Public Missiles - MR-1

Contributed by John Lee

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

Public Missiles, Ltd. MR-1

Brief:
The MR-1 is something that looks like it comes out of an ordnance inventory. Opening the bag, that impression is confirmed as one looks at the parts. The Quantum tubing and glass fins make this a heavy and substantial rocket. The NC makes it even more so.

I am hoping to get a chance to do some HPR flying in May at the West Texas Thunder event so I started looking through some of the bigger kits sitting around and this one came up first. Mine came with a 29mm mount but it is available with a 38mm mount as well.

Construction:
My first step on reading through the instructions was to take a closer look at the Quantum tubing. I had never worked with this stuff before. It came with a high gloss and an insert dealing with this material said that all surfaces to be epoxied or painted should be scuffed with sandpaper to promote greater adhesion. That being the case, I gave it a good scrubbing which removed the high gloss.

The kit came with two plywood centering rings. One of them has a slot to accommodate the nylon harness. I test fit them in the BT and the motor tube and found both to be extremely tight on both the inner and outer circumferences. I started to sand them down. According to the instructions, a bit of tightness is desirable in the forward ring (the one with the slot) but the rear one should be loose enough to slip off without too much trouble. Eventually, these criteria were met.

Public Missiles, Ltd. MR-1 A mark was made on the forward end of the motor tube and a band of epoxy was run around the circumference with a 1" gap for the strap hole. The ring was then seated. When the first bit of epoxy had set, the forward ring was filleted, again leaving a gap for the strap.

The rear ring was then slipped on but not epoxied. To facilitate removal later, the instructions directed that I attach 3 strips of cellophane tape to ring.

The kit uses a piece of flat nylon strap for the recovery harness. It is supposed to slip through the notch of the forward ring. Mine would not and my attempts to get it to do so resulted in a frayed mess. I used a razor knife to cut off the fraying and form an angle at the end of the strap. I also used the knife to whittle away a bit more material and make the slot bigger. After doing that, I was able to use a pair of pliers to pull the strap through so that 4" were along the motor tube. A bed of epoxy was laid down and then the strap was embedded in the epoxy and held down with masking tape.

The next step was to install the motor mount into the airframe. The instructions called for placing a ring of epoxy 7 inches in from the aft end. My swabs were only 6 inches long so I used some CA to glue a swab to a mixing stick. The lengthened swab was then marked at 7" and a ring of epoxy was applied. The motor mount was shoved in, making sure that the strap was offset from all fin slots. It was pushed in until the end of the motor tube was flush with the airframe.

Public Missiles, Ltd. MR-1 Fin attachment began by applying a bead of epoxy along the root edge of the fin and then inserting the fin into a slot until it comes to rest on the motor mount. Once in place, alignment was checked and the fin was taped to hold it in position until the epoxy set. Then the next fin was done in the same manner as was the third one.

With the fins in place, I used the tape tabs put earlier on the aft centering ring to pull the ring out. This gave access to the joints between the fins and motor tube and the fins and inner BT. Small batches of epoxy were mixed and a long swab was used to fillet the inner and outer joints. At the same time, the outside of the BT was filleted to the fins. The epoxy fillets were smoothed by a glove clad finger dipped in alcohol.

At this point I need to confess up to a blunder. My thought was that the inner fillets did not need to be pretty and I was kind of messy applying them. This led to later problems in getting the aft centering ring back in place. I ground the blobs down as best I could but the ring still wouldn't go in. I used a sander to remove more from the outside and my finger with some sandpaper to work on the inside. It helped but not enough. Then I got the bonehead idea of forcing it. I used a rubber headed mallet to get it started and it did start. It was also apparent that it was never coming out again. I was committed. Then I got dumber. I placed the handle pieces of a pair of pliers on the ring and rapped the other end with the mallet. This drove the ring down but also split the wood. It wasn't split enough to be removed, but it was pretty awful looking. I finally finished seating the ring with the mallet and pliers method and then covered it up with epoxy. It's ugly but should work. Besides, people have no business looking up the behind of strange rockets.

