Monday, December 20, 2010

Review - The Grand Whazoo

The goal of this project was to build an eight inch diameter rocket that was light enough to be flown on a mid-power motor. I decided to use foam board for the fins and centering rings, and thick paper for the outer skin. After playing around with RockSim, the design evolved into something reminiscent of a V2 (although not even semi-scale), with the following specs:

  • 70" x 8", 3lb 3oz loaded (barely under the 3.3lb limit!)
  • motor: G80-4 (manufacturer's recommended max weight is 52oz)
  • predicted alt: 600' (highly optimistic)

This review will cover both the original and re-built versions.

Original Version

Parts List
1. 5 sheets of 3/16" foam board for centering rings and fins
2. 3 sheets of white poster board for the outer skin
3. Misc. paper and cardboard
4. 30" x ~32mm cardboard tube for nosecone core
5. 24" of LOC 29mm tubing for motor mount/airframe core
6. 1/8" plywood for reinforcement of aft CR
7. Section of hardwood dowel and eyebolt for shock cord attachment to NC
8. Elastic and Kevlar cord
9. Scrap 1"x2" wood blocks for rail button attachment
10. One pair of Matt's rail buttons
11. Fiberglass for reinforcement of upper portion of airframe

1. Elmer's exterior carpenter's glue
2. Thin CA
3. Krylon white primer
4. West Epoxy

Design Tools
1. Nosecone calculator - InfoCentral
2. Wrap templates - VCP
3. Design and simulations - RockSim5

To get my feet wet with this project, I decided to try to build a nose cone using multiple foam rings and heavy paper wraps. I decided I would put rings every 4" along the length of the cone. Using the nifty calculator on InfoCentral, I designed a tangent ogive cone. Inputs included the nose cone diameter (8") and length (36"). The output is a series of points along the length of the nosecone, representing the distance from the base end and the corresponding radius. These distances did not line-up with the 4" increments I had chosen, so some interpolation was required. Since I was not concerned with a mathematically perfect shape, I chose to guesstimate these points in my head. This was the right way to go, since it turned out the accuracy of my cuts was only good to around +/- 1/16".

I decided I'd try cutting the rings with my RotoZip. This was quick and easy. However, there was some variation in the rings due, I think, to the fact that the pilot hole in the soft foam board did not support the circle cutter firmly. The cuts were rough but were easily cleaned up with rough sandpaper. Because the RotoZip circle cutter couldn't cut a hole under around 2" in diameter, I decided to truncate the main cone structure at the 30" point, and complete it with a 6" reinforced cardboard cone.

I made the wrap for the shoulder section from some heavy paper that was glossy on one side. I thought that this surface would make ejection of the large cone easier. The next 2 wraps were essentially cylindrical so they were made from parallel strips of white poster paper. The following wraps were made from VCP templates. Finally, the conical tip of the nose cone was fabricated from thicker cardboard, and strengthened with a circle of foam board and thin CA.

The resulting nose cone weighed about 14 oz. The first photo shows the bottom of the cone, some blank 8" rings for the airframe, and the shock cord attachment plug. The second photo shows the completed cone.

The body tube was constructed much like the nose cone. Three 8", one 6", and one 5" ring were place along the tube. The 8" rings form the main body and the smaller rings form the boat tail. Two pieces of scrap wood were added to serve as attachment points for the rail buttons. Originally, I was going to also mount the rail guides internally, but I decided that too much of the centering ring material would have to be removed. The next photo shows the airframe core.

White poster board also serves as the skin on the airframe and the tail cone. Because the large fins overlapped the airframe, the airframe wrap went on first, then the fins, and then the tail cone sections. As it turned out, the structure was pretty strong, except for the top of the body tube which was unsupported cardboard. So, I applied some fiberglass to a rectangle of poster board which was in turn epoxied to the inside of the airframe. This structure supported the nose cone nicely and would help prevent zippering.

The fins were also made from foam board. To-the-motor-mount tabs extend the length of the tail cone. The tabs fit between two rings and are slotted to slip over the intermediate ring. Heavy fillets of carpenter's glue were used throughout.

The recovery system included a section of heavy elastic, long enough to clear the airframe, and a section of 1000 lb Kevlar cord. I used a Nomex® bag and a 60 inch chute, both from Giant Leap.

