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Build Thread for Whopper Flopper Chopper

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BABAR

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Okay, here's my first try at a build thread. Be kind.

Always hazardous to suggest something is really new. These are features of this helicopter that I think are either new or at least uncommonly used:
1. Size. Certainly not the largest ever launched, but I think it is bigger than anything you can buy in the store at the moment.
2. Integrated Rotor-Fin (the component that functions as a fin for stability in boost phase is an actual functioning part of the rotor on descent.) This has been used on the FlisKits Tiddlywink, otherwise I have not seen it.
3. Reinforced floss/tape hinges. Double tape hinge has been in use for a while. I first found it on a QCR flopwing glider (I think.) Sewing the hinges in with dental floss is something I haven’t seen elsewhere. (Other types of thread will probably work as well and might be lighter.) Sewing it in makes it a lot stronger with what I think is negligible weight penalty.
4. The flop-rotor design with the Standoff Hinge.
5. The “burn band” motor retention system with “Burn Chamber” and “Blow-Out Assist” deployment of the rotors.
6. Pyramid Nose Cone

Goal was to create a flop-rotor helicopter with at least a 10 foot rotor cone diameter, and keep it within the realm of low power engines. Note I had actually hoped for a 12 foot rotor cone but early on felt the weight would be prohibited by low power engines (at least in this prototype level)
Also was hoping for a model with engine retention rather than my typical engine eject models—mainly because while engine ejection is accepted with sport models and most people probably wouldn’t whine too much about getting conked with an A, B, or C engine, and maaaaybeee a D, dumping an E casing from 300 or 400 feet didn’t sound very smart.
Decision for 4 rotors rather than 3 had to do with weight. To create a continuous “fuselage” of balsa around the engine mount, you can use less balsa with 4 “sides” than with 3. (The smallest square you can draw around a circle has smaller total circumferential diameter than the smallest triangle you can draw.) Tim Van Milligan tells me that you also get more DRAG during launch with 4 blades, but I felt that in my case launch weight was more critical. Also, my engine retention method used here works much easier with 4 than 3 rotor-fins.
Understand before this I had never launched anything greater than a D, and basically I thought D was pretty high. At 4 bucks an engine at Hobby Lobby WITH the 40% off coupon, going up to the E9-4 was a stretch for me.
Biggest challenge on a Flop Rotor of this sort, with a single elastic actuator which operates BOTH the central hub hinge and the flop hinge, was getting the central rotor blade to be stiff enough NOT to flex. Finally figured I'd try 1/4 inch balsa-- which was CERTAINLY stiff enough but obviously presented weight issues.
Note for reference from here on out I will name these rotors according to their position during the BOOST phase. Since the central rotor is on the OUTSIDE of the rocket in boost, I call it the OUTER-ROTOR. The peripheral rotor is on the INSIDE during boost, so it is the INNER-ROTOR. When these two are attached, they are referred to as the Rotor-Fin.
I am writing this as if I was telling you how to build it. I found the grammar easier to keep up with that way.

Parts:
Parts:
one sheet of 36" x 6" x 1/4" balsa
two sheets of 36" x 6" x 3/32" balsa
Duct Tape
Dental Floss
Kevlar Thread (for pull strings and nose dowel loops)
2 small paper clips to make s-hooks.
3/8 inch dowel 3 feet long.
BT-50 body tube
BT-50 nose cone (just about ANY shape nose cone will work)
Mylar Tape
Thrust Ring for D engine BT-50
E size engine hook recommended
4 short (1 cm) carbon fiber strips, 1/4" thick or less.
4 short (6 cm) carbon fiber rods, 1/8" is fine
Lots of #16 [2.5” x 1/16”) rubber bands (you can get a 1 Lb bag at Office Depot for $5.29. I don’t know how many are in a pound, but it is a lot. https://www.officedepot.com/a/product...bber-Bands-16/.) The rocket uses 24 for pull strings, which are re-usable (haven't had to replace them after 7 launches), and two "burn bands" are consumed at each launch.
Qualified Competition Rockets ejection protecting "plugs" for D-engine rockets for centering "rings" for the dowel. Note you can make centering rings out of lots of different materials, I just happened to have some of these.
Large Crochet Hook
3/16 inch launch lug, can cut them from a 1 inch segment.
Small piece of heavy card stock for centering squares.

