Aerotech G-force Build Thread - WIP

[overklock]

Hey folks, Merry Christmas! Documenting the build of my level 1 rocket here. I decided to go with the Aerotech G-Force. Reason being - I'm familiar and used to 29mm reloads, and I know that with such a large heavy rocket, an H motor will fly nice, low and slow. Additionally, it's a "somewhat" easy build. I say somewhat because I screwed up the CG by adding too much epoxy on my first build. Pictures below, there's not many, I'll try to take more as I go. Any advice is always appreciated!



Starting with the motor mount, I used epoxy to secure the areas I knew would receive the most amount of stress, super glue for everything else.



Following up on the motor mount comes the fins. So, here's the thing. I know Aerotech builds generally do not need fillets as the fins are meant to "pop out" should there be a hard landing. However, there are two things at play here as to why I added fillets:

1. This is for my level 1. In order to get my level one, the rocket has to be flyable again after landing. A fin popping out defeats that purpose.
2. I think they look cool

Unfortunately, this wound up being too much for this seemingly delicate balance of CG to CP on this rocket. More on this later.



So, due to the excess rocketpoxy adding additional weight to the aft-end, my CG wound up being wonky. The Barrowman's method put the CG up just over 1" from the CP. However, the RockSim formula put it just above 4". This is obviously a huge discrepancy. Regardless, I was not comfortable with a CG/CP that close, and I decided to start over. Luckily, I had a second G-force for spare parts. I began to rebuild the lower half. Important to note that internal fillets using epoxy was done on both of these as well.

Fin filets before:




Fin fillets after. Much smaller, really just fills the gaps is all:



Redoing the bottom half knocked an additional 20 grams off the lower half of my rocket, resulting in a more stable simulation. The base weight of the aft end pre epoxy came out to 520 grams, total weight after epoxying everything together: 535 grams. This is in comparison to the whopping 555 grams of the previous aft build.

CG/CP on first aft build:



CG/CP after rebuilding the aft end:



Rocksim Stability Equation puts it in a much more favorable light, my understanding being that it accounts for base drag.



Everything glued together, now for my least favorite part of every build, filling the spirals and sanding. I keep promising to only run fiberglass builds in the future, yet here I am.




Anyway, this is where I am for now. I will be adding to this in the future. I'm still debating on using superglue on the coupler with sandpaper in order to harden/smooth the section that slides into the body. Apparently this particular rocket can have a hard time separating. Never done any kind of superglue "glassing" before. So if anyone recommends this or has tips please let me know.

Cheers, more updates to come!

 

[overklock]

Fill, sand, fill, sand.

If anyone has an easier way to do this, I'm all ears.

 

[thzero]

Glass it.
Don't buy tubes with spirals?

 

[overklock]

Glass it.
Don't buy tubes with spirals?

Glassing is something I’m looking into.
And yeah totally. This is a kit so, dealing with it for now lol

 

[Hobie1dog]

Fill, sand, fill, sand.

If anyone has an easier way to do this, I'm all ears.

life is way too short to spend the remaining short moments of your life filling spirals. Fiberglass is much tougher and smooth as a baby's butt.
no one has ever laid in a hospital bed on their last day of their life and made the comment, " I'm glad I took all that time to fill all those spirals in all those Rockets"

 

[overklock]

Finished product! Still not a fan of Aerotech's decal design. Waterslide is so much better.

Fingers crossed for my level 1.

 

[thzero]

Good luck

 

[James Owen]

Looks great! Let us know how the flight goes/went!

 

[crossfire]

Finished product! Still not a fan of Aerotech's decal design. Waterslide is so much better.

Fingers crossed for my level 1.

View attachment 553649

Nice build

 

[ShadowSpire48]

If a fin pops out on landing, that shouldn't ruin your cert because if you have a bottle of super glue, it's an easy fix and 100% flyable again so it's well within the rules of a cert flight (provided the person doing the cert judging isn't against that somehow). The outside of the G force rocket design is nice but the way they designed the inside has much that needs fixing. The motor tube does not need to be that long if you glue the coupler into the upper body tube with a bulkhead and not the wrong way like Aerotech suggests with gluing it into the bottom tube. It's a good looking rocket but a poor design that has caused many crashes due to midpower motors not having enough BP to fill the whole upper body tube to separate it.

 

[mrwalsh85]

If a fin pops out on landing, that shouldn't ruin your cert because if you have a bottle of super glue, it's an easy fix and 100% flyable again so it's well within the rules of a cert flight (provided the person doing the cert judging isn't against that somehow).

As a person who routinely signs off on L1 certifications in our club, I don't feel comfortable with that statement being shared with a candidate for L1. According to the NAR guidelines (and I'm sure TRA is along the same wavelength), the following is quoted in the L1 cert procedure... https://www.nar.org/high-power-rocketry-info/level-1-hpr-certification-procedures/

1. The Level 1 High Power Certification Candidate will fly their model. The flight must be witnessed directly by the Certification Team. Stability, deployment of the recovery system, and safe recovery will be considered when evaluating safety of the flight. Models experiencing a catastrophic failure of the airframe, rocket motor, and/or recovery system (e.g., shock cord separation) will not be considered as having a safe flight.
2. The model must be returned to the Certification Team directly after flight for inspection to verify engine retention and for evidence of any flight-induced damage. The Certification Team will check the appropriate blocks in the HPR Level 1 Checklist indicating that a safe flight was made and that the post-flight inspection was satisfactory. In general, the guideline for acceptable flight damage is that the model could be flown again without repair. It is left to the judgment of the Certification Team to differentiate between flight damage and “normal” maintenance to assure reliability (e.g., shock cord replacement to prevent future flight problems). “Zippering” of the body tube is another area of flight damage left to Certification Teams judgment for acceptability.

In short, a popped fin is not acceptable for a pass on L1 - and I know it isn't acceptable by me and I imagine I'm not alone here. The purpose of certification procedures is to prove the ability of an individual to build a rocket and fly it. The process of building includes the selection of a kit, evaluating the instructions (if applicable), and building it - including modifications they feel needed to ensure that the rocket will be durable enough to experience the stress of rocket preparation, flight, and recovery.

Yes, you are right, it is up to the certifying authority, but we shouldn't be presenting the image that they can get away with just about anything as long as the thing moves off the pad.




Now, if a fin pops off, and you can glue it back in at the field and feel confident that the repair is better than your original flight, and you can find another motor, by all means, make another attempt to get your certification. I have no qualms with that. That's your prerogative. I don't suggest waiting until the last flight of the day if you think that the possibility of needing a reflight is there.

 

[Handeman]

Just a couple of notes.
Since you plan on flying this on H motors and not Gs, I would have just added a few grams of weight to the nose cone and left the larger fillets on the bottom end. The extra weight won't bother H motors that can easily fly 2000 g rockets.
As for the way the fins are attached to the MMT, that is a MPR design Aerotech came up with to fly G motors with. It will work with small H motors also, but that is actually pushing the upper limits of the design. That's why I would keep the larger fillets.
When you build your next L1 rocket with a 38mm MMT so you can fly I motors also, you'll learn a lot more about the power of HPR motors and TTW mounted fins. That's something we all get by experience.

I'm sure you'll get lots of great flights with this one. Good luck on the cert.

 

[gldknght]

Fill, sand, fill, sand.

If anyone has an easier way to do this, I'm all ears.

I never bother with the spirals. Just spray on a couple coats of automotive primer, light sanding between coats, then paint. You can't see unfilled spirals when the rocket is on the pad, mush less when it's going up. You won't see a noticeable performance difference either.