MAC BlackFly build thread

viciouspeanut

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Love this design, going to have to order one.. birthday is soon.. lol

What does it sim to on F's and G's? I'm guessing it will come out heavier than the 14oz listed?
 
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mpitfield

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Love this design, going to have to order one.. birthday is soon.. lol

What does it sim to on F's and G's? I'm guessing it will come out heavier than the 14oz listed?

Thanks.

Yes mine will be closer to 25ish oz once built. I will be adding electronics (altimeter, tracker battery) into the nosecone. Funny I designed it to be an easy quick-build, simple pop and drop, and in my typical style I have to complicate it. :facepalm: Still out of the box it will do what it was designed for, quick build, simple and really tough.

I have an issue with the RockSim file on my Mac so I converted it to OR, however my OR file exceeds the max upload size, so if you want it just send me a PM and I will email it to you. Sims, I am getting anything from about 1,000 on a CTI 24mm F51 Classic to just under 4K on an AT H97 Blackjack.
 

viciouspeanut

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Yes please! I'm really planning on picking one up soon. I love the 5 fins and tailcone, really makes it special.
 

Deke

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I just received an e-mail saying mine shipped today with the fin guide!

Question on the motor retainer since the kit doesn't come with one: It looks like the 3D printed tail cone was engineered around the 29mm Aero Pack screw on retainer but I am finding different sizes.

"L" - Fits 29mm tubes with an O.D. of 1.21" (LOC, Apogee, North Coast Rocketry, and Madcow Cardstock tubes)

"L2" - Fits 29mm tubes with an 1.225 OD: (Estes Pro Series II, Q-Modeling, Madcow fiberglass, Sunward & Semroc motor mounts.)

"P" - Fits 29mm tubes with an 1.270 OD: (Blue Tube, PML and Giant Leap phenolic, Performance Rocketry and Hawk Mountain fiberglass. Slightly loose on Aerotech kits.)

Does anyone happen to know the OD of the "kraft phenolic" MMT supplied with the MAC kit?
 

mpitfield

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I would confirm with Mike at MAC. I ordered my retainer from Mike. Whatever retainer Mike packed with my kit fits a bit lose, but not bad. I can tell you that the motor tube is the heaviest gauge 29mm phenolic motor tube I have ever seen.
 

mpitfield

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Thanks Michael!
Have you decided on a parachute size?

My preference is to bring down my rockets relatively hard, 20-30'/s. That being said, my config puts the chute size in the range of 18" on the aggressive side to 24" on the slow and gentle side. I have several Fruity Chute Classic Ellipticals in the 18' and 24" sizes, and I have a Fruity Chute TARC 24" on order. Depending on how they work out I may go with one of them depending on the field conditions, or I may pick up a TARC 20" as a happy medium.
 

mpitfield

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I just received an e-mail saying mine shipped today with the fin guide!

Question on the motor retainer since the kit doesn't come with one: It looks like the 3D printed tail cone was engineered around the 29mm Aero Pack screw on retainer but I am finding different sizes.

"L" - Fits 29mm tubes with an O.D. of 1.21" (LOC, Apogee, North Coast Rocketry, and Madcow Cardstock tubes)

"L2" - Fits 29mm tubes with an 1.225 OD: (Estes Pro Series II, Q-Modeling, Madcow fiberglass, Sunward & Semroc motor mounts.)

"P" - Fits 29mm tubes with an 1.270 OD: (Blue Tube, PML and Giant Leap phenolic, Performance Rocketry and Hawk Mountain fiberglass. Slightly loose on Aerotech kits.)

Does anyone happen to know the OD of the "kraft phenolic" MMT supplied with the MAC kit?

I just picked off the O/D from my motor mount and it is 1.263", so possibly the retainer I have is the "P" version, which would make sense based on the fit. One other thing on the fin guide, mine was very accurately measured and as a result a bit tight. However just with prepping the fins for mounting, I was able to sand off enough so the fin guide went on well, still a tight fit but it slid all the way up and down.
 