WFC Finished Prepped.jpg


WFC_Pad_View.jpg


WFC_1st_Landing.jpg
 
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BABAR

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Outer-Rotor:
Outer-Rotor is pretty standard. Start with a 6” x 36” sheet of ¼” thick balsa, cut 4 strips 36” long and 1.5” wide. Cut each section back to 31.5”. (Save the rest, you will use it for the Stand-Off Adapters.) Unless you are planning on painting this (not recommended) you should take a heavy black marker and mark one long edge with it. Designate this the “Lead Edge.” I can't emphasize this step enough, as all my descriptions that follow will use position of the LEAD EDGE to help orient. Note the nose end will always face away from you in my orientation/drawings. Thus if I say, "Lead Edge Left" that means the rotor piece is oriented with the nose end away from you and the black edge to YOUR left. This makes the other edge the “Trail Edge.” Mark one end of this “Nose.” Measure down 1-1/2 inches down the lead edge from the Nose, make cross-cut, 15 degrees off perpendicular to the long axis of the blade (or 75 degrees parallel to the blade....make it look like the picture), angled BACK TO THE NOSE toward the trail edge to allow provide angle of attack for rotors. With the Outer-Rotor held Nose (or Hub) end up, the lowest part of the 15 degree cut is on the LEAD EDGE of the rotor, the highest part is the TRAIL EDGE. If you get this backward, the rotor will rotate with the fin forward (still works, but looks funny.) This makes central rotor 30” long and the hub approximately 1.5” long.
After this cut you have two pieces. The smaller nose piece will be the HUB. The longer tailward piece is the OUTER ROTOR.
Note this next section is not what I DID, but what I WOULD do if I was doing it again. See the diagram to mark the location of a NOTCH to cut into Nose-ward end of the OUTER Rotor (in the middle of the the 15/75 degree angle you just cut). This is centered in the middle of the rotor (from side to side), 1/8 inch wide, and 1.5 inches long. Note: This line must be a perfectly aligned with the length of the rotor, as it will be used later to position the Rotor-Stops. Because the Rotor-Stops will act like anterior finlets, they promote instability, particularly if they are off –angle. Once you mark the notch, cut it out with a hobby knife.
Cut a 1/8 inch “notch” 2.75” long on the TAIL END (away from the hub) in the LEAD EDGE. This will leave room for the Fin (which is attached to the INNNER ROTOR on the adjacent Rotor-Fin) to pass.

Addendum: Could consider decreasing the angles on the hinge, dropping it to 10 degrees. Also could consider decreasing the angle on the rotor stop to 10 degrees, maybe even zero. The weight of the motor mount should be sufficient to torque this rocket in the appropriate motor mount down position. Both these would give you more effective rotor surface (parallel to the ground, perpendicular to the descent path) and thus a longer flight.

Outer Rotor Notch.jpg


Dimensions.jpg
 
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BABAR

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Make a double tape hinge out of duct tape. Best way to do this is to set the two pieces down with the OUTSIDE facing you (lead edge will be to your left.) Mate/match the cut edges of the hinge perfectly. Place a piece of duct tape 2 cm. wide across the gap (1 cm toward nose, 1 cm toward tail) leaving a small amount overlapping the lead and trail edges. Press this firmly into the wood--- reeeeallly firmly. Turn the hinge over and cut off the excess on each edge (lead and trail.) Now fold the hinge back so you have the cut edges perfectly overlapped. Because the cut is at an angle, the respective lead and trail edges will NOT exactly overlap. Place a 2 cm wide strip of duct tape over the hinge. Again press really firmly into place.

WFC_HubHinge1.jpg


WFC_HubHingeGraphic2.jpg
 

BABAR

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Now “sew” the tape into the balsa with a needle and dental floss thread. Wick thin CA into the floss on the inside of the rotors. The 1-1/2 inches of balsa at the front will be used to create the hub when all 4 rotors are combined. It really isn’t as complicated as the picture looks.

