>These weren't Estes "D" engines were they?
>They had a real problem with cracked cores (it's basically black powder)
>and would explode more often than not.
>
>Try some Aerotech G reloadables. $40 for the casing, about $6 for the
>propellant reloads, but 8x the impulse in 29mm diameter!
>
>They also do F engines in the 24mm casing, but the price favours the F ang
>G reloads.
>
>
>
>
>
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>
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> > and on the second test, the engine exploded on the pad
>
>Wow, was this a standard ESTES engine?
>
>Never heard of that happening before.
>
>Just curious, what would you say the blast radius was (ie: how close could I
>have been without getting hurt). I ask because I always have to argue with
>people to stay well clear of my model launches and they laugh when they
>see/hear the little pfffffffft of the engine.
>
>Bob Ammerman
>RAm Systems
>(contract development of high performance, high function, low-level
>software)
>
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>Pressed black powder motors such as the estes c6-5 are known to be
>sensitive to temperature cycling.  The paper casing and the black powder
>slug have slight different thermal expansion ratios, and repeated or
>extreme temperature changes can cause the propellant to separate enough
>from the casing to allow the flame front to burn between them.  When this
>happens, the slug ignites all over, overpressurizes the casing, and
>(usually) flies out the front of the motor/rocket like a roman candle star.
>There's a rule of thumb that goes something like "don't launch at a motor
>temperature more than 30F lower than the max temperature the motor has been
>stored at."  (Didn't the original message come from someone up at Cornell,
>where I imagine it's very cold at the moment?)

>
> > The shuttle engines are ammonium perchlorate, aluminum, and a binder,
> which
> > is what the Aerotech reloads are made from.  Not black powder. The failure
> > was due to a rubber O-Ring that lost it's flexibility in the low
> temperatures.
> >
>
> The solid rocket boosters are ammonium perchlorate, aluminum and binder. The
> failure was due to a combination of poor judgement on managment's parts, and
> bad luck.
> The O-Ring was not rated for use at that low of a temperature. There was ice
> on the shuttle that day. Several people advised against a launch attempt.
> Management decided to go anyway. This happens all the time, for a variety of
> reasons. It is still going on today. There were at least 4 counts that I
> know of in the last 12 months that were recommended against. (Usually for
> low probability of acceptable weather.) One was a successful launch. That's
> what they pay the guys for, to make the go/no-go call on the launch
> attempts. They almost always try, and they frequently get away with it. One
> time they didn't. Actually they fail to get away with it all the time, its
> just that it usually doesn't result in quite so press coverage.
>
> James Womack Sr's first launch as director of expendable vehicles was a real
> disaster. He is the father of a hunting buddy of mine, and he had been
> working on the manned side for many years. On the expendable side the rules
> a lot different because the payload is owned by a company interested in
> getting it in orbit and on line to get the revenue stream going. They have a
> whole lot more say in when an attempt is made and when you scrub. This
> results in different language being used when you get weather advisories.
> The time of launch approached, James asked for a call on the weather, which
> was dicy at best, and the weather advisor told him that it was go if James
> desired, meaning if the customer wanted to risk it, it was his payload.
> James was used to manned weather reports. They launched, the bird blew up
> and a grand time was had by all.
>
> Back to the bad luck bit. Few people know it, but the SRB nozzles were
> slewwed over, trying to compensate for the side thrust from the leak at the
> field joint. (The SRB's are actually sections because you can't cast that
> much propellant in one go. The sections are then pinned together and a metal
> band hold the pins in place. The result is called a field joint.) They kept
> the shuttle on track, leak and all. If that leak had developed on a slightly
> different section of the O-Ring, the flame would have jetted out into space,
> never would have burned through the external tank, and only a few of us
> space workers would have ever known about it. 30 degrees of danger and we
> ended up unlucky.
>
> Wynn Rostek
>
> Former Shuttle Worker
> CBEP (SRB Power Distribution and Control)
>
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