Vortex – helicopter scratch build

[Rktman]

I debated about doing a build thread since the model I’m about to build is not particularly wild or cool looking, not outrageously small or large or an upscale/downscale of anything. Plus I just became a “born again rocketeer” this past Fall 2017 and missed a heck of a lot of changes that happened in the intervening decades. But I’m a fast learner and have caught up quickly, though admittedly there are a lot of techniques and practices that I’m still catching up on. So constructive comments and guidance are appreciated.

My main goals in designing/building this are that I wanted something:
1. Sturdy, fairly bullet proof so that it can be reflown many times without having to worry about delicate parts or having to make constant repairs.
2. Uncomplicated and reliable. My first Heli Roc scratch build used a piston system which required cleaning out after each use.
3. Relatively easy to build. I’ve built downsized competition Heli Rocs and dislike all the small parts that require tiny nimble fingers and crazy dexterity to build. (Or maybe it’s just my fat fingers, all of which happen to be thumbs). This is a medium sized LPR model.
4. Easy to prep and fly.
5. A rotor deployment system that is simple and reliable. (My earlier designs were overly complex and I’ve seen some that aren’t all that fast and easy to build. This design simply releases the rotor tips at ejection by popping off the top body tube and nose cone piece. The only thing simpler is a burn string, but then that requires cutting pressure-relief ports and having to protect the rotors from the hot ejection charge gases). Besides, the rotors are held very simply and securely in place in launch mode by the upper body tube.
6. A fun to fly sport model. It’s not for competition use or contests so it doesn’t necessarily have to be purty, and weight isn’t as much a concern as sturdiness and reliability. (I reserve the right to totally contradict myself on that though—purty is always nice if I can somehow work it in).
7. Lastly, I have a spare set of back up rotors for my earlier model that I needed an excuse to use.

Maybe this will help the Heli Roc newbie and anyone else interested in helicopter recovery rockets start out on an easy build level with something reliable so that they can gain experience and then move on to more involved or challenging Heli Roc projects in the future.

So okay I’ve never done a build thread before so be kind.

One other reason for designing this that I didn’t mention above was that for external-rotor Heli Rocs, I dislike the humbug of having to cut the hinges to fit the curve of the body tube and then bind it down with Kevlar thread, which you then have to coat with CA to ensure a secure joint. Time consuming and adds weight.

So I decided to provide a flat surface to mount the hinges on. In this case it’s a balsa “mounting plate” which incorporates the fins. No Kevlar, no thick CA layer.
Below is a simplified sketch of what I’m envisioning building. This is going to be more a proof of concept kind of thing. The fins are incorporated into the hinge “mounting plate”, with the units attached in a triangular spiral pattern. I intend to glue some thin 1/64” ply over the lower hinge piece to more securely hold it in place. I should have pics of the fin/mounting plate pieces soon, as I’ve already laid out the templates on the balsa.

I intend to sand in 120° bevels on those root edges where they join…I guess that means building some kind of jig. I already have an idea on that and some leftover foamcore I can use, so pics of that soon too I hope.

 

[Rktman]

Okay put together a quick 120° angle jig and waiting for the glue to dry. I figure I can also use this as a fin alignment guide for the 1st 2 fins. After that the 3rd fin should be self-aligning.

 

[TangoJuliet]

I built a Rot-A-Roc back in the 80's when I was a young teen to fly in competition and I loved it so much I would often fly it just for sport. I tried to build a new one last year as a BAR, but I think I used balsa that was too light-weight for my rotors. They flexed quite a bit and wouldn't hold a good twist for washout, so it never rotated like it was supposed to. I think I'll build another one soon.
I look forward to seeing how your design works out op:.

 

[Rktman]

I built a Rot-A-Roc back in the 80's when I was a young teen to fly in competition and I loved it so much I would often fly it just for sport. I tried to build a new one last year as a BAR, but I think I used balsa that was too light-weight for my rotors. They flexed quite a bit and wouldn't hold a good twist for washout, so it never rotated like it was supposed to. I think I'll build another one soon.
I look forward to seeing how your design works out op:.

