aerotech delay delayed

aerotech delay delayed

Post by Davi » Sat, 07 Jul 2001 06:38:25



PML Black Brant VB on an F40-4W RMS:  This rocket flew it's second flight
yesterday afternoon on an F40-4W and pranged.  For some reason the ejection
charge didn't fire until the rocket was only about 5 feet above the ground
coming straight down ballistically.  The nose cone came off and the chute
made it out and unfolded enough to have the body tube cut half moons in two
of the panels.  The piston was still inside the body tube.  The only damage
appears to be a flexure dent in the body tube just below the upper launch
lug, and two small longitudinal cracks about two inches apart in the QT on
either side of the dent.  The flexure was enough to pop off the upper launch
lug epoxy and all.  The paint cracked a little on the fin fillets, but no
apparent damage to the fin joints which still feel solid.  The rocket
apparently flexed then popped back to original shape.  I used 30 minute
epoxy everywhere.  My questions are the following:
1.  Is there a way visually to tell if the delay element was a 4 or 7.  The
package said 4, and it had the little maroon spacer.
2.  Could too much masking tape on top of the RMS F40 fuel element have
caused late ignition of the delay charge?  I was following AT instructions
to put a small amount of masking tape there so that the igniter stops at the
top of the fuel element and does not go all the way to the delay element.
What else may have caused a slower than normal delay?
3.  Is my rocket safe to continue flying?
4.  If not, what repairs should be done to restore this rocket to full
strength integrity?
5.  I assume I should epoxy on a new launch lug as the detached one already
has solid fillets around it and I would just be gluing a rounded epoxy
surface to the QT body tube?

Thanks,
Dave Fergus

 
 
 

aerotech delay delayed

Post by Hilty Information Syste » Sat, 07 Jul 2001 22:38:28




Quote:
>PML Black Brant VB on an F40-4W RMS:  This rocket flew it's second flight
>yesterday afternoon on an F40-4W and pranged.  For some reason the ejection
>charge didn't fire until the rocket was only about 5 feet above the ground
>coming straight down ballistically.  

Ouch.  I had an F40-4W that ended up being closer to an F40-15W which
nearly trashed my AT Strongarm.  Odd, as I'd flown close to 10 of
those reloads before with absolutely no problems.

<snip damage report>

Quote:
>My questions are the following:
>1.  Is there a way visually to tell if the delay element was a 4 or 7.  The
>package said 4, and it had the little maroon spacer.

IMHO, they all pretty much look the same, but awile back someone
posted a "delay chart" to RMR that helped in identifying the various
delay grains.  Bob Kaplow, or Ted Cochran, IIRC..

Quote:
>2.  Could too much masking tape on top of the RMS F40 fuel element have
>caused late ignition of the delay charge?  I was following AT instructions
>to put a small amount of masking tape there so that the igniter stops at the
>top of the fuel element and does not go all the way to the delay element.
>What else may have caused a slower than normal delay?

Literally every 24/40, and 29/40-120 reload I've used uses the
"masking tape method" to ensure the correct positioning of the
ignitor.  It's been put forth before that the masking tape could cause
a delay in delay grain ignition, but I don't recall any really
conclusive evidence supporting that.  I've not done any research on
the subject, but I'd think that a small piece of masking tape would be
incinerated at the time the propellent ignites.. probably within
milliseconds.  Now, it has been proven reasonably well that assembly
grease contaminating the delay grain will cause a delay, or possible
failure in its ignition.

Quote:
>3.  Is my rocket safe to continue flying?

It sounds to me like the damage is fairly minimal.  I don't think
you'll have any trouble bringing it back up to speed again.  FWIW, the
above mentioned AT Strongarm expierenced a zipper all the way down to
the tubing coupler.  It now sports a spiffy "conduit" covering the
repair, and has flown many times since.  It *was* in good shape until
it snapped a fin due to an asphalt landing a couple of weeks back.

Quote:
>4.  If not, what repairs should be done to restore this rocket to full
>strength integrity?

Sounds like you'll definitely need a new 'chute, and the longitudinal
cracks can probably be sealed up just fine with thin CA glue.

Quote:
>5.  I assume I should epoxy on a new launch lug as the detached one already
>has solid fillets around it and I would just be gluing a rounded epoxy
>surface to the QT body tube?

Rough both surfaces up with sandpaper before gluing, and it should
stick fine.

Good luck!

tah

Tod A. Hilty  NAR #72099
Hilty Information Systems

Member MTMA, NAR Section #606  

Mantua Township Missile Agency
http://web.raex.com/~markndeb/rockets/mtma/

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