Tuesday, January 25, 2011

Mega Review: r.m.r. DesCon

This post presents several of my DesCon entries.  I've listed all of them below.  Shaded items with links point to rockets documented in other posts.
  1. DesCon 07 - Skyrocket A rocket made with left over fireworks parts.
  2. DesCon 08 - Stratosphere Made from a plastic daiquiri glass. 'Never drink and fly!'
  3. DesCon 08 - The Whole Enchilada Made from tortillas and a jalapeno pepper. 'The name is the rocket, the rocket is the food.'
  4. DesCon 09 - The Grand Whazoo  8" diameter paper rocket, light enough for mid-power. (-- Descon 3rd Place Winner --)
  5. DesCon 10 - DC Pod Racer Gemini DC turned into a Star Wars Pod Racer.
  6. DesCon 11 - Dust Devil A 2 x 24mm + 32mm clustered monocopter.
  7. DesCon 12 - M.M.X. (MicroMech-X) A flying Mech-X Robot? Yep. (MicroMaxx)
  8. DesCon 13 - Deuce XL5 Fireball XL5 taken to new heights with a Deuce's Wild Cluster.
  9. DesCon 14 - Fat Boy - 3 x 4 3" diameter stretched upscale of the Estes Fat Boy (4x24mm)
  10. DesCon 15 - Hot Rod II (Project Orion Test Vehicle) Quasi scale model of Project Orion's 'Hot Rod' pulse detonation test vehicle. Mine flies on 29mm power.


Several summers ago, I became reacquainted with the hobby for the third time, having just picked up a copy of High Power Rocketry. While vacationing at Myrtle Beach, I spent many hours reading the magazine, contemplating my first high power project, and generally thinking rockets. Since it was near the 4th of July and there is no shortage of fireworks stands in South Carolina, there was also no shortage of fireworks 'leftovers' on the beach. I couldn't resist grabbing nose cones and plastic fin units, which were stashed safely with the shells the kids found (not high power stuff, but what the heck?). When I got home, it wasn't long before I wanted to put some to use.

The diameter of the plastic fin unit and many of the nose cones are pretty close to BT-50 and, to my amazement, the fin unit had a small shoulder that fit perfectly into a BT-50 tube. However, a 18mm motor would not fit through its aft end. Then the idea hit me - use the fin unit as part of a motor retention scheme. I scavenged the following from the leftovers of an Estes Designer's Special:

1. 18" section of B-50
2. shoulder section of a 2-part nose cone (could use any BT-50 coupler, crunched nose cone, etc.)
3. elastic shock cord
5. 18mm motor mount for BT-50
6. launch lug
7. two (2) 18mm motor retention clips

I first built the motor adapter, which included a thrust ring. This unit was glued into the BT-50 by inserting a spent casing, placing the plastic fin can over the end of the casing, and pushing in the adapter until the fin can was seated in the body tube. I then took the engine retainer clips, placed the ends over the fin can, and marked where the forward tabs would go. Slits were cut to accommodate the tabs on the retainer clips. To hold the clips, I cut 1/2" strips from some reinforced packing tape, placing one near the forward tabs and one about 1/4" behind that. I put a thin layer of epoxy on the tube before the tape and used 2 wraps of tape.

I wasn't sure of the stability of the rocket so I added some of clay inside the nose cone and glued the cone onto the nose cone shoulder using plastic glue. This was later proven to be a mistake.

Flight Report
Flight #1
I prepped the rocket and inserted a C6-5 engine. The fin can was slipped over the motor and was secured with the clips. I used parachute recovery but since all my Estes chutes were equipped with hook eyes, I used whatever I grabbed.

The flight was high and straight. The body was recovered undamaged but the nosecone separated and was lost. Too much weight and the wrong glue.

Post Mortem
After my copy of Rocksim arrived (or more accurately several months after it arrived), I discovered that the added nose weight was not required and that a C6-7 was more appropriate. Another nose cone was installed and secured with a small screw (not worth buying glue for this small application...and who knows what type is appropriate anyway?).

Flight #2
This time I tried a C6-7. The flight profile appeared identical to the first flight, with the exception that the nose stayed on!

DC Pod Racer

Prologue: In a modeler’s forum prior to the contest…

Sebulba: I protest! The human is cheating. Solid rocket propulsion is not allowed under the rules of Descon 3610, Sub-contest 312.

Star-El: Most illustrious Jabba, this is nonsense. There is no such rule.

