Quantcast

Please offer advice on JL Chute Release in Rocksim

The Rocketry Forum

Help Support The Rocketry Forum:

SaltyCracker

Member
Joined
Nov 24, 2020
Messages
17
Reaction score
11
Location
Coastal Va.
I have a question that I'm sure many have had.
I'm fairly new to Rocksim but am getting pretty familiar with the basics. I haven't designed any rockets with it yet but use it for figuring out delays and safe takeoff/landings.
My son has a JL Chute Release he wants to begin using on his mid-power park fliers.
I just can't figure out how to get the right info into Rocksim.
First I went to the Rocket Design Attributes tab and tried changing the stock design to two-stage but that asked for a second motor mount.
Then back at single stage... in the Rocket Design Components tab, I added a small streamer or drogue to the 36" chute already there.
In the Flight Events section, the drogue set to be deployed at max ejection delay and the chute set to be deployed at altitude.
The simulation sees the streamer/drogue but not the main chute.
I am noticing that in the Flight Events section where I set the chute altitude, my setting doesn't seem to save. I enter my number and hit OK and the window closes. When I open it again to verify, it's showing 0.00. So I tried hitting the Launch or Flight Profile button instead but my flight still lands at almost 40MPH under drogue alone.
I know it's input error but I can't figure out what. I've watched all of the Rocksim training videos too.
 

Antares JS

Well-Known Member
Joined
Mar 5, 2020
Messages
693
Reaction score
615
Location
Eastern Shore, VA
I have a question that I'm sure many have had.
I'm fairly new to Rocksim but am getting pretty familiar with the basics. I haven't designed any rockets with it yet but use it for figuring out delays and safe takeoff/landings.
My son has a JL Chute Release he wants to begin using on his mid-power park fliers.
I just can't figure out how to get the right info into Rocksim.
First I went to the Rocket Design Attributes tab and tried changing the stock design to two-stage but that asked for a second motor mount.
Then back at single stage... in the Rocket Design Components tab, I added a small streamer or drogue to the 36" chute already there.
In the Flight Events section, the drogue set to be deployed at max ejection delay and the chute set to be deployed at altitude.
The simulation sees the streamer/drogue but not the main chute.
I am noticing that in the Flight Events section where I set the chute altitude, my setting doesn't seem to save. I enter my number and hit OK and the window closes. When I open it again to verify, it's showing 0.00. So I tried hitting the Launch or Flight Profile button instead but my flight still lands at almost 40MPH under drogue alone.
I know it's input error but I can't figure out what. I've watched all of the Rocksim training videos too.
Can you show me a screenshot of your fully expanded parts list?
 

SaltyCracker

Member
Joined
Nov 24, 2020
Messages
17
Reaction score
11
Location
Coastal Va.
Ooh yeah, I should have done that up front.
Literally, the only thing I did to the stock file is add the 15" chute and the H128 motor.
 

Attachments

Antares JS

Well-Known Member
Joined
Mar 5, 2020
Messages
693
Reaction score
615
Location
Eastern Shore, VA
I think what you need to do is enter your number into the altitude box, then either hit enter or click on another window in the box before hitting OK. It's not only like that for that altitude deployment setting but for every single parameter.

It's a weird thing with Rocksim that I'm used to and do without thinking about it.
 

SaltyCracker

Member
Joined
Nov 24, 2020
Messages
17
Reaction score
11
Location
Coastal Va.
I think what you need to do is enter your number into the altitude box, then either hit enter or click on another window in the box before hitting OK. It's not only like that for that altitude deployment setting but for every single parameter.

It's a weird thing with Rocksim that I'm used to and do without thinking about it.
Oh man! I knew it was a silly oversight.
I'm slightly embarrassed but more relieved.
Thank you.
I get over to your side of the Bay occasionally during sailing season. :)
 

hball55

Well-Known Member
Joined
Nov 20, 2013
Messages
1,508
Reaction score
52
Am I missing something? Don’t you just need to add the mass of your JL Chute Release to the parachute and you’re done?

Edit: I’m confused as to why you’re using a drogue when you have a JL Chute Release, unless you are referring to the main chute as the drogue since it’s reefed (bound) by the JL Chute Release. What you should be concerned about is the apogee event, that since your main chute is going to be reefed it doesn’t really matter so long as the apogee ejection isn’t early (no sense in denying yourself max altitude). The event of opening your main using the JL Chute Release is not relevant in my mind.