I did the same thing; scratch built a heli roc as my first model when I "rediscovered" the sport late last year.

In keeping with the aim of making this sturdy, I've decided to use some backup rotors I carved from basswood for another helicopter. It's much harder and stiffer than C-grain balsa. (That also makes it a pain to sand an airfoil into). There's no built in twist in the rotor though--this was carved before I even knew anything about air foiling in a twist to accommodate washout. (It still spins my model at a high RPM though--just dumb luck I guess).

 

[Rktman]

Cut out the fin/mounting plate units. The foamcore angle jig should hold up long enough to get those root edges sanded.
I previously built another foamcore angle jig to sand in the dihedral on my glider and it held up surprisingly well, so here goes.

Forgot--have to bulk sand them to a consistent shape first.


I didn't even attempt to cut those curves on the fin ends since this is 1/8" thick hard C-grain balsa. It really doesn't like that and tends to chip and end up ragged. Much better to just sand them to shape after cutting.


While 1/8" balsa might seem like overkill, the rotors and hinges will be attached to these so they do need to be sturdy.

 

[TangoJuliet]

There's no built in twist in the rotor though--this was carved before I even knew anything about air foiling in a twist to accommodate washout. (It still spins my model at a high RPM though--just dumb luck I guess).

I sanded in an airfoil to the blades, then tried to set in a warp by holding the root edge flat to my work bench and twisting the tip and holding that twist in while I brushed on balsa filler and let it dry. The super-light 3/32" "Contest Grade" balsa didn't hold the warp after it dried. The next one I build will incorporate the angled hinge-line in George Gassaway's enhanced version. :wink:

 

[Micromeister]

I did the same thing; scratch built a heli roc as my first model when I "rediscovered" the sport late last year.

In keeping with the aim of making this sturdy, I've decided to use some backup rotors I carved from basswood for another helicopter. It's much harder and stiffer than C-grain balsa. (That also makes it a pain to sand an airfoil into). There's no built in twist in the rotor though--this was carved before I even knew anything about air foiling in a twist to accommodate washout. (It still spins my model at a high RPM though--just dumb luck I guess).

I've been building and flying Rota-Roc and Rose-a-Roc Helicopter recovery Competition models for several decades. Longevity has nothing to do with making it "Sturdy". I'm still flying a simple 13mm Rota-roc (1/4A-A motors) that was built in 1990. It's currently working on flight #44.
During all that time I've also designed several Micro Maxx to 24mm to 3-D12 clustered Helicopter Recovery rockets using Contest grade (A grade) super light weight balsa, Foam Core, Styrofoam and other parts to get the overall mass down while ensuring long rocket usable life.
Several other models in my club have designed Triangular body type HD models with limited success.
I'm not exactly sure what your problem is with very light weight 13lb test kevlar hinge wraps with medium CA covering but I'll bet you dollars to donuts anything you come up with will not be able to compete with most standard RotaRoc or Rose-a-Roc competition construction or durability.

 

[Rktman]

Finished sanding them all to a consistent uniform shape.
I may just leave the edges square since this isn't a competition model.

I'll tackle beveling (chamfering?) the root edges tomorrow. I want to take my time
with this procedure since a sharp even 120° edge will mean a tight clean join where the
fin/mounting plates meet.

 

[Rktman]

I sanded in an airfoil to the blades, then tried to set in a warp by holding the root edge flat to my work bench and twisting the tip and holding that twist in while I brushed on balsa filler and let it dry. The super-light 3/32" "Contest Grade" balsa didn't hold the warp after it dried. The next one I build will incorporate the angled hinge-line in George Gassaway's enhanced version. :wink:

Have you tried soaking it with ammonia (windex works fine) for 15 minutes or so? It softens the lignin in balsa so that you can bend it around a form (PVC pipe?) of the right size and Ace-bandage it in place till it dries. Once the ammonia solution evaporates the balsa gets hard again and the shape is locked in. I was able to bend contest grade balsa the long way into a 5" diameter tail ring, just to give you an idea of how flexible you can get it if you're careful. And since that twist in the rotor is a mild one, it might be the solution you're looking for.

