Atlas Mercury 1/12 scale

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aerostadt

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This will be a build thread for the Atlas Mercury 1/12 scale based on the Atomic City 1/12 scale Mercury capsule.
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I have been working on this project for over a year and do not know when it will be done. Originally, I thought that this project would be the first of its kind, but I have found that Matt Johnson has already built one and flown his model. Matt has given me a lot of good advice on how to continue! You can see his project on page 11 of the Nov/Dec 2012 issue of Sport Rocketry magazine. A video for the flight is here:

https://www.youtube.com/watch?v=CTNzBkHH-rI

This shows that the project is doable. Matt used clear plastic fins around the central (sustainer) motor. The Sherry Rocket's Atlas Mercury model did the same thing. I, also, did something similar to convert the 1/35 scale Estes Atlas Mercury to a 3-motor cluster. I recently posted this conversion for the Estes Atlas Mercury on the Rocket Reviews EMRR website. The original Estes model had auxiliary tubes with fins placed in the outer booster motor locations to make the model stable.
 
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I bought the 10" diameter fiberglass tube and cardboard coupler from What's Up Hobbies (Polecat Aerospace). I made a pattern of the Estes aft bulkhead. I took this pattern along with the Estes tube marking guide to a copier shop in a nearby city and had the patterns enlarged. At one time this copier shop was Kinko's. I think it is FedEx now.

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The scale factor to go from the Estes model to the new large model is S.F. = 35/12 = 2.9167 . In some ways I was not very careful in developing the scale factor and I now realize that things would probably have gone easier if I had been more careful. For example, the 10" diameter tubing is not exactly 10 inches. A better number would be to measure the actual circumference and divide that distance by pi. This becomes important in making centering rings and finding the locations of things on the model circumference
 
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Cut-outs were made in both the fiberglass tube (this is really a cardboard tube with a thin outer layer of fiberglass) and the cardboard coupler tube. The two tubes and then glued together. Since the epoxy will not run in this situation, I used the Aeropoxy ES6209 A/B which is strong, but needs at least 24 hours to cure. The nice thing about the inner coupler tube is that it forms a lip on the aft end for mounting the rear centering ring.

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Subscribed!

I'll be watching this one.

Are you planning a three-motor configuration?

Also, which Mercury mission are you going with?

Greg
 
Subscribed!

I'll be watching this one.

Are you planning a three-motor configuration?

Also, which Mercury mission are you going with?

Greg

I will go with John Glenn's mission. Last year was the 50th anniversary of John Glenn's flight. Unfortunately, I was not ready. The option is available to go with the outboard booster motors, but it is not necessary. I do not know what I will do, yet, in that regard. There is a small CTI I-motor that I was looking at for the outboards. I think CTI motors for clustering would be good here, because they can be assembled quickly and the CTI motors ignite quickly. The motors are far apart, so there is a concern that all motors must ignite. The central motor will need to be a K-motor. The thought has occurred to me to maybe use a cluster of BP E-motors for the outboards.
 
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So, the pieces go together something like this as shown below. If you look closely at the first photo, you can see a small ledge that has been glued into place to rest the second bulkhead, which is very convenient for the dry fit and final gluing of the rear assembly. This small ledge piece was made from left-over scrap pieces from the booster tube cut-outs shown previously. The polycarbonate fins are cut on a scroll saw from 3/16" plastic from United States Plastic. Two walls are needed to form each fin slot. The heavier bulkheads and slot walls are cut from 3/16" aircraft plywood on a scroll saw.

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The idea shown below is to glue the new slot wall in line with first slot wall with the clear fin clamped in place. This way the alignment will be neat and snug and the fin will not be loose. The trick is to put no epoxy on the inside slot where the fin goes while the epoxy is curing, otherwise the fin will be glued in place. In this manner a fin can be easily replaced. The small tabs on the slot walls will allow a hole to be drilled all the way through the walls including the clear fins. The fins can then be secured in place with a bolt. One aft bulkhead plate has a small block of wood glued on. This will be the location for the aft rail button.

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I am missing a few details in the construction photos, so I am skipping ahead to the current end product to describe some of the items that were inserted into the aft bulkhead plate. The outboard booster locations were fitted with blind nuts, so that the option to use some type of motor canister would be available. Also, electrical connections were installed. One set of connections lead to the vernier motors. The other set of connections are available for an in-flight ignition of the outboard motors. This latter option might never be used and I may discard it.

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I used the Public Missiles (PML) phenolic tubing that corresponds to the 54 mm motor for the central (sustainer) motor and I bought a few of the smaller PML centering rings. I bought the bell nozzle retaining system from Giant Leap. Unfortunately, I wanted silver and the only color they had at the time was black. The management did offer the suggestion that I could buy the black bell nozzle and paint it with VHT (Very High Temperature) Flame Proof paint (silver). GL gave me the website and I ordered the paint. The results are good enough. The bell nozzle is glued in place with JB Weld. I want to go back sometime and try to get some more JB Weld down into that joint gap. Bulkheads were glued into place for the outboard (booster) motors locations. Wires that were talked about in the previous post were brought up through the large centering ring as shown.

