Paint Stick Monocopters
Presented at the 2011 Pyrotechnics Guild International Convention on Monday the 8th of August by David and Patt Gustafson
There are times when a simple firework is wanted but the noise of a shell is too much and simple fountain is too little. The monocopter is the perfect in-between device with the subdued whoosh of a small rocket, the smell of BP but with a 50’ or better vertical rise, and a completely reusable frame.
In order to make one of these, you will need to gather some parts.
Parts List:
1- Paint stirrers. Don’t use the Home Depot ones, they are too heavy, the ones from Menards are half as thick.
2- Cross piece. I use bamboo paint stirrers but even using a regular paint stick that has been cut in half and then split will work just as well.
3- Drill bit. We will use a 3/8” spade type drill bit.
4- Pivot tube. Pyrodirect.com has the ¼” x 2” ID spiral wound tubes that I used in this project.
5- Chip board. I used .030 from Uline.com.
6- Fiberglass tape. I got mine from the Home Depot; it is used to join sheetrock panels. Split it in half for this project.
7- Pennies. You will need two of them to counterbalance the motor.
8- Strapping tape. This is used to hold the pennies on the stick.
9- Glue. Hot glue, Elmer’s, epoxy, or just about any glue you have can be used.
10- Tissue. Not the kind you blow your nose in, the crinkly kind you wrap presents in.
11- Motor casing. We are using a ½” x 3” convolute wound paper tube for this project, if you have a different size case, be sure to compensate the counterweight.
12- Black powder. We are using 116 Fuse Powder from addictedtoblackpowder.com that has been treated with 4% mineral oil to control the burn speed and extend the burn time.
13- Embellishment. We are using 70% Fuse powder with 30% fine Titanium turnings.
14- Clay. A good nozzle needs to be made with good clay. We are using (in equal parts) Bentonite, Kaolin, 40 mesh Grog clays mixed together.
15- Tooling. I couldn’t find any tooling commercially available so I made my own. The spindles are 7/64” and the rammers are made from aluminum.
16- Skewers. Grab the thick 12” bamboo ones for the launch stick, the thin ones like to break off before launch.
17- Visco. Green Chinese 1/8” Visco burns hot and will light an ice cube in a glass full of lemonade.
Paint Stick Monocopters
Directions
Theory of flight:
The monocopter flies because there are forces acting upon the wing that cause it to rise as it slices through the air.
1- The rocket motor creates thrust and it is this thrust that makes the monocopter spin.
2- As the rocket motor forces the wing to turn, the wing creates lift due to a partial airfoil and the angle of the wing relative to the ground, much like a ceiling fan pushes the air down to the floor.
3- The motor is also angled downward slightly and this also creates lift on the other end of the wing.
Rotation-Lift-Thrust
There are other forces that work against the wing as well. The wing wants to immediately flip over as the rocket motor provides thrust but it cant because of the cross brace and while there is much speculation as to why this keeps the wing from flipping over, the most widely excepted theory is that gyroscopic forces are created by spinning the cross brace and it is this force that keeps the wing right side up.
Drag also causes the wing to slow down as is demonstrated by the immediate stopping of the wing at the end of its flight.
Now that you understand the reasons for flight, think about what you could do to change the flight characteristics. What would happen if the rocket motor was level to the ground? What if the wing had no twist? What if the pivot was in the middle of the wing?
Step 1:
(This step has already been done for you but is included for the sake of making your own monocopters at home)
Shaping the wing:
Find a thin paint stirrer that is in good shape with no cracks, knots or blemishes. If you wish to make more then one wing at a time, take four paint stirrers and wrap them up in an all cotton dish rag alternating the sticks so that each one is completely covered with towel and are not touching each other.
Run the dish rag under water (hot or cold, it does not matter) and squeeze out most of the water from the rag so that it is not dripping.
Take a dinner plate and place it in the microwave and place the sticks all wrapped up in the wet rag on top of the dinner plate. Set the time for 3:00 minutes, set it on high and press start.
