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Adjustable Nose Weight

Instructions

[For adjustable Nose Weight assembly & Spanner-Driver]

The original design of this system was for a LOC Precision, Minnie Magg. But the principles of the design of this system, in its basic concept and functionality, can be easily applied to the rocket of your choice. With the integration of this design, two things are made possible: The first being a means to favorably affect a rocket’s stability by adding weight to the nose when the weight of the motor being used causes the rocket’s center of gravity to shift aft of its center of pressure. And, by its creation, the second benefit of this system also enables the flyer to adjust the rocket’s weight when the achievement of optimal mass, for higher flight, is the goal.

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Nose Weight Assembly Parts Needed:

List of required Parts, in chronological order of Item numbers, for adjustable Nose Weight Assembly in LOC Minnie-Mag:

  • Item 1: LOC Precision Nose, for LOC Minni-Mag. This item has to be modified. The tapered end of the shoulder and the (less than adequate) turnbuckle must be removed in order to accommodate the integration and assemblies of Items that are numbered as and from 2 to 9. Remove the aft end of the nose at or about where the radius of the shoulder meets the taper. (Refer to Nose Cone Cut-Away drawing)
  • Item 2: 29 mm motor mount tube, approximately 15 + inches long. [I used PML tubing on mine, but the radial dimensions and diameters that are specified in the drawings of the other components only apply to that particular size of tube]. (See Pic)
  • Item 3: ½” aircraft plywood. (See Pic)
  • Item 4: ¼-20 nylon all-thread, approximately 16” long and cut from a 3-foot piece purchased at a hardware store. This item needs to be trimmed to fit flush with the aft end of Item 2 after being installed with Items 5 & 8 as per the assembly drawing.
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    Item 5: ¼” aircraft plywood. The fit of this item, inside item 2, should be snug. It should be drilled through its center to allow free passage of Item 3. 2 each, of Item 8 are then attached to opposite sides of the bulkhead, on the all-thread, and glued in place with epoxy. Then, that assembly is introduced to the forward end of Item 2 and glued in place with epoxy. Be sure to rough-up the inside diameter of the forward end of Item 2 with a coarse grit of sanding paper (and clean it of any residue with denatured alcohol) prior to the application of epoxy. Its location, as well as those of Items 8 and 4 in this assembly, is permanent once the epoxy has cured.
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    Item 6: ¼” aircraft plywood. This is an adjustable manifold that will allow the addition or subtraction of lead shot. It should be brought to bear against the lead shot that has been poured between it and Item 5 after ascertaining the desired relationship of a center of gravity that is one airframe diameter ahead of the center of pressure. That way, the lead shot that is between Items 5 & 6 won’t be moving around too much. It has one of the ¼-20 nylon nuts attached on the forward side with epoxy. Its fit within the tube should be loose, so that it can be driven into or out of the tube by an extended spanner wrench mounted in a drill motor.
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    Item 7: ¼” aircraft plywood. This item closes the openings of the holes in Item 6, and keeps it from backing off from lightly compressing the lead shot. It too needs to have a loose fit so that it may be driven into or out of the tube. It has one of the ¼-20 nylon nuts attached to the aft side with epoxy. Do not break-through the forward side of the disk when you create the counter bores for the spanner wrench. They are counter bores, not through holes. The hole in the center goes through, while the other two do not.
  • Item 8: ¼-20 internal thread, nylon nuts. A total of 4 each are required for the assembly and use of Items 1 through 9.
  • Item 9: ¼-20 thread X 1” X 2”, steel, U-Bolt. 4 each, ¼-20, steel, nuts. 4 each, steel, ¼ inch flat washers. (See Pic)

Spanner-Driver Parts Needed:

List of required Parts, in chronological order of Item numbers, for the Spanner/Driver Assembly. This Item is a Tool that can be turned by hand or chucked in a drill motor. It drives Item’s 6 and 7 into and out of the weight container in the Adjustable Nose Weight Assembly.

[Editor's Note: We have changed the items to s# to help differentiate the Spanner parts from the Nose Weight Parts in the instructions]

