Dr. Zooch Mercury Little Joe Build Thread

The Mercury Little Joe had always been a favorite. Even in High School I had plans to build a scale model and enter it in a NARAM competition. This was in 1974, and internet searches didn’t exist yet. I collected what photographs I could find and wrote a lot of letters trying to get scale data. I still have that data, plus a Little Joe CD from Mike Dorffler. Someday I’ll build a scale entry. This Dr. Zooch kit should tie me over until then.

Entry 1: OPENING THE BOX
I picked up the kit in person (it had been waiting for me at JonRocket.com.)
I scanned the wrap sheet, just in case I screwed up and had to print another. All the parts were there and in great shape. I started dressing up the parts, sanding the body tube ends and strengthening with CA. I numbered the pages.

MAKING THE BOILERPLATE MERCURY CAPSULE
This kit starts with the capsule construction. First up is painting the exposed shoulder area with black paint. While the illustration shows brushing on the paint, I wanted to spray it.
I filled just the shoulder area (to be painted black) with Carpenter’s Wood Filler. I learned on earlier Zooch kits that it isn’t necessary (or desirable) to fill the entire nose cone. The shrouds always fit perfectly and filling all the balsa might raise the surface and ruin the shroud fit.
I masked off most of the capsule and the shoulder. Gloss black was sprayed, I’ll follow with flat clear after all the wraps are in place.
The recovery compartment wrap is glued next, followed by the “Strange Black Dot”. The antenna fairing is made and centered on the dot. The nose fairing fit perfectly when glued on the antenna fairing.

Looking forward to following your build. Keep the why and how tips coming.

BUILDING THE ENGINE MOUNT
I didn’t take many pictures of the Engine Mount because the construction is pretty standard.
A Reinforcement Band is shown on the instruction drawings and is found on the wrap sheet, but it isn’t mentioned in the instruction copy. I added the Reinforcement Band beneath the upper bend of the Engine Hook. I’ve had engine clips tear a BT-20 tube at ejection. Dr. Zooch is smart to add this reinforcement.

With the Rear Centering Ring flush with the main Body Tube, the engine tube will extend 3/4" from the back of the main tube. I’ll fill the seams and spray it black before gluing the whole mount into the main tube.

I made a change in the Engine Mount construction. You are instructed to make two rings of glue, White Glue inside the Main Tube and Yellow Glue for the Rear ring. Personally I don’t like using yellow glue on an engine mount. White glue gives you time to slide the mount in. Yellow glue has more tendency to grab in the wrong spot. I made one White Glue ring inside the body tube and slid the Mount into position, slightly recessing the rear Centering Ring about 1/16" inside the Body Tube.
This way I could glue the Mount (using just the forward ring of glue) let it dry, then later make a rear fillet between the inside Main Body tube and Centering Ring joint.
To glue the Front Ring, the instructions have you run a line of White Glue 1" inside the body tube. I decided to make a single White Glue ring 1 ½" inside the tube, a closer location to the Front Ring final position.
With the change of “slightly” recessing the Rear Ring I only had to make a single ring of Glue, positioning the Mount and letting it dry. Afterwards I added a White Glue Fillet at the Rear Ring joint.

MAKING THE BODY TUBE
The Zooch kits have you glue the body wraps using white glue only around the edges. For whatever reason, I don’t have much luck using white glue on larger wraps so I used spray adhesive. I know later on I may have to deal with adhesion where the wrap is cut away at the fin roots. I’ll tackle that before the fins are glued on.

Neat build thread!

Great build thread, this kit is one of my favorites, tried to pick one up at Red Glare this past weekend but the Doc was out of them (he flies at MDRA). Will get one next launch. I should start my Roachwerks LJII....hmmmmm

I love mine. Lose a fin every now and again from handling. Only lost the escape tower twice during flight.

Found it in the grass both times. :y:

Now next time I fly it I'll surely lose it now that I said something.

To all, thanks for the positive responses!
Back to the build:

CUTTING OUT THE FINS
The fins are cut out of 3/32" balsa stock. While the instructions don’t specify, it shows the knife edge taper to be about 3/16" wide along the leading edge. The real Little Joe fins are thicker, wedge tapered all the way from the leading to the trailing edge.
I have plenty of scrap balsa and decided to double the fin thickness to 3/16" by laminating another piece of 3/32". This is just my personal preference, I’ve always liked the thick cross section of the Little Joe fins. I doubt the 3/16" thickness is scale, it’ll just look closer to the real rocket.
The fins cut from the kit’s template were glued to 3/32" sheet and set in some heavy books to dry. I’ll cut around the glued fins when dry.