When the microwave chimes the end of the cycle, you should be wearing some insulated gloves, have a vice and a pair of locking pliers with a couple of small blocks of wood to clamp the clamp on.
This next step has to be done carefully and quickly.
Unroll the rag quickly and place all four sticks (one if you are only making one at a time) face up in the same direction. Align them and place them handle end first 1” onto the vice and squeeze them only hard enough to hold them firmly, don’t crush them.
Quickly take the two small blocks of wood and place them on each side of the four sticks 3” above the vice jaws and clamp the locking pliers over the blocks and sticks. Again, make sure it is good and tight but do not crush the sticks.
Care must be taken at this point to not break the sticks.
Take the locking pliers and rotate the handle of the pliers 90° to the vice. This will establish the twist of the sticks so watch that you are twisting all four sticks and that you are not going too fast and break the sticks off.
The handle must stay in the position for a good half hour or more. Tie a string to the handle or use another pair of locking pliers to block it from turning. Now go get a cookie or rustle up the drill and a bit for the pivot hole.
Step 2:
While the paint stirrers are drying, lets make the cross braces.
We need a stick that is 6” long by ½” wide and about 1/8” thick. A little thinner or thicker is fine and since we are making four monocopters, lets make four cross braces as well.
Done? Good. Let’s go get those paint stirrers.
Step 3:
Did you notice that the stirrers didn’t hold the full 90° of twist? That’s a good thing; we are looking for 45°-60° of twist. If you have more then 60° of twist, go ahead and untwist them a little. Go easy, they will unbend quickly.
If you want them to spin faster but not rise as far, 45° is what you want, if you want them to fly higher, 60° is your angle.
Step 4:
Let’s go grab the drill and 3/8” spade bit that was in the parts list, we will need that to make the hole that the pivot tube fits in.
It’s important to use a block of wood to back your drill bit. Failure to do this will result in a cracked paint stirrer.
Measure back 3” from the handle end of the paint stick(s) and mark the middle of the stick at that point. Place the stick(s) as flat as possible on the backing block and drill a 3/8” hole all the way through them.
Now pick up the cross braces and mark them ½ the way across their length. It does not matter if they are longer or shorter, you want the middle. Mark the center and using the backer block, drill a 3/8” hole through them.
Step 5:
Its time to grab some glue and the pivot tube. Pick up a wing and take a look at the curve it has. We want the curve to be placed down like a frown :(
Take the pivot tube and push it through the hole in the wing 1/3 of the way with most of the tube sticking out the top. Place a drop of glue on both sides of the tube where it meets the wing and give it a turn to get the glue in the seam.
Next, grab that cross brace and push it down over the long portion of the pivot tube and glue it down with a drop of glue.
Give it a spin as well to get the glue into the seam. The cross brace should be as close to 90° to the wing as possible.
Step 6:
For this step we need the rocket motor tube and a piece of chip board that is 1” wide and long enough to wrap all the way around the rocket motor plus 1/2”.
Make sure you cut your piece of chip board so that it curls around the motor, if you cut it the wrong way, the motor will not fit tightly and you’re friend will post a video of your monocopter on YouTube with the banner !EPIC MONOCOPTER FAIL!
Go ahead and wrap it around the tube a couple of times, get it nice and tight but leave the 1/2” end open so that you can put a little dab of glue on the flap.
If you get glue on the rocket motor tube, immediately pull the chip board off and wipe the glue off the tube. Failure to do so will make it impossible to ram the tube with fuel.
Go ahead and put a little dab of glue on the inside of the flap, a LITTLE dab! Press the tab down and hold it tight for a good 15 seconds, now lay it down to dry the rest of the way and repeat with all of the monocopters you are making.
Step 7:
The monocopter frame should now be dry or nearly so. Before grabbing it, go ahead and cut three pieces of that fiberglass tape 1” wide by 6” long.
