trying to understand how the rules work:)

[T-Rex]

@Lt72884: Re-check your simulations. You have ignored the 2 posts where it was pointed out that a LOC-IV with an H550 gives an optimum delay less than 14sec. I just ran it myself and agree.
I realize we are just stupid old people, and y'all have all the answers (I was there myself a couple decades ago), but listen to the advice given.
I'm glad you finally accept that the rocket was not safe to fly in it's pictured condition, But analyses is required so y'all understand what happened, so you don't repeat it. (Hint: has NOTHING to do with surface finish)

 

[bobbyg23]

all 5 kits are the LOC IV, all motors were the same, H550-14. His rocket was hte only one flown naked and not painted, which i think was the problem. It had more drag and the delay that worked for us did not for him

H550 on the LOC 4 should have about a 10 second delay max. How heavy were your rockets?

 

[Alan15578]

well, we did just hire 2 witches, a preist and a cleric to help us out... lets see how this goes

You might be on the right track there, but initially you wanted the HPR equivalent of a Pink Book Lawyer.

 

[Terry Dancer]

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.

View attachment 541930

You’re joking right??? That’s like what? An 8” zipper??? That’s 110% a fail.

 

[bobbyg23]

correct, we have owned it and thats why i said im not slamming the committee but we need to understand the rules and why its deemed catastrophic so that we can learn and fix this rocket for the next flight. I have now learned some things from some searches and others who are RSO's. its catastrophic because if we were to put a new H550 in it, it would be destroyed on flight. This makes sense to me now. I was under the impression from some others that to get lvl 1 it goes up, and must come down safely and be recovered. We were not told that in order to pass, it had to be able to fly again immediately.
in one of my earlier posts on this thread, i mentioned that the rocket that failed was not painted or smooth. it was rough, therefore causing drag, and so you are correct, this rocket was not the same

The lack of paint has no impact on this rocket. At least not enough to make any difference.

 

[Sandy H.]

Only somewhat related, but I went to a launch today and heard that a group of college students were there on Saturday to do their L1 certs. They were choosing the H550 as well. Is there some college challenge going on nation-wide that is driving the choice for the H550 as the motor of choice for beginner college L1 attempts. I've honestly never flown one. I got my L1 on an H97, L2 on J350 and largest motor I've flown to date was a K1100.

I think most of the L1 attempts I've seen over the years were on an H128. H550 is a much more aggressive and higher impulse motor. Just curious why people are choosing that for L1 attempts if they are in a college program.

Sandy.

 

[rharshberger]

Only somewhat related, but I went to a launch today and heard that a group of college students were there on Saturday to do their L1 certs. They were choosing the H550 as well. Is there some college challenge going on nation-wide that is driving the choice for the H550 as the motor of choice for beginner college L1 attempts. I've honestly never flown one. I got my L1 on an H97, L2 on J350 and largest motor I've flown to date was a K1100.

I think most of the L1 attempts I've seen over the years were on an H128. H550 is a much more aggressive and higher impulse motor. Just curious why people are choosing that for L1 attempts if they are in a college program.

Sandy.

My guess is its the H550ST DMS motor, most the college programs we see use DMS motors which helps increase successful certs, and prevents others in the group from getting to cert if the hardware is destroyed on a cert (many times we have seen college teams only have one set of hardware for the fliers to use, if it gets lost or destroyed everyone else is done). As for the H550ST its a cool motor but as Sandy asked...why, there are a number of better H motors in the DMS line to use for certs and that are more forgiving. If the delay was off as much as some are pointing out from their sims, then its lucky ANY of your team passed, a 4 second too long delay coupled with a + or - 3 second motor cert allowance for the delay, AND the seeming propensity for AT delays to be slightly long...you people got lucky.

 

[Sandy H.]

