Apollo LES 4"

g_boxwood

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Here we go again... I didn't get what happened to TRF but since this project isn't finished yet I must resume it somehow.

We're talking about the Apollo Launch Escape System...

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... that Gordon and Gus already modeled around BT-70 tubing: as you see the results speak for themselves, both from the craftmanship and the flight perfomance point of view:

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g_boxwood

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With such a positive input I couldn't resist the urge to model one on my own... just on a bigger scale!

The first 3D mockups involved 6" PML tubing that I down-scaled to 4" to test the design prior to commit myself to the bigger challenge.

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g_boxwood

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Being quite done with it I must say that the six-incher was the right scale for a number of reasons, the most important being that

. the MMT don't stick out as much as they do in the 4" version (I'm forced to use 38mm...)!

Not only they do look ugly and totally out-of-scale but they'll affect the aero somehow even if they could help with the overstability issue.

The reason why the MMTs stick out this much (pic on the right)...

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... is because I was forced to allow plenty of length for the Pro38 3G cases which are way longer than the equivalent AT 3G motors... I'm still having troubles to light multiple AT reloads at once so I wanted to be on the safe side.
 

g_boxwood

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I wanted to keep the 4-incher simple with a very low functionality: I then changed my mind and I provided it with a certain degree of freedom.

The typical 'mission' should work as follows:

0. lift-off under booster motors

1a. burn-out of booster motors
1b. jettison motors light, capsule is released

2. jettison motors burn-out, tower coasts to apogee

3a. tower reaches apogee and deploys main chute
3b. capsule reaches apogee and deploys main chute(s)

4. tower and capsule touch-down

Since the design needs to be proven it is likely that the previous sequence won't take place at the very first flight (no capsule release for istance).

This is how the airframe was thought out: it is still the same, electronics only were cut to the minimum (one or 2 in the tower to light the jettison, release the capsule and deploy the main, one or 2 in the capsule to deploy the main, the "2" being for redundancy).

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A wireless video link TX will be placed above the jettison motors.
 

g_boxwood

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This project will require a lot of custom components, the first I made being the nosecone.

The nosecone is designed around a 29mm MMT:

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Balsa stringers are added...

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... and the frame is skinned with 1/64 ply:

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g_boxwood

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The tip is a solid-balsa-filled ply frame that fits snugly into the 29 mm MMT...

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... while the final finish is achieved with 2 layers of fiberglass cloth:

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Pantherjon

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Ahhhh, welcome back! :D This was a project I was following closely the first time around! Glad to see you(and the project) back to oodle over your great craftsmanship! ;)
 

g_boxwood

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Glad to see you(and the project) back to oodle over your great craftsmanship! ;)
Thank you! Let's move on then!

Jettison Motors Subassembly

I started with the Jettison Motor (JM from now on) subassembly. I designed it to fit 24 mm motors, either BP or composite.

It all started with a 3D mockup...

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... pieces were cut...

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... and the assembly started right away:

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g_boxwood

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The canted MMTs were dry-fitted in place...

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... and finally slid into the coupler and permanently epoxied in:

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Trimming and topping with the bulkplate ended the job:

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g_boxwood

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A look from the aft end:

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The aft bulkhead with the shock-cord attachment:

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E15Ws dry-fitted:

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The finished payload section with the JM subassembly in place and the trimmed openings:

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g_boxwood

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The rest of the components to complete the tower (something like 1 or 2 more couplers are missing from the pic, plus all the wood):

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The airframe sections got reinforced with a glass sleeve:

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It was too coarse so I had to add an extra veil to smooth it out:

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g_boxwood

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Booster Motor Subassembly

The Booster Motor (BM) subassembly is designed around 4 38 mm MMTs and requires:

. 3 custom centering rings
. 4 interlocking triangle supports
. a central 38 mm MMT used as an alignment jig

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The triangular supports were epoxied in place AFTER the BM subassembly had been slid inside the airframe tube:

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g_boxwood

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The BM subassembly is completed by adding a fore and a aft coupler section prior to airframe joining.

Fore end:

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Completed with dry-fitted triangular supports:

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g_boxwood

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The matching airframe section needs some trimming to clear both the supports and the MMTs:

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Then the trial fit took place...

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... followed by the actual epoxying (both the subassembly and the supports were glued at once):

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Everything is trimmed once more as the epoxy set:

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g_boxwood

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For added strength I went for a heavy cloth reinforcement:

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The finished booster section:

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g_boxwood

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Command Module (CM) Plug

I'll make the CM a 2 pieces fiberglass entity thus requiring 2 different molds: the conical section and the heatshield one.

I started with the conical plug, being it the biggest one.

I designed a lite-ply frame and I cut the required pieces on my own: the largest (base) ring spans something more than 24" but it is still Dremel cut-table!!!

The templates were transferred to the wood...

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... and cut:

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It was still possible to cut the inner 4" dia hole with the Dremel!

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g_boxwood

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The twelve stringers followed...

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... and the assembly began around a 4" airframe core section:

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The very first overall impression:

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g_boxwood

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In the meanwhile I put the parting board together (thick MDF):

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I added small MDF blocks to the CM frame to better support the joining screws:

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g_boxwood

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Skinning the frame required some thought. I started by sanding the frame smooth:

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Then I rolled it over 2 layers of cloth to mark the skin outline:

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Next I laminated those 2 layers on a flat surface:

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Finally the skin was applied to the frame using Gorilla Glue (whose foaming action fills most of the voids):

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g_boxwood

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The tip was added (again it consists of a balsa-filled ply frame)...

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... it was sanded to shape...

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... and finally glassed:

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g_boxwood

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While I was filling some of the defects...

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... I felt the plug needed some more stiffness so I went with 2 more external layers of cloth:

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g_boxwood

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Then it came the mandatory yet boring fill'n'sand part of the business:

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g_boxwood

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Just a few days before Christmas I had the chance to give it the very first primer coats!

I started with a paint-promoter coat...

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... followed by the primer:

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g_boxwood

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Heatshield Plug

Before finishing the conical section plug I need to put together the heatshield plug to match them precisely!

I spent a little time in front of the PC to figure out how to model the curvature of the heatshield. I came out with the following solution based on lite-ply framing and foam.

Notched base ring with 29 mm core:

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Vertical frames and interlocking diagonal plates:

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Raw foam blocks:

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g_boxwood

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The raw blocks will then be sanded down to the desired shape and a custom rotating spatula will spread the filling compound homogeneously around the plug:

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dwmzmm

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Wow! Excellent job you got there! Keep it going and let us know how it goes.
 

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