You can also easily curve rotors the short way using ammonia so they form a sort of airfoil. Here's a video of the process; it's starts at about 1:08

Being the impatient type (and admittedly one who dislikes spending long periods of time sanding airfoils...okay I'm lazy) the rotors on the next model I'm planning will use that angled hinge-line method you mentioned. BTW could you point me in the direction of Gassaway's enhanced version?

[video=youtube;d6qTJk3n1_I]https://www.youtube.com/watch?v=d6qTJk3n1_I[/video]

 

[TangoJuliet]

I've been building R/C airplanes for years and have known about bending balsa for quite a while. Some people swear by ammonia (Windex), but to be honest, it isn't really required, and some argue that the ammonia actually breaks down the lignin. Warm water works just fine when bending balsa. On my Rot-A-Roc, I didn't try to bend the blades at the start. I don't recall doing it at all with my original back in the early 80's and it auto-rotated great, but when I flew my new one the first time, it didn't auto-rotate at all, so I tried to go back and add the warp after assembly. There's a couple of other methods for the blades that I like and might try. One has you split the blade from root to tip at a diagonal and then gluing it back together with a bit of a flex to create an artificial airfoil (and that might be what I did with my original ), the other splits the blade in the middle, root to tip, then is hinged on the bottom and uses three short lengths of elastic/rubber band on the top. As I recall, I tried the latter method also when I was younger and it worked well. It makes for a slightly heavier model, but you can get twice as much blade chord because you fold it in half and when it's open, it holds a bit of an arc/airfoil shape.

Go to www.georgesrockets.com to see his Rot-A-Roc plans (and other contest model plans). His enhancement is the angled hinge mount (and a jig to make it easy) and a rounded blade tip. While I enjoy building stock LPR kits, I really enjoy contest model rocketry. For me, it gives some kind of purpose to my launches beyond the typical woosh-pop. :wink:

 

[Gary Byrum]

Since keeping it "on the simple" appeals to you, then consider this. Cut your prop and sand all edges rounded off. In the diagram below, the prop shows a cut line from one end to the other diagonally. This cut should be about 1/2 way through or slightly deeper. Depending on your prop size, take a dowel 1/8 - 1/4 " and place underneath the cut line. Bend the two sides downward opening up the cut line like a gorge or a canyon. Apply enough CA (if you like) for a fast fix to keep it open, or just weigh both sides down and apply wood glue in the cut. Let dry completely. Fill remaining opening with wood putty and sand smooth. This is where some CA may come in handy. You can seal the putty with CA & a Q-tip until coated completely. Usually I take a long strip of copy paper and skin over the whole cut and coat with CA again. Sand smooth. This approach puts a sort of kink in the prop which enables it to spin on the way down. No need for any time consuming airfoils that are likely to ding up and/or break pretty easy.

 

[TangoJuliet]

Yeah, Gary's drawing shows what I was explaining above. Though in my version the diagonal cut runs end to end rather than starting/stopping on the LE/TE.

 

[Gary Byrum]

Yeah, Gary's drawing shows what I was explaining above. Though in my version the diagonal cut runs end to end rather than starting/stopping on the LE/TE.

My Cloud Chopper has even less of a cut than the diagram is showing. A little over 1/3 the length, but in the center of the prop. Any less than what I used would be undesirable.

