Keeping it Simple first self build

[dford]

I was just about to suggest a paper shim for the centering rings. That should work well.

Great minds think alike

 

[martinjaymckee]

This is coming together nicely. I think designing and building new designs is my most favorite part of the hobby. There's nothing quite like taking a batty idea and stack of raw materials, and turning it into a functioning, flying "thing" ( I love my planes too ).

You have me beat on craftsmanship though. There is no love lost between myself and sanding. I avoid it, when possible.

Martin Jay McKee

 

[Rex R]

how long are the fin tabs and how does that compare to the distance between the centering rings? if you planned on having the tabs in contact with both rings, then you will need to notch the tab to allow for the cord around the tube. I could say something about leaving the rear ring unglued so that one could do internal filets...but trying to apply glue in the amount of space that you have(bt60 > 29mm motor tube) would be messy at best but you might keep that in mind for larger builds .
Rex

 

[Rex R]

suggest that you read up on the double glue method and use it(if using wood glue), otherwise the double(or multiple) dip for epoxy.
Rex

 

[dford]

Oh dang. I never even thought to place the fins in contact (top-bottom) with rings. Man that would be far more durable. I've done one kit through the wall and don't think it instructed to do so. But that totally makes sense.

I really wish I had left the upper ring off now also! Could have killed three birds one stone there. Fin tab fillet, internal lower ring fillet (upper body side) or vice vetsa and tabs sandwiched by centering rings.
Learning curve.
I place fillets on pretty much every bond point. I'll CA the corner of a library card to a wood dowel to at least get some fillets on the upper ring.
I have a bunch of fiberglass leftover from my old job I'm thinking of using in the future. I'm leary of using epoxy for wood builds for some reason, for now. Maybe because I'm so used to using it for carbon fiber and fiberglass only. Habits...

 

[martinjaymckee]

For wood-wood bonds, I certainly recommend using a proper wood glue. It really does create a bond that is stronger than the glue -- there's no reason to use anything else. Same, really, for wood-cardboard. On larger builds ( large MPR and HPR ) with traditional modeling materials, I often do use epoxy on the fin/motor mount assembly, but mostly because it does such a good job creating fillets. Wood glue just doesn't have a viscosity high enough to do anything similar without running. Besides, epoxy has excellent dimensional stability through the entire set, as opposed to the shrinkage typical of wood glues. Because of that ability to create a nice large, smooth, fillet, I prefer epoxy on fins, but, it does add weight in contrast to other options. Of course, if multiple materials are being joined, the best options begin to change.

Unless I am building a minimum-diameter bird, I always go through the wall and but up the centering rings. Not only is it much stronger, it actually makes alignment of the parts an absolute breeze.

Cheers,
Martin Jay McKee

 

[dford]

I wake up super early usually to build without bother from my kids. This morning I woke up a little later and they woke up early. That along with other frustrations, it was a bad morning.
The jig was pretty shot ty at best. It is going straight in the trash after this.

I redrew the angles to locate where the fins should go on the body tube. I also lined out a launch lug line close to in line with the motor hook and fin in hopes to reduce drag.


I ran into problems with the fin slots on the jig being too wide and long. The fins wouldn't hold tight in place so I had to shim them as best I could once I began glueing. So much I didn't even snap a photo before I set it to dry. I did however double glue them on both points of contact, the fin tab and MMT.

Before glueing and whatnot I measured the distance between body tube and MMT. It read something like 6.07mm. I had left the fin tabs long enough on the template to trim them for this reason. So I did and followed as described in the above photo description.

Basically I learned that cheap foam really sucks to work with and I need to make a way better jig. Trying to keep this simple as such really sacrificed this steps ease. I feel like I got it right but not after a lot of added stress that could have been avoided.

Once the fins dry I'll shoot a photo of it and the MMT installed which I forgot to do but really it isn't much to see.

