# Rocketarium Hydra Sandhawk Build Thread

### Help Support The Rocketry Forum:

#### rocketguy101

##### Well-Known Member
I don't buy many kits, as I love scratch building. But when I saw this model being offered by Rocketarium, I was intrigued and ordered one. This is my first Rocketarium kit, and I like it.

I was impressed with the quality of the parts. The body tubes have a very light spiral which will be easy to fill, and the centering rings are thick and sturdy. They are laser cut and fit nicely in the body tubes.

I am not sure who produces the nose cone, but it does have a rather large seam that will require some sanding and filling. I am not sure what type of plastic it is molded from, it has a similar feel to the blow-molded cones Centuri used to produce. The instructions say to sand it before applying primer.

I wish the instructions had an exploded view of the assembly to give a feel for where the parts all go. I took the liberty of modeling the rocket in SolidWorks and making my own exploded view.

View attachment HydraSandhawk.PDF

#### rocketguy101

##### Well-Known Member
Assembly is pretty straightforward, although I have minor nit w/ the instructions in step 2, the booster motor mount assembly. The illustration makes it appear the forward centering ring is 2 5/8" from the aft centering ring. Reading the instructions indicates the 2 5/8" is from the end of the motor tube, at the end of the engine hook.

I elected to use a Kevlar line mounted to the sustainer motor mount to attach the shock cord rather than the folded "paper flap" method. Prior to gluing the sustainer motor mount in the tube, I drilled two holes in the forward centering ring, then looped the Kevlar line around the motor tube for strain relief. A little epoxy anchors the line, and seals the holes in the CR. I will tie the elastic shock cord to the Kevlar loop.

#### rocketguy101

##### Well-Known Member
Although the web site states the fins are pre-cut, my model came with plain balsa stock and templates to trace the fins on the balsa. I actually prefer tracing and cutting my own fins so this was no biggie.

The instructions mention being careful with the layout to fit all the fins on the provided stock. Perhaps my model is an early production version. FWIW, here is a picture of my layout..

#### rocketguy101

##### Well-Known Member
The instructions don't say anything about what cross section the fins should be. Looking on this Hydra Sandhawk web site, there is a photo album with various views of the rocket and the unique launcher. The album is some sort of java script, so it is hard to copy or download the photos. I did find a couple pictures on some of the other pages on the site that had urls I can link to here...

The two views shown here indicate the fin has a wedge cross section, and might have a taper from the root to the tip.

There are larger versions of the above photos in the album. Plus a rear view that shows the root-to-tip taper more clearly, you just have to scroll through to find them.

#### rocketguy101

##### Well-Known Member
I have hand-sanded tapered fins before, and thought my fingers were going to fall off! I decided to try sanding the wedge cross section with a table belt sander equipped with a 220 grit belt. I skipped on trying to taper the span direction, I figured I would end up breaking the fin.

I built a tool to hold the fin from a coat hanger epoxied to a piece of thin plywood reinforced w/ a strip of nylon stocking doped down with more epoxy.

Using a piece of 0.060" plastic stock, I scribed a line down the center of the leading edge and tip of the fin for guidelines while sanding.

I used Gorilla Tape to attach the plywood "foot" to the fin, and using a LIGHT touch, began sanding the wedge starting at the leading edge, then blending into the rear of the fin. I made some practice fins to develop the technique.

I tried regular duct tape to attach the foot to the first practice fin, and it didn't feel as secure as the Gorilla Tape--that stuff is tenacious!! You actually have to be careful to not pull balsa fibers off as you remove the handle.

After shaping one side, I removed the handle, and attached it to the other side with new tape. Rinse, lather, repeat. It actually took longer to tape the handle in place than to perform the sanding, but it beat hand sanding with a sanding block! I am pretty pleased with the results.

#### rocketguy101

##### Well-Known Member
The instructions tell you to drill a 1/4" all the way through the booster tube and the inner motor tube to vent the gasses from the booster motor to allow the sustainer motor to ignite before the booster blows off the rocket. I should have drilled one side, roll 180 degrees, and drill the other. Instead I drilled through from one side so my exit hole is a little messy. I put some CA glue around the holes and will sand it smooth. While I was at it, I ran a bead of CA around the inside of the top of the sustainer tube to reinforce it.

I filled the body tube spirals with Elmers Stainable Wood Filler. According to the Elmers web site, this has micro balloons, so I thought it was like the old Fill-N-Finish. This new stuff is not creamy like the FnF we loved, it feels like wet beach sand. It did fill the spirals (which were pretty small anyway) and it does sand fairly easy, but I wish we could get FnF back!

#### rocketguy101

##### Well-Known Member
Attaching the fins is pretty straightforward. Go easy on the glue fillet so the cardstock Fin Attachments will fit against the fin.

The instructions say to cut a strip of balsa 3/16" x 3 for the launch lug standoff. My lug is 2" long, so I will make a shorter standoff. I am substituting spruce for the balsa. I have had balsa standoffs break along the grain, so I like spruce better. I have used small dowels as standoffs in the past too.