Piston construction began with sanding down the piston bulkhead so that it would slip into the piston tube without using a mallet. This did not take too long with a belt sander. The nylon strap attached to the motor mount was then fished through the provided slot, passed through a D ring, and then passed back through the slot and snugged up. Epoxy was then used to bond the strap in place.

When the epoxy around the strap had dried, the piston bulkhead was inserted into the piston tube and epoxied into place with fillets on both sides.

The transition section still needed to be put together. It had to be epoxied to a 1" length of Quantum tubing that would receive the nose cone. I scuffed up the plastic with sandpaper and the epoxied it into place.

The transition was slid onto the BT down to the fins. The strap from the nose cone was then pushed down into the BT on top of the inserted piston and the nose cone settled around the top of the BT as far down as it would go. The transition was then moved up until it housed the lower end of the cone and a line was marked on the BT and the transition slid back down. A ring of epoxy was then applied at the line and the transition slid back into place. You must be careful at this point to make sure that the nose cone does not get bonded.

All that was left, except for the lug, was to attach the strap from the nose cone to the top of the piston.

Public Missiles, Ltd. MR-1

Finishing:
Finishing began with the scuffing of all exterior surfaces with sandpaper. I started with 220# and then went to 400# because I didn't like some of the gouges.

Then it was into the booth for the first of 2 coats of Kilz. When it came out a few days later, the Kilz was lightly sanded and I masked off the part of the rocket from the transition aft.

I am not overly fond of flat paints so I decided to go this something similar too, but not like the "publicity photo". I proceeded to give the forward section a coating of flaky metallic silver. I had gotten a case of the stuff for another project and it has worked well for me.

The silver had a couple of days to dry and then I peeled off the masking and reversed it. The bottom of the rocket was then sprayed with a glossy, dark green. I don't know where I got the can from. I didn't even know that Valspar made rattle cans.

When the green had dried, the masking was peeled off and the results inspected. I was satisfied and needed only to get to work on the lug.

Construction Rating: 4 out of 5

Public Missiles, Ltd. MR-1

Flight and Recovery:
The first flight of the MR-1 was a comic tragedy of errors. I checked and saw that I had put the chute in place and loaded an EconoJet F20-4. It came with a Copperhead igniter, of course, but I had never had too much trouble with those...until today. It didn't even tickle the motor.

I replaced the igniter with a First Fire and got ignition, after a fashion. The motor chuffed for a while but then decided to go with the flow and the rocket took off describing a parabola. At this point, we all knew that trouble was brewing but I kept hoping that, somehow, the chute would eject. I ran around a truck that was obstructing my view and had just enough time to see the following:

  1. The ejection charge fired about 10 feet off the ground.
  2. The chute was in the tube but had not been tied into the harness (It flutters nicely, by the way)
  3. The rocket takes a core sample.

Some of the excitement can be seen here on video.

Things got stranger after that. The first really strange thing is that the rocket had no damage. That made me think it was indestructible and ready it for another flight.

Public Missiles, Ltd. MR-1 This time I loaded a G38-4J. I tried another Copperhead with the same result as before and replaced it with a Quick Fire which did indeed fire quickly. The rocket flew well, went up, sounded good, the piston deployed the chute just the way it was supposed to and the rocket came drifting down. That's when the winds decided to act up and take it towards the Alamo Fireworks warehouse. Ignoring my pleas, it landed on the wrong side of the fence.

Several of us saw it land gently. I decided to go on Monday to reclaim the rocket. Alamo has always been very good about that. At the end of the day though, another club member was driving off and noticed their gate was open. He retrieved his own rocket and my MR-1.

To summarize thus far: the rocket augured in on its first flight and sustained no damage. Now it had landed gently the way it is supposed to and it popped a fin. A video of the second flight can be seen here.

Flight Rating: 4 out of 5

Summary:
I like this strange little rocket. It will be fixed and fly again.

Overall Rating: 4 out of 5

Flights

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