I first became familiar with the KN-sucrose propellant from Captain B.R.Brinley's book "Rocket Manual for Amateurs", where it was referred to as the "Caramel Candy" propellant. Of the two and a half pages devoted to this propellant, however, a full half of this was spent describing how difficult and messy it purportedly was to use. As far as more useful information is concerned, the book goes on to mention that it was one of the two most widely-used amateur propellants, the other being micrograin (zinc-sulphur). Also mentioned was that it delivers a fair impulse, ignites readily, that the most frequently used oxidizer/fuel ratio was 60/40, and that it readily absorbs moisture from the air. In addition, the text stated that it had not been successfully fired as an end-burning grain, requiring the use of a tubular grain to provide sufficient burning area. Beyond this, the book said little, other than suggesting that additional investigation into the properties of this propellant may prove worthwhile.|
This was back in 1971, when the "glory" days of amateur rocketry were long since past. At this time, the new generation of rocket enthusiasts seemed to be quite content with model rocketry, in fact, so was I...for a short while. Model rocketry seemed , to me, to be too much like learning to paint by numbers. Certainly, it produced a marvelous end product...but it tended to stifle the natural yearnings in me to know the gritty details of what it took to make a rocket fly, what it took to make a rocket motor work. And even more so, I wanted to create a marvelous end product -- a successful rocket -- from "nothing"! Materials from the workshop (and kitchen). To me, that was the ultimate challenge rocketry had to offer.
So beginning early in the new year, 1972, I began experimenting with the KN-sucrose propellant. Success came quickly, and I launched my first amateur rocket on February 26, 1972. Admittedly, it didn't go very high -- only about forty feet. But, I was buoyed by the recollection that Robert Goddard's first liquid rocket only flew to this height!
I was enthralled by this propellant, and so, over the next dozen years or so, I conducted a great deal of tests to learn as much as I could about this propellant. Of course, I also launched rockets powered by this propellant -- 57 flights, in total. And conducted static firings -- over 75 of them. When I went on to study engineering at university, I gained the opportunity to learn about rockets and propellants from a whole new perspective -- the theoretical principles. I made the most of this opportunity by combining my practical knowledge of rockets with the basic principles of chemistry, thermodynamics, fluid flow, mechanics of materials, etc., and wrote my graduation thesis on the "Design and Testing of Solid Rocket Motors" in 1984. The propellant that I based my thesis on? KN-sucrose, of course.
At this time, I was not aware of any others who were using the KN-sucrose propellant. In those days, before the internet opened up a whole new world, "amateur rocket engineers" were pretty much isolated. As it turns out, on the other side of the Atlantic, at about the same time that I was conducting my rocket experiments, a group in Belgium (B.V.R.O.) found this propellant to be very worthwhile of investigation. They spent some five years investigating this propellant, conducting many static tests (with decidedly mixed results), and eventually produced a comprehensive treatise, reporting on the outcome of the experiments in addition to a theoretical investigation of the propellant's performance. Interestingly, this report mentions the fact that a Brazilian group (S.E.F.) had also done a fairly extensive investigation into this propellant at about this same time.
But where, when and how did this propellant , one that became so popular, originate? Most devotees will answer this question with the vague statement, "in the U.S. sometime in the fifties".
In fact, the KN-sucrose propellant was originally concocted much earlier than this. It was first formulated in San Benito County, California, in 1943, by a young Bill Colburn. Originally coined "TF-1", this precursor to the "caramel candy" propellant was originally used in rocket motors in the compressed powder form, compacted with water as an aid. Between 1947 and 1965, over 1200 rockets powered by "TF-1" were flown by the RMRS group of Watsonville, California. Prior to the publication of Brinley's book, news of this unique propellant spread by word-of-mouth. But this is Bill Colburn's story to tell, not mine! The following captivating passage was contributed to this web page by Bill Colburn.
Bill Colburn was born in Hollister, San Benito County, California in 1936, in the very week that Robert Hutchins Goddard and the Boys at Roswell [New Mexico] were preparing an 18 inch diameter rocket by 13 feet long for flight. There is something in the geology in San Benito County that attracts pyro[technics]; there are four Ordnance Companies located there! So it is certainly not unusual that in this pyro oriented county that one of the two most widely used amateur experimental propellants was born.
The propellant discovered by one of the three boys in the Tracer Club, around 1944, was used in 1/2 inch pipe rockets, the first one having been fired on the San Benito River Bed in 1947. That propellant was named TF-1 by the young boys in the Rocket Missile Research Society (later Rocket Motor research Group) started by the propellant's discoverer after moving to Watsonville, California, a scant 24 miles from Hollister. That stood for "Tested Fuel Number 1"; in their naivete, they took the popular nomenclature for rocket propellant, i.e. "Fuel". That list eventually grew to over 140 propellants.
But the origination of TF-1 is somewhat interesting, as it is similar to the discovery of the first amateur experimental propellant used widely-- Micrograin or Zinc/Sulphur (discovered by George James, the RRS [Reaction Research Society] founder). That is, it was the outcome of experiments from the Gilbert Chemistry Set manual that resulted in both propellants! In the case of TF-1, young Billy noted that wooden splints burst into flame when immersed in molten KN because the wood contained carbon, and on the opposite page a reference to sugar decomposing into water and, yep, carbon. The obvious ensued, and TF-1 was born, at first in a ratio of 1:1 by volume. (actually not a bad mix when using granulated sugar and 150 mesh or so KN).
