[sugpro] Re: Verifying Motor Performance Through Flight Tests
- From: "Michael Monteith" <dmarc-noreply@xxxxxxxxxxxxx> (Redacted sender "michael_r_monteith@xxxxxxxxx" for DMARC)
- To: sugpro@xxxxxxxxxxxxx
- Date: Tue, 17 Feb 2015 08:23:17 -0800
Yeah I was just looking at Digikey. They're priced within reason at least.
I thought about the fouling and thinking of using activated charcoal inline
to absorb chemical and particles. The other way is a length of tubing,
possibly spiral. I think the first option is best. Might be a good chance
to fly one of my Arduinos with it to record. Anyway sounds like fun.
Michael
--------------------------------------------
On Tue, 2/17/15, Ben Brockert <wikkit@xxxxxxxxx> wrote:
Subject: [sugpro] Re: Verifying Motor Performance Through Flight Tests
To: sugpro@xxxxxxxxxxxxx
Date: Tuesday, February 17, 2015, 10:54 AM
I haven't used their
miniature range, but I have used MSI transducers
on liquid rockets before with success. I
usually just buy them off
Digikey or Mouser,
selecting by what's in stock. The challenge with
solid rockets is making sure that the
transducer isn't fouled by the
rocket
motor.
On Tue, Feb 17, 2015 at 10:43 AM, Michael
Monteith
<dmarc-noreply@xxxxxxxxxxxxx>
wrote:
> Jon,
> I
haven't decided yet. First I need to know which
pressure range. But these look
>
promising as they are very small and lightweight:
> http://www.meas-spec.com/pressure-sensors/pressure-transducers-and-pressure-transmitters/miniature-pressure-transducers.aspx
>
> I'm thinking
the EPRB-2. I contacted them and see make sure they
aren't to pricey for my use.
> which
might be the case. Don't know if you don't ask.
>
> Michael
>
>
--------------------------------------------
> On Tue, 2/17/15, Jon Cherba <joncherba@xxxxxxxxx>
wrote:
>
> Subject:
[sugpro] Re: Verifying Motor Performance Through Flight
Tests
> To: sugpro@xxxxxxxxxxxxx
> Date: Tuesday, February 17, 2015, 10:31
AM
>
> Which
> pressure sensor would you recommend for
using during
> flights?
> On Feb 17, 2015 9:29 AM,
> "Michael Monteith" <dmarc-noreply@xxxxxxxxxxxxx>
> wrote:
> Great!
> Something non-trivial. lol I like
that. As one suggested
> using
>
> a pressure
measurement on the chamber. I found a very
> small one that would
>
> work. Plus I do a
lot of programming so that's a
>
distinct possibility to work
>
> on. All my books and all will be here
in a month so I can
> tackle that more
then.
>
> Now to
decide which altimeter. lol My to-do list is
> growing. Thanks
>
>
>
> I'd
like to make a contribution to rocketry as I know
> so many people have been so
>
> helpful to me. So
much I've learned and so much to be
> learned. That never grows old.
>
>
>
> Michael
>
>
--------------------------------------------
>
> On Sun, 2/15/15,
Steve Peterson <steve_peterson@xxxxxxxxxxxxx>
> wrote:
>
>
>
> Subject: [sugpro] Re:
Verifying Motor Performance Through
>
Flight Tests
>
> To: sugpro@xxxxxxxxxxxxx
>
> Date:
Sunday, February 15, 2015, 7:11 PM
>
>
>
> Michael,
>
>
>
> The
basics: if you have
>
> position (altitude) with
respect to time, then
>
> the change in position over
time is the
>
> velocity. The change in
velocity
>
> with
>
> respect to time is
acceleration. If you have the mass
>
(at
>
> the same
>
> moment
in time that you've
>
> calculated the acceleration
for, then
>
> rearrange Mr. Newton's
formula (F=ma) to
>
> get the net force. Any
decent
>
> altimeter
>
> will
give you altitude (to some precision/accuracy) vs.
>
> elapsed
time (to some precision/accuracy).
>
> After that is when the
>
> gremlins
get
>
> you....
>
>
>
> Altitude: change in
>
> altitude
may not represent a true change in position
>
> (that
is, distance) because the rocket may be
>
> headed
off at an angle.
>
> You will have to
>
> either
assume a certain angle of flight and calculate
>
> the true
distance, or assume that it flew
>
> vertically (in which case
the
>
> change in
>
> altitude
is the change in distance).
>
>
>
> Mass: it isn't constant,
so you'll have
>
> to calculate it based on
the
>
> grain geometry
>
> and your
static tests, etc. I don't know if any of
>
> Richard's spreadsheets
list mass burned vs.
>
> time, but if they do, that
>
> would
give you a
>
> good start, assuming your
manufacturing is under tight
>
> enough control.
>
>
>
> OK, so
you've calculated F--but hang on,
>
> because
that's *net* F. That
>
> is, thrust
>
> minus
the force of gravity and minus the force of drag.
