Marc G's Interchangeable Engine Mounts

Marc Goldstein (Marc_G on the Rocketry Forum) has come up with a very smart method for interchangeable motor mounts.

In the picture at the right, short half round dowels are glued directly opposite the root edges of the fins, inside the body tube.

Click to enlarge the picture and read the copy detail.
In the picture, the half dowel pieces are flush with the end of the body tube. In this earlier version, the half dowels sit below the lower centering ring of the engine mount with the mount is slid in, turned and "locked" in place.

Here's Marc's interchangeable motor mounts, 24mm on the left and 18mm on the right.
Notice the the half circles cut out of both the top and bottom centering rings.
These half circles allow the mount to be slid in over the dowels.
You could also build cluster mounts the same way.

When the mount butts up against the forward centering ring (already glued in the main body just forward of the engine mount position) the mount is turned, locking it in place.

Marc's first engine mount builds are HERE
His new version using basswood strips instead of dowels is HERE

This mount reminds me a little of the Semroc SLS interchangeable mounts. With the Semroc mounts, short thru-the-wall fin tabs lock onto the centering rings of the engine mount.
With Marc's half dowel mount idea, you could use this in most any kit, maybe BT-55 and above. From an existing kit you could use the included surface mount fins.

Refinishing the Red Max Part 3 Epoxy and Masking

Some 220 grit sandpaper was wrapped around a dowel and the dried epoxy fillet lightly sanded.
This wasn't needed on each fillet, two fillets had minor high spots. Again, be careful not to sand into the fin and scar the balsa.

I've still got to fill the body tube seams. They were marked with a pencil.
The seams will be shot with primer.
Normally for an isolated seam fill, I'd mask just the seams to lay a coat of primer directed right on the seams.
But with the fins and lugs already glued in place, no tape will be used. the primer will simply be shot close and directly on the seams.
The Duplicolor primer has a nozzle tip that you can turn, changing the paint coverage from a wide fan spray to a narrow line. The tip was turned to spray the narrow line down the seams.


To mask the engine mount, tape was set sticky side out around the inside of the main body tube. Remove some of the tackiness by pressing the tape on your pant leg a few times, otherwise it might lift some of the body tube when removed.

More tape was added to the end of the motor mount tube and engine hook.






Paper towel strips were stuffed into the rear void with tweezers and a dowel.

Super Alpha Open Rocket Results

I loaded the BT-60 based Super Alpha into the Open Rocket software to check it's stability and predicted altitudes.

I was concerned if nose weight might be needed with a 24mm D12-5 engine installed. The Super Alpha was designed for 18mm engines.

According to the software simulations,
The 18mm C6-5 altitude is 696 feet. (Super Alpha with an 18mm mount installed)
The 24mm C11-5 altitude is 622 feet, less than the 18mm C engine!
The 24mm D12-5 altitude is 1076 feet.
The 24mm D12-7 altitude is also 1076 feet.

I didn't think the the C6-5 engine to get a higher altitude than the C11-5.
I would expect the D12-7 would get a better altitude over the D12-5 - it should coast longer and go higher.

This probably isn't accurate, I'm new to inputting information into a simulator. I may have left something out.
Still, interesting results.

Refinishing the Red Max Part 2 Epoxy Fillets

A 1/4" diameter dowel was picked to even out the epoxy fillets.
It was marked with a wide tip Sharpie pen to transfer the width lines onto the fillet area.
This idea comes from Crazy Jim's tutorial on TRF HERE

I thought I'd have to continually add more marker to the dowel, but one application did the trick for all six root edges.
Gently rub the marked dowel on the body tube and fin and the black lines are transferred. Be careful not to "scar" the balsa.

Masking tape was applied down the faint black lines to control overflow of the the epoxy.

When you use the dowel to even out the epoxy, it will go over the masking tape. I'm using 15 minute epoxy. When the epoxy just starts to set up, just a few minutes, remove the tape. Otherwise - the tape might get glued to the fins.



After pulling the tape, ther'll be a slight epoxy ridge where the tape edge was.

Dip your gloved finger into a small cup of rubbing alcohol. Shake off the excess.
Run your finger down the epoxy fillet. This should knock down the epoxy ridge left after removing the tape.

