Custom Solar Explorer Build Part 13 BT-55 Section Gluing

In the next few posts I'll refer to the lower body tube assembly (BT-55 and 50/55 Centering Rings) as the BT-55 section.

The BT-55 section will slide over the lower BT-50 body tube from the rear.

You don't want the centering rings to catch and roll over the edges of the BT-50 body tube.
Use a smooth dowel or the back end of a Sharpie pen to roll over and smooth out the rear edge of the BT-50 body tube.

The inside edges of the 50/55 centering rings should be sanded to allow an easier sliding fit over the lower BT-50 body tube.

Take a good look at the inside edges and remove any rolled over edges with 220 grit sandpaper.

I marked the top (T) and bottom (B) of the BT-55 section for reference.

The top end of the BT-55 section was already slipped over the end of the BT-50 tube lower end.

This picture was taken to show an area of concern. This area takes an extra moment to line up the inside BT-50 tube through the rear centering ring.
You may have to sand away some of the centering ring lip forward of the letter "B".

I noticed a crack forming where the filler was in the centering ring seam.
The BT-55 section was removed.

To fill the ring a bead of medium CA was set around the ring and sanded smooth.

Custom Solar Explorer Build Part 12 Fin Fillet TIP

A line of Titebeond Molding and Trim Glue was used for the inside fillets.

Lonnie Buchanon gave me this tip:
TIP: Be sure your fingernails are trimmed close when you smooth a fillet in a tight corner.
A long fingernail can easily scar the balsa when trying to smooth out a fillet like this.

Custom Solar Explorer Build Part 11 Fin Gluing

While the instructions don't get into any detail about gluing the outside fins -
Alignment of the top of the "T" fins should be straight and centered.

The masked strip is your gluing surface for the outside fins.

Find the center again and draw a pencil line over the top of the leading and trailing edges of the smaller fins.

Run a thin line of glue down the outside edge of theCenter this pencil tick mark down the outside edge of the larger main fin.

I'm not sanding down the edge here!

I'm just using my sanding block as a flat surface to be sure the ends of the two pieces are even.

Press both pieces down on a flat surface and double check the pencil marks to be sure the parts haven't shifted during alignment.

As a final check, the back of my machine square was set in the corner joint to get the 90 degree angle.

AVI Nike Tomahawk Build Part 19 Fin Can Fin Prep

The leading edges of both plastic fin cans had some rough edges.

This is the before shot. The upper right corner looks almost rounded off.

And after squaring up with 400 grit.

Most all the flat surfaces were fine, only one fin needed some molding "dots" sanding off.

Behind every fin was a molding line that needed to be taken off.

This one was the largest.
A simple sanding with a block took it down to surface.
Be sure to check the fin unit after the first color coats to see if the sanding scratches show through the paint.

The rear of the fin can squared up with 220 and then 400 grit.

This back end of the fin can was uneven and rounded on one side.

Custom Solar Explorer Build Part 10 Fin Priming

In this picture, the CWF has already been sanded down with 400 grit on a block.
All the flat surfaces and edges were sanded flat.

Here I'm just "kissing off" the rough corners of the leading and trailing edges at a 45 degree angle.
Sometimes the squared edges will be rough, that will show up when the color coats are applied.
This is a very light pass of the sanding block, not
enough to lose the sharp edges.



The two fin pieces are glued together in a "T" shape.
I've been filling the balsa before gluing it all together. It'd be very hard to get filler into all the inside corners if the model were all built up.

Before priming, the center strip (the gluing area to the main, large fins) square of the rectangular outside fins will have to be masked.

Use a ruler to find the center and draw the line with a pencil.

Here's all the fin pieces flat side up ready for the primer.
One side will be sprayed and let dry. The fin pieces will be flipped over and stuck down again to prime the other side.

Look close at the long rectangular pieces. Down the center line is a strip of masking tape to keep the primer off the gluing line for the outside edge of the main fins.

