Dandelion Seed Helicopter Build Thread

[BABAR]

Okay, I cheat. I don't post until I've actually flown the thing to make sure it works. This is a "rebuild" with some modifications cuz I didn't photo this the FIRST time I built it. Also experimented with some paint and priming techniques, which obviously are NOT recommended for a helicopter. But I digress.

Pictures of Original Dandelion Seed and "New Version"

 

[BABAR]

First of all, since these is a rebuild, and a non-competition bird, figured I would try out a painting idea while I was building it. I've always like the caps on the Kryon X-metals paints at the store (you know, "paint is the color of cap"?) I've got a futuristic rocket planned called the "Defiance" that is sort of a modification of a Mars Snooper, and I think Red Metallic would look great.

Anyhooo, I tried to prep the balsa before I cut it. So this is with three coats of Rustoleum grey auto primer. Even with sanding it didn't fill all the grain (okay JR, what am I NOT doing here?) Decided just to go with it.

 

[BABAR]

Start with sheet of 36 x 6 x 1/8 balsa

Fins are 2" wide and 2.5" long. There is a Diagonal Cut that will "mate" up with the Rotors. Note the angle of the grain.:bangpan: (that's for me)

Rotors are 19" long by 24mm wide (sorry about mixing English and Metric, but it works for me.) This is minimum diameter for a standard engine, as there will be some overlap and this design retains the engine inside a 20mm body tube motor mount.

Because of the angled cut, you can and should cut two 19" rotors from a single 36" strip. Simply mark the midline at 18", measure one inch each direction, and cut your diagonal.

 

[BABAR]

Here they are cut.

Using Carpenter's Wood Glue and Double Glue technique, attached rotors to fins along the diagonal cuts.

Added some extra glue for strenth. Could also put paper over this joint.

Okay, now need to take a burger break. BTW, got a great flight out new SpyderD today, will be posting later!

 

[BABAR]

The Rotor and Fin now that they are connected will be referred to as the "Rotor-Fin" (originality isn't my strong suit.)

The side with the fin sticking out is the TRAIL EDGE. The other side is the LEAD EDGE.

Mark the TRAIL EDGE 2.5" from the nose end. Draw a 15 degree angle DOWN TOWARD THE FIN to the lead edge. Note the pic is wrong, should be 2.5", not two inches.

Check your angle, if you do this right, the shorter side (the 2.5" will be on the trail edge, lead edge will be about 2.75" from the nose end.) The direction of this cut is important, as the otherwise this will spin backwards (and probably do something to the Space-Time continuum.)

 

[BABAR]

I love these things.

They are easy to do, and even easier to screw up. Orientation is key.

The outside hinge is put on first. Out the outside of the Rotor-Fin facing you (fin toward you, lead edge to left, trail edge to right), with the hinge edges butted tightly together, put a 1 cm wide strip of tape over the hinge joint. You will have the edges sticking out over both the lead and trail sides. Push the tape down hard.

Turn the whole thing over on your cutting board. Trim off the edges with a sharp knife.

Photo one is after I put the tape on and flipped it over. Photo 2 shows cutting. Photo 3 shows the outside surface after tape is trimmed.

 

[BABAR]

Flex the hinge completely. This will also let you press the tape firmly into the balsa.

The graphics are taken from my Whopper Flopper Chopper build thread, but they are similar. This gives you an idea what is going to happen next.

 

[BABAR]

Here is the placement of the inner tape layer. This is a 2cm wide strip.

With the hinge fully flexed, press this really hard against the "butt end" surfaces (I mean REALLY hard-- you can press it down against your cutting surface to get more force.) Than burnish the edges down around the flat (inner) surfaces.
Then open the hinge. Use sharp scissors to trim off the excess on the lead and trail edges.

 

[BABAR]

Use a needle and dental floss to "sew" the hinge into place. Initially with the Whopper Flopper Chopper (WFC) I got pretty fancy, all you really need is two loops at the edges. Remember to always poke needle thru the HINGE from the inside, to make sure you go through the center of both pieces of tape.

