Timer Staging Discussion

[boatgeek]

...The plan for my N-T is M to L so it might be time to get some tilt inhibit.

I had a hilarious misreading for a moment where I saw N booster to T sustainer and not Nike-Tomahawk there.

 

[Steve Shannon]

Finished I/S coupler & started Motor mount conduit assembly and fin install:

https://www.rocketryforum.com/threa...ager-75mm-to-54mm-motors.149523/#post-1835721

I did check with Steve Shannon on Tripoli's ruling regarding timers;
As of now they recommend against it, especially high power 2-stagers, but officially there is no rule against it.
They feel same as I do, it's a must to use some type of safety check before upper stage ignition.

Remember [can't emphasize this enough] safety is high level concern when it comes to staging.

I appreciate this message!

 

[Cameron Anderson]

I've been think about this a lot lately and I'll say it...I want to see the data.

I want to see a comparison of the average fail rates of single stage rockets to multi-stage. Specifically I'd love to ser failures that presented a legitimate safety risk. A CATO at a 500 foot pad is bad and potentially unsafe but in reality, poses no risk to spectators (that's why we position pads and spectators the way we do. I've been flying for a long time and I can say anecdotally that the overwhelming majority of failures I've seen in all rockets is a failure during recovery (maybe 2/3 if those failures are failure to deploy the chute at all and 1/3 is a chute deployment but then it cigarette rolls or blows suspension lines or a panel).

I think if we wanted to make rocketry safer dual, redundant electronics should be standard since that (to me, purely anecdotally) is the highest fail rate aspect of flight and is one that poses a legitimate risk to flyers and spectators. I've seen RSOs nitpick internal fin fillet epoxy choice but I've not once seen an RSO ask to see chute packing method. As an Army parachutist and Pathfinder, nothing scares or infuriates me more than watching people shove their parachute into the end of their rockets haphazardly like old laundry.

I absolutely agree that inhibits (altitude, tilt, velocity) allow for a more controllable flight profiles but I do not think that "controllable" necessarily means safer than timer-controlled events. After discussions on this thread my Nike Tomahawk M to L will have an inhibit set up, not because it safer to me, but because I don't want to light a full L at 8,000 feet at 20 degrees off vertical and end up chasing my sustainer all the way back to Gerlach. That is a desire for flight control and not due to fear of some unsafe condition. Yes, deviation of cleared airspace is bad and should be avoided, it is contrary to the overall safety of the hobby but is not in and of itself "unsafe." There is a difference between "against the rules" and "legitimately putting people in danger." They are not intrinsically tied as some people want to believe.

Furthermore, I would love to see instances where two stage failues that actually posed safety hazards would have been prevented by the three inhibits addressed before. I have seen many two stage failures but have not seen any that poses a real risk (maybe I'm just lucky. Also, I am discounting the recent spat of college research two stage issues...those were caused by fundamentally unsafe construction and prep methods and not by timer vs inhibit issues). In my 25 years of high power flight, I've never seen anyone injured at a launch. I've only seen two instances of property damage (motor case kicked out and hit a car windshield and a rocket came in ballistic and hit a set-up table on the flight line where, fortunately, no one was standing). Again, maybe I'm lucky and haven't seen a true statistical representation of launch accidents, which is why I want to see the data.

I don't think the data supports the idea that timers alone are unsafe. If it does, I'll whole-heartedly support mandatory inhibit use and champion it. But I do not think the data indicates that inhibit use is safer than timer use.

At best, I see the love affair with inhibits as misguided in the name of safety. Far too often people use "safety" as a sort of unobjectale trump card and anyone who dares argue against something the collective deems "safe" makes you a paraiah. At worst, I see it at as hubris and ego in the vein of "this is how I do it and I am smarter than you so you have to do it this way to because safety."

Rocketry is a science so data and not anecdotal opinion should govern flight considerstions. I agree that safety is a paramount concern and the future of the hobby depends on it, but real safety precautions, and not assumed safety concerns, should govern decisions.

 

[Cameron Anderson]

I dont want to derail this build thread, I am a big fan and would never question your build or launch experience, and maybe there is a better venue to discuss this, but I'm legitimately interested in the data. If anyone has it, I think it would be you Jim (or you know someone who has it)

 

[blackjack2564]

You are not derailing anything. I reserved posts in beginning so continuity of build procedures will be in order regardless of the noise in these and other posts beneath the build phase. This issue being discussed is why I do my threads this way.
I always welcome any discussion such as this.................

