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REV 2.4 - Mon Sep 27 00:05:35 2010

Semroc
Mark
Box 1271
Knightdale, NC 27545
(919) 266-1977
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SPECS: 9.2" x 0.767" - 0.4 oz
ROCKSIM FILE: MISSING - please submit here
SpaceCAD FILE: MISSING - please submit here
REC'D MOTORS: A8-5, B6-6, C6-7

Rating
(Contributed - by Chan Stevens [Who's Who Page] - 10/13/08)

semroc_mark-xkitBrief:
Not being much of a rocketry historian, I was a bit confused when I heard that Semroc was releasing the Mark. After all, I already had stashed away a numbered Mark II kit, as well as a Mark II offered in 2007 at NARCON. Looking over the JimZ archives, I could see very little difference between the Estes Mark and the Estes Mark II.

After a bit of research, I learned that the Semroc Mark II is really a replica of the Carlisle Rock-a-Chute Mark II, which featured one of the ugliest nose cones I've ever seen (fashioned from a crayon sharpener). The Semroc Mark (plain) is modeled after the Estes K-2 design (which in turn was based upon the Carlisle Mark II). It was Estes' second design, which followed on the heels of the tumble recovery Scout, intended to demonstrated additional recovery methods. This small, lightweight rocket flies to eye-straining (or even vanishing) altitudes and uses streamer recovery.

Construction:
This is considered an xKit, meaning it's marketed as a bag of parts without instructions, though instructions are available at the JimZ archive site. Semroc had previously had a couple befuddled customers of their bag-o-parts kits who did not have the savvy to navigate online to find the archives, and as a precaution Semroc will only sell xKits direct to online customers.

semroc_mark-xkit_partsYour $6.50 retail buys the following parts:

  • Balsa nose cone
  • BT-30 body tube
  • Balsa engine block
  • Laser-cut balsa fins
  • Crepe paper streamer
  • Rubber shock cord
  • 1/8" lug
The instructions as noted are not supplied, so construction follows the instructions from the original kit, preserved from 1961 on Jim Z's archive site.

Construction on this is pretty simple, as it's just a basic 3-fin/nose cone style rocket, and by upgrading to laser-cut fins, Semroc has eliminated the hand cutting from the original.

This is a minimum diameter model, so there is no motor tube assembly. Instead, you simply glue a thrust ring into the body tube. In sticking with the 1961 design, Semroc provides a balsa block that's been bored out (roughly 1/2" long) instead of the more modern (and cheaper) 20/5 centering ring approach. There's certainly nothing with this, but I was curious what that part was for, and needed to confirm its use by checking the instructions. Other than that one step, I did not actually need the instructions for this.

I did deviate from the plan slightly, by ditching the rubber shock cord and tri-fold mount in favor of Kevlar line looped around that balsa block, attached to 15" of elastic as it clears the body tube. I know the rubber is sticking with the original design, but I've had less than stellar success with rubber and so think the upgrade is well worth the effort.

The fins were attached using a bead of medium CA followed up with white glue fillets.

Nose cone attachment is via screw eye in the shoulder. The crepe paper streamer is held on via an adhesive band cut onto label paper.

semroc_mark-xkit_headercardFinishing:
The cover art from 1961 shows a pretty complex paint pattern, especially considering this doesn't come with any decals--checkerboard black/white pattern on the fins, and vertical stripes. The Semroc cover art looked a little nicer and easier, so I tried to follow their lead a bit. I started with a gray primer base, then followed by painting the body tube and fins a dark red metallic. The nose cone was painted with a gold metallic left over from my Sky of Gold spree.