The first motors were made from 30 calibre brass cases. They were fired on little test stands in which the rocket plume impinged on a hinged metal plate! The angle of the plate deflection was used to determine thrust! The next motors were custom made from paper and glue; the nozzles were made by compressing the paper into a rough nozzle shape and the TF-1 powder was poured in and barely compressed. This type of motor really set the style for the RMRS, since nearly every motor they made used a "mass-action" or highly erosive and/or permeable burn as a rule. A brief description might clarify: a mass-action event is one in which the entire mass of propellant ignites nearly simultaneously, the pressure-time curve then taking the form of pressure decay in a vented pressure vessel. (Micrograin propellant burning comes very close to this description, with an optically measured burning rate over 1000 inches per second!); Erosive burning takes place when the velocity in the core of a grain is high, the mass flowing through the core is high, the core is restricted in diameter to something like the nozzle throat diameter, or the propellant is mechanically weak under the combustion conditions. What do you know! TF-1 in the typical pipe rocket fulfilled all those conditions. Permeable burning takes place when the propellant is quite porous or the pressure is extremely high and porosity moderate, or with low porosity when a flow path exists from the core to some vent outside the core.The second condition exists in TF-1 pipe rockets with a start transient meeting the latter condition.
Over 1200 pipe rockets of 1/2, 3/4 and 1 inch sizes were fired between 1947 and 1954. Motors as large as 6 inches in diameter were constructed, but were not generally successful. Nearly all were core burners save for two very successful designs, one using a 1-1/4 inch pipe about 2 feet long which had a range of about 1-1/2 miles; and a second 2 inch pipe rocket.
The above long winded discussion relates only to compressed powder form of KN/Sugar rockets and not to the "caramel candy", "sugar baby", "fudge" propellant, etc. That method of making KN/Sugar propellant was devised by Dirk Thysse circa 1950. Dirk was a clever fellow adept at model making, automobile design, chemistry, electronics, and candle making. When we built model rockets (long before Estes!) using vulcanized fibre fuse bodies, Dirk's rockets usually had wings or very fanciful, however successful, fin designs. One day, Dirk showed up at my door and said "Hey Colburn, look at this!" He threw down a hard piece of what appeared to be tan colored plastic. We went in the back yard and he lit it and it burned with a very steady orange fizz and loads of smoke. I could tell by the smell that it had our standby sugar in it so I retorted "you mixed TF-1 with nitrocellulose (collodion), Right?" He said, "Nope, I made Fudge out of it!" As I didn't get it, Thysse was very pleased. "I melted the sugar and mixed in the potassium nitrate and let it harden. Its Fudge!"
We made many grains using Dirk's method, but had problems with hygroscopicity. We would usually make motors up to a week ahead of time, and with the cast variety they would sit and usually had a puddle at the base of the motor after a week. I continued using the compressed powder, Dirk continued with the cast material.
I did, because of that experience, then search for castable materials, this search eventuating in over 140 types of propellants, most of them castable. Later, as part of this search, TF-1 was characterized officially with a specific impulse of 140 seconds (at 1000 psi to 1 atmosphere expansion), a mean molecular weight of 35, a specific heat ratio of 1.16, a density of .056 lb/cubic inch, a strand burning rate of .65 inch/second at 1000 psi (this rate did not work for motors for the reasons outlined above). Much later, with actual flight tests performed for Frankford Arsenal, the flight specific impulse was determined to be 110 seconds in the pipe rockets.
Those early rocket experiences set the tone for my life. I wanted very much to be part of the Moon Project. That was a seemingly impossible dream in my childhood. My knowledge of rocketry came in very handy in the [U.S.] Air Force, as I was selected to be on a team surveying Russian [Soviet] Aerospace Technology. Excitedly, I learned that they had a satellite project in the offing. On the ostensible day of their launch, I was in Washington, D.C. Knowing through channels that it might take place, I was outside looking at the night sky over D.C. Late that evening, a giant red cloud appeared over the city. I thought "What a clever Ploy! They injected NO2 into the upper atmosphere to drift over the Capitol of the USA!" As I learned later, the launch had been scrubbed and the red cloud was a rare aurora borealis....or was it?
After my discharge from the Air Force, I went into Aerospace in charge of an Ordnance Test Laboratory. After two years there, I was promoted to an engineering position and later was lucky to fulfill my childhood dream. I designed 5 mission critical pyro systems on the Apollo Missions. I later went to Thiokol in their Igniter Section and then to Advanced Design.
The main purpose in recounting this brief history is to indicate what an early interest in the technical [fields] can create. There certainly are many persons who find a career late in life, after college perhaps, but many of the the shining ones begin early, as children. It is important to give youth guidance and support in their inquiries into matters technical. Regulation, poor education systems, public indifference, apathy, addiction to hedonistic activities, all play a part in weakening this nation [and others] technically. It is web sites like this one which give me hope, that the spark of mechanical ingenuity may not die out, that propulsion engineering will live on!
Bill Colburn, Los Gatos, 1998
Tracer Club 1944- Barney Bernstein, Bill Colburn, Gary Sheldon
Note that the comments in [ ] are my own, added for clarification. -- R.N.