MWP 12: 2 stage failure and bullet?`

Picking motor combos is fine, but I don't think that is 100% a guarantee that something won't happen like this, what if the motor were to spit a nozzle early in the flight, maybe before fully leaving the rail and the rocket slowed sufficiently to arc over before the timer ignited the upper... I'm not picking on you, I'm just asking the question.

Frank

pnobile said:

I'm going to disagree on that I have used and will continue to use the Pefecflite timers for staying and air states , that being said I use smart motor and rocket combos to ensure this would never happen and it hasn't .. ...if people have a better solution or can show they have done something different please share it....it's not that hard in my opinion. I have done several two stage and cluster rockets using timers with no issue because I never pushed the envelope, be smart and be safe

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New fancy electronics is not the answer to safe 2 stage flights.
No electronics are absolute .
I hade one of the new super ones you all are talking about set off the 2nd stage motor instantly once powered up ,luckily I pulled the lighter from the second stage motor before testing.
NASA spends billions and they still have things go wrong .
This exact same thing happened at least 2 LDRS's that I witnessed with N to M 2stage flights why is this one so different
So what was learned from this not much. If you fly a 2 stage rocket with an underpowered motor it doesn't work so well.

A few comments on the information discussed in this thread.

Regarding an altitude check, there is no reason not to do this on a high-power two-stager (or an airstart at altitude). You need electronics anyway, and there are a variety of options that are now available. I'm sure this list is incomplete, but the ones I'm aware of are Ravens, the Telemetrum products, the RRC3, the Eggtimer and the Gwiz HCX. If you do not use an altitude check, you are unnecessarily putting yourself and others in danger. Period.

Some folks talk about using a velocity check instead of an altitude check. A velocity check calculated from altitude data is fine. However, a velocity check based on inertial measurements is not fine. A rocket with an inertial velocity calculation will continue to accumulate velocity even while flying in circles.

Some folks have stated that a tilt measurement is an alternative for an altitude check. This isn't always the case. The "tiltometer" terminates a flight if the critical angle is exceeded at any point in the flight. It would have shut down the flight in question here. However, the Telemetrum products read the angle at the moment that ignition is called for. Had the rocket in question here been a bit more vertical at the time that ignition was called for, a Telemetrum would not have prevented ignition. However, those products can be programmed to use an altitude check in combination with an angle check.. My personal knowledge of the Telemetrum capabilities is limited, so if my beliefs above a wrong, someone please correct me.

There are a few other safety practices that are important for two-stagers. One is to use a shunt of the sustainer igniter and/or open the circuit between the altimeter and the igniter. This is the last thing you open and/or close when you leave the pad. If you use a shunt, it is important to design the circuit properly. It is entirely possible to shunt the leads of the igniter, and yet have the igniter fire if the altimeter fires. This is a function of the type and length of the wires, the characteristics of the igniter and the altimeter firing circuit and battery type. If you are designing a shunt and you don't know what I'm talking about here, ask some questions so that you actually get the protection you think you're getting, and then ground test your circuit.

Another practice that I would highly recommend is to do an "all up" test of the electronics just prior to putting the rocket on the pad. This should include all electronics in operation, including tracking, but with the sustainer igniter out of the motor. This step can save your bacon. If this would be difficult for your particular rocket, such as using head-end ignition or pre-wired air starts for example, then the firing circuit of the rocket should be designed and constructed from the start to allow this test.

Over the last few years, I have also taken to clearing folks out of the pad area when I arm the rocket. On my bigger flights, no one is allowed within 100 yards of the pad when the rocket is armed. When I am arming from a "rack" of pads, I try to wait until everyone else leaves before arming.

Jim

JimJarvis50 said:

Another practice that I would highly recommend is to do an "all up" test of the electronics just prior to putting the rocket on the pad. This should include all electronics in operation, including tracking, but with the sustainer igniter out of the motor. This step can save your bacon. If this would be difficult for your particular rocket, such as using head-end ignition or pre-wired air starts for example, then the firing circuit of the rocket should be designed and constructed from the start to allow this test.

Over the last few years, I have also taken to clearing folks out of the pad area when I arm the rocket. On my bigger flights, no one is allowed within 100 yards of the pad when the rocket is armed. When I am arming from a "rack" of pads, I try to wait until everyone else leaves before arming.

Jim

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Some very good points Jim, i also like too do "all up" checks whenever i fly my humble little Two Stagger. I think that anytime you can double check your electronics before in a less crowded environment is a good time. Currently i'm still using the *Fire in the Hole" method and, have not moved on to drag seperation then head ignition but, when i do i will most likely use my Marsa's over my current combination of Perfectflite 1G activated timers. They have worked very well in the past for me as i really DO NOT like the idea of breakwire style timers...

