Staging issues in Open Rocket

[BDB]

I'm planning to practice electronic staging in the LPR/MPR regime before moving up to HPR, so I built a BT70 booster for my trusty Magnum (BT60) Payloader. I'm planning to put an Eggtimer Quantum in the sustainer's payload bay to ignite the BP motor for the 2nd stage. Both the booster and sustainer will initially use motor eject for chute deployment. After a few successful flights in this configuration, I'll incorporate electronic deployment, and eventually a stage separation charge.

My issue is that the simulations are screwy. If I include delay times for my motors, about half of the simulations say "Recovery Deployment at High Speeds," and I don't know why some of them give this error and others don't. If I adjust the delay times for the two motors to 'None" my simulations are all green, but I suspect that the apogee values are incorrect. Could you guys take a look at the file to see what I'm doing wrong?

Thanks,
Brenton




View attachment Magnum (electronic staging).ork

 

[cerving]

Check the setup on your sustainer motor mount, you have the sustainer motor firing at launch instead of "after burnout of previous stage". Change it, and make it go at about 1 second after the booster burnout. You can change this to 2 or 3 seconds too, to see what the effect on the apogee will be. Just be careful that the velocity when the motor fires doesn't go too low, or you're likely to start going a bit horizontal when it fires. Velocity is your friend... it keeps the rocket going straight.

 

[BDB]

Thanks, Cris. That did the trick. Eventually there will be a Quantum in both the booster and the sustainer. I'll be sure to report how the they work for all phases of this project.

 

[CORZERO]

Are you set on 29mm for your booster? If so, why for such a light vehicle? I changed a few things. Try this:

View attachment Magnum (electronic staging) V2.ork

I didn't like the thrust curves for your booster motor selections. The overall performance seemed poor even after applying only the fix Chris had given. I only included one motor pair in the modified file. This combo keeps your BT60 under 2k'. Should be cake to track. Note the thrust curves of each motor (gotta love the versatility of the mighty D12!), the delay times, the booster separation time, sustainer ignition time and you'll get the idea that I'm shooting for with mine in terms of performance. But that's just my philosophy, and I could be wrong.

 

[CORZERO]

I apologize, somehow I had two D motors in the above file. Here is the intended file with a 29mm F motor:

View attachment Magnum (electronic staging) V2.ork

 

[BDB]

Are you set on 29mm for your booster? If so, why for such a light vehicle? I changed a few things. Try this:

View attachment 321747

I didn't like the thrust curves for your booster motor selections. The overall performance seemed poor even after applying only the fix Chris had given. I only included one motor pair in the modified file. This combo keeps your BT60 under 2k'. Should be cake to track. Note the thrust curves of each motor (gotta love the versatility of the mighty D12!), the delay times, the booster separation time, sustainer ignition time and you'll get the idea that I'm shooting for with mine in terms of performance. But that's just my philosophy, and I could be wrong.

Thanks for looking at the file. I built the booster with a 29 mm MMT to give me versatility. The thinking was that I could always adapt down. After starting the thread last night I also simulated a F31 (29 mm) in the booster. It looks great, but I think the best booster motor for good performance but keeping everything below 2k ft is a 24 mm E30.

This exercise has confirmed my belief that the D12 is one of the best motors ever manufactured, and the E16 sucks.

 

[BDB]

I am going to make my second attempt at electronic staging tomorrow. The first one, using the E30 in the booster, did not reach the lock-out velocity that I had programmed into the Quantum, so the sustainer ignition charge didn't fire. I'm calling it a "successful failure."

This time around, I'm planning to use an F44-4 in the booster and a D12-7 in the sustainer. Since I will get more thrust out of my first stage, I'll set the minimum safe altitude to 700 ft.

I'm posting the updated .ork file and a image of the simulation plot. Any suggestions to help me ensure success would be appreciated. Thanks.


View attachment Magnum (electronic staging).ork

 

[cerving]

Your sim i showing ignition at about 700', the purpose of the altitude/velocity lockout is to prevent an unwanted ignition if the rocket doesn't appear to be going "up". I generally use 80%-85% of the sim's altitude-at-ignition value, so you might want to think about setting it to 600'.

 

[BDB]

Your sim i showing ignition at about 700', the purpose of the altitude/velocity lockout is to prevent an unwanted ignition if the rocket doesn't appear to be going "up". I generally use 80%-85% of the sim's altitude-at-ignition value, so you might want to think about setting it to 600'.

Crap! Thanks, Chris. Last time I used the velocity as the lock-out parameter, so I was looking at the wrong line. Sustainer ignition will happen 2 sec into the flight, so I need to either set the lockout to [email protected]' or [email protected] ft/s.

 

[cerving]

Crap! Thanks, Chris. Last time I used the velocity as the lock-out parameter, so I was looking at the wrong line. Sustainer ignition will happen 2 sec into the flight, so I need to either set the lockout to [email protected]' or [email protected] ft/s.

Velocity works too, just make sure that you take a little off your sim to account for wind or motor thrust variations.

 

[BDB]

Velocity works too, just make sure that you take a little off your sim to account for wind or motor thrust variations.

Thanks. That may have been my issue last time. I set the lock-out too close to the sim.

 

[CORZERO]

Get video!

 

[BDB]

If the last flight was a "successful failure," today's flight can only be described as "boneheaded stupidity."

Prof. Iman Idiot (me) made a last minute change to the flight plan. I found an F50-4 motor in my launch box and decided that it would be the perfect booster motor. I was right about that; the first stage of the flight was excellent. I'll definitely use this motor again in the booster.

But that was the end of the clear thinking. The Eggtimer Quantum works as a timer to airstart the sustainer motor at a certain point in the flight. For some reason, I decided to change the air start time from 2.0 s to 0.5 s. I was thinking that I only wanted 0.5 s between the booster motor burnout and ignition of the stainer. But this number should be for the time in the flight that the sustainer lights, not the time since booster burnout. Consequently, the altitude lock-out had not been met at 0.5 s, so the sustainer didn't light.





I'm such an idiot! Who the hell ever let me be a scientist?!!!

 

[BDB]

The other thing that I have realized during this saga is that I shouldn't rely on motor ejection to deploy the chute in the sustainer because that means that a successful recovery is predicated on a successful ignition of the sustainer's motor. I thought that I would keep everything simple buy using motor eject, but I have now destroyed my sustainer twice, and neither of these crashes would have happened if I was using electronic deployment.

 

[CORZERO]

You're fired!