Re: Dr Rocket Casing has a bulge

David wrote: << This happens when hot gasses impinge upon the casing long enough to heat it to a soft state, and the pressure expands the casing at the soft spot. It is
usually caused by a failed liner or failed o-ring, allowing gases to escape to the casing. Normally the o-rings keep the hot gasses against the liner only, which lasts for the length of the burn. It could have been an error in assembly or greasing, or an o-ring that got pinched or came out of place, or a faulty component of the reload. >>
David's right. This is either user error or a reload issue, not a casing defect. Contact AT either by email or phone. If it turns out to be a problem with the reload they'll make good on it -- they have excellent warranty service.
Don't try to use the damaged case unless you want to launch your rocket in several directions simultaneously. :)
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That thing's a paperweight now. Roy's on the money.
BTW, wattsamattu, Joe?! Couldn't come over and see me last weekend?
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I was there Thursday and Friday only. I saw Dennis and others, but not you. Were you hiding? I didn't see any signs and flashing search lights so I assume you weren't there. 8-)
Joe C.
wrote:

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I was there Friday through Tuesday.

From Joe Cool?! Ya kiddin' me??!!

there. 8-)
You didn't hear the sirens, JC? THEY were for me..... :-)>
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First, I made a mistake, the engine was an H128, not H180. I know it doesn't matter except the H128 burns a litte bit longer. I used the "normal" about of grease I think. I did not notice the problem until after I cleaned out the liner so I don't know what it looked like. I used the standard igniter that came with the engine.
BTW, Dr. Rocket got back to me and for a small fee they will replace the casing.
Joe C.
wrote:

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On Thu, 08 Jul 2004 13:13:06 GMT, snipped-for-privacy@joecool.org (Joe C) wrote:

Why for a fee? I thought they warranted these things?
Unless, of course, the fee is just a token shipping charge....
- Rick "Disappointed that they would charge" Dickinson
--
"Imagine standing at a street corner and spitting on people to
get their attention, then trying to sell them something.
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They charge $10. I assume for shipping.
Joe C.
wrote:

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snipped-for-privacy@joecool.org (Joe C) wrote:

If it is warranty work it is overpriced.
If it is consumer repoonsibility, it is underpriced.
Sounds like a "compromise" to me.
Jerry

--
Jerry Irvine, Box 1242, Claremont, California 91711 USA
Opinion, the whole thing. <mail to: snipped-for-privacy@gte.net>
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Does the engine suppose to rattle when assemblied? I know some motors do and it is acceptable. I think I remember this one did. If it is not suppose to than I would suspect a liner defect. Either way I am sure AT won't do anything now since the flight did return safely.
Joe C.
On 08 Jul 2004 02:22:39 GMT, snipped-for-privacy@aol.com (JAO6469) wrote:

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<< [Is] the engine suppose to rattle when assembled?>>
The grains may rattle, and that's ok. If the liner is too short, that would be a problem.
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I think the motor rattled a little when assemblied. For some reloads this seems to be OK. For an H128 I don't know. Sounds like a good topic for the FAQ section.
Joe C.
wrote:

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On Thu, 08 Jul 2004 13:21:28 GMT, snipped-for-privacy@joecool.org (Joe C) wrote:

Grains rattling is fine, as long as the o-rings are compressed. If you put in the phenolic "washer" things and the o-rings, and could feel the o-rings compressing as you closed the casing, then you are fine.
A Bates-grain motor design, like most of the Aerotech motors, relies on the ends of the propellant grains being exposed, in order to provide a fairly even thrust curve. Since thrust depends on surface area of propellant burning, the grain getting shorter as it burns from both ends is supposed to compensate for the core getting larger as it burns from the center. So, the grains must be free to move apart a bit, in order for flame to propagate to their ends in addition to their cores. Thus, they tend to rattle slightly in the small motors, and sometimes quite a bit in the larger motors.
The motor's proper operation is due to the liner pushing, through the discs at each end, in both directions to compress the o-rings at each end. If the liner is cracked or otherwise damaged (or worse -- too short), the o-rings won't provide the necessary seal, and you can get flame and pressure escaping where they shouldn't do so. Similarly, a cracked liner can allow flame to directly impinge upon the sides of the casing, which can soften and bulge the casing, as you've seen....
Hope this helps,
- Rick "Motor geek" Dickinson
--
"Imagine standing at a street corner and spitting on people to
get their attention, then trying to sell them something.
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Nice response Rick. I think recently I heard about the J420's which had a short liner causing problems. Once a motor is assemblied I would think it is not easy to determine if the rattle is coming from the grains themselves or the liner moving. Maybe if one was to measure the liner length but who knows how long it suppose to be or who is going to do that during a launch?
Joe C.
wrote:

