Delay vs opening shock

[Mr G]

Having a backup motor eject is a nice security feature I use whenever practiable.

Open Rocket indicates that my dual deploy Super DX3 on a J575FJ will be at 63 mph when the installed 10-sec ejection charge blows. Optimum delay, according to OR, is 12.6 sec.

If I cannot pick up a 14-sec delay tomorrow at the launch site, I am tempted to go for it and the risk the effects of premature ejection. Or is there a chance of serious damage at 63 mph going straight up? If so, I can always pour out the BP charge, put in some grease, and just hope the Adept 22 does it's job.

 

[Zeus-cat]

Just rely on the electronics. 63 is too fast to deploy the laundry.

 

[MikeyDSlagle]

The Adept22 will do it's job if you have have it hooked up right. I have used one several times, it even saved my level 1 flight when another altimeter clonked out on me.
Pour out the BP and let the Adept22 handle it.

 

[kevinkal]

Having a backup motor eject is a nice security feature I use whenever practiable.

Open Rocket indicates that my dual deploy Super DX3 on a J575FJ will be at 63 mph when the installed 10-sec ejection charge blows. Optimum delay, according to OR, is 12.6 sec.

If I cannot pick up a 14-sec delay tomorrow at the launch site, I am tempted to go for it and the risk the effects of premature ejection. Or is there a chance of serious damage at 63 mph going straight up? If so, I can always pour out the BP charge, put in some grease, and just hope the Adept 22 does it's job.

How vulnerable is your SDX3 to zippering? A small drogue at 88 ft/sec (60 mph) shouldn't be too bad... unless you have a thin shock cord and cardboard tube that might easily zipper.
It's been my experience that the darn motor delays are usually shorter than specified... something to consider... how fast would your rocket be traveling if the delay was only 8 seconds?

I've had 10 second delays that fired the ejection at just 7 seconds a few times on my LOC Athena 3, cardboard rocket with 15 feet of ~3/16" Kevlar shock cord for the drogue. It's happened about 4 times now. It has a small drogue, 9" or 12", thus the early deployment didn't create too much force and there's been no sign of zippering.

The plot below shows a typical early ejection at 100+ ft/sec

 

[markkoelsch]

I would ditch the motor delay and just use the electronics. As others have mentioned, there can be a quite a bit of variation in delay time.


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[scsager]

Having a backup motor eject is a nice security feature I use whenever practiable.

Open Rocket indicates that my dual deploy Super DX3 on a J575FJ will be at 63 mph when the installed 10-sec ejection charge blows. Optimum delay, according to OR, is 12.6 sec...

I personally would NOT call it "back-up" when the motor delay fires before apogee. Ejection more than 2 seconds early is a potential disaster.

 

[Handeman]

Having a backup motor eject is a nice security feature I use whenever practiable.

Open Rocket indicates that my dual deploy Super DX3 on a J575FJ will be at 63 mph when the installed 10-sec ejection charge blows. Optimum delay, according to OR, is 12.6 sec.

If I cannot pick up a 14-sec delay tomorrow at the launch site, I am tempted to go for it and the risk the effects of premature ejection. Or is there a chance of serious damage at 63 mph going straight up? If so, I can always pour out the BP charge, put in some grease, and just hope the Adept 22 does it's job.

Just dump the powder and use the altimeter. Where and why would you add grease? It's just my experience, but with over a 100 DD flights and never a motor backup charge, I only remember one very early flight where it might have helped.

Personally, I thing motor eject is way too unreliable on timing and would prefer altimeter every time.

 

[dhbarr]

I believe some people grease the touch hole end when they dump powder to make sure that potential burn surface is inhibited.

I'd jam dog barf in the charge well and electrical tape it, but that's just my personal opinion.

30m/s no es bueno.

 

[Handeman]

I believe some people grease the touch hole end when they dump powder to make sure that potential burn surface is inhibited.

I'd jam dog barf in the charge well and electrical tape it, but that's just my personal opinion.

30m/s no es bueno.

Yes, I don't even do that. I don't grease or put anything in the well, I just don't add the powder. Maybe I'm not PC, but I've never had a problem with that.