Hi everyone! A few Qs from an old rocketeer back from the rim.

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Brainlord Mesomorph

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Hi guys!
I’m new here but I’m back to rocketry after a 40 year absence. Haven’t launched anything (since I was 12), but I am jumping back in with both feet.

So right now, I have a couple of hundred dollars worth of kits, motors, and the Big Box o’ Estes parts on their way via snail mail. I picked a local park via Google Earth. I’ve got Open Rocket, and was able to remember that last design I was working on when I was 12. And I’ve had Open Rocket “optimize” that design (that is SO cool) to a stability of 3 cal(ories?*) and an Ap of 800 ft on the good ol’ C6-5.

I’ve been watching Youtube videos and think I’m pretty much up to speed on modern construction techniques (I already ordered the acrylic floor polish) but I do have some questions:

1. What happened to dope?
In the 1970’s we *had* to coat all our rockets in airplane dope. No one is doing that now. Is it just that modern paints and primers (or acrylic floor polish) make it obsolete? We were told the paper tube and wooden fins would catch on fire if not for the airplane dope. Was that just a scam?

2. Tell me more about the wood putty and the wood glue.
In the 1970’s Elmer’s white glue was *the* material of choice not just for gluing parts but also for building up fillets and any other areo-smoothing things. (I don’t think Elmer’s wood glue or putty existed then.) I see you’re using wood filler on the tubes. What about wood filler fillets? Anyone know the relative density (weight) and strength of these products?

3. Laminating fins in paper?
Good idea, but why not laminate entire sheets of balsa (like foamboard), and then cut the fins? (seems more direct)

4. Open Rocket help
*yes, I know its Caliber, but what does that mean? Can someone point me to they right Wiki that explains that ?
 
Welcome to the future!

1. What happened to dope?
Dope is gone for the most part. Rocket tubes and fins of today definitely don't catch on fire at the drop of a hat, so that may have been the good old group-think at work. Then again, I wasn't alive in the 70s, so things may have been more flammable after all! These days there are multiple techniques for getting smooth fins (self stick label paper, glued on paper, wood filler/sanding, etc...) and tubes (spot putty spirals, wood filler, filler primer, etc)

2. Tell me more about the wood putty and the wood glue.
Titebond II or III is a very popular choice for rockets these days. They're much stronger, they bond naturally to fibrous materials like wood, paper, and cardboard, there's no appreciable weight penalty in their substitution, and they set up very quickly (**on that point, make sure you get the coupler in the right place the first time, cuz it won't move again!). For fillets, there's a product called Titebond Quick and Thick which doesn't sag or shrink as much as II or III and makes great fillets (Similar formulas are Molding and Trim and No-run No-Drip, basically the same stuff). I wouldn't use wood filler as fillet material without some added adhesive. It's basically just dried powder paste.


3. Laminating fins in paper?
You're more than welcome to experiment and report back on the results! People love experiments.
My initial thoughts are that the paper would make the fins a lot more annoying to cut out and shape properly.


4. Open Rocket help

A caliber refers to the diameter of the rocket body just like it refers to bullets. 3 calibers means your CG is 3 diameters ahead of the CP and is stable (maybe overstable, but that's a lesson for another day). If the stability is negative, the CP is ahead of the CG, and your rocket will try and turn itself around midflight. There's a great series of quick youtube videos explaining OR very well, and there are good guides here in the electronics and software sections of the forum.

~Nyt
 
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Thanks glad to be here.
I'll have to pour a drink and read that.
:)

Not a problem... feel free to ask any questions you like about using OR.

K'Tesh's OpenRocket Tutorials
Decals in OpenRocket: a not-so-quick and fairly complete tutorial

Oh, and then there's my files for your viewing enjoyment...

K'Tesh's OpenRocket files...

27914380154_cc9b52ce98_o.png
 
Welcome to the future!

3. Laminating fins in paper?
You're more than welcome to experiment and report back on the results! People love experiments.
My initial thoughts are that the paper would make the fins a lot more annoying to cut out and shape properly.

~Nyt

While covering the entire sheet of balsa is doable, for me it's a waste of glue and time. I do however print fin templates out, apply them to balsa (with a seam allowance), and then cut the fin from that. One downfall is that sometimes the paper does get messed up from cutting if the knife isn't sharp enough, or the glue doesn't hold.


