redundant charges

When using a backup altimeter and not using motor deployment. How do you keep both charges from going off at the same time at apogee. For the main I can separate the charges with different altitude settings. I am using a Missile works RRC2X-25 and a Perfectflite HA-45. Theres not much out there to read on this subject.

Some altimeters (like the Perfectflite MAWD) have a programmable delay. I don't think the HA-45 does. I do not have a RRC2X, so I don't know if it has an option for it.

When you are using different altimeters there will probably be enough difference between them that there won't be a problem, but you never know.

I don't worry about it. I figure that two altimeters, even from the same manufacturer, will trigger at slightly different times.

I Thought there may be enough difference in the two altimeters reading and triggering for this to be ok but, yeah the you never know part My luck would make them perfect lol, and they would trigger at the same time. That would be a mach delay? I should know this I just never had to use it before.

No, the mach delay is used if you think the rocket will reach or exceed mach. I use one ejection charge with two altimeters.

Originally posted by sandmantoy
My luck would make them perfect lol, and they would trigger at the same time.

Click to expand...

While possible but unlikely, the only way to know if your airframe is up to the -pressure- is to ground test the charges with double the BP. Better to see what happens on the ground than in-flight if you're worried about it. To state a much used phrase in HPR: Blow it out or Blow it up

While possible but unlikely, the only way to know if your airframe is up to the -pressure- is to ground test the charges with double the BP. Better to see what happens on the ground than in-flight if you're worried about it. To state a much used phrase in HPR: Blow it out or Blow it up

Click to expand...

Roger that! Once I figure out the charge size, if it looks kinda big I will probably just use one charge. But testing is a must My concern was poping the nose cone off from the 2 charges once at the end of the SC. I am going to use shear pins, I haven't got a final weight yet on a few things. The rocket is a 5.5 Hawk and the nose is going to have some weight to it.

It's unlikely that the charges would go off at the same time. But with the altimeters you have, it's even less likely. The RRC2 units that I have tend to go off a little late relative to the perfectflights. I have seen this with two units both in flights and when testing in a baro chamber.

Originally posted by sandmantoy
When using a backup altimeter and not using motor deployment. How do you keep both charges from going off at the same time at apogee. For the main I can separate the charges with different altitude settings. I am using a Missile works RRC2X-25 and a Perfectflite HA-45. Theres not much out there to read on this subject.

Click to expand...

You don't have redundant parachutes so why do you need redundant charges? Simply put an e-match from each altimeter in the pyrocharge. When the primary fires, the pyro goes, and if the primary fails, the pyro goes when the backup fires.

Bob

Originally posted by bobkrech
You don't have redundant parachutes so why do you need redundant charges? Simply put an e-match from each altimeter in the pyrocharge. When the primary fires, the pyro goes, and if the primary fails, the pyro goes when the backup fires.

Bob

Click to expand...

Excellent point, Bob. Hobby rocketeers do not run fully redundant systems. For that matter, NASA makes these same decisions. We hobbyists make lots of choices as to what things are likely to fail. Some we make redundant and some we decide to accept the risk.

The case Bob brings up is very interesting. Most of us decide that we distrust our avionics (or, more likely, our ability to engineer and operate the avionics system) and therefore put in a dual altimeter system. Typically that means running redundant initiating pyrotechnics.

The decision now is: do I trust my ability to implement a single containment vessel for the two e-matches that will not fail to activate?

I had this discussion with my L3 committee. They had seen flight failures that were attributed to failures of the ejection charge containment system. So I go with separate charges. Your decision may be different.

Some things that could cause a single deployment charge with multiple e-matches to fail:
-if you botch making the charge holder all the powder could leak out.
-acceleration could cause your recovery system to shift and damage the charge holder or the wires of an e-match
-if you're using pyrodex the container must hold up until the entire charge is consumed before bursting. If the container ruptures without fully activating the entire charge the second ematch will likely do no good.

I'm sure there are lots of rebuttals to these points. And I'm sure there are lots of failure modes I've missed. And this is only one of the myriad engineering choices we make with each rocket, so I hope Bob doesn't mind that I yammerred on about his particular example.

Will, I would add one more example. I've had two flights on two-inch rockets where the single charge has gone off, but the parachute didn't come out. On my larger rockets, I like a second bullet.

Originally posted by JimJarvis50
Will, I would add one more example. I've had two flights on two-inch rockets where the single charge has gone off, but the parachute didn't come out. On my larger rockets, I like a second bullet.