My guess is its the H550ST DMS motor, most the college programs we see use DMS motors which helps increase successful certs, and prevents others in the group from getting to cert if the hardware is destroyed on a cert (many times we have seen college teams only have one set of hardware for the fliers to use, if it gets lost or destroyed everyone else is done). As for the H550ST its a cool motor but as Sandy asked...why, there are a number of better H motors in the DMS line to use for certs and that are more forgiving. If the delay was off as much as some are pointing out from their sims, then its lucky ANY of your team passed, a 4 second too long delay coupled with a + or - 3 second motor cert allowance for the delay, AND the seeming propensity for AT delays to be slightly long...you people got lucky.

Ah. Totally missed that it was a DMS, but that makes sense for group projects from some perspectives, I guess. But, as you mention, it seems there are more forgiving DMS motors for newer fliers.

Thanks for pointing out the DMS aspect.

Sandy.

 

[rharshberger]

Ah. Totally missed that it was a DMS, but that makes sense for group projects from some perspectives, I guess. But, as you mention, it seems there are more forgiving DMS motors for newer fliers.

Thanks for pointing out the DMS aspect.

Sandy.

The H550ST is one of the few (maybe only) DMS motors that is also available as a RMS reload, it would be easy to miss that unless you either fly them or see them an awful lot at the preflight safety checks. I like punchy motors in small rockets for myself, love W9 and Vmax's.

 

[smstachwick]

I would think that the H283ST would be more popular, given its not-quite-as-excessive thrust and lower total impulse that’s more suitable for a risk-averse certification attempt.

 

[user 30299]

Please stop beating this

View attachment 541981

Short and to the point.

 

[Tractionengines]

My GUESS for the reason behind tye H550 is the following from a few comments : They got the model onto OR, and kept changing motors till they find one that "worked" with the supplied delay. They don't know the Universal Delay Drilling Tool will allow them to adjust delays of DMS motors. They won't post their OR file for us to see why OR thought 14sec was optimal, when everyone here with SIMs think 9-10 seconds is more realistic.

Their capstone committee and mentor all sound like inexperienced observers, not people actively involved in the Rocketry Hobby themselves. His comments in another thread were that the class proffessor/mentor was a maybe L1 from years ago, and would be working on L2 /L3 too.

[ I could be off, but I have followed these threads from this "team", and I don't think there is much HRP experience or exposure. We all started somewhere, but this team really needs a skilled mentor who can guide them to better solutions. (NOT GIVE them the answers, but steer the conversations.) ]

 

[Hobie1dog]

They won't post their OR file for us to see why OR thought 14sec was optimal, when everyone here with SIMs think 9-10 seconds is more realistic.

Exactly, 14 seconds is just too long for 75% of the rockets out there.

 

[boatgeek]

Only somewhat related, but I went to a launch today and heard that a group of college students were there on Saturday to do their L1 certs. They were choosing the H550 as well. Is there some college challenge going on nation-wide that is driving the choice for the H550 as the motor of choice for beginner college L1 attempts. I've honestly never flown one. I got my L1 on an H97, L2 on J350 and largest motor I've flown to date was a K1100.

I think most of the L1 attempts I've seen over the years were on an H128. H550 is a much more aggressive and higher impulse motor. Just curious why people are choosing that for L1 attempts if they are in a college program.

Sandy.

My guess is its the H550ST DMS motor, most the college programs we see use DMS motors which helps increase successful certs, and prevents others in the group from getting to cert if the hardware is destroyed on a cert (many times we have seen college teams only have one set of hardware for the fliers to use, if it gets lost or destroyed everyone else is done). As for the H550ST its a cool motor but as Sandy asked...why, there are a number of better H motors in the DMS line to use for certs and that are more forgiving. If the delay was off as much as some are pointing out from their sims, then its lucky ANY of your team passed, a 4 second too long delay coupled with a + or - 3 second motor cert allowance for the delay, AND the seeming propensity for AT delays to be slightly long...you people got lucky.