 

[Rex R]

I like to do the final adjustment of the fin slots until after the fins are ready to install(fins and slots are indexed), I like to leave the slots just tight enough to hold the fins in place. easy enough to adjust slot width with a dremel sanding disk.
think most folks radius their fin guides at the tube fin interface so as to reduce the chance of glueing the guide to the rocket .
Rex

 

[dford]

I like to do the final adjustment of the fin slots until after the fins are ready to install(fins and slots are indexed), I like to leave the slots just tight enough to hold the fins in place. easy enough to adjust slot width with a dremel sanding disk.
think most folks radius their fin guides at the tube fin interface so as to reduce the chance of glueing the guide to the rocket .
Rex

What kind of material do you use for a jig? I'm thinking about going with the flower arrangement type foam next time.
How thick of material to you use? The wheel on the dremel doesn't seem to trim super deep.
I can certainly see the benefit of waiting until right before install final adjustment. In my mind (now) the slot should represent a crescent moon on both sides sort of speak with the fin thickness at the crescent.
Having the body tube area notched out for the glue was in my mind. The foam really irritated me to the point I missed the step and widened the slots too far giving me issues.

The slots on the body tube for the "through the wall install" seemed to pinch the fin and push it back away from the MMT which in turn I had to finagle my exact in there to pull the wall off and out the fin.
I trimmed the fin slots on the body tube larger to prevent this during the dry fitting and they slid in nicely. Of course once I went for the actual bond it happened again.
:y:frustration:y:
Not sure if you have had this pinch\reject push out of the fin, but do you think it could have been the jig squeezing the tube so much it narrowed the diameter of the tube? Even after a dry fit? It errked me pretty good I tell you what.

I decided to paint it lime green. It'll be called "the booger" due to this fin jig booger of a problem!

 

[Rex R]

use the MK 1 eyeball(which is probably how I got one fin leaning on my 'jart', which given Murphy & Finagle...that fin will stay firmly in place till the end of time ). think most people use 1/4" foam board for 'fin jigs'.
I don't use a dremel to cut the slots in the tube(angle aluminum and hobby knife). I suspect that you didn't have the mmt glued in place when you fitted the fins/slots, and when the glue dried (and shrank) it distorted your tube a bit (search for 'coke bottle effect' for more info), this is less of a problem with heavier walled tubes. or the tube might have swelled due to a change in humidity, such are the joys of using Estes type thinwall tubing. some people use; emery boards or popsicle sticks wrapped with sandpaper to sand slots(which works nicely for paper tubes, rather slow going with fg tubes).
main thing is to remember that this is a hobby, its' supposed to be fun, and that most rockets look good from 10' away . also you get a fair amount of slack for your 1st few scratch builds as you get some practice doing new things(we were not born knowing how to build rockets). you will likely get better the more you build.
Don't forget, your launch guides go on before you paint .
Rex

 

[Cabernut]

...Don't forget, your launch guides go on before you paint .
Rex

I still have the hardest time remembering that myself...

For me, fin jigs were more trouble than they're worth. Now I just put one fin on at a time with high-tack glue and just eyeball it.

Sometimes I'll put a spent motor in the end so I get a good center point for the tube, then use a ruler to make sure the fin lines up with the center.

...forgot to mention, one of my TTW builds had the coke-bottle thing going on - noticed after the glue dried - so I just filled in the rest with CWF and moved on.

 

[dford]

use the MK 1 eyeball(which is probably how I got one fin leaning on my 'jart', which given Murphy & Finagle...that fin will stay firmly in place till the end of time ). think most people use 1/4" foam board for 'fin jigs'.
I don't use a dremel to cut the slots in the tube(angle aluminum and hobby knife). I suspect that you didn't have the mmt glued in place when you fitted the fins/slots, and when the glue dried (and shrank) it distorted your tube a bit (search for 'coke bottle effect' for more info), this is less of a problem with heavier walled tubes. or the tube might have swelled due to a change in humidity, such are the joys of using Estes type thinwall tubing. some people use; emery boards or popsicle sticks wrapped with sandpaper to sand slots(which works nicely for paper tubes, rather slow going with fg tubes).
main thing is to remember that this is a hobby, its' supposed to be fun, and that most rockets look good from 10' away . also you get a fair amount of slack for your 1st few scratch builds as you get some practice doing new things(we were not born knowing how to build rockets). you will likely get better the more you build.
Don't forget, your launch guides go on before you paint .
Rex

I'm known to take things to the extreme and I was getting into that point earlier. Thanks for the head check because it is really a fun hobby. I will for sure utilize all of your tips on the next build.

