4 inch Polecat Goblin Replica - Build Thread

[DabCat]

Goblins at ROCstock?

Planning on launching the 4" fibergoblin on a J1799. .6 second burn time, 53G's.

Mike K

Chase, I think you are bringing you 6" goblin but are you bringing your 4" one too? wanna drag race the 4"?

What does your 4" weight? What's your velocity off the rail? Deciding between an H550 and H999.

 

[Hobie1dog]

Take pictures guys while at the launch.

 

[cwbullet]

Video please. I did design a 4 inch 3d printed version.

 

[kramer714]

Mine is much heavier than a stock polecat goblin. The Fibergoblin weighs 3,000 grams, twice as much as a stock polecat goblin.

What does your 4" weight? What's your velocity off the rail? Deciding between an H550 and H999.

So about the speed off the rail....

The fun thing about 'polecat style' goblins is they are REALLY robust. What I built is even more robust-er, thick wall fiberglass, thru the wall internal filleted cartridge fins, it is a beast. With the J1799 it sims out as leaving the rail at 90 MPH, stable in like 10 inches of rail The thrust to weight is 60, pulls about 52 gees. For this rocket / motor combo, speed of the rail isnt an issue.

The other thing to think about is the delay, FAST motors can be bad for getting a proper delay, mine has a flight computer in it.


A stock Polecat goblin only weighs about 1500 grams, all in less motor. The old school polyester layup nosecones are really light, just not a lot or rocket to launch. So with an H 180 you only need like 3 feet of rail to be stable. With anH999 or an H550 you will be going plenty fast off the rail, might even use tape to shorten the rail. Question I have for you is can it handle 90 plus Gees the way you built it? Both motors are fun but i gotta say the 'cannon ball' launch is always a good time. Both sims below. I just guessed at the 12 seconds, looks spot on for the H999, maybe a little long for the H550.

Mike K


Polecat-Goblin 4 in - Simulation results Engine selection [H999N-12]

Engine manufacturer Aerotech

Launch conditions

• Altitude: 2700.00000 Ft.
• Relative humidity: 50.000 %
• Temperature: 80.000 Deg. F
• Pressure: 29.9139 In.
• Wind speed model: Slightly breezy (8-14 MPH)
  • Low wind speed: 8.0000 MPH
  • High wind speed: 14.9000 MPH
• Wind turbulence: Some variablility (0.04)
  • Frequency: 0.040000 rad/second
• Wind starts at altitude: 0.00000 Ft.
• Launch guide angle: 0.000 Deg.
• Latitude: 0.000 Degrees

Launch guide data:

• Launch guide length: 72.0000 In.
• Velocity at launch guide departure: 103.6101 MPH
• The launch guide was cleared at : 0.081 Seconds
• User specified minimum velocity for stable flight: 29.9919 MPH
• Minimum velocity for stable flight reached at: 6.9309 In.

Max data values:

• Maximum acceleration:Vertical (y): 92.048 gee Horizontal (x): 0.069 geeMagnitude: 92.048 gee
• Maximum velocity:Vertical (y): 393.7103 MPH, Horizontal (x): 14.9000 MPH, Magnitude: 393.8523 MPH
• Maximum range from launch site: 1697.91196 Ft.
• Maximum altitude: 2761.58948 Ft.

Engine ejection charge data:

• Using a delay time of : 12.000 Seconds
• Velocity: 9.3817 MPH
• Altitude: 2759.73138 Ft.

Recovery system data

• P: Parachute Deployed at : 12.330 Seconds
• Velocity at deployment: 9.3817 MPH
• Altitude at deployment: 2759.73138 Ft.
• Range at deployment: -83.95322 Ft.

Time data

• Time to burnout: 0.330 Sec.
• Time to apogee: 11.990 Sec.
• Optimal ejection delay: 11.660 Sec.

