Thank you for mentioning that Greg. Yes, Kurt and others did see that move
during the video.
One of the best things about helping to set up the range is learning how the
launch equipment goes together. Don’t take launch pads for granted. Once you
help set up, you find that you become aware of important things outside of your
rocket that affect launching and success.
Some things like bolts that tighten various parts of the pads have wings for
hand-tightening. That’s why I tried to emphasize not to strip things by
over-tightening using something like channel locks. Channel locks should only
be used to pound on things. (Sorry, JK of course.)
However, even if things are tightened properly, I am suggesting that there are
other potential things that should be studied more and addressed. I think the
middle and even those large pads in the back row are moving during some
launches.
Don’t take things for granted, and also, don’t just accept things. Think
critically of how things work, not of other people. Otherwise, we will not
move forward with improvement.
Richard
On Jul 25, 2019, at 11:52 AM, Gregory Lyzenga
<lyzenga@xxxxxxxxx<mailto:lyzenga@xxxxxxxxx>> wrote:
On Jul 25, 2019, at 11:23 AM, R Dierking
<applerocketry@xxxxxxxxxxx<mailto:applerocketry@xxxxxxxxxxx>> wrote:
I did some evaluation of 5/16” rail buttons on 1515 rail. It’s the same rail
that ROC uses for 5/16” buttons on some of the back pads. I believe it’s
called 1515 because it’s 1.5” x 1.5” extruded aluminum with a channel. 1010
rail is 1.0” x 1.0” and the 1/4” buttons fit that rail.
There are a different suppliers of rail buttons and they are typically made of
Delrin or Nylon. Since the recent post showed damage with a Delrin, I took
some I had and checked them. Basically, I wanted to get a ‘feel’ for what
might be happening and how important this could be. I’m going to try and keep
this short with a few photos. But, there’s a lot of info. I would like for
people to comment.
…snip…
Now, remember, the blast deflector can only influence the rocket because it’s
connected to the rail through the pad base. If the base of the pad moves
during the launch, all sorts of things can happen.
I’m not suggesting that people remove the blast deflector on the ROC pads.
That’s up to Kurt and the Board. However, as a flyer, there’s some things you
could do. First, check tightness on all the fasteners on the pad, but don’t
strip them.
This raises a point that occurred to me a few days ago when this subject first
came up, but I didn’t mention it at the time. It has to do with the question
of an asymmetric torque from the blast deflector. As Richard (and others)
correctly point out, the blast deflector can only transmit a torque to the rail
and rocket if the base of the pad is free to move. But those pads are nicely
stuck into the surface of the playa with some substantial mass and don’t seem
to be going anywhere. BUT… There is a freely rotating joint between the pad
base and the head that holds the rail and deflector on our back row pads.
Normally it is secured from rotating by a heavy lock knob that is tightened by
hand. However if when the range is set up, or when a flyer is placing their
rocket on the pad, they neglect to tighten this lock knob, the deflector and
rod can very definitely rotate about the vertical axis in the manner that is
speculated here (and appears to be seen in the YouTube video). So I would
suggest that we all be mindful and aware of the status of that lock knob when
using the back row pads, especially with high thrust motors.
- Greg
----------------------------------------------------------
Gregory A. Lyzenga <lyzenga@xxxxxxx<mailto:lyzenga@xxxxxxx>>
Dept. of Physics, Harvey Mudd College (909)
621-8378<tel:%28909%29%20621-8378>
Claremont, CA 91711-5990 mobile (626)
808-5314<tel:%28626%29%20808-5314>