I think you are complicating matters by trying to use that portion of Rocksim that you are using. Just enter the motor you want and make sure the delay isn’t short, that way even if your rocket is coming in ballistic, the ejection of a reefed main chute isn’t going to cause a damaging event. Your rocket ought to come in a flat trajectory after ejection, thus slowing it down enough to be safe. The JL chute release will do its job at the elevation you choose.

As far as a safe speed at deployment, are you asking about the apogee event or the secondary JLCR event? I honestly don’t believe you have to worry about the apogee event since your chute is going to be reefed. As for the second event, the rockets I have used with the JLCR have all fallen slow enough that no damage occurred when the JLCR did its job. I’ve never felt the need to even try to simulate what the air speed was for the second event. As for what speed the rocket lands at, that’s the job of properly choosing the right size parachute.
 
Last edited:

SaltyCracker

Member
Joined
Nov 24, 2020
Messages
17
Reaction score
11
Location
Coastal Va.
Am I missing something? Don’t you just need to add the mass of your JL Chute Release to the parachute and you’re done?

Edit: I’m confused as to why you’re using a drogue when you have a JL Chute Release, unless you are referring to the main chute as the drogue since it’s reefed (bound) by the JL Chute Release. What you should be concerned about is the apogee event, that since your main chute is going to be reefed it doesn’t really matter so long as the apogee ejection isn’t early (no sense in denying yourself max altitude). The event of opening your main using the JL Chute Release is not relevant in my mind.

I think you are complicating matters by trying to use that portion of Rocksim that you are using. Just enter the motor you want and make sure the delay isn’t short, that way even if your rocket is coming in ballistic, the ejection of a reefed main chute isn’t going to cause a damaging event. Your rocket ought to come in a flat trajectory after ejection, thus slowing it down enough to be safe. The JL chute release will do its job at the elevation you choose.

As far as a safe speed at deployment, are you asking about the apogee event or the secondary JLCR event? I honestly don’t believe you have to worry about the apogee event since your chute is going to be reefed. As for the second event, the rockets I have used with the JLCR have all fallen slow enough that no damage occurred when the JLCR did its job. I’ve never felt the need to even try to simulate what the air speed was for the second event. As for what speed the rocket lands at, that’s the job of properly choosing the right size parachute.
"What we've got here is failure to communicate." ;)
Sorry... I saw your quote of one of my favorite movies and couldn't help myself.
So what I'm doing is for simulation purposes only.
I'm simulating a non-existent drogue deployed at apogee to act as a stand in for the drag of my falling rocket until the chute deploys at the set altitude. Otherwise it would simulate as traveling at ballistic speeds until the chute altitude. Doing so has my chute opening at 200ft/s and a landing range of 53ft.
When I add the pretend drag, I get the more realistic 50ft/s and a range of 288ft.
As far as speed of deployment, I look at speed at apogee and now that we'll be using the chute release, I'll be watching that speed too and keeping it under 50ft/s.
I keep my landing less than 20ft/s. That's what I've been told the safe speed is.
Though I was forgetting to add the mass of the JLCR. Thanks for bringing that up.
 

Nytrunner

Pop lugs, not drugs
TRF Supporter
Joined
Oct 15, 2016
Messages
7,751
Reaction score
3,377
Location
Huntsville AL
I'm simulating a non-existent drogue deployed at apogee to act as a stand in for the drag of my falling rocket until the chute deploys at the set altitude. Otherwise it would simulate as traveling at ballistic speeds until the chute altitude.
I've had pretty good success simulating falling with reefed chute by making a faux-chute with ~the same area as the booster.

To do that I use the following:
Tube profile area + Fin profile area

Tube profile~=Length*Diam*.5
4-fin profile~= area of fin side*2
3-fin profile~= area of fin side*1.5
 

SaltyCracker

Member
Joined
Nov 24, 2020
Messages
17
Reaction score
11
Location
Coastal Va.
I've had pretty good success simulating falling with reefed chute by making a faux-chute with ~the same area as the booster.

To do that I use the following:
Tube profile area + Fin profile area

Tube profile~=Length*Diam*.5
4-fin profile~= area of fin side*2
3-fin profile~= area of fin side*1.5
Just the booster?