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I remember I felt normal resistance when screwing in the aft closure so I think the liner was long enough.
Joe C.

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You don't get any rattling with AMW motors. Also, you may notice that a J570 coughs near the end of the burn. This is due to the propellant grain dropping down as they get shorter & burning left over propellant.
JD
(Joe C) wrote:

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Dunno if this is the same effect, but I've noticed on quite a few Pro38 flights that at the end of the burn, there is a distinct 'cough' (as you put it) and a change in the smoke trail. I'm sure i've seen a Pro38 thrust curve with a peak just before burnout, could this be the same sort of thing going on?
Weren't J570s also subject to an issue with grain compression under high acceleration?
BTW I saw a J570 casing at the last launch I was at - makes the Pro38 6G casing look a little on the short side! There are at least 2 J570s in people's boxes over here, I hope I see one go!
-- Niall Oswald ========UKRA 1345 L0 EARS 1151 MARS
"Gravity assisted pieces of the rocket raining from the sky should be avoided. It is also financially undesirable." -Portland State Aerospace Society
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They are my favorite motor ever!!!!!! They rock...an initial Thrust peak of 400 lbs or so...dropping to about 200 lbs for about 2 seconds....Talk about a heavy lifter.....I have a project that I am rebuilding that will take a cluster of 5 J570's....lost it not too long ago on 2 J570's and J420....Lost it in December and got it back in April....Can't wait to get it rebuilt.
Mark A Palmer TRA 08542 L3.

put
curve
going
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of
about
J420....Lost
Having missed getting into rocketry before the AT stuff dried up, I havent seen much AT WL flown. However the K550 that I did see was awesome, and its possible that three of those rare J570s may end up being flown together :-) That would be something to see! My L1 rocket is designed to hold all the Pro38 motors (intended for L2 as well), but the new J330 isn't quite the same. I think its pretty close (on paper) to the J350, but nowhere near as much smoke/flame. The older J360, however, had quite a different thrust curve, with a pretty high peak thrust. Paul Brooks' Tiny Pterodactyl on a J360 really shifted at UKRA.
-- Niall Oswald ========UKRA 1345 L0 EARS 1151 MARS
"Gravity assisted pieces of the rocket raining from the sky should be avoided. It is also financially undesirable." -Portland State Aerospace Society
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SNIP ON>>>

haven't
its
:-)
Come across the Pond...I hope to re-fly this rocket in its originally intended configuration 5 X J570's for an M2850....5460 n/s in November. J570's are cool....lots of smoke...lots of fire...lots of lift...and a pressure wave that you can feel at the LCO desk ;-)
I have 9 of these bad boys set aside (yes I am hoarding) ;-)
My L1 rocket is designed to hold all the

Somewhere between a 350 and a 570...cool motor too. I actually think the CTI motors are more efficient...cleaner...and are cool....but alas...not nearly as much smoke and fire.....the Pro75's do seem to have a little more smoke.....
The older J360, however, had quite a different thrust

Now THAT is insane!!!! LOL
Mark A Palmer TRA 08542 L3

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I believe I put it together properly using the right amount of grease, etc. As I stated earlier I think it rattled a little when it was together. I threw out the liner before I noticed the problem so I can't tell for sure. I know AT is a great company but I don't think they would do anything in this case.
Dr. Rocket got back to me and will replace the casing for a small fee. I am mailing back the old one today.
Joe C.
On 08 Jul 2004 05:03:21 GMT, snipped-for-privacy@aol.com (RayDunakin) wrote:

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