How to (re)build a Rocketry Warehouse Formula 200 booster.

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Bat-mite

Rocketeer in MD
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As some of you know and the rest don't care, I catoed my Formula 200 a few months ago when an EX motor blew the forward closure. The result was that the epoxy bonding the booster, MMT, CRs, etc., completed melted, leaving the booster looking like a mess of spaghetti. If you never knew why they call it "fiber" glass, you would after seeing that carnage.

Well, now, thanks to the government shutdown, I took today off. My wife and kids are out of the house, and I have time to get this build thread going.

This is my rebuild of the Formula 200 (8" D, 124" tall) booster, including MMT and fins.

I will upload what I've done so far, and add as I go.

I intend to make this useful to newbies to fiberglass, epoxy, and large rockets. You more experienced guys may find it boring.

STEP 1 -- Wash the fiberglass parts.

Always wash your fiberglass parts when they are new. They are covered in chemicals that are not good for your skin, nor will they bond well to adhesives.

I use plain old dish detergent and do it in the bathtub.

IMG_2495.jpg IMG_2496.jpg

Dry with a soft towel, or let air dry as you see fit.

STEP 2 -- Sand the parts.

Sand all parts of fiberglass that will be epoxied, starting here with the MMT, fin tabs, and edges of CRs.

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STEP 3 -- Measure / mark airframe for rail buttons.

I use a piece of aluminum angle to get a straight edge on a round tube. I wanted my aft button near the bottom of the booster (but above the bottom CR), and my forward button about where the CP will be.

IMG_2506.jpg IMG_2507.jpg

STEP 4 -- Check fit of fins in slots.

Always good to make sure the fins will fit before you start gluing things. In my case, they fit prefectly, so no widening or lengthening of the fin slots was necessary. If it had been, then I would have done it with a Dremel.

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STEP 5 -- Prepare to drill CRs for threaded rods and U-bolts.

I used a paper template from PayloadBay.com to get the precise measurements for my threaded rods. Since I already have an aluminum thrust plate that survived the cato unscathed, I needed my CRs to match so that the T-rods wouldn't be bent.

I hand scribbled where the U-bolts would be in the top CR. The U-bolts are recovery attachment points. Simple trace around the U-bolts with a Sharpie.

Why are the U-bolts off-center? I didn't want one to straddle a T-rod, so I offset them. If the MMT is built correctly, it will withstand plenty of force from the harness, so I am not worried about it.

IMG_2504.jpg
 
STEP 6 -- Drill the CRs.

To get my CRs even, I put them on the MMT, then tightly taped them together with masking tape. I then taped the PayloadBay.com template on top.

I used a simple Harbor Freight drill press. I drilled through all three CRs for the T-rods, then I removed all the tape. I increased the bit size, then drilled through the top CR for the U-bolts.

By putting a piece of wood under the CRs, I eliminated shredding of the FG around the holes.

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STEP 7 -- Attach the U-bolts to the top CR.

I used nylon insert nuts, and a little RocketPoxy, to secure the U-bolts. Once the MMT is inserted and glued in, I will not have access to the nuts. So they have to last as long as the rocket.

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STEP 8 -- Assemble the MMT for marking.

This is the trickiest part! The top CR can be anywhere, but I prefer it close to the top of the MMT for strength. The bottom CR will be put on after the fins are in. But the middle CR has to be exactly above the fin slots, such that the MMT sticks out of the booster to the exact measurement for the thrust plate.

BTW, the thrust plate does not come with the kit. I got it from S.C. Precision.

So, I assembled the MMT with CRs dry, measured and marked for the top CR and middle CR. The top nuts on the T-rods are nylon insert nuts. T-rods, nuts and washers are #10-24 aluminum.

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STEP 9 -- Epoxy the top CR to the MMT.

I removed the other CRs and T-rods, and placed the top CR onto the MMT. The gap was pretty big, so it needed some support.

IMPORTANT!!! Make sure you put your top CR on with the U-bolts going in the right direction!

I used duct tape under the top CR to make sure it was even with my marking. Then I epoxied the top and let it dry.

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STEP 10 -- Epoxy the middle CR to the MMT.

Now for the crucial middle CR! Even though I already marked it, I wanted to be absolutely sure it was in the right spot on the MMT.

So I reattached the other CRs and T-rods, but I also added the thrust plate.

IMG_2522.jpg

I then held the entire assembly against the booster so that the thrust plate was where it will be nestled into the aft end of the booster.



