Enerjet by Aerotech Initiator Build, Part 2, Parts Prep, Fins

The leading edge tips are uneven. 

Here's the before and after.

It's easiest to check the tip shape from the other side.

There is a mold nub where the fin was broken off the molding tree.

This root edge should sit flat against the motor mount tube so sand it off.

Here's the underside of the trailing edge. 

The center mold line should be sanded smooth.

Enerjet by Aerotech Initiator Build, Part 1, Parts

Above is all the parts. Everything seems to be great quality.

The parts of interest:

Heavy walled tube 2.6" diameter.

24mm & 29 mm Aluminum Motor Retainer

Ejection Cooling Mesh

"Launch Lug" Rail Guides

Fin Lock Rings

Molded Plastic Fins (Thru-The-Wall)

The instructions and self adhesive decal sheet are tightly rolled up in the main body tube.

TIP: You may not be able to reach and pull them out. Lightly tap the tube on your open palm and they will work their way down and out.

Enerjet by Aerotech Initiator Build, Background

I'll be building quite a few of the Enerjet by Aerotech kits. 

First up is their starter set model, the Initiator.

Bob Sanford designed the Initiator when he worked at Enertek. 

I understand it is based on the old Centuri Starfire model rocket. The R&D team was looking for a design that company president Lee Piester would like. Mr. Piester designed the Starfire when he was president of Centuri.

Enertek was sold to Gary Rosenfield and Aerotech was established. 

The Initiator and other Enertek designs are still being produced.

Bob Sanford commented with the correct history:

"AeroTech was established in 1981. Enertek did not begin until 1987 and closed in 1988.

One of the Enertek investors bought up the assets and IP of Enertek after it closed and contributed them to ISP (AeroTech's parent company at the time) in exchange for stock.
The only Enertek designs that were ever directly manufactured were the Initiator and Strong ARM (With some changes from the originals). The Enertek Astra 2000 was released at a smaller size by Quest and named the Striker AGM.

From the install last October, 

A giant Initiator greets rocket enthusiasts at the Aerotech facility in Cedar City, Utah.

New Aerotech Builds

The Wac Corporal paint will have to wait - 

Every time I'd go out to spray around 2:30 p.m. there was rain!

That and allowing 48 hours between fully dried, sandable undercoats.

This arrived today - 

Two BIG boxes. 

Where there is multiples, 

One will be show grade, the others will be for flight.

The show builds have filled tube and nose cone seams.

More time goes into the show builds.

Flight models aren't quite so detailed.

In the second smaller box were five Initiator kits. 

Two of these will be show models, three are built to be flown.

The last Grunt build is show.

How did I get a job building for vendors? I asked if they needed some finished models. Build coverage on the blog also helped get my name out there. 

I'll start on the Initiators tomorrow.

Semroc Wac Corporal Build, Waiting For Paint To Dry

I'll get back to the final white undercoat today on the Semroc Wac Corporal.

Here's the fin areas after the second white undercoat and some light sanding. It'll still take one more light undercoat before sanding and color.

Too many Odd'l Rockets kit orders pushed this build to the back burner.

Also - expecting a major kit build for Aerotech/Quest in the mail. 13 MPR builds in all!

Semroc Wac Corporal Build, Waiting For Paint To Dry

This shouldn't really count as a build step -

I'm stuck waiting for the second white undercoat to dry on the Wac Corporal.

Finishing up a big Odd'l Rockets order for ERockets. 

Spent most of the afternoon machining ADEPTOR camera tripod adapters.

I'm about halfway through a kit order for Apogee.

Semroc Wac Corporal Build, Part 14, Watching Paint Dry

I see too many posts on the rocketry forums and Facebook about paint problems.

"Did this ever happen to you?" followed by a picture of a rocket with wrinkled paint.

Back to the current Wac Corporal build - 

Before another spray coat, I'm waiting a full 48 hours for the first white undercoat to dry. The rough areas have been sanded. 