The Semroc cover art also included a neat looking set of black trim stripes--one vertical stripe with horizontal bands at each end. Having just masked and painted a couple Saturn 1b's, I felt up to the challenge and so cut some rectangular bands of tape about 2-3/8" long, then drew a vertical line up the body tube (from forward fin joint) using a short piece of angle. That line would represent my centerline for the vertical black band. I then applied the 2-3/8" strips of tape about 3/8" short of each end of the line, with the gap (2-3/8" is too short to make it around the body tube) centered over the line. I then masked off horizontal bands for the other end of the 3/8" top/bottom bands, and shot the exposed areas with Rustoleum gloss black.

The finished effect doesn't look quite as nice as the Semroc cover art, but I was fairly pleased. I'd like to have gone a lighter red, but the metallic is a nice effect.

Construction Rating: 4 ½ out of 5

Flight:
Recommended motors are all long delay 18mm's of A8-5, B6-6, C6-7. I grabbed an A8-3 from an open Blast Off Flight Pack I'd picked up for half price. It absolutely boogied off the pad and even on an A8 was a strain to track to apogee. The delay was very clearly too early and even a -5 would be slightly before apogee. I suspect I could also track this on a B, but unless you're feeling lucky avoid using C's unless using some tracking powder as truely out of sight flights would be in order.

Recovery:
The tiny (8") crepe paper streamer is mainly decorative/complying with safety code and does not really affect the descent rate. The model is small and light enough not to care. Despite upgrading to Kevlar/elastc shock cord, I still managed to suffer a smiley dent in the nose cone. Guess I should have gone with even more elastic.

Flight Rating: 4 out of 5

Summary:
While there's nothing all that striking about this design (other than the fact it's less ugly than the Mark II), it is a nice simple construction, uses quality components and there's clearly a nostalgic retro aspect to it. It flies great. The only cons I'd offer are related to the adherence to the original design--rubber shock cord/tri-fold mount and a decal for stripe to match the cover art would be sweet (though certainly add a buck or two to the cost).

Overall Rating: 4 out of 5


Rating
(Contributed - by John Thompson [Who's Who Page] - 10/16/08) Semroc Mark Semroc Mark

Brief:
I received this kit from Semroc at NARAM 50. Semroc gave the Mark to anyone who purchased a kit from them. The Mark is a reproduction of the Estes kit #K-02 and is part of the Semroc XKits line. The XKits line of rockets are beautifully recreated reproductions of classic Estes, FSI, and Centuri rockets we remember as kids.

The Mark is a simple, super light 3FNC rocket that will really get some altitude on A and B impulse engines, and will fly out-of-sight on C impulse engines. I wouldn't recommend flying this on a C engine as it may become a fly-and-forget-you-ever-had-it rocket.

Construction:
The kit comes with a beautifully turned balsa nosecone, three laser-cut fins, a balsa engine block, a sturdy body tube, crepe paper streamer, a screw eye, and a rubber shock cord.

  • BT-30B Body Tube 6.125" Long
  • BNC-30E Balsa Nose Cone
  • EB-30 Balsa Engine Block
  • FES-K2 Laser-Cut Balsa Fins
  • LL-2B Launch Lug
  • SC-1A Shock Cord 9"
  • SM-1A Streamer 1" x 8"
  • TD-1 Tape Disc

Construction directions are not included with the kit. The directions are to be downloaded from JimZ's website. The kit does come with an "instruction manual" that gives a complete history of the rocket. In this "instruction manual", Semroc acknowledges that the streamer is a little short, but is the same length as the original. I have to agree with that assessment and I should also mention that the shock cord is a little too short as well.

Because the instructions were scans of the original Estes instructions, the build was smooth and error free. There were no "gotchas" or alignment issues, and all the parts fit together perfectly.

The only special tool you will need is an empty engine casing to push the engine block to the proper place inside the body tube.

After you have the engine block and fins attached to the body tube, two slits are cut into the top of the body tube just below the nose cone shoulder. The two slits form an opening that will become the shock cord attachment point. This is the first time I have attached a shock cord in this manner. I have to say that this way is very solid, and might outlast a standard tri-fold mount. The down side is the bump that is left on the outside of the body tube.