Papering balsa/ply Fins... A foolproof method
 
While covering the entire sheet of balsa is doable, for me it's a waste of glue and time. I do however print fin templates out, apply them to balsa (with a seam allowance), and then cut the fin from that. One downfall is that sometimes the paper does get messed up from cutting if the knife isn't sharp enough, or the glue doesn't hold.


Papering balsa/ply Fins... A foolproof method
Another thing about papering the whole sheet is that locating the grain direction is a must beforehand as the paper hides it afterwards. For me its easier to paper one side of a fin a then trim paper then do other side. If using laser cut or die crushed cut fins papering the sheet before hand hides the fins from you. 😀
 
OK so "Stability Caliber" is just the ratio between diameter (and which diameter is a problem) and the distance between CoM and CoP.
That'a bit of an over simplification.
 
Welcome! When I got back into rocketry a couple years ago I poured over the information on the Apogee website: https://www.apogeerockets.com. The "How to Guides" (in the drop down menu) and the "Quickstart Guides" (on the right) are fantastic. I remember seeing the quick start guide titled "I want to fly bigger rockets" and thinking "They read my mind!!!"
 
Another thing about papering the whole sheet is that locating the grain direction is a must beforehand as the paper hides it afterwards. For me its easier to paper one side of a fin a then trim paper then do other side. If using laser cut or die crushed cut fins papering the sheet before hand hides the fins from you. 

Oh I didn't think about the pre-cut fins (we didn't have those in the 70s)
 
When I was a kid flying rockets in the late 60's the kit instructions all said to paint your models with dope, never enamel paint. Reason was dope was lighter than enamel. But now, weight considerations are not as much of a concern: if your rocket is too heavy for one motor, move up to the next bigger motor. The 24mm C, D, and E motors were not available at the time. Trying to even buy butyrate dope nowadays is next to impossible: maybe you can find one or two vendors that carry it. The march of progress.
 
Looks like a lot of your questions were answered. I'm from basically the same era. I used dope on a lot of rockets. It had to be brushed on, and because it was thinner and didn't cover as well (things show through layers of paint), many layers had to be brushed on. I've used it a couple of times recently, but mostly mixed with baby powder as a sanding sealer*. It's still available at some hobby shops that have old-style airplanes (paper-over-balsa). Spray paint, especially high buildup sandable primers have come along well enough that they're a lot easier/cheaper/faster to use. The colors that are available now, are amazing (color-changing paint!).

Thinned, non-VOC wood putty is frequently used as grain or sanding sealer. I think people first started using Elmer's Fill N Finish, thinned to the consistency of thin peanut butter. It's non-toxic, has no smell, and can be re-thinned if it dries out (as long as it's not a solid lump). * I've also used clear water-based polyurethane top coat mixed with baby powder as a sanding sealer.

Glues are another area of advancement. There are four basic types of glues in use in hobby rocketry today. The old Elmer's white glue is polyvinyl acetate (PVA)*. It's good, especially when used with double-glue method, but there are better glues. The next category are the yellow "carpenter's" glues. These were available back in the 70'a as SigBond (among other names). They are alephatic resin glues (there are two basic types of hydrocarbons, alephatic and aromatic). They form a better bond with porous materials, and the glue itself is stronger than the white glue. Both the white and yellow glues shrink as they dry. If you use a lot to glue in a centering ring on a large diameter body, it can produce a noticeable "pucker" where the ring is. The third type used are the epoxies. There are quick-setting (a few minutes), medium setting (an hour or so), Long setting (over night or more), and specialty epoxies like metal-filled epoxies that are very tough and have higher heat tolerance (JB weld is an example). The last category are the cyanoacrylate (CA) or super-glue formulations. These were available in the 70's under names like Hot Stuff. They come in a variety of thicknesses from water thin to gel. There are even foam-safe formulations (helpful for making foam gliders).
* PVA glue can also be mixed with bubble-blowing soap to make long lasting bubbles. AMAZINGLY long lasting, as long as they don't get poked and popped. You can use a hair dryer to blow bubbles on a cool, still day and they will float up out of sight.

Laminating with paper is a quick and easy way to make a paint-ready surface. One thing you have to watch out for, and probably the best reason not to laminate an entire sheet, is that you risk warping the wood. The glue you put down first is water-based, and this can cause the grain to swell. The glue can set while the wood is distorted, making the warp permanent. You have to be fairly quick when doing this (but don't rush), and you almost always have to clamp or weight down the parts while the glue sets up.

