Friday, July 12, 2013

Where and When?

There are always questions about where and when to launch. The circumstances vary wildly depending on where you live: city or rural, rainy or none-dry. And of course, what are the local laws and regulations? This is another topic that is interesting to revisit now that I'm a "responsible adult" rocketeer, as opposed to my days launching as a kid, without adult supervision. And I'm not lucky enough to live near friendly Farmer Brown and his gazillion acre fields. So I thought it would be interesting to document what I've learned in case anyone else can benefit from it - particularly any rocketeers in the Denver area.

I'll start by stating two assumptions: (1) All laws and regulations should be followed: those of the city, state, and the NAR. (2) You have a car to get you someplace (not really an option when I was a kid).

The first and most obvious answer is to launch with a club. Here in the Denver area there are CRASH and NCR, or farther south, COSROCS. I've launched with CRASH once and plan to do it again - especially when I'm launching high or with mid-power engines. But I also like to launch on my own schedule, with family and friends, sometimes making a picnic of it. So that is more the direction of this post: where can I do that?

There I several things to consider, so I'll discuss them in sections:

Finding a Site That is Physically Appropriate

NAR guidelines specify minimum site dimensions. Maybe there is an obvious spot near you, maybe not. I've used Google Maps to search for areas that look big and open, are mostly devoid of trees, and are public. Car accessibility is also a factor. But you can't tell everything from a map, so you need to scout it out to see what it really looks like. I'd rather launch in the soft, well-watered grass of a public park than in a field of tinder-dry brush or in the middle of a bunch of dirt and prairie dog holes.
Also, who else uses the park? A big open field is no good for a launch if it is full of soccer games. You need to be aware of the safety of others who won't be looking out for rockets. 
Finally, what borders the area? We all know that rockets can and do go out of the "minimum site dimensions." Could it land on private property? Power lines? In a lake? On the roof of the nearby rec center? On a highway?

Is It Legal to Launch There?

So you've got a site that you think will work. Is it legal? My initial assumption was to check fire codes, again turing to Google. In Denver (and every other municipality in the area that I've checked), the fire code does make a distinction between fireworks and model rockets. In all cases, the wording is something like this: 

The storage, handling and use of model 
and high-power rockets shall comply with the requirements 
of NFPA 1122, NFPA 1125, and NFPA 1127

Inconveniently, the NFPA rules are not immediately available online. But you can read (not download) them for free if you create a logon to the NFPA site. PITA, plus they then send you weekly (or more) emails about buying their products. But here it is in a nutshell:

NFPA 1122 -- Code for Model Rocketry - This is the NAR code, almost word for word. I don't know the history, but I think the NAR helped develop it. Hooray for the NAR!
NFPA 1125 -- Code for the Manufacture of Model Rocket and High Power Rocket Motors - A big N/A for me.
NFPA 1127 -- Code for High Power Rocketry - Maybe this will apply to me someday, but in that case I'd be off in the desert launching with NCR.

It is interesting to note that while the fire code makes a distinction between fireworks and model rockets, any fire fighters you talk to may not. Consider their perspective. They're not exactly in the business of encouraging people to find new ways to burn things fast and hot. If they aren't familiar with model rocketry, they may just assume that rocket = fireworks if you ask. I was lucky enough to speak with a very nice guy from the Denver FD who, despite a lack of familiarity, took my name and number, looked into it, and called me back a couple hours later to confirm that yes, I'm "good to go" in Denver.

But then there is another question. Recently I was launching in a public open space in Northglenn, Colorado. An officer drove up and approached - very friendly. I immediately told him that, though I'd never launched there before, I'd checked fire codes for the town. His answer was that while it may be OK according to fire codes, it may be against municipal codes. Though he said it in an odd sort of way, like he didn't know or care all that much. He checked out my gear, asked a few general question, took my name and number, and left with a friendly "be safe" and that was that.

(I'll also point out that, while he said that he saw a launch from the road and came to check it out, the area was also bordered with houses on one side. While I never got anything near them, that is something else to consider: Are nearby residents going to freak when they see missiles going up from the field near their house, and call the police? It may be legal, but it may also be a hassle for you and the police.)

I've honestly never known of a place where it was actually, all-around illegal to launch model rockets, but I'm sure some places exist. Bottom line: Ask the Fire Department. Ask the Police. CYA.

(You might also ask your local hobby shop or other rocketeers that you meet. I imagine the local hobby shop may have liability concerns about recommending places. As far as any other advice, I'll say it again: CYA.)

Really? Is It Legal to Launch There *Now*?

As I write this, at least half of Colorado's counties have fire restrictions in place due to wildfire danger. The rules on what constitutes a fire restriction vary by county, and even within counties there may be different stages or levels of restrictions - and they may split the county, with different restrictions in different areas. It gets complicated. And on top of that, there may also be municipal or state-wide bans. And not every county or city clearly posts when there is or is not a ban in place. Colorado just lifted its statewide ban a week ago, and the only way I know is from a Denver Post article that came up in a Google search.

