LOC Magnum/Dr. Rocket/J350 Failure

LOC Magnum/Dr. Rocket/J350 Failure

Post by Jena » Mon, 19 Aug 1996 04:00:00



I suffered an identical fate with a H123 in stock Aerotech hardware at
this year's Airfest in Argonia. The post-flight inspection proved that I
had placed the cardboard delay spacer ring above the delay charge. Your
description of the results match mine. I was a bit more fortunate that my
rocket only went about 35 feet before doing a few loops and falling to the
ground undamaged. I discovered the delay o-ring inside the airframe abopve
the motor. It had been blown through the forward closure.

This is one of those no brainer mistakes we are reluctant to admit.

St. Louis Rocketry Assoc.
TRA #4521

 
 
 

LOC Magnum/Dr. Rocket/J350 Failure

Post by Doug Gilmo » Mon, 19 Aug 1996 04:00:00


In a previous thread, I stated that I had a 98% success rate with AT
reloads.  That now drops to 97%.  My brand new Magnum popped its head on
its maiden flight due to ejection blow-by in a brand new Dr. Rocket
38/720 motor. Not a good way to start the day.  Luckily, this all
happened at 320' so the altimeter saved the payload section.  Tumble
recovery on the booster section, one fin broke on landing.  Didn't use
any Kevlar on the fins, this will be changed before next launch in 2
weeks.  

Inspection of the motor reveals:

1) Phenolic tubing cracked, badly bubbled and crimped at angle on one
side    at forward end.
2) No apparent damage to motor case or closures.
3) delay o-ring, sleeve and spacer vaporized.
4) metal forward spacer/o-ring undamaged

There were no apparent problems on assembly, and there was no problem
with the 2 outboard motors, also reloads (the red ejection caps with no
powder inside were still mounted afterwards).  The one bit of good news
is that the 3 Firestar ignitors that I had silver soldered together at
the leads worked flawlessly in the cluster.

Although I am not by any means blaming the Dr. Rocket motor, I had a very
successful (albeit somewhat controversial <g>) flight three weeks ago on
a J350 in an AT motor.

Will fix broken fin by:
1) grinding down what's left flush to body tube
2) drilling 4 holes flush to remaining inside body tube part of fin
    on each side
3) epoxying small dowels to MMT, sticking out of bodytube by 1/2"
4) surface mount new fin between dowel stubs
5) Use massive fillets, topped with Kevlar/fiberglass reinforcement
   over all 4 fins.

Comments, speculation invited.  Flaming will be quickly and severely
punished.

DOUG GILMORE
TRA #4666 level 2

 
 
 

LOC Magnum/Dr. Rocket/J350 Failure

Post by Doug Gilmo » Tue, 20 Aug 1996 04:00:00


Quote:
>The post-flight inspection proved that I had placed the cardboard
>delay spacer ring above the delay charge.

This was definitely not the case with my flight.

Having thought about it a hundred times, I think I know what went wrong.  
I will split the blame three ways between Aerotech, myself and my dog.  
How could it be partly my dog's fault?  Read on.

After staying up until past midnite getting everything ready, my dog woke
me up twice in the middle of the night barking at imaginary boogymen.  I
had to get up at 6 AM to be on time to pick up my friend and then drive 3
hours to this launch.  When I got to the site, I was so bleary-eyed that
I didn't notice that AT had put two fiber spacers in the kit instead of
the required one.  I remember putting the extra fiber spacer over the
metal seal ring as if it were a 38/360 motor without the metal ring.  
This is a no-no.  I can't imagine how this would cause the motor to fail,
but there was definitely a degree of operator error involved.

Even NASA has problems with o-rings.  

DOUG GILMORE
TRA #4666 level 2

 
 
 

LOC Magnum/Dr. Rocket/J350 Failure

Post by Jack » Tue, 20 Aug 1996 04:00:00


Quote:

>Date:       18 Aug 1996 22:23:23 -0400


>Newsgroups: rec.models.rockets
>Subject:    Re: LOC Magnum/Dr. Rocket/J350 Failure

>I suffered an identical fate with a H123 in stock Aerotech hardware at
>this year's Airfest in Argonia. The post-flight inspection proved that I
>had placed the cardboard delay spacer ring above the delay charge. Your
>description of the results match mine. I was a bit more fortunate that my
>rocket only went about 35 feet before doing a few loops and falling to the
>ground undamaged. I discovered the delay o-ring inside the airframe abopve
>the motor. It had been blown through the forward closure.

