How can I slow deployment?

[dford]

Other than the obvious answer...longer delay charge, if I sim out a rocket for ideal delay at 11.5 seconds and the longest delay is 10 seconds how can I slow down the chute from opening?

My thoughts so far
A)longer shock cord
B)small chute to open before initial shock
C)bridging rubber bands
D)chute release but it isn't feasible yet. not in budget (yet) and won't fit with altimeter and 15' of shock cord.

Is there a way to lengthen the manufacturer delay?
How do record altitude holders get them so high without a longer delay. Or do they just shoot it and hope for the best upon landing?

 

[Charles_McG]

You are wondering about extending the coast time, rather than slowing the speed the chute snaps open, yes?

 

[Bat-mite]

Is there a motor with a similar thrust curve that has a longer delay? Specifics on your configuration might help.

 

[dford]

You are wondering about extending the coast time, rather than slowing the speed the chute snaps open, yes?

Actually the coast time I've designed to go further but was worried about it being too high with the delay.
So I'm more worried about it snapping open throwing a zipper in it or shredding the chute.

 

[dford]

Is there a motor with a similar thrust curve that has a longer delay? Specifics on your configuration might help.

I plan on using an aerotech G76-10. I hAvent seen a longer delay for Aerotech RMS 29mm.

 

[Zebedee]

When you start getting into fast rockets with long coast times it's also a good time to think about altimeter based deployment rather than motor deployment and even dual deployment.

 

[Bat-mite]

When you start getting into fast rockets with long coast times it's also a good time to think about altimeter based deployment rather than motor deployment and even dual deployment.

Agreed. Your rocket may have exceeded the motor's limitations. Snag an RRC2+ and outfit your nose cone with a bay.

 

[Charles_McG]

My Titan IIIe boosters separate and deploy at burnout. Which means at high speed, if not the peak speed (the booster keeps burning with the current motor selection).

One booster came down on an orange Estes plastic chute with only one shroud still attached. No damage. So you might consider a streamer or a big spill hole and a faster descent than you might normally be comfortable with. Might be good for recovery from higher than normal altitude too.

The other tip I received was to use a ring or bead around the shroud lines. Slide up to the chute when packing. It slides back down as the chute opens - but slows the opening.

 

[dford]

Ahhh yeah. The shroud line ring! I forgot about that. Sweet idea. Thanks a lot a lot.

I wanted to see how far I could get with a G motor.

 

[ksaves2]

One thing you could try would be to purchase the same kind of delay grain and cut a small portion off to add additional length to the stock grain. How much to cut? Divide the length of the grain by the time and perhaps add a "sliver" more of length.
The cardboard delay "holder" can generally hold a much longer delay in length and could cut down the "delay" spacer and even use a small amount of epoxy to hold the internal spacer in place. I'm considering trying something like this for
a 29mm I200 to get 16 seconds as the max delay is 14 seconds. Kurt

 

[Coop]

Time to go electronic. There's a good many inexpensive options out there. RRC2+ comes screaming to mind...


Later!

--Coop

 

[watermelonman]

As the others said, long term, go electronic.

Short term, if you have a rocket you want to fly now, popping a second or two early is not going to hurt. Fly it!

 

[dhbarr]

I have a theory that an hdk23 ( full length, slow delay formulation) in place of an hdk19 should give ~14 sec delay on an AT g76. Disclaimer: haven't tried it.

 

[dford]

One thing you could try would be to purchase the same kind of delay grain and cut a small portion off to add additional length to the stock grain. How much to cut? Divide the length of the grain by the time and perhaps add a "sliver" more of length.
The cardboard delay "holder" can generally hold a much longer delay in length and could cut down the "delay" spacer and even use a small amount of epoxy to hold the internal spacer in place. I'm considering trying something like this for
a 29mm I200 to get 16 seconds as the max delay is 14 seconds. Kurt

I am 100% on board with electronics for future builds. I fully intend on using them for cert flights and beyond.

