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MAC 4" ARCAS Build for L2

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I was originally planning on using the Binder Design Excel I built and flew for my L1 for my L2 flight, but I start debating building a new rocket for L2. After looking at the various vendors and kits, I was drawn the MAC Performance and their 4" ARCAS. I received the kit, along with a couple of extras, a few weeks ago, and was still undecided if my Excel would be used for my L2 or not. Well, the 3rd flight of the Excel did not go very well at the Tri Cities Rocketeers June launch, and after it was heavily damaged after a failure of the main to deploy, it was clear that the ARCAS will be my L2 bird.

Today I finally was able to start working on this beast!

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The obligatory dry fit photo, since we all know that you MUST do this with every build!

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I chose the option for the Wildman fiberglass nosecone, and I must say, I do not regret it! I also ordered the nosecone electronics bay kit, and I will be adding it for the future addition of a GPS tracker.

Today I located the forward centering rings and epoxied them into place with US Composites epoxy, then went back and added fillets to one side with Rocketpoxy. I will apply the fillets to the other side tomorrow.

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I also took the time to epoxy the E-Bay switch band in place. For electronics, I will be using a MissileWorks RRC3 for primary, and a RRC2+ for backup, with both mounted on a Additive Aerospace sled. My motor choice will be firmed up once the build is complete and I have the final weight, but I am currently planning on a 54/1280 size J motor, most likely a J401FJ, but it looks like the cases are unobtanium at the moment. I have a fallback option of using a J350W instead. I am hoping that the first flight will be the Tri Cities Rocketeers September launch, and I plan to put it up on a I600R for a shakedown, then the L2 flight.
 

jd2cylman

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Kris,
Look here for your 54/1280 case. No closures though, those can be bought still.
 

mpitfield

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Nice choices. Looking forward to seeing the build progress. Being at the paint stage of a MAC build right now myself one thing I would recommend is to sand and prep the fins as well as the slots and body, before you tack them in place.
 
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Nice choices. Looking forward to seeing the build progress. Being at the paint stage of a MAC build right now myself one thing I would recommend is to sand and prep the fins as well as the slots and body, before you tack them in place.
Michael, Ive been watching your build, and it's looking very good! I saw how you prepared your fins and the airframe, and I plan on doing the same. Thanks for the advice!

Yesterday I went back out to the garage and marked out on the lower airframe the locations for the rail guides, and epoxied two 1/4" ply strips to the forward and aft centering rings to mount some threaded inserts for the guides. Today, after those were cured, I drilled mounting holes in both the airframe and the strips, and attached the inserts. I plan on locking in the back sides of the inserts with some epoxy when I epoxy the motor mount into place.

IMG_5319.jpg IMG_5320.jpg IMG_5321.jpg IMG_5332.jpg IMG_5331.jpg

Today, I spent some time concentrating on my electronics, and fabricated the harnesses the bay. My goal is to have the sled wired in a way that I can move it between rockets fairly easily within a few minutes. I also "murphy proofed" the connections, by using a different size JST connector for the drogue side than from the main.

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I also mounted the charge wells on the bulkheads, as well as the terminal strips. The stock open-ended eye bolts have been replaced with forged ones from McMaster & Carr as well.

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Over the past week I have spent most of the time I had devoted to build getting the fins tacked epoxied in place and working through the fillets. Prior to installing the motor mount, I roughed up all of the mating surfaces inside the booster airframe with some 80 grit, and at the same time I sanded the tabs on the fins, as well area surrounding the fin slots to ensure proper adhesion.

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After sanding, everything got a good cleaning with isopropyl alcohol. The motor mount go epoxied in place on the 3rd, and I let it cure over night. While I was in between keeping an eye on the brisket I was smoking for the 4th (it was excellent, by the way!), I epoxied the fins in place, slid the jig over them, and then taped them down as well.

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The next day, I started to apply fillets with Rocketpoxy. I must say, I love that stuff! I used a long dowel to apply the internal fillets, and while they are not pretty, and I made a mess inside the tube, they are functional. The external fillets were completed by masking off the fins and then applying the Rocketpoxy.