The fins were tapered close to the photographs I had. They were filled with Carpenter’s Wood Filler, sanded and followed by grey primer. All were sanded to surface and sprayed a white undercoat.

The next step has you cut away the fin root area of the wrap so they will adhere better to the body tube underneath. Because my fins roots had a different cross section than recommended, I didn’t cut along the printed dotted lines on the wrap. The fins were set over the printed lines and small tick marks were drawn with a pencil.
I changed out my X-Acto with a new #11 blade and cut through the wrap using a straightedge.

PAINTING THE FINS
The first three pictures show the first attempt at painting and trimming the fins. The fourth picture shows the second and final try.

The instructions mention an orange fin. That line is followed by “we’ll detail that later in the instructions.” I didn’t see a reference to it in the remaining pages. But, the enclosed pictures on the “History of the Little Joe” page do show orange stripes out the outside edges of the fins.
Off the model, the fins were sprayed with the cheap 99 cent Walmart Aluminum. I wanted to paint the outside edges orange, but was concerned about using a tape mask over the aluminum. I remembered my past experience with masking aluminum, silver and chrome. Any tape tends to pull up or dull the metallic paints.

The Dr. Zooch kits use printed paper wraps, why not use this on the orange fin tips? It’ll certainly be easier than trying to mask the aluminum.
I sprayed some 20 lb. printer paper with orange. I’ll cut strips and glue them to the outside edges of the fins. This way, the outside wedge edge and bottom of the fin will still stay silver like the real Little Joe.
Spraying orange on white paper turned out too bright compared to the printed orange on the main body wrap. I tried again, this time spraying paper with aluminum, followed by the orange. This helped slightly darken up the orange for a close match.

Before gluing on the orange tips, I searched for Little Joe pictures on the internet. The Little Joe had a thin black strip down the leading edge of the fins. When these fins were shaped, the leading edge wasn’t sanded to a knife point. I left a very thin “flat” edge for strength.
A 30 year old Marks-A-Lot felt tipped pen made the black line down the leading edge. It actually covers better than a new Sharpie. It’s not scale, but it gives the impression of that black strip.
With metallic paints, fingerprints show up very easily from handling the model. I made a point of holding the fins with a paper towel when gluing on the orange tips.

The forward edge of the orange strip was pre-cut to match the angle of the leading edge. This way I can recess the orange slightly back so the black line is seen all the way down the leading edge. The trailing edge of the orange strip will be trimmed afterwards with a razor blade.

Earlier the fin root edge locations were cut out of the body wrap for a better glue joint. Because spray adhesive was used on the wrap, the edges had lifted a little. I put a very small amount of white glue on my knife tip and pushed it under the raised wrap. After it had dried a minute, it was burnished down. There were no problems gluing the fins to the main body.

The launch lug seams were filled and sprayed with Aluminum paint before gluing in place. The lug is cut in two and glued onto the wrap’s seam. With the lugs over the wrap seam, the launch rod covers up the seam at launch.

The fins got white glue fillets. White glue dries clear and I knew after applying the final clear dull coat they would be almost invisible.
After spraying with the Krylon clear flat, it dulled the metallic sheen a little. The aluminum paint was now very close to the gray color of the body wrap.

THE ESCAPE TOWER
I actually started on the rocket before the kit arrived.
While I was waiting, work was started on the tower. The Mercury Redstone was the first Zooch kit I’d built and I saved the instructions and tower gluing template. I knew the Little Joe is a BT-60 based kit like the Redstone so I figured Dr. Zooch used the same tower patterns. Luckily, my hunch was right.

When building that first Redstone, I wasn’t happy with the first attempt at the tower. I didn’t have any more dowels in the right diameter, so it was rebuilt using toothpicks. The toothpick diameters were reduced with 220 grit sandpaper on a block. Final smoothing was done with 400 grit. The first picture shows the difference in diameters. The toothpicks on the left are for the three legs, on the right all the interior steps and crossmembers.
Before cutting all the toothpicks were sealed twice with clear varnish, sanding between coats.