EXPjawa

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The tail cone was designed to clear the Aeropack retainer, as you surmised. It is made so that the closure ring approximately half protrudes; this is enough to grip easily but is still tucked enough to clean up the look. The only part of the retainer that matters to the tailcone is that closure ring; the size differences are for the inner diameter that goes on the motor tube. The tailcone could be conceivably used with either version of the retained, assuming the correct sized motor tube went with it. I think that it is the "P" version that works with the MAC 29mm tube, though it is slightly loose. That clearance gets absorbed by the JB Weld film anyway, so it works out fine. I do know that the "P" is what I used on my 38mm MAC tube.
 

mpitfield

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The tail cone was designed to clear the Aeropack retainer, as you surmised. It is made so that the closure ring approximately half protrudes; this is enough to grip easily but is still tucked enough to clean up the look.

As per Rick, below is a profile pic from my original post. This is with the MMT fully seated in the retainer and the retainer fully seated tailcone.

 

EXPjawa

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Another example (though not a Black Fly), showing the cone fully finished and painted:

34802267570_8e63849811_c.jpg
 

mpitfield

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Time to tack the fins on. I always find it much easier to sand the fins when they are not on the rocket. Using a palm sander with 150 grit, I placed each fin on a hard surface covered with a sheet of 150 grit sand paper and sanded both sides. Depending on the material I may use a finer grit but these canvas phenolic fins are surprisingly hard.

34805452640_51ec5236aa.jpg


While that prepped the surface for paint I also like to prep the surface for the internal and external fillets. Because I don't like to unnecessarily sand I like to figure out where fillets stop. To do this I took two fins, inserted them in the fin slots and marked the fillet area by taking the tool below, which is what I decided to use for the radius of the fillet, and I dragged the round tip across some carbon paper where it meets the plane of the fin and the body.



This leaves a well defined black line where the fillet will end on the fin and body tube. This will create a relatively small (to scale) fillet for this build.



Using a light angle iron I lined up all five fins, with the two marked ones on each end and extended the marked line from one end to the other. This is simply an easy way to do all five fins, vs. insert each fin in the fin slot an mark it with the carbon paper.



I then used some 80 grit sand paper and sanded enough to get a good bite into the fins. Again the grit I am selecting is based on the fin material, the point being I want some good grooves for the fillets to bond to.



I also took this time to sand the BT where the fillets will end up bonding to it. Again I simply do this at this stage because it is a lot easier to sand without the fin in the way.

35129513566_70367fbd62_b.jpg


I then slid the fin guide on the BT and dry fit all of the fins and tailcone to ensure everything was well centered. I purposely kept the fin guide close to the the aft end of the rocket to allow me to easily remove each fin, butter the root with a small bead of Aeropoxy ES6209 structural adhesive and press it fully down onto the motor tube. One thing I did not mention when I assembled and installed the motor tube is that I prepped the tube by sanding it along it's vertical axis. Again I try to prep the surfaces and sand so the potential forces are perpendicular to the groves made by sanding.



Once all five fins were tacked I removed the tailcone to inspect each root to ensure adequate bonding.

34347529164_6bb4e76dd9_b.jpg


At this stage I slid the fin guide up to the mid point of the tip cord and put a large rubber band on each side of the fin guide to keep all the fins tight against the motor tube. I then temporarily reinstalled the tailcone and set it aside standing vertically to cure for 24 hours. Next up is marking and drilling the pressure relief hole in the BT, drilling for the rail buttons and installing the backers, as well as light internal fillets.
 
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mpitfield

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Time for one of my least favourite parts of the build process...internal fillets. I was going to foam the can just so I didn't have to deal with this, however I opted to do fillets on the inside of the body where it meets the fin, mostly in an effort to mitigate the weight in the aft.

While contemplating the process I realized that there may be a better way to go about this. Normally I mix up a batch of epoxy, feed it into a large syringe that has a length of aquarium airline tubing connected to a long dowel, work out the air, then while holding a small flashlight in my mouth, I painfully squeeze the epoxy into the fillet area while drawing out the tube/dowel. This typically takes a lot more time than it should, just in prep and cleanup, and results in about 50% epoxy waste, uneven fillets that are messy, and a fillet that is much larger, in places, than required.

So after a bit of thought I decided to take a .2" diameter dowel, butter it lightly with epoxy along the length of the fillet I planned to do, and insert it into the fin cavity. Once the dowel bottomed out on the forward CR, I moved and rotated it towards the fin while holding it flat against the BT. Once it rotated 180 degrees I then drew it out and just like that I had a small, efficient, very even fillet with almost no mess or waste. As a matter of fact it was so easy I decided to do fillets on both the body tube/fin and fin/motor tube. I was done in 15-20 min, and there was almost no waste and very little clean up.