Super Alpha Build Finished

I added a 5/16" wide stripe like the picture from the 1974 Estes Catalog.
It was cut from the same black Contact paper roll used in the Mini Honest John build.

Overall a good build. It should scream with 24mm C11-5 and D12-7 engines.
I'll look up the center of gravity (CG) on the Super Alpha and add nose weight if needed. But with the size of the trailing fins, it's probably stable the way it is.

Wasted Balsa

I was going to build a Ranger using some parts from a Baby Bertha kit.
This is two of the fins included with the Baby Bertha kit. Two sheets like this are in the kit.

I thought I could use these for the Ranger, but these fins are a just slightly smaller and are cut from 3/32" balsa. The larger Ranger fins were cut from 1/8" thick balsa.

In the reissued Estes Classic kits, balsa nose cones were once included. Now, plastic nose cones are substituted along with a note explaning of a "world wide balsa shortage". Considering a claimed shortage, this seems like a lot of wasted wood.

That laser cut balsa sheet shown above is 4" wide.
To the right is how the larger Ranger fins sat on my 3" wide X 1/8" thick balsa.

In the old Estes kits you were shown how to lay out the fin pattern on the balsa sheet. You were supplied with enough balsa to cut out the fins needed for the build.
If you didn't lay the fin pattern properly, or with the leading edge running down the grain, in the end you didn't have enough balsa.
By carefully placing your fin pattern, you could save some wood for a future project.

After cutting out the larger Ranger fins, I set them on one of the two 4" wide Baby Bertha fin sheets.
I was able to fit all four of the Ranger fins on the one, 4" wide Baby Bertha sheet.

I'm not trying to tell Estes how to cut their fins for the kit. But, this does strike me as a one way to save balsa and some production cost on each kit.

Refinishing the Red Max Part 1 Future Clear Coat Test

This was the first clone I did when I got back into the hobby.
While the balsa grain was filled pretty well, I didn't fill the body tube seams.
The finish is rough and pebbled.

Another kit could be built, but I really wanted to restore this one properly.
Fill the seams, use epoxy for smoother fillets and paint it RED this time!



I hadn't had much luck with Future, or Pledge with Future shine, or whatever they have renamed it this month.

I applied two coats to one decaled fin to see if it really protects the decal.



You could simply sand off decals, but there would be decal dust and pieces everywhere.
It's much easier to use some tape. Press down the tape and remove. The decal will lift and be stuck to the sticky side of the tape.

This is the same fin that got two coats of Future.
The coated decals came off as easily as the other decals that didn't get clear coats.

This isn't a great test for clear coats and decal adhesion. I thought the decals coated with Future would be harder to remove. It was just an experiment.

Super Alpha Build Part 9 Cleaning Up

Before any spraying was done, a strip of masking tape was set sticky side out around the inside base of the lower main body tube. Reduce the stickingess of the tape by pressing it on your pant leg a few times. Otherwise, the tape could pull and lift a layer of the rough inside surfaces of the body tube.
Paper towel pieces are pressed into the recess and down to the lower centering ring.
This keeps all the paint out of the engine mount, it gives a cleaner look to the finished model.



After the paper towel pieces and tape removed there shouldn't be any paint in or on the mount.

The rear edge of the tube needed some black on the rim.
I used a permanent Sharpie pen.

In the picture the right side of the tube edge has been blackened.





I still have to scrape a bit of black paint off the engine hook.

Super Alpha Build Part 8 Black Mask

This is the mask for the black, both sides of one fin and the body tube panel to the white fin to the right.

I should have taken more time on the mask. It looked simple and I treated it as such.




After the tape was pulled off, the root edge lines were sharp.
The line around the body tube wasn't as good. I spent more time on the root edges making sure they were well sealed. I obviously didn't take the time to seal the horizontal line on the body tube between the two fins.

Super Alpha Build Part 7 Red and White Paint

Ya' gotta love a simple body tube/nose cone color separation.

The body and fins were sprayed with the generic Duplicolor gloss white.
While it looked "wet" going on, after drying it had a flat or "blued" surface. This is because of the high humidity in Florida.
Some rubbing and polishing compound and I got a good gloss.

The nose cone is Rustoleum 2X Gloss Red, no polishing was needed.

This shows the final fillets.