Model Profile - Dr. Zooch Atlas Agena

On the Zooch website you are reminded:
"This kit is NOT for beginners- nor is it for people who don’t bother to read the text."
The cardstock flares around the nozzles will take a little more time but are doable.
I've flown this one many times with great success.
The flame fins were painted with white and yellow spray cans. I left off the orange this time after looking at NASA launch pictures. Real engine flame goes from bright white, a little yellow to gray smoke.

Custom Solar Explorer Build Part 9 Balsa Fin Filling

On the forums, some have asked what Carpenter's Wood Filler looks like when it's dry.
It is "grainy" and shows the brush strokes.

This rough surface is a good guage to tell if the surface is smooth after sanding.

The top fin shows the brushed and dried CWF.
The lower fin shows the surface after sanding with 400 grit on a sanding block.

In my experience, when sanding dried, thinned CWF I don't need anything rougher than 400 grit sandpaper. The CWF doesn't load up the sandpaper. I just hit the block on my jeans pant leg to knock the dust offr the sandpaper.

TIP: I wouldn't sand CWF indoors. it doesn't smell like the old sanding sealer.
You don't want to be breathing it in and it does leave dust everywhere!
There is a warning on the tub: Caution, Eye/Mucous Membrane Irritant. The back panel recommends wearing goggles and a mask!

When you think you are close to the surface, hold the fin up to a bright light.

Enlarge the picture and you can see some shallow brush strokes still on the surface. I'll have to sand a little more.

At the top of the fin you can see the balsa grain just starting to show through.
Don't sand beyond this or you might have to apply another coat of filler!

Custom Solar Explorer Build Part 8 Filling Tube and Lug Seams

I've noticed that the narrower the body tube seams is, the CWF stays in better when sanding.
I have the best luck using a slightly thicker mixture of CWF on the body tube seams. When it's thicker, the glues aren't watered down as much and the filler seems to stay in the seams.

I've been dabbing the filler onto the seam with a cheap brush.
Apply the CWF on the seam for a few inches, then remove the bulk with a razor blade. Wipe the excess CWF off the blade between removing the filler.

I'm not trying to remove it all with the razor blade! Notice how much is left on the tube. Don't pull out the filler you just applied in the seam.

The top tube shows the filler after drying.

The bottom tube has had the filler sanded to surface with 400 grit.
For me, I never have to use any rougher grit than the 400 to remove the filler.

A 220 grit would take it down faster but would also leave deeper scratches in the tube. Deeper scratches means more primer and more sanding.

When the bottom tube is sanded to surface as shown, I only do one (slightly thick) coat of gray primer.
That gray primer gets sanded with 400 grit and is then ready for the first white undercoat.

I've read where some builders do two fill coats of  CWF then four coats of gray primer. That, and all the sanding between every coat! That seems like a lot of extra work. This is what works for me. Everybody has their own way to get it done.


I also fill the lugs before gluing them onto the body tube.

TIP: A simple holder for brushing on the filler is three toothpicks held like a rounded triangle.

The tapered ends of the toothpicks give a good friction fit of the lug ends.

Custom Solar Explorer Build Part 7 Nose Cone

Sorry, no posts tomorrow. I'll be in transit going back to Orlando from a cruise.

The nose cone base was slightly wider than the BT-50 tube diameter.

It was sanded down while in a scrap piece of BT-50.

You can see the slight molding recess in the plastic near the base of the nose cone.

After sanding to shape with 220 grit, 400 grit was used to smooth it all out.

There was some small dips in the plastic.
A small drop of medium CA glue was set in the recesses.
Let it totally dry, a drop of CA could take 15 minutes.

Sand again with 220 then 400.

I won't go into detail about the parachute assembly.
One interesting thing were the tape disks.
There was a small addendum to the instructions showing the new tape disks.

These are big disks, 3/4" in diameter.
In the older instructions, the disks were stuck over the shroud line, old style.
Now the disks have the center hole. You are instructed punch a hole and tie the shroud lines onto the parachute.

