Keeping it Simple first self build

[dford]

After many years I have gotten back into rocketry. I now live in a near perfect area for flights and figured I'd get my son (five) interested. Hopefully his interest carries into many life aspects.
Anyhow, after building a few kit vehicles and the two stage hyper-bat (epic fail)(wind\weathercock) I figured I have enough hands on experience to build a mid power on my own.
So I bought the "Model Rocketry Handbook" and set off for the first of several custom builds.
Not sure how interested any of you will be in my KISS (keep it simple) build. Here I will pretty be using nothing super fancy and creating my own fin alignment jig out of "laminated" shipping foam.
So here it is. Please, anyone with suggestions please do suggest. This is my first mid power build and would be open for advice.
Picked up a 1/16 sheet of balsa wood and created a template off of a sheet of poster board. From my understanding TMRH (model rocketry handbook [I will reference this often]) says fin length should be twice the body tube diameter. I am using a BT-60 which is 1.6" I believe. I will snap a photo as soon as I can of my template with some distances and such I measured out. For now I have some other fin photos.

First off I will say my original idea was to bond two pieces of bass wood over balsa would to create a sandwich panel. Well, my panel warped rendering it useless. I clamped it together and everything using children's hardback books. Still warped. My second idea was to simply bond a measured portion of my template onto the same position on an entire fin. I sandwiched my entire fin this way and ran a library card from the bottom edge of the complete fin and the portioned fin to create the middle and right fin in this photo. As you can see I have also opted for a "through the wall" bond of the fin for added strength. I will also paper laminate these later for additional strength. I feel the thin balsa/wood filler combo is not nearly strong enough.

The fin to the right shows where I have measured at .3" and .5" and taped it off to maintain a general taper line.

After sanding for about three hours this is what I have come up with.

As you most likely already noticed, I am doing an eliptical shape with a through the wall fin attachment. I have opted for a "tear-drop" airfoil type skin shape as well. In order to achieve this I used a children's flat wood puzzle piece as a sanding block to get a general even sanded leading edge angle then broke the edge with finer sand paper to round it out. For the trailing edge of the tear drop I wrapped sand paper around a spent BP motor and sand next to the tape line I created. I then removed the tape and broke the tear drop smooth all around. Using the puzzle piece sanding block I did my best to taper the trailng edge into the tear drop. I continued a near knife edge on the very trailing edge portion. The leading edge is rounded gradually leading into the trailing edge near knife edge.

So that is the beginning of my build. I have ordered the 29mm motor mount tube, 29mm 40-120 aerotech casing, 300 lb fire proof Kevlar string, BT-60 body tube and nose cones. Ahh the nose cone. I searched high and low at big and small hardware stores as well as craft stores for a balsa wood block big enough for a nose cone. The closest thing I found was bass wood. I opted to purchase a set of nose cones for now. Considering I am using TMRH I will be conducting a swing test and cardboard cut out to find CG and CP relationships. If I find using basswood for a nose cone beneficial I will carve and sand my own.
I also plan to utilize radio shack to find parts for an ignition system. I will also be build my own launch pad.
The next step is creating a fin alignment jig at perfect 120 degree locations with absolutely straight placement.
I ordered a G76-7 reload for this flight. I may order a smaller E for the initial flight. I am also using a mylar space blanket as a parachute.
I will continue to post photos and updates as the build progresses. Indeed, I plan to KISS this build.

 

[dford]

Any suggestions are welcome and encouraged.

 

[Rex R]

one should keep in mind that the formula for fins (in the Book) is intended for low power rockets(up to about 1.3" dia.). while there is nothing wrong with it for larger rockets...the fins tend to get Huge in a hurry, also the rockets will usually be over stable. I have found that, in general a root edge of 1.25d and span of 1.25d works well.
swing testing; you're going to need a longer string (8 - 10') to properly test longer birds. I do recommend design software for mid power and up size birds, Open Rocket will handle most rockets and it is free.
I generally call 3/32" balsa(papered) as my minimum thickness for mpr rockets. there is a trick to papering fins, work fast, do both sides at one sitting, and let both sides dry at the same rate(goal is to have the same moisture levels on both sides). a 1" foam paint brush makes a nice spreader for white glue.
Glue:
white glue, carpenters wood glue, and tite bond 'no-drip' are my go-to glues for wood and paper rockets.
misc:
you should be thinking of 1/4" launch lugs(or rail buttons) for this size engine(F - G impulse motors), brass or Aluminum tubes will work. old windscreen wiper blades are a source of spring steel to make motor hooks from. have fun,
Rex

