Monday, January 03, 2011

Review: Standard Cray-ARM

This is a review of my first Crayon rocket. I decided not to go with the typical clear fins and instead went for a 'goony' version of the Standard Missile. This one used an original 'Ralphco' brand bank. These Crayon banks are now available from Toys-R-Us, although they are now produced by another company.


1. One Ralphco 4" crayon bank
2. 3/16" plywood for the main fins and nose cone bulkhead
3. 3/16" balsa for the strakes
4. A 1/4" x 9.5" carriage bolt, 2 washers, and 2 nuts
5. Two eye bolts
6. A 12" piece of Giant Leap 38mm flexible phenolic
7. Three 38mm-to-3" centering rings (also from Giant Leap)
8. Two 38mm-to-4" centering rings (ditto)
9. Four inch section of a 3" mailing tube
10. 10' of ¾" braided nylon
11. Two quick links
12. A 1000 lb swivel
13. Two tee-nuts
14. One pair of Matt's nylon rail buttons
15. Nylon chute, picked from my existing stock

1. 20 minute epoxy
2. Titebond
3. Thin CA
4. 2-part urethane foam from Giant Leap
5. Hot glue
6. Blue holographic contact paper

I knew a fair amount of nose weight would be needed since this rocket was going to be stubby (less than 10:1 length:width ratio) and the strakes would make its stability even worse. At a recent launch, I saw a crayon rocket that had a carriage bolt extending from the tip of the nose through a bulk plate in the middle of the nose cone. This bolt held the bulk plate against the shoulder where the nose cone begins its conical transition. This sounded like what I needed so I borrowed the idea. I made the bulk plate myself and installed an eyebolt for recovery system attachment. In the nose cone tip, I cut a square hole to accept the shoulder of the carriage bolt. To insert the bulkhead, I had to bend the shoulder of the nose cone to an oval shape. I completed the nose cone assembly by filling the coin slot with hot melt glue.

For the fin design, I entered the crayon bank into Rocksim and started with a fin set from my NCR Archer. I then played with the fin dimensions until they looked 'right'. Since I wanted through-the-wall fins and they barely extended to the crayon bank's cardboard tube, I was worried about the support that the rear plastic cap could provide. This worry was exacerbated when I knocked over one of my crayon banks, shattering its cap. This lead me to the construction of an inner, 3" diameter tube structure within the end cap.

To build the fin can, I started by cutting a hole in the end cap to accept the 38mm tube. I then placed a 3" centering ring so that the motor tube would extend through the cap, just far enough to accept another 3" centering ring on the outside. Thus, the end of the plastic cap would be sandwiched between the two centering rings. Using epoxy for all wood-phenolic joints and Titebond for all wood-cardboard joints, I built an inner fin support tube, which extends the length of the plastic end cap (including its shoulder). The fin tabs extend through the plastic cap and this inner tube, to the motor mount. For added support, I filled the inner tube with 2-part urethane foam. Unfortunately, I didn't do a good job sealing the fin can, so some of the foam escaped into the plastic end cap. Luckily, this isn't too noticeable. I slid on the rear centering ring and drilled holes through both rear rings to accommodate the motor retention bolts. The outer ring was then removed, tee-nuts were installed, and the ring was epoxied back on. Two 4" centering rings completed the fin can assembly. These had to be sanded to fit since the crayon bank ID is slightly smaller than a standard 4" tube. An eye bolt was also mounted in the forward ring.

The recovery harness includes a 10' length of tubular nylon, a 1000 lb. swivel, and two quick-links. Loops were made in the ends of the tubular by folding it over, wrapping it with cloth fishing line, and gluing it with both CA and epoxy. This technique was documented by Giant Leap in an old HPR magazine and works well.

One nice thing about crayon rockets as the bulk of the finishing is done for you. Since the body has a holographic finish, I decided I'd finish the fins using holographic contact paper. I would have liked purple paper to match the nose cone and end cap, but couldn't find it. Instead, I picked up some blue holographic contact paper on sale at a craft store.