First picture shows the cut, the hub is to the right, rotor is to left. (Gap is shown for illustration, before you tape this butt the two edges up tightly.) Second shows the tape on the outside.

3rd shows the inner tape hinge applied. 4rth Shows passing the floss through the hinge, coming from INSIDE to OUTSIDE. Note it is important the needle starts from the INSIDE of the hinge for each pass, if you come from the outside you might not hit the center of the inner piece of tape.

5th Picture Outside view showing needle coming from INSIDE to OUTSIDE.

WFC_Hub_Hinge_Cut.jpg


WFC_Hub_Hinge_Tape_Flange.jpg


WFC_Hub_Hinge_InsideTape.jpg


WFC_Hub_Hinge_Thread1.jpg


WFC_Hub_Hinge_Thread2.jpg
 

BABAR

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Note: You don’t see the notch for the Rotor Stop in these pictures because I figured out it was needed AFTER I built this. Originally I just glued the Rotor-Stop on the outside (I cut away the tape.) This worked, but the landing stress on the Rotor-Stop tended to pull rip it sideways off the edge of the rotor after a few flights.

FrontHingeGraphic3.jpg


Broken Rotor Stop 1.jpg


Broken Rotor Stop 2.jpg
 
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BABAR

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Take a 4” x 36” sheet of 3/32” balsa. Cut 4 strips each 1” wide (remember, this has to fit INSIDE the Outer-Rotor.) Mark the Lead Edge 5.5” from the tail end, and mark the Trail Edge 8.25” from the tail end. Connect the marks. Cut across this line. The longer section is the Rotor, which will be 31.5 inches long. This should match the dimensions on the diagram.
Take a 3/32 balsa sheet and cut the fins as shown in the diagram, paying attention to the direction of the fin grain.
Note there will be a 1.5” overlap of the Inner-Rotor and Outer-Rotor when extended, giving a total of 60” extended rotor length. Gives a 10 foot rotor cone diameter (technically a bit less when you account for dihedral.) For those wondering how the inner rotor can be LONGER than the outer rotor, the solution is the Stand-Off Adapter. Actually the Inner Rotor extends out below the Outer Rotor.

You should be able to mate up the diagonal cuts of the rotor and the fin. and the Fin will stick out 90 degrees from the Rotor. When you mate these up the fin only extends 5.5” lateral to the trailing edge of the Inner-Rotor. In fact, when you fold the Outer-Rotor over the Inner-Rotor, the effective width of the fin is only 5.25”. (What’s magic about 5.25”? Absolutely nothing, it was a guess and it worked.) Inner-Rotor and Fin are glued with medium CA. Once dry, reinforce with white or wood glue.

WFC_Fin_Hinge_OuterTape_InsideView.jpg
 

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BABAR

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Stand-Off Adapter: Take the left over ¼” by 1.5” by 5.5” remnants from the the OUTER FINS (not the inner fins segments you just cut in section above.) Cut 4 sections 1.5” long. Trim 1/8” from the lead edge. Place the Inner Rotor with nose away from you, lead edge to the LEFT, trail edge (the way the fin is pointing) to the RIGHT. Line up the Lead Edge of the Standoff Adapter with the Lead Edge of the Inner Rotor. The Standoff Adapter covers (and adds more support) to the joint between the Rotor and the Fin.

WFC_Fin_Hinge_Parts.jpg
 

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BABAR

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The Flop-Rotor hinge is tricky. Note for reference from here on out I will name these rotors according to their position during the BOOST phase. Since the central rotor (the one attached to the hub) is on the OUTSIDE of the rocket in boost, I call it the OUTER-ROTOR. The peripheral rotor is on the INSIDE during boost, so it is the INNER-ROTOR. The two combined are called the Rotor-Fin. The Inner-Rotor does not require the stiffness of the Outer-Rotor along the Inner-Rotor’s entire length, but it must be strong at the hinge. It also requires an “extension” beyond the hinge to provide a “moment arm” to pull it open. There are two solutions I found to this problem. First, if I integrated the Fin into the INNER-ROTOR, it provided a “wider” rotor over this hinge segment which made it stronger. Second, I added a “standoff adapter” (which was actually just a piece of the ¼ inch Outer-Rotor.) When considering hinges, I needed to account for the considerable thickness of the rotors, particularly the ¼ inch Outer-Rotor. The standoff adapter intentionally displaces the actual contact points for the hinge to the outer margin of both the Outer-Rotor and the Inner-Rotor
As previously noted, the “gap” here is really for illustration purposes. All the pieces here are actually in tight physical contact.

