figuring the proper delay

[SpartaChris]

Is there a way to figure out what the optimal delay prior to ejection is? I ask because everytime I fly something, I seem to either be too short or too long, yet I see some people with that perfect deployment.

Thanks guys,

-Chris

 

[shreadvector]

http://www.wrasp.com/

Use the easy and simple simulation program OR you can simply use the motor tables provided by manufacturers - they list "recommended maximum lift-off weight". If you exceed the max lift-off weight you will have a motor with a delay that is way too long (and it may hit the ground or shred the recovery system after deploying while heading back downward at high speed). If you are way under the max weight it may eject while heading upward. If you are just below the max weight for that delay time and still not below the max weight for the next shorter delay time it should be OK.

Things that will screw the above info up:
WIND - will make models arc over sooner and they will need shorter delay times.
DRAG - If the rocket is FAT or has lots of 'stuff' hanging out into the airstream it will have more drag and need a shorter delay. If it is super narrow and sleek it may need a longer delay.

Eaxmples: Estes Wizard can use a C6-7 in no wind and pointed straight up. If aimed at an angle or in wind use the C6-5.
Estes Big Bertha uses a C6-5 in no wind and pointed straight up. In wind or at an angle use a C6-3. If carrying a parasite glider on the side use a C6-3.

 

[DynaSoar]

Originally posted by SpartaChris
Is there a way to figure out what the optimal delay prior to ejection is? I ask because everytime I fly something, I seem to either be too short or too long, yet I see some people with that perfect deployment.

Thanks guys,

-Chris

http://ghiz.org/cgi-bin/rsim/rsim_form_ghiz.pl

It's the update of one of the flight profile simulators on EMRR. Put in your diameter and weight, and it'll tell you the coasting time to apogee. You then pick the closest delay.

It'll also tell you a bunch of other stuff and let you do "what if" comparisons.

The results are quite close to the results I've gotten from Rocksim and Spacecad, and you don't have to go through the entire design model construction process (Spacecad does have an equivalent shortcut calculator in it).

Unfortunately it doesn't have all currently certified engines in it (frinstance no Estes E9).

And you do need your correct weight, or if a kit, use the manufacturer's weight. This is one thing I've found both Rocksim and Spacecad to be off in.