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Old 10-11-2005, 07:42 PM
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Carl@Semroc Carl@Semroc is offline
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Join Date: Mar 2005
Location: Knightdale, NC
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Some time ago I noticed the Estes Patent Application that gave some insite into modern delay compositions.

From the patent: [0066] Delay powder is then fed into the engine casing and pressed to achieve the desired time delay prior to igniting the ejection charge. In this example, a time delay of less than 8 seconds was desired, and 1.5 grams delay powder was added, based on trajectory analysis calculations. Delay powder used in this example was Pyrodex HF-20.TM. made by Hodgdon Powder Company, but may be selected from other slow burning compositions (0.05 inches per second) as is known in the art.

The HF-20 burns at about 20 seconds per inch and produces very little ash and very little smoke. I have tested the more available Hodgdon RS black powder substitute. It also produces very little smoke or ash and produces a much more measurable thrust than the old delay formula that we used. In talks with Vern, he used a low grade black powder mix with a few extra ingredients to produce the long burn times and volumes of smoke characteristic of the early engines. We made ours by wetting black powder into a paste and adding sulfur and hexachlorethane. We dried it back out and granularized it so we could meter it on our machine. The resulting delay burned slow, had little flame, and produced volumes of smoke. When a C engine burned out the flame from the top of the engine was very small.

The flames after ejection from the top of today's engines is amost 1 1/2" long and lasts well over a second. That is what we think is burning Kevlar (which melts at 750 degrees F) and weakening body tubes from flame damage. The actual ejection charge only lasts about 50 ms maximum and does very little damage by itself.

We have fired and filmed many old and new engines and are analyzing the results to try to adapt our designs to be protected from the modern delay flames.
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Carl McLawhorn
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