If you are not interested in the details of my Burst Disk Valve, don't read
any further!
After the initiators fire--and both were fired--I would expect that
applying pressure to the QD would 1. NOT result in the four pins extending,
and, 2. would cause venting through the diffusers. That is, the burst disk
is punctured due to the piston driving the hammer through it when the
initiators fired and any gas in the system is vented past the burst disk
and through the diffusers.
The recovered flight hardware instead extended all four pins, did not vent
through the diffuser, and did vent through the outlet reserved for the hot
initiator gases. This means that the burst disk was not open and
pressurizing gas was somehow leaking into the hot gas circuit. (See the
attached image of the burst disk, as found upon opening.)
Further disassembly showed that the O-ring separating the hot and cold gas
circuits (around the hammer that penetrates the burst disk) appeared
damaged from heat; that damage was allowing the cold gas to escape into the
hot gas circuit and then vent. Further, the o-ring preventing hot gas from
getting to the subject o-ring (around the piston that drives the hammer
through the burst disk) was in two pieces and showed clear evidence for
melting at the edges.
Thus when the initiators fired, the piston o-ring failed (or had previously
failed, although it was undamaged when installed); this allowed hot gas to
leak past the piston (which none-the-less hit the burst disk sufficiently
hard to dent it) and to damage the o-ring separating the hot-gas and
cold-gas circuits in the valve. These two damaged o-rings then allowed cold
gas to vent via the hot gas circuit, resulting in the payload seperating
from the rocket.
Naturally, none of these failures ever occured in previous testing.
The venting of the hot and cold gas _may_ have caused the sudden pitch over
seen in video; for now I'm carrying that as a working hypothesis. However,
none of this explains why the initiators apparently fired a few fractions
of a second after lift-off.
I will next download the telemetry data from the ground station to see if
it shows any indication of the beginning of this sequence of events.
Because the ground station showed LOS at 119 feet, and that Loss of Signal
appears to have been the result of the antenna snapping off in the course
of the sudden pitch change, it might not have recorded any of the relevant
accelerations or rates.
Bill
Flight Valve Failure.tiff
<https://drive.google.com/file/d/1JG6G_dcTad-WXNxWhnoRLE1yOEgQvTQv/view?usp=drive_web>
On Fri, Oct 22, 2021 at 8:28 AM Rick Maschek <dmarc-noreply@xxxxxxxxxxxxx>
wrote:
We've considered 'wind shear' and observations have shown it will occur
maybe one time in a launch that often is during volleys of four or five
rockets and on days when 50 or more rockets might be launched and often
with a rocket with a high acceleration rate. On windy days we'll often see
weather cocking especially with large or low-velocity rockets off the pad
and in the direction of the wind. We are in a desert and so we've sometimes
wondered if it were going through a dust devil not visible without any dust
in it. Since you cannot 'see' it, that explanation is just a possible
hypothesis.
On that day, I think Bill's flight is the only one that was observed to
have this sudden direction change.
Years ago on our MiniSShot II flight we observed a nominal Mach+ flight
and then a sudden wiggle course change at ~15,000' and then back to nominal
flight. At the time we couldn't explain it until we picked up the signal
from the nose cone transmitting back at FAR. The nose cone and recovery bay
had snapped off and landed just outside the fence.
Rick
From: William Claybaugh <wclaybaugh2@xxxxxxxxx>
Date: Thu, 21 Oct 2021 08:12:21 -0600
Subject: [AR] Re: Test Launch
Rick, Troy:
There is a well known wind shear about 100-120 feet up at the MTA.
Apparently due to winds from the dry lake separating from the terrain as
they reach the top of the rise where the MTA is located.
However, that shear only occurs on windy days and pitches rockets on the
down range direction.
This pitch was in the opposite direction on a windless day.
After sleeping on it I’m increasingly thinking that Troy may be right:
venting of the pneumatic system could cause that sort of pitch change.
I’ll pressurize that system today and see if it leaks.
Bill
On Wed, Oct 20, 2021 at 8:37 PM Rick Maschek <dmarc-noreply@xxxxxxxxxxxxx>
wrote:
I have no idea 'why' but every year at 'HPR' events, I'll see a few solidagain
propellant rockets leave the rail straight and fast and about 50 to 100
feet above the launch rail take a quick change in direction and then
proceed in a straight line nominal flight. I'll try to find some videosof
this phenomenon.
Rick