Landing data

• Successful landing
• Time to landing: 110.172 Sec.
• Range at landing: 1697.91196
• Velocity at landing: Vertical: -18.9243 MPH , Horizontal: 13.2567 MPH , Magnitude: 23.1056 MPH

Polecat-Goblin 4 in - Simulation results Engine selection [H550ST-12]

Simulation control parameters

• Flight resolution: 800.000000 samples/second
• Descent resolution: 1.000000 samples/second
• Method: Explicit Euler
• End the simulation when the rocket reaches the ground.

Launch conditions

• Altitude: 2700.00000 Ft.
• Relative humidity: 50.000 %
• Temperature: 80.000 Deg. F
• Pressure: 29.9139 In.
• Wind speed model: Slightly breezy (8-14 MPH)
  • Low wind speed: 8.0000 MPH
  • High wind speed: 14.9000 MPH
• Wind turbulence: Some variablility (0.04)
  • Frequency: 0.040000 rad/second
• Wind starts at altitude: 0.00000 Ft.
• Launch guide angle: 0.000 Deg.
• Latitude: 0.000 Degrees

Launch guide data:

• Launch guide length: 72.0000 In.
• Velocity at launch guide departure: 79.3368 MPH
• The launch guide was cleared at : 0.110 Seconds
• User specified minimum velocity for stable flight: 29.9919 MPH
• Minimum velocity for stable flight reached at: 11.5145 In.

Weathercocking

• With current settings, the rocket stays inside the 40 degree weathercocking cone before apogee which is considered safe.

Max data values:

Maximum acceleration:Vertical (y): 36.047 geeHorizontal (x): 0.169 geeMagnitude: 36.077 gee

• Maximum velocity:Vertical (y): 381.2369 MPH, Horizontal (x): 13.1595 MPH, Magnitude: 382.1259 MPH
• Maximum range from launch site: 1175.12223 Ft.
• Maximum altitude: 2707.16285 Ft.

Engine ejection charge data:

• Using a delay time of : 12.000 Seconds
• Velocity: 19.5865 MPH
• Altitude: 2701.08678 Ft.

Recovery system data

• P: Parachute Deployed at : 12.580 Seconds
• Velocity at deployment: 19.5865 MPH
• Altitude at deployment: 2701.08678 Ft.
• Range at deployment: -220.19111 Ft.

Time data

• Time to burnout: 0.580 Sec.
• Time to apogee: 11.965 Sec.
• Optimal ejection delay: 11.385 Sec.

Landing data

• Successful landing
• Time to landing: 109.562 Sec.
• Range at landing: 1175.12223
• Velocity at landing: Vertical: -18.6584 MPH , Horizontal: 13.1597 MPH , Magnitude: 22.8322 MPH

Competition settings


Competition conditions are not in use for this simulation.

 

[DabCat]

Mine is much heavier than a stock polecat goblin. The Fibergoblin weighs

So about the speed off the rail....

The fun thing about 'polecat style' goblins is they are REALLY robust. What I built is even more robust-er, thick wall fiberglass, thru the wall internal filleted cartridge fins, it is a beast. With the J1799 it sims out as leaving the rail at 90 MPH, stable in like 10 inches of rod. The thrust to weight is 60, pulls about 52 gees. For this rocket that isnt an issue.

The other thing to think about is the delay, FAST motors can be bad for getting a proper delay, mine has a flight computer in it.


A stock Polecat goblin only weighs about 1500 grams, all in less motor. The old school polyester layup nosecones are really light, just not a lot or rocket to launch. So with an H 180 you only need like 3 feet of rail to be stable. With anH999 or an H550 you will be going plenty fast off the rail, might even use tape to shorten the rail. Question I have for you is can it handle 90 plus Gees the way you built it? Both motors are fun but i gotta say the 'cannon ball' launch is always a good time. Both sims below. I just guessed at the 12 seconds, looks spot on for the H999, maybe a little long for the H550.

