4" Madcow Phoenix Build- Dual Deploy and AV Bay

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sed6

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Before jumping into my L2 1/2 scale Phoenix build I decided to put some of my planned build practices to the test on my Madcow Phoenix. I read a lot of tips and tricks and hope to be able to apply them to the small build and then the big build. I began in Openrocket with Madcows basic 4 inch rocket. I upscaled it to 1/2 scale and then added an AV Bay in the nose, dual deploy and changed some scaling and the fins. I then scaled it back down to 4 inch and began building.

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Here's the basic 4 inch Mad Cow kit. I built the cradle to work on it and you can see my small 1.6 inch Phoenix from launchpad. I tried to build it to scale as much as I could and I'm using it as a guide for the larger rockets.

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First up is the easy Bay. Here I've built the bulkheads for the nose cone using my router.

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I mocked up an Eggfinder which I plan to use in this and my bigger rocket, just to make sure it all fits. I did the same for my two planned altimeter.

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A Jensen circle cutting guide from Amazon really makes it easy to cut perfect bulkheads and centering rings.

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Hope you like.
 
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Up next comes the electronics bay. The challenge here was to make it small enough to give me enough room on both ends of it for a parachute while at the same time large enough to fit my planned altimeter. That was difficult to do because my intention is to keep the scale body panel separation line exactly where it should be which gave me a very tight set of parameters to work around.

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Here's a look inside. At the back side of the ebay you will see three t nuts those nuts index and allow the ebay to be screwed into the upper body tube.

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Cutting body tubes can be difficult but I stumbled upon this great way to do it. The fence on my saw and a couple of screws on the front serve to index my tubes perfectly. A simple line and a steady hand gives me extra clean cuts! I used some CA and sandpaper to reinforce then ends.

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The ring with the cutout was glued nside the body tube to give an attachment point for the e bay. It was a pain getting all three nuts to be spaced perfectly 120 degrees apart, so the bay could index in any position.

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Quite a relief to get this done with no major setbacks. There no nose weight inside yet, but I plan to used steel BB's and there just enough room ahead of the AV sled for about 16 Oz.

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Hope you like.
 
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The fins come next. I want a good fillet between the fins and the motor mount tube. I don't want to try and reach all the way in from the back end of the rocket with a blob of epoxy on a stick, like I've seen some people do. Instead then pockets seem like the best route for me.

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I cut these dams out of foam and hot glue them to the motor mount tube. Once the tube is inserted into the body I can then pour epoxy through the body fin slots to collect in these foam pockets. I then insert the fins through the body making contact with the motor mount tube and they are essentially then encapsulated in epoxy forming a fillet.

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Here I used my sander to bevel a nice edge on the leading edge of all the fins. Before installing I plan to do tip to tip fiberglass on them. Not because they really need the strength but because I need the practice for when I build laminate fins on my half scale Phoenix.

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Here I've got pockets on for all eight fins. A little bit of work, a little bit of tedium, but I'm sure it's going to make for an extra strong build and make my fillets perfect. I also plan to fill my fin can with expanding foam. Again not cause its needed, but because I need the practice.

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I hoped to get to the fins started tonight but no such luck. More pics soon. Hope you like.
 
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Looking great! The epoxy pockets were a good idea, and the foam even better. Keep us posted :w: I am interested to see the final product and flight results.
 
Foaming the can and epoxy fillets. That's over kill.

The foam sticks to anything. I dropped a bit on the slab outside 3 years ago. Sun, cold, wet, jet washer and 3 kids playing games on it has not moved it.

I tacked my fins with 5 min epoxy in a jig then foamed the can. External fillets done
 
I know you are practicing and all, but filling those pockets full of epoxy AND foaming the can is way overkill and putting a lot of extra ass weight into a stability-challenging design. Frankly, these 4" Madcow kits can probably be fine without any internal reinforcing. I built a 4" Frenzy with minimal internal fillets, and it is sturdy as a rock. No problems through small K motors.
 
I hear you guys. But the expanding foams only going to add about 2oz which shouldn't be too big a deal on a 60oz bird.
 
Your bulkheads and centerings rings look great! Could you post a link to the circle cutting guide that you used? I searched Amazon for "Jensen circle cutting guide" to no avail. And after hacking together an av bay for a nosecone this weekend, I'm definitely interested in a jig that could help me get a more professional look.
 
Your bulkheads and centerings rings look great! Could you post a link to the circle cutting guide that you used? I searched Amazon for "Jensen circle cutting guide" to no avail. And after hacking together an av bay for a nosecone this weekend, I'm definitely interested in a jig that could help me get a more professional look.

Was thinking the same things.... I did find this https://www.amazon.com/dp/B00009K77A/?tag=skimlinks_replacement-20

Looking very nice so far!
 
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Was thinking the same things.... I did find this https://www.amazon.com/dp/B00009K77A/?tag=skimlinks_replacement-20

Looking very nice so far!

Thats the one. Thank you both for the compliment. Indeed the guide is the way to go. A little pricy perhaps but you make up the cost after a dozen (or less). Plus the freedom to make them on demand in any dimension is great.

