Build thread: MAC Performance Rocketry Scorpion.

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Bat-mite

Rocketeer in MD
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This is an introduction to a planned build thread for the MAC Performance Scorpion, 3" diameter x 38mm MMT kit. Received yesterday, I started weighing parts for an OpenRocket sim file. I don't know Mike at MAC Perf., but perhaps he would like to make the OR file available to customers. We'll see. Also, right now the pic on the web site is naked. If mine turns out "display worthy," I will shoot him a picture and see if he wants to use it.

Color scheme will be all black, with some white trim, hopefully by StickerShock. I have never done a black and white rocket before, so this should be fun.

I build slow, so this will not be a rapid fire thread. And I plan to steal all of Dan Patell's techniques, so it won't be anything new, either. :w:

Tonight I plan to do the parts picture, clean the parts, and maybe start the MMT and/or AV bay. I'll get my pictures up as time permits.
 
Cool! Looking forward to this build!

I gotta ask...was it worth adding items to get the free shipping?

:)
 
Ha! I was going to reuse some old harnesses, but then I decoded to get new ones, and that put me over the threshold.

I ordered pour foam and an Aeropack from RW, so now I am way over budget anyway. :)

Update: last night, I was tired and just didn't feel like doing much. Do others get that way? All day at work I was looking forward to going home and getting started, and then once I was able to build, I just didn't much feel like it. Weird, huh?

So, I epoxied the struts to the Av sled (will add small screws later), epoxied the forward CR to the MMT, epoxied the harness holder to the CR, and epoxied the switch band to the coupler. I also took parts pictures. Will upload soon, maybe tonight.

Tonight I want to get the middle CR on and maybe finish the AV bay. Pics coming.
 
Update: last night, I was tired and just didn't feel like doing much. Do others get that way? All day at work I was looking forward to going home and getting started, and then once I was able to build, I just didn't much feel like it. Weird, huh?

Are you kidding? Not weird at all, unless it lasts a long time! I once took 16 months to finish a kit.
 
Okay, so here is two days' worth of progress.

DAY ONE

Laid out the parts. You can see the polished fins and sled. Pretty cool.
IMG_0802.jpg

Epoxied the guides onto the sled, and the switch band onto the coupler.
IMG_0803.jpg

Epoxied the forward CR onto the MMT.
IMG_0804.jpg

Filleted.
IMG_0805.jpg

And epoxied the harness holder in place.
IMG_0806.jpg

DAY TWO

Here you can see my first mistake. I didn't get the switch band on evenly, so I don't have flush joints. If anyone has any ideas on how to fix it, or at least how to avoid this in the future, let me know.
IMG_0808.jpg IMG_0807.jpg

Marked where the middle CR will go.
IMG_0809.jpg

Tacked and filleted. No fillet on the bottom so the fins will fit flush against it.
IMG_0810.jpg

Top and middle CRs finished.
IMG_0811.jpg
 
DAY TWO continued...

Reused Av bay parts from a scrapped rocket. The kit comes with bent eyebolts, but I replaced them with forged circular.
IMG_0812.jpg IMG_0813.jpg

Finished AV bay (minus wiring).
IMG_0814.jpg

I also plan to put a couple of tiny wood screws through the sled into the guides. I have them, but didn't get to it tonight.
 
ere you can see my first mistake. I didn't get the switch band on evenly, so I don't have flush joints. If anyone has any ideas on how to fix it, or at least how to avoid this in the future, let me know.

14334318905_2977ba8766.jpg

tape makes a "level" mark, and when you pull it off, cleans off the excess epoxy
 
Thanks, Dave. I think a little less epoxy under the ring would have helped. And maybe I could have butted the tubes together, then pulled off the booster and payload tubes and wiped them out with alcohol if necessary. Tape seems to work, too. Well, live and learn.

DAY THREE:

I used the epoxy ring, slide in method to attach and fillet the CRs. I used the thrust plate and Aeropack to get the right depth.
IMG_0815.jpg

I also did a little belt and suspenders, and added screws to the sled. Between that and the epoxy, the guides should stay firmly attached.
IMG_0816.jpg

I cut a window in the NC shoulder. This serves two purposes: one is for sliding in the BRB900 transmitter; the other is for screwing on the eyebolt.
IMG_0817.jpg

The NC comes with a very small hole for the eyebolt. I drilled mine out to take a 1/4" bolt.
IMG_0818.jpg IMG_0819.jpg

Here's the eyebolt attached.
IMG_0820.jpg IMG_0821.jpg

Lastly I added reused terminal strips to the bulkheads of the AV bay.
IMG_0822.jpg


It is going to be a busy weekend, so I'm not sure when I will next get to work. But when I do, the next step will be attaching the fins.
 