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Then yesterday, I assembled the nose tracker bay. I do not have a tracker yet, but I am hoping to purchase one over the winter, so I decided to build it into the rocket to be ready. Since I wanted to use room in the shoulder for the recovery gear, I mounted the tracker bay at the top of the coupler, and I added a 3" to 54mm centering ring for support at the top of the bay. After assembling everything with Rocketpoxy, the whole assembly was securely epoxied to the fiberglass nosecone.

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This morning I completed the main part of the build by locating and drilling the holes for the mounting screws to hold the payload section to the avionics bay, and locating and drilling holes for shear pins on the nosecone and booster section.

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The major work that I have left is to prime and paint this bird, then perform the ejection tests.

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Dry weight without paint or motor retainer is 9.4lbs, so it should come it at right around 10lbs minus a motor.

With any luck, I should be flying it at the September TCR launch in Pasco.
 
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The Arcas is all primed and the first coat of paint is on it. Decals have been ordered from Mark at Stickershock and will arrive next week. My recovery gear arrived this past week... Drogue will be a Top Flight 24" X-form, and for the main I have selected a 7ft Rocketman. I also picked up a deployment bag, and I am tempted to try it out on my first flight with an I600.

I ran the ejection tests today, and drogue separates cleanly with 1.5g of BP. Main ejection is another story. I started with 1.5g, and the nose cone popped of, but no chute or harness extraction. I tried it again, and this time I packed the chute in the deployment back into the shoulder of the nose cone, and got the same result. The nose popped off, with out enough force to pull the chute out of the bag, or extract the harness. So, I repeated it a third time. The first two tests I was using a hand full of dog barf, and a 18" nomex square. The third time I eliminated the dog barf, and switched to a 12" nomex protector. I left the chute packed into the nosecone, and I upped the charge to 1.75g of BP. This time, I got a perfect separation, and the the deployment bag separated cleanly from the nose cone shoulder, and the chute pulled out of the bag perfectly. I think thats the route I am going to go!

Sorry, but I forgot to get video of the testing, and I didnt get any photos of the priming or first coat of paint. Ill post completed photos once I get the decals on.
 

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I've been watching that auction... I'm waiting towards the end to make a bid.
Kris,

Looking forward to seeing it fly in Sept! I've got a 54/1280 case I can loan you if you don't find one between now and then.
 
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I think I can safely call this build completed. After I spent a few hours over the weekend wet sanding the entire rocket after I let the white top coat cure for four days, and then I started to prep for the decals I ordered from Mark at Stickershock. I decided not to apply the red vinyl striping, as it is a lighter shade of red than the Rustoleum paint I used for the nosecone, so I decided to attempt and mask off the red striping and paint it on myself. I figured if the masking didn't look right, I could always just apply the decal. The masking actually turned out pretty good! It's by no means perfect, but its great for a sport scale rocket such as this. After applying the red yesterday, I applied the markings today. Overall, I feel that this is my best work yet. The paint is not perfect, and there are a few minor cosmetic defects here and there, but she sure does look great from a couple feet away!

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First flight will be on an I600 at the Tri Cities September launch, followed by my L2 at the October WAC launch in Mansfield on a J350.
 
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After patiently waiting for three months to fly the ARCAS, I finally got a chance today.

I made two attempts to fly, and both attempts ended the same way, with my backup charge going off on the pad. I have no clue what caused the issue, but after talking it over with a few other veteran flyers, I am guessing that it comes down to a perfect storm of a slightly breezy day, and the alignment of my vent holes. When I was taking the altimeter bay apart after the second occurrence, I accidentally pulled a wire out of a contact on one of my wiring plugs, and since I didnt have the materials to fix it, I elected to bring it home, make the required repairs (which might include a slight redesign of the bay configuration), and try again at the next launch.
 

mpitfield

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After patiently waiting for three months to fly the ARCAS, I finally got a chance today.

I made two attempts to fly, and both attempts ended the same way, with my backup charge going off on the pad. I have no clue what caused the issue, but after talking it over with a few other veteran flyers, I am guessing that it comes down to a perfect storm of a slightly breezy day, and the alignment of my vent holes. When I was taking the altimeter bay apart after the second occurrence, I accidentally pulled a wire out of a contact on one of my wiring plugs, and since I didnt have the materials to fix it, I elected to bring it home, make the required repairs (which might include a slight redesign of the bay configuration), and try again at the next launch.
Hi Kris,

That is unfortunate but I am sure you will work it out and be a better builder for it.

