Overbuilding Modrocs

Hi Gang,

I have been musing over various threads concerning building techniques for BP model rockets, an I want to state right out of the gate that this thread is not meant to be critical, but I am just curious about what others are thinking/building.

I am pleased with the advances in building techniques, and glue-technology. I use yellow glue, CA, and a bit of epoxy here and there.... I have however seen what I see as a trend of overbuilding of BT-60 and smaller modrocs.

Although most of us on the forum fly for fun vs competition, I personally have no desire to glass tubes and cones, add G10 fins, have epoxy laden fin cans and motor mounts for BP powered sport rockets under 2" in diameter.

My impression of model rockets is to build an inexpensive, lightweight rocket for max flight characteristics, including altitude. The heavy duty techniques borrowed from Mid and HP do add considerable strength, but they also add a ton of weight to a BP powered rocket.

Yes, I am sad when I prang a nice project, (I just bounced my BT-60 Blue Bird Zero clone when it hung on the launch rod.) But on the other hand, I just thisweekend launched and recovered my first rocket: a 1971 Gobln that my dad built for me when I was 6. (That is a small bird for a D engine).

Of course, glassing a 'touring' rocket that will be hammered by UPS and launched by many hands needs a bit of extra strength. I also feel that if you are going to fly a modroc on AP motors, then you need to boost your construction accordingly.

I was just wondering how others feel about 'heavy duty' building of modrocs.

What's the difference? I build them my way, for me, and others build them their way, as they see fit. If I want to use polyurethane glue to secure a motor mount in a Goblin clone, which I did last night, then It's my money and that particular choice isn't going to make the rocket less flight worthy or durable. I don't care for white glue for most projects. That is a personal opinion, and not of any consequense to anyone else.
I like to use more progressive adhesives, though I have been using yellow glue a little more on things like assembling a motor mount. Of course, I used the outdoor rated kind, which might seem like overkill to some folks.

Great Goblin, by the way. I printed the decals for my clone on inkjet paper, and will probably go for orange and black paint in keeping with the coming holiday. If it looks presentable after it is finished, I'll be sure to post a picture of it. Hopefully my son will be flying it in thirty years.

I agree in theory. Other than the shock cords, it's possible to get a large number of flights from a stock estes kit built with white glue. I must say I often add larger motor mounts and build accordingly. I also try stuff out on modrocs which technically may classify as overbuilt. Certainly nothing wrong with that, whatever makes it fun for you. I happen to have used polyurethane glue on the MMT on my Estes Cluster Bomb that's currently in the finishing phase.

My last modroc was intentionally overbuilt. I was practicing the techniques I'd use a month later when scratchbuilding my Level 1 bird.

The CC Express was heavy, yes, with most of a double-syringe of 5min epoxy and TTW-mounted basswood fins... but she's darn near indestructible as far as modrocs go. At least the ones I've built.

The Wizard I built just before that was simply tacked together with CA and painted over, and aside from having to replace the shock cord after only three flights (it was literally hanging from a single charred thread ) it's just fine.

I recently helped my son build his first wood finned rocket, a Fat Boy. I ALWAYS substitute lite ply for main fins in model rockets, except gliders and throwaways. The stuff is at least three times as tough as balsa and twice as strong as basswood. Anyway, I went against my better judgment and built the Fat Boy fins stock, figuring that it was thick balsa and fairly hard compared to some I've seen. Don't you know, on the second launch the little rocket cracked a fin on landing. I was able to quickly repair it with thick CA, and it flew again that day, but the fin will have to be refinished. I guess the boy will learn that s**t happens, fix it and move on, but he could have also learned that I generally don't use balsa so that doesn't happen. The lite ply is a little heavier and costs a few cents more, but repairing the fin will also cost a little when you figure in the adhesive, sandpaper, masking and paint. Not to mention the time involved in the repair.
I see others here are reinforcing the balsa with cardstock and paper laminates. This would be just as heavy as the lite ply, and just as expensive.
So is the lite ply or laminate overbuilding? In my experience, not really. I am sure that many balsa finned rockets have flown for decades without mishap, and that's great, but I can't count the balsa fins I've seen cracked, chipped or just plain snapped off. Sometimes it might be a case of underbuilding. Just because something has been done in a traditional manner with certain materials since time began, doesn't mean that there isn't a better way now. Kevlar shock cord mounts are a perfect example. They are now becoming an accepted or even expected mod of low power rockets. A few years ago anybody who would have the temerity to put kevlar in a model rocket would have been the butt of a few jokes, I'm sure.
When my son builds rockets he will view balsa finstock as a highly specialized material, suitable for certain specific purposes only. Lite ply will be his material of choice. This is the opposite of what many of us do now, but may be the wave of the future. Of course, there is no way to know that at the moment, is there?

