OR Multi-Stage Tracking & Error

I have always wanted to know how to "track" the flight of the booster in a multi-stage rocket. Now that OR 13.05 has this function. I was wondering how it all works. I see that if you plot the total motion vs time plot it shows the booster and sustainer flight data graphs. I wondered if the export data would show the booster separately. I wasn't able to do that but maybe I don't understand the data either or didn't do it right. Can someone (KRuland) help me with that?

Thanks,

What I really need to know is how to figure the delay on the booster deploy since it be motor deploy. When I plot the flight side profile and just show the booster I get some weird things and I don't see the booster deploy. I attached my OR file for reference.

View attachment 2-Stage Shortened Rocket wo AV-Bay.ork

I have another problem with this sim file. I have deployment at high velocity error and a discontinuity of rocket diameter error. I don't see what the problem is in either one.

Hi Dave,

I don't see anything wrong with the model or they way it's simulating. I reran your simulation on the H148-6/I245-10 and plotted the "vertical motion vs time" plots. I've attached a screen shot of the booster portion of the the plot. You can see the recovery device is deployed at about 11 s with a velocity of ~-100fps. I suspect you should drill out the delay 2-3 seconds.

I noticed you don't have any recovery in the sustainer. The plot looked weird because it didn't have any appreciable drag on descent and the "recovery deployed" event was not plotted. After replotting with the "ejection" event shown, I see the delay is a little too short on the sustainer.

I'm not seeing the warning about body tube discontinuity. I checked the outer diameters of the external components and they all seem to match to 3 decimal places (in inches).

Kevin

Dave,

You asked about export... I never checked what export would do. Apparently it only exports the primary "branch" of data - that is the data from the sustainer plot (this includes the booster's boost, stage separation, ignition of sustainer, etc...) I never thought about what the exported data should look like for multiple stages.

How do you think it should be presented? It's producing csv so we cannot have multiple sheets of data. Interleaving the data doesn't make much sense - unless we add a column for "stage". Maybe you should select the the stage you want to export?

Kevin

kruland said:

Hi Dave,

I don't see anything wrong with the model or they way it's simulating. I reran your simulation on the H148-6/I245-10 and plotted the "vertical motion vs time" plots. I've attached a screen shot of the booster portion of the the plot. You can see the recovery device is deployed at about 11 s with a velocity of ~-100fps. I suspect you should drill out the delay 2-3 seconds.

I noticed you don't have any recovery in the sustainer. The plot looked weird because it didn't have any appreciable drag on descent and the "recovery deployed" event was not plotted. After replotting with the "ejection" event shown, I see the delay is a little too short on the sustainer.

I'm not seeing the warning about body tube discontinuity. I checked the outer diameters of the external components and they all seem to match to 3 decimal places (in inches).

Kevin

Click to expand...

Thanks Kevin. Not sure what happened to the sustainer chute. I put it back in. Here is a screen shot showing both booster and sustainer. I have the sustainer ignition set at booster burnout + 2.0 seconds. The part I am really worried about is that I am deploying one of the chutes at a high velocity (either early or late). Can you explain your 2-3 seconds delay drill? Are you going to be at AirFest? I also attached an export csv file.

Not sure what is going on with the tube discontinuity. Are you running v13.05?



View attachment KC Chief 2-Stage H148R - I245G 081713.xls

Dave,

You caught me! I'm actually using a hacked up prelease version of 13.0x - which has a few bug fixes in it. I'll try over lunch with the release 13.05 to see what I can figure out.

So, here's my disclosure... I've never done HPR staging, though I want to and that's why I added these features to the last release of OpenRocket. Therefore you should really take my rocket advice (and perhaps the OpenRocket simulation) as simply another data point. Please, please confer with those who have some actual experience.

In the plot, you can see the apogee of the booster (the lower of the two red lines) happening at about 7.5s. However the ejection charge/recovery deployment happens at about 11 seconds. The lower blue line shows the velocity of the booster after separation and from that I read the velocity at deployment is ~-100fps this seems fast to me.

In your new plot, I still don't see the sustainer chute being deployed. There should be a vertical bar between the "second apogee" and the "first ground hit" representing "recovery device deployed". Are you using dual deployment on the sustainer, or just motor deployment of the main?

Yes, I'll be at Airfest this year! Can't wait and hope this nice cool weather holds out a couple more weeks.

kevin

davdue said:

Thanks Kevin. Not sure what happened to the sustainer chute. I put it back in. Here is a screen shot showing both booster and sustainer. I have the sustainer ignition set at booster burnout + 2.0 seconds. The part I am really worried about is that I am deploying one of the chutes at a high velocity (either early or late). Can you explain your 2-3 seconds delay drill? Are you going to be at AirFest? I also attached an export csv file.

