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Worth taking 1s off the delay? Chute Release OK for a big flight?

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ActingLikeAKid

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Hoping to two two launches of the Mega Vector Force this weekend - the first, smaller one on the smallest AT 38mm motor I could find, mostly as a shakedown; the second with a big honkin' I280DM - that should get me within about 500 feet of the mile mark.

On that note... OpenRocket says optimum delay on that flight is 13s. The I280DM comes with a built-in delay of 14s. I'm using a Chute Release, so I'm not yanking out a massive chute. Worth drilling the delay, or just let it do its thing and maybe it pops a second or so after apogee?

Also: I've used my Chute Release on big-ish flights and big-ish rockets before (2300' AGL on my L1 in an Estes Argent), but this is a lot bigger: >4000 feet on a rocket that's about 1kg dry. I figure it'll hit terminal velocity pretty quickly, but should I be worried about the "yank" of the CR opening? Suggestions for an opening height? I usually do 200' on F and small G, 400' on G and H. I'm thinking 600 feet just to make sure everything comes out.

Looking forward to this one....I've been working on this rocket all winter!
 

ksaves2

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What are you using for tracking? A mile high is pretty far and the out of sight time is going to be protracted. If the winds aloft are quite different than at the surface, the rocket could end up in a part of the sky you're not looking at. If you can recruit many to look in different areas you could pull off a visual.
I assume this is a Blue Tube rocket and likely resistant to a zipper? If so, you could be right about the 1 second excess delay which might be off +- 1 to 2 seconds anyways.

You need to sim under a variety of wind conditions many times to gain a consensus as to how the flight might go or if it weathercocks a lot. I try to point my
rails downwind so the rocket "curves" up to a minimum energy deployment under wind conditions. I rarely point into the wind because that will aggravate
weathercocking.

You are correct that the restrained chute with the CR will lead to less force on the harness at deployment and decreases the risk of a zipper. I have a tendency to
have the CR deploy at higher altitudes like 800 feet as I've seen rockets slam into the ground with a CR because the chute filling was delayed for one reason or another. Another reason is I fly trackers and it's easier to establish a bearing or receive GPS coordinates with the rocket up a bit higher when the main is out and the descent is slower.

Me suspects you'll be OK with the 1 second added delay but have a little concern about the actual recovery and finding of the rocket. 600' would be better than a lower deployment because it gives you more time to get a visual. You have to remember if winds carry the rocket out of visual range for the main deployment, without a tracker it will be a more difficult recovery.

I've had a Wildman Jr with a Ham band Beeline GPS come down .6 to 1mile away on different flights and it was completely sight unseen on all of them.
I came up to it with the tracker and it was obvious the apogee/main deployment sequence was nominal as the rocket was lying there ever so nicely with the
main chute out (even with an 800' deployment still not seen in descent) and unharmed.

Another thing if one has an electronic deployment at apogee, one can use the longest smoke generating delay they can to optimize the visual on the up "side".
I do that with MAD apogee deployment rockets as the MAD unit deploys the CR/chutepack at that optimal altitude and smoke may still be coming out of the
motor. If there is a weird drift of the smoke trail at altitude, it gives one an idea as to how the rocket track might go on the downside and give you an idea of
where to look for the main event. Best of luck. Kurt
 
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ActingLikeAKid

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Wow, thanks for all this info!! I've got an Eggfinder in the nose cone; I've tested it in a suburban neighborhood. Even with substantial buildings between me and the rocket, I've got ~1100 feet of range, Cris has assured me that I'll get much, much more than that with line-of-sight.

This is a Blue Tube rocket, zipper shouldn't be an issue. Recovery is a loop of 1/4" kevlar to the top of the body tube, , a 300#-rated swivel, 12 feet of 1/2" nylon, a 36" parachute, 6 feet more of 1/2" nylon, then a heavy-duty eyebolt in the upper section. I like the idea of a high-ish EF deployment; I'd rather walk an extra half mile to get my rocket than walk a quarter mile to the remains of my rocket :)

In addition to the eggfinder, I'm going to stuff at least 10 feet of flagging tape (the super-lightweight plastic surveying ribbon stuff) in the rocket, just in the hopes of maintaining a visual.

I like the thought of going slightly downwind with the launch - stability on this thing is about 2 cal, so it ought to weathercock a bit.

