Picture courtesy of Public Missiles

Brief:
The PML Phobos is a 2.15" HPR with payload section. I selected it because PML website indicated that is was capable of flying with a J350. This would allow me to use it for both for a TRA Level 1 certification as well as Level 2.

Construction:
The PML Phobos is a 2.15", 57” long HPR with payload section using the PML Quantum (smooth gray plastic) tubes. The Phobos has 3 triangular fins of .062” G-10 with through the body tube mounting to the motor tube. The kit comes with a pre-slotted body tube 34” long, a 12” long payload section and a plastic ogive nosecone. The kit comes with an 8" motor tube and two centering rings. It uses PML’s piston deployment system. The piston is basically a coupler tube and bulkhead attached to the motor mount by a 6’ long, 1” nylon strap and the parachute shock cord attaches to the piston’s D-ring.

Because I planned to fly a 14” long J350W, I changed to motor tube to a 15” long one with three centering rings. The middle centering ring was located just forward of the fin to motor tube attachment. The forward and middle centering were glued to the motor tube along the 1” heavy nylon strap for the piston. The forward centering ring has a slot in it that allows clearance for the nylon strap, which is glued to the side of the motor tube. The motor tube assembly was then glued into the body tube with thickened 30-minute epoxy.

The fins were glued in with thickened 30-minute epoxy with generous fillets on both the outside and inside of the body tube and on the fin to motor tube joint. It is a real challenge getting the internal fillets done with only about ¼” of clearance between the body and motor tubes. I used a bamboo skewer to dab the epoxy in trying not to get too much where the aft centering ring location.

I also glued aluminum circuit board standoffs that were about 1” long x 3/16” OD with #6 internal threads for a motor retention system at each of the body tube to fin junctions. I found the standoffs at a surplus electronics dealer.

Next step was gluing on the aft centering ring with 3 holes drilled in it for the #6 screws for the motor retention system.

The remainder of the kit was built stock. The piston required extensive sanding to get a smoothly sliding fit it the body tube. The body tubes, parachute and nose cone were first rate. The fins required some cleanup so that all were exactly the same. I thought the plywood in the bulkheads and centering rings were of only of okay quality due to some splitting of the wood.

My rocket came in a 35-oz or 3 oz heavier than listed. This was mostly likely due to the longer motor tube and larger amount than normal of epoxy on the fin fillets.

Finishing:
The Quantum tubes are very easy to paint since they are so smooth (no spiral line!).

Construction Rating: 5 out of 5

Flight:
PML recommends motor ranging from hotter F's to J350’s.

My first flight was a TRA level 1 certification flight using a 38 MM H123W-10 at San Diego’s Tripoli Ocotillo Test Range (500’ elevation, FAA waivers from 10,000’ to 12,500’). Perfect flight to about 2800’ landing 100 yards away.

The next flight was TRA level 2 using a J350W-14 with a Missile Works RRC altimeter recording altitude. Good flight with a little weather cocking in the wind to an altitude 6956’ on the RRC (PML says 6915’ with 15.6 second optimum delay) and drifted about ¾ mile way taking two of us about ½ hour to find.

Third flight was on an I161W-14 going about 4600’ up landing about ½ mile away.

A friend built a Phobos with similar modifications at the same time and has done his level 1 with a H123W and level 2 with J350W as well.

I have since modified mine for dual deployment and have flown it on an H123W-10 with perfect results.

Recovery:
The rocket has not sustained any damage other than minor paint chipping. The Quantum tubes and G-10 fins are tough. Landing area at Ocotillo Test Range is open desert with hard dirt and some rocks. The piston deployment system has worked well and no wadding is required. I have used about 0.6 grams (1/8 teaspoon) of black powder for the ejection charge with good results.

Flight Rating: 5 out of 5

Summary:
This is one tough rocket that can fly on a wide range of motors from F's to 700' to J350's to 7000'.

Overall Rating: 5 out of 5