The results speak for themselves and the technique is so easy that it can make anyone look like a pro.



This was the fifth fillet of what would be 4 per fin, times by 5 fins, 20 in total...and they all looked this good.



Next up, what to do about rail guides. My initial thought was to use the mini rail buttons, however Rick (EXPJawa) quickly talked some sense into me. Then Rick generously offered to give me some really nice surface mount rail guides, that he designed and had 3D printed. I believe Rick had them printed at a relatively high resolution so they do not look like the typical 3D printed components that we are used to, they look high quality and they appear to be pretty strong. However after giving my theme some thought and whether I would mask/paint the theme, or use the decals, it occurred to me with the tight space between the fins that it would be a bit trickier to work with Rick's rail guides. So I decided to use the 3 piece 1010 rail buttons that have the backer/threaded post that you epoxy in the the airframe, and can then easily swap out the buttons for maintenance. Plus painting is a breeze with them.

Because the airframe can distort when they are tightened, I profiled both the backer/post and button to roughly match the airframe.

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Once I did this I realized that if the post turned while I installed and or tightened the button down, that I would need an easy way to turn it back into position. So I simply took a red sharpie and marked the aft side of the post, which allowed me to quickly see it if was still aligned correctly and adjust if not.

34362131784_d3ee2a53ee.jpg


To install them I used a long popsicle stick with some tape wrapped around it that had some sticky side up. This allowed me to stick the backer/post to the popsicle stick and butter a small ring of epoxy around the top edge of the backer/post, insert, then once in line with the 11/64 holes I drilled, I pushed it through the airframe. These holes are a perfect fit and once in they provide enough resistance that it kept the post aligned so no adjusting was necessary.

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Then I installed the rail buttons, tightened them up and set the build aside to allow the epoxy to set for 24 hours.

35041299852_e1a7dbbfb5_z.jpg


Today I started re-marking the fillet area so I could then mask it off in prep for the fillets. The plan is to use Red Barron 30 min Flex Cure epoxy mixed with roughly 50% micro-balloons. This should result in a very light fillet and considering the internal fillets this is not required for strength but more appearance. I have used this mix on several mid-power builds and it results in a somewhat flexible fillet that is really easy to work with from a body work perspective as it sands very well.





I masked the fins and tried to mask the body but the low tack green frog masking tape does not stick very well to the canvas phenolic BT. So I switched gears and epoxied the tailcone in place, now that I am finished with the internals. Currently the build is sitting aside curing. Tomorrow sometime I will grab some higher tack tape and finish masking the BT, then hopefully lay down some, if not all, of the fillets. This is how she looks now, rail buttons were removed now that the mounting posts have cured.

 
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Jozef

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I am curious as too why mini rail buttons did not make sense for this build. Can you share your experience?
 

EXPjawa

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I think its limiting in that we (URRG) tend to put the mini-button rail on a pad that's limited to F-motors (based on distance from people). If a flyer wants to put a H into a rocket such as this (which the rocket can easily handle), it would have to go out onto the bigger pads, placed farther out. So, you'd need 1010 buttons. But if you wanted to build one of these light, and keep in on small motors, then yeah, mini buttons could work.

Mike, I guess you'll just have to build another 54mm rocket to use those airfoil buttons. I suggest the Scorpion... :rolleyes:
 

mpitfield

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I am curious as too why mini rail buttons did not make sense for this build. Can you share your experience?

Basically what Rick said plus the following:

Mini rail buttons require the 20x20mm rails and not all clubs have those yet, so I am more likely to have better compatibility with the launch equipment by using the 1010 buttons. I literally just got home from a LPR-MPR launch and our club has all the rod sizes and a 1010 rail, but no 20x20mm rail. I have 48" 20x20mm rail and will bring it when I am launching any of my rockets with the mini buttons, but if I don't have to pack it then I would rather leave it behind. Actually today I forgot the rail and had to turn the car around, and in the end I did not launch the rocket that needed it. I also feel that the the mini rail buttons are likely to need replacing sooner than the 1010 rail buttons.

Mike, I guess you'll just have to build another 54mm rocket to use those airfoil buttons. I suggest the Scorpion... :rolleyes:

I was just thinking where I could use them and have a nice scratch design that they would work well on. Plus the theme I have in mind does not interfere with where I would likely place them. I just need to get through the embarrassingly large build pile :flyingpig:
 

DavidMcCann

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Those fins are on there. Nice.

