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Wow! Kudos on successful ignition!
Starstreak (3D Printed Parts + Plywood Fins + BT-80/BT-5 tubes)
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GlenP
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Great ground test and validation of your staging system. Those three sustainers probably needed a 3' launch rod to get up to speed, pretty much any rocket would dance like that if you launched without a rod. Probably not an issue once they are going full speed when the booster ignites them in flight.
Thanks Glen - yes, I assume if they are already moving at a good clip they will stage into a smooth flight.
I am trying to reduce interference from the frame on the booster. I need to look back at your design to see how you kept the frame out of the way.
Have you tested the sustainers on their own? By which I mean have you swing testing one and/or gluing a launch lug to one and flying it. Or are the simulation results satisfactory on their own? (A 4FNC with healthy margin probably doesn't need that.)
Good question.
I did not (well not exactly), but loaded them up with a good amount of noseweight. The booster+sustainer needed noseweight so put a good portion of that in the sustainers (as much as I could fit which came out to nearly .5oz in each sustainer nose + 2oz in nose of booster, which is all the way in front next to tips of sustainer darts).
My logic was: I do not want them to go too high + wanted to be sure they were stable with the little canards not to mention lack of launch rod. Best as I can tell (although OR is giving me bug report errors) is that the rocket will be going 65m/sec when it separates (if I use a D12 in middle and C5-3 in 3x outer spots -- I might go with B6-4s in outer slots but OR is not behaving right now).
I say "not exactly" as far as testing the darts separately since the ground test saw the darts flying pretty far on their own -- i.e., they seemed stable once they got going. One made it all the way to the access road to the field I was in and got run over. One launched pretty much straight up and ejected / recovered on its streamer properly. Another one wedged itself pretty good under the grass since it had a pretty horizontal trajectory.
One nice thing about the way that I set this up in OpenRocket based on advice from others (with just 1 dart as the sustainer and the other two as separate boosters) is that I can see the stability of a single dart (sadly, it keeps crashing so a bit difficult to figure out what is going on).
Perhaps try copying the dart portion out of the full OR design, and making it a separate design of its own. I'm pretty sure that if I ever buy this kit from you, I'd request extra parts to make a fifth dart, and put a launch lug on it just for fun.
I was actually thinking of including parts for an extra dart just in case someone lost one
Exciting progress! Well done on a successful ignition process and design.
The Dart stability issue straight off a static ignition reminded me of my own unforeseen test issue, and I'm glad yours worked out Ok and no-one hurt too. I too believe that they will be better behaved when launching off the top of a flying booster.
What's the next test? Maybe a fully loaded GLOW weight test to see if the main motor will deliver the Darts to a suitable separation speed? That reminds me to ask, what is the build weight so far and how does it look stability wise in OR?
That's a very, very wise idea! Especially for someone like me who is ultra long distance for shipping. BTW I want one!I was actually thinking of including parts for an extra dart just in case someone lost one
I lost my first full size "final production" Dart on a test flight when it went up on its own to test the timer settings and stability. It went soooo high and I had it on a 12inch chute so it floated away and was far too small to see and track. Still haven't found it.
I had to cannibalise a test Dart for canards and some extra fins I'd made while I was making batches and so I made some tiny 7inch hexagonal chutes to bring the 125gm Darts down fast and close. Streamers might work better for yours depending on your Dart weights.
I did pretty much as you advised, test flying the Dart a couple of times on its own off a 1010 rail to check for it inherent stability versus the OR simulations, and all was really good. Its a slow process and it builds confidence for safe flying with better chances of positive outcomes, so when other members encouraged me to "get on with it" I felt I could meet their demands!
As a suggestion for testing:
1) Test fly a Dart on its own to verify inherent stability. Looks like its over-stable on OR so you should only have to do this once.
2) Test fly the booster with extra weight in forward section to simulate final GLOW and CofG for the 3 Darts configuration. That should give confidence in your separation speeds.
3) Fly it with one or more Darts loaded with B motors WITHOUT any launch lug or mini-rod design modification yet. See how they go. They may not need it.
Thank you for advice and following thread.That's a very, very wise idea! Especially for someone like me who is ultra long distance for shipping. BTW I want one!
I lost my first full size "final production" Dart on a test flight when it went up on its own to test the timer settings and stability. It went soooo high and I had it on a 12inch chute so it floated away and was far too small to see and track. Still haven't found it.