I've realized kits are more geared towards the "stock" systems.
Once getting into my own designs and pushing higher altitudes electronics and or the type of additional delay spacers will be needed.

Thanks for all the information.

I intend on doing a full build compilation thread once flown and recovered with pictures and the attached .ork file. Club launch is on the second Saturday of each month. I'll post shortly after.

Wish me luck. Nozzle end up right?oint:

 

[tim cubbedge]

When delays were too short, I either found another motor that worked or like everyone says, go electronic!

 

[ksaves2]

That would be fodder for a how-to article concerning AT motors. Mix and match delay grains for longer, non-standard delays. Of course if they standardize and go to a limited number of delays and have people drill them for shorter duration that
might put the kibosh on that.

The stuff like nosecone trackers, GPS or otherwise and the Jolly Logic Chute Release makes the prospect of high altitude motor ejection feasible on small projects. Kurt

 

[rocket_troy]

One thing you could try would be to purchase the same kind of delay grain and cut a small portion off to add additional length to the stock grain. How much to cut? Divide the length of the grain by the time and perhaps add a "sliver" more of length.
The cardboard delay "holder" can generally hold a much longer delay in length and could cut down the "delay" spacer and even use a small amount of epoxy to hold the internal spacer in place. I'm considering trying something like this for
a 29mm I200 to get 16 seconds as the max delay is 14 seconds. Kurt

You need to be a bit careful with this approach for various reasons - some are obvious, but some are not. It's important to note that the delay compositions used in commercial hobby motors are pretty much slow burning propellants ie. the primary ingredients (in particular the oxidizer) is the same. What this means is that we can assume that the delay column won't burn at a linear rate - the burn rate will be exponentially proportional to the chamber pressure r = a p^n. Which translates to it burning much faster during the thrust phase of the motor's operation and much slower after the chamber pressure has dropped.
So, if we assume that you're adding (say) an extension to the top of the delay column and we assume that the chamber exposed end of the column is ignited exactly the same way as a conventional (unmodified column) ie. from that very face only, and we assume the join between the existing column and extension piece is 100% sealed from external penetration (these are all critical assumptions), then you can gauge the length of the extension required by burning a leftover bit of the extension piece in normal atmospheric conditions and measuring the burn rate of the composition in these conditions.
Don't try and calculate the time from assuming delay columns burn at a linear rate.

Troy

 

[Banzai88]

Doesn't messing with the delay in the positive direction (adding delay or swapping in non-certified delay elements) make it a non-cert/research motor?

 

[rocket_troy]

Doesn't messing with the delay in the positive direction (adding delay or swapping in non-certified delay elements) make it a non-cert/research motor?

I'm reasonably confident it would render it non-certified and if it didn't, it should.

Troy

 

[Steve Shannon]

Ask the motor manufacturer if it has an extended forward closure and extended delay.

 

[Winston]

Ahhh yeah. The shroud line ring! I forgot about that. Sweet idea. Thanks a lot a lot.

On that topic:

https://www.rocketryforum.com/showthread.php?56344-Plastic-reefing-rings-for-HPR&highlight=ring

EDIT: These might be useful and have less of a tendency to fall down the shroud lines due to gravity:

https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias=aps&field-keywords=nylon+spacer+bushing

I believe they have these at any Ace Hardware store that has a decent hardware section which, at least area, is more likely than finding a Home Depot or Lowes with an equivalent hardware collection. Lowes has some of the nylon bushings, but not a large selection of ones with an ID/length ratio that would be useful for HPR 'chutes. Might be right for MPR chutes, though.

 

[T-Rex]

Have you run a simulation for the G138T-14? or a G80-14 single use?

 

[dford]

Have you run a simulation for the G138T-14? or a G80-14 single use?

Still good without cert it seems?

