Loc Terrier Sandhawk build thread

[Cameron Anderson]

There seems to be a fair number of people building the Loc Terrier Sandhawk right now so I decided to throw my build on here.

I'm sure plan will evolve over the course of the build, but my two main goals for this build are focused on camera placement. I want one internal Mobius in the Sandhawk with an external lens. Secondly, I want another Mobius pointed forward in the av bay I am building below the ISC. I'm going to create a plexiglass window to capture (hopefully) the separation charge firing and the sustainer ignition.

Tonight I managed to get 2 of 3 centering rings rocketpoxied to their respective motor mounts. I went with the longer motor mount in the Terrier (14" intended for the Sandhawk instead of 11") to beef up the airframe since I want to fly on some quick 38mm motors.

 

[Cameron Anderson]

There are 3 centering rings per motor mount. The top ring will be epoxied to the internal airframe by injected epoxy through small drilled hole slightly above each ring. The lowest ring will be epoxied on the aft end once the fins are in and internal fillets are done. For the middle ring at the top of the fins, I push the motormount halfway into the airframe. I get the motor mount most of the way inserted but with the middle ring just aft of its final position. I tape off a small opening and push rocketpoxy through. Once i have a generous amount in, I push and twist the motor mount into the final position which collects and evenly distributes the epoxy and I allow it to cure.

 

[John Cummings]

Excuse my ignorance but what is the purpose of the graph paper taped around the motor mount tubes?
I look forward to watching your build and camera mounting. Two stage sounding rockets are exciting even more so when it’s recorded from an optimum vantage point!

 

[Cameron Anderson]

Excuse my ignorance but what is the purpose of the graph paper taped around the motor mount tubes?
I look forward to watching your build and camera mounting. Two stage sounding rockets are exciting even more so when it’s recorded from an optimum vantage point!

I use paper to create a perfectly perpendicular line to the motor mount so I put my centering rings on level. I use whatever paper is handy, it just happen to be graph paper this time.

I just got the plexiglass for the ISC camera cover yesterday. I'm waiting for the plywood so I can start cutting and assembling the av sled.

 

[Big_Red_Daddy]

There are 3 centering rings per motor mount. The top ring will be epoxied to the internal airframe by injected epoxy through small drilled hole slightly above each ring. The lowest ring will be epoxied on the aft end once the fins are in and internal fillets are done. For the middle ring at the top of the fins, I push the motormount halfway into the airframe. I get the motor mount most of the way inserted but with the middle ring just aft of its final position. I tape off a small opening and push rocketpoxy through. Once i have a generous amount in, I push and twist the motor mount into the final position which collects and evenly distributes the epoxy and I allow it to cure.

I just started using this method of partially inserting the motor mount and then adding glue/epoxy. Can't believe I never thought of it before. Trying to apply adhesive way down the tube is silly, just to have it pushed away by the forward centering ring. I also just started using syringes to inject epoxy right there and it worked beautifully. No mess at all. I have even mixed the epoxy right in the syringes. I'm using 60cc syringes from Amazon. I think I got a 50 pack. Did this on the Terrier and it worked beautifully. Left off the aft ring and squeezed in some West System 406 colloidal silica thickened slow epoxy all round the fins and spread it around with a dowel. Slapped on the aft ring and it was done. No mess at all. Motor tube, fins, and aft centering ring done one after another in minimal time. Not even adding external fillets. Painted it white today.

 

[Cameron Anderson]

I just started using this method of partially inserting the motor mount and then adding glue/epoxy. Can't believe I never thought of it before. Trying to apply adhesive way down the tube is silly, just to have it pushed away by the forward centering ring. I also just started using syringes to inject epoxy right there and it worked beautifully. No mess at all. I have even mixed the epoxy right in the syringes. I'm using 60cc syringes from Amazon. I think I got a 50 pack. Did this on the Terrier and it worked beautifully. Left off the aft ring and squeezed in some West System 406 colloidal silica thickened slow epoxy all round the fins and spread it around with a dowel. Slapped on the aft ring and it was done. No mess at all. Motor tube, fins, and aft centering ring done one after another in minimal time. Not even adding external fillets. Painted it white today.