 

[dford]

Yup. I did it. Went to what I know, epoxy. I felt like the fins weren't setting enough in the tube making contact with the mmt.

I waited about 12 hours for the wood glue to dry. While it probably wasn't quite long enough for it to fully dry, I wasn't too worried since I wasn't placing epoxy fillets over the wood glue.
I made them large enough to feel comfortable with the surface area covered for strength.
If I had followed steps suggested earlier, I would make these fillets much smaller I think. Mostly to save weight.
Rex was right. The aft end is going to be quite a bit heavier now.

 

[dford]

....progressive prime sanding and painting....

I used pen tubes as launch lugs. Large clicky type.

 

[Flyfalcons]

Looking good. Those epoxy joints look like they'll stand up to a ton of punishment.

 

[dford]

Been working a lot lately. Finding time for rocketry has been slim. But this is it. Learned a lot this build. I think the next rocket will be named El Turd. Haha. Thanks to all for input.

El Booger

Boogers

Aft end

Launch is planned for tomorrow weather pending. I'll try to video it.

 

[dford]

One more question, do you guys wet send the clear coat like the primer?

 

[Rex R]

yes, you don't want the 'paint' to get warm and soften while you're sanding it. though when sanding a 'paper' rocket it is more like damp sanding. looks good as viewed from here. good luck tomorrow.
Rex

 

[martinjaymckee]

Good luck! It looks like it should fly beautifully.

Cheers,
Martin Jay McKee

 

[dford]

Welp. Humbling experience. All around. I should never have sandwich paneled bass balsa bass for centering rings and thought I could easily create something strong enough for flight with the G76.
My absolute best guess judging by the pieces I found is they broke and the motor shredded the entire rocket. I found wings, nose cone, chute and bits of fuselage. All of it glittering the Mojave Desert sky as it tumbled back toward earth. A faint "puff" somewhere yonder signaled delay charge and casing never to be found after a solid 4 hours of searching.
Examining the pieces, judging by the nose cone which the shock cord connecting "hoop" had been lacerated perfectly through, the piece of body tubing with a small bit of centering wood still attached and the chute shrouds perfectly sliced along with the 4 inch tear\burn in the chute I'm convinced the motor mount centering rings were the culprit of stress failure.
I have already ordered a replacement RMS and "factory" centering rings.

This is certainly not the end, rather the beginning.

 

[Steve Shannon]

When laminating for maximum resistance to bending, the outermost layers are the strength layers. Balsa is great as a core; not quite as good as an outside layer.
What did it look like taking off? Did you see it shred? I don't know enough about your rocket to know whether it was centering rings failing (which I don't recall ever seeing except right at launch), fin flutter, which I've seen quite a few times, or something else entirely like drag separation, but I greatly respect that you're getting right back into it.
It sounds as though your rocket failed at high velocity.

 

[Rex R]

do you have(or can take) any photos of the fins post flight that you could post? I would guess that the bond between the fin tabs and the motor mount tube failed 1st, then the mount moved. been my experience that, when built properly the centering rings carry very little thrust load with TTW fins. the fins transfer the thrust load directly from the MMt to the airframe. I have used cardstock/foam/cardstock sandwich rings w/ TTW fins(1/8" balsa w/cardstock skins) and everything moved as a unit at launch. I will grant that they were small impulse motors, but they were lightweight rockets .
Rex

 

[Rex R]

p.s. my bad, should have stressed the importance of securing the motor hook before launch. a couple wraps of masking tape or safety wire will keep the hook from being forced open and allowing the casing to be ejected from the mount. sorry about that.
Rex

 

[cavecentral]

Interesting build. Minus you motor mount issue, it looks pretty good. I will say, this looked like anything but keeping it simple! I was expecting this to be a basic scratch build from all store bought parts with little (if any modifications), as opposed to buying a kit.

