Thoughts on Fail Safe Mode

[mIcahel]

Instead of buying new kits to fly as had been my practice around the holiday sales, this year I decided to refurbish and find new ways to enjoy the models that had been gathering dust in my garage. Enter this Big Nuke which was one of my first ever large kits and has 25+ motor eject flights over nearly 15 years. I scraped the tattered inkjet printer graphics off and painted/stickered to be recognizably LOC Big Nuke. Adding voice telemetry was the initial goal, but once I had made arrangements in the NC for electronics a bunch of new ideas and questions came up:

Use Eggtimer fail safe mode at apogee to backup motor eject. This seemed relatively easy way to add some safety/reduce risk of ballistic, but added the hassle of
making the bp charge safe on landing on a normal flight. New thought was to solve this problem by making electronic deployment at apogee the primary and motor eject as backup. The details of this strategy would require me to add a bunch of prep and additional parachutes that I am trying to avoid to keep this my easy flyer. I'm looking for setup ideas that make use of having deployment electronics on board but keeps additonal prep and pad steps to a minimum. Big Nuke separates mid airframe for motor eject and electronics will be in the NC. Appreciate any advice from those with experience on apogee fail safe setting considerations.

 

[mIcahel]

...I'm keeping it single deploy

 

[Azamiryou]

Why does apogee deployment add more parachutes? Doesn't the electronic deployment charge pressurize the same part of the rocket as the motor ejection? If not, could it?

I'm new to electronic deployment, so I may not be understanding your situation. But I hope to learn from the discussion .

 

[Art Upton]

Why does apogee deployment add more parachutes? Doesn't the electronic deployment charge pressurize the same part of the rocket as the motor ejection? If not, could it?

I'm new to electronic deployment, so I may not be understanding your situation. But I hope to learn from the discussion .

^^ This , my rockets with both motor backup and Altimeter charge pressurized the same place.

Edit: Nice looking Big Nuke, I miss mine lost to an EX motor Rapid Unexpected Disassembly event more then 10 years ago.

 

[mIcahel]

My current planned configuration is that the motor eject pressurizes the booster section and nosecone avbay pressurizes the payload. I could make a connection from the NC through payload to the booster but this just seems like an odd configuration (but now that i think of it not as odd as having 2 fully sized chutes in separate compartments).

 

[Titan II]

Why does apogee deployment add more parachutes? Doesn't the electronic deployment charge pressurize the same part of the rocket as the motor ejection?

Yes

If not, could it?

Yes

 

[Azamiryou]

My current planned configuration is that the motor eject pressurizes the booster section and nosecone avbay pressurizes the payload. I could make a connection from the NC through payload to the booster but this just seems like an odd configuration (but now that i think of it not as odd as having 2 fully sized chutes in separate compartments).

I think the usual configuration is to have the avbay in (or as) the payload section. If you have only one deployment and the electronics are in the nose cone, then there wouldn't be another payload section between the nose cone and the booster.

I would make the electronic deployment the "normal" deployment, with motor ejection the backup plan in case of a failure. Choose a motor with a long delay. If the apogee deployment already succeeded when it goes off, it just blows through the empty tube. But if it didn't separate at apogee, the motor ejection is a second opportunity for it to work.

 

[Art Upton]

My current planned configuration is that the motor eject pressurizes the booster section and nosecone avbay pressurizes the payload. I could make a connection from the NC through payload to the booster but this just seems like an odd configuration (but now that i think of it not as odd as having 2 fully sized chutes in separate compartments).

This seems Odd... The Ebay electronics should fire charge in Booster Section just like the motor will do. Use Motor As Backup.

 

[Titan II]

Just run wire from alt to booster with charge. Set to apogee and use motor as backup. SIMPLE.

 

[Art Upton]

Just run wire from alt to booster with charge. Set to apogee and use motor as backup. SIMPLE.

Yep, I have a LOC 3" Caliber ISP setup this way. And as a plus I can add a Jolly Logic Chute Release on the main if I plan to send it up to close to 5K on an I motor for example.

Or Fly it Pop at the top on a 900 foot flight.

 

[mIcahel]

Thanks Art and Titan. Agree this is easiest approach, I am JLCR curious, and love the idea of a single separation point for DD, but need to dial in my other electronics first.

 

[cerving]

The idea of the Fail-Safe mode is that if the altimeter detects that you're in free-fall AFTER you fire the drogue, it will fire your main chute to prevent your rocket from coming in ballistic or nearly so. It's designed for a standard dual-break dual-deploy rocket, which is about 90% of them out there (not counting anyone using a JLCR, which is not a dual-break configuration). I suppose you could find other creative uses for it, but that's the intent. I almost always turn in on... unless I have completely redundant deployment systems.

If you wanted to use it as a backup, the main channel has a "Fail-Safe Only" mode that only fires the channel if it detects free-fall; it does not fire the channel at an AGL altitude as it would with a standard dual-deploy main. If you're using it as a backup for a single-break rocket, since it's probably going to be separating the same break that didn't separate the first time, unless your ematch didn't fire for some reason then it's probably not going to save you.

 

[mIcahel]

Thanks Cris, in the end I followed the consensus here. Wanted to avoid any permanent wiring to the payload so I used a long
ematch/microcentrifuge tube and hot glue to make the connection from nosecone to booster section. Wifi arming of Quantum helped to
keep this simple without a switch. Appreciate the responses.