Calculation of Delay for timer

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Calculation of Delay for timer

Post by a06145 » Wed, 21 May 2003 03:22:12



Could someone please tell how to figure what is the actual time I should
program into an electronic timer for deployment of chute.  Is it the
thrust duration + delay?  I'm confused as to whether the delays that
come with the aerotech motors include the thrust duration or not.

Thanks, Frank D'Amore TRA #1936

 
 
 

Calculation of Delay for timer

Post by Jerry Irvin » Wed, 21 May 2003 03:42:56




Quote:> Could someone please tell how to figure what is the actual time I should
> program into an electronic timer for deployment of chute.  Is it the
> thrust duration + delay?  I'm confused as to whether the delays that
> come with the aerotech motors include the thrust duration or not.

> Thanks, Frank D'Amore TRA #1936

All manufacturer stated delays are always from BURNOUT to EJECTION.

They may not be accurate, but that is how the data is presented.

Jerry

--
Jerry Irvine, Box 1242, Claremont, California 91711 USA

Please bring common sense back to rocketry administration.
Produce then publish.  http://www.usrockets.com

 
 
 

Calculation of Delay for timer

Post by Steve Humphre » Wed, 21 May 2003 05:03:40



> Could someone please tell how to figure what is the actual time I should
> program into an electronic timer for deployment of chute.  Is it the
> thrust duration + delay?  I'm confused as to whether the delays that
> come with the aerotech motors include the thrust duration or not.

All electronic timers that I know of start timing at liftoff. (They may
wait a 1/2 second or so before deciding liftoff has happened, but that
1/2 second will be included in the total time.)

Your question is a bit confusing. If you are using an electronic timer,
then why do you care how long the motor delay is? Granted, you may want
to use the motor delay for backup deployment (or primary, with the
electronic timer as backup). But you should choose a time for the
electronic timer based on the flight characteristics of the rocket. So
use wRASP, Rocksim, or some other rocket flight simulation program to
estimate the ideal time. Program your timer to the time-to-apogee
reported in the simulation.

As for motor delays: The nominal delay time (for example "7 seconds" for
a C6-7) is timed from the point when thrust stops. This is true for BP
and composite motors, even though in some motors the delay element
starts burning at ignition.

--
Steve Humphrey
(replace spambait with merlinus to reply directly to me)

 
 
 

Calculation of Delay for timer

Post by RayDunak » Wed, 21 May 2003 05:20:16


<< Could someone please tell how to figure what is the actual time I should
program into an electronic timer for deployment of chute.  Is it the thrust
duration + delay?>>

Yes, that is correct. When using a timer, you have to add the thrust time plus
the desired delay time.

<<I'm confused as to whether the delays that come with the aerotech motors
include the thrust duration or not. >>

Motor delay begins after burnout (end of thrust). This is true whether the
motor is an Estes, a single-use composite, or a reloadable.

So if you want to calculate your timer delay based on previously flown motor
delays, you'll have to add the motor's burn time and delay time. That will give
you the total time from ignition to ejection.

 
 
 

Calculation of Delay for timer

Post by Jerry Irvin » Wed, 21 May 2003 05:22:39




> << Could someone please tell how to figure what is the actual time I should
> program into an electronic timer for deployment of chute.  Is it the thrust
> duration + delay?>>

> Yes, that is correct. When using a timer, you have to add the thrust time
> plus
> the desired delay time.

> <<I'm confused as to whether the delays that come with the aerotech motors
> include the thrust duration or not. >>

> Motor delay begins after burnout (end of thrust). This is true whether the
> motor is an Estes, a single-use composite, or a reloadable.

> So if you want to calculate your timer delay based on previously flown motor
> delays, you'll have to add the motor's burn time and delay time. That will
> give
> you the total time from ignition to ejection.

If it is vague, burnout begins when thrust drops below 10% of peak
thrust.  This can be an issue for some of those wierd c-slots that have
crappy thrust curve shapes.

Jerry

--
Jerry Irvine, Box 1242, Claremont, California 91711 USA

Please bring common sense back to rocketry administration.
Produce then publish.  http://www.usrockets.com

 
 
 

Calculation of Delay for timer

Post by Des Bromilo » Wed, 21 May 2003 07:51:29


Frank,

the manfacturers quote from burnout to ejection as the dealy.
But for your timer, you'll need to know how it's triggered.

Some timers (most commercial timers) figure from liftoff - so that means it
needs to include burn time, but osmeo f the home made timers (particularly
timers based on mercury switches) sense the end of trust as the trigger,
therefore with those, the timer needs to ignore burn time.

Des


> Could someone please tell how to figure what is the actual time I should
> program into an electronic timer for deployment of chute.  Is it the
> thrust duration + delay?  I'm confused as to whether the delays that
> come with the aerotech motors include the thrust duration or not.

