Everything you never knew you wanted to know about the Mercury Project

From RixWiki

Problems To Solve

There is one problem in the engineering of the escape tower parts, and there is another issue which is not clearly spelled out in the instructions.

Positioning the Tower Relative to the Capsule

As the description of how to install the antenna fairing in the instructions says, one leg of the tower is supposed to line up with the window (TY see mercury spacecraft coordinate orientation), contrary to the picture on the front page of the instructions, but according to the description of how to install the antenna fairing.

As mentioned in Rotational Alignment The recovery section (part 2) has a tab which fits into a notch on the conical section. This places the pitch and yaw thrusters in the correct positions. The antenna canister(part 1) also has a tab at TY which puts the cannister in the correct orientation with the side horizon sensor at RX. Part 36 fits on the bottom of the cannister and the top of the recovery compartment and the legs of the tower are in the right places.

Now here's the problem. The three notches on the bottom of part 35 are positioned between the v-struts on part 34. Those v-struts have to line up with the tower legs. BUT the "reinforcements" from which the slots provide relief are positioned in line with the legs, not between them. If you position the tower correctly with a leg at TY, then part 35 doesn't match up with the "reinforcements." It looks as if you need to modify part 35 to move the notches in order to build the kit correctly. Perhaps that's why the picture is wrong.

Sorting Out The Different Legs

This is the other thing to watch out for. The three main parts of the escape tower are NOT identical. Part 31 does not have a notch at it's top, while the other two (they are both labeled 33 on the parts diagram, but they are labeled 32 and 33 on the drawing for step 1) do. The ones with the notches should be used for the leg in line with the window, and the leg on the bottom left from the astronaut's perspective. The notches are for parts 12 & 13 (both labeled 12 on the parts diagram) to line up with the parts 10 (for once the instructions and the parts diagram agree) on the escape rocket. These are the fairings for the escape tower wiring which is routed down these two legs. This advice is based on David Weeks' drawings which I trust implicitly. Part 31 should be used for the bottom right leg which had no wires and thus no fairings.

How I Built The Tower

Here's my procedure for building the escape tower correctly. If you don't understand this refer first to WatchRotationalAlignments. We're going to be building this on the workbench and the tower will point straight up when we are done. This might be a tad confusing because when I say "on top of", or down, I mean as it sits on the table, but when I say the top, or the front etc., I'm using these terms relative as described in Mercury spacecraft coordinate orientation.

1. Clean up the tower parts, removing any remaining sprue or flash. A set of FlexiFiles is good to use here.
2. Put the three legs (two parts 33 and one part 31) together. I used a rubber band to hold them together prior to gluing. You might want to place the bottom of the escape motor rocket on top. You now should be able to glue the three tower parts together using liquid cement. I prefer to use a fairly fast evaporating cement like Ambroid proWeld to do this.
3. Place (do not glue) the antenna cannister (part 1) on top of the recovery section (part 2). Make sure that the tab on the back of the antenna cannister fits into the notch on the front of the recovery section. The two sets of half notches on the front of these parts should line up to form two "holes."
4. Identify the *top* of the antenna cannister.
5. Place the base ring of the tower (part 36) on the front of the antenna cannister and recovery compartment with the two raised locating bumps down. Rotate it until the bumps fit into the holes on the front of the recovery section/antenna cannister.
6. Now look carefully at the spacing of the six holes on the tower base. They are not spaced equidistantly. The spacing alternates between a slightly closer spacing and a slightly wider one. The pair of holes at the top (again in reference to Mercury spacecraft coordinate orientation) should be closely spaced. If not, the base ring needs to be turned 180 degrees until the locating bumps again fit in the holes, and a closely spaced pair of holes is at the top.
7. Now it's time to fix the engineering problem with the antenna fairing. Glue parts 34 and 35 together and let them dry, again a fast drying liquid cement is the thing to use here. Then turn the assembly over and examine the notches. We need to provide similar clearances but in line with the centers of the v struts which are part of this assembly. Take a hobby knife and carve away some of part 35 until you can place the antenna fairing over the antenna canister so that it fits without a gap, and the v struts are positioned at 12, 4, and 8 o'clock. Put the fairing aside for the nonce.
8. Place one of the big V struts in the top pair of holes, the bulge should go on the outside as shown in the instructions. Do the same with the other two big V struts at the 4 o'clock and 8 o'clock positions. Again do not glue these parts.
9. Put one leg of the tower sub-assembly from step 2 into the hole at the top of each of the big V struts from step 8. but it's not quite that simple. The leg at the 8 o'clock position should be part 31 which doen't have a notch for part 12 at the top. The two parts 33 which do have the notches should be at 12 and 4 o'clock.
10. Once you have confirmed all this. Glue this with liquid cement, but leave the three small brace tubes unglued for the moment.
11. Once this last subassembly has dried, it's time to dry fit the antenna fairing. Remove the subassembly from the tower base ring, and place the fairing on top of the antenna cannister. Now lower the tower subassembly back down over the fairing. You might rotate it a bit as you lower it to clear the small v struts on the fairing, and then rotate it to get the large v struts into the holes in the tower base ring. Once this is accomplished, you should be able to see how the v struts on the fairing and the small brace tubes interact. You should also now be able to remove the tower subassembly once again and glue the brace tubes, still without the fairing.

This is where my tower stands to date. Note that the box art shows an incorrect color for the antenna fairing which should be black instead of red, at least for the manned spacecraft. Some of the Little Joe towers did have red fairings. Note, however, that the small v struts which connect the fairing to the tower should be red. So I plan to mask off the v struts, and paint the fairing semi-gloss black. When the paint has dried. I will remove the masking from the v struts and mask the now black fairing and then glue the fairing into place and glue the tower to the base ring, add the motor on top and paint the whole thing red.