I was wondering about the button placement too. My top button is well
below the cg by 6" or so and the bottom button is screwed into the bottom
centering ring. So the rocket under thrust is probably trying to rotate
around its cg. So as perhaps as EJ said, one at the cg and one ahead would
be the best location.
Kurt
On Mon, Jun 15, 2015 at 12:41 PM, E J <ejackson1075@xxxxxxxxx> wrote:
I was just skimming and this reminded me of a tip I got many moons ago,
but never really tested. It was off the ancient news boards
(rec.rockets.something), but the tip was to put one guide/button at the
center of gravity and the other a couple calibers above it. The idea was to
keep the contact points from being somewhere that would exert more force on
the rocket than needed to keep it from falling off.
On Mon, Jun 15, 2015 at 11:35 AM, Kurt Gugisberg <kurtgug@xxxxxxxxx>
wrote:
Richard, I'm not sure if stiffer rail is really the answer. Last year
at XPRS, there was a pad out there that had a triangulated super structure
that kept the long rail straight and it was on a huge base anchored to the
ground and I think it even had guy wires. I watch for four days as
rockets came off of it and kicked out at an angle just like on our loosey
goosey pads. Asymmetric thrust might be one reason but this pad had a long
rail that should have helped. I'm beginning to think it might have
something to do with the spacing or location of the rail buttons. The fact
that one button is off the rail prior to the second one may allow it to
torque sideways. I wonder if one continues rail guide would solve that.
Kurt
On Mon, Jun 15, 2015 at 9:55 AM, R Dierking <applerocketry@xxxxxxxxxxx>
wrote:
First, I’m wondering how much stiffer a 1515 is than a 1010 rail?
Cross section is 50% more, so approximately double?
One of my last fights over a year ago now (way too long ago) was a
K1275R off one of the back pads using a 1010 rail. The rocket went
noticeably West immediately after leaving the rail and it wasn’t the wind.
Luckily, the rocket landed close to the pad because of the wind during
descent. One time the wind really helped.
There’s always a lot of discussion about rocket stability, but think
about how important a reliable launch pad is. Of course, what engine in
what rocket is very important to how massive/stable the pad must be and how
long the guiding structure should be. Regardless of size, I think there is
some occasional thrust vectoring with AP engines that takes place moments
after ignition that seems to stabilize. What would be the reason that some
rockets left the rail in the Punisher drag race at an angle? I’m curious
if other people believe momentary thrust vectoring occurs?
If you are going over say 10K’ in a location like Lucerne Dry Lake, you
need to be reasonably sure that the rocket is stable (of course), and that
it’s going to fly in the direction you choose.
I’ve been considering launch pad designs for several years, and checked
out all the custom pads at the last two BALLS launches I’ve gone to. Some
are really cool with elaborate pad leg designs and lifting mechanisms but
the ones with a sturdy/stiff launch rail adequately supported along its
entire length seem the best to me. This is my opinion, and I might be a
little jealous of the money some spend on their launch pads.
I’m considering purchasing a 12’ x 5” utility trailer for the base of a
launch pad that would also be a platform for a test stand. The pad would
use the triangular aluminum tower material that seems to be popular for
many large launch pads. A link follows that shows a base for an antenna
tower. * I would like to know if anyone else is interested
in participating in the construction of a large launch pad/test stand. It
would serve as our launch pad/test stand at ROC and FAR launches and be
very useful for XPRS/BALLS.*
*http://www.dipolnet.com/footing_for_aluminum_antenna_tower_E9151.htm
<http://www.dipolnet.com/footing_for_aluminum_antenna_tower_E9151.htm>*
Richard Dierking