I don't recall seeing any details on your AV bay sampling holes, did you opt for 2, 3, more, how are they spaced, what size, what size is the AV bay? In all of my AV bays, except my GLR Mariah 38, I have gone with 3 or more. It may sound a bit frivolous but I like to match my sampling holes with my fins, 3 fins 3 sampling holes, 4 fins 4 sampling holes. Of course that is not required but the general rule of thumb is to have a min of 3 @ 120 degree intervals.
 
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Hi Kris,

That is unfortunate but I am sure you will work it out and be a better builder for it.

I don't recall seeing any details on your AV bay sampling holes, did you opt for 2, 3, more, how are they spaced, what size, what size is the AV bay? In all of my AV bays, except my GLR Mariah 38, I have gone with 3 or more. It may sound a bit frivolous but I like to match my sampling holes with my fins, 3 fins 3 sampling holes, 4 fins 4 sampling holes. Of course that is not required but the general rule of thumb is to have a min of 3 @ 120 degree intervals.
There are three holes in the switch band. Two on the front side for access to the screw switches for arming, and one on the back. After the backup main charge went off the first time, I replaced the charge, repacked the chute, and went back out to the pad, and after arming both altimeters, I placed a piece of masking tape over one of the arming holes. After I hooked up the igniter and was walking back to the LCO table, the backup altimeter, a RRC2+, popped the nose again. The first time it happened right as the LCO was getting ready to press the button.

It was a breezy day, and I am wondering if the fact that the rear vent is masked by the rail when on the pad might play a part. I have no clue, though. I might do some testing with an air gun to see if I can get it to repeat on the bench.
 

mpitfield

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If you align the sampling holes with the fins then when she is on the rail there won't be a chance of the rail blocking a hole. Assuming that it matters.

Can you relocate one of the screw switches opposite, 180 degrees, from the other? If so then block the hole that is no longer needed. I would then drill two more sampling holes, so you end up with four evenly spaced holes 90 apart, aligned with the fins.

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REK

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This is just a theory, but it could be possible that having too many vent holes is a bad thing. If anything in my opinion one is more than enough.
Here is what I assume is happening, considering it is breezy, its possible that air is entering the e-bay on one vent hole and then escaping on another vent hole. This causes an increase and then a decrease in pressure and the altimeter could be interpreting it as apogee or set altitude reached.
In the high powered rockets I’ve flown (or helped fly), only one vent hole was used and have had no problems.


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mpitfield

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This is just a theory, but it could be possible that having too many vent holes is a bad thing. If anything in my opinion one is more than enough.
Here is what I assume is happening, considering it is breezy, its possible that air is entering the e-bay on one vent hole and then escaping on another vent hole. This causes an increase and then a decrease in pressure and the altimeter could be interpreting it as apogee or set altitude reached.
In the high powered rockets I’ve flown (or helped fly), only one vent hole was used and have had no problems.


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From my experience and several threads I have read on TRF, as well as several of the altimeter manufacturers installations guides, it suggest otherwise. That is more than one hole and in most cases a min of three. With one hole in fact you can get a pressure spike because there is no other hole to equalize the AV bay. I know GLR uses one hole in their shotgun AV bays but that is the exception from what I have seen.
 

REK

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From my experience and several threads I have read on TRF, as well as several of the altimeter manufacturers installations guides, it suggest otherwise. That is more than one hole and in most cases a min of three. With one hole in fact you can get a pressure spike because there is no other hole to equalize the AV bay. I know GLR uses one hole in their shotgun AV bays but that is the exception from what I have seen.
I dont know why it is recommended for three. Even two seems to make more sense. Consider you have three, air can flow into two ports and air escape from just one or vise versa. This can cause a spike in pressure and thus fooling the altimeter. It still makes no sense why you should have more than one when the formula for just one vent hole is provided. Acquire the correct calculated vent hole size and just drill that one vent hole and your done.
If the giant leap Mariah’s have no problem with one, then why should the rest be any different?