Mike K


Polecat-Goblin 4 in - Simulation results Engine selection [H999N-12]

Engine manufacturer Aerotech

Launch conditions

• Altitude: 2700.00000 Ft.
• Relative humidity: 50.000 %
• Temperature: 80.000 Deg. F
• Pressure: 29.9139 In.
• Wind speed model: Slightly breezy (8-14 MPH)
  • Low wind speed: 8.0000 MPH
  • High wind speed: 14.9000 MPH
• Wind turbulence: Some variablility (0.04)
  • Frequency: 0.040000 rad/second
• Wind starts at altitude: 0.00000 Ft.
• Launch guide angle: 0.000 Deg.
• Latitude: 0.000 Degrees

Launch guide data:

• Launch guide length: 72.0000 In.
• Velocity at launch guide departure: 103.6101 MPH
• The launch guide was cleared at : 0.081 Seconds
• User specified minimum velocity for stable flight: 29.9919 MPH
• Minimum velocity for stable flight reached at: 6.9309 In.

Max data values:

• Maximum acceleration:Vertical (y): 92.048 gee Horizontal (x): 0.069 geeMagnitude: 92.048 gee
• Maximum velocity:Vertical (y): 393.7103 MPH, Horizontal (x): 14.9000 MPH, Magnitude: 393.8523 MPH
• Maximum range from launch site: 1697.91196 Ft.
• Maximum altitude: 2761.58948 Ft.

Engine ejection charge data:

• Using a delay time of : 12.000 Seconds
• Velocity: 9.3817 MPH
• Altitude: 2759.73138 Ft.

Recovery system data

• P: Parachute Deployed at : 12.330 Seconds
• Velocity at deployment: 9.3817 MPH
• Altitude at deployment: 2759.73138 Ft.
• Range at deployment: -83.95322 Ft.

Time data

• Time to burnout: 0.330 Sec.
• Time to apogee: 11.990 Sec.
• Optimal ejection delay: 11.660 Sec.

Landing data

• Successful landing
• Time to landing: 110.172 Sec.
• Range at landing: 1697.91196
• Velocity at landing: Vertical: -18.9243 MPH , Horizontal: 13.2567 MPH , Magnitude: 23.1056 MPH

Polecat-Goblin 4 in - Simulation results Engine selection [H550ST-12]

Simulation control parameters

• Flight resolution: 800.000000 samples/second
• Descent resolution: 1.000000 samples/second
• Method: Explicit Euler
• End the simulation when the rocket reaches the ground.

Launch conditions

• Altitude: 2700.00000 Ft.
• Relative humidity: 50.000 %
• Temperature: 80.000 Deg. F
• Pressure: 29.9139 In.
• Wind speed model: Slightly breezy (8-14 MPH)
  • Low wind speed: 8.0000 MPH
  • High wind speed: 14.9000 MPH
• Wind turbulence: Some variablility (0.04)
  • Frequency: 0.040000 rad/second
• Wind starts at altitude: 0.00000 Ft.
• Launch guide angle: 0.000 Deg.
• Latitude: 0.000 Degrees

Launch guide data:

• Launch guide length: 72.0000 In.
• Velocity at launch guide departure: 79.3368 MPH
• The launch guide was cleared at : 0.110 Seconds
• User specified minimum velocity for stable flight: 29.9919 MPH
• Minimum velocity for stable flight reached at: 11.5145 In.

Weathercocking

• With current settings, the rocket stays inside the 40 degree weathercocking cone before apogee which is considered safe.

Max data values:

Maximum acceleration:Vertical (y): 36.047 geeHorizontal (x): 0.169 geeMagnitude: 36.077 gee

• Maximum velocity:Vertical (y): 381.2369 MPH, Horizontal (x): 13.1595 MPH, Magnitude: 382.1259 MPH
• Maximum range from launch site: 1175.12223 Ft.
• Maximum altitude: 2707.16285 Ft.