WFC_FinGraphic1.jpg


WFC_FinGraphic2.jpg


WFC_FinGraphicStressPoints.jpg


WFC_FinGraphicThreadLoops.jpg
 

BABAR

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The side of the Inner-Rotor the Fin “sticks out from” I designate the TRAILING EDGE of the Rotor-Fin. (So the other side is obviously the LEADING EDGE. Also please note that the “Trail-Edge” of the Rotor-Fin has nothing to do with the trail edge of the FIN itself in boost phase, which is obviously at the tail end of the rocket.) The Inner-Rotor is placed on the work surface with the tail toward you, the fin (TRAIL EDGE) extending to the RIGHT, the LEAD EDGE to the LEFT. The Outer-Rotor is mated up, the hub away from me, the TRAIL EDGE to the RIGHT, the LEAD EDGE to my LEFT. The “notch” cut in on the LEAD EDGE of the TAIL END of the OUTER-ROTOR should now match up with the LEAD EDGE of the Standoff Adapter of the Inner-Rotor. If everything is correct, the FLAT SIDE of the Hub Hinge should be facing upward toward you.

On the left is the Inner-Rotor with the Stand-Off Adapter. On the right is the Inner-Rotor with the Outer-Rotor “mated up” with the Stand-Off Adapter. Notice the NOTCH on the Outer-Rotor along the LEAD EDGE is lined up with the margin of the Inner-Rotor. This notch is where the adjacent Fin will come out.

WFC_Fin_Hinge_Position.jpg
 
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BABAR

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Once lined up, a piece of Duct Tape 2 cm long is placed across the outside of the hinge joint. 1 cm overlaps the Tail End of the Outer Rotor, the lower 1 cm overlaps the Nose end of the Stand-Off Adapter. It is pressed down HARD (a rubber ink stamp roller works really well. Thumbs are adequate, though, if you press really hard.)

WFC_Fin_Hinge_OuterTape.jpg
 

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Flip the combined hinges over. Trim off the excess tape. Do NOT put an overhanging flange here
This is the combined Outer-Rotor and Inner-Rotor, with the Inner-Rotor inside face up. You can see the excess tape that you will trim off.
 

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BABAR

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After trimming off the excess tape, open the hinge 180 degrees and flip it over. Make sure the hinge is aligned perfectly (you should just BARELY be able to see the tape between the two sections.)

Picture 1
This is the hinge halfway open.

Picture 2
This is the hinge fully open. You can just barely see the tape (here a strand of light gray) between the Stand Off Adapter and the Inferior (tailward) edge of the Outer-Rotor.

WFC_Fin_Hinge_OuterTapeFlexed.jpg


WFC_Fin_Hinge_OuterTape_FullFlex2.jpg
 

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Take a 3 cm piece of tape, with about 1 cm over the Inner-Rotor, 1 cm pressed along the side directly over the hinge, and 1 cm left over the Outer-Rotor. Work on pressing the tape into the “corners” first, then press it HARD into the balsa of the Inner and Outer-Rotors.

WFC_Fin_Hinge_InnerTape.jpg
 

BABAR

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Figuring out how to “sew” the tape onto the balsa is a bit more tricky here than with the Hub Hinge. The diagrams show where I pre-drilled 1/8 inch holes in the balsa. You have to be very careful that each time you poke through the hinge itself, you are going through the hinge joint itself (in other words, you poke through tape on one side, you come out through tape on the other side, WITHOUT going through any balsa in between. A curved needle might have made this easier on this section.

Note in picture 1, the holes are drilled where the floss goes through tape AND balsa. You don't need to drill holes through where the actual hinge is. You can see on picture 2 where the thread went. I didn't have a consistent pattern for placing the floss, it was kind of random. The key factor is to make sure the tape is fixed firmly to the balsa at the stress points. Knock on wood, I have never had one of these hinges fail or loosen. On some of my latest models, I've gone down to 2 thread loops, one near each edge.

