BMS School Rocket, Build, Finished

A sharp, well designed rocket for school programs looking for something other than a snap together build. Thru-the-wall fins, Kevlar shock cord and a Mylar streamer.

The instructions only suggest an A8-3 motor, but it would certainly be stable with a B6 or C6 engine. 

You might not get it back with the C6-5 motor.

Taller than an Estes Alpha, with the extra length it should be easier to pack the wadding and streamer.

BMS School Rocket, Build, Part 9, Tying It All Together

The nose cone shoulder was masked using a rolled sheet of copy paper and masking tape. 

Normally I don't tie on the shock cord until after it is painted. 

The kit is supplied with a Kevlar shock cord. I added a length of elastic.

The elastic and Kevlar was tied together using interlocking loops.

The elastic was tied to the screw eye using a Duncan Uni-Knot. 

From the instructions - 

Tape, fold and staple the streamer to the shock cord.

The shock cord is chrome Mylar. 

It is thick Mylar, 2" wide x 24" long.

BMS School Rocket, Build, Part 8, Paint & Mask

After a few white undercoats - The body was painted and overall gloss yellow.

A paper towel was rolled and slid into the front of the body tube to keep the paint out.

The four fins will be painted black.

I used my standard Scotch tape masks, the edges marked with an off brand permanent marker. I'd recommend using an actual wide point Sharpie to mark the tape, some of the off brand marker ink rubbed off on the fins and body.

Here's the rounded leading edge mask made up of a few small pieces of Scotch tape mask.

After the tape was pulled,

There was traces of black marker ink on the yellow body paint. This was cleaned off using a Magic Sponge. 

The Magic Sponge can dull the gloss, some polishing compound brought back the shine.

BMS School Rocket, Build, Part 7, Filling The Fin Grain

Here's one side of one fin with the filler brushed on.

Notice I didn't brush filler onto the TTW fin tab.

Many builders comment on forums about how CWF filler warps their  fins.

With the filler on just one side of the fin, the fin will warp as it dries.

Don't worry, the fin will flatten out when CWF is brushed on the other side and allowed to dry.

BMS School Rocket, Build, Part 6, Gluing In The Engine Mount & Filling The Nose Cone

I use a dowel set a ring of wood glue inside the main airframe tube.

A dowel is set next to the mount with the end just below the upper centering ring. The bottom of the mount tube will extend 1/4"  below the end of the main airframe tube. The dowel is marked at the 1/4" extension.

A ring of glue is placed around the top of the dowel. Using the pencil mark as a depth gauge, roll a ring of glue inside the tube. 

Slide the mount into place, up to the 1/4" mark.

I like to center the engine hook between two fins.

Right now there is only glue at the upper centering ring.

There isn't much room to apply and smooth a glue fillet around the rear ring. Apply some glue and smooth the fillet with a Q-tip formed into a "tip" by rolling it between your fingers. 

The shoulder lip on the nose cone wasn't as square as I would like.

Notice the CWF filler is painted just over the edge of the shoulder.

Push the nose one all the way into the BT-50 tube and turn.

Turn and remove the nose cone.

What you are left with is a raised filler bead right above the balsa shoulder.

Let dry and sand with 400 grit on a block.

The shoulder lip will end up sharper and a better fit against the end of the body tube.

BMS School Rocket, Build, Part 5, Fin Prepping

The pre-cut fins are 3/32" thick.

Laser cutting cuts the sides in a slight wedge, widening out on the backside.

On the left, some of the laser ash has been sanded, squaring up the cut angle. This makes it easier to glue the fin on straight.

With the fin tabs in the slots, 

The trailing edge is even with the end of the body tube.

Just the leading edge is rounded.

I knock off the sides with my sanding block with 220 grit sandpaper.

Smooth off the leading edge with 400 grit.

BMS School Rocket, Build, Part 4, A New Kevlar Cord Protection?

I can't take credit for this idea - 

Props go to Rick Randall at New Way Model Rockets. He has incorporated this Kevlar protection cover in many of his LPR kits.

Kevlar lines start to break down and can fail at 10 to 15 launches.

Near the low end of the Kevlar, near the engine mount - Rick adds some heat shrink tubing over the Kevlar line. When you consider how hot a heat gun gets (to shrink the tube around a wire) it makes sense!

An black powder ejection charge is momentary, the heat gun take a few seconds to shrink around the Kevlar line.

Heat shrink tubing is not included in the School Rocket Kit. I found some on Ebay and am starting to use it in my builds.

For reference, here's a 1/16" diameter heat shrink tube slid over a 135 lb. LPR Kevlar line.

To fit it over the Kevlar knot under the engine hook,

I flared the open end a bit using a sharpened dowel. The flared end makes it easy to slide over the knot.

On the left,

The heat shrink is slipped down and over the knotted Kevlar line.

On the right,

A heat gun was used to shrink the cover tight over the Kevlar and knot. The hear gun was used on the LOW setting.

There is that square hole left on the other side. Some ejection gasses could escape out of the hole.

A small piece of scrap BT-20 was cut and glued over the hole.

BMS School Rocket, Build, Part 3, Engine Mount

From the instructions:

This shows a dry fit, the centering rings aren't glued over the laser cut lines yet.

