Public Missiles - Andromeda

Contributed by Ken Bracey

Construction Rating: starstarstarstarstar_border
Flight Rating: starstarstarstarstar_border
Overall Rating: starstarstarstarstar_border
Manufacturer: Public Missiles

Picture courtesy of Public Missiles, Ltd     
Pic

Brief:
The Andromeda is a new kit in the Hybrid Ready series from Public Missiles, Ltd. (PML). "Hybrid ready" means that the motor mount is extended to accept the longer hybrid motors. It also has a new style of electronics bay specifically designed for hybrid rockets called the ERM (Electronics Recovery Module). Other than being hybrid ready the rocket is a typical 3 fin and a nose cone style rocket. Being over 7 feet tall and 4 inches around makes it an impressive looking rocket.

Construction:
The rocket was purchased from Kingston Aerospace, an authorized PML dealer, and was delivered to me promptly in large rectangular cardboard box. The components were well packaged and included the following:

  • Pre-slotted main airframe
  • Recovery airframe
  • ERM airframe
  • Nose cone
  • 3 G10 fins (0.093" thick)
  • 54mm motor mount tube (36" long)
  • Various centering rings and bulk plates
  • Various couplers
  • PML piston ejection system
  • 54" parachute
  • PML tubular nylon shock cord
  • Piston system strapping and 'D' rings
  • ERM aluminum threaded coupler
  • ERM aluminum threaded sleeve
  • Altimeter mounts
  • Ejection charge holder and caps
  • Altimeter mounting tube
  • Safety switch and wire
  • Socket head mounting screws and Allen key
  • O-rings for the ERM system
  • Launch rail lugs
  • Instruction manual
  • Decals

This is a standard PML kit which has the usual PML features: piston ejection, Quantum Tubing, etc. The quality is quite good and the fit of the parts is excellent. The centering rings and bulk plates are high quality aircraft plywood and cut with a high degree of accuracy. The instructions are very clear and well written with good clear diagrams. I followed the instructions exactly and had no problems assembling the kit. I used West Systems epoxy (206 slow hardener) for the entire construction. The instructions remind you to sand the parts to be joined to give good adhesion. This is especially important with the Quantum Tubing since it has a very smooth surface and epoxy will not stick to it unless roughened with a good sanding first. I used a PML PMR-54 motor retainer (purchased separately) which as installed after the kit was completed. I also used PML plastic rivets to hold the nose cone on to the ERM airframe instead of permanently gluing it on since I wanted to have access to the nose cone later for installing a tracking transmitter.

Since I planned on using a blacksky AltAcc-2C for the electronics, I had to purchase adapter mounts for the AltAcc so it could be mounted in the ERM system properly (available from PML also). I did not install the safety switch for the altimeter since the blacksky AltAcc is completely safe when the arming screw is not engaged and the arming screw is accessed through a small hole drilled into the airframe making the switch provided by PML unnecessary. The only modification to the internal construction was to the altimeter bay. The ERM system screws together with the altimeter floating inside the altimeter housing tube. Since the altimeter is floating in the altimeter tube and is held in place when the ERM system is finally screwed together, it was possible that the altimeter could rotate in the altimeter housing as the ERM was being screwed together. It is imperative that the AltAcc be properly aligned to the external airframe since there will be an access hole drilled through the airframe to allow arming of the AltAcc. To prevent the AltAcc from rotating out of alignment in the altimeter tube, I glued a small dowel lengthwise in the altimeter housing tube and then notched the altimeter mounting brackets to accept the small dowel. Now the altimeter can only slide into the housing tube in one orientation and cannot change. This allowed me to correctly align and drill the arming hole in the external airframe which is needed to arm the AltAcc.

The supplied launch lugs for this rocket are a major headache to install. If not installed absolutely perfectly they will cause the rocket to bind on the rail. I recommend that you throw away the supplied launch lugs and use a pair of blacksky rail buttons instead - easy and cheap with no binding. They can even be installed at the field as a last minute item before launch prep!