Pull the floss really tight, and then wick CA on it from the inside.


This makes a really stronge hinge that is very lightweight. I don't think the floss adds that much DIRECTLY to the hinge (although it doesn't hurt.) The INDIRECT effect is huge, however, as it keeps the tape tightly butted up against the balsa. Thus the tape itself is bearing most of the stress, the floss keeps the tape from just pulling off the balsa, which in my limited experience is the key failure point for tape hinges.

As mentioned, these are the same as the (front) hinges on the WFC. Also use these hinges on the Spyder, SpyderD, the Swirly (in process), the Gyskelion, and the Boomerang (also in process.)

 

[BABAR]

Materials and Hinge

 

[BABAR]

You will need anchorage points both for the pull bands and (in this case of the Dandelion) for the internal tether "rotor-stops." I chose to integrate those into a single attachment point. Because of the GRAIN of balsa, particularly in this longitudinal direction, you cannot just rely on typing a loop through or around the balsa and expect it to hold. Here is what I came up with.

I use old hotel door key cards, credit cards, or gift cards to get the plastic.
A standard hole punch cuts both the plastic tether AND a perfectly fitting hole in the balsa. I have a leather punch that cuts the little "edges" out.

 

[Elon]

That. Is. Way. Kool.

 

[BABAR]

I find this works well with balsa up to 1/8 inch thick.

Mark the area with ink. Wrap with masking tape 2 layers thick (you should still be able to see your mark, but remark it so you can see it well.)

Put the hole punch over the mark, check in both axes to make sure you are centered correctly. You have to punch hard, but you should be able to get through the balsa and the tape. Make sure the punch goes all the way through (you will feel a "give") otherwise you won't get a clean hole. Tip, have the punch go through from the INSIDE, you will get a flatter hole edge on the OUTSIDE where it matters more.

 

[bradycros]

I like what I'm seeing! More please.

 

[BABAR]

Push the anchor it so it is midway between the inner and outer surfaces. It should "stay in place" by itself (you shouldn't have to hold it in place.) Thin CA dripped over it seems to glue it in pretty well, and probably tightens up/reinforces the balsa around it.

 

[BABAR]

Because I work with medical biopsy needles regularly, I pull the covers off the sterile field before we start so I can save them for lauch lugs. They are probably a bit heavy for competition birds, but they work well for me and they SLIDE really well.

Because the rotors will be spinning, I use two SMALL lugs. In this case, because I had "pre-primed", I use a file to re-access the raw balsa surface.

 

[BABAR]

This is an engine eject model. Holes for the "burn bands" are placed 2.5 inches nose-ward from the tail end of the RotorFins. Notice that due to the way the fins are attached (the diagonal joint), the grain at the tail "end" is perpendicular to the axis. This is a good thing, as it keeps the bands from "digging in" to the balsa when prepped for launch. BUT, the grain at the "hole" site is parallel, so it will need reinforcing.

Again, mark the site, put a couple of wraps of tape around it, remark it, and punch. Punch from inside out to keep the outside surface smooth. You can see how the inner surface gets a bit "scrunch" even with the tape.

 

[BABAR]

As mentioned, the grain adjacent to the burn band hole is parallel to the long axis. This will also be parallel to the direction of pull of the rubber band. Means good chance the band will "cut" into the balsa.

The rear hold brace is a piece of 1/8 balsa, cut 1/8 inch wide and 12 mm long. Placement is on the INSIDE of the RotorFin (the side that will be facing the engine.) Place it just at the bottom (tail end) of the hole--- in fact, if you let it overlap the bottom 1 mm of the hole it is even better.

The spacing from the trail edge is critical. It should be just 1/8" inside the trail edge. In fact, the best way to set this is to use a scrap piece of 1/8" balsa as a guide.

This brace will not only keep your burn band from "cutting" in, but will also serve as a "ledge" for the lead edge of the adjacent RotorFin when you prep the bird for flight. Don't worry if this doesn't make sense now, it will.

