Dual deploy redundancy question

If you are using a charge canister such as a Blastcap, you can use a single BP charge with two ematches. That way, regardless of which ematch fires, the BP charge will be consumed.

Just one way to do it...

G.D.

I can't say that it doesn't happen, but I've never seen it happen, nor has it ever happened to me. When flying adjustable alt's for backup, I always set them ahead a second or two. When flying non-adjustable units together, I've never seen them (heard, actually) fire simultaneously. Always seems to be a second or two between either way.

gdiscenza said:

If you are using a charge canister such as a Blastcap, you can use a single BP charge with two ematches. That way, regardless of which ematch fires, the BP charge will be consumed.

Just one way to do it...

G.D.

Click to expand...

Oh yeah, I hadn't thought of that. I was going to use centrifuge tubes with Q2G2 igniters, but I could put two igniters into one tube. What a simple solution. Brilliant!

chadrog said:

I can't say that it doesn't happen, but I've never seen it happen, nor has it ever happened to me. When flying adjustable alt's for backup, I always set them ahead a second or two. When flying non-adjustable units together, I've never seen them (heard, actually) fire simultaneously. Always seems to be a second or two between either way.

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I realize that the chances of the two charges firing simultaneously are slim. But with a big, heavy, high flying rocket, I want to eliminate as much chance as I can.

gdiscenza said:

If you are using a charge canister such as a Blastcap, you can use a single BP charge with two ematches. That way, regardless of which ematch fires, the BP charge will be consumed.

Just one way to do it...

G.D.

Click to expand...

qquake2k said:

Oh yeah, I hadn't thought of that. I was going to use centrifuge tubes with Q2G2 igniters, but I could put two igniters into one tube. What a simple solution. Brilliant!

Click to expand...

Very elegant solution. Just curious, does this method meet criteria for dual redundancy in a level 3 project?

Quaranta said:

Very elegant solution. Just curious, does this method meet criteria for dual redundancy in a level 3 project?

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That would depend on the L3CC or TAP. As a failure mitigation it should be sufficient, as I've never seen black powder fail to ignite when a Q2G2 fires. I have seen igniters fail to fire for reasons ranging from the pyrogen head separating all the way down the component chain to battery issues. To design a failure mitigating system, you would duplicate all parts of the system that could possibly fail.

G.D.

Sent from my iPhone using Forum Runner

the stratologger has an apogee delay setting for when you have two alts you can set one to fire one or more seconds after apogee.
rex

gdiscenza said:

That would depend on the L3CC or TAP. As a failure mitigation it should be sufficient, as I've never seen black powder fail to ignite when a Q2G2 fires. I have seen igniters fail to fire for reasons ranging from the pyrogen head separating all the way down the component chain to battery issues. To design a failure mitigating system, you would duplicate all parts of the system that could possibly fail.

G.D.

Sent from my iPhone using Forum Runner

Click to expand...

I have seen charges that successfully separated on the ground inexplicably fail in flight; the rocket had two charges (would have worked) but the wiring for the second one got screwed up somehow. That's why you ideally want multiple independent charges, and set one of the altimeters to delay the apogee charge until 1 second after it thinks it has achieved apogee.

Rex R said:

the stratologger has an apogee delay setting for when you have two alts you can set one to fire one or more seconds after apogee.
rex

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You can buy an Adept22 and a DDC22 for the price of one Stratologger.

Since it's similar to your project, I'll pass on that for flights of my Little Dog, I use 4 ejection charges - two for Apo & two for Main - as redundancy. This schema has saved me once.

The backup charges are bigger. The backup Apo fires 1.5 seconds after the primary; the backup Main charge is set for 330' (primary @ 660').

I figure flying totaly redundant charges costs me ~$3.60 and 15 minutes per flight. Given the consequences of a charge failure, in potental injury or damage to vehicles (let alone lost man-hours in rocket construction) I find this worth it.


All the best, James

Fdog said:

Since it's similar to your project, I'll pass on that for flights of my Little Dog, I use 4 ejection charges - two for Apo & two for Main - as redundancy. This schema has saved me once.

The backup charges are bigger. The backup Apo fires 1.5 seconds after the primary; the backup Main charge is set for 330' (primary @ 660').

I figure flying totaly redundant charges costs me ~$3.60 and 15 minutes per flight. Given the consequences of a charge failure, in potental injury or damage to vehicles (let alone lost man-hours in rocket construction) I find this worth it.


All the best, James

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Which altimeter(s) do you use?

Quaranta said:

Very elegant solution. Just curious, does this method meet criteria for dual redundancy in a level 3 project?

Click to expand...

It would NOT for me. Redundant means just that.....2 of everything.

Even then, that does not guarantee success, case in point:

L-3 flight, one altimeter failed to fire main, [it did apogee]the other [altimeter] had a faulty e-match hooked up to main. Upon autopsy the charge showed continuity, but when hooked up to a battery would not fire.

