The Vulcan is an old Centuri design made to look like an alien ship. I gets its unusual appearance by being formed from a paper shroud. It uses 18mm motors and recovers under a parachute.
When I was a kid, my favorite looking rockets were the ones made from paper shrouds. That meant the "Bug" and the "Vulcan". The "Point" was already OOP by the time I got started in rocketry. Unfortunately, my clumsy fingers and impatience doomed my efforts and I never got a single one of them to fly.
In my first incarnation as a BAR, I still found myself drawn to the "different" looking paper rockets. This time, Quest was my supplier instead of Centuri. The only one I got to try was the Space Clipper but it too never got finished. The pressing needs of family and school saw to it that all I did that time around was lose a few Mosquitoes (I still have never seen one actually take off; they just vanish) and a LOC Onyx.
Now, I am back and one of the first things I tried was a Semroc Point. It worked! Then I found the EMRR review and the plans at JimZ for that old nemesis of mine, the Centuri Vulcan. I had to give it a go.
The parts list:
I ordered body tubes in various lengths of size ST-8, a nosecone, and an engine mount for 18mm engines in an ST-8 and waited for the parts to come in. In the meantime, I took my "The Point" to a local paper supply house and asked them to match the shroud for me. They came very close. The paper I got is just a tad heavier. I didn't want to wait for them to special order the exact match. Then the parts came in and...
The previous reviewer on EMRR gave the body tube as a Semroc ST-8. Maybe he got it to work but I sure didn't. The body shroud was just not large enough to fit around the tube. I checked the print settings to make sure everything was printing at 100% and it all checked out. Something was clearly wrong.
I went back and took a closer look at the Centuri instructions. After a while it hit me. The body tube is minimum diameter for an 18mm engine. That means an Estes BT-20. A quick check of the standards revealed that an ST-8 has an outer diameter of 0.908" while a BT-20 has an OD of 0.736". When I found a scrap of BT-20 it was just the right size. All the stuff I ordered (nose cone, body tubes, engine adapters, etc.) from Semroc, who provides great and quick service, went into the spare parts bin and the search for the real components began.
The Estes engine mount kit (303158) had the thrust rings I wanted along with the style of engine hook I prefer so I purchased it figuring the other parts would come in handy some day. I bought some more BT-20 and assumed I was ready to go.
My first step was to take the body shroud which had spent the night tightly rolled and use a steel straightedge to apply creases at the appropriate places. The shroud was then cut out with a #11 X-Acto and test fitted around a long BT-20. The fit seemed perfect so I cleaned up the edges of the shroud with some 220 grit sandpaper. I then used thick CA the glue the tab and prayed the alignment was right. It worked.
After I had the body shroud in the rough shape of a cone, I creased and folded the fins, tail, air scoop, and cockpit. I cut them out and affixed them to the body shroud with CA. It was starting to look like the pictures.
My next step was to set the body shroud in its tail and push the BT through the nose opening until it was resting on the table. I marked the spot on the BT, removed it, used a prodigious amount of masking tape to make a guide and cut the tube to length.
My final step for this first round of activity was to cut out the paper appliqué for the aft bulkhead and glue it to a piece of 3/32" plywood. I set this aside to dry and called it a night.
Life intruded for several days before I had a chance to work on the Vulcan again. When I finally had a few spare moments, I used a razor saw to remove as much of the excess material around the after bulkhead as possible, however, I cut it a bit too close. A hasty swipe with the saw scratched the appliqué, which will have to be replaced. Before doing that, however, I wanted to finish getting it to the right shape and size.
I used #60 sandpaper to finish getting it into the rough shape and test fitted the bulkhead into the shroud. It was a bit tight but I knew that before. Before sanding to the final outer shape, I used a 9/16" spade bit on the drill to pierce the central hole in the bulkhead for the BT. At this point, I had to make a choice.
All of the logs I looked at report that this model has some poor flying characteristics. These characteristics seem to be blamed on two separate issues. The first is weight forward so that the CG is sufficiently far forward of the CP. Even after this is supposedly taken care of though, the problem seems to persist in many cases and is attributed to the location of the launch lug in one of the fins, giving it an angled ride up the launch rod. One suggestion on EMRR is to place the lug on the body tube itself. I decided to follow this advice and that called for a couple of modifications.
The aft bulkhead appliqué has a 1/8" x 1/8" notch on the ventral "down" side in order to accommodate the engine hook. I decided that I would cut an identical notch for that purpose on the dorsal (top) side and use the one on the ventral side for the launch lug. I figured it would look better on the rod that way. The notches were cut from the basswood by using an 1/8" Dremel bit to punch the holes and then an X-Acto knife to clean them up. I used a piece of 1/8" rod to make sure it would slide through the gap just fine.
