MWP 12: 2 stage failure and bullet?`

Cl(VII) said:

Does this include an altitude check on a barometric altimeter, or is something like a tiltometer always needed?

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Tilt-o-meter is out of production due to lack of an essential electronic component. Only "fully" intelligent device(s) are the Tele Mega and Easy Mega. Any others out there? Those are the only two I'm aware of currently.
By fully intelligent I mean the device can sense the angle of the rocket and lock-out staging and activate recovery. The Raven can do altitude checking but can't sense angles.

I agree that the launch detect altitude wasn't detected, set too high or the altimeter wasn't able to sense it. If it had detected an apogee, an apogee and/or main chute should have blown. If the sustainer was on a timer, that wouldn't have made any difference. It still would have fired.

One needs to remember that MWP is an Indy launch so neither TRA of NAR are on the hook. Nonetheless, it's still poor form to have stuff like this happen at a major launch.

Actually there were two modroc two stagers staging into the ground on Saturday. Apparently was an estes rocket of the same type that fired the sustainer into the ground. It's like, "Why is that BP rocket taking so long to fire the sustainer?" Both times went into the ground.

I have witnessed some pretty hairy flights but it's a different matter when there are only 3 pads, 6 flyers and no spectators in attendance.

I will say one thing about an Easy Mega, it's small, very capable and would lend itself to a small project easily. Kurt

Loki Research said:

As explained to my by the flier, it seems a few things happened that prevented this from being a safer launch than what it was. He is a very good friend and I trust 100% what this he tells me, and yes, as David said the result disturbed him quite a bit. As they say, hind sight is 20/20 so it was good for him to discuss this. So the same should be true here.

My first thought, which he agrees with is that the 1st stage did not have enough thrust to get the rocket moving fast enough for the fins to provide stability. You can see the yellow tape blowing in the wind and when launched, the rocket seems to instantly weather cock and never recovers. (SNIP FOR BREVITY'S SAKE)

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Scott I witnessed the flight from the south and I thought weather cocking was when the rocket points into the prevailing wind? The winds were from the northeast so that would be on the right side of the screen. A scrap of paper or something blows by the lower left side of the screen from :06 to :08 seconds on the screen timer. The rocket was knocked downwind and simply did not have enough velocity to curve upwind. Looked grossly underpowered for the conditions.

Lesson learned: One may use simulation as a base but best to have some sort of intelligent electronics onboard at a large organized launch. Personally, my sympathy goes to the flyer. I'd feel terrible for a flight like that but no adverse event developed. Closest thing I had was a Starlord with three E9-6's bind on a rod, tear the rod out, tip over a 100 feet in the air and tear out over the launch range away from anyone at 5 degrees to the horizon. Actually elastic shockcord saved the rocket and the launch lug got a good reaming out. Kurt

One needs to remember that MWP is an Indy launch so neither TRA of NAR are on the hook.

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The national clubs may not be "on the hook" but the flier is very much on the hook. By having a membership in TRA or NAR, you agree that as a member, you will conduct yourself in a safe and responsible manner and above all else, you will follow the safety code.

If you are drag racing a HP rocket at less than 1/2 the distance set forth in the safety code, you are in violation.
If you are with a group of ~12 people watching said drag race from 1/4 the safe distance, you are in violation.
If you fly high power rockets at night without a waiver you are in violation.
If you intentionally break the waiver altitude, you are in violation.
If you drink alcohol and fly rockets or launch them, you are in violation.
If you are running said launch and knowingly do and/or allow things like this to happen, you are both in violation of your memberships safety code and you are responsible. You will be "on the hook" when something bad happens.

The TRA, NAR, or a local club could potentially be "on the hook" for not reprimanding club members and allowing them to keep their memberships and continue flying after they are made aware that a member has violated the safety code. If that member later injured someone, I could see liability there, even if it was not at a sanctioned launch.

Well said....and received...and thank you.

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You're welcome Jason. I hope the same goes for the above.

I don't like being "on the hook" for anything. This is probably a product of my chosen career for the last 16 years.