I confirmed that indeed my middle CR was just at the top of the fin slots, all the way around.

I then epoxied the top of the middle CR.

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Last edited:
Batmite, the shutdown is over...

Almost before it began...

We got a sweet new...

2 year deal for the US...

DVmHbpBV4AA1MWO.jpg
 
Batmite, the shutdown is over...

Almost before it began...

We got a sweet new...

2 year deal for the US...

I know, right? I woke up at 6:45, called my agency, heard we were shut down, said to the wife, "Let's go out for breakfast and do a little shopping." Got home at 11:00 and found out I could have gone in to work. Ah, well, three day weekend for me.
 
Thanks Bat! I love Formulas and am about to start on my 98 which is my first fiberglass build so this is super relevant to a glass noob like me!
 
STEP 11 -- Epoxy bottom of middle CR.

Since I expect the tops of the fin tabs to butt against the middle CR, I did not want to put a full circle fillet on the bottom of the middle CR. Since it will bear absolutely no load, a little tacking is sufficient.

I tacked behind the T-rods where I know the fins won't be.

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STEP 12 -- Sand inside booster.

Since the booster will have the CRs and rail button nuts epoxied to it, it needs to be sanded. The booster is 4.5' long, so I made a little sanding tool.

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Here are some pictures of the sanded insides.

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To get rid of the nasty FG dust, another rinse in the shower was in order. I included this picture as a visual reminder not to epoxy your MMT in without getting rid of the dust.

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. . . Since I expect the tops of the fin tabs to butt against the middle CR, I did not want to put a full circle fillet on the bottom of the middle CR. Since it will bear absolutely no load, a little tacking is sufficient . . .

I guess that if you are using a thrust plate then the centering rings don't need to do anything but keep the motor tube centered because all the propulsion force gets transferred directly to the airframe tube.

I don't use thrust plates, so I apply big fillets to the middle CR and then use the belt sander to notch the fin tabs just enough to allow space for the fillets.
 
I guess that if you are using a thrust plate then the centering rings don't need to do anything but keep the motor tube centered because all the propulsion force gets transferred directly to the airframe tube.

I don't use thrust plates, so I apply big fillets to the middle CR and then use the belt sander to notch the fin tabs just enough to allow space for the fillets.

The forward CR needs to withstand the drogue ejection charge and sustain the booster under descent. So the top CR gets a good fillet with a little carbon fiber mixed in. Middle and aft CRs just, as you say, to keep the motor straight. I also like them to butt the fins for more support.
 
STEP 13 -- Insert MMT assembly.

Well, my first mistake. I neglected to see if the CRs fit into the booster prior to building the MMT assembly. So they needed to be ground down. For that I used ye olde angle grinder with a masonry wheel.

IMG_2530.jpg

Next, I inserted the MMT assembly all the way in. When I epoxy the top CR to the booster, it will be at the exact right depth.

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While it was in there, I cut off the T-rods to an appropriate depth.

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Finally, I pulled it back out, and once again washed all the FG dust off of everything. I keep showing these pictures to drive it into newbies' heads to keep those tubes clean and clear!

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Good God,
My spouse would kill me if I did that in our bathroom. You must wait until she goes somewhere and clean like crazy before she gets home.
Me? I have to go outside with a garden hose in fair weather to clean tubes. Kurt
 
Nice job John..
Keep up the solid build..
This is totally unnecessary for you at this point,,
thank you much for paying forward to those this can help..
It certainly is time consuming doing this thread..

Teddy
 
John now that you have this opportunity to rebuild, do you plan on doing anything differently than the original, or are you happy with your original decisions?

Great question! Yes. The first time through I did not know for sure whether or not I was going to get a thrust plate or foam the fin can. So I measured the MMT so that the retainer would be screwed onto the rear CR and be inside the booster. That way, when it stood on the ground, it would rest completely on the airframe instead of the retainer. Then I changed my mind and got a thrust plate; so I had a gap between my MMT and the thrust plate. No issue, just unusual.

This time I knew I had a thrust plate and I have taken care to make the MMT fit into the recess of the thrust plate where it belongs.

Other than that, I am solid on what I did. Well, I used 18 fillets last time; I think I am going to use 12 this time (six external, six internal fin root to MMT). If anyone strongly thinks I should use the other six (internal booster wall to fin tab), please let me know soon, and why. Thanks.
 
