lakeroadster
When in doubt... build hell-for-stout!
Thoughts and comments on this.....
Lakeroadster's "Hammerhead Shark"
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Yes, Aerotech kits have thicker metal motor hooks than the wimpy Estes ones. Real mid power kits!
lakeroadster
When in doubt... build hell-for-stout!
I looked on the Aerotech site and didn't see these. But it certainly makes sense.
I find their website to be difficult to navigate around in. I get a lot of "Search Results: "0" Matches"
lakeroadster
When in doubt... build hell-for-stout!
I forgot to post a photo of our launch site. 8,200 feet elevation, Continental Divide to the west.
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For standard 3FNC or 4FNC rockets (I.e., NOT OddRocs) I might find obvious deviation from “straight and true” flight path disappointing. For OddRocs, if the net trajectory is mostly vertical, it gets up over 50 feet, and recovers without hurting anyone or anything, and damage if any to rocket is easily fixable, i chalk it up as a win. I think @Daddyisabar would agree, fishtailing, coning, corkscrewing, who cares, as long as as it’s safe and you have fun. Personally, perhaps because I am a low power guy, when I went to NSL a few years ago after a while the only really interesting high power launches from a spectator standpoint were the ones that DIDN’T go picture perfect.
for OddRocs, a little waggle just adds character.
in fact, it actually INSPIRED one of my favorite builds
https://www.rocketryforum.com/threads/squirrel.69006/
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Funkworks
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A normal scratch-built would spiral, but this one is so symmetrical, it rocks instead.
lakeroadster
When in doubt... build hell-for-stout!
I agree. But to be clear, my goal is "Straight, True Vertical Flight Paths, and Safety". That's why I follow the NAR rules, run simulations in Open Rocket, perform swing tests, etc.
But since these aren't kits that have been vetted and tested (and they aren't 3/4 FNC designs, as you stated).... stuff happens.
I bet the folks at Apogee, Estes, Quest, etc. have this same level of "wonderment" when they're designing and testing new "Odd Rockets".
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concur in part, safety is always number one concern. Interestingly “stability” May have more than one definition, technical and practical.
I suspect many have experienced rockets, often kits, that were by design, build, and even swing test stable but when launched were….not. OTOH, I am not sure that some OddRocs either are unstable on sims or more commonly probably CANNOT be simmed because their contours are outside sim parameters (my understanding is that sim programs don’t like rockets without round body tubes. There are work around s but sims themselves are estimates, and when you workaround you are compounding estimates with estimates. While I admire your adherence to ”straight and true”, and i am not sure if sim programs like RockSim and OpenRocket would find rockets like Odd’l Rockets’ “CorkScrew” stable, many of them fly just fine despite some corkscrewing or waggling. I would call those rockets “practically stable”. I do confess that while I get a kick out of some asymmetric fin designs that screw their way into the sky, leaving entertaining smoke trails along a (net) straight trajectory, it is kind of fun to have a wacky looking rocket fly straight. It will be interesting to see how @neil_w ’s Shear Insanity actually flies.
I was going to use the story that scientists proved the bumblebee couldn’t fly, but I googled it and the story is a myth. Same with breaking the sound barrier. Light speed, on the other hand, is going to be a lot more challenging!
lakeroadster
When in doubt... build hell-for-stout!
Tim Van Milligan: “Stability” for us essentially means to fly a predictable flight path.
Coning, Corkscrewing, etc. It's all good, as long as it's predictable. Of course, it may take a couple of flights to ensure it is indeed predictable.
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true, and this may be the death Nell for Back Sliders. If I understand the physics, the post ejection flight mode is dependent on orientation after the forward puff yanks the rocket out of stable flight, at which point the rocket stops (or nearly stops) in the air, and starts falling. The orientation post “puff” is pretty random, can be anywhere in an infinite number of positions in a sphere around the center of gravity. For a long rocket, as long as it is not pointed straight downs it should transition to a back slide recovery. The longer the rocket the closer it can come to being NEARLY vertical and still backslide. But if it unfortunately happens to randomly orient straight nose down, it’s gonna come in ballistic. I fear this is unsolvable for “pure” back sliders, although fixable with a small streamer for the less finicky.
Indeed. Regrettably, I have no launches anywhere on the horizon right now. Gotta figure something out.
"Wonderment" is not a term I have heard when discussing commercial oddroc kits with the top designers from those companies. More like " Idiot Factor."
lakeroadster
When in doubt... build hell-for-stout!
I'm betting some of the commercial oddroc kits, during the development phase, were full of wonderment, until they got them dialed in.
lakeroadster
When in doubt... build hell-for-stout!
Another factor is nose cone weight. Oddrocs, more than meets the eye. Oddrocs, rockets in disguise.
The hammerhead nose cone is crazy heavy, 9.3 ounces (the rocket w/ motor weighs 18.3 ounces). Normally we think of an ejection charge as "popping off the nose cone". On the Hammerhead I wanted it to eject after apogee, thus the ejection charge is pushing the fuselage back and allowing that heavy nose cone to keep falling, thus pulling out the parachute.
It really depends on the rocket design.
Take as an example my F-79 , which is a rear eject design without a spool. During flight the rocket never "nearly stops", and the nose cone doesn't come off, so it never becomes unstable / non-aerodynamic. That's why it's so important to get the chutes out before apogee.
Pre-apogee also gives the chutes a chance to deploy while the rocket is slowing down on its own, instead of picking up chute shredding speed.