This is exactly the type of discussion I was hoping for. I agree that lite ply is probably a better bet for certain designs, like the Fatboy. I guess that I am a sentimentalist when it comes to balsa.

I am a total fan of CA glue and use it liberally to soak body tubes up near the nose cone.

Fred

(I re-read this before I hit submit-reply and realized my rant here could be taken wrong. this is not intended as flames for any of the posters here, it's just a general rant. thanks and


great topic! I've been thinking about this for quite a while. I have seen a LOT of epoxy-abuse in rocketry in the last year. people just put tons of goop on - that is not how epoxy or any glue works, people!!

and then, insult to injury - and I have seen this a bunch lately - people chop up carbon fiber or kevlar to make filler out of their buckets of epoxy goop. that's like using old growth forest timber to make freaking matchsticks!!! what a waste and what an insult to the material. carbon fiber and kevlar are really great materials but they do not work best in short strands. besides, the supposed advantages of CSM as bulk material was disproved 40 years ago.

at a launch recently a fellow was showing me a couple of his birds. they were way over built - nearly 100% overweight - and he was proud of that fact. now he has to put way bigger motors in them to get them to even lift off. sturdy as heck, sure, but where is the elegence, where is the finesse, where is the "just right" engineering that gives you that glow of satisfaction knowing you made the compromises and the results are just GREAT?


put me firmly in the "simplify and add lightness" school of thought. yellow glue is the best stuff on cardboard and balsa. wanna know my deepest secret? I used yellow glue on the crayon rocket - the same one we used for Level 1 qual flights. it's plenty sturdy, it's lasted a dozen high powered flights and it's ready for more. (it's retired for emotional reasons. though.)


I got some trouble saying this in the V2 thread but here goes again. people take a perfectly good rocket like the Estes V2 kit and they don't like the fins so they use way oversized plywood and then they glue the whole thing together with epoxy and put epoxy fillets on the fin seams and over-paint the whole mess and then the rocket is 50% overweight and guess what? yeah it won't fly on E9s any more, hey must be Estes' fault, what a crummy kit!

gee, my Estes V2 was built with the same thin plastic fins and it flies just fine on E9s. I wish Estes made E15s but what the heck. we even put RMS F12J-3s in the V2 and it flies just fine.


I sure understand powering up, putting bigger motors in a rocket. that's fun, good clean fun. "overbuilt" to accommodate bigger motors is fine, up to the practical limits of the design. but there's an art to it, overbuilding just the "right" amount... not sure how to quantify it but I know it when I see it. I think when you have to start adding nose weight to counter the weight of the motor, on an otherwise stable rocket, that's too much motor!!


as a point of comparison, a popular high power 4" V2 kit is comparable in size to the Estes V2 (BT-101). the HPR V2 weighs a lot more and the motors cost 4 times as much. granted the Estes V2 is not going 2000' but horses for courses, different rates for different freights, and all that... what's the better deal?

There has already been a lot of good discussion on this point and I don't know if I can really add anything. My bias is toward building light, without using the mother-of-all fillets, but with appropriate upgrades (most notably, better shock absorber cords). And while sympathizing with the lust for indestructable plywood fins, I am a fervent believer in laminated balsa for most low-power designs.
cls made a very good point about preserving the balance between sturdiness and performance, as far as the way the designer intended for the kit to be built. Since modrocs are so light to begin with, it doesn't take much added weight before you get a significant change in performance (and stability).
Several of you have also commented on excessive applications of epoxy and fiberglass. I think what scares me most about this is that we tend toward one of two outcomes: added weight in the rear reduces stability (I have talked to lots of folks at high-power launches that don't understand the basics of stability and control), or added nose ballast (to offset the heavy tail) makes the whole thing that much heavier and greatly increases the urgency of maintaining a visual track in the event of failure-to-deploy.
At the same time I can understand if someone chooses to build a heck-for-stout version, and has a launch location where they really can expect to fly the same bird several dozen times (and actually get it back!).
We all have to remember that we all have slightly different needs and preferences, and as long as we don't skewer some innocent bystander, it is just fine to 'play' with the assembly sequence.

We have a Big Bertha with 60+ flights, including 3 prangs and a D21T flight. Stock fins, recently upgraded to a nylon chute, and after the last prag it's zipper-less now. Otherwise, all woodglue.