The last picture here shows the inside side of the Inner Rotor, I haven't trimmed the threads.

WFC_Fin_Hinge_Inside_Holes.jpg


WFC_Fin_Hinge_Inside_Threaded.jpg


WFC_Fin_Hinge_Threaded__Inside_View.jpg
 

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geof

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Okay, I *never* do this, but you've got me hooked: I'm going to make a flat-out clone. Did you make a consolidated parts list so we can go shopping all at once?

Please don't tell anyone that I've abandoned all creativity :)

Geof

PS. This is assuming that the flight(s) were successful! Maybe I should postpone shopping until we hear the end of the story!
 

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Sorry about the break here. Computer glitch.

Regarding successful flights, so far 7 of them with no failures in flight. Have had to repair the rotor stops a couple of times due to damage on landing, but I believe I've corrected that problem by using a tab notch insert as noted in the instructions.

Last one is the best. I don't know how to edit video, so just jump to the one minute mark to catch the landing.

https://www.youtube.com/watch?v=PYRsmrQLZXQ
https://www.youtube.com/watch?v=mnbKgRoBrCo
https://www.youtube.com/watch?v=kUWFtYaRgYs
https://www.youtube.com/watch?v=w2YTd5pyIoY

I'll try to remember to post the parts at the end.
 
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BABAR

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I also found that no matter how “tight” you try to make a tape hinge, there is always a certain amount of “slop” or lateral mobility. Therefore instead of single pull at the end of the Inner-Rotor, I attached pull lines (actually a ½ circle pull “loop”) at the edges, with a sliding hook to attach the elastic band (in this case, bands.) When this loop is pulled, it distributes the “tug” on both edges equally. Once the hinge is fully extended, the loops actually end up pulling the hinge tape taut. This pulls out the “slop” in the hinge and keeps it pretty straight in extension. You can see when the rocket lands however the rocket falls over and the force of gravity actually considerably bends the hinge out of kilter.

Cut 2 duct tape strips 1/4" x 3/4". Wrap the around the tail end of the inner rotor as pictures. Cut a piece of kevlar thread about 16 inches long. Using a sewing needle, thread each end through the tail end through your tape reinforcers, leaving a 12 inch loop "dangling". This will be the pull loop.

Note these pictures show the completed tail assembly, I just put this here so you can understand the "slop" concept.

WFC Tail Detail.jpg


WFC Tail Detail Arrows.jpg


Side View Pull Strings Closed.jpg


Side View Pull Strings Half Open.jpg


Side View Pull Strings Fully Open.jpg
 
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BABAR

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Once connected, I measure 3.25 inches from the combined “tail” of the Inner-Rotor. This is where the tail-most end of the “Burn Chamber” will be on the motor mount. With the hinge folded drill a ¼ inch hole ABOVE (nose-ward) of this line (so technically 3-3/8 inches from the tail edge.) Hole is CENTERED in the middle of the Inner-Rotor and goes through the Outer-Rotor as well. Make sure Both Rotors are perfectly lined up. Remember that the Inner-Rotor lead edge should be 1/8” inside the lead edge of the Outer-Rotor (you lined it up with the cut-out notch.)

With the rotors folded closed (in boost position), place the combined Inner/Outer-Rotor unit with the Inner-Rotor (fin side) up. Place a piece of mylar tape 4” long over the Inner-Rotor. This will start at the tail just “tail-ward” of the hole you drilled, and extend “hubward” about 3.75 inches. This will protect the balsa from the ejection blast. You can use a hobby knife to poke “slices) in the tape over your ¼” hole, push the edges into the hole.

Now flip the Rotors over so the Outer-Rotor is face up. Cut a ½” strip of carbon fiber strip and place over the tailward edge of the hole. It should just barely extend over the tail margin the hole. This will keep the “Burn Band” from “cutting” into the balsa. Pictures on on the previous post.

Note: the carbon fiber provides a firm "rest" for the rubber band to fold over. If you don't have carbon fiber, other solutions would be a piece of credit card/hotel key card, piece of flat hard plastic like a cast off from a plastic model plane kit, whatever. I don't want anyone to think you can't build this puppy without going out and buying some carbon fiber.
 