Both showed proper function when tested...IE there was flight ready continuity.


In this case everything was done correctly, the rocket gods just wanted an offering that day.

More than once I have seen the first charge fire, pop the NC & the chute hang in the pipe...then the 2nd fires and pushes it out.....saving the day. It has happened 2x's to me on very large rockets.

Is the price of a bit more BP really worth the risk.......no.

blackjack2564 said:

It would NOT for me. Redundant means just that.....2 of everything.

Even then, that does not guarantee success, case in point:

L-3 flight, one altimeter failed to fire main, [it did apogee]the other [altimeter] had a faulty e-match hooked up to main. Upon autopsy the charge showed continuity, but when hooked up to a battery would not fire.

Both showed proper function when tested...IE there was flight ready continuity.


In this case everything was done correctly, the rocket gods just wanted an offering that day.

More than once I have seen the first charge fire, pop the NC & the chute hang in the pipe...then the 2nd fires and pushes it out.....saving the day. It has happened 2x's to me on very large rockets.

Is the price of a bit more BP really worth the risk.......no.

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Thanks for the examples Jim. It seemed to me it would NOT satisfy redundancy,... but wanted confirmation.

Something else to consider...

1) What happens if you somehow contaminated that one BP charge? Now, all the eggs are in one (bad) basket.

2) Some altimeters don't like it when an apogee charge suddenly loses continuity before the altimeter fired it. If I remember right, some will then fire the main charge, if they suddenly lose continuity on the drogue.

-Kevin

I do not worry about two apogee charges firing simultaneously. The baro sensors and somewhat imprecise devices and in practice simultaneous also means instantaneous, which just doesn't happen. I have 3", 4", 5.5" and 8.5" rockets that are all equipped with redundant altimeters and all are set-up for apogee firing of the drogue charge. I have never experienced a bad outcome from simultaneous instantaneous firing of two charges.

Typically, I'll set the main charges to two different altitudes to push the main 'chute out in case the first charge doesn't get the job done.

I also always use two BP charges on both sides. My reasoning is that some unforseen failure could shake the BP from containment on boost is remotely possible. A second charge is true redundancy and I'm not risking the flight for a few cents worth of BP.

--Lance.

Fdog said:

Since it's similar to your project, I'll pass on that for flights of my Little Dog, I use 4 ejection charges - two for Apo & two for Main - as redundancy. This schema has saved me once.

The backup charges are bigger. The backup Apo fires 1.5 seconds after the primary; the backup Main charge is set for 330' (primary @ 660').

I figure flying totaly redundant charges costs me ~$3.60 and 15 minutes per flight. Given the consequences of a charge failure, in potental injury or damage to vehicles (let alone lost man-hours in rocket construction) I find this worth it.

All the best, James

Click to expand...

You know I never looking at it that way, I think its time for another altimeter.

TA

qquake2k said:

Which altimeter(s) do you use?

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Raven3 on a PowerPerch.

The Raven is nice because it easily accomidates all 4 charges on the same board, and it's easy to program the 3rd & 4th outputs. Actually it comes from the factory set up with 3rd & 4th outputs set up and ready to use.


The Raven & PowerPerch. The 3rd output is set for Apo + 1.5 seconds; 4th is 330' AGL.

My L3 project will have dual Ravens. I've had quite a few conversations about having two different makes/models of altimeters, so a congenital failure wouldn't affect deployment reliability. I believe there is an argument to be made on both sides of this concept.


All the best, James

Quaranta said:

does this method meet criteria for dual redundancy in a level 3 project?

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For NAR, absolutely yes. The rules explicitly say "Redundancy is not required in the energetic materials (e.g. black powder charges)" and this is how I did my L3.

As this thread says, some people feel very strongly that everything be redundant anyway, but NAR isn't making you.

mikec said:

For NAR, absolutely yes. The rules explicitly say "Redundancy is not required in the energetic materials (e.g. black powder charges)" and this is how I did my L3.

As this thread says, some people feel very strongly that everything be redundant anyway, but NAR isn't making you.

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NASA takes the same approach on most parachute recovery systems. One charge per chute mortar with multiple redundant e-matches and multiple redundant firing circuits make for a very low probability of failure to fire at least 1 e-match. On high value items they may have multiple chute mortars so if one chute fails there are spares.

Bob

Put me in the "redundant means two of everything" camp. Separate matches and BP charges on each output - it's just not that much more work. I've been using two MAWDs side by side for years, and for a long time, never bothered to set the apogee delay on the backup. Even if they did fire together, I've never noted any damage from having done so. I *do* like the idea of the backup having a chance to push out the laundry that might not have made it all the way out on the first charge. As has been mentioned, you don't get that chance with two matches in one charge.