One handy place to check for county fire restrictions is the Colorado Office of Emergency Management.
The Denver Fire Department can be contacted at 720-913-3473 Monday through Friday, and they've always been helpful when I've called to check on things.

There are a couple big parks in the area that I like for launching. One is in Golden, but Jefferson County is always among the first to enact fire restrictions, so this year and last, this has been out from late spring through summer. I've launched many times at Ruby Hill Park in Denver. It's not perfect - it's surrounded by big trees, and beyond them are power lines. But while I've had a couple of severe weathercocking launches, I've never gone near the power lines or surrounding roads (though I did have to wade into a pond once) and I've never lost a rocket in a tree. The Denver FD has confirmed for me that I'm OK to launch there. The center of the park is a big basin (the name Ruby Hill strikes me as the opposite of what it should be) that is never overly dry, and that section has no soccer fields or anything. I never see more than the occasional person stroll through, though the nearby playground gets a lot of action, and I have had a landing there. It's a bit of a walk from the parking area to the center of the field, but it is a pleasant setting, and feels surprisingly isolated given its location.

Update - 12/2016: It gets even more complicated. I was with a small group of friends and their kids, many launching their first rockets, at Ruby Hill Park a couple months ago. We were approached by a ranger from Denver Parks (who even know that never parks had rangers?) who told us that although it is OK with municipal and fire codes, launching is a violation of parks codes. Jeez, how can you ever know? He was super friendly, and lest us do a last launch or two, but then we shut it down. Sadly no more launches at Ruby Hill.

Since I first wrote this post over three years ago, I've attended many launches with CRASH, NCR, SCORE, and even one with Tripoli Colorado. Unfailingly, they are fun and friendly. So while I'll miss the family-only spur-of-the-moment option, it looks like it will only be club launches for us from here on in. (Unless we make a new friend with loads of empty farmland!)

DISCLAIMER NOTE:    This information  presented  only as my personal experience, and is not intended as specific or authoritative advice..  The  author  is  not   responsible  for  any  liability  or  loss  related  to  the  launches of others, and all individuals are responsible for selecting and verifying the viability of their own launch areas.. 

Tuesday, July 9, 2013

The Secret to Perfect Fins

It's shaping up to be another skimpy summer for rocket launching in Colorado. Fire bans have been declared almost everywhere in the state, and even in places where there are none (including Denver) you can't help but feel guilty just thinking about launching with all the wildfire destruction going on.

But there is always building. I've just finished two kits: Pemberton's Little Bucky Jones and FlisKit's Buck Shot.

The Buck Shot is my first MicroMaxx kit, so I'm excited to venture into that territory. I know my limitations, and my build skills aren't up to the challenge of making a high quality small model, so I just put it together and painted it as best I could without sinking in time going for perfection.

The LBJ, on the other hand, is such a unique and gorgeous kit that I found myself obsessing over it for weeks. Which brings me, sort of, to the topic of this post.

For several months I'd been vaguely planning on writing my tract on the ultimate solution to perfect fin finishing. Of course, most of the delay involved figuring out how to perfectly finish fins. There is no shortage of information out there on blogs, vendor videos, and message boards, and everyone has their favorite techniques. But something must be the best, right?

I have, I'm proud to say, discovered the true, absolute best solution. Are you ready?


There's sanding sealer, Elmer's Fill 'n' Finish, microballoons, CA glue, Kilz, urethane, on and on. But ultimately, no matter what materials you use, it comes down to patience. Lots of layers, lots of sanding, until you have it just right.

Sanding sealer stinks, FnF can be a little delicate, watered down Elmers can warp fins. But for me, the patience thing is harder to manage than any of those. Though if I stick to a willingness to always do another layer of fill/sand, or primer/sand, the imperfections that I see (and there are always some) get smaller and smaller.

That said, here is my current process when I'm tying to do a really nice job on a rocket. I'm not going to go into extreme detail on any particular technique; there is so much info on the web, and really you just have to try things out and experiment. But here are my favorite methods. And I couldn't help myself - I've gone beyond fins to describe all of my "best practices."

Construction Adhesive

I've barely dabbled in mid power rockets at this point, so for me the go-to glue is wood glue. I've used a lot of Elmer's, but lately I've been using Titebond. Used properly on balsa and cardboard/paper, this will make a bond stronger than the materials themselves. I do, however, sometimes use 5 minute epoxy in two cases. First, because it doesn't grab as quickly as wood glue, it is handy for doing things with a tight fit, like engine mounts, centering rings, and couplers. Second, it is nice to use if I have to fill a nose cone with some lead shot to weigh it down. Stinky stuff though. I avoid it when I can, and wear nitrile gloves when I do use it (but even here, the web has lots of conflicting information on what gloves are best protection from epoxy).


Light plywood and basswood are great because the grain is typically a lot tighter than balsa. I've gotten some terrific, smooth finishes on these with just one thin layer of FnF, sand, and then a couple primer/sand cycles.

