200 grams is a lot of nose weight (as if I have to tell you that; that's almost enough to give it an actual warhead)! Swing testing this guy might be a challenge, but it may be worth the effort.
"Fritz X" Guided Bomb
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lakeroadster
When in doubt... build hell-for-stout!
Does the frontal area of the (6) fins approximately equal that of the ring?
Does the weight of the (6) fins approximately equal that of the ring?
I also use (6) rings to simulate the ring fin.... Per Issue 27 of the Apogee Peak of Flight newsletter.
My F-79 weighs 500 grams...
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The challenge I anticipate is from the likelihood that the CG will by on a tapered area, not from the weight. It's fastening the string. No doubt doable.
lakeroadster
When in doubt... build hell-for-stout!
Sorry, you mentioned the weight, so I though that was your point?
Make a couple temporary rings using painters tape on the body, one in front of where the strings aligns with the cg, and another behind. Easy peazy.
I overrode weight of the fins and set them to the weight as the actual ringtail.
I will need to check on the frontal area. The frontal area on the ring fins should be pretty close.
Maybe I will swing test with the lower weight. One benefit of the plastic parts is I can duct tape the string to them which usually holds it in place pretty well.
I understood, but no, my point was it'd be better to take the trouble to swing test than to put on 200 grams of nose weight "just in case".
Yep, this is a good idea!!!
lakeroadster
When in doubt... build hell-for-stout!
Isn't that a foregone conclusion? New LPR / MPR designs should always have a swing test conducted before the 1st launch, unless the design makes it impossible.
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If the design is simple enough to fall well within the ability of a well proven simulator (i.e. RS or OR) then I for one do not think it's always necessary. And it doesn't have to be just a 3/4FNC; there's quite a bit of room in between those and, well, this. And I think it'd be possible to approximate this in OR with sufficient conservativeness to skip the swing test, I think. But that's what leads to a half pound of nose weight.
That's a beaut
icyclops
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Geepers me thinks you worry too much. I would worry more about the roc‘s parachute working, or a straight normal flight, or the motor ignition and not a CATO….more than if it’s too strong to take a hard landing.
lakeroadster
When in doubt... build hell-for-stout!
Taking 10 minutes to do a swing test.. vs.. possibly crashing the rocket... to me the 10 minutes is time well spent. But opinions vary.
I have yet to verify, with a swing test or an actual launch, Bruce S. Levison's advice on the use of 6 flat fins to simulate a ring fin in Open Rocket. Since the rocket being discussed here has a ring fin, not doing a swing test here would be haphazard, IMO.
I'm also wondering, especially in the case of ring fins, if the slow ft/s experienced with a swing test gives an accurate reflection of high speed stability?
Agree on doing the swing test -- this definitely fits in the oddroc category.
I also wonder if internal elements matter for a ring tail. Seems like it might make a difference if you had 2 support fins attached to ring fin vs. 8 (just an example) or in this case all the little extra fins inside the octagonal ring tail (not to mention the spaces in the ring tail and tubular elements). This all obviously adds drag but wonder how it affects CP...?
Anyway, I am using pennies for weights in these big rockets these days so easy enough to tape some pennies in and do a swing test with a lower weight, add weight as needed, etc... Maybe I will do the experiment without the front canard fins just to add some data about them and how much the rotating mounts really take away from their impact on CP calculation (although maybe speed matters more there).
Why pick one?I would worry more about the roc‘s parachute working, or a straight normal flight, or the motor ignition and not a CATO….more than if it’s too strong to take a hard landing.
I have a habit of seeing trouble on the horizon and watching out for it. Usually it turns out to be nothing, but more than once I've averted disasters.
Almost ready for my swing test...
Found my canard fins (they fell behind my filament spool bin), reprinted the ring tail, did a final print of the canard fin mounting plates that work better than earlier versions, etc... Started gluing things together tonight. Need to wait for some stuff to dry well so I can dry fit and do last set of gluing.
I decided not to use a launch rod for this one and instead use the Makerbeam rail. However, my earlier print had at launch rod lug. Trying to decide if I try to cut that off and sand (or maybe patch the hole with epoxy). It annoys me but I think I will launch like this since there is a good chance this will be a version 1.x
Big Bertha for size comparison...