> The
>
>
>
> force due to gravity is just
g*mass and
>
> we've already dealt with
mass.
>
> However,
>
> the
force due to drag is more problematic. As you know,
> it
>
>
>
> consists of the Cd of the
rocket (which
>
> will vary with velocity),
the
>
> angle of
>
> attack,
atmospheric conditions (launch pad altitude,
>
> altitude
>
> of the
rocket at any instant in
>
> time, temperature, barometric
pressure
>
> at
>
> launch, etc.) and, of course,
the square of the
> velocity.
>
>
>
> Your
question then becomes,
>
> will you know all that stuff
with sufficient
>
> accuracy to give you a
meaningful result? And
>
> will your altitude be
>
> accurate/precise
>
> enough
to allow you to do all the math on it to get the
>
> acceleration with any kind
of
>
> accuracy/precision?
>
>
>
> From
>
> what I
recall, the Featherweight altimeters are about
> the
>
> most
>
> accurate/precise out there
(although I
>
> would also check with the
altus
>
> metrum guys
>
> because
I've read that their stuff is pretty darned
>
> good,
>
> too).
Both will record fast enough to
>
> get you data with short
enough
>
> time
>
> intervals. I know Adrian
Adamson (Featherweight) has done
> a
>
> lot
of
>
> study on this--you might
check the
>
> Featherweight forum and also
over on
>
> TRF.
>
>
>
> I should
>
> also
mention that the Featherweight altimeters (or at
> least
>
> the
>
> Raven), and possibly the
altus metrum
>
> products, will also
provide
>
> acceleration
>
> data so
that you don't have to do the double
>
> differentiation to calculate
acceleration from
>
> altitude. I haven't
>
> looked
into how
>
> accurate/precise it is,
however. But you still have to
>
> know the atmospheric info and
the aerodynamics
>
> of your rocket--and those
>
> two are
usually
>
> the killers.
>
>
>
> A lot
of
>
> people have looked into doing
this and, as I recall,
> very
>
> few
>
> have
managed to come up with anything
>
> that was very persuasive (and
they
>
> were
>
> using commercial motors),
although I am certainly no
> expert
>
> on
this
>
> stuff. It's pretty
easy
>
> (especially if you can
program) to simulate a
>
> few data points and do the
calcs to see what
>
> you come up with. Munge
the
>
> altitude data a
>
> bit to
simulate inaccuracies and see how much it throws
>
> off your
answer. Vary the Cd by .1, .2, .3 or
>
> so and see what happens.
>
> Etc
etc.
>
> You'll soon get a feel
for just how hard this is.
>
>
>
> --Steve
>
>
>
> On
>
> 02/15/2015 10:17 AM, Michael
Monteith (Redacted sender
>
> michael_r_monteith@xxxxxxxxx
>
> for
DMARC) wrote:
>
> > I hope
>
> this
isn't off topic as it has to do with verifying
>
> motor
performance really. I was thinking on what I
> would
>
> need to verify rocket motor
performance during a flight
>
> test. So I was thinking of
what would be the
> requirements
>
> to
gather the data in flight. There is so many
> altimeters
>
> and ranges of price. Some
show they output thrust
> time.
>
> But not
sure exactly if it's what I'm thinking it
> is
>
> or I'd be better off
getting one cheaper and
>
calculating
>
> it.
>
> > http://data.rocketsetc.com/altimeter_data.html
>
> >
>
> > So to my
>
> question. What data is
required and how
>
> fast? I see all
the thrust curves for static
>
> testing but trying to figure
out how you backtrack and
>
> figure from a flight test
what the thrust curve is for
>
> comparison? This is what I
want to arrive at, a
> thrust
>
> curve
for flight test vs thrust curve on static
> testing.
>
> >
>
> > My initial guess is
>
> at least
having time and altitude and having rocket
> mass
>
> etc. From there you can
calculate acceleration etc
> and
>
> arrive
at thrust. I don't want to think of the
> formula
>
> right now for this. It
might be in my pile of books
> but
>
> those
are boxed up in Missouri and won't see them
> for
>
> about a month now. But
don't recall anything like
>
> that.
>
> >
>
> > I figured I
might as well buy
>
> the right recording altimeter
to begin with. I
> don't
>
> mind
spending the money but only if I do it preferably
> once
>
> and right. Specifically the
right data, accurate, and
> the
>
> right
speed. I think the more time I spent on it the
> more
>
> confused I was with all the
options on them all. At
> least
>
> until I
know the bare minimum. I don't know
>
> if
anyone has gone down this road or not. I saw Richard
> made
>
> mention on one of his pages
that it was something for a
>
> future page.
>
> >
>
> > If
we
>
> need to take it offline feel
free to email me.
>
> >
>
> > Michael Monteith
>
> >
>
> >
>
>
>
>
>
>
>
>
>
>
>
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