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    Item s1: Heat welded paper tubing or Kraft-phenolic tubing that is at least as long as Item #2 being used in the adjustable nose weight assembly. (Approximately 15 inches +) Make sure that whatever types of tubing you decide to use are compatible with one another inasmuch as the spanner/driver tube needs to move in and out of the weight container, while it is being rotated and without interference.
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    Item s2: ¼” aircraft plywood. Drill one hole through the center that is only slightly larger than ¼” in diameter, to allow the ¼-20 all-thread rod (Item 4 of the nose weight assembly) to pass through it. Drill two, 3/16-inch diameter holes through, 180 degrees apart and spaced ¾” between centers.
  • Item s3: Two each, 3/16-inch diameter X ¾” long, hardwood dowels. Push these into the two 3/16” diameter holes that were drilled in Item #2 and glue them in place with epoxy or a (heavy viscosity) CyanoAcrylate adhesive.
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    Item s4: ¼” aircraft plywood. Drill a 3/8” diameter hole through the center. Make sure the outside diameter fits snuggly with the inside diameter of Item s1.
  • Item s5: 3/8” diameter X 1 3/4” long, hardwood dowel. Push this dowel into the hole in Item s4 until it is flush on the opposite side. Its position needs to be as perpendicular as you can get it, so that when the tool is turned in a drill motor, any probable eccentricity will not be excessive.
  • Note: The assemblies of Items s2 and s3, and Items s4 and s5, are glued in place at opposite ends of Item A after you have made certain that the tool fits easily within the weight container (Item 2, of the Adjustable Nose Weight Assembly). And that the forward end of the Spanner-Driver will fit its mating features on the adjustable manifold (Item 6), and the adjustable closure (Item 7) for the Nose Weight Assembly.

Constructions:

Item 2, of the nose weight assembly and Item s1 of the spanner-driver have to be compatible in their fit with one another. The spanner-driver is merely a tool. But it has to fit loosely enough inside the weight container, in order to effectively drive Items 6 & 7 of the nose weight assembly, and then be removed. Purchasing these tubes from the same manufacturer is recommended. And so is the use of a dry lubricant to prevent seizing if or when the fit may become too tight.

Assemble the forward end (Items s2 & s3) of the spanner-driver first, making certain that the Nylon all-thread (Item 4 of the nose weight assembly) passes through it without interference.

Assemble Item’s 5, 6 and 7 of the nose weight assembly; making certain that the axial holes in Items 6 and 7 will receive the wooden dowels installed in Item s2 of the spanner-driver. Start with Item 5, and glue the nuts in place on the plywood using the Nylon all-thread for alignment and timing the orientation of the nuts. Do the same with Items 6 and 7 so that the end result will be a better fit when one is brought to bear against the other, inside the weight container. Keeping in mind the fact that they too will have to turn freely along the length of the all-thread (Item 4) and inside the weight container tube (Item 2) of the nose weight assembly.

Assemble the weight container of the nose weight assembly as follows. Taking the Nylon all-thread in hand, thread it all the way through the nuts on Item 5 until the length of all-thread protruding from the nut on the opposite side is at least ½ of its outside diameter. Then put the assembly inside the weight container tube, deep enough to provide a shallow well for an epoxy fillet to be applied soon after. Next, at the opposite end of the weight container, thread either of Items 6 or 7 onto the all-thread into that end of the weight container. –This operation is very important, as it aligns the all-thread within the longitudinal axis of the weight container tube at each end. –

With CA, tack Item 5 in place and the all-thread as well. But do not tack anything else at this time. Allow the CA to cure, then remove whichever Item is being used to hold the opposite end of the all-thread at the other end of the weight container tube. Stand the tube on end and fill the well in the forward end with epoxy. Set it aside to cure.

Next, we move on to the completion of the tool, the Spanner-Driver assembly.

Item s1 of the spanner-driver assembly, aside from the necessity of a free fit that rotates and slides within the weight container tube, should also be of a length that is at least one inch greater than the length of the weight container tube used in the nose weight assembly.

Assemble Items s4 and s5 of the spanner-driver assembly, then glue them in place with epoxy or CA, or both. After that, you may permanently install their assembly at the other end of the spanner-driver tube, with epoxy or CA, or both.

Now, since Items s2 and s3 of the spanner-driver have already been assembled, their installation will finalize the assembly of the Spanner-Driver. Install each assembly according to the drawing provided, and set the completed tool aside.

In the next phase of this particular plan, the nose weight assembly will be nearly complete as it is introduced to the inner sanctum of the rocket’s nose. Moreover, there is a certainty that is often found in the necessity for any implementation of modifications to commercially manufactured noses for amateur rockets when the end user’s consideration toward over-building, for the sake of safety and success, precludes all else.

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First, we have to modify the base of the nose so that it will accept a rather large piece of plywood. This particular piece of plywood, referred to, as Item 3 in the nose weight assembly drawing, will serve in three purposes. (1.) It provides a far superior hard-mount for the shock cord. (2.) It centers the aft end of the weight container tube. (3.) It also strengthens the lower end of the shoulder of the nose. Which also raises the question of how to get that big thing inside there, once it’s been built.

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Please refer to the drawing of the nose weight assembly while holding the rocket nose of your choice in hand, and then take careful note of what part of the nose that has been set aside in one illustration named as “Cut-away, Aft end, Nose”.

