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Madcow Megacowabunga
#1
Picked this up at Madcow's Black Friday sale last November.  I think I may have got the last one because I don't see it on their web site now.  Short, squat 8" fiberglass rocket with a 75mm motor mount.  I want to be able to lob it up a couple thousand feet on a high thrust K. Here's my Rocksim file:


.rkt   megacowabunga.rkt (Size: 109.04 KB / Downloads: 3)

This will be an abbreviated build thread just concentrating on the interesting stuff.  The big challenges for me are trying to keep the back end light (no thrust plates here), and putting the electronics and main chute in the standard-style fiberglass nose cone.  I'm generally following a couple year old build thread by Gary Tortora in TRF for the nose cone approach.

Comments and suggestions always appreciated!
NAR 98479 L3
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#2
Preparing the centering rings.  Drill guide for the front u-bolts and the flanged Aeropack retainer:

   

Drilling and tapping the Aeropack holes:

           

The front CR with the u-bolt holes:

   

I want to glue the CRs right to the fin tabs, so I plan to tack in the motor mount and the fins in at the same time. Since the rear CR has to be flush with the motor tube for the flanged Aeropack to fit, it seems easier to attach the rear CR to the motor tube first, and then attach the forward CR after the internal fillets are completed.

Tack in the aft CR flush with  the motor tube:

   

Glue in backing t-nuts, and then a healthy fillet.  I'm leaving a gap for each fin so it will glue in flush to the the CR and the motor tube:

           
NAR 98479 L3
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#3
Fins tacked in with 30 minute epoxy.  I slid the motor mount in from the rear and made sure it was butted up against the fin tabs.  The front CR is friction fitted only:

       

Fin guides are reused from our Formula 200.
NAR 98479 L3
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#4
Over the last 2 days I got all the internal fillets done and the forward centering ring tacked in place with the recovery u-bolts.  Next step is to put a nice healthy fillet on the forward centering ring, and a smaller one on the aft ring:

   
NAR 98479 L3
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#5
Don, I can always count on you to make me feel bad about my building skills. Wink
John S.
NAR #96911
TRA #15253
MDRA
Level 1, 2014-Mar-15 -- Aerotech Sumo, H133BS
Level 2, 2014-Jun-21 -- Giant Leap Vertical Assault, J240RL
Level 3, 2016-03-12 -- MAC Performance Radial Flyer, M1101WH, 13,028 feet
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#6
Ha, not too sure about that John, but thanks!   Smile

Just moseying along...the front CR is filleted in and the upper rail button support block epoxied on:

   

I need to put the fillets on the outside then I'm done with the fin can.  I'm eager to move on to the Nose Cone.
NAR 98479 L3
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#7
Rear CR gets a small fillet too:

   

And here it as after sanding the nose cone shoulder for about an hour to get it to fit:

   
NAR 98479 L3
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#8
Adding Nose Weight:

   

I thoroughly stirred in 4 pumps of West Epoxy for a nice coating:

       

Left in a bucket of water to cure:

       

Total weight approx 4 lbs 8 oz.
NAR 98479 L3
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#9
Making the Nose Cone.  Cutting the Primary Bulkhead out of 3/16" G-10.  The three cutouts are for the two altimeter sleds and the GPS Eggfinder:

       

8-32 PEM nuts to hold the altimeter lids and 5/16" U-bolt epoxied to the underside of the bulkhead for security:

   

Bulkhead tacked to the 23" parachute tube with 5 minute epoxy:

   

Everything dry fitted to the Nose Cone.  I forgot to take pictures but the parachute tube is a 4" FWFG tube with a 1/8" bulkhead epoxied and heavily filleted so it can't get knock loose by the ejection charge. It's set in the Nose Cone so it buts against the front, just about where the nose weight ends:

   

Bulkhead and parachute tube epoxied into Nose Cone:

       

After everything sets I'll put a big fillet around the insider perimeter of the Nose Cone.  All the fillets used around the nose cone are Rcoketpoxy thickened with West 404 high density filler
NAR 98479 L3
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#10
Nose cone fillets completed.  Had to make these healthy since all that nose weight energy has to be absorbed when the harness hits its limits:

       

Here is the first altimeter sled mocked up with the AV lid.  The sled is 3/32" G10 and the lid is 1/8" G10.  I found a few minor fitment issues which I will have to clean up:

       
NAR 98479 L3
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