I got a little carried away with the amount of injected epoxy on the top ring and had a shocking amount run down my motor tube. I lost a fair bit of the first layer of cardboard when I ripped it out.

I've done syringe injection for fillets before and never been comfortable with not seeing how it turned out which is why I tend to not use that method.

I am a fan of external fillets with at least one set of internal fillets - either on the inside of the airframe or along the motor mount. Nevada has lots of rocks and my rockets always seem to find them so I need to secure my fins well.

 

[Big_Red_Daddy]

I got a little carried away with the amount of injected epoxy on the top ring and had a shocking amount run down my motor tube. I lost a fair bit of the first layer of cardboard when I ripped it out.

I've done syringe injection for fillets before and never been comfortable with not seeing how it turned out which is why I tend to not use that method.

I am a fan of external fillets with at least one set of internal fillets - either on the inside of the airframe or along the motor mount. Nevada has lots of rocks and my rockets always seem to find them so I need to secure my fins well.

I like thin epoxy in areas I can't see and just turn the rocket around slowly until I think I've coated those areas. But that middle ring doesn't seem too critical. It's going to get some epoxy in the other side when the fins go in. I usually apply appropriate adhesive to the centering ring down the tube from the forward opening - drizzle thin epoxy and rotate until things are coated. And do the same on the aft end, maybe with JB Weld.

As for the fillets, I've seen lots of different methods and fins rip off easily with external fillets. There isn't much strength keeping the fillet from pulling away from the body tube. Same goes for the fin root against the motor tube. You always see the fin take the fillet with it. The critical spot is on the inside of the body tube where the fin meets. Put a big fillet there, then the fillet is pulling against the wall of the tube and is way stronger. Never seen a fin pop out if it had a good fillet there.

 

[Cameron Anderson]

While I did a poor job of documenting my buildz here is the finished stack set to fly next Saturday for the first time. I'll start with the booster.

Terrier
979 gram flight-ready weight (no motor).
First flight on an Aerotech i305 Fast Jack for easy tracking. My Marsa 33 armed by a 3/32" hex screw switch will handle primary and backup (+1.5 seconds) drogue charge deployment, via redundant Rocket Junkies charge wells, of 36" Spherechutes main chute. JLCR unreefs the chute at 600.

I chopped 5 3/4" of the booster airframe to make an av bay. I gained 1 5/8" of space from the av bay coupler on the aft end but lost 2 5/8" of bay space to the aft end of the Interstage coupler. All told, I had 4 1/2" of clean space for my electronics. Since I'm not using a traditional av bay setup with allthread, I glued the sled to a section of coupler to keep the electronics from rattling around. Electronics are powered by a 7.4v 800mah lipo. Primary charge is 20 grains (not grams) of FFFg black powder, back up charge is 25. Separation charge is set to fire booster engine cutoff +0.5 seconds. Sep charge is 15 grains FFFg balloon charge. Interstage is attached to the forward end of the av bay via 5/32" rivets, the aft end of the av bay is attached with 4 small masking tape strips. I tested the strips to make sure they would break when the ejection charge fires but were strong enough to keep the ac bay attached to the fin can when the separation charge fires.

 

[Cameron Anderson]

Sandhawk

971 grams flight ready (no motor). First flight on a CTI i223 Skidmark. 28" Loc circular main chute, 12" x-type drogue. Airframe was set up to test head end ignition but for the first flight I just ran my sustainer ignitor down the side of the airframe. For motor ignition I'm using a pyrogen-dipped e-match. Raven 4 is handing sustainer events...main and apogee channels still functioning in those roles, event 3 is main backup at 600 (main primary is 1,000), and event 4 is motor ignition with G and altitude gates built in. I chopped the fin can airframe several inches and used a slightly smaller upper air frame as well. I added the Loc av bay/sled combo and I really liked it. It was a tight fit but I was able to get my Raven 4, Featherweight magnetic switch, and T3 in there, albeit with some creative placement and gorilla tape.

Apogee, depending on staging events is between 9,400 and 11,000 AGL. I have a 13,500 foot waiver to play with so I have a good safety margin.