I had to cannibalise a test Dart for canards and some extra fins I'd made while I was making batches and so I made some tiny 7inch hexagonal chutes to bring the 125gm Darts down fast and close. Streamers might work better for yours depending on your Dart weights.
I was planning on some nice silver streamers (bird scare tape). The NC will be a little heavy (13-14g or so) but the body is a very light. NC will be filled with weights and epoxy / glue so should be pretty durable. I will try to setup Kevlar shock chord so that NC hits ground first followed by body.
Loading A3-4 in darts keeps them lower than A10-3 in simulation. Planning to try to keep Booster low as well so I can still see separation.
2a) (Optional) test it with three darts with no engines, to check stability including the dart fins acting as canards in the pad configuration.
Any suggestions on mounting Kevlar shock chord into BT-5 tubes?
I could include a hole in the motor block but that seems to put the chord too close to the ejection charge.
I could maybe make a channel around this part that would let the Kevlar hide and provide a buffer from ejection charge (still seems some risk of it getting below wadding and exposed to full ejection blast).
Alternatively, I could 3D print a separate small ring with a shock chord mount that could be glued down inside the tube an inch or two above the motor block. Could maybe pack wadding below this but streamer would hopefully stay above this (some risk of it slipping below it and getting stuck).
Last option - I might be able to create a buffer that could absorb the ejection charge and could include a Kevlar mounting point. This is a bit more complex and would require its own testing.
I could include a hole in the motor block but that seems to put the chord too close to the ejection charge.
I could maybe make a channel around this part that would let the Kevlar hide and provide a buffer from ejection charge (still seems some risk of it getting below wadding and exposed to full ejection blast).
Alternatively, I could 3D print a separate small ring with a shock chord mount that could be glued down inside the tube an inch or two above the motor block. Could maybe pack wadding below this but streamer would hopefully stay above this (some risk of it slipping below it and getting stuck).
Last option - I might be able to create a buffer that could absorb the ejection charge and could include a Kevlar mounting point. This is a bit more complex and would require its own testing.
That’s an option that also tests the backup safety feature for pushing the Dart nose cones off if they fail to ignite.
Testing the stability of the booster with a GLOW simulated is also to ensure the recessed main fins are grabbing enough air at rail/rod exit speeds to give confidence to maybe bypass the Dart canards risk. In my build I did two tests with one restrained Dart with no adverse stability effects observed.
Even though the nose cone weight sounds nice and low, don’t forget to consider the risk of zippering from the Kevlar thread shock chord.
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Reminds me somehow of a certain Chad Staged Twin Factor flight in Honolulu, I am guessing @Ronz Rocketz and @kuririn remember it well
go to 16:55
haha... yes it does... brother from another mother!
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At the risk of sounding cowboyish, assuming you use the lowest practical power motors in the darts, “does it matter if they are stable?”
Rationale:
I don’t think the Estes MIRV sustainers were stable (of course, just because Estes jumps off a bridge….). The concept seemed to be that they relied on the booster to be high and roughly vertical when they deployed. Before you say, “that’s a bad assumption” (my first thought), if the booster is not high and particularly if it is NOT vertical, I am in more trouble if the darts ARE stable (lateral or downward flight coming in hot!) then if they are UNSTABLE, in which case they skywrite a bit, pop, and come down.
Next, either by unstable design or by weak motors (or both) you keep the dart sustainers from going too far from the “mudda ship.” Depending on your field flatness and number of trackers, with at least four separate rockets to recover, this is a good thing.
Not sure about on board space for recovery, but this is a case where putting extra long shiny streamers on the dart sustainers may pay off. Agreed, per Stine anything over 10:1 streamer length to diameter doesn’t SLOW the rocket anymore, but a lot of rockets recover fine with just nose-blow. The STREAMER makes it easier to see on descent and likely just as importantly in the ground, as it waggles in the slightest breeze. So “long” and “shiny” (or fluorescent) are your friends.
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Regarding need for on board launch rod:
I’ve done the single booster to multiple sustainer a couple times. One without, the second WITH. I added it in the second NOT to “guide” the sustainers until they were up to speed, but because my DESIGN needed “something” to keep the tips of the sustainers “together” and straight. You can see from Cerberus that the sustainers “splayed” outward (still flew fine)
https://www.rocketryforum.com/threads/successful-launch-and-staging-cerberus-iii.46235/
You seem to have a reliable secure and release mechanism, and the stack of booster and sustainers will likely be at Max Q for the stack at deployment. So I don’t think you NEED a dart guide. I am more concerned that the darts release cleanly and don’t bump into anything that will veer them off whatever heading the stack is going at deployment.