Reprinted ring tail.
The pivoting front canard fins will work like my BT-60 version. I like this design where the 3D printed mounting plate parts slip through the shell from the inside and I glue these parts to either side of the fins on outside (thin CA is wicked in between 3D printed plate and wood fin - seems to get a good seem without gluing to body, might put a bit of painters tape on body to be sure). Circular tabs/nubs on 3D printed parts keep fins from falling off but let them spin freely. Tab on fin that sticks through shell also adds strength.
This is what engine mount looks like inside BT-80 tube.
Found my canard fins (they fell behind my filament spool bin), reprinted the ring tail, did a final print of the canard fin mounting plates that work better than earlier versions, etc... Started gluing things together tonight. Need to wait for some stuff to dry well so I can dry fit and do last set of gluing.
I decided not to use a launch rod for this one and instead use the Makerbeam rail. However, my earlier print had at launch rod lug. Trying to decide if I try to cut that off and sand (or maybe patch the hole with epoxy). It annoys me but I think I will launch like this since there is a good chance this will be a version 1.x
Big Bertha for size comparison...
Reprinted ring tail.
The pivoting front canard fins will work like my BT-60 version. I like this design where the 3D printed mounting plate parts slip through the shell from the inside and I glue these parts to either side of the fins on outside (thin CA is wicked in between 3D printed plate and wood fin - seems to get a good seem without gluing to body, might put a bit of painters tape on body to be sure). Circular tabs/nubs on 3D printed parts keep fins from falling off but let them spin freely. Tab on fin that sticks through shell also adds strength.
This is what engine mount looks like inside BT-80 tube.
I don't think there is much of a problem with speed (IMHO, based on experience), but the swing test should try to emulate a straight flight to some degree. That can be problematic for larger rockets as larger rockets need longer string to approximate a straight flight. The good news is that the test is conservative in that it is more likely to fail if using too short a string. If you pass the swing test it should just work.
lakeroadster
When in doubt... build hell-for-stout!
I'm with Joe... "Save The Lug" ;-)
boomtube-mk2
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What motor are you going to fly this on?
Looks like 1x E12-4 + 2x or 4x A10-PTs as "boosters" Depends on weight. I could also change out the motor mount setup to go with 2x or 3x 24mm motors if needed.
And didn't you make it with room for eight 13 mm engines? 8×A10 would make it really zippy.
haha... yes, but that would break the budget ceiling for launching a low-powered rocket
Also I have heard that clusters are a PITA...
Sacrilege!
Pretty addictive watching Octoprint (although I need some lights for my enclosure)...
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Yeah, same here. Funny thing is my printer is about 5 feet behind me while I stare at the OctoPrint stream.....
My one enclosure is not transparent, but Ironically it is all white so its the only one that shows a picture when lights are out (due to glow of LCD reflecting off white interior walls).
I made another one of these BT-60 versions (this time with details) and launched it successfully again - so first time was not just a fluke - the moving canard fins work. This time parachute deployed successfully as well.
My 7-year-old is a better videographer than me but here is a video: https://youtu.be/1JfLlYJYKSw
FWIW - I posted the kits for sale on Facebook but only have 2 left of the 12 I made. I wanted to keep price down since it is not a huge rocket but this model has too many large 3D printed parts to make it really viable sell many at this price.
https://www.facebook.com/groups/1078069588922549/?multi_permalinks=5946419395420853
Maybe if I can get the BT-80 version flying that can come in at a viable (albeit much higher) price point.
My 7-year-old is a better videographer than me but here is a video: https://youtu.be/1JfLlYJYKSw
FWIW - I posted the kits for sale on Facebook but only have 2 left of the 12 I made. I wanted to keep price down since it is not a huge rocket but this model has too many large 3D printed parts to make it really viable sell many at this price.
https://www.facebook.com/groups/1078069588922549/?multi_permalinks=5946419395420853
Maybe if I can get the BT-80 version flying that can come in at a viable (albeit much higher) price point.
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