Thank you again for all the input!!
 

ActingLikeAKid

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And hopefully the smaller motor will give me more of a real world picture of what it's going to do in terms of weathercocking. Even the H242 says it should do 2800 feet, which is higher than I've flown before.
 

ActingLikeAKid

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Whoa. Turns out that going a tiny bit downwind (like 3 degrees on the smaller motor, 2 on the bigger) will not only get me closer to the pad, but altitude actually increases!
 

mccordmw

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On the note of the delay, the motor delay can vary by +/-20%, so I wouldn't bother fiddling with it. It's not that exact of a delay, more like nominally 13s. Expect 12-14s range. Any one of those would be fine.
 

ksaves2

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Another bit of advice. secure your chute protector 6 inches or so down your harness from the chutepack so the protector is completely free from the chute/CR after it's blown out of the rocket. I've had a chute "stay" in the protector due to stiffness of the material. Once the charge has blown, you don't need a protector anyways. Keep it away from the chutepack so it doesn't interfere with the release once it's out in the breeze. You do that and it greatly increases the chance that your
chute won't get fouled. Kurt (who found out the hard way)
 
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ActingLikeAKid

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On the note of the delay, the motor delay can vary by +/-20%, so I wouldn't bother fiddling with it. It's not that exact of a delay, more like nominally 13s. Expect 12-14s range. Any one of those would be fine.
That's kind of what I was thinking.

Saw a kid getting his L1 last fall ... don't know what happened (didn't drill? Bad delay?) but his Batray went up, arced over, no event.... still no event....RSO gave the "HEADS *** call....started whistling like something out of a Wile E Coyote cartoon.... and maybe 300 feet AGL, the chute popped. Had a tiny zipper that the cert team deemed acceptable, but other than that it was fine.
 

woferry

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My personal experience with AT motor eject delays is that they're more likely to fail short than long (not that I haven't had a few burn up to 4 seconds longer than the stock or drilled-expected value). So I'd err on the long side vs. shortening it in case the delay decides to go even shorter than your target.

So long as you have the right band for the chute you're using (not too loose, not too much force on the CR's pin) I don't think much else matters (weight of the rocket, altitude of the flight [provided it's higher than the CR's programmed altitude, obviously], etc). Most of the failure modes (short of forgetting to turn it on or it running out of juice) are going to result in the main coming out early rather than not at all, so you're more likely to have a long walk than a damaged rocket. I use a Chute Release on a 8-9 lb 4" FG Nike Smoke to deploy a 48" parachute, had two flights to 4800+' this past weekend with no issues.

Personally, I'd never do a main deployment below 500'. That goes for a traditional DD altimeter OR the Chute Release. Less than that and I think you're not giving anybody on the ground enough time to prepare for what happens if the chute doesn't properly deploy (even 500' can get a bit scary). Sure, for a lightweight model rocket the chance of injury would be less so lower might be okay, for anything bigger I think it's a bad idea. It also depends on your field, if it's flat then that's probably fine, if it's hilly then consider the height of the hills and ensure that you have enough margin on top of that (remember that the deployment altitude is based on the altitude of the launch pad, the CR can't tell it's actual distance from the ground wherever it's about to land). Chute opening time is another factor, for my Nike Smoke I typically descend around 60ft/s under drogue, and my chute typically takes a second or so from when the CR releases to full opening of the chute, so it's generally fallen almost another 100' before the descent rate actually slows.

One thing I'd add, if the 'smallest AT 38mm motor' flight is the first flight of the rocket, I'd say be sure to compare your sim to reality before going for the bigger flight. I.e. if you're flying electronics verify the sim parameters to the actual flight data, or if you're not flying electronics do the best you can from visual clues (like when the rocket seemed to actually nose-over), and consider throwing in an AltimeterTwo or AltimeterThree just to get the actual flight data (they're great units to have anyhow). I've often found (especially when starting with someone else's .ork file) that the initial sim is way off, like projecting a 4000' flight when it actually goes to 6000' (that was due to the surface smoothness settings all being 'rough' when 'polished' seems to be the right answer, even though that gives me more credit on my paint job than I deserve). The longer flight meant more time in the air, so OR suggested a 10s delay when the right value was actually more like 14s. But it could just as easily be off in the opposite direction also. So just suggesting to use the first flight to get a better confidence in the 13s projection for the I280DM delay, if the sim is off on the first flight then tweak your settings to get that flight more accurate and re-evaluate your second flight sim results after that, you may find that the right delay value becomes something longer or shorter than 13s. Worst-case it might even take a second flight of a smaller motor to continue to tweak parameters and increase confidence in the sim accuracy. Be mindful of 'go fever' and if the first flight seems off don't just blindly proceed with the second flight, that's what I'm trying to say.

