Vortex – helicopter scratch build

[Rktman]

You're making good progress now. I still haven't tried to make a replaceable shock cord mount, but I have switched to using Kevlar cord combined with 1/8" flat elastic treated for heat (from Apogee).

Exactly the combo I'm going to use on this one, mostly because that 6" upper body tube will make it a bit more difficult to stuff 5' of kevlar cord into the lower body tube.
So I'll substitute 2' of 1/8" flat elastic heat resistant cord from just below the top of the lower body tube. I'm thinking it should be easier to stuff 2' of flexible rubber vs 5' of stiffer
kevlar into the lower body. And doing it pretty much by braille the last 6 inches or so.

 

[Rktman]

Making good progress on sanding & sealing the nose cone. Filled in the tiny pin holes and deeper grain marks with Elmer’s Carpenters Wood Filler.
Instead of continuing with thinned down CWF to get a smooth surface, I went back to using sanding sealer for my final coats because it builds a hardened shell around the balsa to protect it.

It also fills the grain much faster and more efficiently than CWF, which is softer and sands off far too easily IMHO.
The sanding sealer goes on in a thicker coat and allows you to sand down to a smoother surface much faster and with far fewer coats.

This is only my 2^nd coat and it’s already looking glassy.

 

[BABAR]

Ummmm, I have a question?
If you are just shooting for a sport model, why bother to twist or warp the rotors AT ALL?
If you are flying for fun, flat rotors work great, drop your rocket safely, look cool, are sturdy and easy to make. I have had some of these thermal away.

I am enjoying your build threads, and like your creativity.

Regarding flat blade helis

Here is one

https://www.rocketryforum.com/showt...sanding-sport-Helicopter&highlight=Helicopter

Here is another

https://www.rocketryforum.com/showthread.php?32170-DandyLion-Seed&highlight=Helicopter
Here is another

https://www.rocketryforum.com/showt...on-Competition-Helicopter&highlight=Gyskelion

 

[Rktman]

Ummmm, I have a question?
If you are just shooting for a sport model, why bother to twist or warp the rotors AT ALL?
If you are flying for fun, flat rotors work great, drop your rocket safely, look cool, are sturdy and easy to make. I have had some of these thermal away.

I am enjoying your build threads, and like your creativity.

Regarding flat blade helis

Here is one

https://www.rocketryforum.com/showt...sanding-sport-Helicopter&highlight=Helicopter

Here is another

https://www.rocketryforum.com/showthread.php?32170-DandyLion-Seed&highlight=Helicopter
Here is another

https://www.rocketryforum.com/showt...on-Competition-Helicopter&highlight=Gyskelion

Are you aka: the RocketRadiologist on YouTube? I love your designs and coincidentally have subscribed to your channel. Also the Easy Prep was on my list of 'must-builds' and I'm glad your link to the Gyskelion is a close if not exact match (haven't had time this a.m. to go through your build thread but will definitely study it with enthusiasm). I'm especially happy about the added info in the thread because the closest I could come was your Whopper Flopper Chopper build from somewhere else in the forum. (This was before I started using the forum on a regular basis and knew how to use it).

Anyway, in answer to your question I had a set of back up rotors for the first helicopter I built as a BAR so I just decided to take them off the shelf and put them to good use.

 

[Rktman]

Ummmm, I have a question?
If you are just shooting for a sport model, why bother to twist or warp the rotors AT ALL?
If you are flying for fun, flat rotors work great, drop your rocket safely, look cool, are sturdy and easy to make. I have had some of these thermal away.

I am enjoying your build threads, and like your creativity.

Regarding flat blade helis

Here is one

https://www.rocketryforum.com/showt...sanding-sport-Helicopter&highlight=Helicopter

Here is another

https://www.rocketryforum.com/showthread.php?32170-DandyLion-Seed&highlight=Helicopter
Here is another

https://www.rocketryforum.com/showt...on-Competition-Helicopter&highlight=Gyskelion

Are you aka: the RocketRadiologist on YouTube? I love your designs and coincidentally have subscribed to your channel. Also the Easy Prep was on my list of 'must-builds' and I'm glad your link to the Gyskelion is a close if not exact match (haven't had time this a.m. to go through your build thread but will definitely study it with enthusiasm). I'm especially happy about the added info in the thread because the closest I could come was your Whopper Flopper Chopper build from somewhere else in the forum. (This was before I started using the forum on a regular basis and knew how to use it).

Anyway, in answer to your question I had a set of back up rotors for the first helicopter I built as a BAR so I just decided to take them off the shelf and put them to good use.