I find balsa tricker. I've gotten decent results with one or two FnF/sand cycles, followed by a couple of layers of sanding sealer (sanding in between), then primer/sand/primer/sand. But lately, I've become a fan of this:

  1. Before mounting, laminate the fins with ordinary copier paper, glued on with a thin layer of wood glue. It is very important to make sure you smear the entire fin surface with the glue before sticking on the paper. I smooth out the paper as best I can - I use a small section of PVC pipe. The fins may warp like crazy with the wet glue on them. Put them between wax paper sheets and press them between two very flat surfaces, weighted down amply, for a day or so to dry.
  2. Smear the fins with a thin layer of CA glue (crazy glue) and let them dry. This will turn the white paper covering translucent as the CA glue penetrates and hardens the paper and wood fibers.
  3. Sand sand sand until smooth. The CA glue will leave a bit of texture, but with a lot of sanding you can get them glassy smooth.
  4. Mount the fins on the rocket.

This process adds a ton of strength, and you don't have to worry about grain showing. I recently did a test where I weighed fins before and after this process, and also compared the weight to lite ply fins of the same size. The laminated fins were still a lot lighter (but I lost my data!).

Body Tube Spirals

This is something that I never considered early in my rocket career, but now I can't stop myself from doing it - I'm compulsively bothered by visible spirals on a painted rocket. I use some slightly watered down Elmer's FnF (now just called Wood Filler) and paint it along the spirals. Then after it dries, I sand the whole tube. It's not a lot of effort, so it is totally worth it (though I might not say the same thing if I built an Estes Mean Machine). Some people claim to get rid of spirals with several coats of primer and sanding, and that might work with a thick primer like Kilz, but I think this is a good approach. Sanding the tube also helps with fin and paint adhesion.


I have two favorites here. For small, light rockets, I like Titebond Molding and Trim glue. It doesn't run, and shrinks and bubbles less than other wood glues. (I had a hard time finding it. Regular hardware stores don't seem to carry it. I had to go to a specialty woodworking store.)

For bigger and higher power rockets, I like Fixit epoxy clay. You can find some good directions for its use on the Apogee Components website. It's not quite as easy as it looks. When mixed, it's just a little too firm to just smooth out with a swipe of your finger. You have to work at it. In fact, you need to work at it. When dry, it sands nicely, but of course is much harder than the body tube and fins, so if you need to do a lot of sanding to get the fillets nice and smooth, you might end up digging in to the other components. It takes practice - my first rocket using this had OK-looking fillets. My second one had a few that were perfect, and a couple with minor imperfections. But in the end, you can get super solid joints, with fins that look like they grew right out of the body tube.

Nose Cones

For balsa, I've gotten amazing looking results with a layer or two of Fnf/sanding, then the same with sanding sealer, then a few coats of primer and sanding, finishing with wet sanding with a really fine grit. Totally worth the effort, though it still results in a nose cone that will get dinged the first time you chuck it in the back of the car with a bunch of other stuff. I've seen recommendations to add a couple layers of CA glue to harden it up and give it a sort of shell, so I'm still experimenting with that.
For plastic nose cones, like BT spirals, I'd never considered anything to do in my early days. Now, I always sand the seams *completely* down so they cannot be seen or felt at all. Then I need to smooth it out with successively fine layers of sandpaper. Ten more minutes of effort, but a way way nicer looking nose cone.


Lots and lots of people swear by Kilz because it goes on so thick. And it is great for hiding all the little blemishes - just like the "orange peel" texture applied to drywall in all modern residential work. So there is typically a lot of sanding needed to get back to a really smooth finish. If you're willing to do that, Kilz is great. However, I prefer not to use it on small models, or ones with lots of detailed pieces and angles that are hard to sand. In that case, I'll use a "regular" sandable primer (I use Rustoleum).


I don't have experience with enough brands to give a strong recommendation here. I can only say that Valspar is awful, and that I use Rustoleum Ultra Cover 2x glossy pretty exclusively and am happy with it. It goes on pretty well and there is a good color selection.

Clear Coat?

Question mark here. Do you need a clear coat? It is often recommended over decals (though I'm not a huge decal user), but many say that it will eventually dry and crack/peel the decals. I found this process on the web, using Pledge and Simple Green. It works, but it is not magically transforming. I use it occasionally and am still undecided if it is worth it.

So there we are - that's the state of my technique as of mid-2013. Perhaps, even hopefully, I'll want to totally revise this in years to come. I like to try new materials and methods, and I'm sure I'll get new favorites.

But it all comes back down to the P-word. Without lots of patience, nothing is going to look good.

Of course, despite all this, I look at every rocket I build, especially the ones I really really tried on, and just see the little flaws. And the parts, that were perfect? Well, they get bashed up in flight anyway. So at some point in a build, I always end up saying "enough is enough" and I just call it done so I can get the bird in the air. Patience has its limits, at least with me.