Kind of explains why I did some of the things I did when I used to be prefect/club prez.

Also explains why I make a point of not attending some launches - particularly "indy" ones. But that is completely and utterly my choice and not a criticism of any/all who do attend and orchestrate indy launches. I do what I think is right for me.

Egads I am off topic. We were talking about a 2 stage rocket that went awry - right? Thanks for the info Scott. That was enlightening. I don't think this was mentioned already but don't the Featherweight line of altimeters qualify as "smart?" I seem to recall them being able to detect flight angle and if it is over a certain threshold off of vertical it won't ignite the second stage...is that correct?

Loki Research said:

The national clubs may not be "on the hook" but the flier is very much on the hook. By having a membership in TRA or NAR, you agree that as a member, you will conduct yourself in a safe and responsible manner and above all else, you will follow the safety code.

If you are drag racing a HP rocket at less than 1/2 the distance set forth in the safety code, you are in violation.
If you are with a group of ~12 people watching said drag race from 1/4 the safe distance, you are in violation.
If you fly high power rockets at night without a waiver you are in violation.
If you intentionally break the waiver altitude, you are in violation.
If you drink alcohol and fly rockets or launch them, you are in violation.
If you are running said launch and knowingly do and/or allow things like this to happen, you are both in violation of your memberships safety code and you are responsible. You will be "on the hook" when something bad happens.

The TRA, NAR, or a local club could potentially be "on the hook" for not reprimanding club members and allowing them to keep their memberships and continue flying after they are made aware that a member has violated the safety code. If that member later injured someone, I could see liability there, even if it was not at a sanctioned launch.
You're welcome Jason. I hope the same goes for the above.

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All of your points are valid and well taken Scott even if independently insured, an adverse event would nail us all with increased costs or be completely unable to
afford coverage thereafter. Kurt

I think we just need to stop posts on this. I hope we all learned something from this and use info to keep this from happening again at the next launch. Thank God no one was hurt.

DAllen said:

I don't think this was mentioned already but don't the Featherweight line of altimeters qualify as "smart?" I seem to recall them being able to detect flight angle and if it is over a certain threshold off of vertical it won't ignite the second stage...is that correct?

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Nope. They can use velocity and altitude checks to not trigger ignition (as can the Missileworks RRC3 and the MARSA54) but can't directly sense flight angle.

Even a simple timer with an acceleration threshold like the Perfectflight miniTimer4 is safer than a g-switch based timer like the one used in this mishap -- the mT4 could detect low thrust off the pad.

I certainly don't want to make anyone feel bad, or ruffle any feathers.

I have never flown any HP 2 stage or air starts. It might be something for me to try in the future... and that's why I actually like this thread. I have learned a lot of new things so far.

I have learned that actually detecting tilt in a moving rocket is not as simple as you might think. >>> Link

I am thankful to those who have added thoughtful insight to this thread. Thanks!

I'd love to know more about the safe/smart or preferred methods for HP staging and air starts.

LW Bercini said:

I never suggested it be swept under the rug. I simply wanted to avoid the same kind of toxic discussion that occurred elsewhere. Yes, people provided very intelligent discussion this time. But let's face it, that is not always the case - even here on this forum.

I'd like to think that my comment might have even been a contributing factor in making this conversation a civil one.

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I'd absolutely agree. I'm sorry I suggested that's what you meant. I know it was more of an "oh god not another fight".

I've seen all too many of these go south as well. We've just got to fight to keep them on track.

crossfire said:

I think we just need to stop posts on this. I hope we all learned something from this and use info to keep this from happening again at the next launch. Thank God no one was hurt.

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I think the main thing to remember on threads like this is that it's not a crucifixion. It's education and discussion on how to prevent it in the future. No one is perfect. This year I had a chute ball up, a lil' rascal unstable on a G78BS, and I forgot to put BP in a motor for ejection and buried it into the dirt. I'm by no means perfect.