Take two of those pieces and put them together sticky side down (not facing each other) with 2” of the tape on the end of the handle side of the wing.
Place your chipboard motor nacelle on the end of the wing, put a small dab of glue between the frame end and nacelle, then wrap the tape around the nacelle (a nacelle is the little tube you just rolled around the motor tube) and over to the other side being careful to push the tape down flat against the frame and nacelle with no air gaps.
Take the third piece of fiberglass tape and wrap it around the end of the frame across the other two pieces of tape and snuggling up against the nacelle.
This tape will provide 90% of the strength and rigidity the motor nacelle needs so that the motor stays put when lighting the fuse.
Step 8:
It is officially dirty hands time.
If you get glue on the rocket motor tube, immediately pull the motor tube out and wipe the glue off the tube. Failure to do so will make it impossible to ram the tube with fuel.
Using your glue sparingly, squeeze out a spot of glue out onto the tape and rub it into the tape, repeat until all of the tape is covered. Don’t get sloppy here, too much glue gets the nacelle all wet and takes forever to dry and you want to shoot these things today, right?
Once you are done with the glue, twist your rocket motor tube out and get ready for the next step.
Step 9:
OK, I lied, step 9 is coming up soon but first we need to go over all the safety stuff. Now hang on there, don’t skip over this section, this is important stuff that you need to know so that you and your buddies don’t get hurt.
These motors require the use of black powder which has been ruled as an explosive and can ignite from friction, flame, spark or lightening. You should use PPE (Personal Protective Equipment) when pounding on BP so that in the case of an accidental ignition, you don’t lose a hand or an eye and don’t get burnt. Wear Gloves, Eye Protection, Cotton Shirt and Pants.
Now, on to step 9:
For a 3” long motor, you will want to measure out 3 grams of nozzle clay and 12 grams of BP and place them in small containers with a lid. This motor will burn for about 5 seconds. I use 116 Fuse Powder for my rockets; it is pretty tame burning and with the addition of about 1% mineral oil mixed in with Coleman’s camping gas, it burns nice and slow allowing for a 13/128” nozzle (7/64” spindle).
Grab your tooling and hammer, lay it out in front of you. You should have a spindle and base, a convergence rammer that has a green band around it, a flat rammer with a red band around it, a scoop that holds 3g of BP when filled to level and that hammer I just mentioned.
Place the spindle and base on a 4x4 in a bucket of sand or a stump, in any case, the thing we are pounding on should be solid but not hard like concrete that will damage the base bottom.
Place a rocket motor tube on the spindle, it should fit tightly. Make sure it is seated all the way down and make sure it is sitting flat; we don’t want to make a banana.
Take your funnel and place it into the end of the tube, measure out 1 full but level scoop of nozzle clay and put that into the funnel, tap it down into the tube. Remove the funnel.
Grab your rammer with the point; it has a green band around the top and push it down into the tube with the point facing down. Grip the tube and the rammer in your off hand, making sure that it is still sitting flat.
Pick up your hammer and with 15 good stout but not hard blows, pound the nozzle into the tube.
If you fail to ram the nozzle hard enough, the nozzle will blow out and your monocopter will not fly. If you pound too hard and split the tube, the motor will burst and the monocopter will not fly.
Once you have rammed the nozzle, remove the rammer by twisting it out of the tube being careful to not remove the tube from the spindle. Once you have removed the rammer, look down into the tube and look for the tip of the spindle. The black powder goes on top of the spindle and it needs to be exposed to the fuse to burn so if the spindle is not visible, stop now and change your method so that you can see the tip of the spindle. Tap out any remaining clay in the tube.
Look into the end of your rammer and make sure it has no clay stuck in the end. Clean it out right away so that you don’t ruin the spindle when you make the next motor. Now set the rammer with the green band out of the way.
Place your funnel in the tube and measure out 1 full but level scoop of black powder and place it into the funnel. Tap the powder down into the tube and remove the funnel.