Long post, I probably over-explained everything, and missed what you most wanted answered.

Welcome back to the addiction, I mean hobby!
 
I just got back into the hobby after a 25 year hiatus too.. It might have been said further up but join a local club if you can. Watching other people burn their money is almost as much fun as burning your own, it’s a fun way to spend a Saturday, you’ll learn lots of useful stuff from the “old timers” and get to see lots of different approaches to the hobby...


Sent from my iPhone using Rocketry Forum
 
Hi guys!
I’m new here but I’m back to rocketry after a 40 year absence. Haven’t launched anything (since I was 12), but I am jumping back in with both feet.

So right now, I have a couple of hundred dollars worth of kits, motors, and the Big Box o’ Estes parts on their way via snail mail. I picked a local park via Google Earth. I’ve got Open Rocket, and was able to remember that last design I was working on when I was 12. And I’ve had Open Rocket “optimize” that design (that is SO cool) to a stability of 3 cal(ories?*) and an Ap of 800 ft on the good ol’ C6-5.

I’ve been watching Youtube videos and think I’m pretty much up to speed on modern construction techniques (I already ordered the acrylic floor polish) but I do have some questions:

1. What happened to dope?
In the 1970’s we *had* to coat all our rockets in airplane dope. No one is doing that now. Is it just that modern paints and primers (or acrylic floor polish) make it obsolete? We were told the paper tube and wooden fins would catch on fire if not for the airplane dope. Was that just a scam?

2. Tell me more about the wood putty and the wood glue.
In the 1970’s Elmer’s white glue was *the* material of choice not just for gluing parts but also for building up fillets and any other areo-smoothing things. (I don’t think Elmer’s wood glue or putty existed then.) I see you’re using wood filler on the tubes. What about wood filler fillets? Anyone know the relative density (weight) and strength of these products?

3. Laminating fins in paper?
Good idea, but why not laminate entire sheets of balsa (like foamboard), and then cut the fins? (seems more direct)

4. Open Rocket help
*yes, I know its Caliber, but what does that mean? Can someone point me to they right Wiki that explains that ?


1. What happened to dope?
In the 1970’s we *had* to coat all our rockets in airplane dope. No one is doing that now. Is it just that modern paints and primers (or acrylic floor polish) make it obsolete? We were told the paper tube and wooden fins would catch on fire if not for the airplane dope. Was that just a scam?


I never heard that dope was flame-resistent. Hot fuel proof ? Sure, it said so right on the label. :wink: Anyway it's still available. SCIGS30 uses butyrate sanding sealer on his beautiful builds of vintage kits: https://www.rocketryforum.com/showthread.php?145133-Vintage-Estes-Crusader-Build

brodak sanding sealer.png
https://brodak.com/sanding-sealer-4-oz.html



2. Tell me more about the wood putty and the wood glue.
In the 1970’s Elmer’s white glue was *the* material of choice not just for gluing parts but also for building up fillets and any other areo-smoothing things. (I don’t think Elmer’s wood glue or putty existed then.) I see you’re using wood filler on the tubes. What about wood filler fillets? Anyone know the relative density (weight) and strength of these products?


Elmers Carpenter's Wood Filler (CWF) is a very popular filler. As far as fillets go the first layer should be your glue of choice for strength. Then you can use the CWF to make'um smooth and pretty. hcmbanjo has written about his techniques here: https://modelrocketbuilding.blogspot.com/2013/11/get-right-carpenters-wood-filler.html and here: https://www.nar.org/educational-resources/model-rocket-building-techniques/

elmers wood filler.jpg

BTW a few hours/days/weeks reading Chris' model rocket building blog is time well spent.


The Chief Designer at Estes, Jumpjet, is partial to sandable spray primer and Bondo Glazing and Spot Putty: https://www.apogeerockets.com/education/downloads/Newsletter450.pdf

bondo.jpg


Lots of ways to skin the balsa filler cat. Pick one or try'em all and see what works best for you. Hope this helps.
 
Welcome back.

As learn, you will develop your own favorite methods and techniques. Have fun. I have flown since the 60's and I never doped any of my rockets back then, mainly because I flew over the mud flats behind my house on the beach. Three thousand feet of recovery area, no power lines, trees or any thing to catch my rockets except mud. Enjoy!
 
