Scale Bash



A Research and Development report
by Peter Alway, NAR 26985



Note: This June, 1999 version is revised from that entered at NARCON in March of 1999 and may be further revised before entry at NARAM in August of 1999.



Contents copyright © 1999 by Peter Alway (PeteAlway@aol.com).

Summary - Scale Bash

Peter Alway - June 1999

My objective was to advance the state of the art of scale model rocketry by producing as many different basic scale model plans as possible and making them available to modelers.

My approach was to use existing scale drawings on disk to create plans built around parts found in Estes kits. I used computer drawing and spreadsheet software to "mass-produce" a large number of plans. I had drawings on disk of over 200 rockets from previous projects. I found that Estes mass-produces kits with five nose cone shapes suitable for scale modeling. Putting the data and the parts together yields around 30 candidate scale subjects that can be built mostly from Estes kits. I scaled fins to Estes body tube sizes with computer drawing software. I calculated tube lengths and center-of-pressure locations for each model using a spreadsheet with prototype dimensions and the Barrowman equations. I found shroud dimensions with a spreadsheet and laid them out with a draw program. I reduced drawings from earlier scale projects to produce Sport-Scale competition packets. I added generic instructions to benefit beginning modelers.

I used MacDraw Pro for drawing, Excel for calculations, and ReadySetGo for text layout on a 5-year-old Macintosh Performa 450 computer. I also needed samples of all the relevant nosecones.

I presented iterations of Scale Bash on modelers at NARCON in 1998, at a meeting of the Huron Valley Rocket Society, and in the first photocopy runs of the booklet. Results of and problems with these trials led to numerous improvements.

The resulting Scale Bash is a 32-page booklet with 78 plans for 29 different rockets. The plans are simple modifications of existing Estes kits, and represent a big jump in the number of simple scale modeling projects available to the beginner.

About 225 copies of Scale Bash are in the hands of modelers today. This project is just beginning to show its value to hobby rocketry.

Peter Alway
PeteAlway@aol.com


Table Of Contents


Objectives

My objective was to advance the state of the art of scale model rocketry by producing as many different basic scale model plans as possible and making them available to modelers.

Since the publication of this author's The Art of Scale Model Rocketry (Saturn Press, 1994), many parts have gone out of production, or are available only in larger packages. As a result, several of the plans in that book have become obsolete. Kits are now the most reliable source of many useful parts. Late in 1997, Steve LaFleur at Commonwealth Displays suggested that I draw up plans for kits that he could produce during slack hours at his business simply by adding or substituting parts in existing kits. I had been kitbashing-turning kits into unique models-for years, but early in 1988, I realized just how many simple scale models could be produced from Estes kits. Such designs would be an ideal introduction to scale modeling to new and "born-again" rocketeers. The confluence of these factors precipitated my scale kitbashing project, resulting in the booklet, Scale Bash: Build and Fly Scale Model Rockets from Non-Scale Commercial Kits.


Approach

My approach was to use existing scale drawings on disk to create plans built around parts found in Estes kits. I used computer drawing and spreadsheet software to "mass-produce" a large number of plans. I laid them out in the most compact manner possible, in order to bring as many as possible to the public with the lowest reproduction costs.

I had drawings on disk in MacDraw format for 137 prototype sounding rockets and space boosters from Rockets of the World (Saturn Press, 1995), roughly 40 experimental rockets from Retro Rockets (Saturn Press, 1996), and about 50 drawings of sounding rockets, launch vehicles and missiles that had been published in Sport Rocketry (National Association of Rocketry) or T Minus 5 (Huron Valley Rocket Society), or had not yet seen publication.

I surveyed the most easily available parts--those in Estes kits, and found four nose cone shapes that were suitable for multiple scale subjects: 3:1 ogive, 4:1 ogive, 5:1 ogive, and 11x cone. While the Estes parts did not exactly match these shapes, they were close enough to produce models at least as accurate as most commercial scale model rocket kits.

Surveying the prototype drawings, I found something over 30 single-diameter subjects with nosecones reasonably close to the Estes shapes. To keep the final plan collection compact, I wanted to keep the designs simple enough that one generic set of instructions could cover the construction techniques. While not quite limiting designs to "four-fins-and-a-nosecone," I only allowed simple detail parts, paper boattails, and sawed-off-nosecone boattails. In the end, 29 subjects made it onto the printed collection. Counting different scales for most of the models, there were 78 plans. In addition to the plans, each subject would need a small scale data packet to allow entry into Sport Scale competition. I added one-paragraph histories to give modelers a feel for what they were building, and perhaps to inspire them to build.

The first phase in each design was the creation of fin patterns from the original scale drawing files. I scaled each drawing for a 1" diameter body in MacDraw Pro. Then I copied the fins to a generic fin pattern file. Once all patterns were scaled to 1" tubing, I duplicated the lot, and scaled them to Estes BT-5, BT-20, BT-50, BT-55, BT-60, and BT-80 body tubing. I deleted patterns that did not have an appropriate nose cone for their tube size. The patterns for each subject were then grouped together.

The next step was to calculate tube lengths and center-of-pressure (C/P) locations for each model using an Excel spreadsheet. I entered station numbers for the nose tip, nose base, tube base, boattail base, and fin leading and trailing corners. I also entered body diameter, boattail base diameter, and fin span.

The spreadsheet first calculated the scale of each possible model, dividing the prototype diameter by the tube diameter to give the reciprocal of the scale factor.

To calculate tube length, the spreadsheet scaled the combined tube-nosecone length for each body tube diameter, and subtracted the measured length of the model nosecone. The result was a tube length that would bring the model to the correct length regardless of slight mismatches between true scale nose length and the Estes nose cone length.