First, measure the outer diameter of the shoulder. Then subtract 1/16 inch. The result of that calculation, rough as it may seem, will be the outer diameter of Item 3. Start cutting the shoulder of the nose cone right about where the radius meets the taper, and go all the way around. Remove burrs and sharp edges with sandpaper (heavy grit). At the same time, rough the inside of the shoulder too. Set the nose aside.

Now build Item 3. Before installing the steel U-bolt, test the fit of Item 3 inside the nose. Retrieve the nose. Then, squeeze the shoulder of the nose and slip Item 3 inside. Like putting a slice of bread into a toaster. Once it’s inside, put a strong finger through the hole in the center of Item 3 and relax your grip on the shoulder of the nose. Flip the dang thing so that it is perpendicular with the longitudinal axis of the nose, and then bring it to bear against what’s left of the aft end of the nose’s shoulder.

A slightly sloppy fit is OK! But a tight one is not. In the event of a fit that seems too tight, check the outer diameter of the shoulder again. If its diameter is larger than was previously measured, you need to remove a little bit more material from the outer diameter of Item 3. Take it out the same way you put it in, do what you’ve got’s to do, and try it again. Once the fit is deemed to be 3D and cooperatively aesthetic in your personal standards, take Item 3 out and install its U-bolt assembly.

Re-install Item 3. Then insert the weight container assembly. Push the weight container assembly all the way into the nose until it can go no further. Hold it in place with your thumb while pulling on the U-bolt with the index finger and thumb of your other hand. Now, yell for help. When the Cavalry arrives, instruct the first member approaching you from that group to apply a bit of CA around the base of the weight container tube where it mates with Item 3. And be sure to tell them that the digits of your hands are not to be included with the fastening of these parts of the assembly. [By the way: children will listen to instructions and are fully capable of following them. Girlfriends, wives, and/or a significant other, however, are quite tempted in being given the opportunity to make a slight mistake.]

Once the CA has cured, mix a small batch of epoxy and make fillets around the end of the weight container as well as inside the radius of the shoulder of the nose, on Item 3. Wait for the epoxy to cure. Through one of the ¾” holes in Item #3, shoot just a little bit of a commercially manufactured “canned” expanding foam into the nose cavity. Give it plenty of time to expand and cure. It’s kind of like shooting paint, because too much at once is NO GOOD. If you shoot too much, it’ll take forever to cure because urethane foam needs exposure to air in order to cure. And you’ll probably be scraping turd-like extrusions of foam for days after. So go light, and wait for the foam to cure between shots. Clean the “shooter tube” and the can’s nozzle between shots, with Acetone. Please be advised that just one (1) can of this stuff (the expanding foam) will easily fill several nose cones like the Minnie-Magg’s.

Believe it or don’t, your very own “Adjustable Nose Weight Assembly” is now complete. TAH DAH! So, Congratulations and Salutations are the order of the day.

Here’s how it works, in the field and on-site.

-A rocket’s center of pressure does not change, but its center of gravity does. Further, the relationship between the two is a very important factor in the properties of stable flight. And there is the basic “rule of thumb” that the rocket’s center of gravity should be at least one airframe diameter (or caliber) ahead of the location of the center of pressure when it is made ready for flight. –

Prepare the rocket for flight, then tie a piece of twine around the airframe and suspend it above your work bench; moving the twine fore or aft along the airframe until the rocket is balanced. If that balance point is not at least one caliber ahead of the center of pressure, you’ll need to add weight to the nose.

Stand the rocket’s nose on the pointy end, and remove Items 6 & 7 from the weight container tube. Pour in an ounce or two of lead shot. Place Item 6 on the all-thread (nut first) and carefully thread it into the mouth of the weight container tube by hand.

With the Spanner-Driver chucked in a portable drill motor, slowly turn Item 6 along the length of the all-thread until it just touches the lead shot in the bottom of the weight container tube. Now introduce Item 7 to the all-thread but with the nut facing “UP”. Slowly thread it into the weight container tube until it just barely touches Item 6. Remove the Spanner-Driver and reattach the nose to the Rocket.

Then perform the balancing act again.

Once the rocket’s balance point (center of gravity) is sufficiently ahead of its center of pressure, you’re good to go.

Comments from the Author:

Each time a different motor is used, take note of the amount of lead shot required in achieving the aforementioned relationship between the rocket’s center of gravity and its center of pressure; either by volume or scaled measurement. Using lead shot instead of steel shot requires less space to be occupied by the amount of weight needed. And for consistency, using just one size of shot when it is being measured by volume alone is recommended.

In the event that you are attempting higher flights with the implementation of Optimal Mass, you already know how much the rocket weighs when it is prepared for flight and exactly how much more weight needs to be added. That amount of weight will however, vary. Because flight conditions at the launch site, namely Weather and Geographical Location are variable factors too in pre-flight calculations or simulation.

Contributed by Steven Pasquier

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