So what did I do today? Well, mowed the lawn, carried a freezer from the basement up a flight of steps to the garage, dropped off some prescriptions off at the drug store, went to an Orioles pregame party and the game, and came home and ...

DAY FOUR

Got the fins on! I used old-fashioned eyeball alignment; tacked the roots with JB Weld; poured in some fillets and patted them down with popsicle sticks; and cleaned everything up with alcohol.
IMG_0823.jpg IMG_0824.jpg
 
DAY FIVE

Had my first ever experience foaming a fin can. First, I taped up the MMT and around the edge of the booster.
IMG_0825.jpg

I started with a very small amount of liquid foam, and when I didn't get a huge expansion, I mixed up a substantially bigger batch. However, I couldn't tell if I was pouring it evenly, and obviously I didn't.
IMG_0826.jpg IMG_0827.jpg

Tomorrow night I'll cut away the excess and clean up the surfaces.
 
DAY SIX

I got all the foam mess cut down, scraped off, sanded away, and cleaned up ... well, mostly. But I forgot to take a picture. :(

But after that, I got the thrust plate/aft CR on, and added the Aeropack retainer with JB Weld.
IMG_0828.jpg IMG_0831.jpg

I am going to go without fillets, since I hate doing them and I don't need them.

It's a rocket!
IMG_0832.jpg

Tomorrow night I have to completely gut and replace the innards of a toilet. Not a job I like, and will probably take me all night. So maybe no updates tomorrow.

What's left?

  1. Sand/clean up
  2. Paint
  3. Trim
  4. Wire up AV bay
  5. Drill switch hole, vent holes, pressure-relief holes, rivet holes, and shear pin holes
 
You don't need external fillets....per-se...but by just wiping a small bead of epoxy, on each side of fin, to seal the joint/crack, you will get a much nicer paint job.

If you leave as-is, when you paint there will be a small open crack at that fin/body tube joint that won't fill with paint and may be unsightly.
 
True, and I considered that; but honestly, the way my fillets turn out, I think they would be even more unsightly.

I have always been impatient, and I have always done things "my way" instead of the "right way," as evidenced if you ever see me play golf, play guitar, bowl, or type. :facepalm:

Bottom line is I think I want to get this bird in the air on June 13th at the sod farm, and it takes me a long, long time to do eight fillets. I think I'm ready to sand and paint.
 
True, and I considered that; but honestly, the way my fillets turn out, I think they would be even more unsightly.

I have always been impatient, and I have always done things "my way" instead of the "right way," as evidenced if you ever see me play golf, play guitar, bowl, or type. :facepalm:

Bottom line is I think I want to get this bird in the air on June 13th at the sod farm, and it takes me a long, long time to do eight fillets. I think I'm ready to sand and paint.

Before you start your toilet project, put a block under the top of the body tube to make the tube level and let it rest on 2 fins.
You can now fillet 1 side of 2 fins. While the tear down of the toilet is being done, the epoxy will dry.
Flip 180 degrees and do 2 more. Flip 90 degrees and do 2 more. Flip 180 degrees and do 2 more.
By this time the toilet job is done and tools put away and the rocket can set over night.
For my LPR I don't use epoxy, just Titebond, and that's the way I do it. Thin coats will dry much faster that way.
Just a suggestion.
As a note, if I don't want to use my finger, I use the end of a popcycle stick. Do it in one smooth stroke and dab up any drips or strings of epoxy.
 
True, and I considered that; but honestly, the way my fillets turn out, I think they would be even more unsightly.

I have always been impatient, and I have always done things "my way" instead of the "right way," as evidenced if you ever see me play golf, play guitar, bowl, or type. :facepalm:

Bottom line is I think I want to get this bird in the air on June 13th at the sod farm, and it takes me a long, long time to do eight fillets. I think I'm ready to sand and paint.

Get wood glue, wipe with finger and your all set. You can do all 8 in an instant. No mus no fus.
 
Hmm, wood glue isn't a bad idea. Quick, easy to clean up, water soluble. That's not a bad idea.
 
I think you need something to seal that joint. Even 5 minute epoxy from Lowes, pressed in with a gloved finger is better than nothing.
 
I have 5-min and 30-min epoxy in the house. 30 tends to run and drip too much, and 5 seems to cure too quickly to get it on evenly. Should I go with 15-minute?
 