You have been trained by military and see things in a different [better] light than most.
First off my mantra has ALWAYS been....

"this is my way, there are many ways to solve a problem that work,& are correct. I just think most of mine are simple,easy to do & highly functional."
I have never tried to cram my methods down anyone's throat, be it build techniques or safety issues. I am not taking offense to your thinking ....just stating my mantra that many have seen before in my threads.

Now for timer issue at hand:
I try to recommend and do something so even a monkey could not screw up. Keeping it simple as possible. That rules out timers for most.
In the 16 years I have been doing this I have witnessed far too many incidents with timers that COULD have been deadly. We as a group have been dodging bullets for a long time.
There was one where a young lady got burned very badly, and it cost Tripoli insurance a bunch. I was there and will not discuss intimate details openly other than this.
A large M-M was put on pad, armed, then lowered to horizontal position, may have been raised & lower again I don't remember. The timer sensed launch from these actions and while horizontal the motor fired with this person standing directly behind.
Several things happened that shouldn't have. Most having to do with too many people milling around that had no need of being there. Yes timer should have been powered off...but it wasn't, before lowering the rocket.

Another event I witnessed was an underpowered booster only getting about 200 ft and stack did it's gravity turn.
Actually pointing down when sustainer lit, flying back over the crowd and into paddock area just missing cars and people. There is a video floating around of that one.

3rd one witnessed was at LDRS Canada in 2005 where a N to M malfunctioned under boost, recovery gear for booster came out under thrust. The upper stage still connected to I/S began spinning wildly around the chute as it came down. We all thought everything was OK.
Suddenly the sustainer lit pointing down. It hit ground under full thrust at a shallow angle [like skipping stone across water] and went into a herd of cows almost hitting 2. I never saw a cow jump straight up before !

These 3 incidents would never have happened, had a simple altitude check been in place.

I used a timer for back up apogee firing in booster. I did settings with designer on phone according to his instructions. Then had them checked by another well versed with this brand. Wanted 20 seconds after motor ignition to fire chute charge. This rascal used tenths of second instead of 1 second intervals when setting the time. [you had to push button 10 times for each second desired.] We even ground tested the darn thing. When launched it fired 2 seconds after booster burn out and chute comes out when coast just began. The sustainer was long gone as booster motor was only 1.5 second burn.
The chute ripped off and booster came in hot, just missing my group of six by 10 feet and our car by inches. First time I ever had a silent ballistic re-entry it came down silent and thud hit...non of us heard or saw it. We did not know what happen till others farther away reported the chute loss...we were directly under the rocket though 2000 ft from pad.

Since that issue happened to me, I will never use a timer again for anything other than separation charge. I consider the incident as Lady Luck tapping me on the shoulder and do not wish to tempt her after being warned.
As careful as I am it happened to me, and I consider myself WAY more safety conscience than most. I must rack that one up to my own user error, even though we will never know what happened.
I just decided that was one issue I could easily eliminate...so I did.

I have seen 2 other instances with same timer, where it fired the sustainer on the pad, shortly after being armed, definitely user error on the settings. These were experienced rocketeers, not rookie by any means.
Why take a chance when a simple solution is readily available?
Granted I have no real statistics, but I have witnessed far too many "bad things happening" with timers
So for me, I just took them out of the equation.

If I thought about it for any length of time, there have been many other incidents I could recall in my 16 years of flying . Those were the first ones coming back from memory.

I think if you talk to most experienced 2-stage fliers they will back me up on timer use for staging.
There has been a plethora of cheap 2-stage kits sold in last 2 years, most of them bought by fliers with little or no experience at all.
Problem today is.....so many want instant gratification. They have a credit card, buy whatever is needed, and build something with no mentor involved.

It's an accident waiting to happen and if it does, may have repercussions non of us want to face on our hobby. You can play Russian Roulette dozens of times and live, but sooner or later you will get bit.

There are always exceptions and you are probably one of them do to your extensive training/background.
But being a TAP I must consider the group as a whole and render my opinion based on 'the worst that could happen" not the best.
You are 100 % correct, timers are not inherently the Boogieman, but their use/setting them up for most is difficult at best.
Respectfully yours....
Cj

Ps after all the close calls I have seen, when it comes to flying 2-stagers...safety is my number 1 concern... period. Even if that means not allowing their use if it's my call. Others may have different opinion regarding timers & I must respect that.