I do like those I280DM's though. For most of the rockets I've built it's the first motor that gets shoved into it. I figure why risk losing a case on the first flight. :)
 

ActingLikeAKid

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Another bit of advice. secure your chute protector 6 inches or so down your harness from the chutepack so the protector is completely free from the chute/CR after it's blown out of the rocket. I've had a chute "stay" in the protector due to stiffness of the material. Once the charge has blown, you don't need a protector anyways. Keep it away from the chutepack so it doesn't interfere with the release once it's out in the breeze. You do that and it greatly increases the chance that your
chute won't get fouled. Kurt (who found out the hard way)
Good info. I love learning from others' mistakes :)
When I dry-fit all the recovery gear, this is what I did (without the barf, because that stuff is messy!) -- keep in mind that I've got 2x1/4" kevlar going from the mmt up to the top of the sustainer:

Couple of handfuls of barf
Slide chute protector onto kevlar and stuff down on top of the barf (not wadded up, but made into a cup, if that makes sense)
Z-fold/tape harness, fold the z-folds in half and put on top of protector.
Z-fold/tape "chute to nose**" harness, stuff that in.
Carefully roll chute*, secure with CR, stuff that in.
Deep breath and put in nose** cone.

*- First roll-up was REALLY snug, so I'm rolling it so it's longer and thinner so it'll come out easier.
** - technically not the nose cone, it's a mid-break rocket.
 

ActingLikeAKid

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My personal experience with AT motor eject delays is that they're more likely to fail short than long (not that I haven't had a few burn up to 4 seconds longer than the stock or drilled-expected value). So I'd err on the long side vs. shortening it in case the delay decides to go even shorter than your target.
Good point. Leaving it alone. The smaller motor is a H100W (the smallest DMS that they have in 38 - I have a CTI 38mm case but no AT gear, it's a long story) and it's not in OpenRocket, so I'm splitting the difference between the H112-J and the H242-T.

So long as you have the right band for the chute you're using ... I use a Chute Release on a 8-9 lb 4" FG Nike Smoke to deploy a 48" parachute, had two flights to 4800+' this past weekend with no issues.
This is a 36" nylon chute; rolled, it doesn't seem much bigger than the 24" ones. Using the small band and it feels snug and secure without feeling like it's going to break. I'll do a couple of pop-tests to make sure.


Personally, I'd never do a main deployment below 500'.
Those are some great points. The field is huge and flat, the only downside to going higher is a bit of a walk. And I'm bringing my hiking boots :) You mentioned a drogue ... How bad an idea is it that I'm going drogueless and popping the CR to open the main? That's what I've done before with no issue. If needs be, I could tie on a little 16" chute and reef or cut it so that it acts like a drogue....

One thing I'd add, if the 'smallest AT 38mm motor' flight is the first flight of the rocket, I'd say be sure to compare your sim to reality before going for the bigger flight....
On it. And I think a JLA3 is in my near future.

Thank you for the great advice!
 

woferry

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Good point. Leaving it alone. The smaller motor is a H100W (the smallest DMS that they have in 38 - I have a CTI 38mm case but no AT gear, it's a long story) and it's not in OpenRocket, so I'm splitting the difference between the H112-J and the H242-T.
That's easy to fix, you can google how to add a motor to OR, it's easy, and you can get the motor data from thrustcurve.org. I added several motors this way, since OR didn't have the H130W, K2050ST, J450DM, etc. It was pointed out on another thread that you can download all of the AT motors in one chunk from rocketryfiles.com (thanks, Mark!), I downloaded it this morning but haven't thrown it into OR yet. On the Mac I created an alias to the place where OR stores the data and put that alias in my folder of rocketry-related stuff, so I don't even need to remember exactly where OR keeps it, I just drop the files into the alias in my rocketry folder.