No one wants a failed launch. The discussion should simply focus on identifying the cause, and ways to prevent it. This discussion is good I think. It sucks it happened, but if we can all learn from it...it's a good thing.

scsager said:

I'd love to know more about the safe/smart or preferred methods for HP staging and air starts.

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Obviously making sure the design is stable and the thrust-to-weight ratio acceptably high, wind speeds low if required, rail long enough, etc, is the first step. Pre-launch safety (arming switches, shunts, etc) to insure motors don't ignite on the pad is critical.

For flight systems, in order of increasing safety:

1) use a timer with an acceleration threshold (Perfectflite miniTimer4, sort of -- though the threshold is fixed and not settable, I had misremembered that you could set it);

2) use a flight computer with settable velocity and/or altitude lockouts and set it appropriately based on the expected flight profile (Raven, MARSA54, RRC3);

3) use a flight computer with active tilt detection (EasyMega/TeleMega, Tiltometer+altimeter).

Unfortunately the only solutions for 3 so far are fairly expensive and/or complicated. It would be technically straightforward for something as simple as a miniTimer to include a three-axis MEMS gyro to be able to sense orientation. I hope somebody is working on this.

mikec said:

3) use a flight computer with active tilt detection (EasyMega/TeleMega, Tiltometer+altimeter).

Unfortunately the only solutions for 3 so far are fairly expensive and/or complicated.

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Expense is relative.

I'd love to see some guidance from TRA and/or NAR on this. Technology has advanced such that a launch and failure as shown are easily avoided.

Let's learn from this. No more timers, more safety. More scrutiny on complex launches. It's good for everyone.

mikec said:

Obviously making sure the design is stable and the thrust-to-weight ratio acceptably high, wind speeds low if required, rail long enough, etc, is the first step. Pre-launch safety (arming switches, shunts, etc) to insure motors don't ignite on the pad is critical.

For flight systems, in order of increasing safety:

1) use a timer with an acceleration threshold (Perfectflite miniTimer4, sort of -- though the threshold is fixed and not settable, I had misremembered that you could set it);

2) use a flight computer with settable velocity and/or altitude lockouts and set it appropriately based on the expected flight profile (Raven, MARSA54, RRC3);

3) use a flight computer with active tilt detection (EasyMega/TeleMega, Tiltometer+altimeter).

Unfortunately the only solutions for 3 so far are fairly expensive and/or complicated. It would be technically straightforward for something as simple as a miniTimer to include a three-axis MEMS gyro to be able to sense orientation. I hope somebody is working on this.

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^+1. But 2 of the 3 would be good practice.

For the flight in question:

1. An altitude lockout would have prevented the command to fire the second stage.
2. An altimeter with an acceleration launch detect would have deployed the laundry making the rocket just flail around when the motor lit.

A tiltometer would not guarantee prevention of this failure. A tumbling rocket could be pointing up when the command to fire is programmed but could be pointing down when the motor actually decides to light.

jderimig said:

^+1. But 2 of the 3 would be good practice.

For the flight in question:

1. An altitude lockout would have prevented the command to fire the second stage.
2. An altimeter with an acceleration launch detect would have deployed the laundry making the rocket just flail around when the motor lit.

A tiltometer would not guarantee prevention of this failure. A tumbling rocket could be pointing up when the command to fire is programmed but could be pointing down when the motor actually decides to light.

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+1. The majority of cases are covered by the altitude/time or velocity/time checks. As John states even a Tiltometer can be fooled. You could also add a #4 to the list, namely, a remote lock out or ignition which I am using in a couple of future projects.

I'm not an HP flyer, so I don't have a sense of whether there is a consensus or conclusion.

But assuming there is, let me "call the question"

Throughout my career in software development, I have attended a plethora of post-implementation reviews. This is where a bunch of people sit around and talk about what should have been done differently. About 10 years ago, I stopped attending them. Why? Because I saw it as an empty exercise. The follow-up steps to change the process and to change the behavior were never done.

Is this discussion going to be another empty exercise?

Or is somebody actually going to propose changes to safety regulations?

Is somebody going to contact TRA and NAR?

