Ejection charges in HPR

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KurtH

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Hello,

I have what may seem like a stupid question, I searched the forum and I was not able to find the same question.

I am preparing for my first Dual deploy launch. I am using 1 altimeter. I built my AV bay with a main charge canister as well as a Drogue canister, in anticipation of using motors with no ejection charge ( like a warp 9). when flying a motor with an ejection charge, is it advisable to also use the drogue charge? If the delay is too long, then you will also have the motor charge go off after separation. If the delay is short and separation has already occurred, there will also be a nice aerial firecracker at apogee, or when ever the altimeter decides apogee has occurred.

Thank you for your input.
-Kurt
 
I'd remove the ejection from the motor. You can keep it in for redundancy, but at least make sure it is not a short delay that will fire before apogee.

BTW - I using for redundancy, make sure you drogue is the main tube with the motor ejection and chute above in the payload. I have mine the other way around and the motor ejection would result in a main blowing near apogee.

Overall, I think the electronics are pretty reliable. The apogee sensing is way more accurate that trying to guess a delay.
 
I am by no means an expert in DD, however in the few DD flights under my belt, I have left the motor ejection charge to act as a backup for my apogee event. I was using cti motors and left the delay at its longest.
 
You can leave the motor ejection in place. I would suggest leaving it at 2 to 3 seconds longer then apogee, but I've never done that myself. The only time I've used motor ejection as a backup was the first flight of my new altimeter.
 
I forgot to remove one. Thanks to my backward chute configuration, it blew the drogue and main at apogee.
 
I also just leave the motor ejection in and use it as a backup to the drogue. Doesn't cost anything, doesn't hurt anything. Little bit of added insurance.
Like the other guys have said, just make sure your motor delay is longer than the time it takes to get to apogee.
 
I also just leave the motor ejection in and use it as a backup to the drogue. Doesn't cost anything, doesn't hurt anything. Little bit of added insurance.
Like the other guys have said, just make sure your motor delay is longer than the time it takes to get to apogee.

+1 with only 1 alt, I would use as much rudundancy as possible.
 
Hello,

. when flying a motor with an ejection charge, is it advisable to also use the drogue charge?

Thank you for your input.
-Kurt

You have not given enough information to get a factual answer. I.E.... rocket size, weight, motor size,configuration etc.

For the most part the advice I normally give would be :When using electronics, trust them, they are far more accurate than trusting the motors delay charge which can be + or - as much as 20%[the standard to which the manufacturer must adhere]

You also can have what we call "bonus" charges which can be extremely late or fire right at motor burn out. Fly long enough, you will be witness to plenty of these.

There are always exceptions for one reason or another, but in general sport flying I recommend when using electronics ...use them and forget the motor charge.
If you are unsure of yourself, do this to gain confidence. Fly a few times using motor eject & take the altimeter along for the ride, just hooking up e-matches but with no BP. This will let you see if all functions correctly and as a bonus you get flight data. When sure of yourself, make the jump.

You will get many answers to this question as there are many, many ways to fly rockets and many ways that all have positive results. However this is what I have recommended to dozens I have mentored and the positive results speak for themselves.

I have seen too many flights ruined by motors firing charges while rocket is under full thrust or just into coast, weather cocking at an extreme angle rather than flying vertical, causing the charge to be late, all with the same results...... damaged rocket. Where if just electronics were used, when apogee is met, bang the charge fires. There are so many variables that you must figure to get an accurate timed delay, then shorten or change the delay it just makes sense to trust your altimeter,not the motor, even for backup. [there are some exceptions remember]
Once you do there will be no going back.:wink:
 
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