Solo launch 8/31/10

Back to the schoolyard for some small, but still fun stuff.

First up was the MMX Cloud Hopper. All was great until apogee when the ejection charge blew his head off. I found the body easily and after a little walking I saw two teeth (on the nose cone head) sticking up out of the grass.

The MMX Downscale Break-Away flew great. All four segments separated and fell close by.



Now for the interesting launches - 35 year old MPC Minijets.
I'd flown old Estes and Centuri engines, but never the old MPCs. I tried them last time using the old MPC igniters with no luck. This time both MPC engines had Estes igniters in them.

The Carded A-20 Demon had a great first flight. The 1/2 A3-3m engine (MPC used the "m" designation, Estes uses the "t"). I didn't put in engine blocks so I could use these longer 2 1/4" Minijets.

Everything worked just as it should. Those old engines really put out a nice smoke trail, newer engines seem to puff out a little smoke right before ejection.

The model tail slid a little after apogee and popped the streamer. This would be a perfect rocket for the Estes 1/2 A3-2T, a second less delay than the old MPC.


Last up was the Cherokee T carded downscale with another MPC 1/2 A3-3m. Great altitude and a walk even with streamer recovery.

As I was walking back to the launcher, the automatic sprinklers turned on!
Luckily they were just outside the reach of my open range box and launcher.

Downscale A-20 Demon Build Part 6 Trim Plates

Wayne Kellner, designer of the Demon, did some great work.

The fin plate trim pieces were a clever design element.

Before cutting them out, score the fold down the center dashed lines as before. These are printed on thinner paper so go easy.

Again, use the dull tip of a butter knife and straightedge. Don't cut through the paper, just make a pre-fold crease.

Don't hit these with the spray adhesive, on pieces this small it's easier to use white glue.

With a straightedge and sharp knife, cut out the plates. There are extras on the print.

Fold them down the crease you made.

Simply apply a thin coat of white glue on the back and center them into the root edge of the fin/body tube joint. Tweezers will make this easier to hold onto.

These plates will also strengthen the fin joint.

Nothing left on this one except to glue the yellow square around a launch lug then glue that into the root area of a fin.

The original big Demon had two lugs, one in the front and one in the rear. On a model this size, a forward lug really detracts for the look of the model. A single rear lug should be fine.

The fin alignment lines on your PDF print were moved slightly rearward from the picture here. Your model will be that much closer to an actual downscale than this first prototype.

It's Finished!

This next launch it should fly with a 35 year old MPC Minijet engine.

Downscale A-20 Demon Build Part 5 Body Wraps

Some builders have luck with just white glue around the backside of a wrap.

I'm not that lucky.

I prefer to use spray adhesive, it gives you a second or third chance at repositioning the wrap. I never seem to get it right the first time.

This Duro Spray Adhesive can is old, maybe over 10 years old. It never seems to run out.

The picture shows all three wrap pieces ready to be sprayed. The cardboard backing was lightly sprayed and allowed to set up for a few minutes. The wrap pieces were placed lightly on the sticky cardboard, just enough to hold them down for spraying the backs.

A pencil line was drawn down the body tube and the first upper wrap was applied, lining it up down the line and with the top of the tube.

The second, longest wrap was started immediately below that using the bottom of the first wrap as a guideline.

Finish up with the third wrap.

The BT-20 tube was long to begin with, I cut off the end and sanded it square with the end of the third bottom wrap.

Be ready - The end seams will lift!

This is a compromise with using the spray adhesive. By using the spray adhesive you have the chance to re-position the wrap. If you apply white glue to stick on the wrap, you get one-shot to get it correct. Once it's down, you won't be able to move it.

Place a few drops of white glue on the corner of your work area. Dip just one side of you hobby knife into the glue. Push some glue under the lifted wrap the run the blade under the wrap edge to smooth out the glue.

Notice that I wrote: Dip just on side of the blade into the glue. This will keep the glue only under the one side of the wrap. Try to keep the glue off the printed outside surface.

Downscale A-20 Demon Build Part 4 Fins

White Glue has been applied and smoothed out on the underside of the printed area.

Here the fin is placed over the straight edge of the cereal box cardboard.

You should set down the leading edge fold first, making sure the entire length of the fold is on the edge of the cardboard. Follow by smoothing the sides of the printed overlay.

Once again I'm using the Sharpie pen to smooth out the surface.

TIP: Lay a piece of clean paper over any printed area before burnishing. This way there is no chance of rubbing off of the print or transferring any dirt from the burnishing tool on your work.