Click to expand...

Agreed. I'm not nearly as worried about a parachute failure as I am a powder containment/ejection charge failure. I do ground test, religiously, but there is nothing in the world that will prevent Murphy from having his way, so like Jim, I like a second charge attached to a second, un-related altimeter.

Ah, Bob I didn't look at it that way. I was going to mount a separate charge holder for each altimeter. I didn't think about putting both igniter's in one charge canister I make my own charge holders. This suggestion sounds good a little extra spark is way better than an extra pop If one fires early it would ignite the other anyway.

Electronics can last forever or a day, You never know when the gremlin awakens. I don't want to have to dig whats left of the rocket up after something goes wrong or worst. Plus I want to fly it again
Igniter wire exits through the side of the canister, I usually just put one of Quickbursts charge canisters in it. It has worked well.

I do not own and am not familiar with the altimeters that you are using. However I would caution you when using a single BP charge and ematches from seperate altimeters. My understanding from a friends experience with an Altacc in a similar setup. The BP was ignited by altimeter A, the ematch connected to the backup altimeter (Altacc) burned and created an open circuit. The Altacc detected an open circuit on the drouge charge, so it fired the main as an immediate backup.

In this case it was not a failure of the Altacc, it did exactly what it was programmed. The failure was not having two separate BP charges and not knowing how the altimeter is expected to perform.

John

Skip the redundant altimeters and use a single 4-channel unit programmed so you KNOW that the main and backup charges will not fire at the same time. Take this "PROBABLY" stuff out of your rocket plans....

Progam the altimeter for apogee and apogee+1 second and two altitudes such as 1000' and 900'.

Wire it to four independant e-matches and charges that are contained in protective containers like the spiffy aluminum shown (I use PCV pipe caps).

Pack the charges with wadding and tape - helps contain the charge and avoid having the backup charge be lit from the main.

If you think you must use more than one altimeter, then do NOT share anything between the two. Independant batteries, wiring, e-matches, charges....everything. It is doubtful that the altimeter manufacturer verified proper operation in any modes beyond those documented in the users manual. This is not the place to be creative and do something unique and assume it will work. Apply alimeters exactly as documented as that is the verified mode(s) of operation.

The fact that none of the user manauls ever document a dual-altimeter setup is another subject......

Originally posted by JimJarvis50
It's unlikely that the charges would go off at the same time. But with the altimeters you have, it's even less likely. The RRC2 units that I have tend to go off a little late relative to the perfectflights. I have seen this with two units both in flights and when testing in a baro chamber.

Click to expand...

I have seen the same thing. Missile Works are really good stuff, but always a bit late.

The chances of both going off at the same time are slim.

I was originally thinking redundant means separate systems completely. It's not a big deal and there are many good points here. I am mostly doing it for experimentation and the fun of it. I was just getting ready to put the 2 e matches in one charge till you spoiled that Freda lol. Most opinions are they wont fire at the same time, still me and Murphy have never gotten along I am going to put 2 separate charges and keep everything separate as well. I will test my charges to the minimum and then beef them up a little and test to see how the bay's do.

I would use PVC but I have to play with the aluminum I am working on a glow plug canister also, not for this rocket. Just tinkering with it, I know so has everyone else. No match looks like he is getting close though

Originally posted by sandmantoy
I would use PVC but I have to play with the aluminum

Click to expand...

When I was building my dual deployment rocket, I discovered that PVC was exactly the same weight as copper, but bulkier. (I think I was comparing 1/2" copper and 1/2" PVC, each with 1-1.5" of pipe and a cap.) I ended up cutting half the shoulder off a copper cap and soldering it to a sort length of pipe. It saved a significant amount of weight because I was using the copper caps that have solder built-in (I don't like them, but it's all Home Depot had individually).

My perk is to pick out of the scrap pile at work and we do a lot of work with T6061 aluminum a favorite to tinker with I had planned on making some of the charge canisters and put them on Ebay but they go as fast as I get around to making them. I try to get a stock pile of them but I even have to make more for my own project They are nice and light weight, only a few grams. They are .050 at there thickest point and during testing they can take a lot of pressure not that it would be needed. They are an inch and a quarter tall with a charge a little better than half way and packed tight a good boom without any distortion of the tube. The bore is .615, forgot that lol. That was about the extent of my testing.

