Fiberglassing Airframes

[bad_idea]

Oh yikes I didn’t even think of that, I’ve never had a motor chuff.

I didn't either until I saw it. Someone explained it to me when we'd just seen it happen, and I instantly understood, but I'd not thought of it before that.

 

[Rocketclar]

If you run 2 complete altimeter systems, I wouldn't complicate it more with motor eject. On some small rockets I have, I've used a single altimeter for DD, but I did use motor eject as a backup to the drogue. Ran the sims and set the motor eject longer as I didn't want the charges going off at the same time. Also, if you do that, you'll need to protect the chute from both ends...the charge forward at the ebay and from the aft motor eject.

 

[tg08]

If you run 2 complete altimeter systems, I wouldn't complicate it more with motor eject. On some small rockets I have, I've used a single altimeter for DD, but I did use motor eject as a backup to the drogue. Ran the sims and set the motor eject longer as I didn't want the charges going off at the same time. Also, if you do that, you'll need to protect the chute from both ends...the charge forward at the ebay and from the aft motor eject.

I’m using a fireproof cloth to protect my chute, so that won’t be an issue. However, I decided not to use motor eject for the fear of two charges popping at the same time if the motor chuffs, or premature separation from chuffing.

 

[AtlPhilip]

Makes sense, altimeters very rarely fail on their own.

They don't, but people, batteries, connections, ematches, dip switches (people), programming (people), etc do. On my recent 2 stage (5 altimeters), the staging ematch just blew off the pyrogen and that was it, no joy.

There is great comfort in knowing there is a second charge waiting coming if the first one fails.
The only thing I use motor ejection on are small single BP motors.

 

[kjhambrick]

Oh yikes I didn’t even think of that, I’ve never had a motor chuff. I’m debating whether or not to use motor eject now. I think it should be fine though because I will drill it to apogee+a few seconds, so if it does chuff it’ll eject at apogee or a few seconds before. However, two e matches should be more than plenty to deploy my drogue. Currently I’m leaning towards no motor ejection.

Check this out: It is a 25-year old H128 that I flew for my level 1 cert last June:
View attachment sj-h128-06-03-2023-video.mp4
I imagine the delay smoldered the entire 10 -or- 11 seconds along with the propelllant ( or maybe that was the delay ? )

Anyhow, without the Blue Raven, the rocket would have crashed.

But the Blue Raven popped the drogue at apogee and then the main just a second later because it was set for main at 700 ft and it only flew 780 ft instead of the 1650 ft expected for the H128 ...

I learned long ago that electronic deployment is MUCH more reliable than motor ejection.

And I am testing AV-Bays to fly that Blue Raven in all my rockets, even in 24mm / BT-50 models.

My $0.02 worth ...

-- kjh

 

[Trenton Baker]

So basically, you are saying that the fact that there is a spare system is what makes it safer, not the fact there is another altimeter. Makes sense, altimeters very rarely fail on their own.

He is stating that you are not improving the reliability of the system, the additional altimeter adds zero improvement. Instead what is happening is that a secondary altimeter is placed into the system to overcome user failure, ie failure to ground test charges to ensure solid separation and deployment for example. What you are doing is increasing the overall cost of the system to get nothing in return for reliability. The secondary altimeter is simply a crutch to overcome lack of preventative maintenance and inspection for any operational and or maintenance induced damage or system degrade between sorties.

A preventative maintenance schedule is going to result in higher reliability and more successful flights than a piece of equipment with a very low rate of failure per million hours of operation, ie the altimeter. So instead, create a list of things to inspect between flights and check them off, before going to the field have a list of things to check and do, like charging battery packs and looking over equipment for damage. During this time of year you might not be flying as much, good time to look over your avionics and look for wear and tear, environmental degrade, poor contacts, and or design improvements. You can have processes between flights, processes days before flights, and during extensive downtime processes that are more expansive.

That is going to lead to more reliability and less cost and avoid a significant failure that is going to result in a catastrophic failure and overall loss.

Reliability & Maintainability, Failure Modes Effects and Criticality Analysis and Preventative Maintenance are cornerstones to optimal system performance.