Watch for any glue that may be pushed out the sides and wipe clean.

Lay the glued fins in a fold of wax paper and set in a heavy book for drying. Let them dry overnight.

TIP: If you are pushed for time, you can use an iron set on "Cotton" - "Dry" (no steam) and iron over the fins to dry-set them quicker. Use a clean piece of paper over the fins when ironing.

Only one side of the fin has a "hairline" cut guideline and the words "Root Edge". Cut the fins from this side. The other side of the fin is printed oversize to insure color coverage.

Cut out the fins using a sharp razor blade and straightedge, cutting through all three layers of the ply.

Apply white glue (not yellow glue, white glue dries clear) along all the outside edges of the cut out fin. After it dries, lightly sand over the glued edges with 400 grit sandpaper. Be careful and don't sand off any of the printed sides. Re-glue, let dry and sand again.

Here the Sharpie pen is used to (slightly) round over the outside and trailing (cut) sides of the fins. Don't do this on the root edge, you'll want that edge square and sharp.

This style of carded fin will have a rounded leading edge, square root edge and slightly rounded outside and trailing edges.

Downscale A-20 Demon Build Part 3 Fins

This is the cereal box cardboard used for the interior of the 3-ply fins.

The printed side should be roughed up for best adhesion. You only have to hit the printed side with some 220 grit sandpaper. I don't sand deep, just scratch it up a bit to remove some of the printing.

Be sure you dust off the surface before gluing on the fin overlays.

Before cutting out the fins score the fold lines. In the picture, I'm using just the tip of a butter knife, just making a line indent. (Use a straitedge for a true line, the straitedge is not in the picture so you can see the indent line itself.) The tip of a butter knife is not sharp or serrated. All you want to do is "push" a straight indent line into the cardstock.

Many kit instructions will have you cut halfway through the cardstock with a sharp knife. This is unnecessary.

For most models, this step will give you a very sharp fold line without the worry of cutting too deep or through the cardstock.

After making all fin center lines, cut out the fins oversize. Use scissors and cut a little larger than the outside the printed area.

Now the center lines can be folded over using the indent line you made and burnished flat with the back end of a Sharpie pen.

Downscale A-20 Demon Build Part 2

The fins on the Demon don't overhang the rear of the main body by much.

I made a 13mm engine mount with the engine hook overhanging the rear of the mount by 1/4".

When dry fitting the mount, the model wouldn't stand upright on the fin tips with the engine hook in the way.

So a second mount was built without the engine hook, I'll just have to friction fit the engine. Those 5/20 centering rings were cut from a empty casing left over from a Semroc kit.

After the centering rings were glued in place, I realized I didn't include the Kevlar shock cord!

I'm old school and tend to fall back on the old thinking sometimes.

I decided to drill a hole in the centering ring to allow the Kevlar to be tied on.

An awl was used to get the hole started. The hole diameter was widened with a small twist drill.

I went to my stash of scrap Kevlar and didn't have anything under 150 lb. strength.

The 150 lb. Kevlar is 4 strand so I undid the wrap and used two of the strands. Simple twisting opened it up to separate the cords, re-twisting got me the two strand piece I wanted.

No knot was tied where it looped around the mount, it's simply wound under itself three times and tightened down. With a white glue fillet over the top, this Kevlar isn't going anywhere.

TRIVIA: Kevlar (insert Dupont Trademark here) was first developed as a tough replacement for the steel belts in car tires.

Downscale Carded A-20 Demon Part 1

I just finished up a downscale version of the Estes A-20 Demon.

The kit #K-58 was sold from 1971 through 1979.

The original was BT-55 based and stood 24.5" tall and was flown with a D12-7. 18mm engines could be used with a 20/50 adapter.

This Carded BT-20 version stands 14.5" tall. It can be flown with 13mm or 18mm engines - your choice.

One of the great design elements of the Demon was the printed metallic body wraps. This set the rocket off and gave it a military or sounding rocket vibe. The fin reinforcement plates were also die-cut from the chrome sheet.

In drawing this one up, I tried to duplicate the feel of the metallic wraps in shades of gray.

The build thread will follow this first post.

This downscale is built in the Greg Poehlein carded rocket style. You print out the PDF on your printer.

Cut out the "skins and wrap around the body tube - this time around a BT-20.

No painting except for the nose cone!

The balsa nose cone is available from Semroc.com. It's catalog number is BNC-20AM

If you are a Patreon supporter, email me at: oddlrockets@bellsouth.net and request the Demon PDF