My concern was poping the nose cone off from the 2 charges once at the end of the SC. I am going to use shear pins, I haven't got a final weight yet on a few things. The rocket is a 5.5 Hawk and the nose is going to have some weight to it.

Click to expand...

1. I've flown over 40 flights with 2 altimeters and two charges. I've NEVER seen them pop at the same time, but I don't think it would hurt if they did.

2. If you're concerned about a weighted nose ripping a shock cord, three things: (1) make the nose connection out of steel -- plastic can rip (2) make the shock cord very long (30' or more) and (3) extend the shock cord with a 6 - 10 foot piece of Giant Leap Kevlar Bungee -- it takes up a lot of shock.

3. I have had a scenario where one altimeter did not fire -- I was glad for redundancy.

4. If you want to see a cool video of redundant charges firing, watch my Patriot go to 9,256 feet (click link below) and carefully watch the smoke trail at the top of the flight (at about 27 seconds into flight). You'll see two little white puffs in sequence. Those altimeters were both set to fire at "apogee".


https://www.rocketsmagazine.com/david greenapple short.wmv

P.S., not that you'll need it for your Hawk, but Mach Delay tells the altimeter to "not read for apogee" for the amount of time in the Mach delay. So, if you're rocket is going "into Mach" at 2.0 seconds and "out of mach" at 4.5 seconds, set the Mach Delay for 6 seconds... Apogee won't really occur on that flight for about 20 seconds....

I will look into that Kevlar bungee. Thanks, David

I don't think the nose cone would rip off but it might snap back and take out the chute lol. Nose cone attachment should be good, I epoxied a 3/8 plywood ring in the nose and put a 1/16" thick aluminum plate with a U-bolt. Epoxy is 2000lb 30min. with micro fibers in it. Here's a look at it, I had one of the engineers look at it, The way it is attached is what makes it strong since it is only 1/16" thick and just under 4 inches in dia.


David, Kevlar bungee is on it's way Here is a look at the fwd bulkhead with the charge canisters. Carbon fiber makes it look pretty spiffy lol.

Originally posted by sandmantoy
Nose cone attachment should be good, I epoxied a 3/8 plywood ring in the nose and put a 1/16" thick aluminum plate with a U-bolt. Epoxy is 2000lb 30min. with micro fibers in it. Here's a look at it, I had one of the engineers look at it, The way it is attached is what makes it strong since it is only 1/16" thick and just under 4 inches in dia.

Click to expand...

Although I think the aluminum plate is way overkill the engineer should have pointed out that it should have been on the backside of the u-bolt connection where it could have done some good.

Andrew

The aluminum plate is mostly for looks and there is a 3/4" wide x 1 1/2" steel strap or plate that comes with the U-bolt behind the aluminum. The many screws which are #2's to hold it in, in the pattern you see is what keeps it ridged. I didn't want to carbon fiber another bulkhead so I put the aluminum in it. I put a hatch on it for accessing the nose weight or to provoke conversation lol. Maybe I could put a GPS in there Sorry I wasn't more clear on that. My guess is the over all screw area and how it is spread out is what makes this strong.

It does look pretty cool with the plate on there. The carbon fiber on the other bulkhead looks good too.

Thanks, It was the first time I have worked with carbon fiber. I do wish I chose a rocket with smaller fins for the first time lol! Three feet long and nine inches wide I like building the rockets a little more than flying them Though.

Tim

The bulkplates beautiful. I wish I had had one like that today. After the 9th flight of the rocket over the last year, the bulkplate cracked on deployment and at 8,350 feet, the fin section was eaten by the sky.

My next bulkhead will look like yours. I might even use two wooden disks to ensure it's indescructible.

The bulkplates beautiful. I wish I had had one like that today. After the 9th flight of the rocket over the last year, the bulkplate cracked on deployment and at 8,350 feet, the fin section was eaten by the sky.

Click to expand...

No Way! Now you are making me nervous just kidding, thats to bad. I guess I will be testing mine out soon I have been way to picky on this rocket, It is coming out awsome, first color is on it already and I am finishing up the av bay. Man is it big I can put both hands in it

I am always nervous when I have to meet a dead line on a build that I will miss something or just not do a step correctly. I don't have my Mawd in this rocket it is in my Horizon that will be going up on a I211. I would really like to see the flight data for the K550 in the hawk so I might swap out the HA-45 and put the Mawd in before the I go for the level 2 the next day. I want to see how the Horizon does on a J350 also.