Those are some great points. The field is huge and flat, the only downside to going higher is a bit of a walk. And I'm bringing my hiking boots :) You mentioned a drogue ... How bad an idea is it that I'm going drogueless and popping the CR to open the main? That's what I've done before with no issue. If needs be, I could tie on a little 16" chute and reef or cut it so that it acts like a drogue....
It's just a comfort thing, you'll probably be fine but use that first flight as a gauge. I wasn't comfortable bringing down a 8-9 lb rocket drogueless, and prefer to have things coming down in an ordered fashion rather than just tumbling in the air. Also it's a 4" airframe so there was no issue with space. But everybody has their own preference. I have decided to re-order things in my harness after watching my most recent flight (I use an ultrazoom camera so I can generally get a good view of things the whole way down), the NC twisted into the shroud lines and for that flight it only resulted in the chute taking a bit longer to fully-open, but it could have easily been worse and tangled, so I'm going to re-order things to ensure the nose is already below the main parachute before the CR releases (up to now I simply had the ~15' harness with the main ~3/4 of the way towards the nose and the drogue attached directly to the nose).
 

NateLowrie

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On the note of the delay, the motor delay can vary by +/-20%, so I wouldn't bother fiddling with it. It's not that exact of a delay, more like nominally 13s. Expect 12-14s range. Any one of those would be fine.
I second this. Don't drill it and you should be fine. I am not terribly fond of motor ejection. Too erratic for my taste. I had a CTI 38mm I eject 6 seconds early on me while my batray was just finished with boost along with a few that were a bit early. But, it should work fine for what you want to do.

Note, if it's a really old motor, the delay is probably too long. Consider replacing the delays on orders more than a few years old.
 

boatgeek

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Also worth pointing out that a typical backup apogee charge would be 1 second after apogee, so you're not out of the realm of totally normal even with a second or two late. Also, if you're not filling a main chute, deceleration after ejection is pretty slow.
 

ActingLikeAKid

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Post-mortem: (yes, it was that bad) ....

You know how sometimes you do that thing where you stress and worry and fret about X, then Y comes and just takes a huge bite out of your....

...yeah.

I brought my freaking laptop to the range so that I could adjust the sim to prevailing winds. I checked and double-checked my electronics. I repacked my chute, twice. I freaked out that the washer that goes under the charge had gone AWOL, but another rocketeer said he'd flown without it, so I shrugged it off & went without. Motor delay drilled, charge installed, motor installed, electronics ready...

...then the rocket fell over and broke into 3 pieces. Turns out 3d-printed ABS isn't the best choice for transitions on HPR rockets.

Back to the drawing board.

Thanks for all the advice.
 

ksaves2

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You mean the neoprene washer? I just thought that made is easier to clean around the touch hole? Kurt
 

NateLowrie

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Post-mortem: (yes, it was that bad) ....

You know how sometimes you do that thing where you stress and worry and fret about X, then Y comes and just takes a huge bite out of your....

...yeah.

I brought my freaking laptop to the range so that I could adjust the sim to prevailing winds. I checked and double-checked my electronics. I repacked my chute, twice. I freaked out that the washer that goes under the charge had gone AWOL, but another rocketeer said he'd flown without it, so I shrugged it off & went without. Motor delay drilled, charge installed, motor installed, electronics ready...

...then the rocket fell over and broke into 3 pieces. Turns out 3d-printed ABS isn't the best choice for transitions on HPR rockets.

Back to the drawing board.

Thanks for all the advice.
...then the rocket fell over and broke into 3 pieces. Turns out 3d-printed ABS isn't the best choice for transitions on HPR rockets.

What infill % were you using? Can you take some pictures of the transitions?
 

ActingLikeAKid

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...then the rocket fell over and broke into 3 pieces. Turns out 3d-printed ABS isn't the best choice for transitions on HPR rockets.

What infill % were you using? Can you take some pictures of the transitions?
Dang. I thought I'd replied. So the infill on one was pretty light; the other was really solid. Pics:
IMG_5256.jpgIMG_5260.jpg

Some solid suggestions over on my build thread: https://www.rocketryforum.com/showthread.php?136668-Blue-Tube-Mega-Vector-Force/page3 ... I think the most important was to print the transitions sideways so that the layers wouldn't shear.

But I just had a brainstorm and I'm very excited about it. Details on the other thread!!!
 

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