 

[Rktman]

I've been building R/C airplanes for years and have known about bending balsa for quite a while. Some people swear by ammonia (Windex), but to be honest, it isn't really required, and some argue that the ammonia actually breaks down the lignin. Warm water works just fine when bending balsa. On my Rot-A-Roc, I didn't try to bend the blades at the start. I don't recall doing it at all with my original back in the early 80's and it auto-rotated great, but when I flew my new one the first time, it didn't auto-rotate at all, so I tried to go back and add the warp after assembly. There's a couple of other methods for the blades that I like and might try. One has you split the blade from root to tip at a diagonal and then gluing it back together with a bit of a flex to create an artificial airfoil (and that might be what I did with my original ), the other splits the blade in the middle, root to tip, then is hinged on the bottom and uses three short lengths of elastic/rubber band on the top. As I recall, I tried the latter method also when I was younger and it worked well. It makes for a slightly heavier model, but you can get twice as much blade chord because you fold it in half and when it's open, it holds a bit of an arc/airfoil shape.

Go to www.georgesrockets.com to see his Rot-A-Roc plans (and other contest model plans). His enhancement is the angled hinge mount (and a jig to make it easy) and a rounded blade tip. While I enjoy building stock LPR kits, I really enjoy contest model rocketry. For me, it gives some kind of purpose to my launches beyond the typical woosh-pop. :wink:

Thanks for George's url, really appreciate it. The guy is legendary and I'm still discovering all the innovative stuff he's pioneered or created over the decades.

I still consider myself a newbie BAR and I'm sure will eventually graduate to contests and more advanced rocketry. For now I'm getting the learning experience and experimenting I missed out on as an adult and enjoying every bit of it.

Thanks to the online world I've been stumbling across a fantastic amount of resource material. I have to say, though, that this forum is the best when it comes to learning. The community here is so willing to lend their advice and the value of their experience that's it's a gold mine, and the info and folks here are something that I value and appreciate immensely.

 

[Rktman]

Since keeping it "on the simple" appeals to you, then consider this. Cut your prop and sand all edges rounded off. In the diagram below, the prop shows a cut line from one end to the other diagonally. This cut should be about 1/2 way through or slightly deeper. Depending on your prop size, take a dowel 1/8 - 1/4 " and place underneath the cut line. Bend the two sides downward opening up the cut line like a gorge or a canyon. Apply enough CA (if you like) for a fast fix to keep it open, or just weigh both sides down and apply wood glue in the cut. Let dry completely. Fill remaining opening with wood putty and sand smooth. This is where some CA may come in handy. You can seal the putty with CA & a Q-tip until coated completely. Usually I take a long strip of copy paper and skin over the whole cut and coat with CA again. Sand smooth. This approach puts a sort of kink in the prop which enables it to spin on the way down. No need for any time consuming airfoils that are likely to ding up and/or break pretty easy.

View attachment 323446

Thanks buddy. I'm going to use this method on my next helicopter model. No definite design yet, but I'm beginning to gravitate toward something larger like your Cloud Chopper.

 

[Rktman]

The temporary jig worked great. Hope it's not too hard to make out that it is beveled 120°.

 

[TangoJuliet]

:clap: It's a start!

I just competed in my first competition in over 30 years 3 weekends ago. Don't knock it till you've tried it. It's another great way to learn new things. When I was a young teen in the mid 80's, George Gassaway came to a few of the Regional Meets we had in Ft. Wayne, IN, where I lived. He left quite an impression on me. I was delighted to see he was still active when I returned as a BAR last year.

 

[Rktman]

:clap: It's a start!

I just competed in my first competition in over 30 years 3 weekends ago. Don't knock it till you've tried it. It's another great way to learn new things. When I was a young teen in the mid 80's, George Gassaway came to a few of the Regional Meets we had in Ft. Wayne, IN, where I lived. He left quite an impression on me. I was delighted to see he was still active when I returned as a BAR last year.

Oh I'm not putting down competitions, I know what a rush they can be. I attended a couple as a teen and the excitement level makes everything so much more enjoyable. Heck even participating in a club launch is an adrenalin rush and beats solitary maiden flights by a mile. This is only my 4th build and the first 2 ended up in one of NC's many rocket-eating trees. :bang:

The 3rd smacked into a trunk and is currently in the rocket hospital so at the moment I don't have anything flyable to even enter into a contest. Hopefully this build goes faster than I expect. I'm aiming for SC's Freedom Launch this coming September. Finger's crossed.