Like Preston said, the flyer has to pick and, determine the optimum combination to take advantage of under powering the rocket in the beginning of the flight. Unwritten rule: Get that thing moving and, get it moving straight from the get go.

Wow. This thread has been a lot of help in determining things to help with Demon and Dopey 2.0 (rebuild of my two stage). So quick question... is it better or worse to use a teleportation motor in the lower stage?

SS/EA 6BBL 71 Cuda said:

Some very good points Jim, i also like too do "all up" checks whenever i fly my humble little Two Stagger. I think that anytime you can double check your electronics before in a less crowded environment is a good time. Currently i'm still using the *Fire in the Hole" method and, have not moved on to drag seperation then head ignition but, when i do i will most likely use my Marsa's over my current combination of Perfectflite 1G activated timers. They have worked very well in the past for me as i really DO NOT like the idea of breakwire style timers...

Like Preston said, the flyer has to pick and, determine the optimum combination to take advantage of under powering the rocket in the beginning of the flight. Unwritten rule: Get that thing moving and, get it moving straight from the get go.

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Thanks Gus. One lesson from the subject flight, though, is that the use of the 1G timers can lead to problems, even for humble little two-stagers. I just want to encourage people to retrofit existing rockets with altitude-check altimeters where they can, and to certainly design new builds that way.

And yes, get it moving is good advice. My rule of thumb is a 10:1 thrust to weight ratio. Obviously, this depends on the length of the rail and the wind. One issue I caution about is the use of Vmax motors to get the rocket moving on boosters that depend on motor deployment. I no longer do that.

Jim

Jim. Thank you for weighing in with such sage advice. It really helps folks like me who are just figuring this stuff out.

JimJarvis50 said:

Some folks have stated that a tilt measurement is an alternative for an altitude check. This isn't always the case. The "tiltometer" terminates a flight if the critical angle is exceeded at any point in the flight. It would have shut down the flight in question here. However, the Telemetrum products read the angle at the moment that ignition is called for. Had the rocket in question here been a bit more vertical at the time that ignition was called for, a Telemetrum would not have prevented ignition.

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It occurs to me that a tiltometer is more about managing dispersion since it can be dialed in to tighter angles. Does a tiltometer offer any incremental safety over an altitude check other than independent verification?

JimJarvis50 said:

There are a few other safety practices that are important for two-stagers. One is to use a shunt of the sustainer igniter and/or open the circuit between the altimeter and the igniter. This is the last thing you open and/or close when you leave the pad.

Click to expand...

I am glad to hear you recommend this. I have started using a twist and tape method to connect the sustainer starter wires at the pad. It makes me feel a lot more comfortable powering up the sustainer start altimeter knowing the sustainer cannot be lit.

JimJarvis50 said:

Another practice that I would highly recommend is to do an "all up" test of the electronics just prior to putting the rocket on the pad. This should include all electronics in operation, including tracking, but with the sustainer igniter out of the motor. This step can save your bacon. If this would be difficult for your particular rocket, such as using head-end ignition or pre-wired air starts for example, then the firing circuit of the rocket should be designed and constructed from the start to allow this test.

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Can you clarify what a good "all up" test of deployment charges might be? The reason I ask is that I have had open deployment connections that I did not detect until the impedance check at altimeter power up on the pad. That scrubbed the launch, so it sure would be nice to have figured that out during prep. That said, I am pretty sure it is not a good idea to power up an altimeter or use an ohm meter in prep with live charges connected.

EXCELLENT thread. Lots of great, and very important, information here. Thanks especially to bobkrech and jimjarvis for extremely useful advice/viewpoints/experience/guidance. I'm learning a lot, and I'm much more confident in the safety of my future multi-stage flights.
This thread right here is another example of what a great place TRF is.

Thanks everyone for keeping it civil and focusing on safety/education. We're all the better for it.

s6

WoShuGui said:

It occurs to me that a tiltometer is more about managing dispersion since it can be dialed in to tighter angles. Does a tiltometer offer any incremental safety over an altitude check other than independent verification.

I am glad to hear you recommend this. I have started using a twist and tape method to connect the sustainer starter wires at the pad. It makes me feel a lot more comfortable powering up the sustainer start altimeter knowing the sustainer cannot be lit.

Can you clarify what a good "all up" test of deployment charges might be? The reason I ask is that I have had open deployment connections that I did not detect until the impedance check at altimeter power up on the pad. That scrubbed the launch, so it sure would be nice to have figured that out during prep. That said, I am pretty sure it is not a good idea to power up an altimeter or use an ohm meter in prep with live charges connected.

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Generally, I would agree that an altitude check is more about safety and tilt measurement is more about dispersion. But they overlap. As an example, once you have a test flight or two, you can make your altitude check pretty tight. You might not be able to do this to guard against a 10 degree tilt, but you can certainly shut down flights that have 30 degrees of tilt, for example. I have a pretty good idea what my two stagers will do, so there is no reason for me not to use a pretty tight check.