I personally do not know what the procedure is to propose rules changes. If one of you folks do, can you take a leadership role and make sure this discussion leads to positive changes -- Before a serious accident or injury?

jderimig said:

A tiltometer would not guarantee prevention of this failure. A tumbling rocket could be pointing up when the command to fire is programmed but could be pointing down when the motor actually decides to light.

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True. Still though, I believe the Tiltometer would be one of the best options, if it or a similar device ever came back into production. Yes, a lengthy delay in the motor, having been lit but slow to come to pressure, could fool a tiltometer. But typically, and definitely in this case, the instability presented itself very early in the flight, certainly before the intended ignition of the sustainer. If the tiltometer at any time exceeds the preset angle deviation from vertical, it subsequently and forever blocks the sustainer ignition circuit. So only a very specific late instability (occurring after sustainer ignition commanded) combined with a slow lightoff would be problematic. In that case, the sustainer would most likely be at a higher altitude, which makes the crowd a smaller target. One of the factors that made this flight significant for discussion is the up close and personal view we got from the low altitude of the sustainer's ignition. IMHO, this flight was heart-of-the-envelope perfect for a tiltometer to showcase its talent.

LW Bercini said:

I'm not an HP flyer, so I don't have a sense of whether there is a consensus or conclusion.

But assuming there is, let me "call the question"

Throughout my career in software development, I have attended a plethora of post-implementation reviews. This is where a bunch of people sit around and talk about what should have been done differently. About 10 years ago, I stopped attending them. Why? Because I saw it as an empty exercise. The follow-up steps to change the process and to change the behavior were never done.

Is this discussion going to be another empty exercise?

Or is somebody actually going to propose changes to safety regulations?

Is somebody going to contact TRA and NAR?

I personally do not know what the procedure is to propose rules changes. If one of you folks do, can you take a leadership role and make sure this discussion leads to positive changes -- Before a serious accident or injury?

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Is this a masturbatory exercise? Possibly. Will the national organizations actually change the rules? Well they did change the drag race rules...so, possibly. (of course some people still ignore those rules......we won't get into that here.)

Even if that doesn't happen.... at least two people here planning two stagers have changed their plans. How many sleepers present and future will see this and do the same. That's enough for me to say we need to keep threads like this going.

As for regs.... I'll toss an email out tomorrow and see what reply I get. I'll share it back here. My vague suggestion will be that two stage composite flights be required to use electronics capable of locking out ignition of the second stage under sub-optimal launch conditions.

As a new builder with big ambitions and who personally witnessed this flight I will never forget this or the suggestions in this thread. Any 2 stage MPR or HPR I build will be staged with smart electronics.

LW Bercini said:

Is this discussion going to be another empty exercise?

Or is somebody actually going to propose changes to safety regulations?

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Why does it have to be written down in the safety code to not be an "empty exercise?" More regulation is not always necessary or appropriate.

CAR has had a recommendation to have some form of staging safety on the books since 2005. See https://www.canadianrocketry.org/news.php?topic=15

In response to some events this past year and in general, the higher risk from higher impulse multi-stage rockets, the CAR is endorsing a recommendation from the RSO Committee that any multi-stage flight with an installed impulse greater than 160Ns must be equipped with a device that will disable subsequent stage ignition in the event of a non-nominal boost phase.

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but all of the devices that they mention failed to materialize AFAIK, and this has remained a recommendation.

Making everyone who flies staged HPR figure out how to use one of the available solutions is simply not feasible IMHO. What we really need is a simpler, cheaper solution.

mikec said:

Making everyone who flies staged HPR figure out how to use one of the available solutions is simply not feasible IMHO. What we really need is a simpler, cheaper solution.

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Cost is irrelevant to safety. Feasible options exist. Ravens and RRC3's are capable and not really cost prohibitive anyways. They're not perfect, but much better than just tossing a timer in. Requiring that isn't really outrageous.

If you don't want to go through that.... don't stage.

mikec said:

Why does it have to be written down in the safety code to not be an "empty exercise?" More regulation is not always necessary or appropriate.