>This is one of those no brainer mistakes we are reluctant to admit.

>St. Louis Rocketry Assoc.
>TRA #4521

I had a blow-by failure with a I284.....The delay cardboard was just not
tight enough.  I now use masking tape (if necessary) and grease the OUTSIDE
of the delay housing!
Jack Wiker
 
 
 

LOC Magnum/Dr. Rocket/J350 Failure

Post by Jerry Irvi » Tue, 20 Aug 1996 04:00:00



Quote:

> its maiden flight due to ejection blow-by in a brand new Dr. Rocket
> 38/720 motor.

I doubt it was related to the "brand" of casing.

Quote:
> 1) Phenolic tubing cracked, badly bubbled and crimped at angle on one
> side    at forward end.
> 2) No apparent damage to motor case or closures.
> 3) delay o-ring, sleeve and spacer vaporized.
> 4) metal forward spacer/o-ring undamaged

This is standard fare for post blow-by damage.
The motor burns at lower than designed pressure for longer than designed time.

Quote:
> There were no apparent problems on assembly

Also not surprising as blow-by is an inherent design flaw in the RMS system.

Quote:
> Although I am not by any means blaming the Dr. Rocket motor, I had a very
> successful (albeit somewhat controversial <g>) flight three weeks ago on
> a J350 in an AT motor.

RMS is over 70% reliable even accounting for "so-called" operator error,
which as you know would not be possible if it were designed to
"fail-safe".

Quote:
> Comments, speculation invited.  Flaming will be quickly and severely
> punished.

I do not deserve punishment.

Quote:
> DOUG GILMORE
> TRA #4666 level 2

TRA #12.  Is that something close to level 2?

Jerry

"Cannot find REALITY.SYS. Universe halted."

--

Box 1242, Claremont, CA 91711 USA
Opinion, the whole thing.

 
 
 

LOC Magnum/Dr. Rocket/J350 Failure

Post by Bill Nels » Wed, 21 Aug 1996 04:00:00


: I had a blow-by failure with a I284.....The delay cardboard was just not
: tight enough.  I now use masking tape (if necessary) and grease the OUTSIDE
: of the delay housing!

Use "Scotch" tape instead. It makes for a better seal - more precise.

Yes, grease the outside of the delay cardboard.

Bill

 
 
 

LOC Magnum/Dr. Rocket/J350 Failure

Post by Jack Wike » Wed, 21 Aug 1996 04:00:00


Quote:


> : I had a blow-by failure with a I284.....The delay cardboard was just not
> : tight enough.  I now use masking tape (if necessary) and grease the OUTSIDE
> : of the delay housing!

> Use "Scotch" tape instead. It makes for a better seal - more precise.

> Yes, grease the outside of the delay cardboard.

> BillI was worried about scotch tape melting.......

 
 
 

LOC Magnum/Dr. Rocket/J350 Failure

Post by Bill Nels » Thu, 22 Aug 1996 04:00:00


: >
: > Use "Scotch" tape instead. It makes for a better seal - more precise.
: >
: > Yes, grease the outside of the delay cardboard.
: >
: > BillI was worried about scotch tape melting.......

I have never seen it happen.  If it did, the grease would keep it from
sticking to the closure.

Secondly, wouldn't you rather reduce the chance of "blowby" to a minimum,
even if it made cleanup a bit more difficult?

Bill

 
 
 

LOC Magnum/Dr. Rocket/J350 Failure

Post by Jack » Thu, 22 Aug 1996 04:00:00


Quote:

>Date:       21 Aug 1996 04:32:14 GMT

>Newsgroups: rec.models.rockets
>Subject:    Re: LOC Magnum/Dr. Rocket/J350 Failure



>: >
>: > Use "Scotch" tape instead. It makes for a better seal - more precise.
>: >
>: > Yes, grease the outside of the delay cardboard.
>: >
>: > BillI was worried about scotch tape melting.......

