[AR] Re: dynamic stability
- From: Bill Claybaugh <wclaybaugh2@xxxxxxxxxx>
- To: "arocket@xxxxxxxxxxxxx" <arocket@xxxxxxxxxxxxx>
- Date: Thu, 21 Aug 2014 15:07:17 -0600
Just a caution: I have an impression that the splash function in RS-Pro does
not generate results consistent with other simulations, notably TAOS and POST.
Others more experienced than I may want to comment.
Bill
Sent from my iPhone
On Aug 21, 2014, at 13:30, Paul Mueller <paul.mueller.iii@xxxxxxxxx> wrote:
> As I understand things, one major aspect of "dynamic stability" is roll-pitch
> coupling, where a certain spin rate can cause resonant pitch response (at the
> pitch natural frequency), causing the rocket to basically "cone" in a
> divergent manner until the angle of attack gets to be too much and the rocket
> breaks up due to aerodynamic loads. The original sounding rocket community
> avoided this by rapidly spinning their rockets (and spinning them up quickly)
> so that the spin rate is well above the pitch natural frequency. As I
> understand it, the pitch natural frequency depends on the mass properties of
> the rocket and the aerodynamic forces (which change with speed and altitude),
> so it can be kind of a hairy problem. I have RSPro and it does not calculate
> the pitch natural frequency (at least not that I have been able to decipher).
> So it's not much help for me.
>
> But those sounding rockets tended to be high-acceleration (high thrust, short
> duration), and misaligned thrust and/or asymmetric drag could really send
> them off course. So they spun them up. I think an equally valid approach for
> lower-acceleration liquid (or hybrid) rockets is the approach used by
> Carmack--slow spin rates (or none at all) to avoid roll-pitch coupling. Slow
> spin rates can help mitigate effects of off-axis thrust, asymmetric drag,
> etc. so the vehicle still goes basically straight.
>
> RSPro does have the ability to calculate "splash" plots of where the rocket
> would be predicted to impact the ground (with no recovery, I believe) with
> varying initial conditions, etc. (launch angle, winds at different altitudes,
> misaligned thrust, etc.). I heard somewhere that a 50 km or so flight in the
> past few years at Black Rock impacted well outside the predicted "splash"
> zone so the FAA was reconsidering how to handle this requirement, but I
> haven't heard anything more recently. My takeaway is that computer simulation
> (RSPro or otherwise) still has a ways to go to be something that can be
> relied upon. My opinion only, and maybe things have gotten better.
>
> Carl, I'd be happy to run RSPro simulations for you. My version is about 6
> years old--I don't know if RSPro has been upgraded since then and whether I
> could get a free upgrade if needed.
>
> Paul M
>
>
> On Thu, Aug 21, 2014 at 12:51 PM, Ken Biba <kenbiba@xxxxxx> wrote:
>> I have RSPro and we are regularly submitting 100k+ projects.
>>
>> RSPro does poor job of estimating drag, there are other tools useful for
>> estimating drag.
>>
>> Is this a single stage of multistage airframe?
>>
>> K
>>
>> Ken Biba
>> Novarum
>> Managing Director and CTO
>> +14155775496
>>
>>
>> > On Aug 21, 2014, at 10:28 AM, Carl Tedesco <ctedesco@xxxxxxxxxxxxxx> wrote:
>> >
>> > Thanks Richard, but this is for a liquid bi-propellant rocket, which I
>> > don't believe Tripoli allows.
>> >
>> > This is for the university rocket project I mentor --- SDSU. I just looked
>> > into Rocksim Pro and it is $1000 which is more than we can afford. Do any
>> > Arocketeers have Rocksim Pro and would be willing to help out a University
>> > team.
>> >
>> > --- Carl
>> >
>> >> On 8/20/2014 6:30 PM, Richard Hagensick wrote:
>> >> If you belong to Tripoli Rocketry they have a Class 3 committee that will
>> >> do the analysis for you and provide you with the paperwork you need to
>> >> file your permit. They use Rocksim Pro. I submitted mine to the FAA for
>> >> a 150K launch at BALLS this year.
>> >>
>> >> Richard Hagensick
>> >>
>> >> -----Original Message-----
>> >> From: arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx]
>> >> On Behalf Of Monroe L. King Jr.
