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Old 10-29-2020, 10:58 PM
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Gus Gus is offline
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Originally Posted by blackshire
The European (especially Central & Eastern European, including Russian) model rocket motors vary a lot in construction and internal arrangement, and there are many different manufacturers; Stuart Lodge has one of the largest--if not THE largest--collection of them. The FAI (non-scale) Altitude event rules, which favored "long first stage/small second stage" competition models, were changed some years ago, and this made blast tubes less necessary and common (the FAI Scale Altitude rules were similar, and made Bumper-WAC Corporal entries 'too common'). But a blast tube would help ignite Quest Q-Jet upper stage motors, by directing a jet of flame along the upper stage motor's propellant grain (the tube could have vent holes).
Blackshire,

I appreciate that you've read quite a bit about gap-staging European motors but I've actually been flying them for 12 years and for the last 8 years have been one of two people responsible for buying them for the U.S. team. I have a really good understanding of how they work.

As for the rule changes for the straight altitude event, the rules still require a very long first stage and encourage a very short second stage. Nothing has changed in terms of "best techniques" for igniting the sustainer engines. Most of the foreign teams still use flash tubes because that's what they've always done. Most of us on the U.S. team don't use them because we've found them more complicated and less reliable than simple gap stage tubes.

Using a flash tube with Estes booster motors is substantially different than using one with European motors. Estes motors send a huge ball of flame up the gap-stage tube which completely envelopes the nozzle of the sustainer motor. A flash tube, if used, would substantially reduce the volume of flame that moves upward to the sustainer motor which is why virtually no one uses them in the U.S. The idea that a much tinier flame more precisely directed is interesting, but I seriously doubt it would be any more helpful igniting a composite motor than it would be a black powder motor. But if you or someone else wants to run some tests and report back that would be interesting.

Steve
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  #32  
Old 10-30-2020, 12:44 AM
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blackshire blackshire is offline
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Originally Posted by Gus
Blackshire,

I appreciate that you've read quite a bit about gap-staging European motors but I've actually been flying them for 12 years and for the last 8 years have been one of two people responsible for buying them for the U.S. team. I have a really good understanding of how they work.

As for the rule changes for the straight altitude event, the rules still require a very long first stage and encourage a very short second stage. Nothing has changed in terms of "best techniques" for igniting the sustainer engines. Most of the foreign teams still use flash tubes because that's what they've always done. Most of us on the U.S. team don't use them because we've found them more complicated and less reliable than simple gap stage tubes.

Using a flash tube with Estes booster motors is substantially different than using one with European motors. Estes motors send a huge ball of flame up the gap-stage tube which completely envelopes the nozzle of the sustainer motor. A flash tube, if used, would substantially reduce the volume of flame that moves upward to the sustainer motor which is why virtually no one uses them in the U.S. The idea that a much tinier flame more precisely directed is interesting, but I seriously doubt it would be any more helpful igniting a composite motor than it would be a black powder motor. But if you or someone else wants to run some tests and report back that would be interesting.

Steve
The European competition space modeling book I had (it went with my house) was considerably older than that, more like thirty-five years. For example, it covered Polish motors (whose front ends were tapered), whose thrust-time curves--for single-stage motors--indicated almost no ejection charge force at all (and they were tested on a stand that was designed to measure both positive and negative thrust forces). The contest rules could have been different so long ago.
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