Custom Solar Explorer Build Part 6 Nose Cone

TIP: To insure your nose cone base fits well against the top of the BT-50 tube, sand the base flat before gluing in the shoulder.

The edge of the molded base is usually a little rounded.
Sand flat on 220 grit on a block.

The nose cone base has a short interior gluing shoulder.

Before applying glue, think about where the excess glue will end up when the base is pressed into the cone.

TIP: Apply plastic glue to INSIDE of the nose cone lip, not on the shoulder as shown in the instructions.

This keeps the excess glue inside the nose cone and not oozing out onto the outside of the shoulder base. That excess glue could hamper the fit in the BT-50 body tube.

New Knife

I usually buy my #11 blades on sale in a 100 pack, that many will normally last me 1 1/2 years. But, my normal source for the blades hasn't had a sale on them in a while.

I'd used break-off blade knives in the past, I always keep a couple in my range box for use at the launch site. For builds at home, I've always used an X-Acto style knife with the #11 blades.

Here's a new "deluxe" break off knife I found at Home Depot for under $5.00.
It's more comfortable in the hand than the cheaper break-off blade knife on the left.

At one time, I could buy 100, #11 blades on sale for under $15.00.
This 10 pack of "Pro 9" break-off blades is under $5.00. There are 13 blades on the strip for 130 blades total.

The picture shows both knives from the back.
The newer deluxe knife has good support around the break-off blade seam so it won't separate from the strip until you want it to.

I'll still keep my X-Acto handles and #11 blades for tight work and use this new knife for most other cutting.

Custom Solar Explorer Build Part 5 5055 Centering Rings

The instructions direct you to glue the 5055 rings onto the body tube then glue the BT-55 tube over the top.
I'd recommend gluing the rings inside the BT-55 and sanding the rings flush and even with the BT-55 first. Then - glue to this assembly to the BT-50 tube.

If you glued the 5055 rings to the BT-50 tube first, you aren't guaranteed the BT-55 tube will be even with the 5055 rings when it is slid on afterward.

So, glue the rings into the ends of the short BT-55 tube, sand smooth then glue the assembly on the main BT-50 tube.

The BT-55 tube is short enough you can smooth your fillets on the inside using a Q-tip.

This makes for a smaller fillet and less chance for the glue shrinking up and puckering the tube.

You still need to fill the joint seam around the inside of the BT-55 joint.

Brush on some thinned FNF. Let dry and sand with 400 grit on a block.

I had to sand the inside edge a bit to allow a good slide over the BT-50 body tube.

Here's the BT-55 and centering ring assembly slid onto the BT-50 main body.

The exposed ring sides are smooth as glass and the seam is filled and gone.

This shows why you might want to go to the extra effort to fill the rings before gluing them on. It would be impossible to get everything smooth if you glued on the parts as they came right out of the bag.

AVI Nike Tomahawk Build Part 18 Body Tube Prime

Before this picture was taken, the tube seams were filled with CWF mixed a little thicker than the filler used on balsa. This thicker mix stays in the seams better.
Both tubes were sanded to surface leaving the CWF filler in the seams.

Both tubes got a single heavy coat of gray primer.

This is the top end of the tubes, small pieces of masking tape were stuck inside the ends to keep out the primer over spray.

Top tube: I usually knock down the bulk of the primer, light sanding with 220 grit.
220 grit is used until the white layer just starts to show through the primer coat.

Bottom tube: I switch to 400 grit to take the primer down closer to the surface.
Enlarge the picture and you can see the gray primer filling in the remaining seam lines.
You can even see some of the yellow CWF in the seams.

Custom Solar Explorer Build Part 4 5055 Centering Rings

One side of each of the 5055 centering rings will be exposed.
You'll save yourself a lot a sanding and filling problems now - if your sand them smooth now before gluing.

Look close at the picture.
Nearest the side of the sanding block you can see the right side of the ring edge is smooth and square.

When the rings are cut, they are rough and "wedge" shaped. the outside is a little narrower than the inside.