Note in the second picture how the cutting lines are extended on the template with a pencil line. This makes it easier to see and set your blade on the correct cutting angle. Otherwise, the dowel is covering the cut line.
There are a lot of pieces to the tower, the third picture shows how I kept track of them.

By the time the kit arrived, three tower sides were already built. The sides were still separate when I started this thread.

THE ESCAPE TOWER - Part two
A slight angle was sanded to the “V” side of the three tower subassemblies to match the angle of the second tower assembly. This would make a tighter, stronger fit when they are glued together.
I didn't use the Green Triangle (from the pattern sheet) to get the angle of the tower sides. At first, very little white glue was applied to hold the initial two sides together. This way I would have a flexible glue “hinge” making it easier to align the final side. After I was happy with the looks of the tower, white glue was added to the joints with a toothpick tip.
The Stubby Dowel (Escape Motor) had it’s ends squared up using 400 grit sandpaper on a block. It was sealed with two coats of varnish, sanding between coats.
The Escape Motor Band was attached by tacking just the end with a little white glue. I made sure it was on straight by the Escape System Dowel on a flat surface being sure the extending edge of the Band was flat on the table. After the start tip was dry, glue was applied and the rest was wrapped around the dowel.

The two pictures show the Aero Spike in place. The installation is explained in the next build entry.

THE ESCAPE TOWER - Part three
I added the Aero Spike Toothpick early so I could paint everything together before gluing the tower on the capsule. The Aero Spike looked a little long. Supplied in the kit, it is 1 ½" long. I did attach it at that length, shown in the last thread entry.
After looking at some Little Joe pictures on the Internet, the Spike was removed and cut it to 3/4". Now it looks a little closer to the original. The instructions have it glued on the top of the LES Motor Casing dowel.
While it would be an easy fix if it broke off, I wanted to give it a little more support. I took a small drill and made a hole in the center of the LES Dowel and down the middle of the toothpick. I cut a pin to ½" to join them both together.

At the bottom of the fourth page you are told to paint the entire tower black. On the next page you are directed to paint the top of the LES Casing black a second time. Because I put the Aero Spike on early, I wouldn’t have to touch it up again.

THE ESCAPER TOWER - Part 4
I test fitted the three tower legs over the top of the fairing. The fit was pretty good. When I took the tower off for gluing, the inside of the legs left black marks which actually helped in the gluing placement of the tower.
A little paint was scraped off the inside of the legs for a better gluing surface. I set the capsule on a smooth countertop and glued the tower in place. The capsule was turned and the tower adjusted until I was sure it was straight.

The lower tower cross members were cut earlier. They were spray painted black off the model.
More had to trimmed off from the left end of the lower cross member so it would fit better on the long vertical leg.

Lookin' Great Chris! You gonna have this ready for the
May 1st ROCK launch?

Hi Brian,
I don't know if I can make it to the May 1 launch! I might have an outside job. To be honest, I'd rather be flying rockets!

Before I fly the Little Joe, I should fly the Ares Stick and the Thor Agena B again. I want to get those into EMRR, they don't have full reviews with flights on those two.

Anyway - I hope to see you guys on May 1.

Nice Job Chris, you've motivated me to build one of these.

Boosterdude said:

Nice Job Chris, you've motivated me to build one of these.

Click to expand...

Please see our special offer on the Mercury Little Joe in the Vendors area:

https://www.rocketryforum.com/showthread.php?t=11138

-- Roger

I like the added lines on the tower template for cutting... I may add that onto future kits. The reasoning behind it makes a lot of sense.

Chris,

I gotta tell you how much I love your build threads. You explain every step beautifully and make the complex understandable. All your builds are inspiring.

Thanks again for the responses, I'm glad some are picking up tips.

TOWER SUPPORT LEGS
I didn’t cut six identical pieces for the inverted “Vs”. I thought it’d be hard to get all the angles right on six separate pieces.
I drew an oversize V on my work area to the same angle I wanted the final V shape to be.

Picture 1: I only had to cut the tips (two at a time) at an angle to fit the top of the V.

Picture 2: I made three Vs. All were longer than they needed to be, I was only concerned about the top V angle for now.