Good God,
My spouse would kill me if I did that in our bathroom. You must wait until she goes somewhere and clean like crazy before she gets home.
Me? I have to go outside with a garden hose in fair weather to clean tubes. Kurt

My wife doesn't know why I clean the parts, so she is not concerned with it. :smile:
 
STEP 14 -- Epoxy the top CR to the booster.

Today I inserted the assembled MMT and CRs into the rear of the booster until I got a nice fit. I then stood the booster onto the retainer.

IMG_2536.jpg

I mixed up three ounces of RocketPoxy, black die, and a pinch of chopped carbon fiber. I let it sit about 20 minutes before application. I taped a plastic spoon to a 3/8" dowel as an applicator.

I stood on a stepstool and applied the top fillet. It turned out to be easier to smooth the fillet by reaching in with a tongue depressor. I was obviously not going for looks! :wink:

IMG_2534.jpg IMG_2535.jpg

THINGS TO WATCH OUT FOR: 1. When inserting the MMT assembly, make sure the threaded rods are not aligned with the fin slots! Don't get epoxy inside the MMT!

Builder's helpers. :clap:

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Once the epoxy is fully cured, I will flip the booster over to stand on the forward end, remove the thrust plate and aft CR, and apply a fillet to the bottom of the middle CR, leaving room for the fins to slide in.
 
Okay, I got a little done tonight.

STEP 15 -- Epoxy the bottom of the middle CR to the booster.

I removed the thrust plate and aft CR. To get the CR out, I tapped it by using a leftover threaded rod through the fin slots. Came right out.

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I then mixed up about two ounces of RocketPoxy with a pinch of chopped carbon fiber. Because the space between the MMT and the booster is smaller than my forearm, I had to use a dowel with a tongue depressor taped to the end. It did not go well. :sad: But I got a little where I wanted it. Once the fins are in, it won't matter anyway.

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STEP 16 -- Drill for the aft rail button.

While the epoxy cured, I set about drilling for the aft Unistrut rail button. I am using weld nuts and 1/4-20 Phillips head screws.

I wanted a nice, clean hole, so I backed the booster with a piece of PVC pipe.

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I used a 5/16" brad point bit.

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And here is the nice, clean hole I got. The second pic is the 1/4-20 weld nut stuck through for sizing. Just right!

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My method is to slide the Unistrut button over the weld nut sleave, and thus the Unistrut button had to be drilled out to 5/16". I did that with the same bit on my drill press.

IMG_2547.jpg

Once the CR epoxy is cured, I will lay the booster flat, drill the second button hole (I'll show my trick for that), and then epoxy both weld nuts into the holes. But not tonight. :wink:
 
More work ... a setback ... and my second and third mistakes.

STEP 17 -- Drill holes and install rail buttons.

My method for drilling clean holes in fiberglass is to back the FG with PVC. I made this tool to get the PVC pressed against the BT.

IMG_2569.jpg

I slid it into the booster until it stopped.

IMG_2570.jpg IMG_2571.jpg

However, I didn't realize that the tool had butted up against the U-bolts, and was not actually under my drill point. Mistake number two! Anyway, the hole turned out pretty good. Good enough for a rail button.

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While there, I drilled a pressure relief hole with a 1/8" bit.

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From the inside:

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Once drilled, time to flip the booster over so that the holes are facing the ground.

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I was all prepared to install the rail buttons, which I will show in a future post; however, I discovered my third mistake and hit a setback.

The story goes like this: after the original booster burned up, I had one Unistrut button left in good shape. So rather than buy a pair and pay for two of them plus shipping, I got one free from a friend. I never noticed that their profiles were so different.

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Woops! So, now I will be buying a pair from Aerocon and installing the fins first. BTW, those are the weld nuts and screws I will be using.
 
I have a question. With that excellent appearing thrust plate aft that holds the Aero Pack retainer, it vaguely looks to me that most of the thrust force from the motor is imparted through the retainer to the thrust plate. Now if the thrust plate is flush with the airframe it seems why do you need to go through the added weight and bother of the all-thread? I could see it if there were no thrust plate but I'd bet that healthy motor tube fillets and liberal epoxy on the centering rings would have been sufficient?

If there is the risk of another mishap, the all-thread could possibly keep pieces from flying apart. Kurt
 
I have a question. With that excellent appearing thrust plate aft that holds the Aero Pack retainer, it vaguely looks to me that most of the thrust force from the motor is imparted through the retainer to the thrust plate. Now if the thrust plate is flush with the airframe it seems why do you need to go through the added weight and bother of the all-thread? I could see it if there were no thrust plate but I'd bet that healthy motor tube fillets and liberal epoxy on the centering rings would have been sufficient?

