Redundant dual deploy apogee setting ????

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threelapfancy

threelapfancy

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Hello. I am using 2 different brands of altimeters for redundant flight control. I plan to set the main charges for 800 on one, and 1000 on the other. What I would like to know is should I set both to fire at apogee or set one for apogee and the other for 1 second after?
Thanks
Steve
 
3lapfancy said:
should I set both to fire at apogee or set one for apogee and the other for 1 second after?
Click to expand...
I've done it both ways and found there's enough variance between
altimeter apogee detection that it usually doesn't matter.
 
There's enough variation between altimeters that it shouldn't really matter either way.
 
What the other guys said.... but, on our SLI rocket, our backup altimeter was set to apogee +2 seconds, just to be sure that both charges wouldn't go off at the same time.
 
I used two RRc2 minis for my L2 flight. I left one "stock" (apogee drogue/500' main) and then programmed the second one for apogee+1 second and 800' for the main. They backed each other up so to speak and I only had one altimeter that may fail due to programming errors on my end. In reality, this scheme was probably really over thought, but it did work well.

I think one would be hard pressed/lucky to actually get two apogee charges to fire simultaneously with identical electronics yet alone with mis-matched altimeters/RLO algorithms.

I think the manner in which ejection charge forces are applied and directed may be of more concern.

:2:

Scott
 
Consider setting them to go at different times and making the charge in the "backup" (i.e. the one that would fire later) larger than normal. At LDRS last summer, one of the backup charges on a rocket was pretty loud when it fired. When questioned, the owner's comment was that if the laundry was not out at that point, he wanted it out "even if it came out through the side of the rocket." When you think about it, that makes a lot of sense. If the chute is already out, the extra energetic charge will do no harm. If it's not out, it is possible that something is jammed and needs more oomph to get it out.
 
Yeah, definitely pack enough powder in your backup charge to "blow it out or blow it up." A blown up rocket comes down slower than a still-stable ballistic one.
 
If they're the same brand/model, set them to go off at different times.

If they're different brands/models, odds are, as others have already stated, that they'll likely go off at different times, anyway.

Regarding the "blow it out or blow it up" approach, I disagree completely. All it really does is put excessive load on your recovery system.

Instead, learn to design and pack your recovery system such that it's reliable, instead of the "shove and pray" approach that's very common.

Ground testing, research and planning will alleviate the need for excessive charges.

As an example, using an ejection charge to shove a 10 pound parachute out of a tube is asking for trouble. Using an ejection charge to separate the rocket and put a small pilot chute in the airstream, which then extracts that same (bagged) 10lb parachute is a much more reliable approach.

-Kevin
 
troj said:
If they're the same brand/model, set them to go off at different times.

If they're different brands/models, odds are, as others have already stated, that they'll likely go off at different times, anyway.

Regarding the "blow it out or blow it up" approach, I disagree completely. All it really does is put excessive load on your recovery system.

Instead, learn to design and pack your recovery system such that it's reliable, instead of the "shove and pray" approach that's very common.

Ground testing, research and planning will alleviate the need for excessive charges.

As an example, using an ejection charge to shove a 10 pound parachute out of a tube is asking for trouble. Using an ejection charge to separate the rocket and put a small pilot chute in the airstream, which then extracts that same (bagged) 10lb parachute is a much more reliable approach.

-Kevin
Click to expand...

I agree completely with what you say about installing a correctly functioning recovery system. You are also exactly correct about expecting an ejection charge to push a chute out of the BT being good way to get into trouble.

No one should expect the ejection charge to shove/push/eject anything out of a rocket!

All the ejection charge does is pressurize the BT.[period] That pressure, acting on the nose cone, will push the nose cone off the BT. If anything is coming out of the tube, it's being pulled out by the inertia of the NC, not being pushed out by the ejection charge. The only exception to this would be if you were using a piston. Then the piston would push things out of the BT.


I think that is where the "blow it up" idea comes from for the redundant charges. If the nose cone is already off, it would take a much bigger charge then the orginal to create enough pressure behind the recovery equipment to get it to move out of the BT.
 

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