Question about setup of redundant Missile Works RRC3 altimeters for dual-deploy

[ManOntheMoon]

I have designed my 4" Madcow Frenzy and 4" Madcow Pike with two Missile Works RRC3 altimeters with dual battery configuration for redundancy. The field for the NAR club in my region is particularly challenging. It is 1500' x 3000' with densely populated trees surrounding the field.

I have set up the altimeter deployment modes to Primary Dual Deploy Mode (Drogue @ Apogee) and Backup Dual Deploy Mode (Drogue @ Apogee + 1 second delay). My black powder charges have been calculated for 15 PSI for the primary altimeter and 20 PSI for the back-up altimeter. Both rockets have three 4/40 nylon sheer pins on both chambers of the airframe. Ideally, I would like the main to deploy at an altitude of 400' above ground level to avoid losing my rockets to the trees.

My question relates to the charges for the main. If I set both the primary and backup altimeters to deploy the main at 400', will there be too much black powder since both altimeters could fire at the same time? Does anyone have any advise for the setup of the charges and/or altimeter settings?

 

[dixontj93060]

Add a delay to your backup altimeter main charge. You really don't want them firing at the same time.

 

[jd2cylman]

Why not set one at 400ft and the other at 300ft. I've deployed at 300ft several times without incident. Just use good chute packing methods, and it'll work.

Adrian

 

[JDcluster]

You will want at least 200 ft difference for main charges.
In my opinion; a Perfectflight Strato-Logger it would be better suited for backup duty.
However, The RRC3 does have a third usable channel.

Another key factor will be to insulate the primary from the backups on both channels.
One charge can set off the others, making for bad day.

JD

 

[JDcluster]

300 ft is too low unless, it's a smaller rocket.
I've seen rockets hit the ground before full deployment.

JD

Why not set one at 400ft and the other at 300ft. I've deployed at 300ft several times without incident. Just use good chute packing methods, and it'll work.

Adrian

 

[rharshberger]

Add a delay to your backup altimeter main charge. You really don't want them firing at the same time.

Set the main at 1000' and the backup main at 700' (or whatever altitude), as dixontj you do not want both firing at thr same time.

 

[jd2cylman]

300 ft is too low unless, it's a smaller rocket.
I've seen rockets hit the ground before full deployment.

JD

I've deployed at 300ft several times on my 4" PML Endeavour without incident. As I said, it's all in good chute packing (which I'll admit I'm not the best at, so if I can make it work, he should be able to also...).
Anyhow, all he can do is do (no try, oh crap, how did that Yoda quote go???)

Adrian

 

[Exactimator]

I have a 4" Pike set up for DD. It's not redundant, but I have another rocket with 100% redundancy. I use the RRC2+ for backup since it's low cost and easy to set up, and i just need something simple to blow charges in case the primary fails. You could use your sexy RRC3 for the primary on another rocket.

I pack my chutes using the PML method https://publicmissiles.com/secure/parachutepacking.asp except I Z-fold the chute instead of folding it over on itself. They pop open pretty quickly, which would help you with your low deploy and keep you out of the trees.

Having both charges fire at once could blow your rocket apart. I'm assuming you're using large amounts of BP since you have 3 4-40 shear pins on each section. On my redundant setup, I have the backup set for 200 feet below the primary (700 feet and 500 feet).

The rockets aren't that draggy, and you probably don't have weight in the nose cones (I don't use any in mine). I friction fit my coupler joint and use two 2-56 pins in the nose. It used 1g FFFFG on the drogue and 1.3 on the main. Fly how you like, but if you try that route you could save BP and wear and tear on your rocket.

 

[WoShuGui]

You probably do not want to fire the main primary and backups at the same time. A 200' seperation is typical, but in this circumstance with a small tree lined field, I might go 400' and 300' understanding that 300' is VERY marginal for deployment on a 4" (I assume fiberglass) rocket. That means you will want a loose packed main. Another consideration is the drogue size which, if too big defeats the purpose of the lower altitude main and if too small means even less safety margin for main deployment. Something in the 18" range (again assuming fiberglass weight) seems about right. Consider wind direction and launch rail angle too. Also, 4/40 sheer pins are on the large size for these rockets, so be sure you have good ground testing with the recovery gear loaded. All that said, it may be that this field is simply not the right one for these rockets.

 

[4kids49]

Another key factor will be to insulate the primary from the backups on both channels.
One charge can set off the others, making for bad day.

JD

That is interesting. How does one accomplish the insulation?

 

[JDcluster]

Tin foil...

JD

That is interesting. How does one accomplish the insulation?

 

[4kids49]

Tin foil...

JD

Does the issue that you are referring to apply to all redundant altimeters? Also, would an RRC2+ be different enough altimeter from the RRC3, or would more diversity be better? I ask because I may have had that bad day. I am not fully understanding the insulation issues.