After completing the design in RockSim and adjusting the CG and weight to match the as-built rocket, I found that it would be stable on an H123 without additional nose weight. The sim also told me that a short, 6-second delay would be about right. I launched the Standard Cray-ARM on this engine at the Delaware Tripoli launch on October 21, 2001. The flight was straight and fast. For recovery, I used worm-bed wadding, a Giant Leap Kevlar® heat shield, and the 48" chute from my DG&A Lazarus. Recovery was flawless. Well, almost. Once on the ground, the rocket was pulled along and quite a bit of dirt was forced into the tube. This made cleaning the casing a bit more work, but no big deal.

The Standard Dray-ARM has subsequently flown on the following motors:

AMW G115-6, AMW G185-7, AT H123-6, Loki H144-8

The Standard Cray-ARM project was highly successful. The rocket is somewhat unique and looks great (at least in my unbiased opinion). The design worked out nicely with the long carriage bolt providing enough nose weight for the rocket to be stable. Just before I placed the Standard Cray-ARM on the pad, Ray Halm interviewed me for the Way Cool Productions video of 3-day DARE-1 launch.

Way Cool productions DARE-1 Video

Way Cool Productions was a relatively short lived producer of rocket (and other) videos. Ray Halm, who is well known here on the east coast, ran the operation. This review will evaluate his video of the DARE-1 East Coast Regional launch. This launch was a three-day event held at Rhodesdale, MD in October, 2001. Ray's video covers only the two "standard" days as he was unable to attend the experimental day.

I bought this video because Ray had interviewed me prior to a couple of my flights. Since I hadn't seen his work before, I was a little apprehensive about the quality of the video. However, my worries were totally unfounded. The quality of both the video and audio are good. His composition editing is also very good (i.e. he did not show the ground during interviews or lose the rockets after launch). The intro included some cool music, he threw in a few slo-mo's of CATOs/shreds, and included some interesting sound effects.

For a regional launch, there were plenty of great flights. The following is a summary from Ray's web site, with a few of my comments added in italics:

* Dennis Lappert's 80 lb, radically painted, Smokin Rockets "Saab RB05A" on an M2000 Redline. It was painted with silver/green 'chameleon' style paint and looked great!.
* Auggi Grey's level three cert flight on an M1419.
* Bill Rossi's "I think I can Honest John" on an L952.
* Roger Dwyer's King Cobra on 3 K1100's.
* John Ritz's 6 Pack launching on a central I motor, air-starting 2 H's then 2 G's.
* Joe Mahulasick's Rocket Dyne "Wild Cat" on an L-952.
* Mike Debey's wet floor cone rocket featured in issue 11 of Extreme Rocketry, on a J-350.
* Kathy Gilliand's 12 lb "Sun Seaker" on a K-550.
* Neil McGilvray's "Cowabunga" complete with sound effects :) MOOOO!
* Gene Costanza's awesome K-1100 flight.
* Alan Gorekki's 54 mm "Transonic 2" on an L-1400. Can you say Mach speed? Projected to break Mach 2!
* Justin Glider's 3-inch diameter, 10 lb rocket on a K-1100, Mach flight. Burned the paint off of the leading edge of the fins!
* Rob Super's "Navigator 6" belching flames out of both ends of the motor casing just second's into the flight. Cool slow motion replay!
* Wayne Anthony's K-185 flight that Ray nicknamed "Hard Right". When you see the flight you see why :o Complete with sound effects. Another slow motion replay.

As for my personal content, he included an interview about, and launch of, my Standard Cray-ARM, the launch only of my M^2 L^2, and shot on the pad of my Beer 'n Pretzels. He missed the launch of the latter, so my second interview remained on the "editing floor", so to speak.

I had a hard time putting a rating on this video since there are not many points of comparison on this site. Instead, I'll offer some summary comments. First, although the quality of this video product is great, the overall quality is not as good as Point-39's products. Ray will have to add more effects, closer shots of the launches, and some more in-depth interviews/how-to's to compete head-to-head here. Still, I think he'd be my second choice. Second, Ray's product line seems to emphasize local/regional launches that Point-39 will never cover, hence he may not have to compete head-to-head. It is really great to see the site you fly at, rockets and people you know, and some of your own stuff on video.