Sebulba: No one has used solids for over 1000 contest cycles! It is ILLEGAL!

Star-El: Ahh Sebulba, if it is so antiquated, why do you fear it so?

Sebulba: I fear nothing! Your pod racer has no chance…(broken off)

Jabba: whi-tok! ze ami estahhh! (silence! you should fear me!)

Sebulba: I will protest to the Federation!

Jabba: ju zui na nach bobbaaa fetttt (if you do you will deal with Boba Fett)

Jabba: Starrr-Elll sup ri dah! (Star-El, your entry will be allowed!)

Scene 1: Introduction

At first, I wasn’t sure I was going to enter this Descon. After winning the LOC Bonanza, I have several projects on the drawing board. When I saw a Gemini DC kit at a Michael’s craft store, however, I couldn’t resist. You just gotta love those 40% off coupons!

To help me quickly visualize and tweak my design ideas, I entered the major components into the Visio drawing program. After much iteration, my inspiration ultimately came from the pod racers in Star Wars Episode I. I thought about trying to make a rocket that more closely resembled a pod racer, but decided I had no hope of getting it to work, so my racer has a long ‘booster’. The result is my DC Pod Racer. The ‘DC’, retained from the kit’s name, signifies my proximity to our nation’s capitol.

Scene 2: Construction

In addition to the kit components, I used 12” of 1/16” dowel (per the Descon 10 parts list), Kevlar® thread to beef-up the recovery system, my first homemade rip-stop nylon chute, and clay nose weight.
top view

I cut the BT-20 tubes in half and they became the forward pods as well as the two tube fins in the rear. The pieces that I cut off when angling the tube fins form the windshield and headrest in the racer’s open ‘cockpit’.

I looked at many odd fin configurations, but between worries about stability and the constraints of the pre-cut fins, I decided I would just stick with the kit’s 4-fin configuration. I cut back the fin tabs so the fins would sit about a half and inch further forward. I also added small balsa triangles to the root edges and tips.

The two long sections of balsa that naturally split off the die cut fin stock became the pod mounts. I laminated these with card stock from the packaging and reinforced them with 5” of the dowel. The large tips of these mounts fit through slots cut in the side of the pods. I used scraps of balsa and dowel to add trim to the pods.

To plug the pre-cut vent holes in the body tube, I used the 1” x ¼” tube that was included in the kit but not listed on the Descon parts list. This tube forms a hole through the main body and provides a convenient place to attach the Kevlar® cord for the recovery system

I added clay nose weight to move the CG to 5 ½” from the tip of the main nose cone. This position was chosen to agree with my RockSIM simulations and was confirmed via a swing test.

Finishing consisted of several coats of Krylon sandable primer and Krylon Chrome. I reused the decals from the kit and added some blue ‘holographic’ contact paper to cover the ‘windshield.’ I also used a ¼” x 3/8” piece of red trim Monokote to hide the black lettering that overlaps the ‘DC’ on the kit’s decal. Finally, I used some brush-on flat black for the ‘inside’ of the cockpit.

Scene 3: The Race Results

I flew the DC Pod Racer on a C6-3 at the Maryland-Delaware Rocketry Association launch held on 4/6/2002 at Rhodesdale, MD. All my worries of instability, shredded pods, and chute entanglement were unfounded. Despite 10+ mph winds, the DC Pod racer flew straight with only a small amount of weathercocking. My home-grown 12” chute deployed as planned, and the rocket landed in a field of some sort of newly sprouted vegetation.

I had originally decided to build a monocopter exclusively for the Estes E9 motor. However, my concept soon changed, and I decided to use a 29mm motor tube. The larger tube would let my fly on either an E9 (with an adapter) or a 29mm motor. Please read on to see how this project continued to evolve...

Construction Notes
I got several ideas from the Mountainside Hobbies site, but mine differs significantly. The wing is made from a 24" x 3" piece of 3/16" balsa, airfoiled, with a couple of strips of 1/64" Birch to stiffen it. It is glassed with 2 oz cloth and has 1/64" G10 plates laminated on the inner 6 inches. Here are photos of the partially completed wing:

And, two photos of the completed but unfinished wing. When the glass was setting, I blocked up the tip so the wing has a slight upward twist. The second photo illustrates this twist; the trailing edge is flush with the counter.

