ARO-B Two Stage Flight: All-up Test and Procedures Dress Rehearsal

[Kane]

After two shake-down flights of the sustainer stage, I’m finally ready to attempt my first two-stage flight. I had originally planned to do a full-stack test with a booster motor only, but have since decided against it. I am confident in my simulations and preparation and have decided to go straight to the first two-stage flight. This will happen at MDRA once the club moves back over to Higgs Farm.

This first attempt will fly with an Aerotech I435T in the booster (ARO-A) and an Aerotech H130W in the sustainer (ARO-B).

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Today I did an all-up test to find any bugs, sus out unforeseen issues, and generally polish my prep procedures.

The following steps are done on the work bench in my shop – usually a day or two before flight.

First up was prepping and threading the separation charge and air start e-match leads through the internal conduits. I’ve opted for the “circumcised JST-RCY” connector for the break-away connection. This just involves cutting away a bit of the male connector sheath. The two terminals pull apart with minimal force but stay together well enough for flight.



Female ends of the JST-RCY connected to the avionics bay terminals.



At the business end, ½ gram of FFFg will go into the red e-match cap and then get taped in. For the air start, I’ll use a single 50 cal Pyrodex pellet lodged into the top of the H130W grain just below the delay grain. (note that the red cap on the air start e-match is just to protect it during transport – this will be removed for flight).



The recovery event charges next get prepped for both the booster and sustainer. The sustainer employs an Eggtimer Proton for the main recovery events (plus the separation charge and air start) and an Eggtimer Quantum for backup. The booster employs a single Eggtimer Quantum to deploy the main (no drogue).

The sustainer charges are prepped. I then connect the separation and air start charges, fire up the electronics, and test for continuity. The electronics can now be loaded into the bay for transport (with all power disconnected)



The booster charge is prepped and continuity is tested by firing up the electronics. A successful test means the electronics can get buttoned up into the bay for transport (with all power disconnected).



The next step is to prep and pack the recovery gear. I roll all my cords for airframes 54mm and up. This keeps them well organized and compact.



Drogue ready for insertion into the aft sustainer compartment (rubber band is temporary). The quick link end is left free for connection to the avionics bay.



The drogue shock cord attached to an eye bolt screwed into the tapped forward plugged closure of the motor. The motor is removed for transport to the field.



The main gets packed into the forward compartment of the sustainer leaving the shock cord leads at the end for later connection to the nose cone and avionics bay.



The booster has a “hard point” with a male-female hex thread adapter. A length of threaded rod screws into this and the tapped forward closure of the booster motor. The booster chute shock cord is attached to the booster harness, and the shock cord and parachute gets packed in. The motor is removed for transport to the field.

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Next post will be procedures performed at the field.

 

[Kane]

Once at the field, the first step is to connect power to the booster avionics and GPS and test for continuity and GPS connection to the ground station.

The booster motor is inserted into the booster.



The interstage coupler is connected to the shock cord and coupled to the booster. A single shear pin secures the ISC to the booster.




Next, power is connected to the sustainer GPS (in the sustainer nose cone). Connections are checked to the ground station.

Power is connected to the sustainer avionics and inserted into the avionics bay. The air start and separation charge leads are connected between the avionics bay and the aft compartment of the sustainer. One last continuity check is performed on the sustainer avionics and event charges.



A pull-pin switch is inserted into the sustainer avionics bay to cut any possibility of power making it to the air start charge. The Proton’s deployment channels are technically “dead” until the unit is armed, but this is an extra precaution.



The sustainer motor is now attached to the drogue shock cord and the motor loaded. The separation charge sits in a “well” in the ISC. The air start charge remains loose and does NOT get inserted into the motor until at the pad.



Next, the avionics bay is attached to the forward compartment with three M3 screws and all the parts of the sustainer get connected to the respective shock cord ends.



The full stack can now be coupled together. Two shear pins hold the aft compartment to the avionics bay and two shear pins hold the nose cone. Booster igniter is placed in pocket and with flight card in hand, we’re ready for a visit to the RSO.



Next post will be a look at the avionics – and especially the air start – settings and procedures at the pad.