To determine stability, I entered the Barrowman equations (from Calculating the Center of Pressure of a Model Rocket, Centuri Technical Information Report 33, by Jim Barrowman) for each component into cells of the spreadsheet. The spreadsheet calculates the C/P for each component and its relative lateral pressure. Then the spreadsheet calculates the prototype C/P location (distance from nose tip to center), and scales it to each model. Finally, it subtracts one body diameter to find a recommended center of gravity (C/G) location one caliber forward of the C/P. (For models with curved boattails with fins, such as the V-2, I found the recommended C/G was unduly conservative. The numbers did not fit with my experience or the experience of modelers polled on the internet and required so much nose weight as to be a recovery hazard. I found that by neglecting the boattail and the innermost fin area with such models, I found the numbers more in agreement with experience.) I entered a table of body tube, scale, tube length, and recommended C/G location for each scale into each subject's plan sheet.

Some models required special boattail shrouds. A separate spreadsheet calculated their dimensions according to equations in The Art of Scale Model Rocketry, and I laid them out in MacDraw. I added instructions for cutting nose cones down to boattails as well. In addition, I included special instructions and patterns for converting the Estes Silver Comet into a V-2 or Wasserfall.

Each set of plans is accompanied by two scale drawings. A color-keyed diagram serves as a thumbnail sketch of the completed model, a painting guide, and as minimum scale data for Sport Scale competition. A dimensioned drawing enables modelers to check accuracy of their models, improve on the accuracy of their models by turning their own nosecones or adding extra details, and to aid in contest documentation. I copied the diagrams directly from my accumulated 8 1/2" x 11" data drawings, reduced them 50%, and simplified them for clarity at the smaller size.

Where practical, I scaled, markings, lettering, or insignia to allow the modeler to copy decals onto adhesive labels.

I grouped the plans according to nose shape, and added lists of Estes kits that would provide the nose cones and internal parts needed to complete the models. I left most of the basic assembly instructions out of these plans, anticipating that the kit instructions would cover such things as engine mounts, shock cords, launch lugs, and parachutes. I adapted a generic set of instructions from material in The Art of Scale Model Rocketry to help beginning modelers in steps not included in kit instructions.


Equipment

I used a Macintosh Performa 450 with a Hewlett Packard Desk Writer for printing, MacDraw Pro for drawing, Excel for calculations, and ReadySetGo for text layout. In addition I needed samples of all the relevant nosecones and body tubes.


Data

The first incarnation of Scale Bash was as talk and handout at NARCON in 1998. It was clear that there was enough interest in the handout (consisting of the tube length spreadsheet, and fin patterns on sheets labeled for the appropriate diameter and nose cone) to merit publication of a Scale Bash booklet

The second iteration was a Scale Bash session at a meeting of the Huron Valley Rocket Society. In practice, I found deficiencies in the original layout of the project. I added generic boattail shrouds, but it became clear that specific boattail patterns were needed. While I had scale data available at the meeting, it was clear that the final publication would need to have it included with the plans. It also became clear that the young modelers needed instruction in some basic model rocket construction techniques. All these lessons were incorporated into the commercial version of the booklet.

After publication, errors have come to light in the booklet. These included typographical errors, errors in the Aries plan, and a scale error introduced by the copy shop that reproduced the booklets in bulk. Because the press runs are small (about 100 copies each) I have been able to correct these in successive printings.


Results

Scale Bash is a 32-page booklet with 78 plans for 29 different rockets. The plans are simple modifications of existing Estes kits, and represent a big jump in the number of simple scale modeling projects available to the beginner. The booklet also represents the first publication in the model rocket community of scale data for over a dozen subjects. A copy of the booklet is attached.


Conclusion

About 325 copies of Scale Bash are in the hands of modelers today-this booklet has not yet seen a mass printing. Yet at a recent regional meet (MSC2, June 12-13, 1999), four of the models were built from Scale Bash plans, either from our club session or from the booklet. Each was the first sport scale entries of its respective modeler. Other clubs have held Scale Bash sessions as well. The techniques for creating scale bash can be applied anew whenever another scale subject comes to light or a new nosecone becomes available. This project is just beginning to show its value to hobby rocketry.


Appendix 1: Annotated Scale Bash Spreadsheets

These are printouts of the spreadsheet used to calculate tube length and center of pressure (C/P) for the Scale Bash models. Hand-scrawled notes should aid in understanding the purpose of the various columns. Essentially, the spreadsheet takes station numbers, fin spans, and diameters, and calculates parameters required for Barrowman C/P calculations. Then it finds C/P and scale tube length for the main Estes tube diameters. I entered three critical results-scale factor, tube length, and suggested distance of the C/G from the nose tip-into tables on the plans themselves.

The Microsoft Excel 4.0 worksheet (scalebash.xls)

Download a zipped version, including this report (scalebash.zip)

Appendix 2: Scale Bash Booklet

A complete copy of the third run of Scale Bash is attached. This booklet retails for $10.00 from Saturn Press. The booklets are photocopied by a local copy shop. Pages 3-8 are generic instructions; pages 9-31 are plans. To gain an appreciation for the effort made to produce as many compact plans as possible, open the booklet to pages 18 and 19. There are 16 scale model plans and four sport scale data packets in that spread.

For obvious reasons, the booklet is not included here.
For more information or ordering information regarding 
the Scale Bash booklet, visit the Saturn Press website
(http://members.aol.com/satrnpress/saturn.htm) or email
Peter Alway (PeteAlway@aol.com).

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