Re: [Rocketworkbench-devel] rocket description

[Konrad H. <ko...@ne...>]

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... )