I've seen that too, and I'm guessing there's a dark cabal of people pushing the very high thrust motors. More seriously, I think there's a "take it to the max" kind of reasoning behind it. More thrust means less weathercocking (in general), which means less horizontal velocity at deployment, and can mean a shorter walk. All of those things are good things, and why I might recommend an H in the 150-200N range for a cert flight. College students tend to want to optimize (I know, I was there myself), so if 50N is no good and 200N is good, then 550N must be better. Plus loud noise is good, a rule my chemistry prof lived by.

There's another possible reason that if you're going to use the same rocket for L1 and L2 certs, you might want to really whack it with the H motor to do a stress test. If it's going to come apart, better on the H than the J.

All of that said, I don't think there's really that much more risk of getting the delay wrong on an H550 than an H87 or an H283. Any way you fly it, you'll have to adjust delays, especially if it's a combo L1/L2 rocket.

 

[wsume99]

@Lt72884 - I appreciate you and your team's eagerness to learn and your ambition to complete the capstone project. I've seen enough in this post to conclude that the 4 members of your team who certified got very lucky. Congratulations to them however the part that concerns me greatly is they will now progress on to using more powerful motors that they clearly should not be. Certification should be given based on a demonstration of skill and knowledge, not blind luck.

PLEASE, PLEASE, PLEASE listen to the advice already given to find an ACTIVE AND EXPERIENCED flyer to serve as your team's mentor. With the proper guidance from a mentor you and your team can be successful. In fact, I would say that this is the single most important element that will contribute to your team's success. Your team does not have enough time to accumulate the necessary knowledge and experience to ensure a successful L3 flight. If you want to be successful then you'll need a mentor. There is no other option, unless you hope to keep getting lucky. Hope is not a good strategy in my opinion.

 

[tsmith1315]

Any way you fly it, you'll have to adjust delays, especially if it's a combo L1/L2 rocket.

This is the bottom line.

And given they’re going towards L3 with a minimum number of flights, it would be a good idea to go ahead and implement electronic deployment on the L2 flight.

Better to address that learning curve with smaller rockets.

 

[David Schwantz]

My club flies a lot of college teams. In fact at the last launch they picked motors from our vender. If I am not mistaken, it was 50 H550ST's. They wanted to buy 50 sparky motors at first, but our field will not allow sparky motors if it is to dry out. This coming weekend, again I think, we have 40 L1 cert flights

 

[FredA]

Certification should be given based on a demonstration of skill and knowledge, not blind luck.

To the OP - do you feel that your flight accomplished a demonstration that you've mastered the necessary skills and knowledge?

 

[Grog6]

We're 4 pages in, and I haven't seen a single helpful post that informs WHY this is a fail. A zipper is thisclose to detaching the recovery system from the airframe, and endangering members of the public. Think of any major piece of your rocket that detaches at apogee, and burns in. Anything that gets dangerous to the Public gets banned. Try to buy a chemistry set, or a pair of lawn darts. Tripoli and NAR are providing insurance for us for following the rules; as the risk of damage increases, so does the level of responsibility. The certification process is the natural progression of this need for responsibility.
yes, this ignores the members of the staff, but they should have enough sense to look up, lol. That's why you get experienced people to work events.
The only thing that keeps this hobby alive is being risk adverse, and keeping the public at large from thinking we're a bunch of whackos reliving the v2 attacks on London.
I'll admit, I joined Tripoli because I was interested in making rocket motors. I used to to a lot of chemistry, and apcp motors seem to me to be a lot safer than the old ways.
In the course of learning urethane chemistry, and a whole bunch of organic chem, I realized just how bad it could go wrong working with these compounds, either as a mix, or a finished motor.
The thing I've learned over life is that the more energy involved, the worse it is when it goes bad. This includes all forms of energy, kinetic, chemical, pressure, temperature, all can bite you hard. And our entire world is one of unintended consequences.

