LOC - Clyclotron

[JAL3]

The LOC Cyclotron looked to be a fairly simple HPR build suitable for somebody with not too much HPR experience. It was a kit I had around for a while but did not get around to building because of few opportunities to launch anything in the HPR range. With some prospects for flight opening up, I dug out this this and got to work.

 

[JAL3]

The first thing that struck me as unusual about this kit is that the directions did not direct me to start with the motor mount. Instead, the tube fins came first. Six tubes were provided already cut to length.

 

[JAL3]

The tubes were divided into three pairs and then an Estes angle was used to put a straight line along the lengths of three of them.

 

[JAL3]

The tube pairs were then compared for length to make sure that they were all identical. One tube was a bit longer than the others but a belt sander quickly solved that problem.

 

[Rocketjunkie]

WARNING!! If your kit is like mine was, the tube fins are *couplers* and will not fully enclose the main tube per the instructions. I put strips of 1/32" plywood in each joint. If you've already glued them in pairs, 1/16" thick spacers will work. Also, the space between the tube fins and main body will not allow a 1/2" rod to fit. I had to use a 3/8" (or 7/16") rod.

 

[JAL3]

Some 15 minute epoxy was mixed and a brush was used to paint it along the lines scribed onto the three tubes so marked. The tubes were then pushed together in pairs, checked for alignment and set on a concrete floor to stiffen up.

 

[JAL3]

About half an hour later, the tube fins were stiff enough to continue work.

 

[JAL3]

Strips of masking tape were placed at either end of the tube pairs to serve as dams. Some 20 minute finish cure epoxy was then mixed and poured into the creases between tubes. They were set aside to harden and a day later the pairs were turned over and the opposite creases were treated to some epoxy filler.

 

[JAL3]

WARNING!! If your kit is like mine was, the tube fins are *couplers* and will not fully enclose the main tube per the instructions. I put strips of 1/32" plywood in each joint. If you've already glued them in pairs, 1/16" thick spacers will work. Also, the space between the tube fins and main body will not allow a 1/2" rod to fit. I had to use a 3/8" (or 7/16") rod.

Thanks for the warning. I'll be on the lookout for this when I get another chance to work on it.

I'm not worrying about the lug because I am going to use a linear rail lug and feed the rail through one of the tubes.

 

[JAL3]

Construction of the motor mount was a simple affair. It consisted of a 38mm motor tube and a pair of centering rings. The interiors of the rings needed a bit of sanding to fit over the motor tube but that was easily accomplished. A line was marked 1/4" from either end of the tube and the the rings were epoxied into place.

 

[JAL3]

When the epoxy had stiffened, a substantial epoxy fillet was laid down on the forward end of both rings. When that had stiffened, a fillet was also placed on the rear side of the forward ring but the rear of the aft ring was left unfilleted for now.

 

[JAL3]

A member on TRF warned me that the tube fins for this rocket were made from coupler tubes instead of the body tube and, as a result, do not close perfectly when arranged around the BT. I found that this was indeed the case. He solved this problem by slipping some plywood spacers between the tubes. I considered doing this and, while I think that is the best way to go, did not do so because I had no plywood of the appropriate dimension sitting around and I was impatient to proceed. I decided to leave a small gap between each pair of 2 tube fins. Accordingly, I mixed some 5 minute epoxy and brushed it on to one of the tube pairs. The pair was then applied to the BT while the BT was sitting on a concrete floor, to keep things straight.

 

[JAL3]

When this initial pair had set up, I brushed some epoxy onto each of the remaining 2 pair and the applied them, judging the spacing with nothing except my eyeballs.

 

[JAL3]

The plastic nose cone had quite a bit of flash on it as well as some ugly valleys at the mold lines.

 

[JAL3]

I used a razor the scrape away the flash and then sandpaper to smooth it down. I was still not satisfied so I applied some Squadron green putty to the valleys and set it aside to dry.

 

[JAL3]

The plastic transition, on the other hand, had no problems with either flash or mold lines. It was ready to go so I put some epoxy on the small end and slipped the payload tube over it. I then had to use a rag and some alcohol to clean up the excess.

 

[JAL3]

By this point, the epoxy on the motor mount had hardened. I checked and found that the outer diameter of the centering rings fit the body tube just fine and that no sanding was needed. I mixed some more epoxy and applied a generous ring around the circumference about 8" up from the aft end; that was as far as I could reach. The motor mount was then pushed in until the forward ring was about 2 inches in and another ring was applied just forward of the aft end. The motor mount was then pushed the rest of the way in and the rocket was stood on its tail to let the excess epoxy drift down and form fillets.

 

[H_Rocket]

Here is something to think on. The tube fins on my Cyclotron invariably get damaged on landing (the aft end gets crushed). I solved this by lining them with a layer of lightweight fiberglass. Basically I painted the inside with resin, laid down 2" wide strips of glass, made sure it was wet, then inserted a large balloon to press the glass in place. When done I had a thin very rigid mirror smooth inside.

