G motors for staging? Can't find any

[Maxhiker14]

I recently bought and am building a "Two the Limit" rocket kit from US rockets. It's basically a large version of one of the staged Estes, using the ejection to light the sustainer. Problem is, I can find any G motors that work for that. The intrructions recommend a G30-0, but I can't find it anywhere. Anyone know where to buy these motors? Thanks in advance

 

[markkoelsch]

I do not believe there is such a thing if you are thinking of staging a composite motor like you would a black powder motor. To stage composites you need a timer or something similar and an igniter. If I am misinterpreting you question I apologize in advance.

 

[Handeman]

I could be wrong, but I think US Rockets are kits that were available when BP G motors were still available. I believe that kit was built for motors that haven't been produced in years. Actually I'm surprised you could still get the kit.

 

[bobkrech]

The ejection charge from an APCP booster motor can be used to ignite a BP sustainer motor.

It takes a lot more energy to ignite an APCP motor than a BP motor. The ejection charge for an APCP or BP booster motor is not energetic enough to ignite an APCP sustainer motor. You need electronics and an igniter to ignite a sustainer APCP motor.

Bob

 

[watermelonman]

The ejection charge from an APCP booster motor can be used to ignite a BP sustainer motor.

Interesting, I thought it possible but had not heard of anyone doing so. Any idea how common or reliable a practice this is? I was under the impression that the burn through on black powder first stage motors was a good deal slower burning and less energetic, which would ease the separation and ignition compared to a hard charge.

 

[Bat-mite]

Possible or not, I wouldn't try it.

The G30 "Comet" was an old Rocket Services BP motor.

 

[bobkrech]

The ejection charge from an APCP booster motor can be used to ignite a BP sustainer motor.

It takes a lot more energy to ignite an APCP motor than a BP motor. The ejection charge for an APCP or BP booster motor is not energetic enough to ignite an APCP sustainer motor. You need electronics and an igniter to ignite a sustainer APCP motor.

Bob

Interesting, I thought it possible but had not heard of anyone doing so. Any idea how common or reliable a practice this is? I was under the impression that the burn through on black powder first stage motors was a good deal slower burning and less energetic, which would ease the separation and ignition compared to a hard charge.

Gap staging is common model rocket competition technique. A BP motor can be ignited by the hot gas generated by a booster motor or BP ejection charge separate by distances of ~1' or less if the intermediated compartment is vented near the sustainer to permit the cold air in the compartment to be displace and replaced by the hot gas generated by the booster.

I've seen it done by the St. John's Prep TARC team from Shrewsbury, MA that I mentored. They qualified at our CMASS TARC Qualification launches in March 2004 and finished second in the TARC Finals in May of 2004. Again the trick is to provide vent holes near the upper stage motor to allow the cold gas to be displaced by the hot ejection gases. They used an AT F50-4 APCP motor as the booster and a 24 mm C11-3 BP motor for the sustainer to apogee at 1250' with 2 eggs. It worked every time.

https://my.fit.edu/~dkirk/1202/Project/Team America Rocket Challenge Article.pdf

Bob

 

[TopRamen]

So theoretically, I would not be insane if I was to try to design a 13mm BP rocket that rode a 18mm Composite booster???

Hmmm.....

Will Openrocket let me do that? D21 to A3 0r A10???

 

[marcusSRG]

A short delay motor would probably work, or you can adjust the delay yourself. Just run a sim and make sure the delay won't be too long.

 

[g zilla]

Or run a piece of sheathed thermalite from the delay to the top of the second stage motor

 

[cerving]

It's a bit touchy firing a BP motor from an AP motor, since there's really no -0 AP motors. There WILL be some delay between burnout and when your BP sustainer fires, so you want to make sure that you have a good boost so that the sustainer is pointing up. and use just a little bit of BP so you get a flame without blowing everything apart. You might want to try Triple Seven or some other BP substitute for this since they don't explode unless they're contained. I'd recommend a minimum of 10:1 thrust/weight, and the shortest delay you can get. Fortunately Aerotech delays tend to run short anyway, so something like a G40-4 would probably be a good choice, maybe a G80-DMS if you drill the delay as short as it will go.

 

[neil_w]

So theoretically, I would not be insane if I was to try to design a 13mm BP rocket that rode a 18mm Composite booster???

Not specifically for that reason, no.

There are already rockets with 18mm boosters and 13mm sustainers, so it's a perfectly normal design.

Will Openrocket let me do that? D21 to A3 0r A10???

Sure, it'll let you do almost anything when it comes to motors.

 

[Trident]

I was going to suggest a cluster of two Estes E16 or F15 BP booster motors in the booster stage, but I looked at the rocket, and the booster body tube is pretty short, and just not long enough to hold them. How about a cluster of three D12-0 or E12-0 booster motors, gap staged to an E16 or F15 upper stage motor?

 

[aerostadt]

I tend to think that the US Rocket kits were designed a long time ago, when things were done differently. I had the US Rockets piston-stager that actually had a piston launcher for the second stage. There was no way that a black powder motor could have been used to ignite the second stage and the directions did not give any information on how to ignite the second stage. I tend to think to think that the piston-stager was designed before the days when electronic ignition became popular. Probably, an external fuse was lit at the time of launch to provide the time delay to ignite the second stage. I bought the model and updated my build to include electronic ignition. The documentation can be found in Rocket Reviews. I also had a brief description in the Apogee newsletter about using electronic ignition for this model. I noticed later that Tim Milligan improved my idea for electronic ignition and documented it on the Apogee website.