 

[dford]

On that topic:

https://www.rocketryforum.com/showthread.php?56344-Plastic-reefing-rings-for-HPR&highlight=ring

EDIT: These might be useful and have less of a tendency to fall down the shroud lines due to gravity:

https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias=aps&field-keywords=nylon+spacer+bushing

I believe they have these at any Ace Hardware store that has a decent hardware section which, at least area, is more likely than finding a Home Depot or Lowes with an equivalent hardware collection. Lowes has some of the nylon bushings, but not a large selection of ones with an ID/length ratio that would be useful for HPR 'chutes. Might be right for MPR chutes, though.

Sweet. Thank you kindly sir. I'll look into it more.
Again, thank you

 

[ksaves2]

Doesn't messing with the delay in the positive direction (adding delay or swapping in non-certified delay elements) make it a non-cert/research motor?

Yes but where I fly it's a research rules/venue. Troy, I understand what you are saying but getting a second or two more delay while not exact is workable. What it means is the added piece might be a little "thicker if it's placed on the
ignition side or a little "thinner" if placed on the ejection charge well side. Very good point and thanks for mentioning it. If pursuing that tact, absolute precision can't be expected so I wouldn't recommend it with a cardboard rocket. Since the rocket is going up high, a robust harness on a glass bird should be doable if the delay is a bit "too long". Especially if a chute is reefed by a Jolly Logic Chute Release. A higher speed deployment would be more tolerable. Kurt

 

[ksaves2]

Ask the motor manufacturer if it has an extended forward closure and extended delay.

With a 29mm H250 the RDK18 gives it 14 seconds. In the cardboard tube the delay is slid into, there is room for a bit more as there is an aft internal cardboard thrust block even with the 14 second delay. Could perhaps use plastic cement/epoxy to secure the delay grain inside of the cardboard tube taking exacting care not to get any cement on the burning faces of the delay grain if trying to extend past 14 seconds. Again, yes it's now a research motor. Outside of the NAR, the lines between a research/commercial launch are very blurred now since the liberalization of the TRA rules. Research venues allow 90% of the waiver for a research motor but even NAR folks can present and fly commercial stuff if I recollect correctly.
Since the intervals at a research launch are plenty long, shouldn't be a problem with commercial loads/flights. No one is going to get yanked by an H motor launched at 400 feet away. Certainly isn't a violation of the rules.
Cripes, at the sparsely attended club launches I'm a party to, they'll put four or five pads at 300 to 400 feet for L birds and call it good. Everyone fires from there. (We use a wireless controller)

In fact, I find I can visually follow a rocket if I'm at a greater distance away from the launch than what is specified as a "safe distance" in the rules. Kurt

 

[JRobinsonUSAF]

Sliders have been in use on full size 'chutes for years. They are one of the things that made the square chute practical for skydiving. Prior to the sliders, the opening shock of a square chute was brutal, to say the least. A nylon ring even loosely fitted to the suspension lines should make a marked difference in slowing down the canopy opening.

https://avstop.com/ac/prh/chapter2_9.html

A sleeve can also slow opening. These were used on the round chutes I jumped in the 70's.

https://kids.britannica.com/comptons/art-53774/1-Ripcord-is-pulled-in-stable-position?

JR

 

[Winston]

Easy creation of a toroidal 'chute (higher Cd) from a normal one, and a mention of reefing rings:

[video=youtube;vMT-97kW9nQ]https://www.youtube.com/watch?v=vMT-97kW9nQ[/video]

The data:

https://www.aircommandrockets.com/day177.htm

 

[cerving]

The smaller CTI 29mm motors have delays of 11-14 seconds, and it has been my own personal observation that CTI's delays are more accurate than AT's (or at least less likely to be significantly shorter). The AT G80-14 DMS motor is the only non-cert motor that they have with such a long delay.

Of course, personally I'd love to see you go electronic...

 

[John Beans]

In the future, separation and deployment (my prediction) will be entirely electronic (i.e. not black powder, just electronic). Your rocket will separate at apogee, and your chute will open when you want it to (e.g. Chute Release). We have the second part already, the first part (electronic deployment) will come at some point. In the future, you'll buy motors just for the "up" part, not the deployment part. They are not particularly good at that...