Performance Rocketry Mad Dog Dual is my first entry into the world of fiberglass rockets. This is also to be my NAR Level 2 Certification project.

    

This is how the Mad Dog Dual arrives. Just the components. No instructions. You have to have some experience building and you have to know a little about working with a G-10 fiberglass high power rocket. I, of course made some modifications. The most import modification was to cut the lower body tube and add a filament wound fiberglass 12" coupler to create a reasonable fin can. That is, the original setup was a very long can where there was no way to reach  a forward centering u- or eye bolt for the recovery harness. The distance from the body wall to the motor tube is pretty short. So various builders have tried to deal with this.

 

 

Fin Can

      


I decided to begin by cutting the lower body tube. The can would be 25 inches. I found it impossible to deal with Performance to get another G-10 coupler for the can. The couplers are forever and ever in back order. They have a e-mail notification for the parts, but I haven't been notified now for 3 months. Giant Leap Rocket seems always to come to the rescue. They are absolutely totally reliable and have a great business, customer oriented, ethic. I cut tubes in a very simply way. I use Tim Milligan's way of circling the tube at the mark so that the ring of paper is perfectly lined up. It gives you a perfect perpendicular line. I take a hobby knife for cardboard tubes and a utility blade for the fiber glass. The point is to simply scribe a groove around the tube. If you going around the tube three or four times, the tube separates. Some gentle sanding is all that's needed to give clean edges. After making a good groove in the fiberglass, I used a hacksaw to work my way around the tube. After three or four turns, the tube separates as cleanly as cardboard. Some flat sanding first with 60 paper, then 150, then 220 you have a very nice edge. It's a perfect fit coupling tubes. You'll barely see the joint. If you look closely, you can see the coupler inside the body tube starting at the pencil. It was epoxied in with 7" inside and 5" out. If you look to the right there's a small arrow pointing at the seam. Tough to see.

Altimeter Bay

I then went on to the altimeter bay.

    

My plan was to "bolt" the altimeter bay to the upper and lower body tubes with 1/4" screw in rivets. No inside nut or t-nut needed. In the photo, all you get with the kit is a 9" coupler and two sets of "airframe" plates and bulkhead plates. This will be a little confusing because the exploded view shows the airframe plate outside the bulkhead plate. There's no way to hold the altimeter bulkhead plate in place. The airframe plate needed to be epoxied inside the bulkhead plate so that the part fits in the altimeter coupler without sliding. It's a reasonable fit. The airframe plate should have been a 1/16" larger. All the hardware in the photo is mine. Note the neoprene washers. I really want a airtight fit so no nasty gases get into that altimeter bay. I use a small one with the wing nuts as well. I forgot to mention the "switch band". I call it that. I cut a 1 1/4" piece from the lower body tube. It was epoxied to the very center of the altimeter.  I drilled holes in the altimeter bay to accommodate  the 1/4 inch screw in rivets.

The 1/4" all thread has a nylon lock bolt at one end and the usual wing nut at the other. Think carefully about where and how you space the holes for the parts. Check the slide tubes on your sled so that the all thread spacing is correct and sled slides easily. You also need the correct space between washers.

      

I decided to use a 1/2" PVC pipe plug for my black powder. It holds up to 2.5 gm of powder. You can go with the 3/4" if you need more. I use the "European" style terminals for the igniters. There's the usual 1/4" forged eye bolt. Note the neoprene washers especially the one for the wing nut.  I really want no corrosive gases to get into that altimeter bay. Finally, put it all together.

   

I like to use a keyed switch for the altimeter. Some don't. I like the Remove Before Flight ribbon. If I goof up my checklist, I will walk away ready to launch and see the flag. That means that I placed the igniter and didn't turn on the electronics. Should there be a launch, I have no chutes. Not good. So, turn the key, pull it out and listen to the beeps. And there's the bigger picture.

There is problem with the space between the motor tube and inside body wall. There's not much room to attach the recovery harness. One way to deal with this has been to cut a 1 inch slot between the motor tube and wall, insert a flat Kevlar harness through the centering ring and epoxy the tag end to the motor tube. The other way has been to but a u-bolt and/or eye bolt in the forward centering anyway, more or less permanently attaching a harness to the anchor, both for redundancy, and just leave it. Another way has been to simply use a plugged forward closure tapped for a 5/16: eye bolt to the motor casing. I thought about this and will probably make it my primary harness attachment. But shortening the lower body tube meant that I could get in there and tie a 1/2" Kevlar or tubular nylon harness to two attachment points. It's a blind tie, but It can be done.


