More likely than not the buttons are mounted at the bottom of the rocket rather
than the center of pressure so even A realitively small pressure at the top of
the rocket or tower vibration will cause amplified movement or rotation durning
launch.
Thanks, Eric
On Jun 15, 2015, at 12:28 PM, <kramer@xxxxxxxxxxxx> <kramer@xxxxxxxxxxxx>
wrote:
Couple of things all add up against you here, in no particular order they are,
1) The relative wind is very much NOT in line with the rocket when it comes
off the pad, the wind was coming from one side, the rocket wants to turn
because of the wind, 2 buttons keep that from happening, once one lts go for
a BRIEF instant the lower one acts like a pivot point.
2) stiff rail, not so stiff mount. Ignoring the rail (assume it as
infinitely stiff) all of the rest of the pad adds to the flex at the top.
This gets magnified by the length of the rail (small angle over long 6')
distance.
3) the thrust isn't in line with the button, small difference but anyone who
has slid a button on has felt what a slight off axis angel feels like.
4) If you leave the rail buttons loose so they spin it creates a gyroscopic
effect off axis creating a torque causing the rocket to twist, stationary
buttons would not have this effect. This is total nonsense but I cant help
throwing another thing for the spinning vs stationary rail button debaters to
obsess about.
Mike Kramer
-------- Original Message --------
Subject: [roc-chat] Re: Rocstock 41 Pictures + Punisher Drag Race Video
From: "Dave Peterson" <woshugui@xxxxxxxxxxxxx>
Date: Mon, June 15, 2015 11:51 am
To: <roc-chat@xxxxxxxxxxxxx>
I have had a rocket take a hard turn even out of a tower. (Darkstar Mini at
01:34 on this video https://www.youtube.com/watch?v=ewsgZf2crAQ ). Even a
tower can twist and bend, so maybe they are no better or even worse than a
rail from that perspective. At the time I attributed it to wind, but this was
a fairly high thrust:weight flight so I also wondered about thrust vectoring.
When a motor is static tested on a stand are there also YZ gauges to look for
off axis thrust?
I am planning to use a K1440 as the booster for a two stage with a K250W
sustainer at Black Rock in September so I hope we get to the bottom of what
happened befiore then.
My Open Rocket simulation was predicting 15,100' but I was taking that with a
grain of salt since RockSim 9 was saying closer to 12,000' which "seemed"
more realistic. That said, RockSim has a reputation for over-estimating mach
drag, which on my simlation was about 50% higher than it was in OR.
From: roc-chat-bounce@xxxxxxxxxxxxx [mailto:roc-chat-bounce@xxxxxxxxxxxxx] On
Behalf Of R Dierking
Sent: Monday, June 15, 2015 8:55 AM
To: roc-chat@xxxxxxxxxxxxx
Subject: [roc-chat] Re: [roc-chat] Re: Rocstock 41 Pictures + Punisher Drag
Race Video
The ground and flight videos are excellent, and I dont want to get far OT
but I noticed the diversions as well Kurt. Interesting that you have
basically the same rockets, engine, and igniter, on the same pads and rails
with lots of differences in the ignition times and way they exited the rail.
Maybe it would be best to start a new thread on launch pads.
Also, hopefully, there will be an analysis about the engine failures because
the K1440WT seems like it would be a great engine for a 2 stage rocket.
And, why did everyone get a much higher altitude than they expected?
From: Kurt Gugisberg
Sent: ýMondayý, ýJuneý ý15ý, ý2015 ý8ý:ý43ý ýAM
To: roc-chat@xxxxxxxxxxxxx
Great Video Dave. It's a little disturbing seeing some of the Punishers came
off the rails at an angle. In the slo-mo you can clearly see a number of
them angling right off the top of the rail. I think that is a common
situation with rails. I think that even thought the rail is so much stiffer
than a rod, they still whip around. Maybe it is slop in the pad but you can
see those rails vibrating back and forth quite a bit in even a moderate wind.
Kurt
On Mon, Jun 15, 2015 at 12:48 AM, Dave Peterson <woshugui@xxxxxxxxxxxxx>
wrote:
Here is my video... https://www.youtube.com/watch?v=vFF-6Dwud9U
Thanks to everyone for putting this event togather.
From: roc-chat-bounce@xxxxxxxxxxxxx [mailto:roc-chat-bounce@xxxxxxxxxxxxx]
On Behalf Of R Dierking
Sent: Sunday, June 14, 2015 7:26 PM
To: RocChat
Subject: [roc-chat] Re: [roc-chat] Rocstock 41 Pictures + Punisher Drag Race
Video
Nice!
How many people had on-board cameras?
From: Payton Kramer
Sent: ýSundayý, ýJuneý ý14ý, ý2015 ý5ý:ý55ý ýPM
To: RocChat
https://www.flickr.com/photos/130292873@N02/sets/72157654165375170
https://www.youtube.com/watch?v=7k1lceVPdbM
--
ROC-Chat mailing list
roc-chat@xxxxxxxxxxxxx
//www.freelists.org/list/roc-chat
-- ROC-Chat mailing list roc-chat@xxxxxxxxxxxxx
//www.freelists.org/list/roc-chat