 

[Rktman]

Aaghhh! Okay I rushed things and didn't take into account that sketches are 1-dimensional and the real world has an X, Y, & Z axis.

I'm not above admitting a goof. I didn't take into account that the balsa is 1/8" thick so that when you sand off a bit of it to bevel it, it throws the overall dimensions off--just a hair, but enough so that now it won't fit around my BT-50 body tube.




If it's true that we learn the most from our mistakes, than I'll never make this one again. Lesson hard learned. Now that age-old carpenter's rule "measure twice, cut once" keeps nagging inside my head. I only built kits as a kid so I'm chalking this one up to a newbie designer's inexperience.

Time to redraw my template and break out the hobby knife...

 

[TangoJuliet]

I think all you might need to do is open the angle up a degree or to on your sanded edge by the looks of it. Or... You could wrap some sand paper around the BT, draw a center line on the fin where the BT would make contact with it, then carefully sand a concave into the fin. It would require a steady hand to get it exact though.

 

[neil_w]

...You could wrap some sand paper around the BT, draw a center line on the fin where the BT would make contact with it, then carefully sand a concave into the fin. It would require a steady hand to get it exact though.

I'd probably try that first just to see if I could do it. Worst comes to worst you're back where you started, needing to cut and sand new fins.

 

[Rktman]

I think all you might need to do is open the angle up a degree or to on your sanded edge by the looks of it. Or... You could wrap some sand paper around the BT, draw a center line on the fin where the BT would make contact with it, then carefully sand a concave into the fin. It would require a steady hand to get it exact though.

I'd probably try that first just to see if I could do it. Worst comes to worst you're back where you started, needing to cut and sand new fins.

Thanks guys, I'll give both a go tomorrow.

 

[Rktman]

Tried softening the glue and prying apart the joints on my fin plate but nothing short of a nuclear detonation is going to budge them. The other alternative of hand grinding a 1/16” deep groove halfway through the thickness of each fin plate seems problematic and daunting.

It’ll probably be faster to just cut out a new set of fin/mounting plates with the correct dimensions.
This time though I’m going to do a test set in scrap foamcore to be sure I have it right.

 

[TangoJuliet]

Oh, I didn't realize you'd already glued everything together. In that case, yeah, maybe cutting new fins would be better.

 

[Rktman]

Amazing what a couple of cups of coffee can help one accomplish first thing in the morning.

The foamcore mock up was a perfect fit so I got started gluing up the new set of fins.
The beveling jig works great as an alignment guide to hold the fin/plates together at the correct angle while the glue sets. Once it does I won’t need the jig since the 3^rd fin should pretty much be self-aligning.

I also got started on sealing and sanding the nose cone while I wait and also got started on bending the aft hooks for the elastic. That’ll take a bit of trial and error to get the right shape and get them all consistently the same shape/size.

 

[Rktman]

Happy with the new fin units, and now the BT-50 snugs in place real nice.





The aft rubber band hooks turned out pretty good too. Took about 7 tries but I ended up with 3 that were the same length/shape. These will slide over the bottom edge of the fin unit and get CAd into place.

 

[Rktman]

I wasn't going to round the leading and trailing fin edges but what the heck, I'm on a roll.
May as well be productive between all the sanding and sealing rounds.

 

[Rktman]

Installed the centering rings that will hold the upper body tube in place and allow it to slide.
I decided to harden them with CA since they’re somewhat flimsy.





It occurred to me that uploading a sketch of the simple rotor hold down and deployment system
might help clarify things. Or maybe the original sketch was obvious enough? Oh well, here it is anyway.

 

[Rktman]

Decided to use the replaceable shock cord mount technique Tim Van Milligan from Apogee suggested…under the assumption that this build will be a workhorse that lasts long enough to start wearing out the shock cord.

Plus this build is my opportunity to try out methods and techniques that weren’t around when I was a teen.
Who said things aren't more fun the 2nd time around?

 

[TangoJuliet]

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).