Considering that, I am still the overbuilder...the Minie Magg I just finished came in at a staggering 6.5# The 6" Der V3 has two layers of glass on the tube, and one fin tip to fin tip, just to make sure it's all together...I just feel so much more comfortable with overbuilding, and then when they end up heavy, it's an excuse for a bigger motor!!!

There are a few reasons I tend to over build my modrocs.
One, most of my damage occurs during transport, not flying. Two, I frequently launch in a good breeze/wind, and use small chutes or streamers instead of chutes. Three, for durability. Fourth, and last reason is 3 years old

Ok, I want to put in my 2 cents worth..... I will only talk about myself here.......

I over build all the time....... This is why I don't built too many LPR kits.... For me, I think it has to do with not being as skilled..... If you are not sure about how strong the fin is on, add more epoxy!!!!

When I am not sure about the construction... add more epoxy..... when I am not sure about the weight...... add a bigger motor.......

Originally posted by DPatell
Considering that, I am still the overbuilder...the Minie Magg I just finished came in at a staggering 6.5#

Click to expand...

A friend/mentor of mine has a Minie Magg that weighs quite a bit... because he has >900g of nuts & bolts for nose weight in there. At least, he claims it's 900g... I think it's more! When he was beginning HPR, he wanted it to be stable on larger motors, so he did some simulations, and figured that's what he needed up there. Apparently short & stubby rockets have different stability requirements, you don't need a full caliber of static stability... but he's got it. And the nose weight is sealed in there with expanding foam, so there's no way to lighten it.

It flies great, though, and he's certified his first three levels on it. I suggested that he use the Minie Magg as a nosecone on a larger rocket for Level 4 to become the first person to ever do all four levels on one rocket, but he won't hear it.

I must agree with Astronboy and powderburner, my bias is also to build as light as the intended model will allow. I'm still flying models I built over 30 years ago outa paper, balsa,and Amborid model aircraft cement. Goblin below.. obtw halloween colors are Orange & black anyway..I have a feeling a lot of folks out here have forgoetten that model rockets ARE to be "Light Weight" by design as a safety issue.
Now heres the main point I wish to make. Every single model. mid-power and HRP model Rocket built is held together with adhesives. I don't give a tinkers Darn how many coats of glassed epoxy are applied it is still a Glue Joint holding these huge overweight monsters together. When the joint fails the model fails....and all that weight comes crashing down. LIGHTEN UP model rocket parts should almost float to the ground after a cato!
Rbeckey: you labor under the misconception that light aircraft plywood will hold up better than basswood.. it dosen't you arecorrect however as it is more expensive. Like you said, it's a free country, you can certainly spend your money anyway ya like.. but don't take offence when nice folks try to show you the follie of your spending ways. Is light ply appropriate for some fin applications.. Sure! for every application..nonsense! but whatever floats you boat Heavy up your shock cords, and should lines, Get back to using that double glue joint. CA your body tubes if you must but remember: Epoxy and CA become brittle over a short period of time, in a max of three years you really should be reworking those joints.
Could it be the the pregressive adhesives you are using do not have the properties that lend thenselves to long term flight use?? Dryed adhesive film flexibiltiy is something we all should be paying more attention to than now many wraps of fibreglass we're applying.
Overbuilding is not a good practice, We should help fellow rocketeers to understand WHY building Light and Durable is FAR better than Heavy building. Lets learn about the materials and products you use in consturction. sometimes newer is not better.

When it comes to "durability"... well...good ol' Elmer's white glue seems just fine after about 30 years.

Now that's durable!

sandman

Does anyone know how well yellow wood glue (Aliphatic) does after a number of yaers? Who has the oldest rocket built with yellow glue?

I'm with ya on the durabiltiy of white glue Sandman:

My clustered Saturn 1B, is all yellow elmor's caprenters glue fabrication. most recent flight on 4 C6-5's was Feb. of this year very close to her 31st birthday.

OOOhhh very nice: A testament to Good old yellow glue!!

This Cobra 1500 is white glue motor mount and Ambroid aircraft cement applied fins and fin fillets. I had to replace the rubberband shock cord and mount many years ago, with elastic, BK (before kevlar) She latest flight was in late 2002. No damage, still ready to go

Ambroid? I would think that this glue would end up too dry and brittle?

Ambriod cement is made specifically to be very flexible, with very long term elastic properties while withstanding many chemical reactions. It smells like all gee-wiz but model airplane builders have swarn by the stuff for generations. model aircraft wings flex like crazy and take an awful beating. This cement is Great for motor mounts and fin/body joints.

Astron,

I can tell you I have some R/C airplanes built with Alphaetic Resin and some build with CA that are around 20 years old...both are holding up well. Even the Epoxy that is used on each plane is holding up well; epoxy is used on one spot on all R/C aircraft...to join the wing halves using ply connectors.