Edit: I am referring to timers without some type of safety check before firing.

 

[JimJarvis50]

Ps after all the close calls I have seen, when it comes to flying 2-stagers...safety is my number 1 concern... period. Even if that means not allowing their use if it's my call. Others may have different opinion regarding timers & I must respect that.

Ditto. Best as I can recall, I've seen 4 flights where the sustainer went in a direction that was decidedly not vertical and not very high. I've seen perhaps a half dozen other cases where the sustainer lit on or near the pad. You really can't build in too much safety into staged flights.

When I started flying multi-stage flights, maybe 2004?, there were several altimeters that could fire a charge at a specified altitude on the way up (in addition to a specified altitude on the way down). The ARTS II and a few of the GWIZ higher-end altimeters could do that. I connected that output to a transitor switch in a timer circuit to provide an "altitude check" for the timer, and I flew staged flights that way until the Raven came along. I never have flown a staged flight with only a timer. Now, there are quite a few altimeters that can do this and some are not expensive. No reason not to use them.

Jim

 

[Cameron Anderson]

Between CJ and Jim here, there is a breadth of knowledge in staging that is probably unparalleled in the hobby.

To CJ's point, two stage flight do add layers of complexity that many flyers underestimate. Internet shopping can be dangerous. I cut my teeth on Estes 2 and 3 stagers and when I got into midpower staging, timers were the only game in town and they were home-soldered breakwire monstrosities that were made in garages with mail order plans. I remember flash bulbs and thermalite being the gold standard for clusters for a very long time. More efficient and controllable electronic controllers are available today, but are they any more safe than older methods? I don't know. And unfortunately I don't know if the data exists (I wish it did). Some of the accidents you mentioned I had heard of and some I had not, but I think the key takeaway from all of them is that multiple failures but many people created the situstions that occurred. I am all for the safe promulgation of the hobby, I actively recruit and enjoy mentoring new flyers. I see a time and place for most techniques, including timers. I think a blanket prohibition on timer use is overly broad. We have TAPs and RSOs and mentor programs who use their judgement to evaluate the flight worthiness of each rocket on its own merit. Luckily for me, my TAP and my club RSO let me fly my last flight timer only. My TAP helped with a lot with my last two stage flight planning which used a timer for separation and sustainer motor ignition (which suffered total booster and sustainer recovery failure despite a rigorous ground testing protocol) because rockets are hard and even with lots of testing and assembly and experience, rockets fail. They used their years of experience to evaluate the flight in terms of flight profile, launch site size, and my history and experience. The timer functioned perfectly. Fortunately for me, my failure occurred on a massive lakebed half a mile from the flight line and only posed a threat to sagebrush, but yes, it could have been much worse. I am just wary of blanket prohibitions.

To Jim's point, with low cost alternatives (to timers that provide inhibit protection), why not use them? I don't have an argument other than timers, the overwhelming majority of the time, work fine. Most failures that I have seen happen in the recovery phase, not boost. But I also fully acknowledge that I haven't seen everything and would love to hear even anecdotal evidence about failite rates. (My guess, based on my experience, is failures are 75% recovery related, 20% shred/airframe failure, 5% CATO/motor) Like I said earlier, my M-L two stage will have a Marsa because I don't want to chase my sustainer 10 miles across the plays, but I have enough faith in my construction and motor assembly skills that I would fly with a timer. But yes, if something better is available, why not use it? My counter argument is that while more complex and customizable flight computers can be used, timer use should also be acceptable. Complex flight computers and timer use should be complementary and not exclusive.

Also, I love this forum and the ability to ask complex questions and get real answers from experts.

 

[JimJarvis50]

To Jim's point, with low cost alternatives (to timers that provide inhibit protection), why not use them? I don't have an argument other than timers, the overwhelming majority of the time, work fine.

When I use an altimeter with an altitude check, the logic statement is "no matter what happens on the flight, don't light the motor unless the altitude is reasonably close to what is expected". When you use a timer, the logic statement is "no matter what happens on the flight, light the motor".

I think when you say that timers work the majority of the time, what you mean is that you haven't had issues where you would have wanted to inhibit ignition. That's fine, but it happens quite often because there are too many things that you can't control, or that you can screw up, and it will happen to you eventually.

