The Big Fix! - Scavenger

After a hard landing at the May NEFAR launch, the Scavenger needs a new upper tube.

The ejection charge pushed off the nose cone but not the parachute.
This should be any easy repair.

I've got a few Quest 50mm tubes.
The bent tube was cut off right at the black color separation line.
A coupler was made from some scrap tube and glued in place.
The newly painted black tube followed.

The Scavenger is already loaded with a new E9-6 engine for the Tampa TTRA launch.

Scavenger! Finished

I used the old Estes Optima scheme for some painting ideas. The fin and body tube trim looks a little like the the new Estes Pro Series models.
The finished model is 29 3/8" tall.
Body Tube diameter is 1.92" or Quest 50mm tubing.
I'll probably fly it with D12-5 and E9-6 engines for now.

Lessons learned:
Study up a little more on epoxy fin fillets before trying them again.
Good use for a 50 cent nose cone.
All parts came from the spare parts box. Nothing was from a new order.
Be sure the surface is really clean before setting down Monokote trim tape. One speck of dust will show through the thin trim tape.
Next time use decals instead of electrical tape for the black trim stripes.
They are a little thick!

Scavenger! Build Part 27 Decal

Only one post today - this is long one!

I ended up printing two sizes of the Scavenger name and picked the smaller of the two.
The only decal on this rocket is the name - big and simple.

The name decal was printed on Bel decal paper on my ink jet printer.
Two light coats of Krylon clear gloss were sprayed, followed by a third thicker spray coat.
The gloss coat was allowed to thoroughly dry before soaking the decal in water.

TIP: The ink on a home printed decal can disolve in the water soak if the clear coats aren't applied correctly. These decals will not stretch like a silk screened kit decal. Be sure the surface you are transferring the decal on has a rub of water on it. If you push or pull on the decal when it has started to set, the printed area will show cracks.

I took a few minutes to find the best placement and visual center from front to rear.
I prefer a decal like this to read "up" or toward the nose. If the rocket is going up, the name should read going up.
Military and NASA names, like on the Saturn V, read down. But, those letters are stacked, not side by side like on the Scavenger.

TIP: Hand written scripts should normally be set in upper and lower. It's hard to read a hand written or brush style font set in all caps. Note I said "normally". This is a rare case where a script font was set in all caps and was still readable.

This is a big, long decal. To make placement easier, it was cut in two before soaking in water.

I had already drew small pencil tick marks on the body tube at the position edge of the letter "S" and ending "R".
The first half of the decal "SCAVE" was soaked for 30 seconds and checked. It wasn't easily sliding off the backing paper yet so it was soaked again for 15 more seconds.
It still was holding tight to the back and had a final 15 second soak.
The body tube got a rub of water before the decal was slid into place. You are working against the clock, especially with home printed decals. That bit of water on the tube surface will let you slide and play with the position before the decal has a chance to "lock" in the wrong place.


Positioning a script font like this is different.
You should sight from the rear and visually center between the fins.
The letters in this font don't follow a base line.

Keep the first half of the name wet while the second half is soaking.
You may have to move it again when the two halves are joined.

Scavenger! Build Part 26 Black Tape Trim

1/8" wide strips of black electrical tape were set on either side of the gold Monokote trim. This helps tie in the black color on the upper body.

I didn't have to cut the black strips at an angle over the root edge. These stripes were thin and would fold over the root edge easier than the wider gold stripes.
You could cut them in a open "V" shape like the wider gold stripes.
I cut them from electrical tape out of convenience. I didn't have any black trim Monokote handy.


This is the finished fin.
The gold and black stripes roll over the top of the root edges and were trimmed off a little above the trailing edge.





The upper body got the same stripe treatment at the black/white color separation line.

All that's left now is the name decal.

Scavenger! Build Part 25 Monokote Trim Stripes

The paper cover envelope was cut on the drawn pencil lines.

We'll only be using the center piece for a template.




The center piece was opened up and taped to the gold Monokote trim material.
You can still see the crease at the middle or the fold at the leading edge.

