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The Discussion about high power failure modes (unedited as of yet):

Date: Mon, 07 Dec 1998 19:00:50 -0600
To: nhrc-list@dars.org
From: mclayton@mailman.ghg.net
Subject: Failure Modes - High Power

At the NHRC high power launch this weekend, there were 6 separation
failures/early ejection failures - with at least 4 different rocketeers.

Motors involved were H97, H123, H128, H180, J357.

In all cases, it appeared that the nose cone or payload section separated
immediately after motor burnout.

I had two failures. On one, it appeared that the ejection charge fired
after separation. On the other it just appeared that there was separation
immediately after burnout. In both cases, there was no apparent blow-by
(no scorching or discoloration around the delay column) noticed during
motor disassembly.

In trying to determine possible failure modes, I have considered:
1) Improper motor preparation leading to blow by in the delay column. On
both of my failures, the delay column was wrapped with tape for a very snug
fit in the closure. As noted earlier, there was no indication of blow by.
2) Drag separation. Nose cone on one, and payload section on the other
rocket were taped and not loose. I have calculated total drag for both
rocket/motor combinations. Although drag separation does seem possible,
the numbers do not seem to be conclusive.
3) hot delay column. It seems possible but not likely for two rockets of
mine, plus 4 others.

I was fortunate, in that there was no damage to one of my rockets, and the
other is repairable - cut off the accordion, add tube coupler and new
section of body tube, paint, fly (inspection shows no damage to centering
rings, motor mount, etc)

Does anyone have any other ideas on faiulure modes and how to eliminate
this kind of faiulure?

Thanks in advance for your thoughts and help.

From: bob.wilson@dssc.hcg.eds.com
Subject: RE: Failure Modes - High Power

> From: mclayton@mailman.ghg.net

> I had two failures. On one, it appeared that the ejection
> charge fired
> after separation. On the other it just appeared that there
> was separation
> immediately after burnout. In both cases, there was no
> apparent blow-by
> (no scorching or discoloration around the delay column) noticed during
> motor disassembly.

> Does anyone have any other ideas on faiulure modes and how to
> eliminate
> this kind of faiulure?

Possibly you might have not drilled some vent holes
in the rocket body tube to relieve the pressure
built up inside the rocket as it gains alititude.

Seperation before ejection charge(ie. during coast phase)
is possible with your faster burning motors.

Seperation right after burn out could be due to the
same thing when dealing with longer burning motors
like an H97.

The LOC kits(at least the LOC Vulcanite) mention
drilling holes near the top of the body tube to
relieve this pressure.

Also your J357...(I357? J350?) might have caused
the failure due to drag seperation. This would
have shown up right after burn out too.
Burn out means absence of thrust. So now you've
got parts of you rocket being subjected to inertia.

The only rule of thumb I know is that if you hold
your fully prepped HPR rocket by the nose cone and
it starts seperating then theres a good chance it
will drag seperate during flight. With an I357
(and the like) theres probably even more stringent
guidelines to follow.

Bob

Seems like you covered the bases if #1 also includes properly greasing the
o-rings. I tend to discount # 3 and only consider #1 and #2 as plausible.
Some rocket failures looked like drag separation to me; but, I must also
admit that my personal opinion is that for reasons unknown to me, the fit
in the reload kits over the past year or two seem looser than before. I
currently find myself taping many more parts than before to achieve a tight
fit. Like the delay column, delay insulator, motor slugs, and the paper or
phenolic liner. I suspect many failures are probably due to blow-by
between the delay column and the delay insulator or between the delay
insulator and the forward closure wall because of the loose fit. I'd bet
money most are due to a loose fit which I would have to chalk up to
operator error for not catching and correcting it. But one thing I also
find ill fitting more now than before is the length of the paper or
phenolic liner. If its a 32nd too long, the end closures won't fully seat
(which isn't necessarily bad, but if the rocket core samples you may ruin
the forward closure and the case if its not fully seated. If possible, in
situations like this, fully seat the forward closure before tightening the
aft closure. But if more than a full turn or two of the aft threads are
showing don't fly the motor or you'll run the risk of blowing the aft
closure. If this is the case, completely disassemble the motor and shorten
the liner by sanding its ends). If its a 32nd too short, the o-rings may
not compress fully and seal the motor. Blow-by will occur even if
everything else is tight. The only way to check for a short liner is to
carfully assemble the motor paying strict attention to the amount of
resistance encountered when seating the closures. If you don't feel an
increased resistance the seals won't hold. Also if the o-rings are not
greased properly they may bind and give a false reading.