The tear drop on the leading edge of the fin is new to me.

1/8" 3=ply Baltic birch will do fine for centering rings if you wanted to cut your own with a fly cutter / drill press. Scroll saws work too if you have a circle cutting jig that you rotate the wood on a pin. I've made some sloppy centering rings with the scroll saw free hand.

 

[dford]

Clean snap through the nose cone "eye"

Bits and pieces


So the fins intrigued me. My son decided to snap them in half when I was looking in the field. Trust me, I wasn't happy about it. Anyhow the intriguing part is, is that the number two fin to the left has most of the root in tact. The two to the right have a chunk missing from the trailing edge. That is why it led me to believe the centering rings failed. But now you all mention it, the flight reached if I had to guess along with my wife's ATC trained eyes, around 1000 feet before confetti flew. The rings probably didn't fail.
I can only assume I didn't get enough contact TTW to the MMT and the paper gave way. That is my best guess, yet Im not exactly well versed in rocketry.

 

[dford]

Interesting build. Minus you motor mount issue, it looks pretty good. I will say, this looked like anything but keeping it simple! I was expecting this to be a basic scratch build from all store bought parts with little (if any modifications), as opposed to buying a kit.

The tear drop on the leading edge of the fin is new to me.

1/8" 3=ply Baltic birch will do fine for centering rings if you wanted to cut your own with a fly cutter / drill press. Scroll saws work too if you have a circle cutting jig that you rotate the wood on a pin. I've made some sloppy centering rings with the scroll saw free hand.

I suppose my intention was to use as many common tools and household items to keep it simple and keep the design simple. I agree it did become kind of "not simple". I already canceled the centering rIng order. Can't do it. I use a dremel at varying speed to sand them. I've fabricated some pretty tight tolerance stuff free hand for a living. My biggest problem is not having the space to do it in where I currently live.

Birch seems heavier. This was my first mid power. I found out real quick how much more thrust these motors have. The weight isn't a huge issue it seems birch to bass n what not.

Trust you me I wanted to build the body tubes myself too but decided to buy some for safety sake.

And now look. Hahahaha

 

[dford]

do you have(or can take) any photos of the fins post flight that you could post? I would guess that the bond between the fin tabs and the motor mount tube failed 1st, then the mount moved. been my experience that, when built properly the centering rings carry very little thrust load with TTW fins. the fins transfer the thrust load directly from the MMt to the airframe. I have used cardstock/foam/cardstock sandwich rings w/ TTW fins(1/8" balsa w/cardstock skins) and everything moved as a unit at launch. I will grant that they were small impulse motors, but they were lightweight rockets .
Rex

I'm guessing what you are guessing.

 

[cavecentral]

Sounds like a shred. The motor mount probably would have gave away right on the pad and slammed up into the nose cone.

A G76 is a pretty good powered motor. Un-reinforced BT-60 / Estes is a bit weak for that power on a very light rocket. Try a LOC 1.52 w/ nose cone. That is a thick tube as it is also the 38mm motor mount tube.

I'm guessing some people here may have the skill / technique to pull it off. I do not without fiberglassing the tube.

 

[dford]

p.s. my bad, should have stressed the importance of securing the motor hook before launch. a couple wraps of masking tape or safety wire will keep the hook from being forced open and allowing the casing to be ejected from the mount. sorry about that.
Rex

I bent the motor hook with needle nose around the aft closer slot, then taped electrical tape around the hook, closure and .25" over hang of the MMT

 

[dford]

Sounds like a shred. The motor mount probably would have gave away right on the pad and slammed up into the nose cone.

A G76 is a pretty good powered motor. Un-reinforced BT-60 / Estes is a bit weak for that power on a very light rocket. Try a LOC 1.52 w/ nose cone. That is a thick tube as it is also the 38mm motor mount tube.

I'm guessing some people here may have the skill / technique to pull it off. I do not without fiberglassing the tube.

Does Estes = Apogee? I technically had an "apogee" airframe.
If I remember correctly Rex did mention something about the airframe not being strong enough a while ago....:eyepop: