Estes Doorknob, #9720 Build, Part 3, Fin Shaping

You can build the model as scale or sport style.

On the left is the Scale fin with the diamond taper leading edge.
The Sport fin has a rounded leading edge.

If you extend a parallel line from the lower left fin tip to the root edge, the shaded taper shown above is a little lower.

The inset picture shows where the taper line ends up at the root edge.

Normally I don't use masking tape to shape a taper like this, but the taper is wide and the balsa stock is thin for a fin this size.

To better see the thickness of the taper when sanding, I mark the leading edge with a marker.
FIRST - give the leading edge a good wipe of medium CA glue. This seals the edge so the marker ink wont soak into the soft balsa.
The CA glue also strengthens the thin leading edge.
SECOND - Run a marker down the leading edge blackening it.

The edge taper is sanded with a sanding block with 220 grit sandpaper.

Constantly check the blackened leading edge when sanding. The blackened edge is easier to see over a light beige balsa. The masking tape prevents you from sanding beyond the wide lower end of the taper.
Go light, you can sand through the tape.
Sand a bit, check the taper, flip over the fin and sand the other side evening up the edge taper.

Estes Doorknob, #9720 Build, Part 2, Engine Mount

The green ring had a burr that needed smoothing.
I turned it against the nose cone, but it still required some sanding to slide over the engine mount tube.




This instruction picture was a little confusing.
The ring is used to position the spacing of the lower B ring.
Don't glue the green ring on the tube!

Apply the glue fillet behind the B ring, then slide off the green ring.

I used my sanding block to press down and even up the end of the tube and the green ring.

The picture on the right shows the fillet on the top side joint.

Use the fin slot to set the position of the middle slotted ring.
TIP: Slide a second fin in the opposite slot to be sure the slotted ring in on straight

With the second ring in place, the green ring is glued against it.





The upper ring is glued on the top of the tube.
Glue it over the end a bit to allow a fillet on both sides.

Estes Doorknob, #9720 Build, Part 1, Parts

The stocky body, orange and white roll pattern set this one off!
The parts were all of good quality. 3" diameter heavy slotted tubing and 18" parachute.



Parts of interest:
That BIG nose cone
Peel and stick metallic trim bands
29mm engine retainer rings




There is also a "sport" decor.
Buy the kit, email Estes and request the sport decal. The black stripe wrap decals are included on the kit decal.

Here's the "sport" decal sheet.

Centuri Vector V #KB-2 Build, Second Build Finished

The second build is in the catalog color and decal scheme. I'm a little more partial to the first build and color variation, the one with the wide span fins.










Here's both builds for comparison.

Centuri Vector V #KB-2 Build, First Build Finished

This was billed as a "Customizing Kit" giving the builder many choices on fins, vane position and decals.
I even put the Centuri decal on one build, it seemed appropriate this time.

Centuri Vector V #KB-2 Build, Part 11, Black Paint & Decals

Here's the mask for the black vanes. This picture shows the upper vane placement







This is the vane mask for the lower placement near the top of the shroud.
The picture on the right shows how to pull the tape off, away and folded over itself.

Whoops!
I got some black over spray on the shroud.

TIPS: With the blue totally dry, I was able to use a Mr. Clean Magic Sponge to scrub off the black.

Using a Magic Sponge can dull the gloss a bit.

Hit the dull area with some polishing compound to bring the gloss back.

Most of the decals are self explanatory, there are extras so you can customize a bit.

At the bottom are "Short Bars" that center between the five fins.






TIPS: I cut the decals off the sheet with the low side wide, leaving an even clear space at the bottom of all five bars. With the even cut at the bottom, the clear area was used to space them up from the bottom of the BT-55 tube.

Centuri Vector V #KB-2 Build, Part 10, Shock Cord & Lower Body Paint

The Kevlar shock cord was tied around a second, upper engine block. An outside layer of the block was peeled off to fit the inside of the coupler.






The Kevlar end was slid into the upper tube, don't glue the tube on yet. The upper tube was then slid into the coupler. The Kevlar line was marked a little below the top of the body tube.
The tube was slid off and a loop was tied with the mark at the top of the loop. Look close at the right side pictures to see the mark.




On the left is the mask for the low end purple (left) and blue mask on the right.







The build on the left is painted like the catalog picture, red, silver and blue.
I did find a Rusto Metallic Blue paint, but it was dark. The black decals would disappear if placed over the color that was too blue.

On the right is the variation, I decided on orange, silver and purple.

Centuri Vector V #KB-2 Build, Part 9, Vanes & Design Placement

Here's how the seven vanes look, placed evenly around the pattern base.








There's good reason why I didn't glue together the upper and lower segments.
I could try two different placements of the vanes over two different fin settings.







My two picks are on the right side of both pictures.