READ and follow THE DIRECTIONS on the can!

Most cans say: Re-spray within one hour or after 48 hours.

Paint dries faster on balsa fins and Kraft paper tubes. 

Balsa and paper tubes "breathe!" and can dry through both inside and outside surfaces.

Plastic nose cones require much more time to dry.

Plastic is "sealed" and dries slower from the outside surface in. 

To prevent blushing of the finish, spray when humidity is the lowest.

Check this address: https://www.timeanddate.com/weather

Type in your city and check the afternoon hours for the lowest humidity.

I'm not saying these tips will prevent all paint problems.

But, it may help with some concerns.

Rustoleum 2X paint is problematic, especially the Gloss White. Random cans can spray pigment (a rough, cottage cheese) that has settled on the bottom of the can. Shaking helps but may not break up all the settled pigment.

Semroc Wac Corporal Build, Part 13, White Undercoat & Sanding

It never fails -

I think I've done a good job making smooth fillets. I think I've picked up all the excess glue before it has dried.

The first white undercoat usually brings attention to all the flaws.

On the left is an uneven glue fillet.

On the right is after careful sanding with some older 4000 grit. 

You can sand yellow wood glue.

A before and after of the flue fillets on the upper launch lug.

Sand under a bright light. Sanding dulls the gloss white. Low areas that need more sanding will still be glossy.

Here's a noticeable glue booger near the leading edge of a fin.

On the right is after sanding to surface. 

In 48 hours, another white undercoat and probably some more sanding.

Semroc Wac Corporal Build, Part 12, Tunnel & Launch Lugs

The tunnel is glued in line with the fin, opposite the engine hook position.

In the old Estes Wac Corporal kit, the open ended tunnel covered the long launch lug. It had to be glued between the fins.

Two short lugs are used in the Semroc kit.

Both are glued in line, directly over the engine hook. 

The lower lug is glued right above the tail cone/body tube joint. 

The upper lug is glued 4" above the end of the body tube.

I could have used Titebond Quick and Thick to do the lug fillets. Instead, I went old school - it took four glue fillet passes to get rid of the glue bubbles.

Semroc Wac Corporal Build, Part 11, Fitting The Fins

There was still some uneven areas around the tail cone/body tube joint.

Wedge shaped pieces of masking tape were cut to keep another shot of filler/primer of the root edge gluing areas.

The filler/primer was sanded down.

Each fin was individually fit to the tail cone and body tube.

Look close and you can see a small gap at the rear and just below the top of the tail cone.

Here's the same fin after fitting. The gaps are gone. 

For a reference I marked the fin at the shroud/body tube joint with pencil.

Semroc Wac Corporal Build, Part 10, Fitting The Tail Cone

I'm using my old Fin Tool (Sorry, they aren't available) to mark the body tube. I want the shroud joint seam hidden under a fin root edge. In this case the seam and engine hook are on opposite sides.

The shroud is glued onto the lower ring and the first ring of the two center rings.

Lightly form the shroud edge by "molding" it into the wet glue underneath. For now, I'm only molding the low, smaller side.

Dry fit the engine mount into the tube.

TIP: Slide in a turn the mount and shroud until you find the best fit against the tube.

Mark the best position with a pencil mark on the tube.

Now you can apply some glue inside the tube and around the exposed middle centering ring. Slide in and turn the mount until the pencil mark lines up with the shroud joint.

Form the wider shroud edge as before, rolling the burnisher over the tube and shroud joint.

This will make for less filling later on.

The raised shroud overlap can be sanded down a bit. Just lower the thickness a little, not too deep.

Semroc Wac Corporal Build, Part 9, Fitting The Tail Cone

The kit supplies one tail cone shroud printed on cardstock. I rarely get a good fit onto both tube diameters with one shroud.

I scan and copy at least three of them onto 110 lb. cardstock. Assemble all three - one of them should have the best fit.

