Determining motor ejection delay in booster?

[Buckeye]

I am designing a MPR/HPR booster stage to deploy a parachute via motor ejection. RockSim indicates that after stage separation, the booster coasts for several more seconds before reaching its apogee. When observing real world 2-stage flights (granted, I have not seen many nor paid close attention), it seems that after separation, the booster almost stops dead with little further altitude gain. Maybe my eyes are playing tricks on me.

I would think that the means of separation, either a separation charge (which I will use) or the sustainer ignition, would impact the trajectory and momentum of the booster. The simulation doesn't account for this. Plus, I am not super confident in the drag model of a rocket with no nose cone.

How do you set the booster motor delay? Use the ideal simulation value or something much less?

Attached is my file, if interested. Thanks!

p.s. This question is related to this build thread:

https://www.rocketryforum.com/threads/first-electronic-staging-mpr-build.182599/

 

[waltr]

I just go with the SIM's estimate for the Booster ejection delay.

Thanks for the Rkt file which I opened in OpenRocket.
You do need to setup Timing for separation and sustainer ignition in the Sim.

My 2-stage is also based on the BMS 3" School rocket. Booster needs a G motor and delay is 4-6 second has worked fine.

The booster does look like it stops but is still going up.

 

[Rocketclar]

The booster keeps going up. Last Sat at NSL-E I launched my stretched Terrier/Sandhawk. According to the data from the Eggtimer Proton, BO #1 occurred at 284', sep charge at 462', sustainer lit at 615', and booster went to 1255' via MW RRC2+. I don't use motor ejection, but a RRC2+ along with an Eggtimer Apogee as backup. The motors were CTI I-345 to an H-110. Apogee at 4158'. BTW...BO #2 was at 963'. I use the graph features of RockSim to show the profiles of the sims.

 

[Buckeye]

I just go with the SIM's estimate for the Booster ejection delay.

Thanks for the Rkt file which I opened in OpenRocket.
You do need to setup Timing for separation and sustainer ignition in the Sim.

My 2-stage is also based on the BMS 3" School rocket. Booster needs a G motor and delay is 4-6 second has worked fine.

The booster does look like it stops but is still going up.

Good to know. Thanks.

In Rocksim, separation occurs per the booster motor delay. In my case, it is currently set to zero, meaning separation at booster burnout. The booster parachute deployment time is controlled by flight events. Sustainer ignition delay is currently set to separation +2 sec. These are just temporary settings until I figure out how I want to configure the Raven.

 

[Rocketclar]

Here's a typical trace I run with my RockSim's. The lines are thin so hard to read on scan. I've flown this about 10x's on various 'I' boosters and all went about 1000' or more.

 

[Rocketclar]

Here's the output from the Proton....I should have looked at this vs the Excel data. BO #2 was at 2049'. I used a 0.6 s separation charge and then a coast of 1.2 s. I've used longer coast times, but when watching on the ground it seems like forever before ignition especially since composites take time to come up to pressure. Sounds neat coming up to pressure from on board video when played back in slo-mo.

 

[Jmhepworth]

I am designing a MPR/HPR booster stage to deploy a parachute via motor ejection. RockSim indicates that after stage separation, the booster coasts for several more seconds before reaching its apogee. When observing real world 2-stage flights (granted, I have not seen many nor paid close attention), it seems that after separation, the booster almost stops dead with little further altitude gain. Maybe my eyes are playing tricks on me.

I would think that the means of separation, either a separation charge (which I will use) or the sustainer ignition, would impact the trajectory and momentum of the booster. The simulation doesn't account for this. Plus, I am not super confident in the drag model of a rocket with no nose cone.

How do you set the booster motor delay? Use the ideal simulation value or something much less?