 

[dford]

The leading edge tear is literally the only portion of my fins that are 3/32. And that is only at the peak of the rounded portion. Minimum of 3/32 overall isn't a feature that is acquire able at this point unless I remake my fins. In your experience do you think the fins I currently have will break under thrust force? My hope was the additional 1/16 thickness added to the leading edge would suffice. Again, my hope is only what it is, hope. Not experience.

I have also downloaded openrocket onto my laptop and my phone. On my laptop I cant for the life of me get the dang thing to open and on my phone it opens but I am totally lost as how to use the program.

I never even thought about rail buttons. Certainly 1/4" lugs. The other question I have had is how necessary is a motor hook? I've read to not use them. Only to tape the thrust ring when inserted. Believe you me I thought the tape job was a little dinky application considering the motor being used.

Thanks for the heads up on papering. I will be sure to move quickly and efficiently.

 

[Rex R]

wasn't thinking so much about flight loads as to landing and handling/transport loads. flight loading isn't generally a problem under 400 mph. you will need to download and install 'Java' on your laptop to get OR to run, tis likely your phone already has java installed. Estes sells 29mm motor retainers that work well and are inexpensive(they also ship fast). I am a triffle leary of taping motors as a method of retention(of course not using single use motors does figure into it). I use a wire cooling rack(for baking) to let my fins dry evenly. mostly a simple rounding of leading/trailing edges will net most of the advantage of streamlining w/o the fragility.
Rex

 

[dford]

OpenRocket is finally a green light. I am now able to get a general idea where my rocket stands. Is there an ideal speed for chute deployment and speed for hitting the ground that would be beneficial for the rocket not to zipper or destroy itself upon landing? I noticed adding more weight to the front not only brought CG and CP into a decent range, it increased overall velocity at deployment also. But lowering the weight brought stability to 1.59 range yet slowed down chute deployment speed.

 

[dford]

Back home again, finally, I continue to keep it simple with the fin alignment jig. Body tubes and motor mounts should be here in a few days. I ordered plastic nose cones but after finally getting openrocket running I need to add weight to the nose and would really like to carve and shape my own out of balsa. I may even get on it with bass wood. We'll see.

Like I said. I'm trying to keep this simple. I used a CD case for a right angle. In my mind measuring out a specific distance on the X and Y axis until the hypotenuse measured 3 inches, marking the 1" and 2" locations and connecting them to the vertex would work. We'll it didnt. It equated to two at roughly 25 degrees and one 40 degree or there abouts.

Again, keeping it Simple and maybe even more simple than my first idea, I cut out a right angle and simply folded it into thirds. Yes the "fold" equated to a very small degree and it took a few tries to get it right. I ended up folding each side away from each other to minimize error. After tracing out each attempt I got the lines to land on each other and knew I had created an angle at 30 degrees. Added it to the 90, retraced my newly formed 120 degree and it landed perfect. I taped over my lines to add strength for tracing and cutting it out.

My wife recently purchased shelving that came with cheap styrofoam. I foolishly didn't even think about width before beginning. More on that later.
Anyhow, I white glued two pieces together only to make it a little thicker then taped the top and sides. I traced my new template out on the tape. I used the CD case to help hold my blade perpendicular to the foam while cutting sits and widening them for the fins. I also lined out four 90 angles matching the three 120 angles' vertex to help measure and find perfect center on the body tube.

As I mentioned, I foolishly never even thought about the width of the foam. I was more focused on the simplicity of establishing the 120 degree angle. Welp, the cheap foam isn't wide enough to hold a 41mm (1.6") body tube plus fins which measure about two tenths shy of double the tube width.
I am contemplating cutting the foam to the edges giving me three slices along with the body tube cut out and working the template larger around the outer edges by adding foam pieces, then rubber banding it once placed on the tube in position.
Or finding other, larger foam that will be large enough.
Keeping it simple, any recommendations in mind?

 

[KidShelleen]

Have you checked out the Alternate Fin Guide Tool on https://www.payloadbay.com/page-Tools.html?