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You missed my point about "empty exercise" Doing forensic analysis of an event without affecting any lasting results is essentially worthless.

As I said, I am not an HP flyer and I don't know what is a process for getting the word out to people. My point was simply a "call to action". I don't know if that means a change to regs, more education, better tools. I don't know. But if there is any desire to prevent future events like this one, it requires more than omphaloskepsis on a rocketry forum.

DizWolf said:

,,,. at least two people here planning two stagers have changed their plans. How many sleepers present and future will see this and do the same. That's enough for me to say we need to keep threads like this going. .

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True. But how is Joe Schmo RSO in Piccolo New Mexico going to hear about such best practices? Of course we all know that not all rocket folks participate in this forum. What needs to be done so that Joe Schmo out in the rocketry hinterlands knows if and when to question a multi-staged flight like this one? What action needs to be taken to make the knowledge collected here, out to the greater rocketry population?

DizWolf said:

As for regs.... I'll toss an email out tomorrow and see what reply I get. I'll share it back here. My vague suggestion will be that two stage composite flights be required to use electronics capable of locking out ignition of the second stage under sub-optimal launch conditions.

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Thank you. Thank you. You stepped up to take an action. People like you do get my point.

Ah, drama...
Happy Veteran's Day, everyone!

stealth6 said:

DizWolf is absolutely spot-on here.

I for one would really like to know what went wrong here, so that I can AVOID the same problems myself. Having just recently started flying multi-stage HPR, any and all information on how to do it right is extremely beneficial - and how to avoid doing it wrong is even more so. I'd be very interested in more details about this flight - configurations/setup/avionics/pre-flight prep/etc.

s6

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DizWolf said:

It's what I suspected, but I'd rather verify.

I'm also building a two stage, and the temptation to use a timer is very high. So I understand. 95% of the flights that go as planned...no issue. But if anything does go wrong you're screwed. With the availability of systems with checks.... it's a better way to go I think. Nothing is fool-proof, but finding the best way to minimize risk is good.

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I don't think anyone did wrong based on their knowledge of flight dynamics and flight simulations, however I think that TRA and NAR need to do a better job in educating RSO and HP flyers on flight dynamics and the limitation of hobby grade flight simulation programs.

The root cause of this incident was a lack training and awareness within the hobby concerning the minimum rod velocity needed to counteract the destabilizing effect of crosswinds on short, stubby and long, skinny rockets, and an unholy belief that simulations are always correct when predicting stability.

1. What is not well known is that the rod velocity needs to be at least 4 times the crosswind velocity to insure that severe weather-cocking, or in the worst case spinning or looping above the pad, will not occur.
   • The increased rod velocity prevents the fins from stalling by keeping the angle of attack of the fin to less than 15 degrees.
     • The "typical" rocket will usually weather cock badly in high cross-winds before it stalls but,
     • Short, fat base drag stabilized rockets can spin rapidly above the pad when the fins stall while under power, and
     • Long, skinny rocket can loop slowly when they stall under power.
2. With a standard length rod, this means that the T/W weight ratio should be equal to the wind speed in mph.
   • You can use a longer rail, but the lengths become excessive well below the 20 mph crosswind limit.
3. Sims tend to handle "typical" rockets ok under most wind conditions but
   1. usually underpredict the stability of a fat, stubby rocket in low to moderate winds, and
   2. usually overpredict the stability of long, skinny rockets in moderate to high winds.
4. The ways to correct a sim for more accurate results for both kinds of rockets has be described in the Apogee Newsletter, TRF, and the technical literature, but since it is not incorporated into sims, it is not well known, and infrequently implemented.
5. Since 1.) and 2.) are not widely known, the RSO training and checklist does not include a check for increasing the T/W ratio with increasing wind velocity.
6. AFAIK L/D checks for short, stubby rockets and long skinny rockets are not incorporated into sims, so flags indicating potential instabilities above a threshold wind velocity are not raised so the average sim user is unaware that their "stable" rocket may actually be unstable in the wind condition at the time of launch.
7. In the case of 2-stage rockets, timers are often used to ignite the sustainer at some time after lift-of, and the time is often chosen to provide a second or two delay from booster burnout to allow for drag separation to prevent damage to the booster.
8. The sustainer will decelerate at > 1g during this coast phase, but is generally set to insure that the rocket velocity is high enough so the sustainer stays well above the minimum airspeed to maintain aerodynamic stability.
   • If this speed is determine to be 30 mph under normal conditions, using the x4 rule it should be 120 mph in a 20 mph cross-wind.
   • A coast time that is adequate in a 5 mph wind will be excessive in a 20 mph crosswind due to angle of attack issues.