Attached is my file, if interested. Thanks!

p.s. This question is related to this build thread:

https://www.rocketryforum.com/threads/first-electronic-staging-mpr-build.182599/

In a 54mm two stage (38mm motors) I put electronics in the booster and have the main come out at apogee. I use the motor for backup and set the delay at 6 to 8 seconds. That’s always been long enough that the motor ejection fires a couple of seconds after the main is out.

 

[Lord Rory Gin]

I am designing a MPR/HPR booster stage to deploy a parachute via motor ejection. RockSim indicates that after stage separation, the booster coasts for several more seconds before reaching its apogee. When observing real world 2-stage flights (granted, I have not seen many nor paid close attention), it seems that after separation, the booster almost stops dead with little further altitude gain. Maybe my eyes are playing tricks on me.

I would think that the means of separation, either a separation charge (which I will use) or the sustainer ignition, would impact the trajectory and momentum of the booster. The simulation doesn't account for this. Plus, I am not super confident in the drag model of a rocket with no nose cone.

How do you set the booster motor delay? Use the ideal simulation value or something much less?

Attached is my file, if interested. Thanks!

p.s. This question is related to this build thread:

https://www.rocketryforum.com/threads/first-electronic-staging-mpr-build.182599/

Tim van Milligan posted a theoretical discussion on booster delays which I found quite interesting. Typically to get max. altitude you would stage your rocket with zero delay but there are exceptions to this discussion depending on the altitude at which you are flying and the density of the air. Note: zero delay is basically what SpaceX was trying to accomplish with its hot staging ring to obtain max. altitude and speed.

One thing to note with timing the delay to separate at maximum apogee of the joined rocket is that you could be playing with an angle off vertical when the sustainer fires off. That would be BAD because then you would not be able to control the direction of the rocket and it could end up going anywhere.

 

[Rocketclar]

One thing to note with timing the delay to separate at maximum apogee of the joined rocket is that you could be playing with an angle off vertical when the sustainer fires off. That would be BAD because then you would not be able to control the direction of the rocket and it could end up going anywhere.

Yes, bad if sustainer fires off vertical. While there is the Tiltometer 3 that uses a gyro to inhibit if not vertical, the Proton I use does has a lockout setting. It uses a setable (between 5-30%) deviation that compares the accel altitude to the baro. I use: if >20%, then inhibit.

 

[BABAR]

Tim van Milligan posted a theoretical discussion on booster delays which I found quite interesting. Typically to get max. altitude you would stage your rocket with zero delay but there are exceptions to this discussion depending on the altitude at which you are flying and the density of the air. Note: zero delay is basically what SpaceX was trying to accomplish with its hot staging ring to obtain max. altitude and speed.

One thing to note with timing the delay to separate at maximum apogee of the joined rocket is that you could be playing with an angle off vertical when the sustainer fires off. That would be BAD because then you would not be able to control the direction of the rocket and it could end up going anywhere.

Real world experience with black powder motors and zero delay. Low power, I think C6-0 to A8-5.

ONCE (there‘s a reason!) I put booster chute in a pod on sustainer

at separation the chute was pulled out of the sustainer so basically zero delay.

Booster chute deployed From sustainer.

near immediate inflation of chute.

7 of 8 risers torn from chute,

streamered in quite nicely!

(To be fair, it was a plastic chute.)

so definite YES, the booster continues at relatively high velocity for at least a short period of time after separation unless you have an electronic delay of sustainer ignition. It makes sense, for black powder staging the STACK is at or near MaxV at separation since there is NO delay on black powder BOOSTER motors. So booster is carrying a lot of kinetic energy at separation. Bleed off time varies, if STABLE post separation booster might coast a good way, if unstable will tumble and bleed of pretty fast, maybe 2-3 seconds For low power.

My current go to for black powder staging with larger boosters (usually long gap stages, up to 53 inches, mostly 15-33 inches) is an auxilliary clustered A8-3 which has its own nose cone and chute. Not very scientific, but has worked well for me. The long gap boosters are STABLE post separation, so without a chute or streamer, they would come in ballistic.

no experience with electronics, but using an apogee detecting system with a long delay motor backup as recommended above sounds like good plan.