Hope this helps and isn't too long winded,

Tom

From: aeng@ghg.net
Subject: Re: Failure modes?

Hello Ray & Everybody...

I've had some time to think the H97 separation during boost incident and
want to run the idea that the bent launch rod on pad 2 played a part.
Comments welcome.
Hang with me here:

1) During setup, I recall Tom telling us to make sure we put the bent
part of the rod into the clamp-the part that gets bent when we're to lower
the rod and load the birds.

2) The Vulcanite had two 1/16" holes drilled in it per the instructions
for venting. We also did a snug check of the nose cone *and* payload
coupling as Bob Wilson mentioned in his post.

3) The H97 motor prep *was* accomplished as described. The bird loaded on
Pad 2 and launched...

4) We observed (and hopefully some videos will show) that upon leaving the
rod, the Vulcanite wobbled in flight a bit, straightened out, began to
wobble again, then separated 8-(

5) That afternoon, I loaded the bird onto Pad 2 again and was going to
drag race with Jeff Butcher. This time, I did a slide check and noticed it
was tight where the upper launch lug came to the rod tip--You could see
that the rod was bent (see 1). I asked Jeff to check it and he told me
that yay verily, it was "stuck". I've got to assume that it was "stuck"
during my morning attempt.

5a) . At that time, I bowed out of the drag race (would have lost anyway
due to a bum ignitor) and let the teacher from Stafford load up as he had
launched off of Pad 2 earlier w/o incident. I noticed that the teacher's
bird appeared "seasoned" whereas mine was new and recently painted (a
broken in versus tighter launch lug?)

5b) The teacher launched w/o incident on Pad 2 so I thought nothing more
of it, and waited for Pad 1...

Okay, here's the theory of the events that occurred--It is independent of
the charring and burnt o-ring we saw supporting the notion that *two*
things were wrong with the flight.

6) The bird during boost hits the bent portion of the rod. Being a young
bird, the tight launch lug "sticks" momentarily with a force greater than
the snugness test we performed. The payload section separates partially
drawing in air through the vents.

7) The bird breaks free from the bent rod and with partially separated
payload, wobbles a while until the frontal forces push the payload section
back in place, *increasing* the air pressure in the bird *above* ambient.
With the payload now in place, the bird starts flying straight.

8) The bird picks up speed until burnout whereupon the newly *increased*
internal air pressure that has yet to adequately bleed out through the two
1/16" vents begins to shove the payload section out.

9) The bird wobbles again the second time and the rest is history...

To test this idea:

a) I've got to assume that the Pad 2 rod was bent at the tip all morning.

b) Everybody who successfully flew from Pad 2 had relatively "broken-in"
launch lugs, free of binding at the top of the rod..

c) I'd hope somebody got the videos of this particular launch to examine.

That's it...

Does this pass the B.S. test?

Andy

Message text written by INTERNET:nhrc-list@dars.org
>From: rnashjr@flash.net
Subject: Re: Failure modes?

I have to interject here that it was the forward case oring not the
ejection
oring. Andy described the instructions saying that he should assemble the
forward closure and screw it in and then drop the components in and seal
with the rear closure. This is directly contrary to existing motor loading
directions that have the propellant loaded in the center of the case and
then the forward components loaded and the closure screwed in and then the
rear components placed in and then the rear closure screwed in to seal up
the motor. What Andy described doing was putting the forward closure on
then dropping components down the long 29mm case and stacking and sealing
them. The oring was crimped during this process I am 99% certain. the
result
was motor gases leaking around the forward threads and igniting the
ejection
charge. Close up study of the video shows the ejection gases expelling. I
believe it is fairly cut and dried incorrect assembly of the motor. I shall
inspect the casing more closely after the deep cleaning tonight and see if
there is any damage but I doubt it. It looked ok to me. I think the second
flight shows that a correctly assembled motor will work correctly most of
the time.
Ray<

I agree that the description above reflects incorrect motor assembly and
this may in-fact be the way the motor was assembled but the instructions do
not now nor have they ever described assembly in that manner. All reload
kits describe assembly in three steps. 1st. forward closure assembly; 2nd.
case assembly and 3rd. aft closure assembly. This 3 step assembly procedure
has not changed (including the order) since reloads were introduced to the
hobby community in October, 1990. Some aspects of the instructions within
each assembly step have changed but only within each step.

