trying to understand how the rules work:)

Lt72884

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My team did a lvl 1 flight today and one of the rockets didnt pass due to excessive damage, but the damage was minor and im not sure how it failed cert. The rocket can fly again easily. Here is an image of the damage. It flew with a H550 and a 14 second ejection delay. Now, im not slamming the committee who said it failed, i just want to understand so that next week our level 2 we dont run into issues.

687558566.jpg
 

smstachwick

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It must return undamaged.

Some witnesses presiding over disputed cases, in which the damage is so minor that the rocket is claimed to still be airworthy, will reply with “alrighty then, hook it up to the pad again and prove it.” More HPR flights and more experience before going to more ambitious projects is always a good thing, anyway.
 

Worsaer

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The purpose of a cert flight is to demonstrate your understanding of all aspects of a safe flight. If you simmed it properly it likely would not have suggested a 14 second delay. What you‘re showing is not minor damage. The rocket clearly needs serious repairs before being flown again.

Don‘t leave it to chance. Simulate the flight with the specs of your rocket when it’s fully prepped for flight.
 

Scott_650

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I’m with modeltrains - is this an “ironic” post? I’m not much of an internet irony guy - way too easy to miss the cues..

But if the original post is serious there’s no way our club LCO would let this fly and no way any of the L2/3 mentors in our club would have given this a passing L1 cert - a zipper that big means the flyer got the delay wrong, besides the level of damage, that clearly demonstrates a lack of L1 experience.
 

smstachwick

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I’m with modeltrains - is this an “ironic” post? I’m not much of an internet irony guy - way too easy to miss the cues..

But if the original post is serious there’s no way our club LCO would let this fly and no way any of the L2/3 mentors in our club would have given this a passing L1 cert - a zipper that big means the flyer got the delay wrong, besides the level of damage, that clearly demonstrates a lack of L1 experience.
Oh well. That’s part of why we have these certification flights, it’s a way of gaining experience under more careful supervision to avoid creating excessive hazard. I say we be patient with the OP. Plenty of students and the like jump directly into HPR, we owe them the opportunity to learn without snark.
 

Lt72884

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The purpose of a cert flight is to demonstrate your understanding of all aspects of a safe flight. If you simmed it properly it likely would not have suggested a 14 second delay. What you‘re showing is not minor damage. The rocket clearly needs serious repairs before being flown again.

Don‘t leave it to chance. Simulate the flight with the specs of your rocket when it’s fully prepped for flight.
we did sim it, about 15 times and all was well. We were recommended a 14 second delay:) we launched 4 rockets all of ther same type and motor and specs. this is the only one that got damage. Open rocket on this motor with a 14 second delay also states no errors or issues
we are in the process of fixing this.
 

Lt72884

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I’m with modeltrains - is this an “ironic” post? I’m not much of an internet irony guy - way too easy to miss the cues..

But if the original post is serious there’s no way our club LCO would let this fly and no way any of the L2/3 mentors in our club would have given this a passing L1 cert - a zipper that big means the flyer got the delay wrong, besides the level of damage, that clearly demonstrates a lack of L1 experience.
this is our first l1 flight and 4 of the 5 passed with the exact same settings. so its a mystery to us haha
We are in the process of fixing it. not to hard to fix this.
 

smstachwick

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we did sim it, about 15 times and all was well. We were recommended a 14 second delay:) we launched 4 rockets all of ther same type and motor and specs. this is the only one that got damage. Open rocket on this motor with a 14 second delay also states no errors or issues
we are in the process of fixing this.
Alright.

Go for the cert again. Reinforce the end of the tube, maybe stick two bits of tape to the cord where it goes through the opening to create more surface area and reduce the cutting force on the tube. Also consider lengthening the shock cord. All this will help if you somehow get a delay that burns too long or too short.

Maybe also verify your drag coefficient, double-check your liftoff and burnout mass, etc. The simulator is only as good as the numbers you throw at it.
 