 

[Buckeye]

In a 54mm two stage (38mm motors) I put electronics in the booster and have the main come out at apogee. I use the motor for backup and set the delay at 6 to 8 seconds. That’s always been long enough that the motor ejection fires a couple of seconds after the main is out.

Yeah, I could put electronics in the booster, but I am trying to keep this project as a minimal build. Good to hear that motor ejection is a good backup.

 

[Buckeye]

Tim van Milligan posted a theoretical discussion on booster delays which I found quite interesting. Typically to get max. altitude you would stage your rocket with zero delay but there are exceptions to this discussion depending on the altitude at which you are flying and the density of the air. Note: zero delay is basically what SpaceX was trying to accomplish with its hot staging ring to obtain max. altitude and speed.

One thing to note with timing the delay to separate at maximum apogee of the joined rocket is that you could be playing with an angle off vertical when the sustainer fires off. That would be BAD because then you would not be able to control the direction of the rocket and it could end up going anywhere.

Yes, I read that article, too. Good info.

The booster delay I am referring to in this thread is not stage separation (Raven 4 will handle that) but for parachute deployment.

 

[BABAR]

Yes, I read that article, too. Good info.

The booster delay I am referring to in this thread is not stage separation (Raven 4 will handle that) but for parachute deployment.

How high will booster be and how fast will booster be going at both separation and potential booster apogee?

If it is gonna be very high, motor ejection with jolly logic dual deploy may be the ticket.

Motor ejecting the packed laundry should make it unstable, will slow it down some (drogue chute may do more), and then JLCR deploys main at selected altitude.

May not be your vision for this rocket, as they cost a bit and you said you were trying to avoid electronics.

Caveat: don’t know how well JLCR holds up to really high speed motor deployments (like really early or really late if bundle or drogue doesn’t slow it down too much,)

Going without electronic PRIMARY booster deployment definitely begs for so kind of antizipper device. Deployments without electronics particularly in boosters are essentially always early or late, although the degree of the error can vary from “just about perfect” to “oh #%^*!”

 

[bobbyg23]

I plug it into open rocket and then graph it. At the apogee of the booster is what you want your motor eject to go off. Mine have all been at 10 seconds and turned out perfectly.

 

[waltr]

Same here, run OR sim to obtain booster delay time.
This has worked very well and booster chute deployment has always been close enough to apogee.
This is on a 3" diameter that doesn't weight a lot (24in chute).
For bigger, heavier boosters electronics would be better.

 

[bobbyg23]

Here is the plot. Booster apogee at 9.5 seconds. It was pretty close to dead on.

 

[kjhambrick]

<<snip>> ... Attached is my file, if interested. Thanks! <<snip>>

Thanks for sharing your BMS_Two_Stage_School_Rocket,rkt file, @Buckeye !

The booster definitely continues to coast upwards to an apogee altitude somewhat higher than the altitude at burnout even with a separation charge.

However, I remember reading long ago that the CD of an open cup ( like an ISC ) is a little higher than 1.0 so I don't know whether the sims account for the missing nose cone on the booster or not.

But I sure can't argue with success, so as @waltr, @Rocketclar say: trust your Sims for a delay time for your booster ejection.

I seem to recall some good plots in @Adrian A's threads showing that the booster continued to coast after separation but I can't find one right now.

Just for fun, maybe the Motor Delay of the booster could be calculated via Rocket Mime's Rocket Equations: Coast Phase: Time to Velocity Zero equation ?

I REALLY like what you're doing with the pair of BMS School Rockets -- there is definitely enough space in the 3-inch tube to work on staging !

You've got me seriously considering two of the 29mm School Rockets for Christmas, one for each of my granddaughters, and a booster ISC for me

Thanks again for the .rkt file !

-- kjh