just some general noob questions

[Hombre]

Hi Gang,

Brand new lurker, first time poster. I made a few rockets when I was in Scouting and 4-H one or thirty moons ago, and my boys are now in Scouting. We thought it might be fun to get into more than what the Scouts do, so here I am. We've built a few kits and want to have a go at some custom designs (and I know about RocketSim and OpenRockets). Most of what I have planned is more or less cloning commercial kits, but in ~BT50-55 size. That is, I'll buy parts from balsamachining, jonrocket, unclemike, semroc and apogee, etc, and reverse engineer the parts to make rockets the size that I want them. That started out because I saw a design I liked, but wanted to do it in blue tube, which was a airframe than the kit. Well, it's kind of grown from there. I have a handful of general-ish questions and I don't see answers readily available. Of course I'm going to continue reading and learning, but it's kind of like doing a wiki-walk on Wikipedia and I keep getting side-tracked by all the cool stuff. I'm going to get some nice components when I can and not just stick with the...ahhh...introductory quality... that most of the cheaper kits seem to come with. For me, that'll be nylon parachutes, nomex wadding, kevlar shock cords, etc.

I'm not likely to get into high power for quite some time, if ever. I'm also not looking for supersonic. I'd just like to build some rockets out of quality materials that can cope with being handled by a pair of pre-teen boys.

I'm generally interested in building ~BT50-55 and working with C engines, though likely to also build some minimum diameter setups to handle D & E engines. They'll generally be 15" - 30" total height (and most likely more like 18" - 24" total height).

Who makes a good paper airframe? Who makes one that doesn't require a lot of filling in of the grooves? BRSHobbies advertises glassine coated airframes that are replacements for the standard Estes sizes. Are they any good? What's the glassine? I assume I can cut it with an X-acto?

Does 29mm Blue Tube correspond with anything on the BT scale? Should I stop using the BT scale? Is there something else? I've only found one nose cone that actually fits 29mm Blue Tube, and it's a FG one from Apogee. It looks nice enough. Are there any others?

Why balsa nose cones? Any particular advantage over plastic?

If not using balsa for fins, what's a good wood? What's a good thickness? I know, loaded question. Check the design in RocketSim. I'm concerned with the gap between s/w and The Real World. It may be stable, but is it fragile?

Thanks for any insights

 

[455 Buick]

As far as motors, you might as well go ahead and build them for 24mm, and build 24mm-to-18mm adapters, if you're going to be building these rockets out of stout heavy materials to handle rough boys.

Balsa cones - You can alter the profile slightly on your own a lot easier without a lathe, but if you're cloning kits, you're probably already ordering the right ones and won't be customizing. Also, It may be easier to add weight to a plastic cone since you don't have to drill and hollow out the wood. And you may need nose weight if you go heavy on the fins.

As for stouter fins, I like basswood, but have also tried plywood from a crate of clementine/cutie oranges. The basswood is less rough to begin with And may be lighter. As for thickness, go thicker if you like and if it doesn't look out of place/scale for ya.

Looking forwArd to some pics!

 

[shreadvector]

Normal Estes body tubes are glassine coated paper.

You asked "What is Glassine?". A simple Google search for "glassine" will provde the answer:

https://en.wikipedia.org/wiki/Glassine

 

[Hombre]

Hey Buick, thanks for the nice response. I still have questions, but that'll help get me going. Sorry, no promises on pics. Can you imagine if you'd have just ignored everything I said and told me to go RTFM? Man, that would have been awkward...

 

[Marc_G]

Hombre,

BRS Hobbies is a great place to go for body tubes, as they are one of the few places you can get a 34" section of tube. Most places cut them into 18" sections. I prefer longer sections rather than coupling together shorter ones, if I'm making a long rocket.

The quality of body tubes is pretty much the same whether you get them from Estes or BRS or whoever. There's only one or two places that actually manufacture them, so the vendor you buy from doesn't really matter... they come from the same mill. However, some are white and some are natural paper color (brownish)... BRS tends to sell the white ones, and again I have a bit of preference there, though it doesn't really matter once the rocket is painted. Some body tube sizes can come in an "H" variant which means heavy walls (thicker). So, you can use the same nose cone on these, but there will be a slight step where shoulder meet the thicker tube.

Some tubes, I think particularly BT20 and BT50, have been the subject of discussion to the effect that people think they are less strong today than in days of yore. The specification on the tubes is essentially materials and dimensions, not crush strength or anything, so I don't think you can say the tubes are out of spec, even if they do crush more easily. There are threads on this somewhere, discussed by folks with more knowledge in the matter than I have.