Because the intent of the airframe was to be a testbed, it was made to be rugged and utilitarian, not necessarily optimized for altitude and aerodynamics. I want to try some new camera placement positions (not used on this flight) and HEI (also not tested on first flight), the fin cans are VERY sturdy with external fillets and dual internal fillets (to the MMT and the airframe) using rocketpoxy throughout.

Pictured are the Aeropack retainer I had to Dremel to get the sustainer ignitor to feed, the av sled, and the lipo connectors I use as my quick disconnect for the sustainer ignitor.

 

[Cameron Anderson]

 

[mbeels]

Good luck, looking forward to some flight results.

 

[Tim51]

Did this fly?

 

[Cameron Anderson]

Did this fly?

Unfortunately no - slower than expected covid reopening prevented it. But we are cleared for a launch this weekend. The extra time allowed me to make a fiberglass 808 camera shroud too...not great, not terrible.

If things go well this weekend I'm flying on J350 to i435 at Mudrock in two weeks.

 

[Tim51]

Unfortunately no - slower than expected covid reopening prevented it. But we are cleared for a launch this weekend. The extra time allowed me to make a fiberglass 808 camera shroud too...not great, not terrible.

If things go well this weekend I'm flying on J350 to i435 at Mudrock in two weeks.

The cam shroud looks pretty good to me. How did you configure your ISC?

 

[Cameron Anderson]

The ISC is one molded piece of plastic. I drilled a small hole in the bottom to run a separation charge into the ISC. The charge is controlled by the Marsa33 in the booster. The stock booster doesn't have any room for electronics so I trimmed a few inches off the the forward end of the airframe, threw a bulkplate in the aft end of the trimmed piece with an eyebolt and then I use plastic rivets to secure it all to the ISC to make a small but usable av bay with the ISC securing the forward end. The upper ISC that fits into the Sandhawk was lightly sanded on the outside and heavily sanded with a dremmel on the inside to allow the motor retainer to fit.

 

[Tim51]

The ISC is one molded piece of plastic. I drilled a small hole in the bottom to run a separation charge into the ISC. The charge is controlled by the Marsa33 in the booster. The stock booster doesn't have any room for electronics so I trimmed a few inches off the the forward end of the airframe, threw a bulkplate in the aft end of the trimmed piece with an eyebolt and then I use plastic rivets to secure it all to the ISC to make a small but usable av bay with the ISC securing the forward end. The upper ISC that fits into the Sandhawk was lightly sanded on the outside and heavily sanded with a dremmel on the inside to allow the motor retainer to fit.

Thanks for the detail - I have a similar piece of plastic from Loc - the 4"/3" reducer that comes with the Expediter kit. With a bit of cutting and drilling I'm now thinking it would probably also serve as an ISC also.

 

[Cameron Anderson]

Thanks for the detail - I have a similar piece of plastic from Loc - the 4"/3" reducer that comes with the Expediter kit. With a bit of cutting and drilling I'm now thinking it would probably also serve as an ISC also.

Just check the Loc website, the Expediter piece looks identical to my ISC (except the Expediter piece is bigger).

 

[Cameron Anderson]

15-20mph sustained winds today, gusts to 40...no flight.

Trying again at Mudrock in two weeks.

 

[Cameron Anderson]

Success!! Finally flew the Terrier Sandhawk yesterday.

Perfect flight and recovery, minus the 808 camera I thought was turned on but was not (it was so bright out I couldn't tell for sure if it was on).

Boosted on an an Aerotech 38/600 i305 Fast Jack, Marsa33 trigger the 1 gram separation at BECO +0.5, separation was flawless, Raven 4 ignited the CTI 38/4 grain i223 skidmark 1.5 seconds later.

Booster hit 1,540'. It's light and a has a lot of fin area and that interstage is draggy. It simmed to 1,900 but I was expecting 3,000 honestly.
The sustainer hit 7,555'. The camera shroud stole some altitude. It simmed to 11,000 but that is always so optimistic.

Booster was recovered by the pad, sustainer hit some winds and landed over a half mile away.

Next flight on a J420R to an i435T in a month at Aeronaut.

 

[Tim51]

Congratulations - very cool images.