[roc-chat] Re: Rail Button Damage on LOC Army Hawk
- From: Gregory Lyzenga <lyzenga@xxxxxxxxx>
- To: roc-chat@xxxxxxxxxxxxx
- Date: Thu, 25 Jul 2019 11:52:46 -0700
On Jul 25, 2019, at 11:23 AM, R Dierking <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>
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