 

[BABAR]

One weakness of "body tube-less" rockets is that balsa and ejection blasts don't do well together. I use a piece of mylar tape to cover the hole and the balsa a couple of inches forward. Works great. Less filling.

Use a piece about 4" long. Cover from about 1/2" tailward to 3 1/2 " nose ward of the hole. This tape WILL go directly over the brace and the hole.

Once you have the tape in place, use a sharp pen or pencil from the INSIDE to re-poke the hole.

If you don't have Mylar tape, foil tape or even aluminum foil should work.

I don't have experience with epoxy as a surface cover, so these MAY be alternatives. As far as heat protective paints are concerned, I am not sure they would work. Seems like the PAINT would survive, but not sure it would protect the wood UNDER the paint. Anybody with experience on this, please feel free to chime in.

 

[BABAR]

The only really unique contruction piece of the Dandelion Seed is the boom. In my case, I used a Midwest Carbon Fiber Square Tube, 40", .196 x .118 MID5854

This isn't where I got it from (I got a set up 10 of them a long time ago) but here is one site that sells them. An no, I am NOT on commission:bangpan:

https://www.ebay.com/itm/Midwest-Ca...469?pt=LH_DefaultDomain_0&hash=item2a1571a7b5

A round carbon fiber rod would also work. A coat hanger wire may violate the safety code, it is also heavy and probably not a good choice. A dowel (by itself) will NOT work without some adaptations, as this is going to run alongside the motor mount (there IS a way to do it with a dowel, using a wire "harness" to attach the mount to the dowel, but I don't want to go into that here.) You will need a piece 20" long (which is cool, cuz it comes in 40" lengths, so you can build a backup!)

I forgot to take a dedicated picture, so here you can see it on the side view of the rocket with rotors deployed. If some of the other pictures make it look "wooden" that's cuz I salvaged this piece from another rocket.

 

[BABAR]

With a regular rocket ya got your centering RINGS. With a 4 sided helo ya got squares.

I cut these out of heavy cardstock left over from some of my Estes Viking kits which I buy in bulk for parts (did I say I drive a 92 Civic that gets 33 mpg city?)

These are 19 mm square. I pre-drilled a 1/16" hole in the middle, then shoved the boom through it to make sure it was adequate before gluing them in. They will line up with the LEAD edge of one of the RotorFins.

The forward "Square" is place just behind the tab (about 1/4" from the nose end). The second "square" is 1/2" in front of the lead edge of the hinge.

Again, these MUST be aligned with the LEAD EDGE.

 

[BABAR]

Test fit your parts. You should be able to get the pieces lined up like the picture from the front view.

Smear glue of choice (I use Carpenter's Wood Glue) along the lead edge of the RotorFin in FRONT of the hinge. Butt each one up against the inside surface of TRAIL edge of the adjacent motor to get the glue on that piece as well. Wait a period of time (I use about 10 minutes, some smarter and more patient people use more.) Roughly align the pieces, and run a couple of rubber bands double up around the Rotor Fins BELOW the hinge (helps to put a BT-20 body tube in place as a spacer below the hinge.) Make sure everything lines up perfectly. Hold in place until set. You can also use masking tape to hold it in place.

 

[BABAR]

There is a lot a stress on the joint just created. And/or perhaps I am insecure. In any case, I reinforce this joint with Dental Floss.

1/16" Holes are drilled about 1/4" forward (nose-ward) of the lead edge of RotorFin about 1/4'' inward from the edge. [Note to self, would have been a LOT easier to do this BEFORE construction:eyeroll:] This (should) be below the aft centering square.

Using these holes and a needle and about 18" of floss. Tape one end of the floss about 4 inches down the Blade of a RotorFin BELOW the hinge. Now, push the floss through the hole on that side and pull it out the OPPOSITE side, then around 90 degrees wrap it 90 degree around the corner and go through those two sides, then 90 degrees again. After 4 goes, you should have wrapped around every corner. I do this twice (floss is cheap and light.) Make sure you pull it TIGHT every time. Now tie it off. Pull it tight with the free ends and wick CA around every "corner" of the floss. Once done (it dries pretty quick) use the needle to pull the free ends through one of the holes to hide the free end.