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The airframe length for the booster stage is about 12" long. The coupler tube goes beyond this length. Originally, I thought that I would build the model in modular form, so it could be dismantled for transportation and storage. Matt Johnson has told me that his model is all one assembly and I am now thinking of doing the same thing. Shown below is the booster shroud installation. I took the shroud pattern from something called a surfduke website and scaled it up along with keeping one eye on the Estes model. I just tried the website and it is no longer available. I am thinking that some of the paper modeler forums might have it. I cut the 2 shrouds from 1/64" plywood. I then epoxied triangular pieces of balsa wood for the base and guide for the 1/64" plywood. The plywood was then epoxied into place. I did apply a thin layer of epoxy on the under-side of one shroud to stiffen it. I checked it afterwards and the thin epoxy layer did not seem to help. I am thinking of maybe glassing the shrouds later, but I don't feel comfortable with my limited glassing experience. In the photos you can see some thin panels (poster board) that were attached near the shrouds. Also, some locations and references are marked in pencil.


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Here is the RocSim9 file for the modified 1/35 Estes Mercury that has three 24 mm motors and is described on Rocket Reviews (EMRR). This file does not show the 2 oz weight that was put in the nose cone. RocSim is saying that it is stable, but my flight experience indicates that it needs the weight.

View attachment EstesMercuryAtlas.rkt

Listed below is the last RocSim file that I have for the 1/12 scale Atlas Mercury. It is not current and will need to be updated at some time.

View attachment 12th Scale MercuryAtlas.rkt

I tend to believe that RocSim may be optimistic on the stability of models with clear plastic fins that extend into the base. The modeler can always compensate for this bias by being a little over conservative on nose weight. Nevertheless, the simulations are worthwhile, because they give an idea of what motors are needed and what the ballpark stability situation is. It is probably best to make an actual measurement by some means to find the actual c.g. rather than rely solely on the simulation.
 
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looks AWESOME so far!!!

Thanks, NJRick !

I wish that I still had the Surfduke Atlas Mercury website working. This seems to be another one of those websites that disappears into the ether. I did find this website, but I don't think it is as good.
https://web.archive.org/web/20050213130708/www76.pair.com/tjohnson/mat.html

For the side fairings (Are they system tunnels?) I used scaled-up patterns from the Surfduke/Atlas-Mercury website, again, keeping one eye on the Estes Atlas-Mercury as a check. I came up with a cross-section for the fairing and cut it out of light cardboard and tacked it onto the straight balsa pieces with C/A. I then cut out strips of 24 pound stationery (paper) and glued them to the balsa with white glue. Someone on TRF gave me the idea to soak balsa in hot water to form the curved strips on the fairings as shown in the photos below. There is one long fairing and one short fairing that go on opposite sides of the Atlas.

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Fasinating - am watching this one:pop:

Thanks, Jim! There's still some distance to go.

I looked at the pointy end of the side fairings and wondered how am I going to do that. I decided to extend the flat surfaces and cut triangles that came to a point as shown below. The pointy end itself does not need to be real accurate, because it will be cut off to have conduits that go from the ends up along the body fuselage. Once the flat triangular surfaces were tacked in place, I put balsa curved-shaped by hot water soaking onto the spaces that are in-between. Usually, I would tack things in place with C/A and come back later and glue things permanently with epoxy.

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At some point in the process I did a dry fit with the fairings on the side of the fuselage holding them in place with masking tape. The thickness of the fairings looked too large. I went back at looked at the Estes model and decided to cut down the sides of the fairings by a small amount as shown below. It is best to get things right on this step, because the next step is filling up the fairings with polyurethane.

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I must say ,this is an excellent build...you have me glued to my screen !

Very nice work my friend ,I`m liking this one a whole lot !!

Sincerely


Paul T
 
Thanks, NJRick !

I wish that I still had the Surfduke Atlas Mercury website working. This seems to be another one of those websites that disappears into the ether. I did find this website, but I don't think it is as good.
https://web.archive.org/web/20050213130708/www76.pair.com/tjohnson/mat.html

I used the wayback site https://archive.org/web/web.php, typed in https://www.mos95b.com/surfduke, and found some hits -- is the 1/48th scale pattern the one you are referring to?

Beautiful work so far! Will be watching this one! I am working on a smaller model f/ "D" impulse or so.
 
that is really NEAT! this is a great build!!

Thanks, Jim! There's still some distance to go.

I looked at the pointy end of the side fairings and wondered how am I going to do that. I decided to extend the flat surfaces and cut triangles that came to a point as shown below. The pointy end itself does not need to be real accurate, because it will be cut off to have conduits that go from the ends up along the body fuselage. Once the flat triangular surfaces were tacked in place, I put balsa curved-shaped by hot water soaking onto the spaces that are in-between. Usually, I would tack things in place with C/A and come back later and glue things permanently with epoxy.