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BABAR

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Rotor Stops
The rotor stops are affixed directly to the Outer-Rotors just below the Hub Hinge. These are made 2 ply 1/16” balsa (two of these actually eventually failed on landing. Recommend reinforce them with paper on the outside.) A total of 8 of these are cut. 4 of them have the cut with the grain perpendicular to the base/tab (just like you would do for a fin.) 4 of them are cut with the grain PARALLEL to the base/tab. The contrasting grains greatly strengthen the Rotor-Stops. As mentioned, I would also paper both sides for your model.

Note: I believe this technique (2 ply balsa with orthogonal grain directions) would work for complex fin shapes as well, especially with a paper covering.

Glue these together with wood glue, then fold a piece of wax paper over both surfaces, stick them inside a book overnight to dry (otherwise they come apart and curl up on you.) For aerodynamics, you can round the front edge and taper the rear edge (AFTER they are glued and dried), such shaping will NOT affect the function. Cut a 4mm segment of a coffee stirrer the length of the outer edge of the Rotor Stop. Then cut it LENGTHWISE in half. Glue this on with the original OUTER (convex) surface of the stirrer against the balsa. This will create an outwardly facing “trough” that will help hold your pull bands in place.

Suggestion: on the inside face of the Outer Rotor just tailward of the notch glue a piece of card stock about 10 x 5 mm. This will help to prevent the notch from "splitting" down the length of the Outer Rotor when you put the Rotor Stop in. Because if you paper the Rotor Stop, it will be a little bit wider than the 1/8" notch.

Tuck the tabs into the notches. (again, I just glued them on the outside surface, and had failures on landings, but not in flight.)

You must line this up perfectly since these Rotor-Stops will act a anterior “finlets.” If they are “off” they will result in instability. Once in place, secure it with wood glue fillets.

Once the Outer and Inner-Rotors are connected, I call the combined unit a Rotor-Fin.

Note: these pictures are from the complete rocket.

IMG_0337.jpg


IMG_0332.jpg
 
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BABAR

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On the TRAIL edge of one of the rotor fins, I put three launch lugs. You will need at least 3/16” diameter lugs, and I cut them ¼” long. The reason they are so short is the rocket will be rotating, so I don’t want them to drag the rotation. I place them at 2.5”, 12”, and 22” from the tail (measurements not necessarily critical). Do NOT put them in the center of the Rotor-Fin or you will hit your Rotor-Stop. Since they are small, and these is a large rocket, used multiple small wood glue fillets for strength

WFC Finished Prepped Lugs.jpg
 

BABAR

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Motor Mount
I have used rubber band “burn” retention on other rockets such as the RhoTorr with good success. https://www.youtube.com/watch?v=YLbv9UbqqCs
They were however engine eject types. Had to figure out how to get the system to release the rotors without ejecting the engine.
The “engine-tube-proper” is 3.25 in long. However, you will start with an 11 inch BT-50 tube.
I decided to create a “burn chamber” above the engine. Also figured as long as I had that ejection blast, might try to use it for more than just burning the rubber band. By placing an inverted nose cone (reinforced with mylar tape for burn protection) just above the ejection, the hope it to deflect the blast force outward, literally “blowing the rotors open.” (It seems to work.) I also knew that the engine ejection gases would tend to burn the cardboard of the engine tube. So I used carbon fiber struts to conned the engine mount proper (the tube that actually HELD the engine) to the deflector/dowel adapter tube. To make sure it lined up perfectly, I actually put the struts on BEFORE I cut the section out.
 
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BABAR

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Use an empty E9 engine casing to place an engine block (BT-50 to BT-20 centering ring from a Custom Rockets Fiesta 20mm motor mount) 3” into tail. Then measured where on the outside of the engine block (another ¼”). Mark this spot on the outside of the tube. Draw a line around the tube circumference here. Then measure from there noseward the length of the Nose Cone (NOT including the shoulder) and add 1/2 inch for the "burn chamber", a space between the engine block and the tip of the nose cone. (My BT-50 Nose cone came with a Fiesta kit, was 2.75 inches long, so the mark was another 3.25cm noseward. Mark the body tube here as well. Again draw a line around the circumference here. Color or otherwise mark the rocket between these two lines (I used orange.) This will be the "cut out area." Note in the picture I didn’t leave as much room as this, made the “burn chamber” a little bit too small. I also WISH I had put in an Engine Hook. Measurements above are what I WISH I’d done.

