Re: [Rocketworkbench-devel] rocket description

[LarryC <cu...@te...>]

Konrad,

Not sure what team you're talking about, but I'm 99.9% sure I'd like to
join :) Your characterization of my dissatisfation with DATCOM is
correct. I am, however, interested in comparing datcom Cd curves with 
those from accelerometers. I applaud your inclusion of Cd/velocity and
Cd mach number relationships in your code. 

Rock On,
-Larry C.

On Tue, 15 Feb 2000, Konrad Hambrick wrote:

> Antoine Lefebvre has written:
> > 
> > Hello,
> > 
> > I have take a look to the Konrad Hambrick rocket profiler and it is very interesting. I suppose it is possible to compute a lot of parameter just by geometrical analisys. It could be a start point to a full rocket caracterisation. If I understand, the profiller compute the CG, and the CP of the rocket (no drag factor of other aerodynamic factor). 
> > There is other value computed by this rocket profiler?
> > 
> > To upgrade the capability of the profiler, we could add information about surface finish and density of different part of the rocket. 
> > 
> > I could be great to add this software in cvs and ftp. Maybe begin to tranlate it in C before. (Could use flex as the file parser).
> > 
> > I will read the code during the week and try to understand it all.
>  
> 
> Antoine --
> 
> Profiler computes the stability info and outputs enough info
> for gnuplot to 'draw' a picture of the rocket with the CLA
> ( center of lateral area ) and CP ( Barrowman Center of 
> Pressure ) marked.
> 
> Various 'standard shapes' are programmed in -- ogive, parabolic
> and elliptical including the shape itself and the 1st and 2nd
> moments.
> 
> It does not yet compute CG from geometry & physical properties.
> That was the next feature I was to add ( back in '96, before
> the AltAcc distracted me ;-)
> 
> The CG and Radial and Longtudinal Moments can be entered directly
> and profiler will compute the Dynamic Stability parameters.  Run
> the mi.pro, hjohn.pro and grad.pro.  I constructed a torsion
> wire and measured the IR and IL and CG and entered the results
> in the .pro files for these rockets.
> 
> Of interest here:  The hjohn and grad are rock(et)-solid stable,
> the mi is dynamically unstable and I wanted to find out why ...
> 
> re:  Mark's Q's,  The CG can be computed by taking a different
> moment than the CLA.  Like I said, I was working on adding it
> but I have been distracted by my real job and the AltAcc.
> 
> I was working on a materials database and also on allowing for
> direct entry.
> 
> As far as computing CD from the geometry -- it is possible but
> as far as practicality goes, other model rocket CD calculators
> based on DATCOM have produced dubious results at best.
> 
> I was looking at using Accelerometer-Based data.  I have some
> excellent results on the LOC Vulcanite, scaled both down and
> up ( 1.9 in-diam, 2.25 in, and 2.9 in ) and I am building
> a 3.99 inch for a Level 3 attempt. 
> 
> This is why the CD-vs-Mach linked-list was included in my
> rocket.h file.  I planned to allow for experimental data
> in the 'physical properties' section.  Experimental data
> would override computed physical properties.
> 
> The Drag vs Velocity data for the Vulcanite series are online
> at:  ftp://ftp.netcom.com/pub/ko/konrad/
> 
> The files to look at are:
> 
>    vulet-dr.gif  -- 1.9  in scaled down LOC Vulcanite ( Vulcanette )
>    vul-dr.gif    -- 2.25 in Vulcanite ( Spock's Johnson )
>    nm-dr.gif     -- 2.9  in scaped up Vulcanite ( Nocturnal Missions )
> 
> For each I have fit a 2nd degree polynomial to the subsonic Drag vs
> Velocity.  Each has gone supersonic and each shows the transonic drag
> divergance in the Force vs Velocity data.
> 
> Larry Curcio has already implemented DATCOM but he is not
> happy with the results on modrocket-scaled vehicles.
> 
> I am sending him a cc of this elm.  He would be an invaluable addition 
> to the team.   Larry has already implemented most of the aero and sim 
> stuff we are discussing.
> 
> -- kjh
> 
> cc:  LarryC ( cu...@te... )
>