That's what I was referring to: a situation where the whole rocket
pitches for an instant. During that instant, the exhaust is shot to
the side of the trajectory even though it remains axisymmetric with
the body of the rocket. This means that when (as in the photos posted
to this thread) the exhaust trail makes a very visible bend, the
actual bend in the trajectory was smaller.
When doing a frame-by-frame analysis, you don't need this sort of
theorizing since you can track the actual trajectory rather than
eyeballing the bend in the smoke trail as viewed or photographed (say)
a second later. Indeed, you have quite enough data to tell me I've
messed up somewhere and am flatly wrong, if that happens to be the
case here.
(In any case, my comment of course isn't of much help in your failure
analysis: it doesn't address what caused the pitching, which is the
main question here. It's aimed instead at the question of photo
interpretation: how you can have a smoke trail that momentarily
deviates quite visibly and yet where the rocket immediately reverts to
what looks like its nominal trajectory.)
On Fri, Oct 22, 2021 at 02:44:28PM -0600, William Claybaugh wrote:
Norman:
I first became familiar w/ this in analyzing a Pegasus failure.
In this case, the frame-by-frame look shows the exhaust axisymmetric with
the rocket in each frame, even as the rocket pitches through about 20
degrees in less than 1/4 second. This means whatever was causing the turn
was not due to a displaced thrust vector.
Bill
On Fri, Oct 22, 2021 at 1:34 PM Norman Yarvin <yarvin@xxxxxxxxxxxx> wrote:
One thing that occurs to me about this: one generally is judging the
course of the rocket by the smoke trail, but if the rocket is pointing
off-axis momentarily its smoke trail will be not just passively
following it but being expelled at high speed off-axis. So the visual
disturbance to the smoke trail will be much amplified from the actual
disturbance the rocket experiences. Thus the return to (very nearly)
the nominal trajectory: the disturbance wasn't really all that large
in the first place, it just looked that way from the smoke trail.
On Fri, Oct 22, 2021 at 02:28:06PM +0000, Rick Maschek wrote:
We've considered 'wind shear' and observations have shown it will occurmaybe 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 tohave this sudden direction change.
Years ago on our MiniSShot II flight we observed a nominal Mach+ flightand 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.
Ricksolid
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
againpropellant 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
ofproceed in a straight line nominal flight. I'll try to find some videos
this phenomenon.
Rick