Heavenly Hobbies H.H. Simit

Heavenly Hobbies - H.H. Simit

Contributed by Dick Stafford

Published: 2010-08-01
Manufacturer: Heavenly Hobbies
(Contributed - by Dick Stafford - 08/01/10)

Brief:
H. H. Simit is the simulation spreadsheet that Heavenly Hobbies distributes for free with their kits. I thought I’d take the time to do a quick review even though it is not separately available.

Simit consists of an Excel spreadsheet and an accompanying instructions file in .pdf format. I initially tried loading this is OpenOffice, but it was not compatible. It works properly in Excel 2003.

Inputs

The Simit spreadsheet is a pretty basic simulator but should be a great help if you don’t have access to a more robust program or don’t want to take the time to enter the design. It can handle up to two stages with multiple motors in each stage. The program includes data for 10 motors, including the ones that would be most commonly used in the Heavenly Hobbies kits. The rocket parameters includes mass values and dimensions for the major components. It comes pre-coded for the Resistor 224, Backdraft and Brutus 2.6 kits. While the motor and kit data seems limited, the instructions describe how to add your own. After using the program and studying the results, you should be able to use it for just about any design. And ThrustCurve has the motor data you'd need. Even though you may select English or Metric values on the input screen, results are provided for both. It appears the factory entered motors use metric units but the designs use English. The units setting needs to match these.

Outputs

The input screen includes the summary results (don’t forget to hit ‘F9’ if automatic calculations aren’t enabled). In addition, detailed tabular and graphical data are provided for acceleration, velocity and altitude. The instructions do a good job of showing how to interpret the results, based on the Backdraft. For that design, interpreting the results are especially important as you have to select the ignition delay for the retro motor.

Comparison to Rocksim

OK, I just couldn’t leave well enough along, so I entered the Resistor 224 into RockSim 9 just to see how its results compare to Simit. I adjusted Simit to reflect my Resistor 224’s actual as-built weight. Noting that Simit only provides acceleration and velocity at tenth-second intervals, these results are remarkably similar.

For 2 C11-3s:

  Max Acceleration Max Velocity Max Altitude Optimal Delay
Simit 362 131 241 N/A
RockSim 358 129 250 3.3

For 2 D12-5’s:

  Max Acceleration Max Velocity Max Altitude Optimal Delay
Simit 407 214 584 N/A
RockSim 481 215 581 4.5

Summary:
I won't provide a rating since it is not fair to compare this spreadsheet to products such as RockSim, SpaceCAD, or OpenRocket. It it however useful for Heavenly Hobbies' kits and is really easy to use. This is especially true for their Backdraft with its retro motor. I wish I had a quick and dirty altimeter like Apogee's AltimeterOne so I could critique its accuracy...and that of RockSim-9 for that matter.

 

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