Mark Joseph
Central Illinois Aerospace
NAR/TRA L2

Some people say to use two different vendors' flight computers too, to eliminate the possibility that some software bug will affect both units. Such a glitch is probably a long shot, but it's a good excuse to try different hardware to see which one suits your needs best, and if they both do flight recording you might see some interesting differences between the two.

I knew I had an example somewhere.

It's a flight where the Main charge failed to push out the parachute at 660'. The backup charge (4th output on the Raven) succeded at 330'.

You can see the whack from the Main charge, but rate of descent does not change until the 4th charge pushes everything out.





All the best, James

Jim,
I think I'm right when I say that the Adept22 and DDC22 do not offer the option to change or delay the apogee charge. And, as llickteig1 pointed out above, "The baro sensors and somewhat imprecise devices and in practice simultaneous also means instantaneous, which just doesn't happen."

This has been my experience as well. I think that you set the main deployments to two different altitudes and you'll be just fine at apogee.
-Chuck

cerving said:

Some people say to use two different vendors' flight computers too, to eliminate the possibility that some software bug will affect both units. Such a glitch is probably a long shot, but it's a good excuse to try different hardware to see which one suits your needs best, and if they both do flight recording you might see some interesting differences between the two.

Click to expand...

I have had the bad luck of purchasing two such altimeters. One was a case where I appararently was the first person to use a feature of the board, and it didn't exactly work correctly. The second was where a battery came from the factory with the wrong polarity. Now in the second case I found it early and wouldn't have flown. But in the first case, symptoms were a bit confusing. I didn't fly it, and a board revision was eventually required, but someone else might well have flown it.

I also have two popular brand altimeters which are well off on their accelerometers, regardless of calibration attempts. Set for barometric apogee that won't matter, but if someone uses accelerometer for that, then the deployment works out to 2-3 seconds late.

We are dealing with consumer level electronics, not high end stuff. I don't trust it until it is proven to work, and even then assume it won't work the next time. I prefer different altimeters as I consider them less likely to fail in the same way at the same time from the same cause. YMMV.

But of course it is an old discussion and there are valid reasons on each side. I just wanted to point out that the failure rate of our altimeters is higher than one might want or expect, even among better respected brands.

Essentially about 50% of the altimeters I've purchased in the last two years did not check out 100% to my satisfaction, between errors from the manufacturer and poor accelerometers. I'm now considering making my own flight computer, for this reason among others.

Gerald

Having two separate charges eliminates the (admittedly rare) possibility of the charge container being jostled or damaged during the flight and spilling the charge contents.

llickteig1 said:

I do not worry about two apogee charges firing simultaneously. The baro sensors and somewhat imprecise devices and in practice simultaneous also means instantaneous, which just doesn't happen. I have 3", 4", 5.5" and 8.5" rockets that are all equipped with redundant altimeters and all are set-up for apogee firing of the drogue charge. I have never experienced a bad outcome from simultaneous instantaneous firing of two charges.

Typically, I'll set the main charges to two different altitudes to push the main 'chute out in case the first charge doesn't get the job done.

I also always use two BP charges on both sides. My reasoning is that some unforseen failure could shake the BP from containment on boost is remotely possible. A second charge is true redundancy and I'm not risking the flight for a few cents worth of BP.

--Lance.

Click to expand...

I thought the same thing until last year when I flew two Strattologgers in a 7.5 inch rocket on an M2000. We picked up the rocket 5.5 miles away as the crow flies from an apogee deploy at 10,000 feet.

This is the first time I had flown two of the same exact altimeters in a rocket. I usually mix them up. After getting it home and checking them I discovered that both altimeters fired the apogee charge at exactly 28.15 seconds. I was amazed. I am assuming the double charge was enough to break the sheer pins on the nose cone (main) since I am a subscriber of the blow it out or blow it up school of thought.

This rocket has been flown several times before and several times since and this is the only time it has deployed at apogee. I now set the apogee delay on one of them when using them together.

Anecdotal evidence at best but it can happen.

You can do a few things:

A)
Use one altimeter for apogee deployment and motor as a backup, and
Use different altitudes on two altimeters for main deployment

B)
Use two altimeters from different manufactures. Since they use different math for apogee detection, it reduces changes of firing at the same time

C)
Use one altimeter which allows deployment with a delay after apogee (e.g. Stratologger and Raven), and second altimeter that deploys at apogee


-Alex

I have my L3 project under construction and plan to use redundant charges with the backups being 50% larger than ground testing shows to be necessary. If the primary blew the chute out, the larger charge firing in an open tube does nothing, but it something jammed, it should be enough to get the laundry out. Call me paranoid, but I don't want 60 pounds of fibreglass rocket coming down with no parachute or on drogue only.

I would like it if there were a feature in altimeters to detect failure to deploy: if the baro alt drops parabolically, blow the backup apogee, and if the rocket's descent doesn't slow down after the main fires, set off the backup main. Save black powder, and save the wear and tear on shock cords and etc.