Use 30 & wait 15 minutes. Or just to be safe, make a test batch & see how long it takes to set.
 
After finishing the toilet last night, I went ahead and put on fillets with 5-min epoxy. Like said, not needed for structural support, just for cosmetics. Too tired to post last night.

Next hurdle is when to paint. This morning it was 57 F and humidity was 99%. Humidity looks to be hanging in there between 70% and 90% for the next two days. But if it dips to 70% tonight, maybe it will be lower in my garage. I would paint at 68%. You never get below that except in the winter here in MD.
 
More important is the humidity/dew point spread, which changes with temp & humidity ratio. Too close to temp & moisture will want to collect on object or not leave paint while drying.

You definitely want to wait till temp rises to 70-80 otherwise the dew-point can be so close [with your type of humidity, I deal with it also living in Savannah] it will cause blushing/streaking.

Check you weather for dew point, I checked Baltimore as I don't know where you are located...it's dangerously close to temp for painting as you can see till Fri. You want a 9-10 degree spread for a good trouble free paint job.

https://www.usairnet.com/cgi-bin/launch/code.cgi?Submit=Go&sta=KBWI&state=MD
Bottom of chart shows spread with current humidity.

You could leave door open between house and garage a couple hours, and let air-conditioning remove humidity before painting.


Ps I was a professional painting contractor for 28 yrs.& we followed Dew Points strictly when painting oil based outside.
 
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That's a really handy site for lots of reasons. Thanks!

Looks like Friday night may be a winner. Meanwhile, there's the AV bay to wire up.
 
Out of curiosity, did the kit come with recovery harnesses included, or did you buy them from MAC performance at the same time?

Looks like an awesome kit, I'm definitely considering it for my next build...
 
Out of curiosity, did the kit come with recovery harnesses included, or did you buy them from MAC performance at the same time?

Looks like an awesome kit, I'm definitely considering it for my next build...

I bought them. Basically, my choice was: pay $18.00 for shipping, or pay $29.90 for harnesses and get free shipping. No brainer.
 
I bought them. Basically, my choice was: pay $18.00 for shipping, or pay $29.90 for harnesses and get free shipping. No brainer.

Thanks. Definitely worth it! Do you need to foam the fin can or will internal fillets work?
 
Thanks. Definitely worth it! Do you need to foam the fin can or will internal fillets work?

I'm no expert, but I wanted to foam mine because I've never done it before, and it saves you having to drill holes in the booster. I did put as much epoxy on the internal fin joints as I could manage.

I can see where foam definitely eliminates breaking off the root joint because the fin gets bent sideways on a bad landing. With the foam it just can't get bent sideways. And in OR, adding the 3 oz. of foam only changed the stability from 1.96 to 1.87 cal.
 
I'm no expert, but I wanted to foam mine because I've never done it before, and it saves you having to drill holes in the booster. I did put as much epoxy on the internal fin joints as I could manage.

I can see where foam definitely eliminates breaking off the root joint because the fin gets bent sideways on a bad landing. With the foam it just can't get bent sideways. And in OR, adding the 3 oz. of foam only changed the stability from 1.96 to 1.87 cal.

I actually meant just relying on the fillets you add before attaching the back centering ring, but the foam definitely will help, and it doesn't add much weight. I think I'll try it if I build one of these.
 
DAY SEVEN

Here are the fillets that I did yesterday. Sorry for the poor pics.
IMG_0833.jpg IMG_0834.jpg

DAY EIGHT

Did a little AV work tonight. Will finish tomorrow, and start painting Friday. May even have this sucker ready to fly on June 13 at the sod farm.
IMG_0835.jpg
 
Sorry I fell off the face of the earth! I have been working on the AV bay and painting. I don't have any painted pictures yet, but...

Here was the start of the AV bay.
IMG_0835.jpg

And here it is all wired up.
IMG_0836.jpg

Only, the screws for the battery holder were running into the allthread.
IMG_0837.jpg

No problem! Just rotate the battery holder 90 degrees.
IMG_0838.jpg

But then, it wouldn't fit inside the coupler! So, I had to put it on the bottom, and when I did, I had to move the location of the altimeter.

Finally, here it is all finished.
IMG_0839.jpg IMG_0840.jpg

Bottom line--I should have taken more time with this "easy" part of the build, and measured more and planned more before I started drilling.

Still to go: finish painting, decal, add rail buttons, and drill vent and pressure-relief holes. Should be ready to fly on Saturday.
 
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