This is going to be a fun ine one to watch fly.
 

mpitfield

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Those fins are on there. Nice.

This is going to be a fun ine one to watch fly.

Yeah she is a tank and I am looking forward to launching her! I was hoping to have her ready for URRF4 but I want at least a week for the paint to cure, so unless I have her ready for paint by Wednesday then it will have to wait for another launch.

Just as a follow up to the discussion on the rail button choice. Below is a pic of the "3" (actually 4) piece nylon mini-rail button from rail-buttons.com, beside the 3 piece plastic 1010 rail buttons that any number vendors sell.

 

mpitfield

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Fillets done, and they were easy to do. They also weigh next to nothing.

I have used the following combination on a few MPR and even some HPR builds (that are not expected to hit the higher velocities) and it has worked out very well. I take Red Barron Flex Cure 30 min Epoxy and mix it 50:50 by volume and then add roughly the same 50% of micro balloons, so a 33:33:33 ratio. Beyond thickening the epoxy, it also cuts a bit of weight and it is also relatively easy to sand. Of course it weakens it as well, but that is why I use it appropriately.



What you end up with is a white creamy epoxy.

35189823256_1185a59ee0_z.jpg


I finished masking the body with a white, higher tack, tape then wrapped the lower tack green frog tape around the body tube fore and aft of the fins. Although the green frog tape does not adhere well to the canvas phenolic body tube, it sticks to itself well. As I mentioned in my previous post, I used the flexible paint tool to draw out the fillets, as the end of the tool has a nice radius. This is the first time I was able to do all fillets in one go and it literally took me less than 10 min, I timed it. This tool is by far the best thing I have used for fillets and I will be looking for one in a bigger size to use with bigger fillets.



I waited until it was set but still rubbery then removed the masking tape.

35100035381_b04d51eeef_b.jpg


Beyond installing the retainer, which I always do after paint, this concludes the build portion of the body. Next up is the body work in preparation for paint, as well as prepping the nosecone for the AV bay, and bodywork to prep for paint.
 

mpitfield

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Deke

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Awesome Michael!
You mentioned at the end of post #44 that next up is marking and drilling the pressure relief hole in the BT. I assume that is what I am seeing in the picture above as the small hole above the two rail buttons? Could you please expound a little on the size of the hole and how it's location was chosen? This is new to me, thanks in advance!
 

mpitfield

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Awesome Michael!
You mentioned at the end of post #44 that next up is marking and drilling the pressure relief hole in the BT. I assume that is what I am seeing in the picture above as the small hole above the two rail buttons? Could you please expound a little on the size of the hole and how it's location was chosen? This is new to me, thanks in advance!

It's more of a best practice than a necessity, but I do it for all MPR-HPR rockets regardless of their potential velocity, and regardless of using sheer-pins.

I am sure you are aware that if a volume is not adequately vented then it could create a higher internal pressure vs. the external pressure. In an extreme case this could force the nosecone off and cause the rocket to split, deploy. The idea is to attempt to equalize the pressure by venting the internal pressure, but not create a large enough vent that it depreciates the deployment charge pressure.

In this particular case the location is somewhat arbitrary and more of a preference, it simply "needed" to be in the payload section. I drilled mine about 15mm above the top of the motor tube and on the same side as the rail buttons.

For sizing I use a calculator and rounded down. I you want the tool (Excel workbook) I can send it to you. It is an all in one workbook containing a number of tools others have developed in Excel, I just consolidated them into one workbook. The estimated volume was just over 450mm cubed, which roughly worked out to a single 3.3mm hole so I rounded down and used a 1/8th (3.175mm) drill bit.
 

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Yes, the Excel file would be great!!! Would you just post on here and I could "grab" it or do you need my e-mail or something?

To be perfectly honest, I would never have attempted this build had you not posted this highly detailed build thread, THANK YOU!

This kit is unbelievably solid as well. I'm just glad the phenolic fins came "pre beveled", I don't think the local Wal-Mart could have kept up with my sandpaper demands!
 

mpitfield

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Yes, the Excel file would be great!!! Would you just post on here and I could "grab" it or do you need my e-mail or something?

To be perfectly honest, I would never have attempted this build had you not posted this highly detailed build thread, THANK YOU!

This kit is unbelievably solid as well. I'm just glad the phenolic fins came "pre beveled", I don't think the local Wal-Mart could have kept up with my sandpaper demands!