 

[JAL3]

Here is something to think on. The tube fins on my Cyclotron invariably get damaged on landing (the aft end gets crushed). I solved this by lining them with a layer of lightweight fiberglass. Basically I painted the inside with resin, laid down 2" wide strips of class, made sure it was wet, then inserted a large balloon to press the glass in place. When done I had a thin very rigid mirror smooth inside.

I have to admit that I know almost nothing about fiberglass.

What kind is used? Where is it obtained? What are the things that everyone (except me) knows to or not to do?

 

[MarkH]

What I was thinking is that I would probably have used a regular sized 3.0 inch LOC body tube for the fins instead of the couplers, and cut them to the right length. This would eliminate the gaps between pairs of fins. Then cut an inch or two off the couplers and inserted these short pieces into aft end of the fins to beef them up at the bottom. (Adding fiberglass would make them stronger though.) I know it is too late now but it's something to consider for someone else building this kit.

 

[MarkH]

Something I noticed with the Rocksim file for this kit is that there is a regular fin set (the fins are hidden if you only look at the 2D setup) included in addition to the tube fins in the simulation. (I could be wrong but I don't believe this fin set should be there) This moves the CP farther back then it should be. Delete the 6 trapezoidal fins and the CP moves much farther forward. My experience with tube fins is that they provide less stability margin than regular old fins. This is only a problem if you put a pretty decent sized HPR motor in that shifts the CG too far back, requiring nose weight. But if one is using say an I motor, then they are probably using dual deploy which adds forward mass which mostly counteracts the extra engine mass and nose weight probably isn't needed.

 

[H_Rocket]

...What kind is used? Where is it obtained? What are the things that everyone (except me) knows to or not to do?

While this is not exactly what I used, it is a good analogy.

For a beginner this would be some usable fiberglass.

And this would be a workable resin.

1. Cut the fiberglass into about 2" wide strips that are a bit longer than the fins.
2. Mix up the finishing resin and use a small brush to apply it to the inside of the fin. Make it rather wet.
3. Lay the strips of glass in a 1/4" overlapping pattern inside the fin and sort of pat them down to sit in the resin. You want the glass to soak up a fair amount of the resin. You might have to paint more on top of the glass to ensure it is wet.
4. Insert a 12" latex balloon and blow it up. You will likely get epozy on yor nose. I'm looking for a way to fill the balloon with a hose.
5. Let it cure a couple of hours and pop the balloon.
6. Trim the edges for appearance and you have a nice stiff tube.

This also works to beef up couplers.

 

[JAL3]

While this is not exactly what I used, it is a good analogy.

For a beginner this would be some usable fiberglass.

And this would be a workable resin.

1. Cut the fiberglass into about 2" wide strips that are a bit longer than the fins.
2. Mix up the finishing resin and use a small brush to apply it to the inside of the fin. Make it rather wet.
3. Lay the strips of glass in a 1/4" overlapping pattern inside the fin and sort of pat them down to sit in the resin. You want the glass to soak up a fair amount of the resin. You might have to paint more on top of the glass to ensure it is wet.
4. Insert a 12" latex balloon and blow it up. You will likely get epozy on yor nose. I'm looking for a way to fill the balloon with a hose.
5. Let it cure a couple of hours and pop the balloon.
6. Trim the edges for appearance and you have a nice stiff tube.

This also works to beef up couplers.

Thanks for the info.

Like I said, I have ZERO experience with fiberglass.

 

[JAL3]

A couple of days later I got back to the the nose cone. The excess putty was sanded away and that removed most of the obviously visible problems.

 

[JAL3]

The instructions say that the nose cone can be either epoxied into the payload bay or friction fitted with tape. I almost epoxied it since I never do the payload thing but decided that I might change my mind later. Accordingly I put some tape on the insert of the NC and gave it a tight fit to the payload bay.

 

[JAL3]

The gaps between tube fin pairs was handled by slipping some cellophane tape into the gap and then pulling it up against the joint in the tube fins from the back side. The ends of the tape were folded up to blockade the ends of the tube. This gave a bottom to the trough that needed to be epoxied. Epoxy was then poured into the trough and allowed to set up after which the tape was removed.

 

[JAL3]

The LOC shock cord mount is an effective piece of low tech. A piece of nylon cord is provided.

 

[JAL3]

A loop was tied into the middle of the cord and then overhand knots were tied at either end.

 

[JAL3]

A piece of masing tape was then used to place the outside ends of the cord against the inside wall of the BT.

 

[JAL3]

Four minute epoxy was then slathered over the tape and string and allowed to set. This method has worked very well for me with some smaller LOC rockets. The question arose in my mind, though, as to how effective it would be with a larger and heavier rocket.