 

[423yjl]

you could have the rrc3 set to go at apogee and at 500 then have the rrc2+ set for apogee + 1 second and then at 300 feet.
insulating the charges from one another is so the heat, sparks and pressure doesn't set off the second one at the same time and over pressurizing the rocket

 

[4kids49]

you could have the rrc3 set to go at apogee and at 500 then have the rrc2+ set for apogee + 1 second and then at 300 feet.
insulating the charges from one another is so the heat, sparks and pressure doesn't set off the second one at the same time and over pressurizing the rocket

Thanks. I know how to set up the altimeters. I hadn't thought about a primary charge setting off a backup charge. Is this pretty common? I haven't read about it. I could see it possibly happening in a small diameter rocket. My charges are stuffed with dog barf, and then taped pretty well. Maybe it's possible for one to set the other off. Having diverse altimeters would not solve that issue.

 

[DizWolf]

I had an issue with charges setting each other off in my darkstar. They were loaded into 1/2" pipe caps. I started making charges in centrifuge tubes and it separated them enough to not be an issue.

Two charges at once aren't going to blow your rocket up, but over time it would stress cardboard. I'd just set one altimeter as +1 second for each event.

 

[Salvage-1]

If you are wanting true redundancy, then you should use altimeters from two different manufacturers. If you use two identical altimeters, then there is a slight chance that if a software glitch, etc, caused non deployment, then the same glitch would probably be on that backup altimeter.

RRC3 + SL100
RRC3 + Adept22
SL100 + Adept22, etc, etc

 

[Exactimator]

I had an issue with charges setting each other off in my darkstar. They were loaded into 1/2" pipe caps. I started making charges in centrifuge tubes and it separated them enough to not be an issue.

Two charges at once aren't going to blow your rocket up, but over time it would stress cardboard. I'd just set one altimeter as +1 second for each event.

That's the system I use. I haven't had an issue yet, but I might change it if you had problems with yours. How were you packing the charges in the caps that allowed the other charge to set it off?

Two charges at once may not blow a rocket up but it could blow a rocket apart, meaning it comes down in a few pieces. It could snap a shock cord, straighten an eyebolt... I saw a rocket with an overzealous drogue charge tear the upper centering ring out of the rocket.

 

[4kids49]

For the original OP, two charges at the same time for the main runs an extra risk of scorching your main chute. +1 second would be good, but you don't have a lot of margin for error at 400 ft.

 

[Titan II]

If you are wanting true redundancy, then you should use altimeters from two different manufacturers. If you use two identical altimeters, then there is a slight chance that if a software glitch, etc, caused non deployment, then the same glitch would probably be on that backup altimeter.

RRC3 + SL100
RRC3 + Adept22
SL100 + Adept22, etc, etc

Disagree. There are pros and cons to both setups (same or both). I am in the same camp. The altimeters are extremely reliable and I know of none that have any specific failure points. More importently is the human factor. Without data, and via strictly random observations, most failures I have seen are due to human error in programming or installation. The more familiar one is with the equipment, the less the potential error. That being said, both methods work, if the operator takes the time to really know the operation of the altimeter along with proper installation and programming. There is absolutly nothing wrong with two RRC3s. It is my most common combination.

 

[jderimig]

^+1.5 yes after several years and 1000's of flights on altimeters, manufacturers have the electronics pretty much down. The only exception to where a different altimeter might be recommended for backup is the case where the altimeter is a new manufacturer or a new "platform" from an existing manufacturer.

If you really want TRUE redundancy then you should have another person setup, program and wire the backup altimeter......

 

[watermelonman]

I certainly understand the concept but have never gone out of my way to split manufacturers between primary and backup electronics. It happens from time to time but I never worry about it.

I definitely to leave a gap between their firing points.

 

[FredA]

Altimeters don't fail (unless abused) - people do.
This whole "redundant" altimeter stuff is crap.
We have testimony here that the electronics don't fail.
We have data from 100's of ARLISS flights where the few (3, I think) failures are attributed to pilot error.

SINGLE ALTIMETERS ARE FINE.
PREFERRED ACTUALLY since there are less opportunity for pilot error.

Buy ONE FOUR-CHANNEL ALTIMETER and LEARN TO USE IT.
You will be far better off and money ahead.

 

[Titan II]

Since you use RRC3s. Something I do frequently is to fly a single unit set up as primary with apogee drogue and whatever main altitude you choose. Leave the motor ejection in (if it has one) and use it as a secondary at apogee. Then program the aux to fire a secondary main charge 100' less than the other.

 

[DizWolf]

Electronics are pretty good. I trust them just fine.

Ematches fail.
Charges fail.
Batteries knock loose.