Here's a shot of how I set mine up, clamped to my workbench. This is NOT how it should be used. Three times my workpiece was pulled from my fingers and left to spin out of control on the router bit. One mangled the ring beyond use, number two flew off and hit my shoulder, number three I regained control and finished the cut. Additionally one time my clamps failed and the router tipped over after I removed my hands from uptop but before I could turn it off (didn't know the clamps were loose until then) and clattered toward the floor, the cord pulling tight saved it from hitting the floor.

A proper router table would be a much safer way to use this and is next on my list to buy or make. I have three routers and two router tables already, just not one yet for my Hitachi plunge router. A plunge router is nice but probably not required if your router has easy depth adjustment.

Safety first!

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I was objecting more about the fillet pockets, not foam! :)

Gotcha. Maybe I'll figure out the weight of the epoxy fillets vs the foaming and sim it out. It's all worth considering for someone with my limited experience!
 
Gotcha. Maybe I'll figure out the weight of the epoxy fillets vs the foaming and sim it out. It's all worth considering for someone with my limited experience!

Okay so I did the math. I have 9.25 cubic inches of fin pocket to fill, minus the 3.84 cubic inches of the fin roots which leaves 5.41 cu in of epoxy needed. 5.41 cu in converts to 3.0 fluid ounces. 3 fluid ounces of 20 minute slow cure epoxy weight just 1.73 actual ounces. So it seems both the fin pocket option or foaming the can will add about the same weight. I have enough of the rocket built that I can probably get a good static CG. I can sim it in OR and add some anticipated weights to see the impact. And I will, but I already know what I'm going to do :)

Edit: or maybe not. She weighs 64oz right now and balances right in front of the fins (1.5 calibers from CP). To stay at that stability margin means each ounce in the fin finishing (attaching, glassing, fillets and foam) means an ounce of ballast in the nose. Eikes! More thinking...
 
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Alright my Fiberglass arrived! Too late to start tonight but perhaps tomorrow. I did break out my vacuum sealer that I've been dragging around since college days, still works like new. Check out those flattened BB's.

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Okay, glassing complete. What a pain. I couldn't catch the glass at the leather stage so when I pulled it from the bags it was fully cured. This meant lots of extra sanding to get the leading edges perfect again. But it was worth the effort. I doubt the 3oz cloth adds too much strength to the small rear fins, but the 6oz cloth on the large fins improves their rigidity noticeably. Anyway it's all practice for my bigger bird.

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As expected the glassing didn't do anything to help remove the warp from the one fin. It's only about 1/8-3/32" out, so I might be able to address that when attaching the fins.
 
I also added a little filler (too much) to remove the spirals. Ugh, more sanding. I also made some rail button mounts to install soon.

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I'm just loving this build. Great work.
 
I'm just loving this build. Great work.

Thanks! More progress tonight. Got all eight fins tacked in place. Tacked is a relative term as the entire length of the fin roots got a thin coat of 20 min epoxy, attaching to either the MMT or outside of the body tube. Those bonds are going to be so strong by themselves that I doubt any additional reinforcement would be necessary for the motors I plan to fly H-J.

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I started with the four rear fins using a large square to keep each perpendicular to the table. Then I used the fins and clamps to line up the front fin and keep it perfectly parallel and perpendicular. Yep I said it. I was able clamp the warp out of my one warped fin!

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I don't like the design of the rear fins and fin slots. The exposed wood is a pain to get and keep flush with the body. I had to CA that short section on both sides of four fins and then sand them flush. What a pain and it's going to require additional work to make super smooth.

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Of course I'm going to fillet the fins to the body tube! I'm also going to foam the can, but decided to pass on utilizing my carefully crafted fin pockets. I was going to foam the can first but quickly figured it was going to ooze out of a mile of fin/body tube joints. I did each fillet with a small batch of epoxy, no way I could have laid all that in the relatively short working time. I also used a large tounge depressor to shape and work the epoxy along the length of the fin and closely to its end. A little fitness let it just leak around the corner where it'll meet the other fillet.

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I didn't take any pics but I did lay down tape about 1/4" from both the tube and fin. If the tape is removed quickly it provides a super clean edge. If you wait a minute or two too long the epoxy can pull up with the tape and being thicker won't settle back out. Notice the wavyness on the edge of the right fillet compared to the much smoother transition on the left? I fiddled with that fillet for too long before pulling the tape. All that said it'll sand flat with nary an effort. I'd planned to use Bondo to make the fillets perfect but might not have to...

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I'll probably get up early (and/or stay up way too late) to get moving on the other fins. I want to get this ready to paint this weekend.
 
Almost forgot, all my electronics came in. Eggfinder TX/RX, Eggfinder Quark and a cool case to put it in. By great chance a 7.4v NiMH battery from one of my RC cars fits perfectly. Gotta get to rocket done first though.

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Made good progress this last week. I only have three weeks and three working weekends until my scheduled L1/L2 cert flights. Did I mention I'm going for both in the same weekend? :) Turns out my local club is full of great guys with lots of experience, and of course are classic enablers when it comes to hobbies like ours.