Picture 1
Parts: Body tube, engine for illustrations purposes, nose cone, thrust ring/engine block, foam plugs with holes in the center for the dowel. Cut the bottom of the base of the nose cone off, leaving enough “shoulder” to hold it in place.
I then glued the carbon fiber struts (1/8” carbon fiber rods) in place (I used 3, should have used 4, as one now gets in the way of the rubber bands). The struts need to extend about 1 inch beyond this section both nose-ward and tail-ward. I reinforced the struts dental floss wicked with CA. I used 3, should have used 4, spread equidistant around the circumference

Picture 2
Then I cut out the section I didn’t need. This is the orange section in the picture. This cutout section is the length of the nose cone (not including the shoulder) plus 1/2 inch. Length of the motor mount is 3 inches plus the width of your thrust ring (i.e., the nozzle of the engine should stick out about 3/4 inches from the motor mount. This extension of the engine provides the "peg" for the "Burn Bands".) You can attach an engine hook with the forward angle just below the thrust ring/engine block. The length of body tube above (nose-ward) of the nose cone is optional, you need enough so you can attach the centerline dowel with two centering rings.

Pic 3 and 4 (these got reversed, pic 4 comes before 3)
After cutting out the orange section, the nose cone was then slipped between the struts (they flex a bit) and pushed into place in the upper tube section. I SHOULD have left the cap off the nose cone, as then I could have slid the dowel further down for more support (plus the cap isn’t needed anyway, just excess weight.) I put mylar tape over the nose cone to protect it from the ejection blast. The "burn chamber" is the space between the tip of the downwardly pointed nose cone and the top of the engine mount. I should have made it wider and the measurements above correct that The rotor retention "Burn Bands" will cross this space on launch.

After 3 flights (Pic 3) , the mylar on the plastic nose cone is blackened but still structurally great.

WFC_MotorMount_Parts.jpg


WFC_MotorMount_PreCut.jpg


WFC_MotorMount_PreMylar.jpg


WFC_MotorMount_PostFlt.jpg
 
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BABAR

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This shows where the mylar protective strip goes on the inside of the Inner Rotor. You can see where it gets blackened from the ejection

Motor Mount pulled away from Hinge.jpg
 

BABAR

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I used 2 of my ejection “plugs” from Qualified Competition Rockets (QCR) as adapters for my 3/8 inch dowel. Just drilled a ¼ inch hole in center of each (intentionally small), Glued them onto the dowel, then slipped the dowel into the upper tube of the motor mount down to the inverted nose cone (again, wish I had left the cap off the nose cone.) Glued in with wood glue (can't use CA on these or they melt.)

You could easily use other materials for the centering rings. Foam core would work well. Again, recommend you cut the holes smaller than the diameter of the dowel. In fact, if you use a pointy nose cone AND you leave the nose cone cap OFF, probably could get away with one centering ring, with the tip of the dowel "wedged" into the point of the nose cone.

WFC_MotorMount_MylarTape.jpg
 
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BABAR

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Hub assembly:
The Outer-Rotor and Inner-Rotor pieces have now been connected into a single assembly. You will create 4 of these assemblies.
Take 2 assemblies and line inner (flat side) on the Trail EDGE of one hub with the actual LEAD EDGE (the skinny 1/4” edge itself) of the second hub. If you do this right, the NOTCH of the second assembly will just fit over the FIN of the First Assembly. Glue together with Medium CA. The angle is 90 degrees. Once dry, reinforce this with a wood glue fillet.
Now take a 3rd assembly, and again attach the LEAD EDGE (the actual EDGE) of the hub to the flat side of the TRAIL margin of the 2nd assembly above. Again, angle is 90 degrees. Once dry, reinforce with a wood glue fillet.

