Delay Time Charts

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I can't begin to count the number of times I have been at a launch where someone has come up to me and asked what delay I thought would be best for such and such a motor in their rocket.  Personally I prefer to always run a simulation on wRASP or RockSim prior to first flight.  However, if that is not possible, then the charts presented below can be very helpful.  These charts can be used to select the best delay time for a wide variety of rockets and motors.  I generated these plots with wRASP for the more popular Aerotech motors.   I did not include any of the larger motors since those are usually either flown with altimeters on-board, or are plugged motors without a delay charge.

These charts are for estimating delay time only!  They show the time to apogee from motor burnout. They do not imply that any specific weight and motor combination will have an acceptable acceleration at liftoff.  They may also be slightly inaccurate for any flights that would go supersonic since CD was a fixed value in all the calculations.    However, they should be quite accurate for the vast majority of flights represented on them.

All of these charts assume the coefficient of drag CD = 0.45.  This is because I have found that for all of my rockets, if I simply assume CD = 0.45, then wRASP will give an estimated altitude that is very close to what I measure during the actual flight.  (See Altitude Charts page.)

Delay time is defined as the time between motor burnout and when the ejection charge ignites.  The Aerotech motors have nominal delay times as listed in this table.

Type Nominal Delay
Short 6 seconds
Medium 10 seconds
Long 14 seconds
Extra Long 18 seconds

The charts shown below are also available as a PDF document.  Click here to get it.  The PDF document can be printed for easy reference out at the launch site.  These charts may also prove useful to the RSO at a launch in order to double check the delay time that has been selected by the owner of a rocket.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The charts shown above are also available as a PDF document.  Click here to get it.

 

 

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 All photos not otherwise credited were taken by Vern Knowles

Vern Knowles 2002, 2003, 2004, 2005, 2006, 2007 All Rights Reserved