I have not personally had instances of an interstage coupler failure (but I have seen several) and I haven't had an unstable rocket (have seen those too). These commonly would result in a sustainer firing towards the ground. But, I have had other cases where "stuff happened" that I hadn't anticipated. You want a couple of examples? The first video is a case where I didn't shear pin the interstage coupler to the booster. On this flight, the sustainer drag separated, but with the interstage coupler still connected to the sustainer. I got away with it, but it could have easily spun the sustainer around. As it was, the rocket went off at an angle and landed quite far from the pad. In the second video, the sustainer lit on first motion of the rocket (you never want to see two contails off the pad!). This was a combination of the Raven perch being energized, which I wasn't aware of at the time, combined with a circuit that actually went through the carbon tube at a break in the air frame. One in a million. But instead of happening on first motion, it might have happened due to a wind gust, with me on the ladder next to it. My point is that if you think you can control everything that can happen in a two stage flight, you are dreaming. Give the folks at the launch an edge, and add a simple safety feature.

Jim

 

[Steve Shannon]

Cameron,
I’ve personally been involved in a two stage project where a timer lit the sustainer after it had already turned horizontally. I don’t ever wish that feeling on anyone. I wasn’t worried about the waiver, the long walk, or damage to the recovery system; I just didn’t want anybody to be injured. That was my only concern and it’s still my primary concern.
Since then I have seen a few flights where those of us watching were saying “come on, light!” only to change our tune to “don’t light, don’t light, don’t light!” It would be better if the electronics did that.
We don’t currently require inhibit circuits, for many of the reasons you mentioned. And the most dangerous part of the process is still the person preparing the rocket. But, since such technology is available, we recommend it, especially for high altitude flights. And, I would not be surprised if the FAA someday mandates such as a condition for a high altitude COA. I believe they’re already required in Canada.
Steve

 

[Cameron Anderson]

Thanks Steve and Jim, these are the kinds of instances I was curious about. I completely acknowledge that I have seen a lower incidence of failure with cluster/airstart/staged flights than one would expect given the number of flights I have seen. Just fortunate I suppose, and of the failures I have seen, they've almost exclusively been recovery failures. Even personally, while sustainer ignition is the highest risk portion of the flight, that's always not been an issue for me.

I would still like to see some statistical analysis on flight failures, just because it intrigues me. I would almost think that failure types are clustered among specific clubs since local expertise and experience eliminates certain failure types, and since expertise varies, high fail flights at club X aren't necessarily the high failure flights at club Y.

Hey experts, what would you say the fail rate is for staged flights you've seen? (Consider any flight that isn't totally nominal a failure)

 

[woferry]

Question is what's considered a 'failure'? I've seen plenty of staged flights where the sustainer failed to light (probably more than half of the 2-stage HPR flights I've observed). This could be because the safety circuitry did it's job, and determined something was not-as-planned (or not-as-programmed, i.e. a configuration issue) and prevented the sustainer from lighting, or there could be other reasons why the sustainer just failed to light (bad ematch, etc). Many of those we've seen the rocket going more sideways than it should have, everyone saying "don't light, don't light", and thankfully they mostly haven't, so it seems to me that a fair number of flyers are using altimeters with lockouts and they're functioning as intended. Though I've seen some videos, thankfully I haven't personally witnessed any true-horizontal (or downwards) sustainer firings, but I've definitely seen some that were more sideways than they should have been, resulting in very long recoveries (or never finding the sustainer, period). I've done two 2-stage flights myself, using an RRC3 with an altitude lockout (since that's the best that altimeter offers w.r.t. staging), both flights were successful. I intend to switch to the Eggtimer Proton for its baro-vs-accel comparison which sounds better to me. But I would never consider simply using a timer, especially not when more advanced electronics exist and are not terribly expensive or complicated.

 

[Cameron Anderson]

I consider failure anything other than nominal flight. I want to define it that way to capture all types and sourcrs of failure.

Cost or availability of timer alternatives isn't a scientifically sufficient argument to prohibit timers for me. To me, cost/availability falls into the "personal preference" category.

I have always understood the variety of flight profile restrictions that inhibit-capable devices offer but i have yet to be swayed based on empirical data that timer-only systems are demonstrably more dangerous than inhibit-capable systems.

The argument that flights have failed in the past and COULD have resulted in injuries/property damage is an emotional one, not valid statistical evidence. Almost every flight has aspects that, if they were only slightly different, COULD have result in a failure.

