1 gram is not enough for deployment of 2 shoots on Astrobee-D

[BareRocketry]

I am using a 29mm G80-7T single use motor for my Aerotech Astrobee-D rocket, and having trouble getting the chutes to come out at all. Carl (all around good guy at www.apogeerockets.com) suggested that I test with 1 gram of BP. I took a spent G80-7T, taped the top hole and loaded the charge cup with 1 gram of FFFF black powder. Carl says that the 29mm G80 comes with a charge of 0.7 grams so a 1 gram charge (roughly 40% more) should be plenty.

Results were unexpected (video attached).

Dimensions of the rocket:
Inner diameter: 2.5"
Length of airframe pressurized during deployment: 14"

Shouldn't 1 gram of FFFF be more than enough?

Some portion of the expansion surely escaped out the nozzle during the test. But wouldn't the same thing happen during a normal launch?

I'm all ears.

 

[3stoogesrocketry]

That's more then sufficient. Repeat the test with it on its side. I'm guessing the chutes are loose enough that the gasses are just bypassing the chutes and not pushing them out.

 

[Spurkey]

While repeating the test with the rocket on its side might make it work, it doesn't solve the problem you have of the laundry not coming out - chute needs to be ejected in the vertical case on the chance of an early deployment. Some questions:

* have you flown this rocket once before on that G80 and the flight failed? Rephrased: does the problem only happen with e-charges you've built yourself? If so you need to investigate how you're building your charges. The FFFF should be tight against the igniter, you mention a charge cup so I suspect you might be just pouring the FFFF in and sealing the top with tape. That's not enough, you'll get a slow burn and minimal pressure. Try sticking a small wad of ejection wadding on top after the BP but before the tape, or putting everything in a silicone glove finger tip, or any of the many other different methods listed in this forum to simply+safely keep your BP around your igniter head

* this is less likely to be the case, but have you triple-checked everything on your rocket to make sure there's no cracks or gaps or anywhere else the pressure could be escaping from? I say "less likely" because from that 'pop' sound the kit makes when it comes apart, implies things are gudentite. In fact, the sound or lack thereof still leads me to think your charge isn't burning efficiently because 1g going off should make more noise than in your video

 

[Initiator001]

The AeroTech Astrobee D and Mirage kits do not 'eject' parachutes in the same way as traditional model rocket kits.

The ejection baffle system does not use wadding which will push out the parachutes.

For this reason, as the instructions state, pack the upper section parachute FIRST. Then, place the lower section parachute on the previously loaded upper parachute.

When the ejection charge fires the upper air frame tube blows off, PULLING out the lower parachute then the upper parachute.

I have never had an issue with the ejection charge of an AeroTech G40 or G80 motor being unable to provide enough energy to blow off the upper section and pull out the parachutes. I modified both of my G-Force models to use dual parachutes with the same method of packing. The only issue I have had is the shock cords tangling while both sections are under parachute and close to each other.

 

[rharshberger]

That's more then sufficient. Repeat the test with it on its side. I'm guessing the chutes are loose enough that the gasses are just bypassing the chutes and not pushing them out.

Chutes don't usually get pushed out by the ejection gasses, the gasses go path of least resistance, which is around the chutes to pop off the nose cone. Once the nose cone is off, then gravity and inertia from the forward movement of the nose cone ejection pulls the chutes out or they slide out of the airframe, hence the reason a tightly packed chute will not slide out of the airframe at nose cone ejection. If you want the chutes to be pushed out by the ejection gasses a seal is required like a piston, which also increases the efficiency of the ejection charge requiring less ejection powder. In the case of extremely lightweight plastic and thin mill nylon chutes they may actually be ejected by the gasses but the weight of the chute protector and harness can be a factor in how reliable it work.

 

[BareRocketry]

While repeating the test with the rocket on its side might make it work, it doesn't solve the problem you have of the laundry not coming out - chute needs to be ejected in the vertical case on the chance of an early deployment. Some questions:

* have you flown this rocket once before on that G80 and the flight failed? Rephrased: does the problem only happen with e-charges you've built yourself? If so you need to investigate how you're building your charges. The FFFF should be tight against the igniter, you mention a charge cup so I suspect you might be just pouring the FFFF in and sealing the top with tape. That's not enough, you'll get a slow burn and minimal pressure. Try sticking a small wad of ejection wadding on top after the BP but before the tape, or putting everything in a silicone glove finger tip, or any of the many other different methods listed in this forum to simply+safely keep your BP around your igniter head

* this is less likely to be the case, but have you triple-checked everything on your rocket to make sure there's no cracks or gaps or anywhere else the pressure could be escaping from? I say "less likely" because from that 'pop' sound the kit makes when it comes apart, implies things are gudentite. In fact, the sound or lack thereof still leads me to think your charge isn't burning efficiently because 1g going off should make more noise than in your video

Thank you, Spurkey
Your feedback is helpful.

*Yes, I have flown this rocket on the G80 before. The upper section did not deploy. That's what sent me down this rabbit hole. Now that I know I have enough BP I'm led to believe there was too much tension on the coupler between upper and lower. With some light sanding and the rocket resting vertically on the fins I can lift the upper section out without holding the bottom section. Crossing my fingers.