 

[BABAR]

Again, boom is a square carbon fiber tube in this case. 20" long, which is 1" longer than the RotorFins.

Make sure the boom easily (but not TOO easily) fits through the center holes of the centering squares.

Shove this puppy up from the bottom through the AFT centering square. You may have to "fish" for a bit to find the the hole in the forward square. I can hear you cussing me now.:rant:

You should have 1" sticking out the top, with the tail end of the boom even with the tail edge of the RotorFins. Use a small piece of masking tape to mark the edge of the boom from the bottom where it enters the Aft Centering Square.

Pull it back out. Take a strip of masking tape about 4 mm wide, wrap it tightly around the boom at your mark. Put a dab of NON-CA glue directly over the hole in the aft centering square. (Non-CA because you want to have a minute to make sure everything is right before it sets.) Now shove the boom back in. Make sure the tail end of the boom is even with the tail end. Once you are satisfied, put a dab around the tape and the centering square and let the glue dry.

 

[BABAR]

This bird has a paper nose pyramid. Currently you have a very pointy rod sticking out the nose. While the nose pyramid will cover it, the paper is relatively collapsable. Therefore, for safety purposes (i.e., in case of fecal turbine interaction) there is a risk if this puppy comes in ballistic (I have never had that happen with this model, and I have found the retention system/release to be VERY reliable. But it is always possible.) I cut a small circle out of plastic, then punched a central hole in that with my leather cutter. I glued this to the tip of the rod sticking out the front.

It also works to help keep the rubber bands on.

You will also note a V-shaped notch in the middle of the forward edge of the RotorFins. This acts as a guide for the pull bands.

 

[BABAR]

I'm sure someone will come up with something cheaper, but I like these. Made out of poster paper. Each of the angles is 20 degrees.

Used a protractor to set up the angle, then a compass to get the lengths to match up.

Use the back side of the Hobby Knife to gentle "score" the bendy parts.

Mylar tape covers up the free edge, then a wrap around the base.

 

[BABAR]

Used a hole punch to poke holes in the center of each "flange" for the rubber bands.

 

[BABAR]

Okay, I'm going to tell you how I did the original Dandelion Seed, so pictures won't exactly match. Reason is the original flew much better.

Cut a piece of BT-20 2.25" long.

Use a door jam or your favorite marking tool to draw a single line the length of tube. Must be arrow straight.

Cut a sliver of 1/16" balsa, final dimensions 1/16 x 1/16 x 2.25"

Glue this along the line.

Now TAPE the tube to the end of the boom, matching the aft tip of the tube to the aft tip of the boom. Notice in picture 4 (which is looking up the tail end with RotorFins deployed) that you line this up with the CORNER of the helo rotors. This is so that with the RotorFins folded, the boom and the wood support fit in the corner and don't prevent a tight enclose of the motor mount.

Once you have it lined up. Use some floss (I should buy stock in this stuff) to secure the tube to the boom. Wick a bit of CA. Voila!

 

[BABAR]

Better Pic. Pretend this is 2.25"

 

[BABAR]

This is the part I don't like about this design. They are certainly much less drag than external rotors stops, but they are a pain to set up.

Wrap a thin (4 mm?) strip of masking tape a few times around the boom 6" below the AFT centering square. Tie loops of string (I used Kevlar Thread, and it STILL burned through---see "crumb catcher" section below) from the boom here through the holes in the anchors above. Adjust the length to get about 15 degree angle ABOVE Horizontal. Theoretically, once you get the first one, you can use the same measurement for the others.

Note this angle may vary depending on the final weight of the rocket. What I mean is, this worked for the original Dandelion Seed unpainted and with the full length 2.25" motor mount. When I went to the painted version which was 10 grams heavier and used a shorter motor mount to save weight, the recovery was SAFE but tumbled rather than rotated. When I adjusted the angle to 30 degrees it worked (but came down quicker.)