If I knew then (pre-flight), what I know now (post flight) the F-79 probably wouldn't have those cool looking speed stripes on its nose.
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There are very few oddroc kits from large corporate suppliers, nothing too extreme. Infamous Estes examples over the years would include the Cosmos Mariner, Dude, RTF Star Wars, Space man, Star Trek, Portapot Shot and Spaceship One E. A handful of foreign and one man shop kits also qualify. Generally they do not hang around for long as they are novelties in the line up.
I am still waiting for the Battlestar Galactica Cylon Raider. It is circled in my '79 Estes catalog as a must have by my inner 12 year old.
I am still waiting for the Battlestar Galactica Cylon Raider. It is circled in my '79 Estes catalog as a must have by my inner 12 year old.
With enough power and nose weight almost anything will fly. I once handed the body of my Albatross DV to a top designer and then the nose cone which resulted in a hearty belly laugh.
Rule number one of Oddroc Club: The rocket looks cool.
Rule number two of Oddroc Club: The rocket looks cool.
I didn't know it isn't true, but I'd rather call it a parable than a myth. And as a parable it's frequently misunderstood.
It's told as if it means scientists are stupid. "Those guys don't know anything, they even think bumblebees can't fly."
No, no. Someone, the story goes, using the prevailing theories of the day, showed that bumblebees wouldn't fly, and that was offered as proof that the prevailing theories were wrong, and he and his colleagues had a lot of work to do. Proof by reductio an absurdum.
Funkworks
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I like how they say it here:
"So, no one “proved” that a bumblebee can’t fly. What was shown was that a certain simple mathematical model wasn’t adequate or appropriate for describing the flight of a bumblebee.
Insect flight and wing movements can be quite complicated. Wings aren’t rigid. They bend and twist. Stroke angles change. New, improved models take that into account."
https://www.sciencenews.org/article/flight-bumblebee
Not trying to hijack. Just had to look this up too. Bye now.
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Good point that rear eject models (ignoring the chute, which is the elephant in the room) remain STABLE throughout the flight.
You presumably can pull the data from your sim, but I am guessing that from a potential chute-shredding event, ejecting too early can be as bad as ejecting late. Does max V on ascent exceed max V on a ballistic recovery? And does a sim program UNDERESTIMATE Max V on ascent if the rocket weathercocks (i.e., if rocket is going sideways instead of up, is MaxV under boost higher? I am guessing yes, since it is competing less with gravity, although drag will increase.)
Regardless, I think ejecting early is a bit safer than late even if kinetic energy is identical at either case (since there is a certain amount of randomness in "how early?" vs "how late?" they won't be, but you get the point) it is SAFER to eject early, as the rocket is likely to be closer to the pad so more likely to land in a relatively clear area. What is frustrating and a bit frightening is where you have a decent size field (say a park in Tennessee that is pretty good sized and completely empty of everybody except the rocket launcher and perhaps the people mowing the soccer fields), but the rocket goes cruise missile and recovery system fails. This puts potential re-entry point in someone's backyard, which is at best poor form.
Good point that for a shredded chute or a shock cord failure, the rear eject models are going to come in hotter than a standard rocket, as for the latter the nose has to blow for the chute to deploy and shred, so rocket will potentially tumble. The exception is high nose weight rockets, where even if nose cone separates, if nose cone weight to drag ratio (or something like that) is greater than the rocket body, the nose cone hangs down and pulls rocket vertically down with it, maybe not technically ballistic but close to it. I'm not a squatty rocket fan, so most of my rockets have no nose cone weight, tumble recovery isn't optimal but certainly beats ballistic.
Your rear eject is also a bit different than many rockets, which rear eject but use a pod that ejects with the motor mount and chute, with a shock cord connecting chute to pod and a second connecting pod to rocket body. These may or may not be stable post deploy, but certainly will be draggier even if chute shreds. Shredding may be less likely, as chute deployment from a pod may be a tad slower than the immediate deployment from your more direct approach. Pod systems also take up a LOT of space which makes chute packing a PITB, and often limits available space so tend to go smaller.
I did learn my lesson on why chutes are not good recovery devices for black powder staged rocket boosters. There are tricks where you CAN deploy a chute from a black powder staged rocket attached to the booster, but when I tried it I didn't think about the fact that the entire rocket is traveling at maxV for the stack at staging, and without electronics (something like a Jolly Logic Chute Release might work, if you staged high enough) the near immediate deployment of the chute is entertaining but not effective. On my attempt, broke 7 of 8 shroud lines. Still recovered okay, but not exactly a shining moment.
Anyway, please post the D12-3 flight I hope is imminent!
lakeroadster
When in doubt... build hell-for-stout!
Max Velocity under power = 109 mph
Max Velocity going ballistic = 92 mph
My Red Columbine utilizes a rear eject spool. Did you see the flight report for it? Red Columbine Flight Report It's an awesome flyer, mostly because it looks nothing like a rocket but performs great.
I need to figure out what I want to do for chutes on the F-79 before I launch it again... a little R&D as to if I can fit an 18" nylon chute into the side pods. If I can't, I've got a plan for some rear deployment extension tubes that will provide more laundry room.
Imminent... well it took me almost 40 years to fly again, then the next launch was 8 days later. We'll see, it'll likely be a few weeks at the earliest.
Thanks for your post @BABAR. I almost always learn something from your counsel, and that's pretty great in my book.
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