 

[dford]

Have you checked out the Alternate Fin Guide Tool on https://www.payloadbay.com/page-Tools.html?

I read about it on another thread. My assumption was it was a site to purchase fin jigs. I now see it would make my life super easy. I feel a bit foolish.
I need to get to the library to use a computer to utilize this new opportunity.
Thanks.

 

[Rex R]

well ideal deployment speed would be zero...but to answer your question. one should aim to keep the speed in the zero to 22mph (32 ft/sec, lower is better) range and landing speed around 10mph(15fps).
Rex

 

[dford]

well ideal deployment speed would be zero...but to answer your question. one should aim to keep the speed in the zero to 22mph (32 ft/sec, lower is better) range and landing speed around 10mph(15fps).
Rex

My delay is at 7. Should have gotten a ten. OR says 8.7 or so. I think I'm going to crochet the shock cord before wrapping it around the chute. Hopefully that buys me a little more time before it opens so it dampens the initial shock. Do you know much about shroud rings? Or should I even venture I to it...
I'm also thinkin I'll be making a larger than normal chute with hopes it slows down on descent. Probably even lengthen the shroud lines.
I could be in for a long walk to recover my bird, but all of this already has been and is for, a real serious learning curve for my next build.
This is a bit different from building composite airplanes
I appreciate your input.

 

[Rex R]

before you get too bent out of shape about delays and cg points. wait until the bird is built and balanced and then update your simulation with those numbers (weight & cg) then see where you are with regard to delays. rockets tend to build heavier than initial expectations. speaking of cg, how long is this rocket going to be? Madcow figures their models at 1 cal of stability, I like to try for at least 1.2 cal.
Rex

 

[dford]

Welp, looks like I'm going to utilize a coupler and make a 20" Body tube with a 6" nose cone and .5" motor overhang. For some reason I was stuck on keeping it shorter would make it better. Toying with OR more is helping tremendously. I'll work the program more before shouting questions.

Update. I need to get rid about 3 seconds off of the delay and deployment hits 2.5m\s and ground hit reveals 6.7.
Not sure if it is possible this being my first time with a reload. Will continue research in this area.

 

[Rex R]

sounds like you are using the default parachute size . my guess is that you will need a chute somewhere in the 15" - 18" range(used my 'ranger' clone design file to 'guess' the weight, roughly 4 something oz.). remember to change the shroud line length when you change the size of the chute.
Rex

 

[dford]

I am at a 17" chute, 12" shroud lines using mylar I have a 26.8g chute. .98ounce or so. It could be heavier considering I am using a mylar space blanket. Stability is at .796
Aerotech has some advice on the delay issue I will be looking into more today.

Since I already have my fin guide template I found more foam material I'll tape together later today to make the jig also.
I am trying to keep the build moving along and be ready once the rest of the parts come in. Im not too privy on cutting MMT rings or an engine block until I confirm sizing, or else I would work that aspect right now.
Fins are papered. I'll post photos later today as well. I used security envelope paper, and a library card to make the glue line even. CA edges, 1000 grit any funky spots.
More on that later.

Update. After some review of TMRH double shroud linew of canopy width. Not much change adding 4" to the lines...

 

[dford]

Papered the fins. Buffed any issues with fine sand paper. I liked the security envelope because I could see the security lines to control depth. This wasnt a final photo, they came out pretty smooth. For a first papering i felt pretty okay about it. Does the CA always appear like this?
Light primer and a fine buff and the body work is finished on them, finally.

I now have a near finished jig. It isn't hard at all to make. Lets hope it works. I will dry fit the fins first for sure.
Waiting on body tube for an exact OD before I continue.

I'm debating on working motor mounts without final sanding any specific dimension. Just getting it close. More on that later.

Really looking forward to getting a package in the mail. Weather doesn't seem to have been on my side between here and south east colorado. Hopefully it arrIves on time, at least.
:marshmallow: I will be super happy whenever it gets here, for sure. :marshmallow:

I wonder if people mostly buy model rocket "model" kits of rockets, or build them on there own idea per scale...

 

[dford]

I have looked up the outer diameter of the MMT I ordered and these are the two inner holes for the centering rings. I'll finish the outer diameter tomorrow. The inner diameter reads about .007" or .2mm off from what my calipers read. Seven thousands is off more than my liking but for now it's good enough. I'll have to see a true measurement once the tube gets here.
I guess I yearn to continue building, doing something...