Flight Report

The first launch was at the NARHAMS launch in Middletown, MD on 7/14/01. I lucked out and managed to find someone who was willing to swap a G80-4 for another G80 with a longer delay. After a long discussion with the RSO and several other experienced rocketeers (including a careful, detailed inspection of the rocket), I was given the go-ahead. I launched the Grand Whazoo from my BlackSky standard rail. The winds were light and the boost was great! It arced a bit into the wind and attained an altitude of around 400' (my guess). Shortly after apogee, the nose cone separated and the 60" chute lowered it gently to the ground. I was fortunate to have a large recovery team, since all the kids at the launch were really pumped about the flight.

The second flight occurred the following day at the Maryland Tripoli launch on Maryland's Eastern Shore. The boost was almost identical to the day before since the weather conditions were about the same. Unfortunately, the G80 failed to eject the nose cone. The rocket landed with an unusually loud thump, almost like it had popped. The top 4' of the rocket was instantly converted into about 1" of trash.

Closing Notes
This rocket was the 3rd place finisher in the R.M.R. Descon #9.  Despite the failure of the 2nd flight, I deem this project a success. The materials and construction held up to the thrust of the G80 and the large airframe allowed a large enough chute so that the foam board fins survived the first landing without a ding. Plus, the rocket itself was a real crowd pleaser, especially with the kids at the NAR launch who hadn't seen large rockets before. Even experienced HPRer's showed a lot of interest. Everyone was surprised how light it was and that it would fly on a mere G motor!

While the Grand Whazoo looks a little like a V2, it was never intended to be even a stand-off scale model. Its main legacy is that it provided the motivation for Mark Hamilton's large paper V2s that was described in the May/June 2004 issue of Sport Rocketry.  Mark up-scaled a small paper rocket, which provided printed wraps and built-up fins.  Printing those wraps took one big printer!

(Son of) The Grand Whazoo

This update provides a description of how I rebuilt my Grand Whazoo after its second fateful flight. The top of the original Grand Whazoo was completely destroyed. However, the rear section, including the boat tail and fins, was intact. I decided to take a different approach to the rebuild. To minimize the volume that had to be pressurized, I decided to use an inner 4" diameter tube extending through the body. After some pondering, I also decided to eliminate the large nose cone in favor of a smaller one that would mate to this 4" tube. I was hoping this design would still stay within the 3.3 lb. limit.

I first performed some surgery, adapting a 4" mailing tube to the surviving tail section. I then added foam rings and poster board to form the body (including transitions). I made the small (4") conical nose cone from fiberglassed poster board salvaged from the original rocket. A small foam board ring and a chunk of 32mm tubing completed the nose cone assembly. This assembly mates with the dowel/eyebolt from the original nose cone.

On my scale, the finished rocket weighed in at 51oz with a G80 installed. The 60" chute that I used with the original Grand Whazoo pushed the weight over 3.3 lb. limit. To use this chute or a smaller one? Ahh, that is the question..

I wanted a bit more decoration on this version so I decided on a pattern similar to a real V2. I looked in ROTW and came up with a hybrid marking scheme. The tail section has a black and white roll pattern, the nose cone is red, and the transition section directly below the nose is painted silver (Krylon hammered silver). Since most of the rocket is poster material, I decided to mark the fins using a large permanent black marker. Finally, I added some text and graphics from my ink jet printer. Inspired by the early V2's fired from White Sands, I created a 'cheesecake' style graphic of a girl riding a V2. And, in a feeble attempt at humor, I also added two labels written in German. One identifies the bar code sticker, which unintentionally remained on the body (oops), and the other tells the launch technician where to install the launch rail.

Since the rocket was potentially over the 3.3 lb. limit, I took it to an HPR launch, with the intent of using the 60" chute. Well, at the last minute, I opted for a very light 48" chute, hoping it would come in under 3.3 lb, and recover without significant damage. Well, on the highly calibrated scale at the RSO table, it weighed in at 3 lb. even.

Once again, everyone was surprised that this big a rocket weighs so little, and there were cheers when it boosted under G80 power. The 4-second delay was just a tad long but the chute deployed nicely. The decent was still fairly slow, and the only 'damage' was a crease in one fin. No rework required.

The rebuilt Grand Whazoo flew a few more times on larger H128 and H165 motors.  On one fateful day in August 2010, it once again re-kitted itself.  R.I.P.

Using an inner 4" stuffer tube with the smaller nose cone seems to be the way to go. It was easier to construct, and  recovery will be more reliable.   (But only if the ejection charge fires).