View attachment 121097View attachment 121098View attachment 121099

At some point in the process I did a dry fit with the fairings on the side of the fuselage holding them in place with masking tape. The thickness of the fairings looked too large. I went back at looked at the Estes model and decided to cut down the sides of the fairings by a small amount as shown below. It is best to get things right on this step, because the next step is filling up the fairings with polyurethane.

View attachment 121100
 
Thanks for the encouragement to Spooks, Paul, Rocketguy101, and NJRick! Rocketguy, thanks for the paper Atlas Mercury website. I have added it to my Bookmarks. It may come in handy later, especially for the vernier rocket mounts. Paul, thanks for the approval, coming from you that means a lot. I have seen the pictures of your workshop. I find myself saying that when I retire someday, I'm going to have a workshop like that or maybe even clean up the workshop that I've got. Oh...wait a minute ... I am retired. (Where does the time go?)

I decided to strengthen the side fairings by filling them with Public Missiles Limited (PML) two-part polyurethane foam. The foam is fairly strong, dense (depending on the water adjustment), adhesive, and sandable (or machinable by hand). You can read the instructions, but by adding a few drops of water, you can vary the final density of the mix. A few more drops of water and the mix will expand quite a bit. I bought some plastic shot glasses (50 ml) at the grocery store that worked fine for mixing up small batches. I decided to fill up the fairings in more than one lift, so as not to run over. In addition I put the fairings on the bottom of a section of aluminum covered 10" diameter coupler tube. I figured that the weight of the tube on top would confine the foam if I put in too much. The photo below shows the fairing on top, but I really put the fairing on the bottom of the big tube after pouring in the foam. The foam starts to expand in about 30 seconds, so there isn't a lot of time to work with it.

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Shown below is the small fairing after the first and second lift.

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Shown below is the under-side of the long side-fairing after the second polyurethane foam lift and some hand machining. By hand machining I mean cutting-off the excess hardened foam with an exacto knife, files, sandpaper, and Dremel tool.

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The side fairings were then attached to the sustainer stage with regular epoxy. However, there were gaps between the fairings and the main body. Some of these gaps I filled with a mixture of regular epoxy and micro-balloons, but for most of the gaps I used epoxy putty. The current dry fit with the booster stage and most of the sustainer stage is shown below.



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WOW!! that looks incredible!! she is really coming together!

Shown below is the under-side of the long side-fairing after the second polyurethane foam lift and some hand machining. By hand machining I mean cutting-off the excess hardened foam with an exacto knife, files, sandpaper, and Dremel tool.

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The side fairings were then attached to the sustainer stage with regular epoxy. However, there were gaps between the fairings and the main body. Some of these gaps I filled with a mixture of regular epoxy and micro-balloons, but for most of the gaps I used epoxy putty. The current dry fit with the booster stage and most of the sustainer stage is shown below.



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I forgot to mention that the booster shrouds taper down to the same kind of PML tubes that are used for 54 mm motors (cut in half lengthwise, of course).

I looked at Matt Johnson's Atlas-Mercury and after corresponding with Matt I decided to go with his design of using the internal 6" diameter tube for the parachute housing and also couples directly to the Mercury capsule. Originally, my plan was to use the 54 mm motor tube as a stuffer tube and then use a centering ring that would open to the parachute compartment in the full 10" diameter tube. Such an idea would work. I believe that there are some large HPR Nike Smoke models that use this method. There are advantages and disadvantages of both methods, but I decided to go with Matt's approach. One of the advantages of Matt's approach is that the model descends in a manner looking the way the Atlas did when it was on the production assembly line.

I bought a 48 inch length of 6" diameter tube from PML and the corresponding coupler tube. Shown below is dry fit of the centering ring needed to attach the PML coupler tube.

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I epoxied the inner centering ring into place and did a dry fit with the U-bolt that will connect with the shock cord.

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I epoxied a standard 12" length of PML 6" coupler tube to the inner centering ring. After putting this tube in place I decided to cut-off the top 5 -inches of the coupler tube. I did this using a Zona saw that Paul (sodmeister) recommended on his "Hellfire" (scratch-build). I was amazed how well this Zona saw worked. It is well worth the money. I think I paid roughly about $7 for the saw and about $7 for the shipping from HobbyLinc. I may use the 5 inches of coupler tube later for a piston.

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Shown below are ledges glued into place with epoxy to hold the outer center ring in place for the dry fit.

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Shown below is a dry fit of the outer centering ring. This centering ring has a 1" thick x 2" wide piece of poplar wood epoxied to it for the upper rail button.

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I put two 60" Top Flight shock cord protectors over the 1" wide shock cord. This will add extra protection over the end that eventually attaches to the piston, especially if I install an ejection charge holder on the piston. After putting on the cord protectors the 4' length of PML 6" diameter tube and the outer center ring were epoxied into place. It turns out that the 4' length is almost the exact length that is needed.

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she is a big girl...but this rocket is going to look AWESOME with that neat Mercury capsule perched up there!!
 
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