Picture 3: After drying, just the tip of the V was cut off trying to make a circle the same size as the diameter of the Vertical Leg.
The cut tip was held against the end of the Leg. I checked how much of the Vs legs overhung the top of the “strange black dot”. The V was removed and set on a block of wood for cutting. A razor blade was set over both of the V legs. I made sure both side lengths were equal and made one straight cut across both legs. A little sanding with a block made for a tight slip fit against all three contact points.

The fourth picture shows the LES nozzles in place, they'll be covered in the next post.

MAKING THE LES NOZZLES
The LES nozzles were cut from the wrap sheet.

Picture 1: The very small circled tip was punched out with the smallest tube on my Rotary Punch.

Picture 2: The nozzles were pre-formed with a pointed dowel in the fleshy palm of my hand.

Picture 3: Holding the glued nozzle tab down with long tweezers until dry.
After the nozzles had dried, I wanted to sand the open end flat and even. It was too soft against the sanding block so I ran CA around the open nozzle end. This hardened it up enough to sand off a little overlap of the end.

Picture 4: The dowel was reshaped to fit the inside of the nozzle and formed them round again.

Gluing the LES nozzles at the correct angle was easier than I thought it would be. After cutting off the tips at an angle, they were lightly tacked in place with white glue. No real adjustments were needed. I touched a drop of CA far into the nozzles to set them in place.

The Orange LES Casing Wrap followed. I pre-rolled it around a dowel and set in place with white glue.

PARACHUTE INSTALLATION
I didn’t take a picture of the parachute and shock cord mounting, everything here is standard. Even though the parachutes are made out of garbage bag plastic, they work great. I’ve never had any problems with other Zooch kit recoveries.

The elastic shock cord is plenty long, 1/4" x 36" before tying and mounting. The shock cord is attached to the body with an Estes style tri-fold mount cut from some leftover wrap sheet.

The screw eye is screwed in the base of the capsule cone, offset from the pre-installed ballast weight.

Instead of tying the parachute to the screw eye, I tied a loop in the shock cord 1/3 the way down from the capsule. This way the chute might have less chance of getting tangled up with the capsule and tower at ejection.

Next up - the finished pictures

I like the way you have presented your build, very much straight foreward and to the point. Your a craftsman, thank you for sharing your tips.

hcmbanjo said:

Picture 2: The nozzles were pre-formed with a pointed dowel in the fleshy palm of my hand.

Click to expand...

Do you need a metric or standard fleshy palm for this step?

GREAT BUILD!!!

rokitflite said:

Do you need a metric or standard fleshy palm for this step?

Click to expand...

Actually neither. My palm is analog but my fingers are digital.

FINISHED!
I think I've built most of the Dr. Zooch kits, at least all the favorites.
That Space Shuttle will be finished someday.

If anyone is curious what a "Golden Age" kit was, these are as close as they come. The Zooch Mercury Redstone and Saturn V are almost like building the pre-Damon Estes versions. They'd be a good stretch for anybody looking for a break from the standard fare.

Thanks again Wes! How do you get all the wraps and shrouds to fit so well?

A good way to make a "C" engine go really high is to put it into the Little Joe. However, avoid flying in very strong winds. The photo seen here is of the very first test flight. I made the mistake of stuffing an over-sized rip-stop nylong chute into it- this both hurt and helped. At launch, the rocket cocked into the wind and went ballistic. It had a C6-7 in it so at burn out, it looked as if it was really going to burn-in. As luck would have it, it headed directly for a deep ditch and when the ejection charge went off, that over-sized chute stopped it cold... almost in a hover. It landed gently in the ditch and was without a scratch. I figured that the wind along with the extra mass of the big chute were the problems. A few minutes later, I had another C6-7 in it and this time a stock chute from the kit. That time it went straight up with no wind-cocking, but when the chute opened- even with the 7 second delay, the rocket drifted in that heavy wind a long way- right off the field in fact. It landed in the road and the impact with the roadway snapped the aero-spike (which was found laying right next to the rocket). To make matters worse, a car was coming! The driver saw the rocket in the road, swirved and missed it. I quickly replaced the aero-spike and the rocket flew two more times that day. On the last flight, on a C6-3 with a reefed chute, the roadway again was the landing site- a broken fin was the result.

Looks great all finished, nice job on the build.

If anybody is looking for some real inspiration check out James Duffy's
Little Joe build site.

https://www.rocket.aero/littlejoemodel.html

This is one place I went to during the build for ideas.