> Thanks, Frank D'Amore TRA #1936

 
 
 

Calculation of Delay for timer

Post by Erik Ebe » Wed, 21 May 2003 07:52:19



> Could someone please tell how to figure what is the actual time I should
> program into an electronic timer for deployment of chute.  Is it the
> thrust duration + delay?  I'm confused as to whether the delays that
> come with the aerotech motors include the thrust duration or not.

> Thanks, Frank D'Amore TRA #1936

You'll have to check the instructions for your timer.  The PML
Accufire timer detects burnout and starts counting from burnout.
Other timers detect launch and start counting from launch.

Motor delays are always quoted as time from burnout.

  -- Erik Ebert, L2
     TRA #09105
     NAR #79868

 
 
 

Calculation of Delay for timer

Post by RayDunak » Wed, 21 May 2003 08:38:58


<< You'll have to check the instructions for your timer.  The PML Accufire
timer detects burnout and starts counting from burnout. >>

Wow, I've never heard of that before. I'll have to remember that. I wonder how
reliably it detects burnout on slow flights?

 
 
 

Calculation of Delay for timer

Post by Erik Ebe » Wed, 21 May 2003 22:53:19



> << You'll have to check the instructions for your timer.  The PML Accufire
> timer detects burnout and starts counting from burnout. >>

> Wow, I've never heard of that before. I'll have to remember that. I wonder how
> reliably it detects burnout on slow flights?

From the PML website:

"AccuFire uses a progressive launch detect algorithm. The timer must
sense either 2g for 0.5 seconds, or 4g for 0.25 seconds, or 8g for
0.125 seconds to determine that launch has occurred and begin
monitoring for motor burnout. Accelerometer-based detection of motor
burnout occurs upon detection of deceleration (negative g`s) after
launch detection; the timing to the firing event begins at motor
burnout."

  -- Erik Ebert

 
 
 

Calculation of Delay for timer

Post by Jerry Irvin » Wed, 21 May 2003 23:00:15






> > << You'll have to check the instructions for your timer.  The PML Accufire
> > timer detects burnout and starts counting from burnout. >>

> > Wow, I've never heard of that before. I'll have to remember that. I wonder
> > how
> > reliably it detects burnout on slow flights?

> From the PML website:

> "AccuFire uses a progressive launch detect algorithm. The timer must
> sense either 2g for 0.5 seconds, or 4g for 0.25 seconds, or 8g for
> 0.125 seconds to determine that launch has occurred and begin
> monitoring for motor burnout. Accelerometer-based detection of motor
> burnout occurs upon detection of deceleration (negative g`s) after
> launch detection; the timing to the firing event begins at motor
> burnout."

>   -- Erik Ebert

That's a good method so long as you do not drop the rocket putting it on
the pad or jerking a payload compartment on the rocket while on the pad.

--
Jerry Irvine, Box 1242, Claremont, California 91711 USA

Please bring common sense back to rocketry administration.
Produce then publish.  http://www.usrockets.com

 
 
 

Calculation of Delay for timer

Post by Bob Kapl » Thu, 22 May 2003 02:10:17




>> << You'll have to check the instructions for your timer.  The PML Accufire
>> timer detects burnout and starts counting from burnout. >>

>> Wow, I've never heard of that before. I'll have to remember that. I wonder how
>> reliably it detects burnout on slow flights?

> From the PML website:

> "AccuFire uses a progressive launch detect algorithm. The timer must
> sense either 2g for 0.5 seconds, or 4g for 0.25 seconds, or 8g for
> 0.125 seconds to determine that launch has occurred and begin
> monitoring for motor burnout. Accelerometer-based detection of motor
> burnout occurs upon detection of deceleration (negative g`s) after
> launch detection; the timing to the firing event begins at motor
> burnout."

Negative Gs are quite possible before burnout. All you need is a vehicle
with a large thrust spike and long low thrust sustainer. Like the old FSI
D18, or even the Extes A10.

        Bob Kaplow      NAR # 18L       TRA # "Impeach the TRA BoD"
                >>> To reply, remove the TRABoD! <<<
Kaplow Klips & Baffle:      http://www.pleimling.org/le/Phantom4000.pdf
    www.encompasserve.org/~kaplow_r/    www.nira-rocketry.org    www.nar.org

 Save Model Rocketry from the HSA!   http://www.space-rockets.com/congress.html

 
 
 

Calculation of Delay for timer

Post by Jerry Irvin » Thu, 22 May 2003 05:13:17




Quote:> Negative Gs are quite possible before burnout. All you need is a vehicle
> with a large thrust spike and long low thrust sustainer. Like the old FSI
> D18, or even the Extes A10.

29mm G25/G30 as well.

--
Jerry Irvine, Box 1242, Claremont, California 91711 USA

Please bring common sense back to rocketry administration.
Produce then publish.  http://www.usrockets.com