The hub started as two strips of 3" x 12" x 1/8" plywood, which will overlap the last three inches of the wing. I left these strips the full 12" long until I could get a better feel of where the lateral CG was, both with live motors and spent casings. I temporarily attached these plates to the wing and started balancing motors and components on them. I found the hub might have to be quite a bit longer than I had anticipated, and was glad I had left them long to start. I also began to worry about whether an E9 would be enough to lift this thing. Should I use an Econojet G35? F23? Should I spring for a 32mm RC casing and go for a G12? Finally, I decided I would have multiple mounts. I'd have a 32mm tube to allow the use of the RC motors, or with an adapter made from LOC tubing, a 29mm motor. I'd also add two 24mm tubes to allow TWO E9's to be clustered. Yeah, that's it! The following is an early photo of the motor mount assembly. It is glassed and has a makeshift plastic ' cone' installed. If the monocopter works, I may re-think the cone later, or maybe add some LEDs in the clear cone for night flights. I have yet to acquire/make 24mm cones.

With the motor mount and various motors, I decided the plates should be about 8 1/2" inches long. This should allow me to position the launch lug at a position between the CG before and after launch. It's a lot longer than most monocopter hubs, but that isn't necessarily a problem - I hope. I used a piece of 3" x 1" x 1/4" ply to support the plates at one end, and would angle the wing between them at the other. I used another piece of 1" tall ply as a spacer while I first glued the end plate on, and later when I installed the wing. When I recomputed the wing's angle, I decided the 1" spacing between the plates would result in too great an angle, so I added two strips of 1/8" ply to the inside of the hub, reducing the spacing spanned by the wing from 1" to 3/4". This resulted in an angle of about 11 degrees (remember the tip is also swept up a bit). After the wing was epoxied in, I used 3/16" balsa to fill the gap between the wing and the opposite plate, forming a solid side panel.

Next, I epoxied on the motor pod, aligning the joint of the two 24mm mounts with the corners of the hub's end piece. This provides a 20 degree angle. I added a 1/8" plywood support on the top front and a strip of heavy fiberglass around the rear of the motor mount and overlapping the hub. I then re-verified the lateral CD with both live motors and spent casings, and installed the launch lug (1/4" brass tubing) in between. It just missed the end of the wing within the hub. I cut two pieces of plywood to fit inside the hub, and drilled holes to fit the fiberglass balance beam. These were trimmed so they abutted the wing, and the beam just missed the launch lug. I once thought the balance beam should be centered on the launch lug, but this isn't the case. Having a continuous beam run throught the hub is a lot easier to mount and should be stronger. I attached the beam supports with carpenter's glue. I used JB Weld to hold the beam in place, and used the extra to create fillets on the support members. The beam itself is 18.5" x 3/8" piece of hollow fiberglass pole from a collapsable tent, with 7.25" extending out of the hub on either side. The final issue were cones for the 24mm motor tubes. I visited several local hobby shops and couldn't find any so I decided to make them. I made them out of papier mache using a plastic cone as a mold. This is not a refined technique, so I won't bore you with the details. The results aren't bad, but if the 'copter flies I may get some from BMS, along with a matching cone for the larger tube. The following photos show various views of the completed item, with a few coats of white primer.

This is the launch lug for my monocopter. It consists of an old, dull 7/32 drill bit, a piece of 1/4" brass tubing, and a washer. The bit is epoxied into a piece of tubing so only the top 3/4" of the shaft is exposed. A washer is slid down to the tubing and is tacked in place. This will clamp nicely into the pad that I use for my launch rail.

Flight #1
I flew the Dust Devil on 10-19-2002 at the Higgs' Farm in Price, MD. The winds were blowing hard (our American flags were outstretched) and the ground was moist (so there wasn't any dust for the Dust Devil to kick up). I used two E9's that I had plugged with epoxy. The Dust Devil rose nicely, but at burnout it turned with the wind until it was perpendicular to the ground. It reached an altitude of maybe 15 - 20 feet. It flopped to the ground and the wing broke off. The following sequence show the start of the flight, the monocopter on the way up, and the smoke trail blowing away. You really can't see the 'copter, but the smoke trail shows where it is/was.

Flight #2
I repaired the Dust Devil, added a bit of weight to the balance beams, and flew it again on two E9s. It was a nice but low flight to about 25'.  It landed hard and broke its wing.   RIP.