The Kevlar shock cord is tied through a cut hole and around the engine block.

I prefer tying a small loop knot and setting that under the top bend of the engine hook. This is an idea from Semroc. 

More later - 

OOPS! Originally I raised the lower centering ring above the laser cut positioning line to give more flex of the engine hook. I had to lower the ring, it would be in the way of the TTW fin tab.

I set the rings in a light ring of glue, applied to the tube. The ring is slid into the glue ring.

Side by side, 

Here's how the engine mount centering rings set when glued onto the laser cut lines.

You have some good space around the rings and fin tabs.

 

BMS School Rocket, Build, Part 2, Some Parts Prep

I like to strengthen the inside lip of BT-20 and 50 tubes with a wipe of medium CA glue.

Think ahead, You don't want any CA glue where wood glue would follow. The CA glue seals the tube, no wood glue can  soak in.

After the CA dries, 

square up the tube end with some 400 grit on a block.

Right out of the bag,

The corners of the nose cone shoulder are square.

Round the ends off for an easier insertion in the body tube.

Here's the rounded shoulder.

The rounded edge won't fray or start a peel of the inside layers of the BT-50 tube.

BMS School Rocket, Build, Part 1, Parts

Parts are clean and ready for assembly without too much prep.

To the right is the nose cone with a hardwood dowel insert.

With the dowel glued in the pre-drilled hole, the screw eye will not easily pull out. 

The main airframe tube (shown above) has laser cut fin slots.

On the left is the 3/16" diameter launch lug. The 3/16" lug was used to make it easier for a younger flyer to slide the rocket down a 1/8" launch rod. 

The engine mount tube has light laser cut lines for the centering ring positions. The square cutout is for the Kevlar tie.

BMS School Rocket, Build, Background

This is the original BT-50 based Balsa Machining Service School Rocket.

The picture is from the BMS website, in yellow and black school bus colors.

14" tall, 0.976" diameter

Balsa nose cone and balsa thru-the-wall fins

The fins and body tube fin slots are laser cut.

Kevlar Shock Cord

Shiny chrome Streamer recovery

3/16" diameter launch lug 

Perfect for school groups looking to actually build a model rocket.

A little like the Estes Alpha, but with four fins and a with a longer body tube for easier wadding and streamer packing.

The price is great for group purchases, $6.75 each in any quantity.

To see the catalog page and link to the online instructions: CLICK HERE

While the model assembly is for the most part standard, I'll incorporate some personal changes.

BMS/Alway Saturn V Build, Finished!

The fit of the fin fairings could have been better, three out of the four were good.
I've mentioned before what a well engineered kit this is. It's a manageable sized Saturn V and flys well with a C6 engine.

I know BMS has sold out of this run, more kits could be made in the future.

BMS/Alway Saturn V Build, Part 28, Decals!

Most all the decals went on with no real problems. This post will concentrate on the small fin decals.

The fin letter decals are tiny!
TIP: To make the placement consistent on all fin sides, extend the corner lines on the full sized template from the instructions.
Cut out the fin letter to the lower right corner.
Making a template like this refers back to the old Centuri Saturn V instructions.

The small body and fin numbers are printed on a white decal sheet. Cut them very close to the edge. Ideally you want to cut to the outside of the black border lines.

Use long tweezers to dip the decal, then "float" it on the surface of the water. Let the decal soak for 15 seconds.

Use the tweezers to pick up the small decal off the top surface of the water. Set the decal (still on its backing) on a paper towel for 30 seconds or until it easily slides off the backing paper.

The positioning template is shown here on the fin. This template was cut from card stock.
Use it to check the positioning of the fin letter decals.

For the other side of the fin, the same template is flipped over to check the position of the second "A" decal.

BMS/Alway Saturn V Build, Part 27, Hydrogen Lines and Nose Weight

The five Liquid Hydrogen Lines are glued in place, centered on the masked rectangle areas.

The instructions don't mention to do this, but I cut away the wrap strips under the glued on lines. The pieces were held in place while the lines were cut with a razor blade.

The Liquid Hydrogen Lines glued in place.

I'll be putting in the nose weight before applying the decals.
The first and lowest penny weight in the stack has a hole drilled in it to tie on the Kevlar line.

The other pennies are stacked on top, inside the Service Module tube.

It's interesting to note the supplied pennies are older, minted before 1982. After 1982, solid copper (heavier) pennies were no longer being produced.

The Kevlar line is tied to the screw eye in the base of the adapter.
Tie a  loop in the Kevlar so the upper body hangs with the tower end up.

BMS/Alway Saturn V Build, Part 26, Fin and Fairing Gluing

Look at the shape of the fairing from the top. You want a good smooth curve of the outside edge.

On the left is the before, on the right is after some very gentle forming.

I set the fairing tip against my finger for support.
A smooth, tapered dowel was rolled over the fairing to gently coax and reshape the fairing edge where needed.








Test fit before using any glue.
This picture shows one of the better fitting fin assemblies.

I only used a good sized glue bead at the center of the support piece.









Rubber bands were set around the fairing and body tube. Notice the rubber band only goes over areas of the shroud that have internal support. I don't want to deform the fairing.