Rocketry, even on its best days, exists on the extreme margins of material performance, physics, and safety. We should continue to keep rocketry as safe as possible, but I still don't see any data set that indicates timer use should face a blanket prohibition. I've had many conversations with smart, experienced flyers on the subject - they can offer many examples of scenarios as to why they prefer inhibits, but I truly believe 30 years of flight data do not indicate timer bans are appropriate.

 

[Steve Shannon]

I consider failure anything other than nominal flight. I want to define it that way to capture all types and sourcrs of failure.

Cost or availability of timer alternatives isn't a scientifically sufficient argument to prohibit timers for me. To me, cost/availability falls into the "personal preference" category.

I have always understood the variety of flight profile restrictions that inhibit-capable devices offer but i have yet to be swayed based on empirical data that timer-only systems are demonstrably more dangerous than inhibit-capable systems.

The argument that flights have failed in the past and COULD have resulted in injuries/property damage is an emotional one, not valid statistical evidence. Almost every flight has aspects that, if they were only slightly different, COULD have result in a failure.

Rocketry, even on its best days, exists on the extreme margins of material performance, physics, and safety. We should continue to keep rocketry as safe as possible, but I still don't see any data set that indicates timer use should face a blanket prohibition. I've had many conversations with smart, experienced flyers on the subject - they can offer many examples of scenarios as to why they prefer inhibits, but I truly believe 30 years of flight data do not indicate timer bans are appropriate.

Because this could become a long discussion, I’d suggest moving it to a thread of its own.

 

[JimJarvis50]

The argument that flights have failed in the past and COULD have resulted in injuries/property damage is an emotional one, not valid statistical evidence.

https://www.safetyandhealthmagazine.com/articles/10994-reporting-near-misses

 

[Cameron Anderson]

https://www.safetyandhealthmagazine.com/articles/10994-reporting-near-misses

Reporting near misses is good for fault analysis. But if event X has a 10% rate of occurrence and 0 reported injuries associated, X = 0. Just because something happens that is aberrant doesn't mean that ia poses a significant threat warranting action.The sample pool for rocketry is sufficiently large that if we had sustainers firing up and smashing into crowds, we would know about it. We have a recovery fail rate that, in my opinion, is astronomical, and there are several easily identifiable fault points that could be easily remedied, yet RSOs lecture people on fin angle and epoxy mixing techniques.

 

[jderimig]

Reporting near misses is good for fault analysis. But if event X has a 10% rate of occurrence and 0 reported injuries associated, X = 0.

I think you maybe conflating failure occurrence and failure severity. Good reliability practice wants to drive the occurrence to 0, the priority in doing so is driven by severity. Experience has taught us the severity is often underestimated with tragic consequences. FMEA practice defines the severity on what could happen, not what has happened so far. I am grateful that commercial aircraft designers follow this practice.

But I agree with you about the recovery hazards. But experience has that ground accidents are the highest hazard (recently).

 

[boatgeek]

Reporting near misses is good for fault analysis. But if event X has a 10% rate of occurrence and 0 reported injuries associated, X = 0. Just because something happens that is aberrant doesn't mean that ia poses a significant threat warranting action.The sample pool for rocketry is sufficiently large that if we had sustainers firing up and smashing into crowds, we would know about it. We have a recovery fail rate that, in my opinion, is astronomical, and there are several easily identifiable fault points that could be easily remedied, yet RSOs lecture people on fin angle and epoxy mixing techniques.

I have personally witnessed one significant injury and two near misses that could easily have caused serious injury at launches. One near miss was a spat motor that landed on an occupied tent. The injury was a rocket that came in hot into the crowd and the other near miss was a ballistic rocket that landed 6” from an occupied tent. I just can’t see how you get from zero reported injuries from spat motors to spat motors aren’t a problem.

You also just blew off both Jims’ experience with near misses that could have been serious injuries if not fatal. Looking fat near misses gives you not only 10x the sample size to learn from, but you also learn what factors aided in preventing injury. That lets you replicate those factors later and spread knowledge about them to other clubs that may have been lucky enough not to have that particular near miss yet.

I’m also curious about the circumstances where the RSO hassled the flyer about epoxy and fin angle. I have never seen that. In my experience they ask about recovery, electronics, motor retention, and give the fins and airframe a good tug to make sure they’re sturdy enough for flight.