The high point in the middle of the strip is the leading edge.
If measured and cut correctly, the cut Monokote should lay right over the leading edge and the two sides will fall straight down the face of the fin and meet at the bottom.



Set the tip of the leading edge at the middle of the 1/8" thick fin and work down from the top.
Don't burnish the Monokote trim until you are sure of the final position looking at both sides of the fin.
Also, don't burnish the trailing edges, those will be trimmed with a razor blade in the next post.

Scavenger! Build Part 24 Back To It - Paint!

Ever have one of those builds you just wanted to be done?

I had too many bad experiences with the Rustoleum 2X gloss white. After sanding smooth again I took a chance with Duplicolor Gloss White.
While the coverage wasn't as heavy or opaque as the 2X Rustoleum, it did flow well.

I copped out a bit on this paint job and will do something like the original Estes Optima scheme.

The picture shows the simple mask for the black. The upper half of the body gets gloss black. This Scotch tape mask line is about 1 1/2" above the upper launch lug.

The thick gold stripes will be paralell to the root edge, centered on the face of the fins.

The wide Monokote Trim will have to be cut at a specific angle to fold over the leading edge.

To make a cutting template, an paper "envelope" was folded over the fin.
A sharpened dowel was used to gently press a crease into the root edge.



The cover was removed. The creased root edge was cut off the paper envelope.

The paper was placed over the fin again. The stripe width and position were drawn on with pencil and a ruler.

Scavenger! Build Part 23 This Model Is Cursed!

After the gray primer was sprayed and sanded, I followed with the first white coat of paint.

Looking closer at the epoxy fillets, they weren't as smooth as I would have liked.
There was some high spots.
If 30 minute epoxy were used, I would have had more time to get it smoothed before the fillets started to set up.
220 grit was wrapped around a small dowel and the high areas on the fillets were taken down a bit. 400 grit followed and then some more primer.

It was after sanding down that first coat of white that I ran into real problems.
A new can of the Gloss White Rustoleum 2X shot out a flat pebbled mess.
I sanded the rough finish smooth.
It was returned and the exchanged second can did the same thing!
That was returned to Home Depot for a cash refund.


I went to the auto supply store to buy some white Duplicolor spray.
The can was well shaken for a few minutes.
The cap was pulled off and the nozzle tip was missing!!!

I need a break.

Scavenger! Build Part 22 Epoxy Sand and Prime

After the epoxy fillets had dried, some high spots were taken down with some 220 grit wrapped around a dowel. As epoxy dries, it self-levels. The surface should be pretty smooth already, requiring little sanding.
Many builders will add Micro-Balloons to the epoxy mix to make it easier to sand.
Others say it diminishes the strength of the epoxy bond.


The entire model was shot with gray primer.
I tend to shoot only one coat of primer and sand almost to surface.
Other people will shoot several light coats, sanding between coats.
Whatever works best for you is right. I just don't enjoy all that sanding!





After all the fillets and prep, here's the back end ready for the first white coats.

Scavenger! Build Part 21 Epoxy Fillets

After the epoxy is transferred to the root edge, smooth out the bead and remove excess with the rounded end of the Popsicle stick.
Do about half the root edge, wipe off the stick and smooth the rest of the root edge.
When the epoxy is just starting to set up, remove the tape.
You might have a slight ridge where the epoxy has gone over the tape edge.
You'll remove that with the rubbing alcohol in the next step.

Put on a Nitrile glove to remove excess epoxy with rubbing alcohol.
The higher percentage of pure rubbing alcohol, the better it will break down the excess epoxy ridge and smooth the fillets.
Most drugstore alcohol is 70%, try to get the highest percentage.

Pour some alcohol in a small disposable cup.
Dip your gloved finger in the cup and shake off the excess into a paper towel.
Run your wet, gloved fingertip down the epoxy fillet. This should smooth out any irregularity in the fillet and start to break down any glue ridge where the masking tape was.

Try not to do too many passes of the alcohol. It can break down the epoxy too much and slow down the epoxy drying times.