#### rocketguy101

##### Well-Known Member
I applied the Elmers filler to the fins and sanded smooth before the next operation in the instructions: In step 9, you cut out the Fin Mounting Attachments that are printed on cardstock. I followed the suggestion to cut the sheet in half, and glue together to make a double thickness sheet rather than cut all those pieces and glue together on the model. There are 8 pieces for the booster fins, and 8 larger pieces for the sustainer fins.

I read through the step too quickly and misunderstood how these attachments were supposed to fit. I thought one piece went on the tube next to the fin, and another piece went on the side of the fin along the root edge...WRONG! All of the pieces go on the tube!!! The header card picture makes this clearer--I wish there was an illustration in the instructions.

There is a typo when the instructions tell you to "Mark the booster fin at 1 3/16"..." that should be the sustainer fin.

#### rocketguy101

##### Well-Known Member
OK! Everything is glued in-place, and filler has been applied and sanded. I still need to fill the seam in the nose and sand it smooth. Next will be primer and paint. I will have to wait for the Oklahoma weather to cooperate, so this may take awhile! I will update this thread when I make progress.

I think I am going to try to paint the crazy flame job on the nose shown on the header card and pictured on the Hydra web site. I may chicken out and go with the tamer paint job.

I really like the lines of this rocket, and can't wait to fly it. The "D" booster should make for a nice liftoff.

#### gdjsky01

##### Whoosh, pop: life is good
TRF Supporter
Very nice build! Thanks for documenting it. Please do follow up. Well done! :clap: :clap:

will do!

#### sodmeister

##### Well-Known Member
Very nice build! Thanks for documenting it. Please do follow up. Well done! :clap: :clap:
I agree ,great build ! I was interested in Marks kits and this is one that interests me.The parts look well made and of good quality.Can you tell if the nosecone is made of styrene plastic ?

Paul T

#### rocketguy101

##### Well-Known Member
I agree ,great build ! I was interested in Marks kits and this is one that interests me.The parts look well made and of good quality.Can you tell if the nosecone is made of styrene plastic ?

Paul T
As I said earlier

I am not sure what type of plastic it is molded from, it has a similar feel to the blow-molded cones Centuri used to produce.
It does not feel like styrene, sort of like a Clorox bottle if ya know what I mean?

#### sodmeister

##### Well-Known Member
As I said earlier

It does not feel like styrene, sort of like a Clorox bottle if ya know what I mean?
Hmmm ,probably some sort of poly ,much like the bigger nosecones Loc and PML make and sell.

Either way ,very nice kit and build.

Plenty of picture if you please

Salut !

Paul T

#### marcs

##### Well-Known Member
Although the web site states the fins are pre-cut
The fins are indeed pre-cut at this time. This is a recent change, they used to be balsa sheet + template.

This was changed earlier this month. I assume your kit was purchased before this change, or from a dealer who has kits from before December 2011.

Marc

#### marcs

##### Well-Known Member
Can you tell if the nosecone is made of styrene plastic ?
The nose cones are HDPE.

Marc

#### rocketguy101

##### Well-Known Member
The fins are indeed pre-cut at this time. This is a recent change, they used to be balsa sheet + template.

This was changed earlier this month. I assume your kit was purchased before this change, or from a dealer who has kits from before December 2011.

Marc
Roger that! I ordered it back in July directly from you, I think right after you announced the kit. I was working on some other projects at the time, and didn't start working on this model until the first part of November.

Are the fins die cut, or laser cut?

#### rocketguy101

##### Well-Known Member
The nose cones are HDPE.

Marc
Hey Marc, could you provide some information on the paint scheme? I think I see now that the nose cone is partially red and silver, and the silver runs below the payload tube (from your header card picture).

How long is the gold band from the end of the sustainer tube? Is there a silver band on the bottom of the sustainer tube, or at the top of the booster tube? How wide is that band?

The pictures on the Hydra Sandhawk .org website show some of these details but if I try to zoom in, the detail fuzzes out.

Great kit, can't wait to finish and fly!

BTW I sanded the cone per instructions and filled the mold seams w/ Bondo spot putty. It should sand out to a nice finish (its drying right now).

#### marcs

##### Well-Known Member
I think I see now that the nose cone is partially red and silver, and the silver runs below the payload tube (from your header card picture).
Correct, the silver on the nose cone is there, in part, to make the nose cone appear shorter, to keep it's appearance closer to scale.

The silver band on the nose cone and below the payload tube are 1/2" long.

How long is the gold band from the end of the sustainer tube? Is there a silver band on the bottom of the sustainer tube, or at the top of the booster tube? How wide is that band?
The gold band at the end of the sustainer tube is 2 1/2" long.

The silver band is on the booster tube and is 1/4" long.

Great kit, can't wait to finish and fly!
Thank you. It is a fun kit to build and fly.

On it's final flight, the Hydra seen on the face card decided to be like it's full sized brother and went for a water landing Sadly, it could not be recovered

BTW I sanded the cone per instructions and filled the mold seams w/ Bondo spot putty. It should sand out to a nice finish (its drying right now).
Bondo spot putty is exactly what I use. Start with primer and apply Bondo a few hours later. Let sit overnight, sand bondo. If needed, add some more Bondo. Add another primer coat and you've got a smooth finish.