Once the shock cord is mounted, glue the launch lug on, and it is ready for primer and paint.

One thing I would like to mention, there seems to be two or three scans of instructions for the Mark on JimZ's website. The instructions show two different launch lug mounting points. One set shows the launch lug mounted at a fin root, the other set shows the launch lug mounted between two fins. However, I really don't think it matters where the lug is mounted.

Finishing:
Finishing the Mark is very straightforward. Fill the balsa with the technique of your choice, prime, and paint. I choose not to use any balsa fillers and just used a high build primer from a spray can found at most automotive parts or home improvement stores.

After the rocket has been filled, primed, and sanded, paint the rocket the color of your choice. I would recommend a highly visible color as this is a small rocket and can easily be overlooked. Especially in high grass.

I choose to paint mine like the cover picture, which has a red body tube and a gold nose cone. I used the same gold "metal" paint for the nose cone that I used for my Golden Scout. I have not put the black stripes on yet.

Construction Rating: 5 out of 5

Flight:
Both Semroc and the Estes instructions recommend A8-3, B6-6, and C6-5 for engine choices. As I mentioned, I would not fly this rocket on a C engine as you will most likely never see it again. I would suggest flying this exclusively on A impulse engines.

The maiden flight was on an A8-3. The flight was straight, fast, and high. I would guess that it went every bit of 600 feet. Ejection was just after apogee. The streamer did not fully deploy though. I am not certain if the streamer got stuck on the shock cord mount or if I put in a little too much cellulose wadding. The rocket came down a little fast but landed in some tall grass and received no damage. Unfortunately, this has been the only flight so far.

There was a small dent on the top edge of the tube. I believe this was from the nose cone snapping back at ejection. Lengthening the shock cord should eliminate this.

Semroc Mark

Recovery:
The recovery was fine except for the streamer not fully deploying. However, even if it did fully deploy, I still think it would have come down too fast. I would recommend lengthening the streamer to get slower decent rates.

Flight Rating: 4 out of 5

Summary:
Main PROs: Easy to build. Fast, high flights on low impulse engines. A great rocket for beginners and school projects. A perfect rocket for small fields.

Main CONs: Short shock cord, short streamer.

Overall Rating: 4 ½ out of 5

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[Enter Flight Log]
Date Name Motor Ejection/
Altitude
Wind Notes
11-15-2009 George Beever Est SU A3-4 Apogee - NC Down 5-10 mph winds - Between burnout and ejection the model went squirelly - and when I recovered it I saw why. One fin failed, Across the grain, at about mid-fin. Never saw that before. Can be fixed and will fly again. Soft balsa the culprit?
07-19-2009 Chris Gonnerman Est SU A3-4 Apogee - NC Down 0-5 mph winds - Perfect flight and recovery.
06-24-2010 Chris Gonnerman Est SU A10-3 Apogee - NC Up 0-5 mph winds - It turned in a good flight but landed hard on the pavement, breaking one fin in half; I'll repair it and it will fly again.
10-29-2008 Jason Orosco Est SU 1/2A6-2 Apogee - NC Up Calm - Good flight.
10-12-2008 Chan Stevens Est SU A8-3 Just Before 5-10 mph winds - Very high flight, very early. Definitely needs a -5.
12-17-2009 Chan Stevens Est SU A8-3 Just Before 5-10 mph winds -
10-12-2008 John Thompson Est SU A8-5 Apogee - NC Down 0-5 mph winds Event: Local Soccer Field
- Nosecone snapped back and dented top of body tube.Need to lengthen shock cord and streamer.
10-26-2008 John Thompson Est SU A8-5 Apogee - NC Down 0-5 mph winds - Estes Smile on nosecone.
10-26-2008 John Thompson Est SU A8-5 Apogee - NC Down 0-5 mph winds - No Damage. Another fast and hight flight.
   

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