In the very beginning, in the 1960's, there was a very high amount of attention paid to safety in all aspects of model rocket flight from walking up to the launch pad to the final retrieval of the rocket and return for preparing for each flight.
The weight limit for model rockets in the "first generation" of the hobby was 1 pound. For anything of any size, this was relatively modest and most model rockets weighed 4-5 ounces or less. The reason for the very low weights of most models was that the typical model rocket motor was a B or C class...which, unless you clustered the motors limited most models to well under a half-pound. Even when "big" D motors became available and popular, the typical model still remained in the half-pound catagory. Of course, there were exceptions. The Estes (and Centuri) Saturn V models weighed around 12 ounces in typical flight-ready trim. And, there were also models powered by the available E and F engines of the day but only the most "enthusiastic" modelers used these motors and again, the models tended to max out at about 12 ounces though some modelers would go all the way to the 1 pound legal limit. I would suspect that anything flown with more than a D motor accounted for well under 1% of all model rockets flown in this period.
Given the materials and the design practices of the day, it was very easy to build very large models which were very light and surprisingly strong. The most used materials were paper in the form of card stock and lightweight tubing, balsa wood for nosecones, fins, and adapters, and occasionally a harder wood most often found in wood doweling which was frequently a popular dress-up or detail element for models. Though there was the occasional plastic nosecone or fin assembly, usually items produced for the fireworks industry, molded plastic components as a major element in model rocket kits came about 10 years after the birth of the hobby.
The first safety code that early model rocketeers were familiarized with was published in Estes catalogs and the catalogs of the few other manufacturers. Referring to the safety code published in the 1966 Estes catalog the section on recovery states:
- "My model rockets will contain recovery devices which will deploy at an altitude of at least 50 feet to return the rocket safely and undamaged. To insure proper operation of my rocket's recovery system I will make a careful pre-launch inspection of the recovery components with special attention to the tightness of the engine and nose cone."
The rocket literature of the day, particularly from Estes, indicated that model rockets safety, particularly if anything went wrong, was improved more because of the "fangible" nature of the model and its construction. From the 1966 Estes catalog we see the passage: "Model rockets are built of lightweight balsa and paper so that they absorb any impact rather than the object struck." That is, though models are constructed in a manner and from materials that make them very strong for their intended function, those very same materials and techniques made for models that in the event that in the event of failure during boost or failure of the recovery system it would destroy itself on impact and in the process of doing so would discipate much of its kinetic energy through its own self-destruction rather than imparting all that energy (and therefore, probable damage) to what ever it might hit. That's not to say that whatever was hit absorbed no energy but at least the intentional design of the model would be a serious effort to minimize the destructive engergy transferred to what ever it hit.
As the hobby entered into its second decade, things changed a bit, particularly with respect to materials. By the late '60s custom molded plastic parts such as nosecones and fin assemblies became part of many kits especially when "plastic model" companies such as MPC entered the model rocket arena. Plastic nosecones began to replace the balsa offerings as individual components you would buy to build custom rockets. This made for much sharper looking and generally easier to finish rockets. Plus, plastic parts tended to be much stronger...and harder...than the wood counterparts they were replacing. Also, models were starting to become generally a bit heavier as "performance" wasn't as important in the minds of moders, particularly those new to the hobby, and form over function became a bit more dominant.
Over the years the definition of "model rocket" changed a bit with respect to the maximum allowable weight increasing to 3.3 pounds and the availability of much more powerful motors that still carried about the same amount of propellant but were three times more powerful for their size. For the most part "model rockets" of today are constructed in basically the same way and from the same materials as those of the '70s. However, larger "high power" rockets, those exceeding 3.3 pounds and using motors many times more powerful than even the larger model rocket motors, were becoming more and more popular. Out of necessity, paper body tubes became thicker, heavier, and stronger. Non-paper tubing such as fiberglass and carbon fiber made their appearance and it was becoming quite common to "strengthen " lightweight model rocket body tubes with several layers of glass or carbon cloth and resin. Plywood and then resin reinforced materials such as fiberglass and carbon fiber sheet and G-10 (the very tough stuff circuit boards are made of) found their way into fins, centering rings, and internal structures. Pretty soon, there were "hobby rockets" that were pretty much indestructable and could easily penetrate structures. Using these materials it was possible to make 6 ounce "model rockets" almost indestructible as well.
In keeping with the various safety codes high end model rockets and beyond still returned the rocket "safely and undamaged"...for the rocket. But many such "safe" recoveries which resulted in a "safe and undamaged" model were anything but safe to any property, critters, or persons that may have been in the way during their recovery. I have personally witnessed "model rocket" flights to well over 1000 feet and out of sight of those on the ground (and in the ensuing "recovery area") wherein the recovery system failed and the model "suddenly appears" impaled in the ground with only the fins visible...and after the bulk of the model is pulled out of the ground the only damage to the model was scuffing to the paint. The owner of the model proudly pronounced his model as "undamaged" and therefore the recovery was "safe" presumably because no property (other than the hole in the ground), critters, or persons were not hurt or damaged.
I would suggest that modelers (and manufacturers of models and kits) do a rewind to the past and think about safety from the perspective of when things go wrong...which is what NASA and other organizations that use rockets professionally do. Engineer models in much the same way that vehicles such as the automobiles you drive every day...survival of the vehicle is second to the safety of people. Go back to lighter body tubes and other components which are completely up to the rigors of flight that the model will encounter in its intended flight envelope plus a bit extra. Consider first just how safe the model is to anything or any one it may strike during any portion of its flight and build accordingly.
I welcome feedback on this topic and I intend to address other aspects of "Safe Recovery" in future blogs.
Be sure to visit my web site at www.accur8.com
John Pursley
The use of an architectural model is the only way to actually see the finished design in miniature.
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