If there is the risk of another mishap, the all-thread could possibly keep pieces from flying apart. Kurt

It just helps keep everything lined up and level. Probably not necessary, but it seems easier to me. Also, the thrust plate will then bolt onto the T-rods rather than the aft CR.
 
So, no one caught my snafu!

The whole point of doing the rail buttons the way I do them is to make them replaceable. Which means that I don't need to have two of the same profile buttons to be able to install them. I'll just swap them out for whatever I get later!

That being said ...

STEP 18 -- Install the Unistrut buttons.

With the holes drilled, insert the weld nuts into the airframe.

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Slather the screws in Vaseline, or some similar lubricant.

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Screw the buttons onto the weld nuts with the lubed screws.

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Then put a big blob of RocketPoxy all over the weld nut.

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Let cure. Once cured, a good twist with the screwdriver will remove the screws and buttons, and leave the epoxied weld nut inside.

Next up: FINS!
 
Don't! It all works out somehow.

A couple of days ago I put the fins on. Pics were taken, but I haven't had time to download them and post yet. I went down last night, still in my good clothes, just to mix some epoxy and let it sit awhile before apply internal fillets.

Then I noticed that one of my fins was not completely in contact with the MMT at the root. It was slanted. :sigh:

So I put some epoxy on the aft tend, took a piece of 2X4 and tapped the fin down. Success ... er, no. :sigh:

Now the forward edge was out of the fin slot about 1/4". So I tapped it down ... and it wouldn't go. :sigh:

So I decided to remove the fin completely and start over; only now it had wet epoxy on the root edge, and I was completely unprepared for this.

Then all the do-do hit the fan at once. I got black-dyed epoxy on the sleeve of my yellow dress shirt, epoxy on my hammer and screwdriver and several other things, and (I being a 50-year type 1 diabetic), my blood sugar plummeted to a scarily low number. But I had to get the fin out.

For those who aren't diabetic, having low blood sugar is a little like being drunk. You brain is impaired to due a lack of oxygen. And you get an adrenal response that makes you edgy.

So, I ran to get my wife, quickly drank some apple juice, asked her to try to save my shirt, and then help me get the fin out.

But the fin would not budge. To save a long story, I tried a lot of things. The aft end would not come up. Finally, as my brain started to clear, I realized I could get the forward end up and then slide the fin forward in the slot until I could get a better grip on it.

This worked and I got it out. I used some acetone to remove as much of the uncured epoxy as I could. The fin and slot will need some sanding, but the good news is that the other two fins stayed on, and I think this one will go back in pretty well.

In hindsight, I tried to be slick and put all the fins on at the same time. What I should have done was put on one fin at a time and let gravity hold it where it belonged.

Well, fortunately, this was not catastrophic. The (re)build continues.

I will document all of this with pictures when I can, maybe Thursday night.
 
Here are the pics from the fin assembly and snafu. For details, see previous post (#26).

For a fin template, I go to PayloadBay.com and print one off, glue it to a half-sheet of foam board, and cut it out.

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Here are the fins after I attached them the first time:

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And here is the one that pulled away from the MMT (prior to my panic attack).

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All's well that ends well. Here are the fins after I put the problem one back on.

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Next will be internal fillets. I always hate this part due to the lack of room in which to work. I don't like injection, so I will probably put epoxy on the ends and push it forward with a dowel. I'll do two at a time with the fins in the Y position, so that the epoxy will settle into the joint.
 
Whoa whoa whoa, don't leave us in the dark here. There is critical information that many TRFers need to know - err.... did the shirt survive?
 
Yes! A picture of the shirt... or it didn't happen. :wink: This started as a pretty good (re)-build thread but post #26 puts up on a whole 'nother level. :pop:
 
Okay, internal fillets are done. It is pracically impossible to get a good picture of them, at least inside the house.

STEP 19 -- Install fins with root epoxy.


(see above)

STEP 20 -- Internal fin fillets.

My method was to mix up 3.4 oz. of epoxy, put a huge dollop on the fin joint, then shove it forward with a 1/2" wood dowel. Lather rinse repeat till it looks like a fillet. I did two at a time and used up three dowels.

Best picture I could get:

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And for the shirt, here's how it came out:

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I have an appointment tomorrow night, but maybe I can squeeze in putting on the rear CR and thrust plate.
 
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