 

[Steve Shannon]

Reporting near misses is good for fault analysis. But if event X has a 10% rate of occurrence and 0 reported injuries associated, X = 0. Just because something happens that is aberrant doesn't mean that ia poses a significant threat warranting action.The sample pool for rocketry is sufficiently large that if we had sustainers firing up and smashing into crowds, we would know about it. We have a recovery fail rate that, in my opinion, is astronomical, and there are several easily identifiable fault points that could be easily remedied, yet RSOs lecture people on fin angle and epoxy mixing techniques.

But there is no “0 reported injuries” statistic. Any rocket that strikes a person point forward is bad, whether it happens because of a recovery problem or because of “sustainers firing up and smashing into crowds.” Both should be addressed. Preventing sustainers from “firing up” at a dangerous attitude is possible through currently available technology.
Here’s your statistic: Nearly all instances of high power sustainers igniting in a dangerous attitude happened because people use timers. I know that first hand and there have been numerous other cases cited within this thread.
Here’s another: At BALLS this year we saw several instances where sustainers did not ignite because of inhibit technology. Although that’s technically a a failure to ignite, in reality it’s a successful implementation of available technology that prevented something worse from happening.
We also had two instances of multi-stage rockets which were being prepared. In one, static electricity is thought to have been at fault. The motor wasn’t even in the rocket yet and the electronics were powered down. An inhibit circuit would have done no good and a timer would have done no bad.
In the other, a human error (powering up staging electronics while vigorously assembling the rocket) started the timer function which ignited the large sustainer motor while surrounded by eight people. Had that rocket been equipped with electronics with an inhibit function the error would not have ignited the sustainer motor.
We’re never going to completely eliminate human error, but we can improve our designs in ways that the results are less risky and we can add mitigation to reduce the risk even further.
New Safety Code rules most frequently happen because people don’t willingly adopt safe practices or safe technologies, much like seat belts. The greater the resistance is by a few, the more likely that we will be pushed into adoption of a rule requiring off-axis inhibitors. That’s best case. Worst case would be if a terrible accident happened which resulted in government regulations or prohibitions. That’s the statistic we want to avoid. It would only take one metal tipped minimum diameter sustainer flying under power into a crowd and passing through multiple human bodies to cause that. Then the question would be “You had the technology to prevent this, but you didn’t use it. Why not?”
Even if the government didn’t regulate us out of existence, our insurance rates would rise so high that many people would have to drop out of the hobby.
Worse yet, imagine looking in the eyes of the families whose loved ones were skewered and having to admit that you didn’t do everything possible, even though it was easy, to prevent off axis firing of the sustainer.

 

[Cameron Anderson]

I have personally witnessed one significant injury and two near misses that could easily have caused serious injury at launches. One near miss was a spat motor that landed on an occupied tent. The injury was a rocket that came in hot into the crowd and the other near miss was a ballistic rocket that landed 6” from an occupied tent. I just can’t see how you get from zero reported injuries from spat motors to spat motors aren’t a problem.

You also just blew off both Jims’ experience with near misses that could have been serious injuries if not fatal. Looking fat near misses gives you not only 10x the sample size to learn from, but you also learn what factors aided in preventing injury. That lets you replicate those factors later and spread knowledge about them to other clubs that may have been lucky enough not to have that particular near miss yet.

I’m also curious about the circumstances where the RSO hassled the flyer about epoxy and fin angle. I have never seen that. In my experience they ask about recovery, electronics, motor retention, and give the fins and airframe a good tug to make sure they’re sturdy enough for flight.

Gents, first off, and most importantly, I do not disregard not question "The Jim's" vast experience or accomplishments. They are unequaled in terms of accomplishments and innovation in rocketry, specifically staged flight. Period. I love their threads, and more importantly for me, their eagerness to share their knowledge. If it appears I have done so, it is purely unintentional and I apologize. Crazy Jim and Normal Jim, honestly, nothing but respect, and envy.

I do, however, based purely on the statistical data that I have seen and that is available, disagree with their assessment that timers alone (without some form of inhibit) should not be used for staged flights. And should data exist to the contrary, I would change my tune and never think twice. That's all it is - an academic disagreement. And I am thankful for a forum like this to exchange ideas in a friendly setting. Anyone who thinks I wouldn't sit down and pick their brains for hours over a drink is mad. I have the utmost respect for their flight records, they speak for themselves. I just have an opinion that differs based on my experience, that's all.

As for RSOs and their penchants for odd inspections (epoxy choice), it was a launch in SoCal MANY years ago, but it has stuck with me. Having watching many flyers treat their parachute look like old laundry makes me wary of recovery and has contributed to what I pay attention to as a flyer.