All the paper airframes cut well with a razor blade. Many of us have made little jigs that let us spin the tube while pressing it against a razor blade, cutting the tube to a perfect edge.
Like this one:


Some people like balsa, some like plastic... I like both, for different reasons. I prefer well made plastic (minimal mold lines) because there is less work to them and I can easily add nose weight if needed.

Note, if you need anything from SEMROC, buy it quickly before they shut down for good. Their stock is dwindling!

Marc

 

[fyrwrxz]

Balsa Machining Services (BMS)-most all tubes and nose cones. Scratch till the itch subsides,but It'll never go away completely-welcome to TRF-home of the afflicted!

 

[JeromeK99]

Welcome back to rocketry and to TRF!

I understand your desire for sturdy components. My little nephew damaged and/or ruined a handful of rockets when he started out at 7 years old. He liked to pay with them, but soon learned their limits. Now 2 and a half years later, we rarely have handling incidents. Light weight components are key to building "model rockets". This is especially true with low power varieties. You like to build with the BT-50 to BT-55 sized rockets. Weight can be an issue not only for performance, but also safety! Rockets in the size range you are going for can weigh anywhere from 1.5 oz. to over 3 oz. using standard light weight Estes style components and construction techniques. An Estes C6-5 has a maximum liftoff weight of 4.0 oz. This is the total combined weight of the rocket and motor on the pad. The motor itself weighs .85 oz.

I went the route of building sturdy models back a decade or so when I first returned to rocketry. My reasons were more for sturdiness due to harsh range conditions. I was launching out in the high desert of Southern California and my rockets were getting destroyed upon landing! I went through numerous methods of beefier construction and components. Learning by trial and error from loss of performance, aerodynamic instability etc... I thought at first, beefier body tubes, plywood fins, plywood centering rings and epoxy was better... nope.. They weighed more so they came down harder and tended to need bigger motors to get them up! So by building "stronger" I suddenly had the choice of fewer motors and needed bigger chutes. The bigger chutes were fine when the wind is very calm, but then even a slight breeze would cause a 1/4 mile or more walk to recover the rocket.

I looked at the high power guys at the club to see what they were doing. The built their birds like "bricks"! So much added weight! For them it wasn't an issue. Their motors could lift so much more and in most of their opinions, bigger was better anyways! I saw the heavy weight fiberglass they were using and thought back to my r/c airplane days (back when we used mostly balsa). We used some light weight fiberglass cloth to reinforce areas of our models. Now most HPR guys are using 6oz. to 9oz. glass cloth to wrap and reinforce their birds... same stuff real boat and airplane guys use! I'm talking 0.75oz. glass cloth! Single wrap on a body tube and 1 layer on each side of balsa fins! Using hobby grade finishing epoxy over the glass. On a BT-60, 21" rocket it added less than 1oz over standard construction. The body tube, unless crushed to a "crease" retains it's shape and the balsa fins are stronger (and lighter) than plywood or even bass wood. It really isn't that hard for an adult to do, it just adds time to the build. I do not however suggest this for kids as epoxy has safety issues when using and the sanding after as well. I don't build all of my birds this way. Just some.

The spirals in the tubes vary. But they all seem to show through unless you take time to fill them.

The glassine question was already answered...

As for balsa vs. plastic.... There are simply more options with balsa. Plastic molds are very expensive, costing upwards of $10k. Balsa can be worked easily on a lathe. Plastic is much easier to finish, but done right, balsa can look just as fine.

I bought Rocksim back about 10 years ago. It is expensive, but I think well worth it. Over the years just about anything you can think of has been done and documented by Apogee. Tons of online reference material is available. Rocksim simply works. I started playing with Open Rocket about a year ago (3 or so released versions now). I must say that it is a very "pretty" and smooth copy of the Rocksim interface. It also "mostly" works. Open Rocket can open and use "most" Rocksim files. Open Rocket is a good (free) alternative if you can't justify the $100+ price tag of Rocksim. It will get the job done. Open Rocket has a good support system and good folks working on it constantly. Upgrades available often. Rocksim however is a commercially complete software program that works now and has online "how-to" support.

Either way... these rocket sim programs will help you work out design stability and motor selection. I have my little nephew draw his rocket designs on paper then I work it up on the computer with him consulting any needed changes.


Jerome