Scavenger! Build Part 20 Epoxy Fillets

Here's a technique I don't have enough experience with!
Epoxy fillets, like any new technique take practice.
Normally I do built up white glue fillets, sometimes I use Titebond Molding and Trim Glue for fillet work. On a rocket this size, the radius (or roundness) of the fillet should be larger.

I'll try to tackle this a little like the MPR guys do.
Masking tape is set down around the fillet areas.
The tape will keep the surrounding areas cleaner. Epoxy tends to get everywhere.

The round end of the Popsicle stick will be used to round the fillet and remove excess.

Be sure you have everything at hand before starting. You don't want to be hunting down anything while the epoxy is hardening up!

You'll need Nitrile disposable gloves, rubbing alcohol, your fillet forming Popsicle stick and plenty of paper towels.

Equal amounts of epoxy (in my case 15 minute epoxy) were set on waxed paper.
I don't mix a lot of epoxy, the A and B parts were about the size of a quarter when they started to spread out and touch in the middle.

You are working against the clock, you'll only be able to fillet two facing fin root edges at a time. Let them dry and mix more to do the next set of facing fins.

This 15 minute epoxy might cure too fast for some builders.
You might have better luck with 30 minute epoxy the first time you use it.

Thoroughly mix parts A and B. Try to keep it central, in a small area when mixing.


I transferred the mixed epoxy onto the root edge area with a toothpick. Enough was transferred to be smoothed with a gloved finger or rounded stick.
Keep the epoxy on the root edge area. Chances are, ther'll be "stringers" and a few stray drops here and there.

Continued next post:

Scavenger! Build Part 19 Launch Lug Alignment

This model will get two, 3/16" diameter lugs.
The lower lug is centered between two fins, flush with the end of the main frame tube. It's positioned opposite the engine hook.

The upper lug is glued on the C/G (center of gravity) location.
Some builder's will glue the lug a little forward of the C/G. Who's right? I really don't know. I just center the upper lug length on the C/G and haven't had any problems in the past.

To get the correct center of gravity (balance point) the parachute, nomex and a 24mm E engine were in place.
TIP: When figuring your center of gravity (C/G) for flight, always load the largest engine you will eventually be flying the rocket with.


Here's another "old school" method for lining up two launch lugs down the body tube.

I use a 3/16" launch rod taped beside the launch lugs while gluing.
In the past I have glued 1/8" lugs in place with a much lighter aluminum rod through the lugs.
This 3/16" rod is steel and pretty heavy. It was just easier to lay it beside the lugs to make sure they were straight.

Scavenger! Build Part 18 Forward Fin Alignment

A straight edged strip of paper was wrapped around the tube, 1" above the leading edge of the rear fins. This assures my forward fins will all be the same distance from the rear fins.
The surface mounted forward fins were glued on with white glue.
The rear trailing edge just touched the paper edge.

Here's something I've seen the mid and high power builder's do.
(This is on a smaller scale, though.)

While the forward fin glue is still wet, Popsicle sticks were clamped on.
Sight from the rear and you'll see the forward fins in line with the root edge of the rear fins.
Before clamping on the Popsicle sticks, be sure they aren't warped!

Scavenger! Build Part 17 Fin Gluing

When you thing about it, Through-The-Wall or TTW fins really changed the structure and strength of mid and high power rocketry.
When I started in 1969, all model rocket fins were surface mounted. For low power models it was fine - for the most part.

The Scavenger fins are Basswood. The interior fin tabs lock against the lower thick card stock centering ring on the engine mount. That and gluing to the engine mount tube gives you a very strong fin can "unit".




Initially 15 minute epoxy was mixed up and applied on the root edge of the fin tab.





The fins were inserted into the slots.

With the 15 minute epoxy set time, I was able to come back every few minutes and check the alignment until I was sure the glue had set up and the fins were tight against the body tube. Even with epoxy on just the root edge tab, it's a very strong joint.

Scavenger! Build Part 16 Upper Shock Cord Mount

I could have used a Estes Tri-Fold mount for the shock cord connection on the nose cone shoulder, but I wanted something stronger.

This is based on what Centuri did at the body tube end on some of their larger diameter rockets.
A half segment about 1" long was cut from some scrap 50mm tube.