Thank you. I'll play with those numbers some.
I've been using:
Square root of (4 x L of rocket x D of rocket / 3.14)
This gives me the diameter of the pretend drogue.
 

hball55

Well-Known Member
Joined
Nov 20, 2013
Messages
1,508
Reaction score
52
"What we've got here is failure to communicate." ;)
Sorry... I saw your quote of one of my favorite movies and couldn't help myself.
When I add the pretend drag, I get the more realistic 50ft/s and a range of 288ft.
As far as speed of deployment, I look at speed at apogee and now that we'll be using the chute release, I'll be watching that speed too and keeping it under 50ft/s.
I keep my landing less than 20ft/s. That's what I've been told the safe speed is.
Though I was forgetting to add the mass of the JLCR. Thanks for bringing that up.
One of my favorite quotes also . . . Strother Martin is one of the great character actors there’s ever been. I now see what you are doing, kudos, I considered it but not very long, as you can see in my post 😧🤫. Happy flying🚀
 

Scott_650

Well-Known Member
Joined
Sep 16, 2015
Messages
830
Reaction score
333
Just to add a bit more to this rather interesting can of worms - when I use my CR with larger rockets - like my Estes Executioner or my 4” crayon rocket - I use a streamer along with the bundled chute. It’s worked well so far keeping everything both falling at a reasonable rate and making it easier to track after the initial recovery event.
 

MetricRocketeer

Well-Known Member
TRF Supporter
Joined
Jun 1, 2018
Messages
257
Reaction score
42
Hi Nytrunner,

So you wrote the following:

I've had pretty good success simulating falling with reefed chute by making a faux-chute with ~the same area as the booster.

To do that I use the following:
Tube profile area + Fin profile area

Tube profile~=Length*Diam*.5
4-fin profile~= area of fin side*2
3-fin profile~= area of fin side*1.5

I would like to make sure that I understand your meaning. Could you please show you calculations given the current rocket. Of course, we have the 3-fin profile in the present instance.

Thank you.

Stanley
 

MetricRocketeer

Well-Known Member
TRF Supporter
Joined
Jun 1, 2018
Messages
257
Reaction score
42
Hi Nytrunner,

I get confused on how to use the quotes feature (although it shouldn't be that difficult). Perhaps, therefore, I did not clearly express my question. I am going to try again, if I may.
I've had pretty good success simulating falling with reefed chute by making a faux-chute with ~the same area as the booster.

To do that I use the following:
Tube profile area + Fin profile area

Tube profile~=Length*Diam*.5
4-fin profile~= area of fin side*2
3-fin profile~= area of fin side*1.5
I would like to make sure that I understand your meaning. Could you please show you calculations given the current rocket. Of course, we have the 3-fin profile in the present instance.

Thank you. (And now I seem to be correctly using the quotes feature, and it is quite convenient.)

Stanley
 

Nytrunner

Pop lugs, not drugs
TRF Supporter
Joined
Oct 15, 2016
Messages
7,751
Reaction score
3,377
Location
Huntsville AL
-
I would like to make sure that I understand your meaning. Could you please show you calculations given the current rocket. Of course, we have the 3-fin profile in the present instance.

Thank you. (And now I seem to be correctly using the quotes feature, and it is quite convenient.)

Stanley
Since I was answering Salty's question, and he had the concept in mind, I didn't expand any further. But I'll break it down for you

This is just for drogueless descents at apogee, where the rocket has been split apart, but the chute is held by a chute release or other means.

If you simulate this as-built in OR or RS, you'll omit the drogue and the rocket will behave as if there was no deployment event and return ballistic until the main chute release point.
When the rocket breaks open in real life, the drag of the airframe itself will slow it down a little. To approximate that, we want to create an imaginary drogue in our simulation.

Assumption: The booster will have more lateral area than the nose/payload, and be the primary drag contributor. I choose to approximate the booster as my faux-drogue

I take the lateral area of the booster tube and apply a fudge factor since it's a cylinder instead of a flat plane rectangle (I choose .5 as a conservative value based on flow past a cylinder)

Let's say your booster tube is 30" long, 2.5" wide.
Plug that in and you've got a body tube contribution of ~37.5 in^2

I treat fins as flat plates and multiply the fin area by a fin count factor . 4fin worst case has 2 fins broadside into the wind. 3 fin worst case depends on the angle, but I take a conservative 1.5 fin area in the wind.
Let's say the area of 1 fin is 15in^2
-A 4 fin contribution would be ~30 in^2
-A 3 fin contribution would be ~22.5 in^2

You wanted 3 3 fin example? sure why not.
To get the pretend drogue area just add up the tube and fin contributions which is 37.5+22.5 = 60in^2, or a ~8.75" diameter chute

Scientific? barely
Close enough? absolutely
 

MetricRocketeer

Well-Known Member
TRF Supporter
Joined
Jun 1, 2018
Messages
257
Reaction score
42
Hi Nytrunner,

Good. Thank you so much for the detailed analysis. That was tremendously helpful.

