Aerotech G8ST Motors at Research Launches

Richard Dierking said:

The website for the BPS Space Thrust Vector Control system recommends the AT G8 or G11 motor and the supplied TVC is 3D printed PLA. PLA has a low glass transition temp and melts at 155C. So, I'm curious to hear testimonials of flyers that have used these motors for rockets with TVC. Additionally, these rockets are not typically high-flyers and would probably be recovered pretty quickly.
Also, please note that the files to print the TVC are also available and other materials for the control are possible. For example, I was going to try ABS and Nylon with CF (NylonX).

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Yeah, Joe needs to update his website. One of my friends bought his kit and ended up melting the included PLA motor mount with an Estes F15 on the very first flight. The G8s get way hotter. If I were you I'd add a cardboard (or better yet, phenolic) insulating tube inside the motor mount, even if you print it with a higher temp material.

Joe reported melting of the TVC mount when using the G8:

https://mobile.twitter.com/joebarnard/status/994827358799630336?lang=en

Thank you Max, and jadebox for the link.
So, I have some ideas, but not really certain what I'm going to do. I might just stand by and see what happens with the G8 before I do anything.
It's interesting how this is playing out. AT creates a really long burn motor for Joe at BPS Space. And, perhaps there were other reasons I'm not aware of. But, the motor evidently messes up the BPS TVC. The motor gets too hot, so the standard may need to be increased in order to be certified. But, the problem with heat remains. So, any kind of engineering solution would have to be for the application, not the motor itself.
I don't know if Joe at BPS is working on this because he's kind of radio silent on the TVC presently and looks like he's concentrating on the vehicle with the ducted fan.
Going back to this testing/experience period for the G8, I hope people do provide their comments and provide some details about their experience. However, I can see the possibility of some bias in this type of "testing". That is, some people really wish to have the G8 approved, and because of this, some may be hesitant to provide any negative comments.
I would like to set up an Arduino, a micro card reader, and some temp probes and get some numbers but I doubt others are going to do something like this. Kind of moot because I don't have access to any of the motors.

I haven't had time yet, but I was considering seeing if the TVC motor mount can be printed with a larger diameter opening so that a liner could be added as well as seeing if another kind of plastic would work better. Both of those options seem more elegant than Joe's suggestion of just printing a new motor mount tube. Another option might be to see if a cardboard tube could be substituted for the plastic motor tube.

Of course, if the G8 isn't available this is all moot.

I sent an email to Joe (BPS Space) a few days ago asking if he would consider designing a 38 mm mount, and asking about possible temperature problems, which I now know exist. No response yet, but I understand he's a busy guy, and he might be hesitant to design a larger TVC, and keep it at model rocketry power and size.
There is space around the TVC and even several holes in the typical 74 mm airframe for movement. Perhaps some additional venting in the motor can may help. I think a technique of dissipating the generated heat would be better than insulating against it. And, changing materials as we previously discussed.
There's actually a bigger problem with amateur rockets with TVC in general for California and perhaps many other states. I don't want to go OT here, and will start a new post on this subject. Unless there is already one?

Richard Dierking said:

T Or, 29mm motor enclosed in a 38 mm case?
So, what I'm suggesting is rather than changing the standards dramatically, mitigate the problem.

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it's a g8. overencapsulate it with another case and it will never get off the pad. certainly being in a bigger rocket as well won't help (cause it would have to have a 38 mm motor mount, not 29....mass is the enemy of this motor

Sorry for the misunderstanding. I was actually thinking of a HP 38 motor with a larger TVC, or a 29 to 38 adapter which would be much higher than a whole 38 mm case. Also, upgrade the servos of course.
I would personally like a more progressive motor for what I would like to do and the G8's a bit too low power as well. But, it's made for a model rocket, not a HP rocket.
I'll continue to work on my rocket. If the G8 ends up being a no-go, I'll just make a motor myself.
What's the grain configuration of the G8?
Also, thinking of wild ideas. How about some dry ice a bit forward of the TVC? Joe likes models that look like originals and it would add to the effect before launch. Might cool the TVC and help keep the temp down during the flight.

Richard Dierking said:

If the G8 ends up being a no-go, I'll just make a motor myself.
What's the grain configuration of the G8?

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I presume it's a Blue Thunder end-burner like all of the Aerotech long-burning RC motors.

Of course there's almost nowhere in California where you can fly EX -- FAR is the only place I know of.

Thank you. Makes sense. Remember the J99? That was a warp 9 reload end burner for about 10 seconds. What a great sustainer motor. I bet that one got pretty hot at the end of the burn! I didn't even know there was a temperature standard back then.
So, as an end-burner the propellant wouldn't offer any insulation to the case aft end forward so yeah, I bet the business end gets really hot during the burn.
Anyone ever heard of a tampered liner with thicker material at the aft end? You could 3D print one, but it would be difficult finding a good material, or how about progressively expanding the ID in a fiberglass liner for the forward end. But, I realize it might decrease the propellant mass, because there would be a minimum of liner thickness you would have at the aft end.

It's a bit of a drive for me, about 3 hours, but I'm an active member at FAR. The TVC is interesting technology and wouldn't take up much room in my truck like my other projects do. Also, recovery would be closer. That's nice in the summer when it's so warm there.

I am also considering the RC motors from Aerotech such as the G12. It is 32mm in diameter. It has a nice long burn, but has a typical regressive thrust curve with a peak at the start and a long, lower tail. I haven't really looked at it hard enough yet to see if the lower thrust will work for me.

jadebox said:

I am also considering the RC motors from Aerotech such as the G12. It is 32mm in diameter. It has a nice long burn, but has a typical regressive thrust curve with a peak at the start and a long, lower tail. I haven't really looked at it hard enough yet to see if the lower thrust will work for me.

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They've discontinued the casing now but still make the reloads.