This is a good subject to talk about, however I have noticed some of you getting oppinionated to the point of insulting...let's keep it friendly guys and remember that if it works for you, the other guy is not doing it wrong...just different. That is the beauty of this hobby...EVERYONE can do it their way and it works. Tell us all how you do things, because we may one day wish to try it or find an application for which we want to use your ideas. Please though, don't tell us that it's your way or the highway...it's only a hobby guys, not a way a life, which means show the same respect you fellow rocketeers show you, especially here in The Rocketry Forum. We have the rep of being a "builders/fliers" forum and will do our best to keep it that way. Ok, nuf said, back on subject...

I usually follow the mfgrs recommendations with low to mid power birds. I use Alphaetic Resin almost exclusively, some CA and tend to build pretty much stock. I have added some noseweight in the past so I could try a Mid Power on a larger motor, but it already had far forward fins thanks to the mfgr (TLP). Sometimes though, I prefer to use epoxy for fin attachment or fillets, but use it sparingly. I have built large rockets with Yellow glue and Micros with Epoxy, just to experiment. For example, I used micro thin G10 for fins on my MMX Harpoon, HARM, Maverick, IQSY Tomahawk and others and even though it is G10, it added very little weight. Since it was G10, I had to use epoxy as an adhesive, however, all of them fly extremely well and get great altitudes. Also, it is very sturdy and looks more scale for thickness.

I am with Dick on the shock cord thing; it's the one weakness I see in kits. What I have noticed though in this topic is some people using big fillets and such, but they may have been refering to HPR...which is a whole different world. This thread I think was dedicated to LPR and MPR, so I will stay on topic. Once again though, if it works for ya, have at it. We may wish to start a different thread for HPR as there is a wide variety of build styles that can be used in that arena.

About the only thing I get carried away with is the finish. I use quite a bit of primer to get the surface the way I want, then pretty much use the thicker/heavier Krylon paints. However, that is one thing I will not give on is my finish, even if it adds weight.

Just my oppinion guys

Carl

OBTW, I do have an example of an old Estes rubber band (not even elastic) being better than Kevlar. My Mean Machine still had the original cord. I generally have kept the original cords and just inspect them before launch. When they show wear, they get upgraded to Kevlar or Kevlar/elastic. Back to the story. The Machine hung on some high wires (power or phone) and dangled there for most of the launch. The cord finally broke and the pieces were recovered. If I had upgraded to Kevlar, it may still be there

I used to build heavy myself.
and still do If I'm purposely overpowering an estes kit.but I treat that as a different thing

normaly
I only use epoxy on estes type rockets if it's the best bond between dissimular materials.
and only enough to glue the part on. large epoxy fillets on a modroc.basically kills the whole idea behind the design
epoxy is HEAVY no other way around it.
tip....try weldbond... its very good on dissimular materials

Once again I have to agree with micro

basswood is a MUCH better choice for upgrading balsa fins.

it's a well proven fact ,the strength to weight ratio of basswood is superior to ply by a large margin (or "lite" ply....lol).

It makes no sense from a strength or weight issue to skip over basswood and use ply on a modroc or even midroc .

plus basswood seems easier to cut and sand and you dont have to deal with the layers and splinters when you bevel the fins.

It kinda bothers me that too many people seem to jump from balsa to ply like it's the ultimate material.......but not in this case, sorry

save the ply for hpr

I agree with Carl, let's keep this thread civil. My original question was directed at Model Rockets, not even mid-power. I do not fly HPR, and all that I know is that they require much sturdier parts and techniques than BP poweered model rockets. My original intent was directed to 1/4A-C powered model rockets, and my observation that some modelers are building these rockets using heavy duty construction techniques.

If you want to go that route, hey, knock yourself out. It is your time and money. The great thing about this hobby is the way that everyone does something a bit differently.

My only real concern I see is is that of safety. A 'stock built' low power rocket is light and fragile. The same rocket can be glassed, with plywood TTW fins and epoxied together. Both will fly, but the glassed bird will be heavier, may need a larger motor, and will not perform as well (altitide wise) as the 'stock' version. If something should go wrong, then a glassed and epoxied rocket is more of a safety concern, whether weathercocking severely, going unstable, or a recovery system failure.

I know that it can be a real letdown when a rocket is damaged. Hey it happens to me all the time. But that is par for the course as far as I am concerned.

Anyway, I thought that for the most part, this thread has generated some excellent friendly debate and discussion about various techniques and the advantages/disadvantages of each.

Lets keep it fun.