Engine ejection charge data:

• Using a delay time of : 12.000 Seconds
• Velocity: 19.5865 MPH
• Altitude: 2701.08678 Ft.

Recovery system data

• P: Parachute Deployed at : 12.580 Seconds
• Velocity at deployment: 19.5865 MPH
• Altitude at deployment: 2701.08678 Ft.
• Range at deployment: -220.19111 Ft.

Time data

• Time to burnout: 0.580 Sec.
• Time to apogee: 11.965 Sec.
• Optimal ejection delay: 11.385 Sec.

Landing data

• Successful landing
• Time to landing: 109.562 Sec.
• Range at landing: 1175.12223
• Velocity at landing: Vertical: -18.6584 MPH , Horizontal: 13.1597 MPH , Magnitude: 22.8322 MPH

Competition settings


Competition conditions are not in use for this simulation.

I'm asking to get a sense of how fast I need to go to at least match yours. Dont want you beating me by too much. H999 is plugged, so it would need an altimeter. H550 could go motor deploy with a 12 second delay. It's flow successfully on both motors and 54mm loads. I'm confident it'll survive.

 

[kramer714]

Will be fun!

0-600 miles per hour in .6 seconds, 300 feet above the ground

Fibergoblin 4 in - Engine selection [J1799N-17]

Engine manufacturer Aerotech

Launch conditions

• Altitude: 2700.00000 Ft.
• Relative humidity: 50.000 %
• Temperature: 80.000 Deg. F
• Pressure: 29.9139 In.
• Wind speed model: Slightly breezy (8-14 MPH)
  • Low wind speed: 8.0000 MPH
  • High wind speed: 14.9000 MPH
• Wind turbulence: Some variablility (0.04)
  • Frequency: 0.040000 rad/second
• Wind starts at altitude: 0.00000 Ft.
• Launch guide angle: 0.000 Deg.
• Latitude: 0.000 Degrees

Launch guide data:

• Launch guide length: 72.0000 In.
• Velocity at launch guide departure: 88.9045 MPH
• The launch guide was cleared at : 0.098 Seconds
• User specified minimum velocity for stable flight: 29.9919 MPH
• Minimum velocity for stable flight reached at: 9.1534 In.

Weathercocking

• With current settings, the rocket stays inside the 40 degree weathercocking cone before apogee which is considered safe.

Max data values:

• Maximum acceleration:Vertical (y): 52.984 geeHorizontal (x): 0.358 geeMagnitude: 52.991 gee
• Maximum velocity:Vertical (y): 603.3531 MPH, Horizontal (x): 14.9000 MPH, Magnitude: 604.1592 MPH
• Maximum range from launch site: 2078.94752 Ft.
• Maximum altitude: 6269.54620 Ft.

Engine ejection charge data:

• Using a delay time of : 17.000 Seconds
• Velocity: 19.1973 MPH
• Altitude: 6266.92915 Ft.

Recovery system data

• P: Parachute Deployed at : 17.653 Seconds
• Velocity at deployment: 19.1973 MPH
• Altitude at deployment: 6266.92915 Ft.
• Range at deployment: -470.94285 Ft.

Time data

• Time to burnout: 0.652 Sec.
• Time to apogee: 18.048 Sec.
• Optimal ejection delay: 17.391 Sec.

Landing data

• Successful landing
• Time to landing: 168.426 Sec.
• Range at landing: 2078.94752
• Velocity at landing: Vertical: -27.3602 MPH , Horizontal: 8.1282 MPH , Magnitude: 28.5420 MPH

Competition settings

• Boy Howdy mode - Activated

 

[DabCat]

My flight went perfect. I got a bunch of pictures and footage. I'm planning to make a youtube video compiling all of it. For now, here's a little teaser:
View attachment 2023-11-14_18-11-10.webm

Let's do it again. I grabbed a couple K2050's and J1799's on the Wildman sale. Maybe next time your motor will work.