Open Rocket and Jolly Logic Chute Release.

[Wrightme43]

Is there any way to plot the results of using a Chute release that opens at 500 feet, into the simulations for Open Rocket?
Ejection is happening where it should. What I have been doing is using 10% of the wind drift from the result from apogee
to the opening of the chute release, then using 100% of the drift from 50' to ground level.

I expect the bluesrocks meet on Saturday will be canceled or postponed again. The wind on NOAA is showing 15 mph.
It doesn't look like a great day to launch. Hoping the wind will settle down as the forecast comes into focus. I have been
running the sim to see what will happen if the launch stays on.
If what I think will happen, does happen, it would land about 500' downwind after going about 200' upwind.

I edited all masses to be correct with a digital scale.

 

[waltr]

Yes, OR is set up the same way as if it was Dual Deploy.
On the Design tab, double click the chute and in the lower right of the config dialod is "Deployment". Set to "Specific altitude during descent" then set altitude to 500 ft.

Re-RUN sim then plot.

 

[neil_w]

File -> Open Example -> Chute release

 

[Wrightme43]

I tried that earlier. It has the rocket continue assembled, arc over into wind, and continue down ballastic, then open deploy at a very high speed way upwind of where it should of started falling down.

 

[Wrightme43]

File -> Open Example -> Chute release

Thank You! How do add it to my rocket so I can use it? I found it in the example.

 

[neil_w]

Just copy/paste the necessary components from the example to your rocket.

I fear it’s not going to give you what you want, though… results will look like those @waltr was giving above. I’ll discuss this with @JoePfeiffer.

 

[waltr]

You do need a streamer or smaller chute that deploys at either motor eject or at Apogee.

The "Chute release" example does work but the the streamer is also set to ZERO Cd so it will NOT slow the rocket.
Set to a Cd value or Automatic and make the streamer much longer and wider.

Note: with Dual deploy or a Chute release the the descent speed will be higher than under chute (this is desired). OR will then give a Warning about "deployment at high speed". This is actually what we want so warning can be ignored.

 

[GalantVR41062]

The decent rate at the time of main deploy should be considered, do not just ignore the warning.

I have a "small" chute deploy at apogee then the main chute at the desired altitude on decent (jlcr). I play with drogue size to match my desired decent rate before the main chute. For my cardboard 4" rockets this is normaly in the 45-50ft/s.

 

[Ronz Rocketz]

Following

 

[JoePfeiffer]

Ouch, that example turns out to not be a good one... modeling the reefed chute as a streamer makes it impossible to size the opened chute to get a good result, and that streamer is tiny.

We don't have a handle on what the drag of the reefed chute will be, let alone the reefed chute and the tumbling rocket, so what follows will be a really nasty hack:

Treat it as a standard dual deploy. Make a guess at the size of the drogue so the descent rate is something you feel is reasonable.

Now size the main so the total area of the drogue plus the main is the same area as your actual chute.

You can see how the hack works by modifying the example:

1. Delete the streamer and replace it with a parachute. Since the main parachute in the example is an elliptical chute with a CD of 1.55, set the CD of the new chute to 1.55. The example seems to be planning on motor eject, so I'm going to set the "fake drogue" deployment as "first ejection charge".
2. Running several simulations and playing with the drogue chute size, I find that a chute with a 10 inch diameter gives a velocity at deployment of just under 50 fps. That seems reasonable to me.
3. The main parachute in the example has a diameter of 30 inches, and so an area of about 700 sq in. The drogue chute has an area of about 80 sq in. So, we set the diameter of the main so its area is 700 - 80 = 620 sq in; the diameter of the "fake main" is now 28 inch.
4. Running the simulations, I get velocity at opening (ie drogue descent rate) of 46.7 fps, and landing velocity of 15.6 fps

 

[Wrightme43]

Ouch, that example turns out to not be a good one... modeling the reefed chute as a streamer makes it impossible to size the opened chute to get a good result, and that streamer is tiny.

We don't have a handle on what the drag of the reefed chute will be, let alone the reefed chute and the tumbling rocket, so what follows will be a really nasty hack:

Treat it as a standard dual deploy. Make a guess at the size of the drogue so the descent rate is something you feel is reasonable.