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REK

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By the way, love the awesome paint job on the rocket


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mpitfield

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Kris, it may help you to read some previous posts on this discussion, as it has come up many times over the years on TRF. Below are two posts from two well respected altimeter manufacturers on the topic. If you read the entire thread you will also see at least one post supporting Alexander's position of one hole, again with a GLR product, and I have read other posts supporting this same 1 hole design successfully.

https://www.rocketryforum.com/showt...s-(not-a-size-question)&p=1621324#post1621324
https://www.rocketryforum.com/showt...s-(not-a-size-question)&p=1621608#post1621608

There is obviously a lot more to this topic than meets the eye, however I go to what has worked for me with 100% success and that is a min 3 hole design, heck in one rocket I even have 5 holes. This includes two 3 hole rockets that have had close to 10 flights between the two of them well over Mach, and one flight @ Mach 2.15. I don't profess to know this subject as well as I would like, but I am active in this hobby in all aspects and as it pertains to this discussion I think experience has some merit.

https://www.rocketryforum.com/showt...017-Newton-Tally-Thread&p=1733934#post1733934
https://www.rocketryforum.com/showt...016-Newton-Tally-Thread&p=1654875#post1654875
 
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If you align the sampling holes with the fins then when she is on the rail there won't be a chance of the rail blocking a hole. Assuming that it matters.

Can you relocate one of the screw switches opposite, 180 degrees, from the other? If so then block the hole that is no longer needed. I would then drill two more sampling holes, so you end up with four evenly spaced holes 90 apart, aligned with the fins.
I am pretty much set in stone on my switch locations, as those are dictated by the design of the sled I am using. Its one of the MissileWorks 3d printed ones from Additive Aerospace.

This is just a theory, but it could be possible that having too many vent holes is a bad thing. If anything in my opinion one is more than enough.
Here is what I assume is happening, considering it is breezy, its possible that air is entering the e-bay on one vent hole and then escaping on another vent hole. This causes an increase and then a decrease in pressure and the altimeter could be interpreting it as apogee or set altitude reached.
In the high powered rockets I’ve flown (or helped fly), only one vent hole was used and have had no problems.
This is the theory that I am working on now. With my L1 bird, I used three vent holes on my Binder Excel, and it worked flawlessly. I had no reason to doubt the same would be the case on this one, and I still think that way. However, for the weather conditions, with breezy winds up to 10-12mph, blowing right at the two switch holes, I am thinking that I had the perfect storm of conditions to cause this. The fact that on the second attempt, I had covered one of the switch holes after arming, and it blew quicker than the first time, confirms this in my mind.

By the way, love the awesome paint job on the rocket
Thanks! Its nowhere near perfect, but it looks great from 5ft away! I think it turned out pretty good for eyeballing the red markings.

Kris, it may help you to read some previous posts on this discussion, as it has come up many times over the years on TRF. Below are two posts from two well respected altimeter manufacturers on the topic. If you read the entire thread you will also see at least one post supporting Alexander's position of one hole, again with a GLR product, and I have read other posts supporting this same 1 hole design successfully.

https://www.rocketryforum.com/showt...s-(not-a-size-question)&p=1621324#post1621324
https://www.rocketryforum.com/showt...s-(not-a-size-question)&p=1621608#post1621608

There is obviously a lot more to this topic than meets the eye, however I go to what has worked for me with 100% success and that is a min 3 hole design, heck in one rocket I even have 5 holes. This includes two 3 hole rockets that have had close to 10 flights between the two of them well over Mach, and one flight @ Mach 2.15. I don't profess to know this subject as well as I would like, but I am active in this hobby in all aspects and as it pertains to this discussion I think experience has some merit.

https://www.rocketryforum.com/showt...017-Newton-Tally-Thread&p=1733934#post1733934
https://www.rocketryforum.com/showt...016-Newton-Tally-Thread&p=1654875#post1654875

I have read a few of those in the past, and it is apparent to me that it can vary. For now, I plan on covering one, or both, of the switch holes with tape after arming and fly it like that.
 

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mpitfield is correct, 3 or more evenly spaced holes is the best way to equalize pressure. Drive your car at 40 mph with one window open, and the pressure fluctuations pound your noggin. Open another window, and the pain subsides. Open 3 windows, and the pressure is relieved.

I am not buying the perfect storm of wind and vent holes. 12 mph is nothing unusual, and you did have three vent holes (albeit non-equally spaced). The vent hole facing the rail is still open and likely seeing ambient pressure.

I suspect the "backup" altimeter is at fault, and ironically, it prevented you from flying the rocket. Must...resist...further...bashing...of...redundant...altimeters...