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First a sad update on my little TLP 1.6" Phoenix. She lawn darted on her maiden flight due to the Estes D12-5 ejection charge not going off. She flew beautifully though, straight up with no spin to prolly 600'. Estes is going to compensate me for the loss. She will be rebuilt. The fin can is undamaged so it'll be a quick repair.

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With the fin fillets done I moved on to foaming the fin can. I carefully calculated out that two pours, .75oz ea of harder and resin in each pour should fill the can. It didn't and required a 3rd smaller pour. Which worked out fine because simultaneously I was mixing a batch of 5 min epoxy to hold the aft CR in place. It was quite a rush to get the ring in place and hold it all the while the expanding foam is trying to push it back out. I planned for the foam expansion and purposely left the rail button screw holes open so the foam could ooze out. I then ran a tap back thru the t-nut.


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I also installed a switch for my electronics. Very simple design that works great and functions great and took me hours to fab up. All for naught. I was keen to have a small REMOVE BEFORE FLIGHT flag and pin to disarm her but that switch turns out to be way too sensitive to vibration. I hooked it up to my ohm meter and watched it cycle on/off as I rapped on the ebay with my knuckles. Ugh, so I ordered that 110/220v rotary switch that everyone likes and I forget the name of.

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I finally calculated out 13oz of ballast is needed in the nose. It's a tough balancing act planning for stability thru all stages of flight and on a wide size of motors and varying recover options. But the nose weight needs a couple of spars through it for security and that needs done before I can apply her finish so I couldn't put it off any longe . Note the 1" dia/deep hole in the middle, that's to make room for my Eggfinder which is about 6" long. Man, everything is tight or crammed in on this gal.

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This bird is stout. She feels like a club or mace when I turn her upside done. She weighs in at just under 4.5 lbs, sans paint. However her tiny little tail end looked thin and weak so I beefed it up with an extra thick coupler and epoxy for strength.
 
That switch might have worked if you removed the lever arm. Then your pin pushes directly on the switch button. See Perfectflite's website.
But the shurter switches are good too.

Adrian
 
Looks great so far! Keep up the good work

Thanks!

That switch might have worked if you removed the lever arm. Then your pin pushes directly on the switch button. See Perfectflite's website.
But the shurter switches are good too.

Adrian

Thanks! Agreed, my problem seems to be the weight of the arm and roller. I'll mod the setup and see if it helps. I also have my Shurter switch in hand already thanks to crazy fast shipping from Apogee Components.

Made some more progress.

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I got my vent holes and shear pin holes drilled. It was a harder process than I thought. Foremost was not drilling the wrong spot on the tubes. I had to also give consideration where the rivet/screws are on the decals I plan to add. And then make then not too big, not too small, and don't forget to separate the tubes before reinforcing the holes with thin CA!

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I'm also fiddling around with my e bay arrangement. I believe this arrangement will work. More to come.

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Yeah that's a lot of paint. Three different primers (wanna test their differences), and a few that might make it as a final coat. I'm prolly going to auto rattle can clear her when I'm done. I used it for the first time on a small project and was amazed with the results. Best clear I've ever applied.

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First up is the nose cone. I know it's gonna need some Bondo so a quick coat of plastic primer first and I'll get at it.

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Paint prep is time consuming. Here I thought I was just gonna tape off the MMT but decided the rear end needed some attention. I plan to paint it black but thought a thinish coat of epoxy would give the paint some help protecting it.

My to do list is long but getting shorter. Off to paint!
 

Ha, thanks! The leaf switch is gone now, replaced by the rotary switch. Still room to stack some e bay components, two plus a battery easily.

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Threw some primer on the body. Seems the thumb is rotated but if you click it's upright.

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As noted the fin joints are going to require some Bondo Glazing/Spot Putty.

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Nose cone came out good. I applied way too much Bondo and had to sand the snot out of it. Still not as 100% round as when I started but the mold lines and ballast drill holes are gone.

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I'm not sure the spirals are 100% gone. It's prolly gonna take another coat or two of primer. Or worse.

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Took a break from paint to fab up some charges. Broken Christmas bulb, drinking straw and hot glue. The 1/2 dozen I tested w/o powder worked perfect. Starting with .5g and may test tomorrow.

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More progress. Red filler, sand, gray primer, sand, Bondo Glazing putty. Next more primer.

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I found a few minutes between coats of paint on the body to test out my Eggtimer Quark. Check it out.

[YOUTUBE]7y6Z9w-DGtY[/YOUTUBE]
 
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Decided to take a break from painting. Assembled my Eggfinder TX. It works! Added the optional bigger antenna. Took just 2-3 minutes to lock on to a satellite once outside. Next up, Eggfinder RX LCD.

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Was a little warmer today so back into the garage to paint. Spent two long hours sanding. Another coat of primer and more sanding ahead! Just over three weeks to go until my L1 cert flight. Stay tuned cause she's gonna be gorgeous when done ;)

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If you look closely at pic 2 you'll see some fiberglass weave poking through. Appears I didn't get enough epoxy on the glass in a few spots. I'll be much more diligent next time cause its a bear to level and smooth after the fact.

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