Marc

Last edited:

#### rocketguy101

##### Well-Known Member
Correct, the silver on the nose cone is there, in part, to make the nose cone appear shorter, to keep it's appearance closer to scale.

The silver band on the nose cone and below the payload tube are 1/2" long.

The gold band at the end of the sustainer tube is 2 1/2" long.

The silver band is on the booster tube and is 1/4" long.

Marc
Thanks! So, is my illustration correct? The Hydra Sandhawk site has a modeling page w/ a list of colors for the different rounds..it states the booster bands are "Gold Anodize" like the booster fins, so that forward silver ring in my pic may be gold instead.

#### marcs

##### Well-Known Member
Thanks! So, is my illustration correct? The Hydra Sandhawk site has a modeling page w/ a list of colors for the different rounds..it states the booster bands are "Gold Anodize" like the booster fins, so that forward silver ring in my pic may be gold instead.
Attached is a higher resolution picture of the booster.

Those bands likely are gold, as are the booster fins. However, as you can tell by the attached photo, they don't look as "gold" as the fin can gold.

To show that difference, I changed the color selection somewhat.

If you want to stay as close to scale as possible, I'd say go with that you see in the attached photo.

#### rocketguy101

##### Well-Known Member
Attached is a higher resolution picture of the booster.

Those bands likely are gold, as are the booster fins. However, as you can tell by the attached photo, they don't look as "gold" as the fin can gold.

To show that difference, I changed the color selection somewhat.

If you want to stay as close to scale as possible, I'd say go with that you see in the attached photo.
NICE! I know "anodize" can vary from nearly natural aluminum to a deep gold color, so scale would not be uniform color.

That photo shows the fin cross section very nicely too! Got any more hi-res shots you can share?

#### marcs

##### Well-Known Member
That photo shows the fin cross section very nicely too! Got any more hi-res shots you can share?
I think that's the only hi-res one that would help with color selection.

Marc

#### rocketguy101

##### Well-Known Member
BTW I sanded the cone per instructions and filled the mold seams w/ Bondo spot putty. It should sand out to a nice finish (its drying right now).
Nose is sanded and I am now ready to primer and paint...WX looks promising towards the end of the week so fingers crossed!

#### rocketguy101

##### Well-Known Member
The weather was fantastic today, it has been in the low 60s, no wind! So I took adavantage of that and started painting this bird.

I decided to paint the booster fins and attachements first. I wasn't sure how well the DayGlo Red would take to having masking tape applied over it. According to the Hydra Sandhawk org (HSO) modeling page the booster fins are "gold andodize". I saw a model at one of our club meetings that had this effect by painting a basecoat of silver, then applying gold over it.

So, after masking the portions of the booster tube that were going to be red, I applied silver. After it dried, I applied a dusting of gold. Since the aft ring appears silver in Marc's picture above, I masked it off for the gold coat.

I decided to follow the HSO website guidelines, and used DayGlo Red for the booster. It looks a little more pinkish than I would have liked, but in the photos it looks pretty close to the HSO pictures. I think the anodize effect came out nice.

#### rocketguy101

##### Well-Known Member
According to the HSO modeling page, the nose is painted "Micarta" Brown. I did a search and found "Micarta" is a phenolic. Phenolic materials I have seen have a yellowish-brown color, so I decided to try a technique similar to what Dr. Zooch detailed in the TRF archives to paint the Space Shuttle External Tank.

I first painted the nose "Equipment Yellow" (around here we call that "CAT Yellow" ). Then I applied a light coat of primer brown. Here is the result of that. The brown has a little more red in it, so the overall color is a little more redish than I had envisioned.

#### rocketguy101

##### Well-Known Member
It is starting to get too cool to do any more painting today, and the paint on the nose is still too soft to mask it for the silver. I want to apply silver to the nose, payload, and the fin can area in one session. I will then dust the fin can with gold to finish the anodize effect.

Anywho, here is where I am at...

Now, on the HSO modeling page there is mention of a "Thiokol logo"...the decals with the kit are only simulations of bolt heads for the fin attachment strips (stick on, BTW, somebody asked if they were waterslide).

I have a scan of some Thiokol literature, and could print something on decal paper, but I can't find any details on the logo...in the following figure from the HSO website, I think a see a black smudge midway on the Sandhawk motor...

Marc do you have a higher resolution version of this picture?

#### marcs

##### Well-Known Member
The highest resolution one I have of that photo is only 966 x 768 pixels.

#### rocketguy101

##### Well-Known Member
Getting closer...

Paint is on, I hand-painted the flames on the nose. I used Testors "Neon Red" enamel, and it goes on sorta squirrly, so don't look too close at the nose.

Masking this puppy was a challenge! You can see in the close up of the fin area (prior to decals) I missed the edge of the one fin. But I am proud of the tapered cross section!

Marc I have a question in Step 13, Decals...

"The last set of decals go between the fins, near the top of the area painted gold (the fin can)"

Just to sure...the decals go on the gold portion or the white?