You can see some slight orange peel in the finish. The picture makes it look more pronounced than it actually is.
I'm pretty happy with the Duplicolor spray, it'll take some practice to get used to it.
(Anything is better than the "cottage cheese" finish from the bad batch of Rustoleum 2X gloss white.)

Jeff Smith's Root Edge Squaring Tip

Jeff (Jeffyjeep) Smith is a true craftsman. Many of his finished rockets have been sold to collectors on Ebay.

Here's a tip from a Estes Scamp build he did on TRF.
"While holding the basswood fin against a small aluminum angle stock for squaring, I prep the root edge of each fin for mounting to the BT. "

This is a great way to keep the root edge square.
Thanks Jeff!

Super Alpha Build Part 6 Fin Fillet Redo

Still not satisfied with the Titebond M&TG fillets I went back and added some Elmer's CWF to hopefully fill the slight valleys.

These were sanded with 400 grit over a dowel.





Then, another shot of Duplicolor gray primer and more sanding.

I'll keep messing with the fillets until they are round and smooth.

Super Alpha Build Part 5 Fin Fillets and Primer

I won't bore you with the details on the fin and launch lug gluing. Everything was standard here.
I did substitute a 2" long X 3/16" diameter lug for the 1/8" lug supplied in the kit.

I'm still on the fence regarding Titebond Molding and Trim Glue for fin fillets.
It does shrink some, certainly not as much as white or yellow glue.
Down the root edge there is a slight "valley". I did three fillet coats of the the Titebond M & TG.

On a model this size, I prefer rounder, deeper fillets. I may go back and add some epoxy fillets after sanding down the primer.



The Titebond M & TG really works well on the launch lug fillets. No bubbles and no argument there.
I wish the root edge of the fins had this nice of a rounded fillet.






You can see the "step" where the raw balsa was on the top half of the re-shaped nose cone.
The lower half was still sealed from when it was on the cloned Red Maxx.

Super Alpha Build Part 4 Fins

It's hard to see in the picture, but the balsa sheet from the kit was made from two pieces of balsa, glued together parallel down the grain line.

The Super Alpha instructions have you round only the leading edges of the fins.


The original Alpha instructions say to round the leading edge and taper the trailing edges. The illustration showed a rounded leading edge and a short taper at the rear.
Enlarge the illustration at the left and look at the "A - A" section.
I decided to round all the edges, except for the root edge.

New Estes 2012 Catalog

This morning on TRF, Bob Sanford (Initiator001) announced the new Estes 2012 catalog is available for download on the Estes website HERE

Items already shown on the forums are the Pro Series, Nike Smoke, V2, Solar Warrior, Asteroid Hunter, Dark Energy and E12 engines.
Two not unveiled until this morning are the individual BT-5 based Mosquito and arrow inspired Fletcher.
A #3552 Pro Series II Launcher is listed, but no picture yet.

Many of the Classic Series I thought were discontinued are still listed. The Saturn V and both Interceptors are not in the catalog.
Two surprises were the (not just spare parts) Designer's Special and re release of the (Astron) Sky Dart II.

Estes is certainly on the right track, some re releases for the old timers and plenty of great new designs.

Semroc Booster 16 in the Centurion

The old Semroc Centurion was refinished recently.
I wanted to use the Semroc Booster 16 I built and reviewed three years ago HERE

While I now cover the open back areas of rockets so paint won't get inside, the Centurion still had paint all over the engine mount from the first time it was finished.
The Semroc Booster 16 wouldn't slide in with all the paint around the body tube lip.



Some 220 grit sandpaper was wrapped around a dowel.
The inside edge was carefully sanded to remove the lip of paint around the edge. I was trying to get a sliding friction fit of the black coupler on the Booster 16 unit.
I checked the fit while sanding until it slid in easily but would still stay in even if shook.


Here's the Booster 16 first stage unit in place with a A10-0t engine installed.
In the Centurion engine mount is a B6-4 for the upper stage.

On the RocketReviews.com comments I read where the Booster 16 unit will stage at 25 feet with an A10-0t engine installed - so there's not much difference in the altitude.
Still, it'll be fun for a change and the Centurion looks great with the large booster nozzle installed.

I wanted to use the re-released A10-0t engines in something other than a small saucer. Maybe I should build the Astron Beta?