You can mitigate these problems. But you can not eliminate them.

Two altimeters is a good idea. Anyone saying otherwise is being cheap or lazy.

 

[FredA]

Ematches fail.
Charges fail.
Batteries knock loose.

Four channels take care of the first two.
Using a battery holder or other nonsense that doesn't address #3 IS being lazy.

Anyone saying otherwise is drinking the Koolaid.

 

[jderimig]

Electronics are pretty good. I trust them just fine.

Ematches fail.
Charges fail.
Batteries knock loose.

You can mitigate these problems. But you can not eliminate them.

Two altimeters is a good idea. Anyone saying otherwise is being cheap or lazy.

David,

Not that I don't agree with you but there is another view...

Ematches fail: 2 usually don't
Charges fail: Charges don't fail, humans fail to size them correctly or fail control the airframe fit.
Batteries knock loose: Humans fail to select and secure power sources correctly.

Some might say that two altimeters are for those too lazy to learn to do the above 3 correctly...:wink:

Fly one altimeter for a while with light and cheap rockets and you will learn those 3 skills quickly. Start with 2 or more altimeters per rocket and one may never master those root skills.

Edit: FredA beat me to the punch, dang it!

 

[4kids49]

This is an interesting discussion. I hope that the OP doesn't mind. It is very relevant discussion. I generally use a single Missile Works altimeter (RRC3 now, RRC2 mini previously). I could not be happier. On a high performance flight, I used an RRC3 with an RRC2+ as a backup. I am nearly 100% sure that the altimeters and charges worked perfectly. Numerous people saw two distinct and separated puffs of smoke at apogee (20k or so) indicating primary and backup charges. Had the two charges gone off at the same time, I would have expected to see one large puff of smoke. I lost the rocket due to some other issue, most likely some kind of human error. I would not hesitate to use the same altimeter setup again. I would have also used two RRC3's but wanted to save a bit with an RRC2+ backup. Interesting discussion though.

 

[DizWolf]

Ok, so I was trolling a bit there, and I do fly single altimeter a good number of my flights.

But I do think 2 altimeters is good practice. Not required. Not "has to be" but a good idea.

Since humans are loading charges and placing batteries, you have to plan for the possibility of human error. The odds of screwing up two charges is lower than screwing up one. Sure, you can try to be really good, but making one mistake = failure in a single alt setup. Dual you'd have to mess up twice.

 

[Buckeye]

Altimeters don't fail (unless abused) - people do.
This whole "redundant" altimeter stuff is crap.
We have testimony here that the electronics don't fail.
We have data from 100's of ARLISS flights where the few (3, I think) failures are attributed to pilot error.

SINGLE ALTIMETERS ARE FINE.
PREFERRED ACTUALLY since there are less opportunity for pilot error.

Buy ONE FOUR-CHANNEL ALTIMETER and LEARN TO USE IT.
You will be far better off and money ahead.

I fully agree with FredA and jderimig, here. Our altimeter vendors are loving this redundancy thing and the double sales that it generates! (Not complaining. More power to them.) In another thread, some poor fellow was lamenting that he just HAD to purchase 10 more altimeters so he can outfit his 5 DD rockets. Totally unnecessary. More altimeters means more rocket, more motor, more complexity, more weight, more wires, more switches, more hardware, more prep time, more charges, more user error, and more cost. Forget about enjoying electronics in midpower rockets or extreme minimum diameter rockets if you feel compelled to put in two of everything.

I can remember only two mishaps in my 15 years of DD flights with a single altimeter (totally my fault and already mentioned above):

1. Poorly constrained 9V battery (I then learned how to do this correctly)
2. Homemade ematches failed to ignite (I now only use commercial matches. I do add some redundancy here on occasion - put two ematches per ejection charge.)

Learn how to use your altimeter, and one will be perfectly fine. They are awesome, reliable little machines. Use the test functions. Ground test the ematches. Ground test the ejection charges. Vacuum chamber. Download the flight data and know what it means. Understand your batteries. Dual deploy a midpower rocket or a low altitude rocket before you "go for it", etc.

I look at redundant altimeters the same as "over-building." Some guys wear it like a badge of honor and think it is good engineering. I think it is inefficient engineering.

 

[watermelonman]

One tricky fact I should point out, when debating the point of redundancy and using different manufacturers, is that sometimes their idea of apogee is different too. I had one that defaulted to apogee+0 and could be set to apogee+1. The other defaulted to apogee+1 and set to backup was in fact apogee+2. If I was not paying close attention I would have set the first to delay for backup and used the second at default thinking it was primary, and had both charges blow at the same time. Flipped around it would have been two seconds between the two, not bad but still not what I was gunning for. The best was to leave them both at default, which resulted in the desired one second gap between charges.