Not sure what is going on with the tube discontinuity. Are you running v13.05?

Click to expand...

It helps if I recreate the screenshot. Now the sustainer deployment shows up. The chute is deployed via the RRC3 controlling the sustainer ignition. It is connected to the drogue output which comes on at apogee + 1 second delay. Could the high velocity deployment be something in my settings or a problem with the 2-stage code? The graph looks ok so I don't believe the high velocity deployment.

View attachment 2-Stage Shortened Rocket wo AV-Bay.ork

View attachment KC Chief 2-Stage H148R - I245G 082013.xls

Dave,

The test used for deployment at high speed is if the velocity at deployment is > 20m/s (65fps). The booster's deployment is at something around 75fps. I suspect the booster is stable by itself (looks long and rocket like..) so it turns ballistic between separation and ejection. This is why I think you need to drill the delay in the booster about 2second or so.

Kevin

kruland said:

The test used for deployment at high speed is if the velocity at deployment is > 20m/s (65fps). The booster's deployment is at something around 75fps. I suspect the booster is stable by itself (looks long and rocket like..) so it turns ballistic between separation and ejection. This is why I think you need to drill the delay in the booster about 2second or so.Kevin

Click to expand...

Can you explain how you came up with the 75fps on the booster deployment? Yeah the booster is very stable. I have flown booster v1.0 (had a 29mm MMT) and it is very stable by itself, of course it has the sustainer nosecone not a coupler catching air. Not sure OR can simulate that. The next question is how you came up with 2 seconds or so and by that do you mean 2 second delay or take 2 seconds off? The tubes on this rocket are 3/16" wall so not really worried about zippering. In fact at the August fun-fly I flew the sustainer by itself and the chute hung up and the rocket came in ballistic and I was able to cut off about 10" and everything is still good.

davdue said:

Can you explain how you came up with the 75fps on the booster deployment? Yeah the booster is very stable. I have flown booster v1.0 (had a 29mm MMT) and it is very stable by itself, of course it has the sustainer nosecone not a coupler catching air. Not sure OR can simulate that. The next question is how you came up with 2 seconds or so and by that do you mean 2 second delay or take 2 seconds off? The tubes on this rocket are 3/16" wall so not really worried about zippering. In fact at the August fun-fly I flew the sustainer by itself and the chute hung up and the rocket came in ballistic and I was able to cut off about 10" and everything is still good.

Click to expand...

Hi Dave,

I read the 75fps off the graph. At about 10seconds you see the "lower" blue line for velocity with a big spike to -75fps. This is the velocity line for the booster section after separation. If I remember correctly, OpenRocket doesn't attempt to simulate any "shock" incurred during recovery deployment so that velocity value is due to falling.

I am suggesting you shorten the booster delay by about 2 seconds. Again, I'm reading this from the chart. It looks like the Apogee for the booster is at about 7.5 seconds and the ejection is at 11 or 12. In fact you might be able to shave off 4 seconds and it would be pretty good.

I don't expect OpenRocket's booster simulation to accurately represent the booster's trajectory after separation. There would be a lot of extra forces acting on the booster during separation (a charge, or blast from the sustainer motor, or what have you). All OpenRocket does is simulate the booster as if it "magically lost the sustainer". The Cd & Cp are changed appropriately but OR just keeps it flying up.

You might be able to see what's going on better if you change the drop down at the bottom of the plot window from "ALL" to "Booster" (or whatever the booster stage is named). Then you will only see the simulation and events from the booster perspective. You can zoom and scroll to get better values of the times involved.

Kevin

The I245G also comes with a 6 second delay option. The booster velocity sims out to almost 0 ft/sec at ejection using that motor.

Yeah I realized that this afternoon after kruland explained the drilling out 2 seconds. I realized trying to get rid of the error I had changed the delay to 10 seconds when the real problem was a lack of a main parachute. Still don't know how that got deleted. Oh well. All is well except for the discontinuity in rocket body diameter error is. I am not worried about that one though.

Dave,

Sorry that took so long to communicate. It would have been much easier together with a piece of paper! In the end though - I'll be waiting to see it fly.

I'm at Airfest Friday through Sunday with an optional extension through Monday if the weather is really nice and I'm still having a good time. Please try to track me down, I'd like to meet you.

Kevin

I will be there Friday through Monday with my camping trailer. If you check in first thing Friday I am working registration with Lance. I would like to meet you too. Can't wait for all the rockets. I only have this as a "big" project and no cert flights this time so I hope to have more time to watch this year. Of course I will fly some other rockets and have a new Madcow Frenzy to fly. See ya at the pasture.