*regarding cracks and gaps, everything looks good. What about the motor itself? It seems the pressure from the BP deployment charge would just blow out the bottom of the motor? Am I missing something there?




Regards

 

[3stoogesrocketry]

*Yes, I have flown this rocket on the G80 before. The upper section did not deploy. That's what sent me down this rabbit hole. Now that I know I have enough BP I'm led to believe there was too much tension on the coupler between upper and lower. With some light sanding and the rocket resting vertically on the fins I can lift the upper section out without holding the bottom section.



Regards

you should be able to pick the rocket up by the top and have the bottom stay on the coupler, but a light wiggle pull and it should slide off. If you leave it loose as you describe the fit, you seriously risk drag separation when the motor burns out.

 

[tsmith1315]

It seems the pressure from the BP deployment charge would just blow out the bottom of the motor? Am I missing something there?

This is not an issue. If it were, motor ejection would never have worked from the beginning.

You’re pressurizing the airframe to separate it, and the resistance back through the motor and nozzle is too high to release an appreciable amount of that pressure in the time it takes the airframe to separate.

It does take time to get the feel for how tight the junctions should be. I tend to err on the loose side.

I’d also suggest listening well to Bob/Initiator001’s comments, I’m pretty sure he was involved in designing that rocket for Aerotech.

 

[rcktnut]

Just to assure OP that the BP supplied in the G Aerotech motors is sufficient, I have the Astrobee-D and the Mirage, launched many times and never had a problem with recovery. Just pack the chutes as instructed.

 

[BareRocketry]

The AeroTech Astrobee D and Mirage kits do not 'eject' parachutes in the same way as traditional model rocket kits.

The ejection baffle system does not use wadding which will push out the parachutes.

For this reason, as the instructions state, pack the upper section parachute FIRST. Then, place the lower section parachute on the previously loaded upper parachute.

When the ejection charge fires the upper air frame tube blows off, PULLING out the lower parachute then the upper parachute.

I have never had an issue with the ejection charge of an AeroTech G40 or G80 motor being unable to provide enough energy to blow off the upper section and pull out the parachutes. I modified both of my G-Force models to use dual parachutes with the same method of packing. The only issue I have had is the shock cords tangling while both sections are under parachute and close to each other.

Thank you, Initiator001/Bob. Very helpful information. I plan to use the G80 as per factory spec and friction test the upper airframe prior to launch.

Regards,

Bare

 

[rcktnut]

The only thing you have to worry about is the fin tips breaking. Unless you are launching on very soft soil good chances are you will break a tip. The Astrobee-D, Mirage, and G Force that I own all have the same fin design and all have had broken fin tips. On my Astrobee-D I reattached the tip and it has been holding out so far. G-Force I just left alone and on the Mirage cut all the tips off because 2 eventually broke off.

 

[BareRocketry]

Thanks to all that contributed to this thread. Some smart folks out there!
I applied a small amount of graphite dry lube to the coupler between the two airframes, and double checked the friction. Perfect launch and recovery. I'm eager to work towards another L3 launch (last one was over a decade ago). This is a good baby step...

You all are awesome!

Bare

 

[Spurkey]

Glad you got things sorted. Congrats on the successful flight!

 

[smstachwick]

I had mine separate but not deploy on an F67 flight. Not good, especially since I had intended to use the thing for L1.

I got a few bits of advice from that that I’ll be combining for the certification attempt. An improved chute rolling technique and enlarged charge are central among them.

Link to my thread here.

 

[Art Upton]

I learned this the hard way. I had a Mirage, and never had the instruction sheet for it. I launched it on a G80 at a NARAM (45 I think) and it did not deploy the chutes Like I thought it would as it was coming in. [ I had declared it a G SuperRock Record Attempt by modifying it to the needed length from the motor end to the tip]

Jake Haggerty came over to me and said, you probably don't know this but you have to pack the chutes a special way for that rocket to get it to deploy correctly.

 

[suborbital]

I am using a 29mm G80-7T single use motor for my Aerotech Astrobee-D rocket, and having trouble getting the chutes to come out at all. Carl (all around good guy at www.apogeerockets.com) suggested that I test with 1 gram of BP. I took a spent G80-7T, taped the top hole and loaded the charge cup with 1 gram of FFFF black powder. Carl says that the 29mm G80 comes with a charge of 0.7 grams so a 1 gram charge (roughly 40% more) should be plenty.

Results were unexpected (video attached).

Dimensions of the rocket:
Inner diameter: 2.5"
Length of airframe pressurized during deployment: 14"

Shouldn't 1 gram of FFFF be more than enough?

Some portion of the expansion surely escaped out the nozzle during the test. But wouldn't the same thing happen during a normal launch?

I'm all ears.

How tight is your nosecone and laundry in the airframe? The Aerotech single use motors only have a small hole in the ejection charge well, so I wouldn't think that you would be losing much pressure through the nozzle end.