     

Here, I have already epoxied the very loose fitting centering rings to the motor tube after scuffing the surfaces with 60 sandpaper. There is a good dose of epoxy on both sides of the rings. I've just test fitted a 1/2: Kevlar harness from Giant Leap. When the motor tube and rings assemble is test fitted in the fin can, it is possible but difficult to get a hand in to tie this or a tubular nylon harness, but it can be done. And the knot is tight. Again, this can be permanently attached and just forget about it. That forward centering ring will rip out before anything happens to the Kevlar. A couple of drops of epoxy in those knots, and the deed is done. I then slide the whole thing into the can. The challenge is to get that solidly epoxy the entire unit in place and have room for the Aero Pack tail cone. More about that later. But here's a peak.

 

 

I'm just test fitting the nose cone bulkhead. This is a very tight fit. I had to sand the bulkhead considerably. That's because I wanted it to slide in a few inches to accommodate the sheer pins that will be placed at the halfway point on the nose cone shoulder. Eventually, I got a good fit and epoxied it in with two-part 30 minute.

                  


..............and test fitting the tailcone retainer (Aero pack). I'll go ahead and prepare the motor tube for the retainer ring.

By the way. Follow Aeropack's exact measurements for the distance of the ring on the motor tube from the end of the lower airframe. If you don't, the tailcone will never fit properly!!! I'm not going to repeat myself here.

Here, I've epoxied the fins applying the usual internal fillets. I used the BSD fin guide for 3 fins to line the fins up. Looking down the aft end, I'm preparing the can for foam. I'm using a two-part PML foam that will produce a rock solid can.

                  

 
Notice the after rail button setup. The brass insert is epoxied in. It will also be foamed over.

OK. Let's start pouring foam. I'll do it in a couple of batches.


     

The will go right over the aft of the fins. I let it dry for about 4 hours and start grinding down this rock hard stuff with a Dremel and burr. It looks like that and the close-up below. Petty neat. Now I can just epoxy the aft centering ring and coat the area with an epoxy sheet.


                       


At this point, I can epoxy the Aeroteck retainer in place and test fit the tail cone. Pretty close.

Well, it's easy from here. I put it all together and paint it with my favorite automotive primer (no need for filler). I like to leave that way (partially naked) until the successful maiden flight coming up. Here's the calculation for the main chute for a 14 pound launch ready Mad Dog.





I used an RRC-2mini altimeter from Missile Works set to deploy the drogue (26 inch nylon) at apogee and the main (Spherachute 84 inch, 12 panel with 6.21" spill hole ) at 1000'. After ground testing, I determined that each black powder ejection charge was 3 grams. I loaded an Aerotech J415 W for the shakedown.

Ignition and lift-off


  
             

                




  Drogue deployment
     
           


              

        Here is that scary moment when the main is deployed, but the fin can and drogue have to assume their rightful positions under the main. But It all worked!!!

Flight #2
September 11, 2010
Rainbow Valley, AZ

Cesaroni K500 RL

        

September 10, 2011
Second flight with a new red with black trim finish
Mad Rocket Dog Series ("Gooboy")
Cesaroni K660

Video

Note the BoosterVision mount on the upper right. I added a TLS GPS transmitter to a new sled.

  














Good flight.

Flight data

Missile Works RRC2mini

Altitude
8,199 (Predicted 10,578)

Maximum velocity
1,310ft/sec  (Predicted 1,040ft/sec)

Time to apogee
24secs (Predicted 24.03secs)


December 10, 2011
Third flight
Mad Rocket Dog Series "Gooboy"
Rainbow Valley, AZ
Cesaroni K500 RL
Predicted altitude: 6000ft

Launch Video
Steve March, Phoenix, AZ


       

Flight Data:

RRC2mini #1

Altitude:                             4851ft
Maximum velocity:             1090ft/sec
Time to apogee:                18sec

RRC2mini backup:

Altitude:                             4848ft
Maximum velocity:             1050ft/sec
Time to apogee:                19sec