Stanley
 

QFactor

L2 - NAR & TRA
Joined
Nov 6, 2019
Messages
189
Reaction score
106
Location
Ohio
Since I was answering Salty's question, and he had the concept in mind, I didn't expand any further. But I'll break it down for you

This is just for drogueless descents at apogee, where the rocket has been split apart, but the chute is held by a chute release or other means.

If you simulate this as-built in OR or RS, you'll omit the drogue and the rocket will behave as if there was no deployment event and return ballistic until the main chute release point.
When the rocket breaks open in real life, the drag of the airframe itself will slow it down a little. To approximate that, we want to create an imaginary drogue in our simulation.

Assumption: The booster will have more lateral area than the nose/payload, and be the primary drag contributor. I choose to approximate the booster as my faux-drogue

I take the lateral area of the booster tube and apply a fudge factor since it's a cylinder instead of a flat plane rectangle (I choose .5 as a conservative value based on flow past a cylinder)

Let's say your booster tube is 30" long, 2.5" wide.
Plug that in and you've got a body tube contribution of ~37.5 in^2

I treat fins as flat plates and multiply the fin area by a fin count factor . 4fin worst case has 2 fins broadside into the wind. 3 fin worst case depends on the angle, but I take a conservative 1.5 fin area in the wind.
Let's say the area of 1 fin is 15in^2
-A 4 fin contribution would be ~30 in^2
-A 3 fin contribution would be ~22.5 in^2

You wanted 3 3 fin example? sure why not.
To get the pretend drogue area just add up the tube and fin contributions which is 37.5+22.5 = 60in^2, or a ~8.75" diameter chute

Scientific? barely
Close enough? absolutely
That's a pretty interesting method for handling a drogueless descent. Have you been able to check it against flight data using one of the flight computer that saves flight info? Curious to see how that compared.
 

Nytrunner

Pop lugs, not drugs
TRF Supporter
Joined
Oct 15, 2016
Messages
7,751
Reaction score
3,377
Location
Huntsville AL
That's a pretty interesting method for handling a drogueless descent. Have you been able to check it against flight data using one of the flight computer that saves flight info? Curious to see how that compared.
Funny thing there, my recording altimeters are my deployment altimeters.
And if I'm using a chute release, Im not using a deployment altimeter.

I could try and run an Alt3 or Flightsketch on one of those flights some day
 

MetricRocketeer

Well-Known Member
TRF Supporter
Joined
Jun 1, 2018
Messages
257
Reaction score
42
Hi Nytrunner,

Actually, may I please ask you a followup to your detailed answer a few posts up?

Using your calculations, you do not use a drogue parachute, correct? Instead, you use only a main parachute, and you make that rather small -- only 8.75 inches in the example you gave. Is that correct?

So then, in simulations, or in an actual flight, what is the flight event that triggers the parachute release? Is it maximum ejection? Is it a certain altitude? Is it a certain amount of time after apogee?

Thank you.

Stanley
 

Nytrunner

Pop lugs, not drugs
TRF Supporter
Joined
Oct 15, 2016
Messages
7,751
Reaction score
3,377
Location
Huntsville AL
Hi Nytrunner,

Actually, may I please ask you a followup to your detailed answer a few posts up?

Using your calculations, you do not use a drogue parachute, correct? Instead, you use only a main parachute, and you make that rather small -- only 8.75 inches in the example you gave. Is that correct?

So then, in simulations, or in an actual flight, what is the flight event that triggers the parachute release? Is it maximum ejection? Is it a certain altitude? Is it a certain amount of time after apogee?

Thank you.

Stanley
Youre correct, i dont use a drogue for these flights, but I think you misunderstood the point of the calculation.

That is so that you can size an imaginary drogue that you use in the simulation. It only exists in the simulation. thats the 8.75" chute.

I also have a main chute in the simulation sized appropriately to bring the rocket to ground safely. That matches the chute that will actually fly in the rocket. Its set to deploy at a set altitude above ground during descent (in the simulation and on the chute release inflight)
 
Last edited:

MetricRocketeer

Well-Known Member
TRF Supporter
Joined
Jun 1, 2018
Messages
257
Reaction score
42
OK. Did you really mean to say that the main parachute is set to deploy during "ascent"? the chute would deploy at descent, right?
 

Dan Griffing

Well-Known Member
TRF Supporter
Joined
Aug 5, 2020
Messages
233
Reaction score
125
Location
Belgrade, MT
Am I missing something? Don’t you just need to add the mass of your JL Chute Release to the parachute and you’re done?

