Tuesday, July 16, 2019

Centurion Project, Part 10, Black and White Paint

This is a very easy model to paint, the low end is white, the upper tube and nose cone are black.
TIP: Always think ahead when assembling a rocket. The instructions tell you to glue the two body tube sections together with a coupler before finishing. Wait to glue the two body tubes and spray them separately - no masking!
After you are happy with the upper and lower sections in their different colors, then glue them together.


Here's one of those examples where the paint can help fill some low areas, here on the launch lug glue fillet.
Sanding with 400 grit took some paint off the fillet . After the final coat of paint you probably won't even notice the dips in the glue line.
On the upper body, I did do an overall white undercoat and followed by light sanding.
There is no need to get a consistent, bright white cover on the upper section - it will end up being black.

Go right to the gloss black!
If the final colors are light colors, you do want a even, bright white undercoat. This isn't needed when spraying the dark black.

Monday, July 15, 2019

Motor or Engine?





On the Centuri Model Rocket Facebook page,

Steven Ross posted this:






Gary Dahlke responded:
"This is the aerospace industry convention: solid propulsion = motor; liquid propulsion = engine. Gary Dahlke, Pratt & Whitney Space Propulsion 1993-2000, Space Shuttle Program 1993-2010."



I call them "Engines" out of habit, that's what I read in the model rocket catalogs. 
This is from the 1972 Estes Catalog. 
Vern wouldn't lie to us, would he? 

The 1972 Centuri Catalog also called them engines.

Here's a clip from a Vashon Catalog. Vashon Rockets used liquid propellant or Freon.
Vashon called their liquid fueled rockets Engines!

So who's right?
Call 'em what you want, everybody will know what you are talking about.

Centurion Project, Part 9, Ends & Edges

The larger Centurion has two 3/16" launch lugs.
On the left is a typical applied line of glue.
TIP: On the right I've placed my thumb and index finger into a "V" shape. This V is run down the glue line evening it up and removing excess. This helps get a cleaner glue joint before fillets are applied.
You can also use the V shaping of glue lines on the root edges of fins before setting them on the body tube.




The lower body is ready for the white paint.






TIP: Try not to let the sandpaper roll over a squared fin edge.
My middle finger is rolled over the outside edge of the fin and acts as a "bumper" preventing the sandpaper from rounding off the sharp fin edge.




This Centuri style baffle was already assembled from a few years back.

I didn't like the 1/4" elastic shock cord, it was an open weave when stretched out. It didn't look as strong as normal kit elastic.
I had to slide a single edge razor blade under the cap piece to remove it. Some new, stronger 1/4" black elastic was tied on and the cap glued back on.

Sunday, July 14, 2019

Name That Rocket -

Johnathan Wilkins posted on the Estes Model Rockets Facebook page:


"Name That Rocket . . ."

There were plenty of responses, most thought it was the original Estes Drifter. You know, the one that had a 12' and 24" parachute in the kit? Guaranteed to be lost on the first flight using the 24" parachute.
To see the Estes Drifter instructions: CLICK HERE 

Steven Perkins got it right by guessing "Calypso". The kit was produced for two years, 1989-1990. To see the Estes Calypso instructions: CLICK HERE

But, there was another guess by Greg Kennedy: "Centuri Starfire?"
Jonathan Wilkins said that answer was incorrect. Or was it?






The Estes Drifter (1964 - 1979) was first, followed by the Centuri Starfire in 1967. The Starfire was Centuri's answer to the Estes Drifter. The Starfire stayed in production until 1982.
To see the Starfire instructions: CLICK HERE
The Estes Calypso was released seven years later in 1989.

Take a look at the fins on the Calypso and Starfire - pretty close, if not the same.
The body tube diameters and model lengths are also very close.

Both the Drifter and Calypso had trailing fins, a paper boat tail and two parachutes. But, the Estes Calypso had streamer recovery.

I've already spent too much time researching these - I'll let somebody else compare the fins between the Starfire and Calypso.

Centurion Project, Part 8, Fin Gluing

These pictures are of the Estes Cosmic Explorer, the slightly down scaled version of the Centuri Centurion.
The Estes Cosmic Explorer (BT-55) has through the wall fins, the root edge of the fins glue to the engine mount tube.

Looking inside the pre-cut fin slot you can see the black electrical tape I used around the engine hook. The black tape also holds the tube for the replaceable Kevlar mount.

In the above left picture the fin doesn't quite seat against the outside body tube. The electrical tape is wider than the slot recess that would have fit the Mylar retention ring.

I've marked the tab with pencil where the notch needs to be wider. I carefully shaved off the pencil area to fit over the tape wrap.

The right side of the first picture (above) shows a better fit of the root edge.


Back to the larger Centurion:
These fins are surface glued onto the body tube - no fin slots.

After the fin lines are drawn, the primer paint is scraped off a little wider than the 3/32" thick fins.
The pencil line is scraped off, but redrawn before gluing the fins on.


From the back end - 
At the edge of the fin you can see a pencil line drawn around the end of the body tube.
These fins totally cover the pencil line at the back. The small pencil "tic" mark gives you something to center the root edge on when you can't see the line.

Inside is the engine lock strip, centered between two fins.

Saturday, July 13, 2019

Centurion Project, Part 7, Fin and Body Tube Fill


The body tubes got the standard CWF seam fill and sanding.

On the left is the rough cut body tubes joined by a coupler. The tube cuts aren't great. True it up with a sanding block.
The picture on the right shows the new joint after sanding the ends with a block.

Here's the body tube after the CWF and sanding, then filler/primer and sanding.
You can see some of the gray filler/primer left in the tube seams. The filler/primer fills any recesses left after the first CWF step.
On balsa fins - I prefer a two-step CWF, sanding then filler/primer and sanding over four applications of sanding sealer and sanding.

The body tube will look mottled after sanding down the filler/primer. Most tubes are not perfectly smooth.


Here's a good example of filled balsa.
Again the filler/primer can be seen left in some of the balsa pores.









The old original nose cone also got CWF and filler/primer and sanding.

Friday, July 12, 2019

Centurion Project, Part 6, Fin Fix

One fin had a broken tip on the trailing edge!
The old Centuri instructions suggest sanding an airfoil shape to the fins after they are glued onto the body tube.
The Semroc instructions say: "Round all edges except the root edges (which will be glued to the body tube). The trailing edge and tip edge can be sanded to a taper for more aerodynamic fins. Be careful that the curve at the end of the root edge does not get broken off. It is fragile until glued to the body tube."
The Estes Cosmic Explorer say to round only the leading edge. Because that trailing edge is delicate, I'll only round off the leading edge.

That broken tip edge was ragged.
FIX: For a flatter gluing edge, the tip was squared off using a sanding block.
Save the leftover balsa from the laser cut sheet for moments like this. A small triangle was cut and glued onto the tip.





After it dried, the tip was shaved down closer to the root edge line of the fin. The root edge was evened up with a sanding block.

Sanding this inside curve could be tricky, you don't want to break it off again.
TIP: Stack all three fins with the repair fin in the center. the outside fins will support the tip and give you a sanding template to follow.

Wrap some 400 grit around an dowel and carefully sand the tip down to the other fins contour.