Gasses leaking around the forward threads will vent to the outside of the
motor and any venting will render the forward closure, and the casing
unusable. As a matter of fact, it will melt the aluminum and when cooled
form a weld making it impossible to unscrew the closure. The ability to
unscrew the closure is proof positive that a forward O-ring failure did not
occur. The ability to unscrew the forward closure is proof positive that a
gas leak at the forward O-ring (except an unbelievably small one just
microseconds before motor burnout) did not occur.

I could go on but it might be easier to explain in person (or over the
phone). I'll bring a motor with a forward seal gas leak failure ( the guy
didn't use grease -thought it didn't really matter ...the O-ring twisted
causing a gas leak) to the Christmas party and we can discuss it more
there. Or if you want, I'll be at Reloadable Systems (DR. Rocket) today
from Noon till around 6 p.m. you can call me at 281.345.7168.

Tom

From: Dave.Funk@COMPAQ.com
Subject: RE: Failure modes?

> I have to interject here that it was the forward case oring not the
> ejection
> oring.
>
[dwf]

<snip>

> The oring was crimped during this process I am 99% certain. the result
> was motor gases leaking around the forward threads and igniting the
> ejection
> charge.
>
[dwf]

look at your how your motor is assembled. I believe that you are
missing something here. To get to the ejection charge, the gasses have to
get THROUGH/AROUND the delay column, and/or around the DELAY o-rings. You
indicated that the FORWARD o-rings were damaged. I believe that what your
video shows is MOTOR gasses expelling out, of which there are a whole lot
more. Your ejection charge could of course get set off from the "top" by
this as well.

Your premature ejection is more likely unwanted, massive
pressurization caused by motor blow by, due to the failure of the forward
o-ring.

> Close up study of the video shows the ejection gases expelling. I
> believe it is fairly cut and dried incorrect assembly of the motor. I
> shall
> inspect the casing more closely after the deep cleaning tonight and see if
> there is any damage but I doubt it. It looked ok to me. I think the second
> flight shows that a correctly assembled motor will work correctly most of
> the time.
> Ray
>
[dwf]

and you are right, no matter how we did it wrong, the right way
works! <G>

> -----Original Message-----
> From: nhrc-list@dars.org <nhrc-list@dars.org>
> To: nhrc-list@dars.org <nhrc-list@dars.org>
> Date: Wednesday, December 09, 1998 12:50 AM
> Subject: Re: Failure modes?
>
>
> >NASA Houston Rocket Club
> >Ray posts that the forward o-ring was cut causing early ejection. But the
> >forward o-ring seals the forward closure at the threads and not the
> >ejection charge. The ejection charge is sealed by the delay o-ring. Did
> you
> >correctly describe it as the forward o-ring or was it the delay o-ring?
> >You also said it was an old G97 with old instructions. Please explain as
> >the old G97 never had a problem with early ejection (baring incorrect
> >assembly of course).
>
>>=== AMROC ===>
David Funk
Advanced Engineering

From: Bob.Supak@COMPAQ.com
Subject: RE: Failure modes?

This subject could make for some interesting show & tell at the Christmas
party. I can bring an Aerotech casing that shows what happens when the hot
motor gases sneak their way around the delay element make their deadly
heated escape. Suddenly the small hole into the ejection charge chamber
becomes the forward motor nozzle and you have flames coming out of both ends
of the rocket. Tom probably remembers this flight (a red Phoenix) at Bomber
field - the rocket almost landed in the small cage where he was running the
launcher, totally engulfed in flames. Aerotech would not replace the casing
in this instance, claiming I had assembled the motor incorrectly. In
reality, I believe the delay element did not fit snuggly enough into the
forward closure, thus allowing the hot gases to bypass. I now pretty much
wrap all delay elements with scotch tape in order to achieve a very tight
fit between the delay element and the forward closure delay element well. I
anyone else has some blown casings, they ought to bring them to the party -
we could tell war stories and all cry on each others shoulders <g>. It
could also serve as a means to provide more information for everyone on
exactly how the reloadable motor components work - or should work, and to
also provide some hints and tricks (from those with a lot of experience)
with regard to motor assembly in the field.

Bob Supak