Hybrid Motors
Working with our airframe
Stiffy
Electronics Bay Construction
Painting
Decal Papers
Motor Retention Securing motors in motor mount tubes
Mechancal Retention Method
Reloadable motors normally include a mechanical thrust ring as part of their aft closures. This keeps the motor from flying up through the rocket by transferring the thrust to the motor mount tube through the thrust rings and to the airframe. These motors don't require a masking tape build up on the nozzle end but they do need some method of keeping them in place when the motor thrust stops and especially when the motor ejection charge actuates.
One simple and inexpensive method of retaining these motors is to use a set screw and a washer or mirror clip to mechanically clamp it in place. I suggest planning for this in your initial construction by adding "blind T-Nuts" to your aft ring for the insertion of bolts set to the width needed to make your washer or mirror clip clamp securely onto the mechanical thrust ring. There are externally threaded versions of these nuts that can be applied after construction if needed. Check the specialty fasteners section of your local mega hardware store for different shapes and sizes.
WORKING WITH OUR AIRFRAME
LOC/PRECISION's proprietary airframe is strong, light weight and easy to work with. It provides a a good base for applying paints and decoration. We bond a layer of glassine to the outside of our paper tubes which can be lightly sanded for good primer adhesion.
Surface Mounting Fins and Motor Tubes - When working with surface mounted fins or when used as motor tubes, the glassine layer should be removed and the surface below roughed up or even cross-hatch cut with a razor knife to allow epoxy or wood glue to better soak into the paper's layers. I have seen this technique yield fins that could not be snapped off without breaking the wood they were made of. (Failing to remove the glassine layer prior to attaching fins will result in having to re-attach fins occasionally - more often than not.)
Adding Strength - Our airframe is very strong in compression. We have flown M power in our 5.38" and 7.51" airframes as is (though we recommend only motors through L power so that our lawyers can sleep better) Additional airframe strength can be achieved by lining standard tubes with tube couplers and if maximum strength is needed, lining the couplers with STIFFY tube coupler stiffeners. Another good way to add strength is to build it in - from the inside out - with a skeleton of vertical spars spaced around a central motor mount. Most real rockets don't rely on their outside skin for compression strength - just aerodynamics.
Fiberglass - It is easy to add a layer of fiberglass to our airframe but not necessary to achieve the compression strengths needed to fly our kits on conventional motors. If you are going to do this, remove the glassine layer first by pealing or you will have bubbles under some areas. LOC PRECISION does not like fiberglass, metal or carbon fiber being used on rockets. Doing so will void all warranties and may cause damage to persons or property. It may also be a violation of NAR bylaws - depending on who is interpreting them.
Drilling and Tapping Paper - When cutting holes in our airframe or in STIFFY coupler stiffeners, drill a slightly smaller diameter hole than you need. Remove excess "tear through" and apply a coat of CA (super glue) to the hole. Once this sets up, go back with the final diameter drill and finish off the cut. This will yield a nice smooth, round hole the size you need with no breakouts or tear through.
When using set screws in STIFFY coupler stiffeners, drill a hole slightly smaller than the screw diameter, apply a drop of CA (super glue) and screw in the set screw - then - quickly unscrew it a bit -then all the way out and allow the CA to fully set-up. This will make a nice hard surface for the screw to seat into.
Cutting + Slotting Airframe - Our airframe is easy to cut with a razor knife. Multiple light passes work better than one hard pass. For a good clean cut, I normally figure 3-4 passes on the white tubes and 6-8 passes on the brown tubes. Whenever I make a cut, I like to finish it off by lining the edge with CA (super glue). It swells the edges slightly and has to be sanded down, but it makes for a nice clean look and strengthens the tube in the cut section.