The design and build of the ARO-B can be found here: https://www.rocketryforum.com/threads/design-and-build-thread-aro-b-two-stage.182419/

 

[Kane]

Planning out the separation charge and air start event timing.

The booster is technically a smaller diameter than the sustainer which would initially lead me to believe that keeping it attached to the stack for a little bit after burnout to exploit the extra momentum would be advantageous. I simulated the I435T to H130W with different separation charge delays (delay on the booster "ejection" in Rocksim) going from 0 to 2 seconds in increments of 0.5 seconds. This seemed to have minimal impact on final altitude. I am not going for altitude for this initial flight, so I have elected to set the separation charge to fire at 0.5 seconds after booster burnout.

Next step is to determine the best air start charge event timing. Even with the Pyrodex pellet in the H130W, I am going to assume that it will take a full second to come up to pressure, so the air start delay as graphed below includes that one second. In other words, the Proton's delay from event trigger will be set to one second less than the durations graphed below.

Iteration 1:
Booster burnout at 1.4s
Separation charge at 1.9s (Burnout +0.5s)
Air start at 2.9s (Burnout +1.5s)
Sustainer motor thrust begins at 3.9s (Burnout +2.5s)
Sustainer velocity at start of thrust = 296 ft/s


Iteration 2:
Booster burnout at 1.4s
Separation charge at 1.9s (Burnout +0.5s)
Air start at 3.4s (Burnout +2.0s)
Sustainer motor thrust begins at 4.4s (Burnout +3.0s)
Sustainer velocity at start of thrust = 276 ft/s


Iteration 3:
Booster burnout at 1.4s
Separation charge at 1.9s (Burnout +0.5s)
Air start at 3.9s (Burnout +2.5s)
Sustainer motor thrust begins at 4.9s (Burnout +3.5s)
Sustainer velocity at start of thrust = 254 ft/s


Finally, a comparison of the three iterations' respective velocities.


Interestingly, Rocksim simulates the highest altitude with iteration 1 (air start delay of 1.5 seconds). Given this also maintains the highest predicted velocity of the three iterations, I'm thinking I'll elect to go this route. This delay will give a full second for the separation charge gases to dissipate and gives plenty of cushion should the sustainer motor take longer than one second to come up to pressure.

 

[waltr]

Analysis look good. I found Velocity at 3nd stage ignition important to ensure sustainer is pointed up.
1/2s to separation and 1.5 to ignition is close to what I've used. These are just enough to see the booster drop away and then the sustainer light.

 

[Kane]

Analysis look good. I found Velocity at 3nd stage ignition important to ensure sustainer is pointed up.
1/2s to separation and 1.5 to ignition is close to what I've used. These are just enough to see the booster drop away and then the sustainer light.

Good to hear. That's definitely all I'm really looking for for this flight. Could go a little longer on the air start delay and still stay safely above 250 ft/s, but the time the H130 takes to come up to.pressure is the wildcard.

 

[cerving]

I'd give the H130 about one second to get up to pressure, so you may want to reduce the burnout-to-ignition time a little so the actual flight curve matches the sim.

 

[Antares JS]

I'd give the H130 about one second to get up to pressure, so you may want to reduce the burnout-to-ignition time a little so the actual flight curve matches the sim.

This. Remember there will be a delay between your igniter firing and the motor starting.

 

[markg]

View attachment 675597

This looks like a very clean setup. Consider securing the separation wires to the eyebolt in case there is any hang-up on separation.

cheers - mark

 

[Kane]

I'd give the H130 about one second to get up to pressure, so you may want to reduce the burnout-to-ignition time a little so the actual flight curve matches the sim.

I've accounted for one second for the motor to come up to pressure. It's the first chart (the air start delay is 1.5s, actual ignition at 2.5s after burnout).
Good to hear my assumption on pressurization time jives with with yours.

 

[Buckeye]

Nice build. What is your plotting software? Kinda looks like Excel, but not exactly.

 

[Kane]

Nice build. What is your plotting software? Kinda looks like Excel, but not exactly.

Thanks! Yes, it's all pivot charts in Excel.