Last year when I first made up the plastic nose cones, I made a shoulder from some body tube. This shock cord mount will be glued inside the shoulder.

1/4" elastic shock cord was tied around the segment.
The half round mount was then glued into the shoulder with white glue.

Scavenger! Build Part 15 Engine Mount Gluing

A dowel was measured from just below the upper centering ring to the rear of the mount tube.
A ring of glue was added to the top of the rounded dowel.
The glue ended dowel was set in the mainframe tube up to the pencil mark.

The dowel was rolled around the inside of the tube transferring the glue into an even ring. Keep an eye on the pencil mark and use the dowel as a depth gauge inside the tube.

Two more applications of glue and the mount was slid into place.

TIP: As the upper ring reached the glue, the mount was twisted before reaching the final depth. By twisting the mount the bead of glue will be evenly spread out by the turning centering ring.
Before inserting the mount, take a moment and plan so you can make about 1/2 a turn to smooth out the glue ring. Think about where you want the engine hook to end up (between two fins?) and the engine mount tube depth. (Even with the mainframe tube or overhanging the back.)

Slide in one of the TTW fins just to make sure everything is where it should be.

If the mount is flush with the mainframe tube, use a block to make sure both tubes are even.

I'm using one of my sanding blocks here. Turn the block to the side to clear the engine hook.

The lower ring got a fillet from the back applied with a dowel.

Scavenger! Build Part 14 Root Edge Fitting

Here's the fin fit after the trimming.

Adding the extra recess for the wrap of tape on the engine mount made a big difference in getting the best fit.




With the rear fin in place, you can now see how they'll both look together.

Scavenger! Build Part 13 Root Tab Fitting

With the fins slots cut the engine mount was slid into position.
On this model, the end of the engine mount tube and mainframe tube are even.

A ruler was slid into the cut fin slot. With the end of the ruler making contact against the BT-50H engine mount tube read the measurement of the ruler.

This shows the thru-the-wall fin tab will need to be around 1/2" long.
I purposely cut the fin tabs longer than needed so they could be trimmed and sanded to fit.




The fins were marked with a pencil.
The TTW root edge line was drawn parallel to the lower mainframe root edge line.







I ended up sanding off the excess tab with 100 grit sandpaper on a block.

I also added a slight recess for a better fit over the tape wrap on the engine mount.

Scavenger! Build Part 12 Fin Slots

The top of the slot is rounded using a small rat tail diamond file.
File a bit, check the fin fit and file some more until the fit is good.







This is the finished slot showing the alignment of the rounded leading edge to the rounded top.





This is the fin fit up to now.
The fin tab was purposely cut long and will be cut and sanded to the correct width.
I wanted to make sure the tab wasn't cut too short. I succeeded here!
After fitting the tab, the root edge of the fin will get a line of epoxy and be glued onto the motor mount tube.

Scavenger! Build Part 11 Fin Slots

Using a fin marking guide, the tube was marked for three fins.
With the trailing edge of the fin even with the end of the body tube, the top and bottom of the thru-the-wall tab is marked.




The 1/8" fin width is marked on the three fin lines.
This is the area to be removed for the TTW tab.

The outside edges of the fins have been rounded.
Above the top of the fin slot rectangle is a drawn half circle to fit the rounded leading edge of the fin.
The rear of the fin slot remains square. The fin tab doesn't go all the way to the bottom of the body tube. The rear of the fin tab will rest right on the lower centering ring of the engine mount.



My aluminum angle was used for a secure straightedge to cut the fin slots.
For now, the three slots are square at the top and bottom. The tops will be rounded in the next post.

Scavenger! Build Part 10 TIP Fin Drawing Transfer

This is the "old school" way to preserve your fin plans.
The idea is to make a fin pattern on cardstock without cutting up your original drawn plan.

Tape down some new cardstock on your work area.
The drawn fin plan is taped over the cardstock.

Punch through all the corners, through the drawing and into your blank cardstock below. You can use a thumbtack or needle, here I used a punch awl.

Connect the punch dots with a pencil and straight edge.
Cut out your new fin template.








Trace around your new template on your fin stock and cut out the fins.