the fins have (relatively) short root chords, I elected to simply surface mount them. They were tacked into place using 5 minute epoxy. I then added my traditional chopped carbon/fumed silica/Aeropoxy fillets for a base. This assembly was then laminated with a layer of Carbon/Kevlar cloth for super strength. At the moment, it is awaiting final trimming and a veil layer of tight weave glass cloth to make finishing easier.

All that's left for the sustainer at the moment is to build the electronics bay, install the motor mount, add rail buttons, and put on some paint. I am hoping to fly it at the ROC launch on the 14th on a J90W to give it a shakedown flight. On-board electronics will be a Loki Research ARTS, and a G-Wiz LC to control staging and back up deployment.

I can't wait to finish it!

A link to photos will be posted soon.

#### Ryan S.

##### Well-Known Member
says the file is not accesible

#### gerbs4me

##### Well-Known Member
its says that too for me

#### GL-P

##### Well-Known Member
Ever try a full scale boattail arcas. Totally Tubular has the correct size tube. Would be cool to see. I wanted to do a full scale but I had trouble finding enough free scale data.

https://www.totubular.com/

#### daveyfire

##### Piled Higher and Deeper
Sorry. Had to set the files to be accessible to public. It works now... I think!

#### Stymye

##### Well-Known Member
nice job ... I bet you won't loose a fin on that puppy !

#### jetra2

##### Well-Known Member
Originally posted by GL-P
Ever try a full scale boattail arcas. [/url]
Performance Rocketry also has the fiberglass boat tail mold available...IIRC, it's almost $200... Jason #### GL-P ##### Well-Known Member Performance Rocketry also has the fiberglass boat tail mold available...IIRC, it's almost$200...
Bet it is!!! Could always try to create a balsa one out of many smaller balsa pieces like you would a nosecone. Use heavy grade balsa. Then you could just fibreglass it

#### loopy

##### Well-Known Member
Wow! That thing is gonna haul!!!!!!1

#### daveyfire

##### Piled Higher and Deeper
Ok, I did some more work. A veil layer of 4 oz glass cloth was applied over the Carbon/Kevlar fin can work. It looks pretty much the same, so no pics of that.

I also did some fit checking on the interstage. After a moment of panic wondering, "Where am I going to route the igniter wires?!", I came up with this solution. Since conduit for the sustainer igniter doesn't fit past the interstage coupler, I ended the conduit at the bottom of the lower centering ring. The wire runs bare from there, down, and into the motor. It all fits -- just barely.

See https://tinyurl.com/4smbf for pictures of the tight fit!

#### gerbs4me

##### Well-Known Member
Loopy is right, that thing is gonna haul
nice job so far