Introduction

These charts are built from data that was gleaned for the most part from Aerotech's Web Site and some from an article on InfoCentral. But some of this data is also interpolation. Aerotech usually publishes only 3 or 4 delays for a specific motor; usually S, M, L, (and XL). All with integer delays like 6, 10, 14, and (18) second "advertised" delays.

As Rick Dickinson points out delay grains are lit along with the motor and burn all through the thrust as well as coast time. The burn rate is dependent on both time and pressure. Now, if you make the assumption that these burn rates are linear during each stage (thrust and coast) and start plotting some of Aerotech’s data, you find some very interesting "inferences". When you examine the graphed date you can easily hypothesize that burn rate may be a function of propellant type (more generally) than just of specific motor. That hypothesis, with the previously mentioned "linear assumption", and one other; namely that when Aerotech advertises an integer delay that it might be more of a range (6 seconds implies more like "somewhere between 5 and 7 seconds"), leads to this spreadsheet... Some of us took this data and started playing with graphs and linear approximations... The “RMS delay charts" of that data follow....

Use this data at your own risk... No warranties implied or stated.... Although Aerotech has not told me this is foolish nonsense, they also have not “approved it”. Nor have they sent me any formulae or graphs of their own.

Legend

For each motor "diameter" there is a separate chart. Each contains complex column titles and row titles as follows:

For the Columns

       RDK Designation

       The length of the delay element.

       The color of the delay spacer.

       The length of the spacer.

These values allow you to identify mixed and matched parts if (like I had them) they are currently unlabeled and mixed up... (This saved my tush at least once already!)

For the Rows

       Reload Name

       Casing dimensions

       Nozzle diameter (if known; I probably should label the ones with Medusa nozzles as well)

In the body of the data

The data in "black font" is the stock "Aerotech data" (although in some cases I “corrected” that data point to better match the interpolated line on the graph. But, it’s relatively easy to figure out which number it matches from Aerotech. For example, the H238T motor with the RDK 4+ delay shows a 10.4 second delay. That's the Aerotech Medium (or 10 second) delay.)

The data in "blue font" are simple interpolations of the Aerotech data. These probably can be trusted. (Most of this is data "between" the Aerotech delays values; I believe that's really safe data... I also believe that "one on each side" of the Aerotech date is probably pretty safe as well as its "close" to the Aerotech advertised data (be careful of the short data).)

The data in "red font" are those simple interpolations taken to extremes. Trust them at your own risk. Especially the shorter ones... (This data was just read off of the interpolated line on the chart). In general, any data in Red Font is suspect...

For the 54mm delays, I have not graphed the data yet, so there are no interpolations... (I’ll post an update)

In collecting the data, I found inconsistencies... The gray highlighted lines are data that should work just fine but was never published, or was inconsistent with other similar data. All I did (in general, was follow the above assumptions for motors where the data just didn't match... Further explanation available on request...)

         The second H210R line is what I think delays for that motor should be based on graphs (Gary never chose to confirm or deny any of it).

         The H268R line is my guess... At the time, there were no published delays for that motor...

The RDK 37+ is in Red because it’s just weird... (It appears that the delay+spacer dimension is too short, so the delay would probably not seal correctly. Never having had this delay in a kit, I don't know if Aerotech did anything to take care of that (extra seal washer?). I have a note off to Gary about it; I'll let you know if he tells me anything...

Acknowledgements

Thanx to Bill Farr and Chris Feenstra, who also participated in producing this data.

If you have any questions, suggestions, further data, corrections feel free to contact Rich Silva at mailto:richsilv@pacbell.net?subject=RMS Delays