Electronics Bay Construction
STIFFYTM and Coupler Tube Assembly Tips
Have some paper towels at hand – you will need them for this procedure. Identify the STIFFYTM tube coupler stiffener and the thinner tube coupler that the STIFFYTM fits inside. Mix a small quantity of 5-minute epoxy. With a Q-Tip or Popsicle stick make two rings of epoxy on the inside of the thin coupler tube. Smear these flat with you index finger or Popsicle stick. Quickly and smoothly insert the STIFFYTM inside the tube coupler and make sure it is centered in the coupler tube (the same amount of coupler tube is showing at both ends. This is critical because the end plates need to fit inside the coupler tube and against the STIFFYTM equally at both ends. The end plates are designed to extend 1/32 “ at each end for strength. While holding the STIFFYTM tube in place firmly between your left hand thumb and index finger (reverse if you are left handed) use a paper towel to wipe any excess epoxy off the inside of the coupler tube and top end of the STIFFYTM tube. Make sure you hold this assembly still and have each end of the STIFFYTM equally recessed into the coupler tube. When the epoxy has setup, lay this assembly on its side to cure for 10 minutes. WARNING: It is critical that you wipe any epoxy off the end of the STIFFYTM tube where the epoxy oozed out when you inserted the STIFFYTM inside the coupler tube.
Eye Bolt Assembly
Prepare the two eyebolts by threading a 1/4 “ nut all the way down the threads of both eyebolts. Mix a small amount of 5-minute epoxy. Place a fender washer up to the 1/4 “ nut. Circle the center opening in one end plate with a thin application of epoxy. Insert the eyebolt/nut/washer assembly through the center hole in the end plate. Immediately slide a fender washer on the threads, followed by another 1/4 “ nut, eyeball the threaded end and make sure it is centered on the end plate, then firmly finger tighten. Quickly repeat this with the other end plate. If the epoxy is still workable, put a thin layer on each threaded end up to the nut. Check for any epoxy smears near the outside of the end plates and wipe them off.
Electronics Slide Assembly
In order to insure proper line up of the threaded rods, it is necessary to assemble the electronics slide now. Identify the small piece of rectangular plywood and flip it on the side where the two lines are drawn so they are facing up. Mix a small amount of 5-minute epoxy and carefully apply a thin bead of epoxy along the lines on the plywood, staying 1/4 " away from the ends of the plywood. Take the two lugs (small, brown paper tubes) and align them along the two lines on the sled, centering the imaginary center of the lugs right over the lines on the sled. This must cure for at least 20 minutes. We will use this sled assembly to make sure the threaded rods installed in the next step are aligned perfectly.
Threaded Rod Assembly (NOTE: The following step is performed on both threaded rods.
For this step, you will need two wrenches that can accommodate a 1/4 “ nut. Thread these two nuts up any end of the 1/4 “ threaded rod about 1” from the end and lock these nuts into place with the two wrenches by moving the wrenches in opposite directions on the two nuts. While keeping a wrench on the top 1/4 “ nut, using a wrench take a nylon insert lock nut and thread it on the end of the threaded rod until approximately 1/8 “ of the threads show though the nylon lock nut end. Repeat this with the other threaded rod. Remove the two 1/4 “ nuts and set them aside (Hint, you may need two 1/4 “ wrenches to separate the nuts.
Mix a small quantity of 5-minute epoxy and apply a small circle of epoxy on the inside hole in one of the centering rings (the eyebolt faces away from the direction you are inserting the rod). Take a 1/4 “ washer and place it against the nylon lock nut and insert this assembly through one of the two holes in the end plate. Quickly apply a small amount of epoxy to the threads of the 1/4 “ rod on the inside of the end-plate. Slide on a 1/4 “ washer and apply a small band of epoxy slightly above where the nut will be when assembled. Immediately thread a 1/4 “ nut down all the way to the end plate and apply some epoxy to the threads and 1/4 “ nut on the inside face of the end plate. Repeat for the second threaded rod.
Test the threaded rod alignment by sliding the electronics sled onto the rods. Move the threaded rods slightly to accommodate the sled and let the assembly cure after you are satisfied the threaded rods are spaced well enough to let the electronics sled slide all the way down the rods.
Using Setscrews
When using setscrews to secure the electronics bay to the payload extension, pre drill the holes in the airframe down into the STIFFYTM heavy wall Kraft tube. Wood screws make good setscrews in paper applications. Remove the airframe and dab a drop of CA on the hole. This will be absorbed well into the surrounding hole area and reinforce it greatly. Do the same for the hole in the EBAY and run a screw quickly into and back out of the wet hole – be sure to remove the screw before the CA sets up. The CA soaks into the STIFFYTM material well and provides a strong hold for your setscrews. Once everything is cured, lightly sand the airframe tube inside to remove any excess CA. This should provide a long lasting, quick disassembly payload section.