Glad to have been some help in giving you the confidence to go with this build...just remember it's only rocket science.

Here's the Excel workbook, feel free to ask questions View attachment Tools.xlsx
 

mpitfield

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Spot putty and post sanding bodywork complete. First step was to apply the spot putty in the fillet areas and the tailcone, the rest of the body tube is fine. I typically use more than required, but not too much as this stuff can crack if you lay it down too thick. It really has to be done in a well ventilated area however the off-gases disappear pretty quickly.

35235989406_2aa680e71a_b.jpg


Now that the spot putty is applied and dried, it is time to block sand 99% of it off. I use a relatively firm foam block about 1" wide by .5 thick and 2" long. It is a great tool for sanding in curved areas and body tubes. It is firm enough that you can actually block sand uneven surfaces but flexible enough for the rounded surfaces. At this stage I switch from 220 to 320, which gives me better control over the sanding. The spot putty comes off with ease and if you use too low a grit then you can easily cut grooves into the ends of the fins, as well as where the fin meets the body. So a higher grit and slower sanding helps to control this.



About half way done.

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All done and she is turning out nice, this canvas phenolic is a dream to work with, it's almost cheating!

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One more a bit closer. I am really happy with the results and to the touch everything feels seamless and smooth, including the layers of PLA in the tailcone. Once I give it a uniform finish with the filler primer I will easily pick up the last defects, and if any use the spot putty to blend them in and they will disappear once the base coats are applied.



This part is now ready for masking, tacking and primer. I will set it aside and try not to touch it as it does not take much to transfer oils from your fingers onto the surface. If I remember I like to wear gloves when handling it at this stage, but that's a bit hit and miss for me.

Before I move forward on paint, I will prep the nosecone so they can be assembled, masked together, and painted together. Otherwise you can end up with paint differences. I have done this several times where I painted items separately and used slightly different processes, and I can tell the difference. I am sure some of you can easily paint separately without seeing a difference, but I am not that good, so this method works for me.

My formula for plastic nosecones is always the same and I get really good results with paint adhering to them, which can be a challenge. I will post the process and results separately. Hopefully I can find some time tomorrow to get the nosecone complete or at least started.
 
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watheyak

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I really like how you rounded the edges of the tips. I think I'll do that on my MAC kit.

I wicked some thin CA into the fin bevels to get rid of some of the fuzziness that filler primer wasn't taking care of. The CA and a little 320 grit did the trick. Yours may not have that issue, I know Mike and others haven't. My painting technique is the suspect.
 

mpitfield

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I really like how you rounded the edges of the tips. I think I'll do that on my MAC kit.

I wicked some thin CA into the fin bevels to get rid of some of the fuzziness that filler primer wasn't taking care of. The CA and a little 320 grit did the trick. Yours may not have that issue, I know Mike and others haven't. My painting technique is the suspect.

The sharp corners and crisp edges looks great on the shelf but the plan is for this bird to see a lot of flights. So I always try to take the sharp edges and corners off my fins before they get compressed with a tough landing, even on my carbon fiber rockets.

Thanks for the insight into the "fuzzies", I will have to pay closer attention. What primer are you using? Did you wick the CA in before priming or after priming?

I don't appear to have a lot of fuzzies right now, but as you know stuff shows up after that first coat.

With cardboard, PML Quantum tube, and the plastic nosecones I have had the "fuzzies" However so far I have had good results by taking a dry 320 (cardboard builds), wet 400 (everything else) and block sanding the initial prime coat relatively smooth, then just laying another light prime coat down. I guess we will see if that works on the canvas phenolic.
 
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EXPjawa

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For whatever reason, your photos don't show up when I check this through the server at work, though I can when I go home (I haven't noticed that elsewhere). Anyway, on thing to watch with the canvas tube is that the phenolic can be porous in spots. Sometimes these spots hold sanding dust, so you don't see them until after you've moved on in the process. I just found that with the PAC-3 that I'm building; I thought I'd finished the filling and priming phase, so I wiped it down and sprayed the first coat of color. Once it dried, I found that there were several spots I missed filling that weren't noticeable while I was sanding and priming. So now, I'm waiting for it to dry enough to fill, sand and respray. If the MAC canvas tube has one drawback, its that. But I'd much rather contend with some spot filling than spiral grooves! And the tubing doesn't really get fuzzies, though the beveled edges on the fins do.
 
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