 

[Rktman]

Just for the heck of it I tried something I never have before: filling the BT spirals with Elmer’s Carpenters Wood Filler.
Takes a steadier hand than I have but I guess it just takes practice. Next time I’ll remember to scrape the excess off.



The spirals are really shallow and it’s hard to tell if they’re filled at all even after sanding.
I also slapped on a coat of sanding sealer. It’s old and thick and tended to clump up,
but because of that I only needed one coat.

An unexpected benefit was that the sealer got tinted pink when I used my paint brush handle
to stir the stuff. It made it really easy to see where the high/low spots were when I sanded it down.

 

[Rktman]

That coat of sanding sealer really smoothed things up, with the added benefit that it added some hardness to the BT.
Wish I’d remembered to snap a pic of how nice the tube looked after sanding.

I chose to start with 220 grit to flatten the globby parts and even everything out, followed by 400 grit as needed
to fine tune things (so as not to risk sanding through the sealer at this point).

Happy discovery: Sanding with leftover 1500 grit got the finish almost glassy smooth. Once that happened I could
clearly see every single tiny pin hole, ripple and bump by holding the BT parallel to my desk lamp.

The only reason I even used 1500 grit was that sanding the sealer with the coarser grits raised fine flaky patches.
This doesn’t happen with balsa, so at first I thought I’d sanded right through to the paper tube underneath. You can clearly see it
in the photo in the previous post.

Now it’s so smooth I almost don’t want to ruin it by painting it (my rattle can painting skills aren’t quite at the “expert” level yet).

 

[Rktman]

Shot my first primer coat and I’m happy about what I can’t see: spirals. No high/low spots or ripples either.

In the past I’ve just painted over the primer, but am I supposed to sand it all off except for any tiny filled crevices/scratches?

I think I used the wrong primer though. I just read in another thread that the preferred primer is the filler/sandable variety.
Any suggestions?

 

[TangoJuliet]

Yes, preferred primer is filler/sandable variety. And yes, the idea is to spray it on to fill any low spots then sand away all the high spots. I've been guilty of not sanding away enough of it, but it doesn't really hurt anything. With what you've got there, I would just give it a quick once-over with a 400 or 500 grit, wipe away the dust and proceed to paint.

 

[Rktman]

The primer doesn’t seem to have filled any scratches or seams (unless there wasn’t any for it to fill?).
I’m going to take the advice of TangoJuliet and just knock down the fine spray bumps and get things smooth, then go to a color coat.

I don’t have a color scheme in mind other than a base white and a darker roll pattern covering half (longitudinally) the lower BT. It should be rotating fast enough that having a whole bunch of vertical stripes would just be a blur, but a single big one should create something like a strobing effect.

If anyone has color suggestions I’ll certainly consider them.

 

[Rktman]

CAd the balsa nose block to the nose cone base.





It might be overkill but I pushed two 1/32” dowels through the block and into the nose cone
to make sure they never come apart, since this is where the shock cord will be attached.



In retrospect I might not have needed the balsa nose block, as I could have had the base of the nose cone
sitting flat against the top of the lower body tube. If this rotor-release method works as well as I hope,
I’ll try without the block on any future models.

 

[Rktman]

Spent the past couple of days getting the surfaces prepped for painting.
Sanding sealer and sanding, sanding, sanding…tedious but worth it, especially if you’re building a scale model.
In my case I’m not but it’s a great learning experience.

Speaking of sanding sealer, let me pass along an excellent alternative for traditional sanding sealer
that I found on the Forum: water-based polyurethane and baby powder. It doesn’t have those choking fumes,
is less toxic, dries faster, and cleanup is a breeze using just water. The easiest to find is Minwax Polycrylic.
Make sure it says “water-based”. You can mix up small batches as needed. Just add baby powder till the consistency suits you.

 

[Rktman]

All that surface prep paid off. That tube is flawless.





Well…almost. Don’t you just hate it when something like a hair or tiny speck of something in the air throws a wrench into the works?
In this case it was fine fibers and sanding dust that maybe came from the Swiffer dust cloth that I wiped it down with. I think I’ll start
using a tack cloth instead. Sanded it down with fine grit sandpaper and I’ll see how things work out after a final pass with paint.

 

[Sooner Boomer]

Speaking of sanding sealer, let me pass along an excellent alternative for traditional sanding sealer
that I found on the Forum: water-based polyurethane and baby powder. It doesn’t have those choking fumes,
is less toxic, dries faster, and cleanup is a breeze using just water. The easiest to find is Minwax Polycrylic.
Make sure it says “water-based”. You can mix up small batches as needed. Just add baby powder till the consistency suits you.