Super Alpha Build Part 3 Engine Mount

The engine block was notched for a better fit when butted up against the upper bend of the engine hook. This idea came from Todd. (Bradycross on TRF)

On the left you can see the split body tube over the engine hook.

The Kevlar went underneath the forward centering ring instead of tied onto the engine block ring. On larger diameter models it makes sense to keep the Kevlar away and outside the path of the ejection charge.

On the right is the finished engine mount.
Enlarge the picture and you'll see the filled spirals in the 3/16" launch lug.

Refinishing the Red Max Part 2 Epoxy Fillets

A 1/4" diameter dowel was picked to even out the epoxy fillets.
It was marked with a wide tip Sharpie pen to transfer the width lines onto the fillet area.
This idea comes from Crazy Jim's tutorial on TRF HERE

I thought I'd have to continually add more marker to the dowel, but one application did the trick for all six root edges.
Gently rub the marked dowel on the body tube and fin and the black lines are transferred. Be careful not to "scar" the balsa.

Masking tape was applied down the faint black lines to control overlow of the the epoxy.

When you use the dowel to even out the epoxy, it will go over the masking tape. I'm using 15 minute epoxy. When the epoxy just starts to set up, just a few minutes, remove the tape. Otherwise - the tape might get glued to the fins.



After pulling the tape, ther'll be a slight epoxy ridge where the tape edge was.

Dip your gloved finger into a small cup of rubbing alcohol. Shake off the excess.
Run your finger down the epoxy fillet. This should knock down the epoxy ridge left after removing the tape.

Super Alpha Build Part 2 Engine Mount

I wanted a vintage look to the upscaled Alpha so that finger tab on the engine hook has got to go.
I can usually "score" both sides of the tab with my wire cutters.
With pliers, bend the tab along the scored line and it will break apart.
Follow with light filing to smooth out the edge and round the sharp corners.


Two 1/8" ply 50/60 centering rings were found in the spare parts box.
The plywood is probably overkill, but it was handy.
The engine hook notches were made with my small diamond files.
The corners of the notches were a little round after the filing so the were sharpened up with some small notch cuts with my hobby knife.

In the picture a small notch in the upper ring is made for the Kevlar to pass through. At the right of the same ring is the notch for the upper part of the engine hook.


Here's all the engine mount parts for a 24mm engine.
The split tube (at left center) will hold down the engine hook between the centering rings. It's simply a split piece of BT-50 and stronger than a wrap of tape.

The engine block is a 1/4" piece cut from an old D engine casing.

NAR Membership Goal Reached

From the NAR Electronic Rocketeer Issue #44 -

I am delighted to report that the membership of our NAR has now reached the goal that we set in 2008, an active membership of 5200. This is the largest that the NAR has been in the last 12 years; our records from the "boom" days that we went through a few times before then are not complete so we are not sure it is the largest that we have ever been but if it isn't, it's close. Congratulations and thanks to all the thousands of NAR members, the supporting manufacturers, hobby shops, and others who have contributed in some way to the steady growth that has brought us to this point. Word of mouth from satisfied members is our best recruiting tool, and member satisfaction is our best retention tool.

It has been the goal of the NAR Board to do everything in our power to deliver the services that our membership tells us in our biennial online surveys and constant in-person communication to Board members that they want from their NAR. Member satisfaction is our top priority. The larger we become the more services we can afford to deliver. Let's keep growing so we can keep improving our services!

Be safe, have fun, and pay forward.

Trip Barber
NAR 4322
NAR President

Not a NAR member yet?
Check out all the benefits of membership at www.nar.org

Super Alpha Build Part 1 Parts

I'll be doing a conversion from 18mm to 24mm engines.
I've got plenty of C11 and D12 engines that should do well in this upscale.

Here's all the parts including the re-shaped nose cone from my old Red Max clone.
The nose cone posts are here:
PART 1
PART 2
PART 3

I had some plywood 50/60 centering rings, BT-50 tube, Kevlar and a 3/16" launch lug.
The picture shows some 1/8" elastic. I'll have to get some 1/4" elastic to replace that.



These are the parts left out from the stock 18mm version. Everything will go into the spare parts box for a future build.

That's a 24" long rubber shock cord, still a little short for me.






This will be painted like the Alpha I never built from the 1974 Estes catalog.