Another issue was the recovery system. As a kid, I liked the shock cord sticker that Centuri used to provide. Now, I wouldn't use one for any reason. I feel much the same way about the Estes style tri-fold. I decided to use Kevlar® tied to an elastic cord fixed to the motor mount a la Quest. The problem is, this is a minimum diameter BT to begin with so there are no centering rings. I had to get the cord into the BT somehow and make sure it was firmly in place. I took a motor thrust ring and cut a small notch in the outside to accommodate the thickness of the Kevlar®. I then tied the Kevlar® to the ring and used a long stick to place a ring of glue deep in the BT. Next, using a spent motor glued to a dowel as a pusher, I pushed the shock cord mount as deep as I could get it. This was almost, but not quite to where the top of the motor would be.
Fashioning the motor mount was easy. A slit was cut for the hook, a thrust ring was glued in place just before the hook, the hook was inserted, and a band was glued around it.
Getting the launch lug right was anything but easy. I had a vision of mounting the lug on the BT just forward of the aft bulkhead and then using a rod to mark where to cut. It turns out that was not such a good idea by itself. The angle of the cone formed by the shroud is such that the rod would bind on exiting no matter what unless the cut in the shroud was taken all the way to the forward tip of the BT. So I cut the shroud all the way to the forward tip of the BT. It still was not right.
Part of the problem was in threading the rod through the aft bulkhead and the lug and then getting it to come out the hole in the front. Another part of the problem was that cutting the front hole/slit was ugly! In order to tame the alignment problem, I glued on two more launch lugs so that I had, in effect, on long lug that extended from the aft bulkhead all the way to the nose cone. That made thing slide easier but it was still ugly. I also had worries about getting everything to align again when I actually tried to glue these assemblies together.
After a breather, I finally did something smart. I changed the X-Acto blade and went back to work trimming the forward hole. I gave everything a test fit and, to my utter amazement, everything fit together nicely. A little thick CA was used to secure the BT to the front of the shroud and then to close the slot cut for the lugs. The same CA was also used to glue the after bulkhead into the shroud. Care needs to be taken at this point to ensure that the hole in the bulkhead lines up with the launch lugs and that there is no binding. I accomplished this by using a short section of 1/8" rod to ensure everything moved freely before and during the gluing process.
The original nosecone I ordered from Semroc did not fit the BT-20 so I ordered another one and patiently waited. When it arrived, it was in good condition but I knew I could remedy that in short order. I filled it with Elmer's Fill n' Seal and sanded it. It was then in a little less good condition than when it arrived (normal for me) and I painted it black.
I connected the Kevlar® to 14" of 1/8" thick elastic to complete the shock cord and then put a snap swivel in line a few inches from the nose cone. I understand that this rocket needs nose weight but I don't really have a feel for that. Altitude is not my concern since I usually fly from a small field. I decided to go heavy rather than light because I want this rocket to stick around for a while. I glued a ¼" washer to the nosecone and then screwed in an extra heavy duty eye screw. It was the biggest one that would fit both in terms of screw diameter and in terms of the shank length.
PROs: not too dificult, a venerable rocket
CONs: shroud subject to getting messy from glue
The Vulcan is mostly finished by virtue of having a preprinted shroud. The nosecone is the only thing that needs work. I think the original had a plastic nosecone but I used balsa, which had to be filled and painted.
Pros: looks very cool
Cons: easy to mess up shroud
Construction Rating: 3 out of 5
The first flight was on an Estes B6-4. I loaded the motor and igniter and the put a bit of dog barf in the BT. I had planned on using a 9" nylon chute but that was unworkable. I could not get it, the shock cord, and the nosecone into the space I had left. Since a 12" plastic chute is smaller, I tried that. It barely fit.
With great anticipation, I hooked up the leads and pushed the button. It took off into the sky with a lazy corkscrew motion at the tail. It seemed that my idea of mounting a lug directly against the BT was not working out. To make matters a bit more hairy, the chute ejected but did not open. I watch the entire thing come crashing to the ground. Fortunately, there was no real damage.
The second flight was on an Estes C6-3. Again, I had problems loading the chute and this time could not get it all in. I snipped out about 10" of Kevlar® and 8" of elastic and then managed to get everything stuffed.
The rocket went up about 30 feet, and from that point, things get rather vague. It went all over the sky but mostly stayed horizontal. It then crashed to earth with a deployed but unopened chute. Upon inspection, I found that the main body shroud had torn too badly to be worth repair.
PROs: It flies
CONs: It does not fly very well
My chute failed to deploy on both flights. It ejected each time but never opened. I think this is because it was packed so tightly.
PROs: bounces well when chute fails
CONs: needs to bounce well because chute fails
Flight Rating: 2 out of 5
I still like this rocket and will probably eventually build another one. When I do, I guess I will need to add even more weight up front. I also need to rethink the BT. The little bit of difference with the Semroc BT might have made stuffing the chute a bit easier.
It flies like a dog but is still a cool looking rocket
Overall Rating: 3 out of 5