My analysis of this and other troubled flights indicates that more educations and training is required, and an expanded RSO check list would go a long way to reduce the occurrence this type of unstable flights.

Bob

I would like to thank the participants of this discussion for keeping it reasonably civil, as I plan to eventually progress to doing multi-stage HPR flights. The discussion here has actually pointed out a number of faults and their possible fixes.

I like this idea of raising awareness regarding launch velocity / crosswind sensitivity.

Bob's comments are very helpful but boy oh boy, it really seemed like that rocket was going waaaaaaaaaay tooooo slow and was underpowered.
I wonder if it had ever flown before in that same configuration on a calm launch day or was it the first flight? It really looks like it wouldn't have been any more stable if the launch rail was twice as long.
Get that puppy going fast in a hurry so it will buck the wind in a stable fashion.
Ahhhhh, another comment. I still can't figure out way folks angle the rods/rails so much into the wind? I saw some serious upwind angles out there. It only aggravates the weather cocking situation and if one has plenty of room, use a few degrees "DOWNWIND". Play with your sims and you'll see the rocket will curve to apogee and will be at a lower speed for deployment of the recovery laundry. I've been doing this and it has drastically cut down on the mini-tears/zippers in the cardboard body tubes. I mean if one has to avoid drifting on someone else's land O.K. but upwind angles and some degree of weather cocking leads to higher velocity at deployment. Doesn't matter whether it's motor ejection or dual deploy. If the rocket is traveling at high speed when the shockcord is deployed, there's going to be stress. Kurt

Really good discussion on the cross wind effect. It looked like this flight initially turned down wind. Would not cross wind instability generally start with an up wind turn? Maybe T/W was so low the wind never came into play.

Not necessarily.

As a rocket weathercocks into the wind, the apparent wind speed increases, quickly reducing the angle of attack towards zero. Although the flight is angled, the rocket is stable.

If a rocket turns downwind, the opposite happens. The apparent wind speed decreases, and the angle of attack increases until the fins stall. Then the rocket becomes aerodynamically unstable and inertial forces take over. The angular momentum of the rocket about the center of gravity sustains the rotation while the motor thrust pushes it forward. Eventually if the rocket has sufficient altitude the rotation will begin to point the rocket down increasing apparent wind speed and reducing the angle of attack. The angular momentum is not damped at low speed to the rocket will continue to rotate and eventually the begin to accelerate as it turns into the wind, increasing the apparent wind speed without increasing the speed over the ground. Angle of attack on the fins are being reduced but the angular momentum is not damped because the apparent wind is not constant in direction and eventually the rocket will complete the first 360 degree rotation and start the second one. The rocket is likely to continue to loop until the motor burns out and a single stage rocket will eventually drop out of the sky.

In the case of a two-stager, the rocket may, or may not, be in the air when the timer ignites the motor, but the rocket will accelerate quickly upon sustainer ignition because the sustainer weight is much lower without the booster. It is likely to become stable quickly but it could go in any direction.......

Bob

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

patelldp said:

Expense is relative.

I'd love to see some guidance from TRA and/or NAR on this. Technology has advanced such that a launch and failure as shown are easily avoided.

Let's learn from this. No more timers, more safety. More scrutiny on complex launches. It's good for everyone.

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ksaves2 said:

I will say one thing about an Easy Mega, it's small, very capable and would lend itself to a small project easily. Kurt

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Who makes the Easy Mega?