>I have never seen it happen.  If it did, the grease would keep it from
>sticking to the closure.

>Secondly, wouldn't you rather reduce the chance of "blowby" to a minimum,
>even if it made cleanup a bit more difficult?

>Bill

Yup!...THe cleanup on the 15 lb rocket was considerably harder after the
blowby!    ;)
Jack Wiker
 
 
 

LOC Magnum/Dr. Rocket/J350 Failure

Post by Lee Re » Wed, 28 Aug 1996 04:00:00



: : I had a blow-by failure with a I284.....The delay cardboard was just not
: : tight enough.  I now use masking tape (if necessary) and grease the OUTSIDE
: : of the delay housing!

: Use "Scotch" tape instead. It makes for a better seal - more precise.

: Yes, grease the outside of the delay cardboard.

: Bill

The old reloads with the dual nylon delay liners were great -- nice precise
fit.  The recent cardboard replacements vary from reasonable fit to
downright sloppy fit.  I use wraps of scotch tape until I get a REALLY
snug fit.  I've never had a failure, and they actually seem to come out
pretty easily -- with no grease.  I may start greasing them just to add
another level of sealing protection, but "snug" is a key word to remember
for the delay unit. :-)
--
Lee Reep  

 
 
 

LOC Magnum/Dr. Rocket/J350 Failure

Post by William Manes » Thu, 29 Aug 1996 04:00:00


A note of caution when greasing the delay end of of Aerotech motors.  Don't
let the grease get into the delay well, especially the small ejection charge
ignition port.  This causes failed ejection and has pranged a number of
rockets.

--------------------------------------------------------------------------
 William E. Maness            |  Manufacturers of Ignition Systems,
 Impulse Aerospace, Inc.      |  Launch Pads, Rocket Kits, and other
 (800) 568-2785               |  Ground Support Equipment.

--------------------------------------------------------------------------

 
 
 

LOC Magnum/Dr. Rocket/J350 Failure

Post by Bill Nels » Sat, 31 Aug 1996 04:00:00


: The old reloads with the dual nylon delay liners were great -- nice precise
: fit.  The recent cardboard replacements vary from reasonable fit to
: downright sloppy fit.  I use wraps of scotch tape until I get a REALLY
: snug fit.  I've never had a failure, and they actually seem to come out
: pretty easily -- with no grease.  I may start greasing them just to add
: another level of sealing protection, but "snug" is a key word to remember
: for the delay unit. :-)

Yep, the new spacers are ***- just so Gary can save a penny or two on
each reload.

Tape may be enough, but the grease forms a much better seal - assuming that
the fit is snug.

Bill

 
 
 

LOC Magnum/Dr. Rocket/J350 Failure

Post by Doug Gilmo » Mon, 02 Sep 1996 04:00:00


Quote:
>Tape may be enough, but the grease forms a much better seal -
>assuming that the fit is snug.

I used tape AND grease yesterday.  The delay column held up fine - BUT
the nozzle BLEW out (non-catastrophic though)

DOUG GILMORE
TRA #4666 level 2

 
 
 

LOC Magnum/Dr. Rocket/J350 Failure

Post by Bob Kapl » Sat, 07 Sep 1996 04:00:00


Quote:

>>Tape may be enough, but the grease forms a much better seal -
>>assuming that the fit is snug.

> I used tape AND grease yesterday.  The delay column held up fine - BUT
> the nozzle BLEW out (non-catastrophic though)

How can the nozzle blow out NON-CATASTROPHICALLY?

        Bob Kaplow      NAR # 18L       TRA # "Abort, Retry, Fail?"

 
 
 

LOC Magnum/Dr. Rocket/J350 Failure

Post by Mr. James J. Clea » Mon, 09 Sep 1996 04:00:00


I guess that the nozzle blew out but the rocket kept on traveling up
and did not blow out the sides, then recovered normally.
                      Jim C.
                      TRA # 3996
                      LIARS
                      METRA