Anyone having difficulties with the attachments Samb put in? Curious to know if it's "just me." I just see "Attachment 342048" instead of a picture pm Firefox. Shows as broken link on Tapatalk, too.
 
Thanks guys, for all the info.

My head is swimming from all the different (and conflicting) construction techniques.

While I certainly don't want to argue w/ the guy from Estes, it sure looks like he's putting on coat after coat of putty and primer and then sanding all the way back to wood. And given the acrylic coating I'll be putting over it, doesn't just have to *look* smooth?

And about laminating the fins, assuming the top edge of the fin is straight, what about folding the paper and using one piece on both sides? that would at least save 25% of the trimming and sanding, and maybe more streamlined.

So while my kits and parts are still a week away, I think I'll go to Walmart and get some balsa start experimenting w/ sanding and laminating.
 
And about laminating the fins, assuming the top edge of the fin is straight, what about folding the paper and using one piece on both sides? that would at least save 25% of the trimming and sanding, and maybe more streamlined.

So while my kits and parts are still a week away, I think I'll go to Walmart and get some balsa start experimenting w/ sanding and laminating.

https://modelrocketbuilding.blogspot.com/2013/12/centuri-flutter-by-build-part-5-paper.html
 
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A little more on stability .... Stability is achieved by having two different forces working against each other to pull the rocket straight. One force is aerodynamic pressure. When the wind blows on a rocket, it will rotate around it center of pressure, or CP. The fins are the widest part of the rocket, and thus offer the most wind resistance.

The other force is gravity. The rocket will tend to tumble on the arc that intersects its center of gravity (CG). As the rocket starts to rotate on its CG, the wind creates a counter-rotation at the CP. If the CG is sufficiently forward of the CP, this causes the rocket to straighten up.
 
A little more on stability .... Stability is achieved by having two different forces working against each other to pull the rocket straight. One force is aerodynamic pressure. When the wind blows on a rocket, it will rotate around it center of pressure, or CP. The fins are the widest part of the rocket, and thus offer the most wind resistance.

The other force is gravity. The rocket will tend to tumble on the arc that intersects its center of gravity (CG). As the rocket starts to rotate on its CG, the wind creates a counter-rotation at the CP. If the CG is sufficiently forward of the CP, this causes the rocket to straighten up.

https://spaceflightsystems.grc.nasa.gov/education/rocket/rktstab.html

<pedantic>The center of pressure is the point at which the all of the forces due to aerodynamic effects (lift and drag) resolve. It is the place where you could a apply a single force to a stationary rocket -- pushing on it with your finger -- and get the same effect as the action of aerodynamic forces on a rocket moving under thrust.

The center of mass of the rocket -- which coincides with the center of gravity -- is the point about which the unsupported rocket in flight will turn under the application of torques due to motor thrust or aerodynamic forces (or any other force). Since drag opposes the thrust, and increases with the cross-sectional area intersecting the fluid through which the rocket moves, putting the COP aft of the COM means that drag will tend to produce a torque opposite to the torque due to the thrust of the motor, or cross-winds, or anything else that might cause the rocket to tumble...

The weight -- the force of gravity on the rocket -- actually doesn't do much for aerodynamic stability one way or another. </pedantic>
 
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The footnote about papering the launch lug is a hell of an idea!

Hi Brainlord,
Welcome back!
Chris here, from modelrocketbuilding.blogspot.com
Papering a launch lug is doable, but the wrapping is more difficult. Hide the wrap seam by gluing it against the body tube.

These are all three posts from the fin papering on the Flutter-By build:
https://modelrocketbuilding.blogspot.com/2013/12/centuri-flutter-by-build-part-4-paper.html
https://modelrocketbuilding.blogspot.com/2013/12/centuri-flutter-by-build-part-5-paper.html
https://modelrocketbuilding.blogspot.com/2013/12/centuri-flutter-by-build-part-5-paper.html

I tend to "butterfly" the one piece paper covering. It will roll over the rounded leading edge making it cleaner with one less edge to fill.
This is just the way I do it, everybody has their own good methods.

