Modification - Longspear 3 {Modification} Modification

Contributed by John Lee

Manufacturer: Modification

(MODS) Sky LongspearBrief:
The Longspear is the recycled body tube and fin can of the Sky Longmarch 3. It still uses an 18mm motor but is now a longneck rocket.

Modifications:
Earlier this year, I bought Sky's Longmarch 3 from Apogee. The rocket was a simple build with a distinctive look to it and, while it would not win any contests, I was quite happy with it. It did, however, have a few problems. One was the extremely large chute, 20" I think, which caused it to drift too far. That was seldom a problem because the shock cord usually failed and the thing would plummet to the earth none the worse for wear.

The original shock cord mount consisted of a piece of sewing elastic held in place with an Estes style mount. It seemed that no matter how much wadding was put it, the elastic would burn through. I decided to solve this problem by mounting some Kevlar® with epoxy, LOC/Precision style and then tie the elastic to the Kevlar. I got to launch this small mod one time, used plenty of dog barf and...the elastic burned through again. The lower body came down a few yards from the launch site with no harm and I got to watch my very distinctive nosecone drift under it's overlarge chute until it was lost in the distance somewhere over US-87.

Not wanting to give up completely, I decided to scavenge the lower body and build something else. I wanted to keep the "Longmarch" theme and decided to build the Longspear 3.

The lower body of the Longmarch 3 consists of a plastic fin can and a pre-detailed paper tube. It is not a kraft paper tube and is not spiraled. It has single vertical seam running the length of the tube and a very glossy finish. It is just a tad larger than a BT-55.

(MODS) Sky Longspear I had some BT-5 tubing laying around so decided to make the upper body out of that since I also had a nosecone which would fit. I did not have a shoulder that would go from BT-55 to BT-5. The best I could do was BT-55 to BT-20. Since I also had a shoulder that would connect a BT-20 and a BT-5 along with a few BT-20 tubes, the spear got longer which did not bother me. I like long, skinny rockets. I decided to used the tubes full length as they came from Estes. I should probably rethink the "3" part of the name.

Assembling the Longspear 3 was simplicity itself. I used CA to glue the nosecone to the upper body tube, the upper body tube to the first shoulder, the first shoulder to the middle body tube and the middle body tube to the lower shoulder. With each addition, I had to check to make sure everything was straight but that was not too hard. I put the screw eye in the lower shoulder with some carpenter's glue and then it was time to try and fit the new assembly to the old lower body from the Longmarch 3. That is where I encountered the only real trouble.

As I stated in the beginning, this Chinese rocket's body tube is not exactly equivalent to a BT-55 and the fit was very loose. The same was true of the old nosecone as well. I used some 18mm Tamiya masking tape to make it a little more snug. In fact, I taped it almost to the point where the tape is as wide as the transition section but not quite. That seems to be just about enough but the upper section is still a bit looser than "normal". An X-Acto knife trimmed the excess tape and the rocket was ready for finishing.

Elmer's filler was used on the balsa nosecone and the transitions. A little was applied to an area of spiraling that seemed to need some work but, frankly, not much effort was put into filling the spirals. A bit of light sanding and it was ready for paint.

 

Finishing:
I am not very good at painting and don't particularly like doing it. No matter how careful I am, I seem to botch things with a run that ruins or at least seriously degrades the project. I have had bad luck with masking tape either letting paint seep under the edge of the tape or peeling up previous layers. A guy in my local hobby shop recommended Tamiya masking tape for models and it has worked much better but it is expensive! While re-reading Tim Van Milligan's book, he recommended using cellophane tape. I decided to give it a try.

The paint scheme I chose was very simple. I was going to paint the shoulders blue to match the trim on the Longmarch 3 and then paint the nosecone red. I decided to try and do a little more and masked off for a simple roll pattern stripe on the shoulder in white. I painted and came out with a mess. The cellophane had leaked badly.

Instead of stripping and trying again, I used Tamiya tape to extend the blue area a bit above and below the shoulders and did away with the stripe altogether. While I was at it, I decided to paint a portion of each of the upper BTs red so I masked for that as well. The results this time were much better. I had one bad spot of leakage that could be fixed but launch day is nigh and she's going "as is".

Final preparation for the Longspear 3 involved ties a 16" piece of ¼" elastic to the Kevlar loop and tying off the other end to the nosecone. It was ready to go.

Construction:

  • Lower Body from Sky Longmarch 3
  • Estes BT-20 tube
  • Estes BT-5 tube
  • Semroc BNC-5W Ogive Nose Cone
  • Semroc TA-2055 BT20 to BT-55 Shoulder
  • Semroc TA-520 BT5 to BT20 Shoulder
  • Semroc SE-1 1" screw eye

PROs: easy, very distinctive

CONs: the long rocket is awkward

(MODS) Sky Longspear

Flight and Recovery:
The first flight was on an Estes B4-2. Everything prepped as normal and it was time to launch the rocket. Up it went doing exactly what it was supposed to do. It almost looked graceful. The 2 second delay was just right and the chute deployed and brought it down gently. I has some worries about this because I used a 12" nylon chute but it did fine. It was a good maiden flight and confirmed my instinct never to try this with an A motor.

The second flight was with an Estes C6-3. Everything went together just like before and the rocket flew off great just like before only higher. Deployment was just right with a 3 second delay on a C. I think this rocket could handle an 18mm D with a 5 second delay but I don't have one.

I didn't have another C6-3 either so I used a C6-5 for the third flight of the day. Again, the rocket was easily prepped and launched but things changed at about 80 feet. It seemed as if the motor stopped thrusting. When that happened, the nose began to drop and it continued to do so, swinging through about 270 degrees so that it was facing down at one point and then swung back to near horizontal. At that point, the motor began thrusting again and it took off horizontally flying a long way. The chute deployed as it was supposed to and it recovered with just a mild dent in the topmost body tube. I am at a loss to explain this weird behavior.

PROs: flew well except for the anomalous final flight

CONs: the anomalous final flight

Summary:
The main pro of this one is that I got to use the lower body for the Longmarch over again. I have no artistic talent and hated to waste that nicely decorated tube.

Related Products

comment Post a Comment