Now fit the 4rd assembly in place. Use medium CA, make sure alignment is perfect (from the nose end the 4 assemblies should form a perfect square. Reinforce the inside joints with a wood glue fillet.

(yes, that is a digital watch.)

WFC_DownBarrel_DigitalWatch.jpg
 

BABAR

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I cut 2 DIFFERENT square adapters of heavy card stock, about the same as the thickness of Estes Viking fins. The smaller one is 1.25” wide. The larger is 1.75” wide. Drill a 3/8” hole in the very center of each. Cut small balsa flanges (3/32” is fine) to place just inside the margins of the smaller square. Push this square down from the Nose end into the Hub, it should go down and stop just above the tape hinge. Make sure it is perfectly straight (should be at 90 degrees with each of the 4 hub sections). Glue it in place.
The larger pink and black square will be placed flush with the top of the hub. The smaller square with the balsa “flanges” will slide into the hub to just above the inner hinge tape. The two pieces will provide a support and guide for the dowel.

WFC_Centering_Squares.jpg
 

BABAR

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Starting from the tail side, push the tip of the dowel from the motor mount (I know we haven’t cut it yet) through the hole in the small square you have just placed in the hub. Pass about a foot of dowel out through the nose end of the hub.

Fold the hinges closed (boost position). You should have a perfect alignment along the length of the rocket, and each of the 4 fins should fit perfectly into the adjacent “notch.” Use masking tape just above the fins to hold the rotors closed. They should just barely fit around the motor mount.

Adjust the motor mount/dowel so the bottom of the motor mount is even with the tail of the rocket. This should place the "burn chamber" at the level of the holes you drilled. Rotate the mount so the carbon struts are not blocking the holes. Put your Crochet Hook through the holes from one side to the other to make sure the area is clear.

Note the rocket motor itself will actually stick 3/4 inch, which will provide the “peg” for the rubber band retention system on launch.

Now take the large square and fit it over the dowel sticking out of the hub. Slide it down to the hub. It should be centered over the hub as well as the dowel. Glue to square to the hub and glue the dowel to the square.

Yes I know you have waaaay to much dowel sticking out the front. We'll fix that soon.
 
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BABAR

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The nose pyramid is cut out of Card Stock (I use poster board.) It has to fit over the hub, since the hub is 1.75 inches wide (remember, 1.5 rotor width plus 0.25” lead edge of next rotor), this has to be slightly larger. 1-7/8” works well. I use a 25 degree angle.

I don't have a picture of the pattern I used, so here is a diagram. You can draw this on your poster board using a protractor and a compass. Use the edge of the posterboard as a baseline, draw four consecutive 25 degree angles followed by a 10 degree angle. Measure out 4-3/8 inches from the center, then another 1/2 inch from there. Use the compass to draw circles which will mark the same distances on the other 4 lines. Draw lines to mark the other areas as diagramed. (There isn't anything magic about 25 degrees, you can go smaller and get a pointier nose cone or bigger and go stubbier.)

Cut out pattern. Score VERY lightly along the fold lines (I use the dull edge of the hobby knife for this). Fold the Nose Pyramid to shape. Tape the free edges (cellophane tape works fine.) Cut 1/8” off the tip of the Pyramid.
Slide the nose pyramid (I know, you want to say “Nose Cone) over the dowel down to and over the hub. The flanges on the edge will overlap the hub, the folds of the base of the nose pyramid will line up with the front margins of the hub. You can tape it down if you want to, but it really isn’t necessary.

Measure the dowel 3/8” above the tip of the nose pyramid. You need to leave enough room for your Elastic ties.

Cut the dowel above this level. Cut a very shallow circumferential notch around the dowel just above the nose pyramid. Tie 4 dental floss (or Kevlar thread) loops around this notch, one for each side of the pyramid. Each loop should be about 1” diameter, to give you enough room to attach the rubber bands. Once these are in place, wick some CA into the loops and dowel to hold the loops in place.

Use sandpaper or a file to blunt the nose tip of the dowel. For safety purposed, do NOT sharpen it.

The last picture is completed rocket with the rubber bands attached to the loops.

WFC Nose Prepped.jpg
 

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