Yea! I'm glad that works for you!

One other small tip - next time you need to fill body tube spirals, mask them off with blue painters' tape. If you get the tape right next to the spiral, you don't have to be as meticulous when dabbing in filler. Don't pull the tape off until you've sanded with a heavy grit as this will 1) let you use a heavier grit to speed things up, 2) without damaging the body tube and raising fuzzies.

 

[Lowpuller]

I primer first and then fill the spirals with CWF to keep from damaging the cardboard while sanding.

How did you center the nose cone block?

That is one of the nicest looking balsa nose cones I've scene.

 

[Rktman]

Yea! I'm glad that works for you!

One other small tip - next time you need to fill body tube spirals, mask them off with blue painters' tape. If you get the tape right next to the spiral, you don't have to be as meticulous when dabbing in filler. Don't pull the tape off until you've sanded with a heavy grit as this will 1) let you use a heavier grit to speed things up, 2) without damaging the body tube and raising fuzzies.

Thanks man great tip. Really sounds like a time saver (and I'm all for that).

 

[Rktman]

I primer first and then fill the spirals with CWF to keep from damaging the cardboard while sanding.

How did you center the nose cone block?

That is one of the nicest looking balsa nose cones I've scene.

I figured the easiest way would be to spread glue on the end of the nose cone, plug the nose block into the lower tube and the
nose cone into the upper tube, then just slide the two together. The centering rings on the lower tube made it self-aligning.

 

[Rktman]

Small hiccup to slow things down—tiny divot that happened when the wet nose cone bumped my hand.
I’m going to try sanding it down and using sealer if necessary. Good thing this is just the first paint pass.





At least I got the asymmetric roll pattern put on the lower body. I’m hoping
the rapid spinning will show up as a strobing effect, so I only darkened only half
the circumference, reasoning that a lot of stripes would just blur out into a gray.

 

[Rktman]

Really happy with the rattle can painting results. Tried out some painting tips from the Forum to get a sharp demarcation line between the black and white—1^st spraying with clear to seal the painter’s blue tape, followed by black, then lightly scoring along the tape line with a hobby knife before peeling it off after letting it dry for about 3 hours. I wanted the paint to still be somewhat pliable, otherwise the tape could’ve lifted off bits of the black coat. Pretty stoked with how glassy smooth the nose cone looks.
I decided to go with a simple asymmetric black/white pattern to match the roll pattern on the bottom body tube.




I also decided to pin the nose cone on with a small dowel so that I can still remove it if need be for things like replacing a worn shock cord or if I have any problems getting it stuffed into the bottom tube (I’m working by braille to do that because of the length of the top rotor hold-down tube). The pattern also helps me orient the nose cone correctly, since the dowel hole will only align with the correct matching hole in the nose cone. Can't figure out why that is because I drilled the hole clear through both using a drill press so it shouldn't matter. Oh well, just one of those mysteries of the universe that will go unsolved.

Time to start thinking about getting the hinges on the rotors and mounting the fin assembly (which I’ll probably leave as unpainted bare balsa. Or maybe tissue them just to make them look a bit more finished).

 

[TangoJuliet]

Your paint-prep efforts really paid off! That looks great!

 

[neil_w]

That is indeed looking wonderful. Keep it going!

 

[Lowpuller]

Where are you in NC?

 

[Rktman]

Your paint-prep efforts really paid off! That looks great!

Thanks Tango, really appreciate that. Nice when something turns out as good as you hoped it would. Now I'm even more enthused.

 

[Rktman]

That is indeed looking wonderful. Keep it going!

Thanks Neil. Picked up a lot of those painting/finishing techniques from your Starship Avalon build thread and your adventures therein.

 

[Rktman]

Where are you in NC?

Triangle area. There's a real shortage of wide open areas to launch much more than LPR stuff though. How about you?

 

[Rktman]

I think I mentioned that these rotors were spares from my 1^st heli roc build. What I didn’t mention was that I made these from basswood after one of my original balsa blades snapped. My fault; long story for another time. But I digress. I think basswood is beautiful. It has a tight grain and sands up silky smooth. As you can see it doesn’t need any kind of surface finishing after being sanded down.

That being said, it is a tad heavier and denser than balsa. That makes it tougher as well…and of course that much more of a chore to sand an airfoil into. These took me 3x as long to carve into shape than the balsa ones. Since I’m not building for competition though I prefer these sturdier blades, and the small amount of weight difference doesn’t bother me.