I had a colleague learn that LN2 will collect O2 out of the air, and a magnet will pull droplets of it out of the ln2.
Anything oily burns in LNo2. See why they say "No food in labs"?

Doing 140 down the interstate feels great, until your ponytail comes out of your leathers, lol. or you hit something; Newton is unforgiving.

 

[kramer714]

Ok, a bunch of things to unpack here, First of all a little background. I'm a Level 3 (NAR and Tripoli) , a NAR L3CC and have personally been involved with over 40 level 1 (mostly Jr level 1 but same criteria) using cardboard / plywood rockets.

So lets hit these one at at a time,

A) If the zipper is anywhere near the length of the nose cone shoulder, I consider that a fail. Um, this is pretty far down the tube hardly a minor repair. I seriously doubt that anyone would say this was a passed flight. I would not. Pass or fail is a seperate question from what went wrong.

B1) When you mentioned 14 second as the delay time before i read any further I thought - that cant be right gotta be like 10 seconds or so (see B2)
B2) Very quick rocksim showed 11 seconds (I'm guessing a better rocksim would be closer to 10), either way 14 seconds doesn't sound right. Perfect build smooth sanded polished rounded fins vs 'just out of the box' only changes things about 1 second on a rocket like this.

C) H550? If you were going for your level 1 and said you were using an H550 I would ask what the logic behind that is? Unless you had a really good reason for that motor (proving you know what you were doing) I would say try a different motor, because.....
C1) do you know how to build and assemble a H550? Did a certified flyer watch what you were doing? An answer of 'little experience with reloadables - and didn't have someone watch / supervise' would certainly make me question the launch at inspection
C3) Simple mistakes during loading, a little grease on the delay, opening and closing the case, black powder around the o-ring, forgetting the forward washer, etc. can cause delay times to 'readjust' faster or slower.
C2) Fast motors have issues with delay times (but you know that before picking a H550 because an experienced member would have told you that), small things like making sure the igniter is ALL THE WAY in against the delay grain, and cutting a slot in the red cap for gas to escape when the igniter lights and before the motor starts, can cause delay issues. Having fun yet?

D1) Chute Folding and zippers - even how you fold your chute can cause zippers, a tightly folded and properly wrapped chute with a chute protector deploys slowly giving time for the shock cord to straighten out and slowly turn the body tube 180 degrees.
D2) how your shock cord is folded will affect the chance of zippering plus the location of the chute relative to the shock cord.


Ok, so, your level 2, you said next week for that? I have to ask, who have you talked to about that, who is signing off on that. It sounds like you and the team doesn't have a lot of experience (yet), I could be wrong but i wouldn't sign off on a level 2 for someone that dosn't have much experience with high power (level 1 stuff) including reloadable motor experience, rock-sim, construction, even altimeters.

Mike K

P.S. OP Contact me off chat if you have more questions

 

[Tractionengines]

C1) do you know how to build and assemble a H550?

They (and a lot of these collage teams) use the H550-14 DMS motor. NOT the reload kit version of the H550.

 

[Steve Shannon]

They (and a lot of these collage teams) use the H550-14 DMS motor. NOT the reload kit version of the H550.

They still need to know how to adjust the delay and assemble the ejection charge correctly.

 

[kramer714]

They still need to know how to adjust the delay and assemble the ejection charge correctly.

... and understand how a H550 is different than than H135W

Mike K

 

[Neutronium95]

I don't really see any problems with people choosing the H550 as a cert motor. It is a high thrust motor, but I think that people worry too much about thrust and acceleration breaking rockets, when the actual problem is airspeed. I have a friend who successfully launched a rocket made out of 3" Estes tubing on a H999. I'd feel relatively confident in the ability of any reasonably well built Loc kit wit a 38mm motor mount to survive a flight on a H550.

Besides it's a fun motor that offers something that you can't really get without a L1 cert. The same goes with the H115. Aerotech makes several DMS H motors that are the same size as it, but people choose the H115 a lot because it is a sparky, and they haven't flown one before.