 

[Steve Shannon]

First, it’s probably not possible to pick my brain for hours.
Second, if you do, it won’t be over “a” drink.

 

[Dipstick]

After the incident at LDRS in Canada, CAR/ACF put a moratorium on 2 stage flights, then lifted it with a requirement that 2 stage flights must have inhibits. Those of us flying 2 stage went ok, that's what we'll do. I've had succesful lights using simple time, speed, distance with a Raven. More importantly, it prevented one sustainer from lighting after a coupler failed and the stack started skywriting...in my opinion its silly not to use the inhibits, who cares about stats, we're trying to prevent bad ones!

 

[Cameron Anderson]

After the incident at LDRS in Canada, CAR/ACF put a moratorium on 2 stage flights, then lifted it with a requirement that 2 stage flights must have inhibits. Those of us flying 2 stage went ok, that's what we'll do. I've had succesful lights using simple time, speed, distance with a Raven. More importantly, it prevented one sustainer from lighting after a coupler failed and the stack started skywriting...in my opinion its silly not to use the inhibits, who cares about stats, we're trying to prevent bad ones!

Because rocketry is a science and blanket prohibitions without data is opinion, and opinions can be wrong, sometimes dangerously so. It's a bad habit and potentially unsafe to start using opinion as the basis for safety practices.

 

[jderimig]

Because rocketry is a science and blanket prohibitions without data is opinion, and opinions can be wrong, sometimes dangerously so. It's a bad habit and potentially unsafe to start using opinion as the basis for safety practices.

Statistics is a science also. Failures follow the Poisson distribution. 0 observations does not prove or even support a 0 failure rate.

 

[Dipstick]

Because rocketry is a science and blanket prohibitions without data is opinion, and opinions can be wrong, sometimes dangerously so. It's a bad habit and potentially unsafe to start using opinion as the basis for safety practices.

So...wait for injuries so we have some more stats, then implement a policy based on those stats (inhibits now mandatory). You get to the same place without any negative middleground if we just use inhibits.

Sure you can parse opinion vs. stats all day and I agree that that would be problematic in many areas of life, but this one just seems common sense to me, particularly as the technology exists...

 

[Banzai88]

The old safety montra is "An abscence of accidents is NOT an indicator of safety". It's hard to measure something that didn't happen, but if you can't measure it, you can't improve on it, either!

In this application, it seems like a cheap, easy to use, easy to confirm, universally accepted product that detects altitude, speed, and tilt in our rockets would seem to be a license to print money.

 

[Cameron Anderson]

I'm not saying wait for accidents, I'm not saying an absence of accidents means everything is okay.

I am saying there is no data available that indicates timers without inhibits are less safe than other staging methods. We can infer all we like, but that point is not debatable. (I would love verifiable data to turn this academic discussion into a finite one)

I am also saying throwing your hands in the air and yelling "safety!" doesn't make a position any more cogent or valid. In fact, treating safety and associated positions as sacrosanct is inherently unsafe. People unwilling to ask "why" are too willing to walk down a well-meaning, and potentially more dangerous, path.

 

[Cameron Anderson]

I guess this is a better statement of my hypothesis...

Two-stage flight with timers (without inhibits) is equally as risky (in terms of flight failure and injury potential) as staging electronics (with inhibits). Ergo, a blanket prohibition on timer use is not supported by flight record data and does not make staged flights statistically safer than alternative methods.

 

[Cameron Anderson]

People keep making the argument "if inhibits are available, why not use them?" My answer is this - choice.

Aerotech has been around longer than CTI so no one can use CTI.

Missileworks is my preference so you can't use Perfectflite.

Black paint is easier to see than white. No more white paint.

That is how silly people sound when their argument tests on preference along and not science.

 

[Steve Shannon]

I guess this is a better statement of my hypothesis...

Two-stage flight with timers (without inhibits) is equally as risky (in terms of flight failure and injury potential) as staging electronics (with inhibits). Ergo, a blanket prohibition on timer use is not supported by flight record data and does not make staged flights statistically safer than alternative methods.

Your hypothesis is incorrect. It’s that simple.

 

[dhbarr]

Two-stage flight with timers (without inhibits) is equally as risky (in terms of flight failure and injury potential) as staging electronics (with inhibits)....

Your hypothesis is incorrect. It’s that simple.

Specifically, your statement assumes the truth of the conclusion rather than supporting it.