The all up test should be a test of everything, with the sustainer igniter removed from the motor. There are likely cases where this is not possible, but it should be the goal. I don't have a problem operating the electronics prior to the rocket being on the pad. Any time you do this, it should be such that if the charges go off, no one will be endangered. There is a lot of difference between a charge going off versus a motor going off. Motors go off from time to time, and I know people who have been injured or nearly injured. The trade-off is worth the all up test.

Jim

First, this rocket was going far too slow off the rail. Clearly not enough thrust. If the flyer was concerned and had questions in his own mind why the hell did he fly it? We are adults- take responsibility and stop go fever.

Secondly, what was the wind speed at time of launch?

Also, typically a 6 foot rail, due to the position of the forward rail button, might have an effective rail length of four feet. We need to be aware of this as it can compromise the best thought out flights. If this flight had been on substantially longer rail it might have gone better.


Mark Koelsch
Sent from my iPhone using Rocketry Forum

WILDMANRS said:

New fancy electronics is not the answer to safe 2 stage flights.
No electronics are absolute .

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Jim - wasn't your 3-stage attempt at BALLS this past year locked down because of a faulty tiltometer?

AlnessW said:

Jim - wasn't your 3-stage attempt at BALLS this past year locked down because of a faulty tiltometer?

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Yes. In some way, the signal coming from the altimeter caused the unit to self destruct. I have one unit that works fine, but this has happened on two of them now. We don't know why.

Jim

JimJarvis50 said:

Yes. In some way, the signal coming from the altimeter caused the unit to self destruct. I have one unit that works fine, but this has happened on two of them now. We don't know why.

Jim

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That IS weird. Bummer since I assume you still have some N motors lying around from that flight...

Another measure that can help is strong recovery systems and electronic deployment at apogee, preferably with redundant altimeters. Had the sustainer and booster in this case deployed at apogee (in this case, both would have deployed at the top of the first loop), there would have perhaps been a lot of thrashing, but not the scary high speed pass.

I'll also note that Jim's advice on keeping people away from the pad was added to the last NFPA revision--it's not just good advice; it's the code .

--tc

Thanks to everyone who has contributed thoughts on this thread!

Not entirely true either, for example adept altimeters will not function properly if the rocket doesn't reach a minimum of 300ft in altitude, or looks like missile works looks to be 200ft in altitude, as many electronics have some sort of feature like this

Ted Cochran said:

Another measure that can help is strong recovery systems and electronic deployment at apogee, preferably with redundant altimeters. Had the sustainer and booster in this case deployed at apogee (in this case, both would have deployed at the top of the first loop), there would have perhaps been a lot of thrashing, but not the scary high speed pass.

I'll also note that Jim's advice on keeping people away from the pad was added to the last NFPA revision--it's not just good advice; it's the code .

--tc

Thanks to everyone who has contributed thoughts on this thread!

Click to expand...

AlnessW said:

That IS weird. Bummer since I assume you still have some N motors lying around from that flight...

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The question of the day was how many motors I would go home with. At least it wasn't three.

Jim

JimJarvis50 said:

The question of the day was how many motors I would go home with. At least it wasn't three.

Jim

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Although if my memory serves, your flight was one of the last ones up before they shut everybody down...
I know you weren't the only one who had to bring motors back home!

pnobile said:

Not entirely true either, for example adept altimeters will not function properly if the rocket doesn't reach a minimum of 300ft in altitude, or looks like missile works looks to be 200ft in altitude, as many electronics have some sort of feature like this

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Missile Works RRC3's allow for a modifiable "arming altitude" as low as 100'.

I have flown my 5.5" Nike Smoke twice on a central 54mm motor and two 29mm outboards. On both occasions the outboards did not light. In the case of the first flight, an old RRC2 Classic had an issue and deployed the apogee charge about 2s after burnout. The outboards did not light because of my design.

I ran a wire from the altimeter bay coupler down through the drogue compartment, through a conduit in the MMT and out the back of the rocket. This wire had a break point directly below the altimeter bay designed to separate when the rocket separated at apogee. By doing it this way, coupled with a 100' arming altitude, it's a pretty fail safe design.

1. If rocket fails to reach 100' due to underpowered flight or unstable flight, the rocket will not fire anything.

2. Rocket reaches 100' in the unstable manner of the 2 stage rocket in this thread, the rocket will fire the drogue at first turn and separate the wires.

3. Rocket reaches 100' plus the programmed time interval, the rocket will fire the outboards.

The only thing really ignored in this circumstance is the possibility of an off-vertical flight. In order to counter that. I fly high impulse motors that will surely lift the rocket off of the long rail.

100 ft arming altitude with a barometric altimeter increases the risk of false launch detect significantly over a 300ft arming due to wind and barometric pressure drifts.