Lt72884

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Oh well. That’s part of why we have these certification flights, it’s a way of gaining experience under more careful supervision to avoid creating excessive hazard. I say we be patient with the OP. Plenty of students and the like jump directly into HPR, we owe them the opportunity to learn without snark.
yeah, 4 of the 5 passed, just this one didnt. Its been a learning curve for sure. not sure why open rocket states the 14 second delay is good and we were recommended it as well. so im not sure what happened with this rocket
 

Lt72884

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Alright.

Go for the cert again. Reinforce the end of the tube, maybe stick two bits of tape to the cord where it goes through the opening to create more surface area and reduce the cutting force on the tube. Also consider lengthening the shock cord. All this will help if you somehow get a delay that burns too long or too short.

Maybe also verify your drag coefficient, double-check your liftoff and burnout mass, etc. The simulator is only as good as the numbers you throw at it.
Oh yeah, he is going for it again in a week or 2. I was thinking of a 25 foot cord and a little thicker to obsorb energy.
the tape idea is good. I will pass this to him.
all the numbers are correct but whats odd, the rockets took off at super speeds rather than 0.5 mach as the sim states haha. I will double check the numbers again though, i may think they are correct but ill check again. maybe i missed something
thanks
 

Lt72884

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Ok, I stand corrected. If you can learn why it zippered you may be able to avoid it in the future. Sometimes things just don’t go as expected.
i have some guesses. Maybe the shock cord somehow got glued to a small portion of the tube, the cord was to short, the motor didnt eject at 14 but maybe 15 or 16, or his coasting velocity was shorter due to more drag. it was a naked rocket so maybe had more drag than normal.
or, my team has forgotten to mention something to me haha
oh and the fact that maybe some numbers in OR could be wrong and i missed soemthing. so many things hahaha
 

Lt72884

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my level one was with a 14 second delay which was way too long and ripped the parachute out. So I used the exact same motor and went down to nine seconds and it popped right out at apogee.
interesting. very interesting. Im goign to have a team metting with my group. I want to figure this out. I can see how and why you all say 14 seconds is to much but what i dont get is why OR says its good, and why other rockets passed. Its all fixed though so we will try again.
 

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That is not an easy fix to do correctly, that tube is now shot and must be cut out/replaced. Since that is the case, there is no way this should have passed certification - It is not reflyable as is. Use this to learn - delay was wrong, shock cord too short, something, but this is trying to teach you something - learn from it.
 

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That definitely is too much damage to fly again. A small zipper (like an inch or two) is arguable, but not that.

Look for differences between the various rockets. You mentioned same kit and motor, but are they all roughly the same weight?
 

Lt72884

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How long after apogee was it when ejection happened in real life?

What delay time did OpenRocket actually suggest?
this i do not know. Ill ask if one of them was counting haha.
my guess is since his rocket was not painted and just naked, it had more drag which in turn shortened the coasting time so it started to fall after apogee and zippered
 

Lt72884

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That definitely is too much damage to fly again. A small zipper (like an inch or two) is arguable, but not that.

Look for differences between the various rockets. You mentioned same kit and motor, but are they all roughly the same weight?
FACTS!!! i was just asking my team this. his rocket that zippered was naked and not painted. i think it had more drag and more mass somewhere hence lower coasting velocity etc etc

thanks for bringing this up
 

smstachwick

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FACTS!!! i was just asking my team this. his rocket that zippered was naked and not painted. i think it had more drag and more mass somewhere hence lower coasting velocity etc etc

thanks for bringing this up

If that’s the case, I’d double-check your settings in the sim. Finish makes a difference and OR supports a bunch of options for that. If you had it set to Polished and flew it Rough, you’re going to be in trouble.

You can’t fool nature by cheating in the sim (even accidentally). I learned this the hard way with a two-stager that turned out to be unstable in the full stack but fully stable with the sustainer only. I was fortunate that nobody got killed.

