[sugpro] Re: Verifying Motor Performance Through Flight Tests
- From: Ben Brockert <wikkit@xxxxxxxxx>
- To: sugpro@xxxxxxxxxxxxx
- Date: Tue, 17 Feb 2015 10:54:36 -0500
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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