Fat Boy - 3 x 4

OK, this is not the most unique design, but I was going to describe this rocket on EMRR anyway and though I'd hit Descon 14 early. Best-case scenario: people spend too much time on summer vacations and on the field and I pick up a prize. Worst-case scenario: people quickly start work on their unique clustered and staged concepts and I get smoked. So, y'all get out your beach towels and suntan lotion ;)

Design Concept
One afternoon I was looking for a quick project and scrounged up a section of LOC 3" tubing and an old homemade elliptical cone. Over the last year or so, I have enjoyed clustering E9s in my Thoy Snipe, a modified Art Applewhite saucer, and my El-Cheapo Pyramid, so I decided to go with another 24mm cluster. I kicked around several configurations, and quickly found out that clusters made from Totally Tubular foil-lined 24mm tubing fit nicely inside the 3" tubing. At first, I was going to stuff it full, but decided that a four motor cluster would be sufficient. The result resembles an upscale Estes Fat Boy, although it is not perfectly to scale.

Nose Cone - The cone is made from foam and is covered in a thin layer of glass. I originally built it for a thicker tube and have had to repair it a couple of times, so it is not in perfect shape. But it is, after all, my own creation and I eventually HAD to re-use it. A 3" plywood bulkhead provides the attachment point for a small eye-bolt, and the shoulder is a plastic cap from a mailing tube. I added nose weight for this project by drilling through the bulk plate and adding lead shot and epoxy until I got the CG where I wanted it.

Motor Mounts - As I mentioned above, the four 24 motor tubes fit snugly inside the LOC tubing. I quickly realized that classical centering rings weren't required and that the inter-tube joints and TTW fin attachments should hold the motor mounts securely. So, I merely made filler sections from scrap balsa to block the ejection gasses from escaping between the motor tubes. I added these near the front of the motor tubes and left the back end open. The mounts employ motor blocks, positioned to fit E9/F24 motors, and homemade retainer hooks. Four pieces of thin brass tubing were epoxied in the joints where the tubes meet. I bent the end of the piano wire, slid it into the tubing and then bent the opposite end to fit an installed motor. At launch time, the wire tabs are moved aside, the motors are inserted, and the tabs are then repositioned over the ends of the motors. A few small pieces of tape ensure that they stay in place. This is the first time I've tried this and it seems to work fine.

Fins - The fins are upscaled from the Fat Boy design and are made from 1/8" ply. The motor mount was installed so that the TTW mounts would be equally spaced between the three outer motor tubes. The fins were epoxied to the central tube and internal fillets were applied, making sure that no glue interfered with the inner tabs on the music wire.

Recovery System - A section of Kevlar cord was epoxied to the motor mount prior to its installation. A yard of thick elastic then connects the leader to the nose cone. Not my preference, but it was the only suitable material that I had on hand. I added anti-zipper protection by adding several wraps of cloth packing tape to the Kevlar leader. This has worked out well on several recent rockets. A 'portable' Kevlar heat shield and a 36" ripstop nylon chute complete the recovery system.

Finishing - The cone was already day-glo green, and I grabbed some Rusoleum day-glo orange for the body. This thing is very visible!

Flight and Recovery
I have flown the fat Boy 3 x 4 once on three E9-8s. Since I wanted to try it first on three motors, I plugged the center mount with a spent motor. The boost was slow and majestic with a bit of weather cocking. With three motors, a 6-second delay would have been better. Although ejection was a bit late, the anti-zipper doohickey did its job and there was no damage on recovery.

The flight on three motors was nice, and one day soon I'll try it with all four. Hmmm, I wonder if I should have gone for a x7 cluster and surface mount fins? Hmmm....

Hot Rod II (Project Orion Test Vehicle)

Before I get started, I want to mention that I don't intend to repeat much of detailed history that is available on-line and in print. If you want to learn more about this interesting project, I suggest reading Project Orion: The True Story of the Atomic Spaceship, by George Dyson. George's father, the renowned physicist Freeman Dyson, served as a consultant on the project. There is also a nice web site with more information about the project at ProjectOrion.com

Project Orion was a conceptual space vehicle whose main propulsion was to be realized through the detonation of atomic bombs. Small bombs, on the order of 0.1 kiloton, would be ejected and detonated behind the ship. Water would be ejected and would in essence be the propellant. The force of the explosions would push against a pusher plate and would yield an Isp of between 10k and 1M seconds. Although the concept was proposed in 1955, the project was started in 1958 at General Atomics in San Diego. The project only lasted into the early 60's. By then the Saturn project was underway. Although the Orion was to be initally launched with chemical propulsion, using nukes was a hard sell and the nuclear test ban treaty hammered the nails in Orion's coffin.

