[roc-chat] Re: Clarification
- From: "Chris Coffee" <chris_coffee@xxxxxxxxxx>
- To: <roc-chat@xxxxxxxxxxxxx>
- Date: Sat, 25 May 2013 13:42:02 -0700
Thank you to all who have answered. Looks like he will be good to go for launch.
I appreciate the insight into the mathematics of this. Since I am by no means a
“seasoned flyer” yet, I was just going by what I learned in Mark Canepa’s book
Modern High-Power Rocketry 2 which didn’t say anything about using the initial
thrust. This is one of the reasons I really love this hobby! Not only do I get
to see fire and hear the roars of the motors, but I get to meet a lot of very
nice and helpful people.
I am using ThrustCurve.org more and more and am learning how to read the graphs
and other data. Unfortunately, I do not have RockSim. I thought it was only a
$40 program so I went to purchase it and saw how much it really is...and just
can’t see myself spending $130 on a simulator. I know I will have to break down
at some point and buy it because this OpenRocket program just doesn’t do me
much good with the high power stuff. I keep hoping that I can find someone that
I can pay a little money to have one of their three installs, but not looking
likely. I know it sounds frugal, which I am at this point because I have dumped
between $900 and $1,000 on the project I will be flying at ROCStock.
Looking forward to seeing everyone at ROCStock in a couple of weeks. Should be
a blast!!!
Chris Coffee
From: Mike Riss
Sent: Saturday, May 25, 2013 12:53 PM
To: roc-chat@xxxxxxxxxxxxx
Subject: [roc-chat] Re: Clarification
I'd like to second Jeff's referral to a great rocketry resource:
thrustcurve.org
You can look at the complete thrust curve over time, and in particular,
the initial thrust. Look in the "Simulator Section" under "Options", one of
which is "View Data" (the icon with the magnifying glass). The initial graph
is in newtons, but there's an option to display in pounds.
Mike
--- On Sat, 5/25/13, Jeff Gortatowsky <indanapt@xxxxxxxxx> wrote:
From: Jeff Gortatowsky <indanapt@xxxxxxxxx>
Subject: [roc-chat] Re: Clarification
To: "roc-chat@xxxxxxxxxxxxx" <roc-chat@xxxxxxxxxxxxx>
Date: Saturday, May 25, 2013, 12:22 PM
Chris I have always used average thrust. But Carlo is right. The first
second of thrust appears to be about 45 or so pounds of thrust. That is a guess
from looking at the ROCKSIM graph on thrustcurve.org.
I have a rocket at 6.5 pounds, and an I100 with a 5 ft guide reaches 41
ft/sec at guide departure (according to RS). I consider anything above 35 to
ft/sec fine under normal conditions. (I have gone as low as 28 to 30 tho some
say that is too slow. But on a calm day I've done it.)
---------------------------------------
Jeff Gortatowsky, Redondo Beach, CA | Twitter: JeffGortatowsky | Yahoo:
indanapt
"(Scientific) Skepticism is not a set of beliefs, it is a set of
methods for asking questions about reality." -- Doctor Steven Novella
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From: Chris Coffee <chris_coffee@xxxxxxxxxx>
To: roc-chat@xxxxxxxxxxxxx
Sent: Friday, May 24, 2013 8:22 PM
Subject: [roc-chat] Clarification
A little help here, please? I need to know if someone can tell me if my
calculations are correct for a Thrust-To-Weight calculation for an upcoming
flight...and whether or not the rocket should be flown on said motor? Thank you.
Madcow Sensor weighing in at 7 pounds on the pad. 54mm motor mount.
Using a Cesaroni I100-RL-LB this is what I got:
Average thrust of motor (according to ThrustCurve) = 98.5Ns
Divide 98.5Ns by 4.45 to get 22.13 average thrust in pounds
Divide 22.13 pounds of average thrust by 7 to get a Thrust-To-Weight
ratio of 3.16:1
Is this correct?
If my math is correct, I would say that the rocket should not be flown
with the I100.
Okay, folks.....school me!!! LOL
Christopher L. Coffee
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