To catch you up, here's some tips articles in the Apogee Peak Of Flight newsletter:
https://www.apogeerockets.com/education/downloads/Newsletter424.pdf
https://www.apogeerockets.com/education/downloads/Newsletter425.pdf
 
My head is swimming from all the different (and conflicting) construction techniques.
Then it sounds like you have understood everything correctly. :)

As a BAR, I got reacquainted with just about everything I needed to know by reading Chris Michielssen's blog and reading the NAR building techniques page that he wrote. I did my first couple of builds following those techniques pretty precisely (worked great for the most part) and then started to branch out and find my own preferred versions. The biggest change I've made is in papering everything in sight with Avery label paper.

While I certainly don't want to argue w/ the guy from Estes, it sure looks like he's putting on coat after coat of putty and primer and then sanding all the way back to wood. And given the acrylic coating I'll be putting over it, doesn't just have to *look* smooth?
I likewise am not a fan of his technique, which doesn't mean it doesn't work great for him (he is a master builder, I'm not one to argue) but it's not the way I want to do it. My personal goal is to minimize spraying an sanding, which is why papering is right up my alley.

However, in order to *look* smooth, the surface must *be* smooth. That means, by one means or another, filling the wood grain. Even high-fill primer won't do it on one coat (or even two) on balsa, which is why other filling techniques are commonly used.

And about laminating the fins, assuming the top edge of the fin is straight, what about folding the paper and using one piece on both sides? that would at least save 25% of the trimming and sanding, and maybe more streamlined.
I don't believe I've ever seen anyone fold the paper over the tip of the fin. Frequently, folks will fold the paper over the leading edge, which ensures that the leading edge will be well-sealed. Also, since the leading edge is commonly shaped, it's often easier to fold over than to get a clean trim on each side.

That said, I often have non-straight leading edges on my rockets, and so folding over is not an option. By default I go right for papering each side individually, and always trim off excess with sandpaper rather than a knife. This has worked for every possible size and shape of fin, including crazy curves, tiny pieces, and whatever. And I seal my edges with wood glue rather than CA.

But you need to find your own path. There are a zillion different ways to do this. I would recommend following a known-good process for a while (and IMHO Chris's process is straightforward and easy to follow, and extremely well documented) to get a feel for things. Then start getting creative after you have a decent base of experience to work from.
 
https://spaceflightsystems.grc.nasa.gov/education/rocket/rktstab.html

<pedantic>The center of pressure is the point at which the all of the forces due to aerodynamic effects (lift and drag) resolve. It is the place where you could a apply a single force to a stationary rocket -- pushing on it with your finger -- and get the same effect as the action of aerodynamic forces on a rocket moving under thrust.

The center of mass of the rocket -- which coincides with the center of gravity -- is the point about which the unsupported rocket in flight will turn under the application of torques due to motor thrust or aerodynamic forces (or any other force). Since drag opposes the thrust, and increases with the cross-sectional area intersecting the fluid through which the rocket moves, putting the COP aft of the COM means that drag will tend to produce a torque opposite to the torque due to the thrust of the motor, or cross-winds, or anything else that might cause the rocket to tumble...

The weight -- the force of gravity on the rocket -- actually doesn't do much for aerodynamic stability one way or another. </pedantic>

I was trying to keep it simple. :)
 
Hey&#8230;welcome back!
Always room for one more.
The water&#8217;s fine!

I BAR&#8217;d almost two years ago, and was astounded with all of the changes that have taken place in the hobby since my own old fleet days in the 70s and early 80s.

I&#8217;m all caught up now and haven&#8217;t looked back!
Here are a couple essential websites that will have you virtually wallowing in model rocket nostalgia.

https://www.ninfinger.org/rockets/rockets.html
https://www.spacemodeling.org/jimz/rp00.htm
https://plans.rocketshoppe.com/

The first (ninfinger) has a lot of the old model rocketry publications, downloadable Estes/Centuri/Many Others vintage catalogs, ad fliers, tech reports&#8230;the whole nine yards.

JimZ and Ye Olde Rocket Shoppe have downloadable plans and patterns of nearly all of the old Estes, Centuri, MPC, FSI, MRI, AVI, etc., etc. vintage kits.

Add these to all of the suggestions above, and you can spend incredible amounts of hours serfing.
As well as information overload!

Be sure to check out my blog as well. Link is below.

Enjoy the Journey!

-Ed
 
Oh thank you!
I've been looking those old catalogs!
Those neurons in the back of my head haven't seen electricity in a very long time! (what a surprising dopamine release).

and forgive my ignorance: "BAR"??


EDIT: rockets that cost a dollar or 75 cents! It looks like a menu w/ 25 cent pie.
 
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