My first flight was my repaired and prettied-up Super Hi-Flier. It got burned and banged up pretty bad at LDRS, but it was fully repaired and given a few coats of paint (the latter courtesy of my girlfriend, who very kindly offered her skilled hands for the job).

View attachment 532726

I wish I had gotten video of this flight, which went on a B6-0 / B6-6 stack. Clearly my nose weight was insufficient, as the thing pitched to a shallow nose-down angle about 100 ft off the pad, staged, then became stable and shot itself south of the access road. I thought I had lost it until another attendee spotted it and helped me track it down.

View attachment 532727

It impacted at a moderate angle and a high velocity, possibly under power, hitting fin-first and also scraping up the nose. Only one small fragment of the impacted fin was recovered.

The nice thing is that the rocket is still pretty quick off the pad, I think a bit of nose weight should be doable. I’m definitely doing my homework on the CG next time though, not just relying on Estes’s built-in idiot-proofing that had served me so well prior to this mishap.
 

krislhull

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we did sim it, about 15 times and all was well. We were recommended a 14 second delay:) we launched 4 rockets all of ther same type and motor and specs. this is the only one that got damage. Open rocket on this motor with a 14 second delay also states no errors or issues
we are in the process of fixing this.
When you ran the sims, did you have accurate data for the launch site? I cannot remember what the default is openrocket, but it is always a good idea to run the sims with accurate launch site data selected. Use the known field elevation, and then for temperature and pressure, you can look at forecasts and get a good estimate on those. Field elevation will have a decent impact on a simulation
 

smstachwick

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When you ran the sims, did you have accurate data for the launch site? I cannot remember what the default is openrocket, but it is always a good idea to run the sims with accurate launch site data selected. Use the known field elevation, and then for temperature and pressure, you can look at forecasts and get a good estimate on those. Field elevation will have a decent impact on a simulation
It’s set to the SpaceX site on the Texas Gulf Coast on my install.
 

Lt72884

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That is not an easy fix to do correctly, that tube is now shot and must be cut out/replaced. Since that is the case, there is no way this should have passed certification - It is not reflyable as is. Use this to learn - delay was wrong, shock cord too short, something, but this is trying to teach you something - learn from it.
oh yeah for sure. hence why i asked. wanting to find out all possibilities of what happened. This way we can learn for next launch. Yeah we are cutting out that section or replacing with a spare we have. Not to tricky but yet it is. Its simple in the idea of cutting or replacing:) not simple like "yeah, we taped it and are trying again hahaha" though i wonder if duct tape would work hahahahaha im kidding of course.. i think
 

krislhull

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If that’s the case, I’d double-check your settings in the sim. Finish makes a difference and OR supports a bunch of options for that. If you had it set to Polished and flew it Rough, you’re going to be in trouble.

You can’t fool nature by cheating in the sim (even accidentally). I learned this the hard way with a two-stager that turned out to be unstable in the full stack but fully stable with the sustainer only. I was fortunate that nobody got killed.
THIS...

I actually nearly did not attempt my L3 flight last month due to overlooking settings like this. I had the finish of my rocket set to "polished" for some reason, and when I changed it to "matte", the simulations were showing an estimated altitude of over 1000ft lower, and well within our waiver. I also had the launch site settings set to a different field, and the sims got even better when I changed them to the lower elevation of the field I eventually flew at.
 

krislhull

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oh yeah for sure. hence why i asked. wanting to find out all possibilities of what happened. This way we can learn for next launch. Yeah we are cutting out that section or replacing with a spare we have. Not to tricky but yet it is. Its simple in the idea of cutting or replacing:) not simple like "yeah, we taped it and are trying again hahaha" though i wonder if duct tape would work hahahahaha im kidding of course.. i think
There is a trick that could be done using duct tape to help alleviate zippers in the future, but I would not use it to repair one
 
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