by Brad Martin

I have purchased a stock Estes Gemini DC with t' intent of usin' every component in it t' create a rather different rocket than what is shown on t' original package cover.

  My Gemini-DX will be a 5 engine cluster consistin' o' 4 C6-7's and  a central E9-8.  T' idea is t' have t' boosters ejection charges reverse  with a cowling-like slice o' t' two smaller nose cones.  This should  make for one last smokey feeble push just before apogee.  Rocksim 's say about 3100' but I have yet t' figure out ways to model  some o' t' subtle design mods.  One problem is how t' create the model  o' t' booster MMT's...  An inside tube placed outside the body sims  only t' CG, apparently nay t' CP,  So I've used 'dummy fins' o' near  zero mass t' help offset t' CP.  I've also created a set o' 'custom fins' t' mimick t' sliced & diced nose cone segments above, but again these are just an approximation o' t' real thing.  Also, I can't rotate them t' way I want!  Even though these things frustrate me, I still think Rocksim is some o' t' best software around, and that's coming from someone that has been buildin' 3D CAD models for over 15 years  ;}

Guesstimated timeline:
Secs/event
0.0 = power t' igniters
0.1 = ignition/lift-off
0.3 = clears pad
1.8 = C6-7's burnout
3.0 = E9-8 burnout
8.8 = C6-7's ejection charge (reversed)
11.3=E9-8 ejection charge (normal)
11.4=Parachutes deployed
220 = Landing


Gemini DX - Rocksim Simulation results
Engine selection
[E9-8   ,C6-7   ,C6-7   ,C6-7   ,C6-7   ]

Simulation control parameters
Resolution: 1000 samples / second.
Simulation method: 4th Order runge-kuta.
Simulation execution time: 16.633 Sec.

Launch conditions
Altitude: 0.000 Ft.
Relative humidity: 50.000 %
Temperature: 59.000 Deg. Avast, me proud beauty! Begad! F
Pressure: 29.914 In. Arrr! Hg.
Wind speed: 0.000 MPH
Launch guide angle: 0.000 Degrees from vertical
Latitude: 90.000 Degrees

Launch guide data:
Launch guide length: 36.000 In.
Velocity at launch guide departure: 46.749 MPH
T' launch guide was cleared at : 0.160 Seconds
User specified minimum velocity for stable flight: 29.999 MPH
Minimum velocity for stable flight reached at: 19.641 In.

Max data values:
Maximum acceleration: Vert: 34.978 g , Horz: 0.000 g , Magnitude: 34.978 g
Maximum velocity: Vert: 524.944 MPH , Horz: 0.000 MPH , Magnitude: 524.944 MPH
Maximum range from launch site: 0.000 Ft.
Maximum altitude: 3187.414 Ft.

Engine ejection charge data:
Conditions at engine ejection charge:
  Usin' a delay time o' : 8.000 Seconds
     Velocity: 6.931 MPH
     Altitude: 3185.814 Ft.

Recovery system data
  P:  Parachutes  Deployed at : 11.186 Seconds
  Velocity at deployment: 0.003 MPH
  Altitude at deployment: 3187.414 Ft.
  Range at deployment: 0.000 Ft.

Time data
Time t' burnout: 2.871 Sec.
Time t' apogee: 11.186 Sec.
Optimal ejection delay: 8.315 Sec.

Landin' data
Successful landing
Time t' landing: 221.228 Sec.
Range at landing: 0.000
Velocity at landing: Vert: -10.124 MPH , Horz: 0.000 MPH , Magnitude: 10.124 MPH