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Discussion in 'Beginners & Educational Programs' started by rickster75, Jan 11, 2020.
What was it’s stability margin at launch? Looks like it weather cocked and then didn’t recover due to aerodynamic instability.
Motor was an Aerotech M1075 Dark Matter. I can only presume that the stability margin was near zero or negative and the RSO was asleep at the wheel, or possibly nose weight broke loose and migrated backwards. I was initially going to guess that this was a motor too small for a minimum-diameter rocket (paradoxically you can have stability issues in this case sometimes) but the M1075 is pretty big.
It could be thrust misalignment. Sparkies will do it, either by uneven nozzle erosion or a build up of molten titanium on one side of the nozzle. I had a DD Mad Dog this summer on a AMW skid fly on an arc exactly like yours off the pad, but it straightened out. There was very little wind, had a stability margin of 1.8 and otherwise always flew straight as an arrow. When I cleaned up the motor, the nozzle had a chunk of molten titanium built up on one side of it. Looking at the flight of your rocket the sparkie/smoky side of the exhaust is really split up and it looks like the sparkie side is doing the steering.
This wasn't the OP's rocket, or my rocket either (it's Steve Jurvetson's rocket). Interesting that you had that much thrust vectoring. I've flown a lot of sparkies and never had anything like that happen.
I've flown a lot of sparkies too with no problems, thrust vectoring like that is just a possible explanation after eliminating other possible causes. There was a thread similar to this one a few years back, and if my memory serves me right Blackjack/ Crazy Jim mentioned that he had seen this happen several times.
Here is negative stability, as propellant weight burns out CG moves forward and rocket gets stable.
I made the motor, P, 1000 pounds thrust for 14 seconds. Had nothing to do with airframe. Rocket was found stuck in ground five miles away.
I wouldn't be surprised if this was the reason:
Yeah, what's up with that? You can clearly see the nosecone isn't seated correctly in quite a few shots in that video. That can't be on purpose...right?
This would be a fairly straightforward way to make a variable-length zipperless single break.
I'm not saying that's what it is, but it's not entirely unreasonable.
I was at that launch, and I was actually out in the field recovering my rocket when that thing came my direction, flipping and skywriting all over the place. I never felt so in jeopardy at a club launch. That motor burns for awhile, and I was praying for it to stop.
Steve Jurvetson flies some awesome rockets, but he also has a higher than normal proportion of major disasters. I think he brings a venture capitalist mentality to rocketry — 9 out of 10 projects fail, but the one that works is a real jackpot. I think if I were an RSO, all of his projects would fly from the away cell, based on past track record.
The NC seems to stay in place but why was it allowed to fly that way?
High power rocket at NSL last year (2019) did a near COMPLETE loop about 100 feet above the pad, very similar to this case, except fortunately completed enough of the loop (still under thrust) that is had at least a partially upward vertical vector and the horizontal vector was away from spectators. It was scary, at least to me.
Yeah, I am wondering the same thing. I would never put a rocket on the pad with the nosecone hanging out the top, even if it was secure. Go fever!
The cone has shear pins I would guess but still I would not let it fly. Maybe the coupler was extra long.
Thats assuming the NC was like that at the RSO table. So the NC may have been seated correctly when it was inspected but you can't hold the RSO responsible for what happens to the rocket between inspection and the pad. Also, the RSO may or may not have been "asleep at the wheel." The RSO inspection is sort of a cursory inspection to make sure nothing obvious is wrong. Also, the RSO relies heavily on the information that the flier gives them such as the location of the CP. Can't say I've ever witnessed an RSO work through a Barrowman Equation to verify CP location much less bust out a laptop to run a few sims. I think pinning this on the RSO is unfair. IMHO it's ultimately up to the flier to make sure the relative CP/CG locations are correct.
Looking at the stills at the end of the Mongoose portion of the video it does not appear that the NC was mis-aligned during flight. But the key word there being "appear." The rather sudden instability right off the rail sort of looks to me like the CG was in the wrong spot right off the get-go.
Nah, it's just an attempt to emulate the THAAD's energy management spiral :
I cast the propellant for the prototype separation motors for THAAD. Pushes the kill vehicle away from the booster.
Even the so called experts get it wrong sometimes
I am less and less impressed with L3 fliers these days, especially those that publicly tout their disasters. I would be ashamed if my large rocket went bonkers and threatened spectators, not putting the video on YouTube.
This is a basic 3FNC rocket merely needing some fundamental CP/CG analysis. Yet, this guy doesn't even have the sense to seat the nosecone. Certification doesn't mean a whole lot in my book.
And... what's with all the electric tape wound around the airframe in a half-assed manner? Geez.
I understand what you're getting at and I can appreciate not wanting to post failures publicly but I think some of those can be good learning experiences for the rest of us. Also, we don't know the whole story on the nosecone. That coupler could have been lengthened (rather than make/buy a longer nose cone) to accommodate a larger payload. The CG could have shifted during lift off because something broke and shifted aft. Just saying, until the flier himself posts here we don't know the whole story just yet.
Most lvl 3 fliers i know are safe, responsible and knowledgeable. Safety really depends on the club and the RSO. But stuff does happen. I wouldnt impugn all lvl 3 fliers. I doubt you meant to. Good flying everybody.
I am going by Thirsty's comments. The guy has a track record. Perhaps he needs to learn, not us.
The guy is fine. I just think he is overly ambitious sometimes, and maybe it would be better to fly some of his stuff far, far away. When I mentioned he has a venture capitalist mentality toward rocketry, I wasn’t joking. He is a well known Silicon Valley venture capitalist who backs high-risk, high-reward ventures. I think he was an early investor in PayPal, for example. Here’s another bonkers flight of his I was witness to. This one was asking for trouble if all the motors did not light simultaneously, which they didn’t...
could that have been a makeshift way to move CG?
”I just think he is overly ambitious sometimes, and maybe it would be better to fly some of his stuff far, far away.”
In both videos it looks like people are standing really close to the rockets at launch. Crazy flights. I’m just glad that kind of thing wouldn’t go at my group’s launches.
Probably not the kind of guy who takes "no" for an answer. No wonder they let him fly whatever...
Yet there’s a guy standing close there and the crowd thinks it’s great ?
"epic", "bad idea rocketry", "3...2...1...Duck!" Yeah, great. So hilarious. Hold my beer while I put this on YouTube. This guy is a buffoon and the crowd eats it up. Where is this club, so I can avoid it?
Not to mention hitting a spectator, we would all be pretty pissed if his pinwheeling rocket wiped out all the other racked rockets at the pads.
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