Finishing:
There are no instructions are even pictures for finishing this kit. The only picture is a drawing on the PML website which has the rocket a very dull gray and white. A decal is supplied with the name of the rocket in black and there are two other decals for the ERM system and the standard PML decal. I decided to paint my rocket blue and white with one side of the fins and fin can being black. I also added some gold trim tape to the area just below the nose cone joint. This is where my rivets went in to hold the nose cone on. The gold trim turned out very well and gave the rocket a nice, finished look.

Because the airframe is Quantum Tubing, preparation of the surface before painting is not necessary except to wipe the dust off first. Quantum Tubing paints exceptionally well and is also great for drilling for such things as AltAcc arming holes, plastic rivets and installing rail buttons. I used Krylon Fusion paint made especially for plastic. It is a couple of dollars more a can than regular Krylon but it states that it adheres to plastic better. I did not see any improvement over regular Krylon though, and I will probably go back to using the regular stuff on my next rocket.

Construction Rating: 4 out of 5

Flight:
First flight was at LDRS 24 near Lethbridge, Alberta, Canada. This rocket is so easy to prep that I had it ready to go in only a few minutes. The piston system was working well and the altimeter setup was easy and installed in no time. The hardest part was setting up the Hybrid motor which was also very easy. I used a Hypertek K240 motor (that’s the 835cc tank with the 0.125 injector orifice and a standard J grain). Just before launch, I installed a Walston tracking transmitter in the nose cone and top of the altimeter mounting tube. It easily packed in place using some foam and the nose cone was the put in place and held on securely using PML plastic rivets.

Unfortunately the winds were strong and the rocket waited all day without flying. The next day wasn't much better but the winds died down a bit late in the afternoon and I put the rocket on the pad. The tank was filled with N20. There was a bit of a delay waiting for the LCO to launch the rocket and I believe the rocket was venting N20 while waiting for ignition.

When it finally launched though, it was a beautiful straight flight. The burn was a bit shorter than expected (probably due to some of the N20 being vented prior to launch) and I got a lower than expected altitude--4200 feet as opposed to 6600. The AltAcc reported a burn time of only 4.3 seconds as opposed to the 6.9 seconds the motor was supposed to burn for. It was still a spectacular flight and I was impressed with the performance.

Recovery:
The main chute was deployed at apogee by the AltAcc and the PML Piston ejection system and the rocket began drifting with the wind. The rocket touched down about 700 meters from the launch pad in a gravel pit for an easy recovery.

The rocket received no external damage but there was some damage to the altimeter housing tube. The phenolic tube had cracked where it was glued to the aluminum threaded ring which makes up the Electronic Recovery Module. It was later discovered that the centering rings holding the altimeter housing tube in place had also broken free from the glue joint at the QT airframe. I believe this was probably caused by using too much black powder in the ejection charge canister (piston systems need a much smaller ejection charge than standard ejection designs) and also poor construction on the altimeter bay housing unit (my failure to sand the QT enough to provide a sufficient glue bond). The damage was easily repairable with a little 5 minute epoxy and the rocket was prepped to fly again the next day.

Unfortunately the winds did not let up and there was no other opportunity to launch the rocket at LDRS 24.

Flight Rating: 4 out of 5

Summary:
I really enjoyed building and flying this kit. It was easy to build and flew great. I really wanted to start flying hybrid motors and this is a great kit to do just that since it has all the design features needed for hybrid rockets. The Electronic Recovery Module makes prepping the rocket a breeze but I wish it was set up for dual deployment. PML feels that there is not enough room in the rocket to use their CPR 3000 system but I think the rocket has plenty of room to do drogueless dual recovery and I think PML should redesign the kit with this feature. Other than that, this rocket is an excellent addition to any rocketeer’s fleet.

Overall Rating: 4 out of 5

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