I’ve done the single booster to multiple sustainer a couple times. One without, the second WITH. I added it in the second NOT to “guide” the sustainers until they were up to speed, but because my DESIGN needed “something” to keep the tips of the sustainers “together” and straight. You can see from Cerberus that the sustainers “splayed” outward (still flew fine)
https://www.rocketryforum.com/threads/successful-launch-and-staging-cerberus-iii.46235/
You seem to have a reliable secure and release mechanism, and the stack of booster and sustainers will likely be at Max Q for the stack at deployment. So I don’t think you NEED a dart guide. I am more concerned that the darts release cleanly and don’t bump into anything that will veer them off whatever heading the stack is going at deployment.
Stability checks for the Dart - If it's not hard to do, then why not do it? A swing test doesn't cost anything. My assumption is that the mission is to mimic the real thing (so no sky-writing IMO), still keep sight of the model performing in a manner similar to the real thing, and get them all back without a long walk.
I'm open to perhaps not flight testing a Dart just for stability checks. Between us (Drew and myself) we've flown the Dart design multiple times on their own and the flight performance for the scale configuration has been stable and a good match versus it's OR simulations.
+1 on the long shiny streamer to aid spotting the Darts' descent and retrieval.
+1 on the "no Dart launch rail", at least on the first fully load flight to see what happens. I think that there is always going to be risk of the Darts bumping into each other at initiation with or without a mini guide rail. I had always felt that the arrangement of the Darts' canards around the upper section could assist in helping them fan out away from each other. In this build configuration the canards look like they are mounted onto the nose cones so there may be a tendency for them to twist, weathercock and all align in the same direction, depending on how tight the shoulder is into the body tube.
Love the Cerberus III.
When I referred to the darts and canards, I meant that the darts' fins, even the main ones, act like canards for the full stack, reducing it's stability. That's why I brought up doing a full stack test with no dart motors.
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you might like this.Love the Cerberus III.
Good example of a “flying launch rod” the purpose of which is just to keep the sustainers in “tight” alignment.
https://www.rocketryforum.com/threads/ho-hum-nuther-3ncb-flight-3-dog-night-post-12.64307/
Thanks everyone for the insights and ideas.
I think my biggest issue is actually the scale brackets hitting the darts and diverting them outward. I tried to put some bevels on the parts to help with this but the goal is a scale model so some compromises need to be made.
I need to print a new booster NC and dart NCs to give it a couple of millimeters of clearance. I liked in the current setup that the darts were nice and tight against the frame but this is part of what caused the darts to go off in different trajectories. It looks like the top small hook in the dart NCs got a bit held up in the booster. The "hooks" are made from 2mm copper rods and are smooth and pretty loose in the holes they fit in on the booster. However, they were under a bit of pressure due to the dart being pushed a little against the frame parts on the booster.
I think my biggest issue is actually the scale brackets hitting the darts and diverting them outward. I tried to put some bevels on the parts to help with this but the goal is a scale model so some compromises need to be made.
I need to print a new booster NC and dart NCs to give it a couple of millimeters of clearance. I liked in the current setup that the darts were nice and tight against the frame but this is part of what caused the darts to go off in different trajectories. It looks like the top small hook in the dart NCs got a bit held up in the booster. The "hooks" are made from 2mm copper rods and are smooth and pretty loose in the holes they fit in on the booster. However, they were under a bit of pressure due to the dart being pushed a little against the frame parts on the booster.
How's the build coming one, or has real life stuff been a bigger demand?
Haha... yeah, been printing neckerchief slides for my kids scout patrol and designing components for his Halloween costume! It has been a nice change of pace printing something besides white ABS
I still need to rebuild the damaged dart and modify the booster a bit to give better clearance for the darts. I may need a new park (or other field) to launch in (especially for the bigger rockets) so trying to figure out where to launch the full two-stage of this as well as the IRIS.
I still need to rebuild the damaged dart and modify the booster a bit to give better clearance for the darts. I may need a new park (or other field) to launch in (especially for the bigger rockets) so trying to figure out where to launch the full two-stage of this as well as the IRIS.
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