>> >> Sent: Wednesday, August 20, 2014 7:44 PM
>> >> To: arocket@xxxxxxxxxxxxx
>> >> Subject: [AR] Re: dynamic stability
>> >>
>> >> I don't think Flowmetrics flies under a TRA waiver for starters. The one
>> >> launch I observed was an atlas vernier modification LOX and Hydrocarbon
>> >> at FAR
>> >>
>> >> As I understand it Class 3 is "P" and above and you can bet they want a
>> >> FULL 3 Sigma 6 degree of freedom analysis.
>> >>
>> >> AT a TRA event such as BALLS if you within a certain amount of their
>> >> standing waiver for altitude you might get some benefit. But they are
>> >> still going to require 3 sigma analysis (although you might get some help
>> >> with it) and they in-turn are going to hand that to the FAA.
>> >>
>> >> Last I remember it's 14 points they look at during the analysis I have a
>> >> list here somewhere.
>> >>
>> >> Monroe
>> >>
>> >>> -------- Original Message --------
>> >>> Subject: [AR] Re: dynamic stability
>> >>> From: Carl Tedesco <ctedesco@xxxxxxxxxxxxxx>
>> >>> Date: Wed, August 20, 2014 5:24 pm
>> >>> To: arocket@xxxxxxxxxxxxx
>> >>>
>> >>>
>> >>> That is what I wondered. From an aerospace engineering point of view,
>> >>> dynamic stability looks to see how a rocket will respond when a
>> >>> disturbance is imparted on it. CP/CG rules determine static stability,
>> >>> albeit still important. So, the Tripoli example you mention suggests
>> >>> that they just want to know how the CP and CG change throughout the
>> >>> entire flight?
>> >>>
>> >>> Monroe, do they require they require 3-sigma or dispersion analysis?
>> >>> Below is an excerpt of what I was emailed (looks like it was cut &
>> >>> pasted from the FAA website).
>> >>>
>> >>> (a) Class 2---High-Power Rockets. When a Class 2---High-Power Rocket
>> >>> requires a certificate of waiver or authorization, the person planning
>> >>> the operation must provide the information below on each type of
>> >>> rocket to the FAA at least 45 days before the proposed operation. The
>> >>> FAA may request additional information if necessary to ensure the
>> >>> proposed operations can be safely conducted. The information shall
>> >>> include for each type of Class 2 rocket expected to be flown:
>> >>> (1) Estimated number of rockets,
>> >>> (2) Type of propulsion (liquid or solid), fuel(s) and oxidizer(s),
>> >>> (3) Description of the launcher(s) planned to be used, including any
>> >>> airborne platform(s),
>> >>> (4) Description of recovery system,
>> >>> (5) Highest altitude, above ground level, expected to be reached,
>> >>> (6) Launch site latitude, longitude, and elevation, and
>> >>> (7) Any additional safety procedures that will be followed.
>> >>> (b) Class 3---Advanced High-Power Rockets. When a Class 3---Advanced
>> >>> High-Power Rocket requires a certificate of waiver or authorization
>> >>> the person planning the operation must provide the information below
>> >>> for each type of rocket to the FAA at least 45 days before the
>> >>> proposed operation. The FAA may request additional information if
>> >>> necessary to ensure the proposed operations can be safely conducted.
>> >>> The information shall include for each type of Class 3 rocket expected
>> >>> to be flown:
>> >>> (1) The information requirements of paragraph (a) of this section,
>> >>> (2) Maximum possible range,
>> >>> (3) The dynamic stability characteristics for the entire flight
>> >>> profile,
>> >>> (4) A description of all major rocket systems, including structural,
>> >>> pneumatic, propellant, propulsion, ignition, electrical, avionics,
>> >>> recovery, wind-weighting, flight control, and tracking,
>> >>> (5) A description of other support equipment necessary for a safe
>> >>> operation,
>> >>> (6) The planned flight profile and sequence of events,
>> >>> (7) All nominal impact areas, including those for any spent motors and
>> >>> other discarded hardware, within three standard deviations of the mean
>> >>> impact point,
>> >>> (8) Launch commit criteria,
>> >>> (9) Countdown procedures, and
>> >>> (10) Mishap procedures.
>> >>>
>> >>> --- Carl
>> >
>> > --
>> > Carl Tedesco
>> > Flometrics, Inc.
>> > 5900 Sea Lion Place, Suite 150
>> > Carlsbad, CA 92010
>> > tel: 760-476-2770 ext. 515
>> > fax: 760-476-2763
>> > ctedesco@xxxxxxxxxxxxxx
>> > www.flometrics.com
>> >
>> >
>
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