Sunday, December 19, 2010

Reviews of two V2's

Semroc's V2 xKit is a reproduction of Estes K-22, which was originally released in 1965. Like the original, it flies on 18mm motors and features balsa nose and tail cones. The xKits don't come with instructions but, since they are classics, copies of the original instructions are available on-line. This was my favorite rocket as a kid, and I couldn't resist grabbing a couple.  The kit comes with two sets on laser cut fins. Once set is over sized for increased stability and one is true to scale.  I have reviewed both versions below.





V2 with non-scale fins

The parts list (applies to both versions):
* BNC-55F balsa nose cone
* BTC-55Z balsa tail cone
* BT-55 body tube
* BT-20 motor tube
* Launch lugs (3)
* Engine block
* Washer weight
* Large screw eye
* Rubber shock cord
* Gauze for cord attachment
* Plastic parachute with separate shroud lines and tape disks.
* Laser cut balsa fins and servo pods
* Dummy casing
* Pattern sheet

The parts provided are true to the original kit. The main difference is the fins are laser cut with both scale and semi-scale versions. The surface of the cones is nice and the tube has almost no spirals. The only negative is the hole in the tail cone is not perfectly centered. This won't hurt and probably is true to the original. However, after seeing Semroc's other products, I was surprised.

Despite the fact that the xKits are recommended for expert modelers, I could have built the kit without any. Well, except for positioning the balsa servo pods and cutting the extra launch lugs into the scale turbine exhaust and pull-out plug details. If you build an xKit, be sure to read the online instructions and the sheet provided with the kit. The provided information includes interesting but unnecessary factoids about Estes and the real V2 as well as a few key bits of data. The instructions identify the CP for both the provided scale and semi-scale fin sets. Also, it's noted that the supplied washer and screw eye are sufficient for the larger semi-scale fins, but ~½oz of additional weight is required for the scale set (not supplied)!

The pattern sheet includes fin patterns and fin alignment guides. The latter have been improved from the originals, which required that the upper and lower guides be aligned by eyeball. Semroc's have a flat face which allows them to be aligned on any flat surface. Simple but a good improvement. I opted for the larger semi-scale fins as I'm not a stickler and these should make sure the rocket is stable in varied launch conditions. The only reason you'll need the fin patterns is for the placement of the balsa servo pods. I merely eyeballed them.

I added a Kevlar® leader and ditched the gauze reinforcement. I wound it around the motor tube, tacked it place with CA and then attached the motor mount with 5-minute epoxy. The original kit said to install the motor mount so the engine was flush with the bottom of the mount. I opted for some overhang to help with friction fitting. I checked stability prior to permanently attaching the nose weight just in case some more was needed. Once verified, I removed the screw eye, filled the hole and nose cone surface with white glue, and reattached the weight. I considered adding a motor hook but decided to keep it like the original.







Finishing:
I used Elmer's Fill 'n' Finish to fill the balsa parts and then shot several coats of primer. I laid down a base coat of Model Masters 'modern' desert tan and added brown and olive drab camo patterns.








Flight and Recovery:
I've flown it on all the recommended motors with good success. I friction fit the motors and added an ample amount of dog barf wrapped in a section of Estes wadding. I used the stock chute, which is typical plastic with twine and tape discs.

The A8-3 is fine for really small fields and windy days, the C6-5 is good for big fields and calm days, and the B6-4 works well for a wide variety of fields and weather conditions.  I guess I've grown out of always liking the biggest motor possible since the B6-4 is my favorite for this little rocket.


(Lift-Off Picture from NARAM Live! by Chris Taylor)







V2 with scale fins

The parts provided in the kit were listed above and I added the following items:
* Lead shot
* 18” of Kevlar® twine
* 3/16” launch lug

The first thing I noticed was that neither the nose or tail cones fit in the BT-55 tube. This is not uncommon and I easily sanded the shoulders down. But then I noticed that neither was flush with the tube. The base diameter of the cone and the top of the tail cone were too big. In addition, the tail cone looked like it got bigger in the middle before it tapered back down. I started merely sanding, but then I took a sharp hobby knife and ran it along the tube until it met the cone’s overhang and trimmed the excess off. I then went back to sanding and even had to backfill a few nicks that were too deep.

I decided to ditch the stock recovery components for a long piece of Kevlar® twine. I tacked the twine to the motor mount with CA and then wrapped it in a loose spiral. I coated the inside of the tail cone with 5-minute epoxy and twisted the mount, wrapped with the twine into position. I used the provided dummy motor to support the mount during this process.

The fins and trim components all were installed in accordance with the original K-22 instructions downloaded from JimZ’s site. Nothing else to add here.

As noted in the brief instructions, the scale fin version requires additional nose weight. I referenced Semroc’s instructions, this thread on YORF and a RocSim model to determine how much nose weight was required. I used the scale file found in that thread and modified it for my design (including a tweak to the fin position). I drilled a 2.75” x 1/2” hole in the base of the cone using my drill press. I also carefully torque the cone while the press was running to expand the diameter a bit. I added enough lead shot (˜0.75oz, plus epoxy) so that it balanced the model at ˜5.2” from the tip without motor.

Finally, since I noticed some rod whip on my first V2 when powered with a C6-5, I swapped the provided 1/8” lug for a 3/16” lug.

Finishing:

Since I used the scale fins, I decided that I’d try a scale-style paint job. I’ve always liked the yellow/black patterns featured on the first few rounds fired at White Sands so I decided to pattern mine after round number two. I started with filling and sanding. When I went to grab the primer, I found I was out. Instead, I used silver XMetals® basecoat as a uniform base color. I used Testors'® yellow spray and coincidentally, silver was one of the recommended base colors. I masked the roll patterns with Frog Tape and used Rustoleum® black, sprayed into a plastic cup to make it brush-on. The Frog Tape didn’t work all that well for me. In retrospect, I knew that I should have used a light overcoat of yellow to seal the edges.  Since this photo was taked, I added thin vinyl stripes to the nose and body to match the actual V2 round.

Flight and recovery:
The first and only flight (so far) was on a C6-5. I also used a 12” nylon 'chute in place of the stock plastic one. The boost was quite wobbly and it weathercocked a little.
It ejected close to apogee and recovered in good shape.