Now size the main so the total area of the drogue plus the main is the same area as your actual chute.

You can see how the hack works by modifying the example:

1. Delete the streamer and replace it with a parachute. Since the main parachute in the example is an elliptical chute with a CD of 1.55, set the CD of the new chute to 1.55. The example seems to be planning on motor eject, so I'm going to set the "fake drogue" deployment as "first ejection charge".
2. Running several simulations and playing with the drogue chute size, I find that a chute with a 10 inch diameter gives a velocity at deployment of just under 50 fps. That seems reasonable to me.
3. The main parachute in the example has a diameter of 30 inches, and so an area of about 700 sq in. The drogue chute has an area of about 80 sq in. So, we set the diameter of the main so its area is 700 - 80 = 620 sq in; the diameter of the "fake main" is now 28 inch.
4. Running the simulations, I get velocity at opening (ie drogue descent rate) of 46.7 fps, and landing velocity of 15.6 fps

Thank You!!!!

I will check this out as soon as I get some free time at home. I am super busy the next two days, so I will start on Thursday, unless today goes extra super smooth. (which I doubt, LOL)

Thank you again. What you said makes sense.

I am using it for the ground plot, it seems the Jolly Logic would let you fly in slightly higher winds safely, but 15 is pretty iffy.

Again I want to thank all of you for your kindness, and willingness to share knowledge, and problem solving. This place is great!

Steve

 

[cerving]

What has worked for me is putting two chutes in your OR simulation... a drogue that has the same area as the cross-section of your rocket, and the unreefed chute at the deployment altitude. It's not perfect, but it's close enough.

 

[JoePfeiffer]

Note: with Dual deploy or a Chute release the the descent speed will be higher than under chute (this is desired). OR will then give a Warning about "deployment at high speed". This is actually what we want so warning can be ignored.

While it's supposed to come in faster than under chute, that warning means it's coming in so fast there's danger you'll zipper when the main does deploy (though it's a hard-coded value). Don't ignore it before you've analyzed what's happening.

 

[waltr]

While it's supposed to come in faster than under chute, that warning means it's coming in so fast there's danger you'll zipper when the main does deploy (though it's a hard-coded value). Don't ignore it before you've analyzed what's happening.

Yes, I should have added that disclaimer.
The Warning does mean one needs to ensure the recovery system can take the stress of deploying at a higher velocity.

 

[Wrightme43]

Ouch, that example turns out to not be a good one... modeling the reefed chute as a streamer makes it impossible to size the opened chute to get a good result, and that streamer is tiny.

We don't have a handle on what the drag of the reefed chute will be, let alone the reefed chute and the tumbling rocket, so what follows will be a really nasty hack:

Treat it as a standard dual deploy. Make a guess at the size of the drogue so the descent rate is something you feel is reasonable.

Now size the main so the total area of the drogue plus the main is the same area as your actual chute.

You can see how the hack works by modifying the example:

1. Delete the streamer and replace it with a parachute. Since the main parachute in the example is an elliptical chute with a CD of 1.55, set the CD of the new chute to 1.55. The example seems to be planning on motor eject, so I'm going to set the "fake drogue" deployment as "first ejection charge".
2. Running several simulations and playing with the drogue chute size, I find that a chute with a 10 inch diameter gives a velocity at deployment of just under 50 fps. That seems reasonable to me.
3. The main parachute in the example has a diameter of 30 inches, and so an area of about 700 sq in. The drogue chute has an area of about 80 sq in. So, we set the diameter of the main so its area is 700 - 80 = 620 sq in; the diameter of the "fake main" is now 28 inch.
4. Running the simulations, I get velocity at opening (ie drogue descent rate) of 46.7 fps, and landing velocity of 15.6 fps

Well thank you for your help. I will keep working on this and trying to understand. It didn't really matter how much I wanted to mow the yard today. There just isn't enough daylight left. It is just going to take alot of work to become comfortable with how to use open rocket. It seems like a amazing program, and a great tool.

I am just going to keep messing with it, until I get it. I was able to definitely see a more accurate ground track and flight profile that makes sense this way.