Marked the base of each rotor for the hinge, which will be offset 10° to pitch the leading edge down. It’s a bit more than the usual 4° to 5° skew but it worked out so well on my first heli roc that I’m keeping it. My reasoning is that although a shallower skew (angle of attack) will yield less drag and a higher RPM, that also causes a faster descent. A higher skew produces more lift but more drag and a lower RPM, but the end result is a slower descent (which I’m all for). The breakeven angle just happens to be 10° according to several studies done on it. Well, enough of that engineering and aeronautics stuff; I’ll leave that to the real rocket scientists.




Buttered the hinge area with a generous amount of petroleum jelly (if any CA finds its way in there it’s all over; just get it off your rotor as fast as you can before the glue sets). Yes, I know this from sad experience. My first build as a BAR last Fall was a scratch heli roc. I used thin CA and no Vaseline and the hinge immediately froze up. Serious newbie mistake but what did I know, I’d only ever used white glue before.







First rotor done. Some people anchor the hinge further by stitching it in with Kevlar thread but I think I’ll pass on that. I’m going to use a pin to punch through those mounting holes and then fill it with CA (sort of like pinning the hinges in, only with CA instead of rivets or screws) then follow up with white glue fillets.

 

[neil_w]

I've been doing some shaping of 1/8" basswood fins lately. Differences I have discovered, relative to balsa:

1) You can go one grade coarser than 220 grit to do initial rough shaping. I have been staying with 220 though, because by working slowly I'm less likely to oversand anything. I seldom go coarser than 400 with balsa, unless it's very hard.
2) You don't have to handle the wood pieces like Faberge eggs. Almost every time I handle balsa fins I put an inadvertent fingernail mark or some other ding in the wood. Even while applying significant force with 220 grit to shape it, I find I don't need to worry too much about dinging the basswood. That is *very* nice.
3) As an addendum to #2, it seems like it'll hold a fairly sharp edge with no problem. I might harden the edges with CA at the end, but honestly it seems like it will only matter for fin edges that are likely to absorb landing impact.
4) Indeed it sands very smooth. In my correspondence with John Pursely, he has stressed that basswood sands best with the grain. I've been doing a round of 400 grit and then 800 and end up with a pretty smooth piece of wood.

Overall I've enjoyed working with it a lot. Might use it more in the future. I think 3/32" would be my preference, but that is less easy to find locally (I think Hobby Lobby has it).

 

[Lowpuller]

Asheville

 

[TangoJuliet]

Triangle area. There's a real shortage of wide open areas to launch much more than LPR stuff though. How about you?

You know, you could add your "more specific" location to your profile location. :wink: I think it's nice to see where the people you're interacting with are located. It helps to find other rocketeers local to you. So far, I haven't found anybody close to me.

 

[BABAR]

Buttered the hinge area with a generous amount of petroleum jelly (if any CA finds its way in there it’s all over; just get it off your rotor as fast as you can before the glue sets). Yes, I know this from sad experience. My first build as a BAR last Fall was a scratch heli roc. I used thin CA and no Vaseline and the hinge immediately froze up. Serious newbie mistake but what did I know, I’d only ever used white glue before.

View attachment 324153


First rotor done. Some people anchor the hinge further by stitching it in with Kevlar thread but I think I’ll pass on that. I’m going to use a pin to punch through those mounting holes and then fill it with CA (sort of like pinning the hinges in, only with CA instead of rivets or screws) then follow up with white glue fillets.

View attachment 324154

Petroleum gel good idea. You can also with some hinges simply take the metal peg out, glue on the hinge, and put it back when glue dry.

Sewing in good idea, but kevlar is overkill. Cotton thread (I use dental floss, partly because it comes with it's own cutter!) with a mid size needle can easily sew by hand throught the hinge and through the balsa (make starter holes with the needle from the plastic hinge side so you can find your way "back" from the other side.) Wick in some thin CA. Presto, hinge attached and balsa will break before hinge comes off.

Hmm, you are using basswood. May make it harder to get needle through by hand. Still easily do-able.

2 options:

1

Put hinge where you want it. Use mechanical pencil or sharp pencil to mark where the holes are.

Use 1/16" drill bit to make the holes.

Sew in place.

2. Glue hinge in place. Use 1/16 drill bit to drill through the plastic holes through the wood.

Sew in place.


either way, the additional strength places in the hinge attachment is huge, at a negligible cost in weight.