This picture better illustrates what I'm referring to.

The ring on the left is rough, the ring on the right has been sanded flat and square.

After sanding with 220 grit, seal and harden up the surface with some medium CA applied with a Q-tip.

Sand this down with 400 grit.
The sanded CA surface will be like glass.

Custom Solar Explorer Build Part 3 Engine Mount Kevlar

Here's the engine mount finished - up to now.

I was surprised to see the instructions telling you to slide the rings in place, up to the pencil lines. (Both rings are set 1/2" from each end.) THEN add glue fillets.
That's really the best way to glue centering rings.
This way you are taking no chance of them freezing in the wrong place.

While the kit has a "Tea Bag" style shock cord mount, I chose to replace it with Kevlar. (The mount was printed on the instructions on 20 lb. paper. In my opinion, a little weak for a shock cord mount.


Typical for me, I forgot to add the Kevlar.

Using my small rat tail diamond file, a hole was "drilled" through the upper ring, opposite the engine hook.
This diamond file makes the perfect sized hole, just right for the 135 lb. Kevlar I had on hand.

I didn't tie the Kevlar on, there's not much room between the interior walls of the BT-20 and BT-50. A knot might make a bulge through the outside of the BT-50.

I weaved the Kevlar under itself three or four times and cinched it down tight.
After some glue fillets, the line is holding strong.

AVI Nike Tomahawk Build Part 17 Decal Draw

The upper half of the adapter has a recess area with two large bolts.

To get an approximate size of the area, I took a picture of the Alway drawing.
This picture was set into Corel Draw and reduced until the lower tube width was 35 mm., the same diameter of the lower tube on the model.

From this reduction I could draw a simulated recess, shown to the right of the Alway drawing.


The screw and adapter decals were set on a master sheet for printing on a half sheeet of decal paper.

Patreon members: If you'd like a copy of this drawing in a PDF format, send a request for the Nike Tomahawk decal to:
oddlrockets@bellsouth.net


After looking at the first print, I went back and made the screws smaller. The picture to the left shows the larger screw heads.

I make no claim that these screws and decals are true scale. At best, they are "close". The model is a semi scale build anyway!

AVI Nike Tomahawk Build Part 16 Decal Draw

Just so you know, I haven't given up on the AVI Nike Tomahawk build!
The weather and my work schedule weren't good for paint and primer so I'm working on the decal drawings for now.

There are many rows of screws shown on the Peter Alway drawing.
From the top down:
One row of 12 round head Allen screws, then
Eight rows of 8 flat head slotted screws, then
Two rows of 12 flat head Phillips screwsround head Allen screws

The three styles of screws were drawn oversize in Corel Draw.
I went back and made the center recesses a lighter gray after this blog entry.

For better spacing, a 1 space by 12 space retangle box was drawn.
The (reduced) screws were set in the corners of the long divided box.
The 1 X 12 and 1 X 8 boxes are 2.50" wide, which fits aroung the upper 20mm Quest tube.

After the screws were set into the segmented box, the box was erased leaving the screws in the evenly spaced positions.

Custom Solar Explorer Build Part 2 Engine Mount

I don't like how  far the finger tabs extend beyond the back end of the model.
I first saw this tip on TRF, I believe Doug Sams posted about it.

TIP: Cut off the finger tab as shown. You might find it easier to use a Dremel and a cut off wheel.
Flip the hook over -
This rounded end goes to the top of the engine mount, the more square bent end goes to the bottom.

This makes for a cleaner looking model and the rear bend of the hook now has a sharper, square bend to lock over the rear of the engine.

While not mentioned in the instructions,
The centering rings should be notched where they go over the engine hook.

Slide them in place over the hook and mark.
Use a sharp knife or jeweler's diamond file to make the shallow notch.

The thin engine block is glued into the front end of the tube.

It sticks out a slight bit, raised beyond the tube by the thickness of the engine hook.

This can be sanded flush after the glue dries.