Design Concept
This photo shows an early test vehicle, known as Hot Rod. The Hot Rod was 'flown' in 1959 at a test facility at Point Loma, CA.(See the video in this post.) It was boosted by a large BP charge followed by five rear-ejected high explosive charges. It was stable, reaching an altitude of 105 meters and recovering via parachute. The vehicle itself is held by the Smithsonian Air and Space Museum. I don't know if it is currently on display. If you want to see a video of the flight, visit the Nuclear Space Multimedia Gallery.

I am a saucer fanatic and am always thinking of new saucer ideas. So, the Project Orion Hot Rod was a natural. Since I am not much of a scale modeller, I decided that a stand-off version was in order (hence the 'II' in its name). I took some rough measurements from the photo and found that using 2" mailing tube for the central body would yield a 12" base. Since the real thing used parachute recovery I also thought mine should, which is a deviation from most of my saucers.

The central body consists of 9" and 3.5" sections of 2" tubing separated by a LOC 1/2" launch lug (3" exposed). The short section will hold the 'chute and the longer section is the motor mount. The 1/2" lug extends through home-made ply centering rings mounted in the ends of the body tubes. Inside, I filled the space between the 2" tube and the 1/2" lug with Gorilla polyurethane glue to help lock the lug in place. The motor tube is 29mm LOC tubing which runs the length of the lower body tube. It is centered with foamboard rings. The bottom ring was also backfilled with Gorilla glue.

The main shroud was constructed with 1/64" fiberglass using the template calculator on EMRR. I chose the fiberglass as I thought it would hold up better if I were to add details later. The bottom of the saucer section is a foamboard ring with the top rim beveled - an idea borrowed from Art Applewhite's line of saucers. The plate was first epoxied to the shroud, and then this assembly was attached to the lower tube.

The flat structures above and below the main shroud are foamboard rings framed with strips of cardstock. I had considered several materials for the struts, including arrow shafts and BT-20 tubing, but decided on 3/8" dowel. I first installed the top plate and shroud. When the glue set, small holes were made to accomodate the struts, which were attached with 5-minute epoxy.

The last structural member was the small triangle which interconnects the struts just above the longer body tube. I should have planned this earlier and installed it prior to assembling the body, since the connecting lug has to pass through the center of the triangle. This wasn't a big problem, but I did have to cut the triangle support in order to install it.

In the photo of the Hot Rod, it looked like the parachute may have been exposed at the top of the tube so that's what I did. This worked fine on my 38mm spool rocket, so I didn't see this being a problem. The recovery harness consists of several feet of thick Kevlar twine mouted through the centering ring at the base of the parachute tube. A 24" piece of elastic is next, followed by a large snap swivel.

The dimensions of bottom saucer section is pretty close to my Aeroshell, which was a modified Art Applewhite 12" saucer. This gave me a warm feeling that it will be stable with the extra weight forward of the saucer section.

Trim and Finishing
I painted the top portion using Rustoleum Hammered Gold and the bottom silver. Trim was installed after painting and included a piece of BT-20 tubing, some sockets from a dead chain of Christmas lights, some wire, and some circular stickers. The latter were painted flat black. The small photo on the right is off the web and the one to the left is mine.

Flight and Recovery
Flight #1 - It was a windy day at Coverdale Crossroads, DE and I was a little concerned that the Hot Rod II would weathercock and thus not attain enough altitude to eject before returning to Mother Earth. Since there wasn't much volume to pressurize, I used about half the ejection charge provided with the G64-4 motor. I added a small 'chute protector and tightly rolled a 12" RocketChutes 'chute. The boost was arrow straight despite the brisk winds. I don't have an altitude estimate but the flight was respectable for its size. The 4-second delay was too long and it was well on its way back down before the charge went off. But all's well that ends well, the 'chute opened and it recovered without damage.

Flight #2 - The second flight was at Price, MD, and again it was windy. I used another G64-4, but this time I substituted an 18" 'chute. This 'chute, despite being larger than the one on the previous flight, fit more loosely in the tube. This had an interesting effect. At apogee, the 'chute drag-ejected (similar to a drag separation), which was perfect! Sorry, no pic - drained battery.


Project Orion was an interesting piece of space history, and my Hot Rod model was an interesting piece of my rocket history. I think I'll have to make a trip to the library and re-read the Dyson book.

05/05 - "I sent the URL for this review to George Dyson. I thought he might get a kick out of it." (S.E.J.)