 

[Rex R]

Re: CA & paper
yup ca will do that, it will also lift most types of ink and raise the grain. a few passes with 320 grit usually takes care of the grain .
Rex

 

[dford]

Rex and I seem to have something going.
Others opinions are welcome!
My order came today. Lots to move forward on.



I bonded together and sandwich paneled a sheet of balsa between basswood for the fins. It didn't work as planned so I used it for centering rings and thrust ring (later). This is the INNER diameter of the body tube rough sand.

I sanded the inner ring to the outer diameter of the MMT.

This is what the BT looks like after the tape is pulled.

This is the taped off body tube. I did this so I could sand the seem back easier.

 

[dford]

Motor mount tube centering ring I made from scratch balsa,bass,balsa bond. It came out really well.

This is the centering rIng for the body tube. Yes it is off a hair, I feal like the bond line will circumvent the issue as wood glue states "stronger the wood"

Tomorrow we move on to bigger things. And Monday is a first, second prime day.

 

[dford]

For whatever reason I can't edit my post on my phone. The first photo is the OUTER diameter and second photo is inner diameter.

 

[dford]

I felt like I should add a final sand of the body tube

 

[dford]

Ya'll want me to continue or not?

 

[dhbarr]

I'm fascinated, and y'all are doing great work. We wouldn't keep coming back to view if it wasn't a great project

 

[dford]

I'm fascinated, and y'all are doing great work. We wouldn't keep coming back to view if it wasn't a great project

Mmmkay. I'll keep posting progress photos

 

[dford]

Looking back, I probably should have waited on the centering rings and traced out the actual body tube and motor mount. But I didn't so here it is.

I tack CA the two together for a more final finish to maintain uniformity.

These are them more finalized. My phone does no justice. They are more round than they look, I promise. The angles and shadowing throws them off.

I forgot to follow up with what I said I would do earlier. This is the template I used for the fins.

And then this. Yes. I am papering the centering rings. Why? Well, mostly because of the tiny gap as seen in the photo above once on the tube. In my mind these are critical components for a straight flight and I really want them to be perfect. Some of you may be wondering why in the world not just buy centering rings? Well mainly because I am trying to get away from buying kits. My next build I'm going to make a nose cone by hand also. I really enjoy building and sanding things to perfection. I also like saving money.
Anyhow, I papered the centering rings with the thought that paper is essentially wood anyhow, and the glue is stronger than wood, especially balsa-bass-balsa wood. So I papered them. I'll re-sand them as needed to get them even more perfect.
For now I'm letting them dry.
Next steps are cutting the motor tube, assembly of the motor mount which includes, centering rings and attaching shock cord to the motor mount. After I install the MMT assembly, I will be locating slots for the fins, attaching fins and doing fillets.
I still need to cut out and assemble my chute which I will probably do in between paint sessions after work this week.
Considering this is my first mid power build and first use of composite propelled I need to build a launch controller. That should be fun times. Also a launch pad. Which should be pretty easy.

 

[Flyfalcons]

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

 

[Cabernut]

Looks like you're making good progress!

The most effective(easiest & accurate) method I have used so far to cut centering rings without a drill press is to use OR to create and print a template, which I then glue on to the material. Then trace the template with an x-acto.

When you do the launch controller, please do a thread. That's one thing I would also like to build. It's nice to see how others are doing things.

 

[dford]

Sure thing. I'll make a thread for the controller. I'm planning on utilizing radio shack a lot for it. Bells n whistles n all...!

 

[dford]

It gives me great pleasure to introduce you to my motor mount. I cut the tube to roughly 5.25". I will most likely do a little fine sanding on the rings before sliding it into the body tube. I also took heed to Rexs' advice with a motor hook. Especially because i am using an RMS i dont want to lose the pricey casing because I didn't take a little time to install one. Yes, it is a little dinky but I figured I would tape the thrust ring and have a small motor hook as a backup. I used my wife's bobby pin. As soon as she woke up and saw it, "is that my bobby pin?"

Yes, yes it is.
Anyhow, I cut small notches in both centering rings for the hook and Kevlar shock cord which I cut to a little longer than three body tube lengths. I also placed one dab on the knot portion of the slip knot around the MMT. Still slippy, stronger hold.