Now I can glue the upper tube segments and move on to the white undercoats and fine sanding.

Centuri Vector V #KB-2 Build, Part 8, Coolant Vane Base

In the original kit, Centuri had you cut the vane coolant pattern off the thin 20 lb. paper instruction sheet. I wanted a little more visual relief so it was redrawn to fit the BT-20 and printed on 110 lb. card stock.

I pre-curled the pattern. Even though it is flattened out for the adhesive spray, the pre-curl will help the fit of the wrap.



From the Centuri instructions:
This shows the possibilities with the four different root edge choices and different placements of the coolant vane pieces.

Plan ahead for your favorite look.

The vane pattern pieces were taped print side down on scrap cardboard.

You could use a thin coat of glue, but might end up with some wrinkling.
I used the Scotch Super 77, the same stuff used on the Saturn V vacu-form wraps. The back side was lightly sprayed.





I'm building two different Vector Vs, one with the coolant vane position at the top, the second almost at the bottom of the 6" BT-20 tube.






As usual with the Super 77 adhesive, the ends can lift.
A small bit of glue was sneaked in on a knife blade.
The ends are burnished down with the back end of a Sharpie barrel.

Centuri Vector V #KB-2 Build, Part 7, Vane Cutting

The vane strip is an interesting size, 1/16" thick x 6" long x 1/6" wide. I cut the strip from some basswood.
Basswood grain is tight but can still be filled with a shot of filler/primer.

On the left is the sprayed strip, on the right is another piece after 400 grit sanding.







Seven 1/2" long pieces were needed.

Interesting design - five fins and seven vanes.

As usual, I cut more pieces than needed and will use the best seven.

I lined up the ends , butted up against  the flat side of my sanding block. I had to do some sanding to shorten and even up a few.

Centuri Vector V #KB-2 Build, Part 6, Fiber Fin Edges

TIP: Card stock fin edges can be sealed and slightly rounded with a bead of glue.

A line of white or yellow glue is run down the edge. Use the side of your finger to smooth the round bead and remove any excess glue. Be sure the glue covers the edge completely from side to side. Make the bead as even and round as possible. The glue bead will shrink down a bit as it dries.




Don't do a glue bead on the root edge, that should remain square.

I set some masking tape sticky side up and set the fin vertically on the root edge. This allows the glue to dry without running or the fin sticking to the work surface.





After the glue dries, smooth the glue bead with 400 grit sandpaper rolled over a fingertip.
This fin glue sealing and rounding step isn't necessary, but makes for smooth edges when painting and a stronger fin.

These fins cut from picture frame mat board  have a smooth side and a slightly rougher side. They will need two shots of filler/primer, sanding between coats.

There are five fins, four are stuck down on tape with the root edges against each other to keep the paint off. The odd fifth fin is on the left.

Centuri Vector V #KB-2 Build, Part 5, Engine Mount

For a time, Centuri produced smaller diameter kits with a two-piece main body. A lower 3" engine mount tube and a longer upper tube.
TRIVIA: This is speculation on my part, but it seems the Centuri designers were trying to get away from the standard engine block gluing inside and up in the body tube.
The engine hook end is pushed into a cut slot. No engine block is used above the upper bend of the hook.
The coupler joining the two tubes ends up as the engine block. A first time builder doesn't have to deal with trying to glue up in the tube and position a standard engine block!

On the left is a dry fit of the shroud, a little below the top of the short 3" BT-20 engine mount tube.

On the right -
The coupler is removed. The shroud is glued on and pressed into place until the top is even with the end of the BT-20 tube.

I also added a Mylar engine retaining ring. That's a homemade engine hook, bent from windshield washer blade spine. It's stiffer than a standard hook. The additional retainer ring might strengthen the tube when the hook is pressed out.

Centuri Vector V #KB-2 Build, Part 4, Nested Shroud

I went to payloadbay.com and printed two shrouds in the "Tools" section. Punch in the outside diameters for a BT-20 and BT-55 x 1.3" tall.

Look close and you can see two shrouds, one stuck inside the other. There is an overhang at the bottom.

Why a double layer shroud? It's just stronger! These work especially well for exposed nozzles on the low end. Imagine a thin card stock nozzle getting bent up after hitting the ground first.


For more detailed instructions: CLICK HERE

A glue stick works a bit better over wet glues. When the shrouds are glued together, set the seams on opposite sides.

After it dries, the overhang is trimmed off with a single edge razor blade. The wide trimmed edge is sanded flat on a block.

On the left, notice the stepped inside edge. These two edges are the same diameter, fit the BT-20 making two ring contact points.

A notch is cut in the 20/55 centering ring for a engine hook.

When gluing in the ring, the notch is lined up with the seam on the outside of the shroud.