What did the altimeter data say? Did it think flight had commenced and reached deployment altitude? Did the main altimeter (same brand, with probably same components and logic) show the same behavior?

I did enjoy this build thread. Good luck next time.
 
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ksaves2

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Replace the altimeter that keeps firing early or go with one altimeter. You're going to be diddling with this for a long time otherwise. The worst would be an unexplained ejection on ascent with a trashed rocket.
Redo the deployment test to be certain you have enough powder and do it with a solo altimeter if you don't replace the backup one causing the problem. Kurt
 

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Sry to hear that Kris, its happened to me twice as well (not same day) talking with others on that windy day said same thing. since I had a backup I opted to fly on one which it did fine - 4 holes.

After finding nothing wrong, it's flown several times since with no issues


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Replace the altimeter that keeps firing early or go with one altimeter. You're going to be diddling with this for a long time otherwise. The worst would be an unexplained ejection on ascent with a trashed rocket.
Redo the deployment test to be certain you have enough powder and do it with a solo altimeter if you don't replace the backup one causing the problem. Kurt

Sry to hear that Kris, its happened to me twice as well (not same day) talking with others on that windy day said same thing. since I had a backup I opted to fly on one which it did fine - 4 holes.

After finding nothing wrong, it's flown several times since with no issues
After the second occurrence, I was getting ready to just fly it on the main (RRC3), but as I was pulling the bay apart to double check everything was good inside, I inadvertently pull a wire out of a pin on a JST connector for the the primary altimeter's main charge. That was a show stopper for me, and I decided at that point to scrub for the day. I am currently in the process of modding the bay to remove all JST connections except for on the batteries, and will be using well nuts instead. I am also adding a secondary sled below the primary one so I can fly either the current RRC2+ or a Stratologger. I'll have it ready for November launch for sure.

IMG_5792.jpg
 

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I use a RRC3 and RRC2+ in at least three different rockets from 8" tube to 4". All with three holes of correct sizes for the AV bay. To date, I've not had a charge go off prematurely. Ditto for a PF Strat 100 with a RRC2. Maybe I'm just lucky :confused2: But the altimeter that fired twice would be getting the wiring checked VERY closely if'n it were me...
 

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Sorry the day didn't go well, Kris. I'd be tempted to send the 2+ to Missileworks and have it checked out.
 
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I use a RRC3 and RRC2+ in at least three different rockets from 8" tube to 4". All with three holes of correct sizes for the AV bay. To date, I've not had a charge go off prematurely. Ditto for a PF Strat 100 with a RRC2. Maybe I'm just lucky :confused2: But the altimeter that fired twice would be getting the wiring checked VERY closely if'n it were me...
Sorry the day didn't go well, Kris. I'd be tempted to send the 2+ to Missileworks and have it checked out.
I am going to give the RRC2+ one more chance before I send it back to get looked at, but it will always be as a backup altimeter. I'll give it a second chance after my L2, either in this bird, or another one.

I went ahead and finished the secondary sled this evening. Having this new lower sled helps to solve a minor problem that I had: where to install a switch for my new RTx that I just received. The old switch for the RRC2 is now the switch for the RTx, so that was easy.

IMG_5793.jpg
 

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Straighten out that antenna wire before you fly. Kurt
 
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Straighten out that antenna wire before you fly. Kurt
It will be straight before flight!

I finished up the rework of the Av Bay today. In total, I added the secondary sled for a SLCF and associated components, stripped the bulkheads clean and added a layer of epoxy for ease of future cleaning, and I removed all wire connections other than for the batteries, and added well nuts to the bulkheads for e-match pass-throughs. I also added markings to the exterior for which switch is which.

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Well, My ARCAS suffered a incident at my house yesterday. While I was working in the garage, I accidentally bumped the cabinet I have been storing my fleet in, and since the ARCAS was the last one to go in, it was the closest to the door, and as such, the booster section fell out onto the concrete.

IMG_5889.jpg

The upper 2.5 inches of airframe cracked in several places, and the only repair I could see that would work would be to cut three inches off the booster. So now I have a ARCAS that is three inches shorter, but I don't think anyone would notice unless I said something. I now need to get a hold of Mark at Stickershock and see if I can order just the AT from Atlantic, since I had to cut those letters off!

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