Performance Rocketry Mad Dog 4" & Competitor 3"

Thinking about building these 2 kits. I have a couple questions....

1. The motor tube that is included with the kit is only 16" long, I plan on flying some "K" motors that are anywhere from 3-6" longer than this motor tube. Should I buy more motor tube and install a longer piece? If I use just the 16" tube, will I just have to use that much more cellulose to protect my recovery harness and parachute?

2. Any body out there know if these kits will hold up to full "K" flights without additional reinforcement? ie: glassing the fins

3. I would like to use a AeroPac motor retainer, would I buy the style for PML tube or LOC tube to fit on the performance rocketry fiberglass tube?

Thats about is for now, thanks in advance!
Steve

Answers to your questions:

1) You should be fine on the length of motor tube. You don't need the tube to be the full length of motor, just long enough to "support" it. I'd say you should be fine even with a full K (~29" depending on company)

2) Fins should be fine for full K flights without reinforcing. Fins on the competitor are small and I think both kits come with 0.125 thick G10 fins...more than capable of withstanding K flights.

3) PML style

In building, really rough up the bonding surfaces with 40-60 grit sanding paper to give the epoxy something to "bite" into.

I'm in the process of building a Competitor 3". I modified it to have a break just above the motor for zipperless, but I left room for 28" of motor (large K or 54mm L). I might add a ply ring up towards the top, sized for the motor casing OD for the long ones. Since it's only the drogue, there should be plenty of space left for recovery.

Going from recommendations of those more experienced, I plan on building the fincan separate, so I can do some good fillets with chopped glass, then do a light tip-to-tip once it's installed.

For the Aeropac, you want the one sized for PML. I am using the bolt-on version that attaches to the aft centering ring. That way, if something bad happens (ballistic), I can easily pull it and reuse it.

Good luck with your choice.
Ken

Just a tip or 2

I have flown the Mad dog on L's just as it comes, so no problem there.

If using the retainer with the bolts: much easier to buy an extra wood centering ring. Way easier installation than trying to deal with the thin G-10. Also this will allow you to mount it flush with the rear of fin can, rather than recessed.

Tip to tip is not needed.
Much simpler to inject your internal fillets, rather than building it outside the airframe.See the Gizmo build thread on how to do this. I have used this technique with chopped carbon fiber, stock G-10 fins, no tip to tip, very small external fillets and flown N motors with no problems. Oh yeah, and had hard landings on playa, with no ill effects.

Lighter builds = higher flights on smaller motors. When done right , no loss of strength.

Well, you guys have answered most of my questions. Now back to only having the 16" motor tube, if the motor extends way past the motor tube, how do you recommend I protect my chute and recovery harness? Do i just fill the crap out of the thing with cellulose wadding or ????

Thanks
Steve

My Mad Dog will take just about anything. I wish I would have put a 75mm mount in it instead of the 54mm. Ive flown mine on J-1999, K-1100, L-1860,next on deck will be KBA K-1750 or an EX 2 K-550 motors put together = L-1100. Maybe some try I'll try to shread it with a Kosdon L-3000.

3lap,

Rather than using cellulose for wadding, invest in some Kevlar or Nomex chute protectors and some Kevlar harness. Use a kevlar leader that reaches out of the tube then tie your tubular nylon harness to that. Tie the protector on the kevlar so any ejection charges don't get to the nylon and burn it up and you will be good to go.

Also, most of the 54mm motors over 16" long don't have an ejection charge so you won't need to protect your harness and chute from the motor side.

Hope this helps.

All of the CTI "K" 54mm motors have ejections charges, as do a lot of the AT motors, I do plan on using motor ejection. If I use a kevlar harness attached to a U bolt and a kevlar chute protector does this mean I do not need any cellulose? Also, I do not understand what you mean by using a harness that comes outside the airframe, any links to a website or something where I can see what you mean?

Thanks
Steve

Look at this build thread for the PR Little Dog. It worked fine for my Little Dog. If you use a little larger Kevlar harness, it should work fine.

https://www.rocketryforum.com/showthread.php?t=41804