 

[Tractionengines]

They still need to know how to adjust the delay and assemble the ejection charge correctly.

... and understand how a H550 is different than than H135W

Mike K

YES, YES, YES... Also because of this, preferably know and understand the Difference between the two types of H550. ... including the difference between the UDDT and the RDDT and which is used for each type of motor.

 

[Steve Shannon]

YES, YES, YES... Also because of this, preferably know and understand the Difference between the two types of H550. ... including the difference between the UDDT and the RDDT and which is used for each type of motor.

Yeah, one of my most strident gripes is the name of the “Universal” Delay Tool.

But you and Mike Kramer are right - this is basic knowledge that is necessary to consistently fly rockets successfully and it can’t be easily learned over the course of two flights in two weeks resulting in two certifications.

 

[dr wogz]

This has been an interesting read!

As I've said to others in this boat:

• It's not a race.
• Learn and advance as your skills, knowledge & understanding improve
• Fly within your limits
• Build for the purpose, not as a general "all purpose" model. Build a rocket for your L1, then build one for your L2..
• Know what the numbers mean! Big number don't mean bigger events.. plan your flights accordingly.
• Experience pays dividends

 

[waltr]

D1) Chute Folding and zippers - even how you fold your chute can cause zippers, a tightly folded and properly wrapped chute with a chute protector deploys slowly giving time for the shock cord to straighten out and slowly turn the body tube 180 degrees.
D2) how your shock cord is folded will affect the chance of zippering plus the location of the chute relative to the shock cord.

These two are much more important than most people think. If the chute and cord are properly packed then even with a delay double the rocket will survive without a zipper or other damage.

On the third flight of my LOC Goblin (2nd was an L1 cert) the delay should have been 5 seconds (yes I did drill it properly) but went to 10 seconds. The Goblin has coming in ballistic from 600 feet when the ejection charge fired about 100 feet above the ground. The chute deployed and it landed about 2 seconds later without any damage.
This is due to the cord being Braided and the burrito wrapped chute that actually takes over a second to fully deploy. The friction from the cord's braid pulling apart slowed and turned BT and it never experienced a SHOCK of when a free cord full extends of a fully open chute.
I have watched other flights when the delay was too long and could see the chute open fast and nearly stop while the rocket is still accelerating down then suddenly the cord pulls TIGHT trying the stop the rocket. Of course the cord then just rips through the BT.

To me this is simple Physics and Engineering. Also since we do Rocket Science one must design to account for all kinds of thing to go wrong and ensure recovery deploys safely and also able to handle common anomalies such as delay times being off by a good amount.

If the Chute and Shock cord were prepared correctly then the BT would not have zipped and the flight would have been an L1 Cert pass even with an extra 3-4 second of delay.

The OR Sim I did with a 14 second delay shows a velocity of 70ft/s. This is a typical speed at which the a rocket descends on a Drogue and at which the Mian chute is deployed. If the OP does not learn how to pack the chute and cord then he/she will Fail L3 and maybe even L2 certs but with much heaver rockets.

 

[Tractionengines]

My "biggest gripe" is with this is the university itself. Based on what is being told, and asked here on the forums; I feel the capstone committee is putting an unrealistic time frame/ expectations on this program. Then instead of relaxing expectations, they made it more complex by requiring a active diagnostic payload of some type on the 10,000ft flight.

The school needs some guidance on what should be expected as a development time for a program like this. I think this is only in it's 2nd year. These students are only attempting to do what the school is requiring of them. Without having proper guidance available.

 

[Ronz Rocketz]

Interesting in that there are 119 posts but don't see a sim file attached yet. Maybe I missed it.

If I'm understanding correctly, there were several of the same rockets but this one zippered? I would weigh each rocket and figure out CG then input into OR for the sustainer to determine optimal delay.