Edit: I’m confused as to why you’re using a drogue when you have a JL Chute Release, unless you are referring to the main chute as the drogue since it’s reefed (bound) by the JL Chute Release. What you should be concerned about is the apogee event, that since your main chute is going to be reefed it doesn’t really matter so long as the apogee ejection isn’t early (no sense in denying yourself max altitude). The event of opening your main using the JL Chute Release is not relevant in my mind.

I think you are complicating matters by trying to use that portion of Rocksim that you are using. Just enter the motor you want and make sure the delay isn’t short, that way even if your rocket is coming in ballistic, the ejection of a reefed main chute isn’t going to cause a damaging event. Your rocket ought to come in a flat trajectory after ejection, thus slowing it down enough to be safe. The JL chute release will do its job at the elevation you choose.

As far as a safe speed at deployment, are you asking about the apogee event or the secondary JLCR event? I honestly don’t believe you have to worry about the apogee event since your chute is going to be reefed. As for the second event, the rockets I have used with the JLCR have all fallen slow enough that no damage occurred when the JLCR did its job. I’ve never felt the need to even try to simulate what the air speed was for the second event. As for what speed the rocket lands at, that’s the job of properly choosing the right size parachute.
As far as a safe speed at deployment, are you asking about the apogee event or the secondary JLCR event? I honestly don’t believe you have to worry about the apogee event since your chute is going to be reefed. As for the second event, the rockets I have used with the JLCR have all fallen slow enough that no damage occurred when the JLCR did its job.
At the July Big Sky Rocketry launch I saw a rocket seriously damaged by zippering while using a JLCR without an additional drogue.

It was a very long rocket and had a much longer shock cord attaching the nosecone and the parachute reefed with a JLCR.

This resulted in the rocket airframe accelerating towards the ground like a lawn dart while streaming the reefed parachute and nosecone behind. When the JLCR finally fired at 400-500 feet, the chute deployment was so sudden that it seriously damaged the airframe. I seem to recall that this was also an L1 attempt that was defeated because of the damage.

I was also using a JLCR on an Apogee Zephyr that day but with a 12” drogue that slowed the airframe sufficiently that it came down in a flat spin and had a gentle deployment of the 36” main.
 

QFactor

L2 - NAR & TRA
Joined
Nov 6, 2019
Messages
189
Reaction score
106
Location
Ohio
Funny thing there, my recording altimeters are my deployment altimeters.
And if I'm using a chute release, Im not using a deployment altimeter.

I could try and run an Alt3 or Flightsketch on one of those flights some day
Might be interesting to see what the descent rate really is.
 

mtnmanak

TRA & NAR L2
TRF Supporter
Joined
May 5, 2020
Messages
584
Reaction score
468
Location
NJ & PA
At the July Big Sky Rocketry launch I saw a rocket seriously damaged by zippering while using a JLCR without an additional drogue.

It was a very long rocket and had a much longer shock cord attaching the nosecone and the parachute reefed with a JLCR.

This resulted in the rocket airframe accelerating towards the ground like a lawn dart while streaming the reefed parachute and nosecone behind. When the JLCR finally fired at 400-500 feet, the chute deployment was so sudden that it seriously damaged the airframe. I seem to recall that this was also an L1 attempt that was defeated because of the damage.

I was also using a JLCR on an Apogee Zephyr that day but with a 12” drogue that slowed the airframe sufficiently that it came down in a flat spin and had a gentle deployment of the 36” main.
Agreed - surprised there weren't more comments about this. I love the JLCR and often use it with a drogue. Using a drogue with a JLCR is a common "poor man's dual deploy" and I have used it many times. Works great in the aforementioned Zephyr and many other large single deploy rockets like the many Goblins I see flying. Putting a 6 lbs rocket up to a couple thousand feet with a cardboard tube and then letting it deploy the main at terminal velocity is just asking for a zipper. I thought using a drogue or streamer with a JLCR on a larger rocket was the norm.
 

SaltyCracker

Member
Joined
Nov 24, 2020
Messages
17
Reaction score
11
Location
Coastal Va.
Agreed - surprised there weren't more comments about this. I love the JLCR and often use it with a drogue. Using a drogue with a JLCR is a common "poor man's dual deploy" and I have used it many times. Works great in the aforementioned Zephyr and many other large single deploy rockets like the many Goblins I see flying. Putting a 6 lbs rocket up to a couple thousand feet with a cardboard tube and then letting it deploy the main at terminal velocity is just asking for a zipper. I thought using a drogue or streamer with a JLCR on a larger rocket was the norm.
Hmm... food for thought.
 
Top