Do plenty of dry test fittings for a smoother final look.

One shroud on the left is a poor dry fit, both ends are a bit wide.

On the right, one of the other shrouds and a better fit. Both the middle centering rings have been dry pressed into the wide end. The second ring is outside the shroud top and gives you an open edge for gluing and a slip fit of the ST-11 main tube. 

The lower ring is glued in place, even with the end of the motor mount tube.

I use the flat face of my sanding block to press the ring even.

TIP: There was still a very slight gap in the small end of the shroud. I wanted to increase the outside diameter of the low ring.

I applied a thin line of wood glue. Smooth and even it out using a fingertip on both sides of the glue ring.

After it dries, run a finger around the ring and you'll feel high and low areas. Some 400 grit will take down the high spots.

Semroc Wac Corporal Build, Part 8, Second Coat Of Primer/Filler

Normally, one coat of CWF then sanding - 

and a spray of primer/filler and sanding,

takes care of the balsa grain. Not today.

Before sanding the filler/primer I had to rub some CWF into the remaining visible grain.

Keep this CWF rubbed in filler thin and close to he surface.

After sanding down the filler/primer, you could see the remaining high spots left from the initial fin shaping. I wanted the surface to have a nice, rounded profile.

Sanding did take down the raised areas but also cut int the CWF underneath and into the balsa.

This will need another sealing shot of filler/primer and sanding.

The root edge was masked off again using tapered pieces of masking tape.

Onto some scrap cardboard to spray one side.

That long masking tape strip has the sticky side facing up to hold the fins for spraying.

Spray one side and let dry.

flip over the fins and spray the other side.

Semroc Wac Corporal Build, Part 7, Forming The Tunnel

 

I had started forming the tunnel when I had worked on the build before.

Sand the underside curvature by wrapping 220 grit around a body tube. Sand straight up and down motions.

TIP: You'll get a tighter fit if you sand the inside contour on a smaller diameter body tube. The kit tube is 1.17" diameter. I sanded the underside of the tunnel on a slightly smaller .976" diameter BT-50 tube.

Here's the side of the tunnel before shaping the end.

Sand the angle diagonal first.

Round off the ends. 

Round off the long sides.

Here's a good fit of the tunnel on the body tube.

Semroc Wac Corporal Build, Part 6, Launch Lugs

On the left are the laser cut, kit supplied launch lugs. The edges are burnt and rough.

I cut new lugs from some extras I had. 

The seams in the launch lugs were filled with CWF at the same time as the body tube.

I slide the lugs onto a Q-Tip for a holder when brushing on the filler.

Leave the lugs on the holder when sanding the CWF to surface.

Some CWF filler may have gotten inside the lug edge. You don't want the lugs to get hung up on the launch rod.

Clear, clean up and round the lug by rotating a sharpened dowel in the lug ends.

Semroc Wac Corporal Build, Part 5, Fin Shaping C

After doing the taper from the root edge - 

Start the leading and trailing edge tapers.

I've again marked the first high point with pencil.

Round off the sides to an rounded taper. The center area is the high point.

On the left is the root edge view, 

on the right is the leading and outside edge view.

The black ink remains for now. 

Each fin took 35 minutes to shape up to this point.

Here's all three, the shaping done.

The fin on the left has had the remaining ink sanded down with 400 grit.  

The edges are lightly rounded with 400 grit. Keep the root edge square.

Semroc Wac Corporal Build, Part 4, Fin Shaping B

Start by sanding the taper from the wide root edge to the thin outside edge. Concentrate on getting the outside edge thin - you don't have to taper the full face yet.

On the right you can see the taper cutting into the black inked edge.

Continue until you get the thin outside edge to about .05" thick.

It's a compromise. You want the outside edge thin while still keeping it strong enough to survive a hard landing.

To show where we're at now, I pencil shaded the fin face down the high point sand line.

Now sand down that face joining the two different widths - a smooth flat face from the root edge to the thinner outside edge.