Modification questions Aerotech G-Force

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sheepdog

sheepdog

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Hello All,
One of my favorite rockets last year was the Aerotech G-Force, on it 4th flight it failed to seperate at ejection and nosed dived into the field.
Needless to say destroyed. I have read many article's on this site on this issue and how to alter the coupler area to help prevent this from happening, CA glue, primer, sanding, etc. to
insure the coupler has a smooth action to prevent binding.
I know this has been an on going issue with this model and I will take all the advice on this site into consideration on my next build of the G-Force. I am
still some what surprized that Aerotech has not changed the design but then again their catalog is 5 years old so maybe eventually they will get around to it.
I have 4 other Aerotech models and love the quality of their rockets.

In the mean time has anyone modified the G-Force so the actual seperation occurs where the nose cone meets the main body? And if so what was required? I have a Mercury
Engineering Integrater which is the same Diameter but 8 inches shorter and seperates at the nose cone, and I have neve had an issue with it. It has 10+ Flights under it's belt.

Any Suggestions appreciated....

Thanks
 
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When you assemble it, use the coupler as is and just glue the two body tubes together. You can omit the bulk plate on the coupler or drill a bunch of holes in it. If you omit it, put a crew eye in the upper CR and tie the recovery there. The only issue may be the low amount of BP in a hobby line reload and the large volume you are pressurizing.
 
I think the main problem would be that the long body tube might require more than the standard amount of BP to pressurize the tube and eject the nosecone. You could add a stuffer tube or supplement the BP charge. If you don't add a stuffer stube, you might want a chute shelf to keep the chute from settling deep into the BT under acceleration.

The G-Force is one of my favorite rockets too. So far I have not had a failed deployment. I coated the inside of the lower part of the recovery bay with thin CA and sanded it smooth. That helped some. It seems like every time I fly the G-Force, the fit is different. Maybe the parts expand and contract with temperature and moisture. I have to double check the fit every time.

Good luck, and let us know what you decide. My nephew told me he'd like a large rocket with his business logo design on it to display in his business. The G-Force is nice and big and easy to build, so I thought about using that. Since it would mostly be for show, not for flight, I thought about breaking it at the NC too.
 
I may be off base, but for the first build, did you make sure all glue joints were nice and solid? Any gaps would mean a lot of the ejection gases can escape into the forward bulkhead or motor tube area and thus lose significant ejection charge pressure (either side can almost triple the area being pressurized). Also I've heard some suggestion to always tape around the motor so that ejection gases don't escape out around the motor; however I'm not sure if that really has any effect unless your motor tube is a very "loose" fit with the motor.
 
That makes sense, now if only some rocketeers will chime in saying they have done it and it works that
would be great. We all use due diligence in the prepping of our rockets prior to launch, last thing any of us need is
the unnecessary aniexety if it's going to eject properly...oh wait we feel that with every launch....

Thanks
 
I would say that your post helped me to realize I need to routinely check rocket structures in the bigger rockets before launching...especially if using CA/superglue since that glue can crack more readily under stress than epoxies or wood glue in my experience.
 
I guess my question would be...in it's current state it must not only eject the 19" upper body tube but also the attached nose cone. In the case of just seperation at the nose cone, you
would still have the same amount of space for ejection gases, but you would only need to eject the nose cone which is considerably less in weight. So for me from a logical sense
is seem like it would work. But then again Math and Science were not my strengths. I will let you know what I decide on. thanks for your feed back
 
I have no experience with the G Force, so, my techniques may not apply. On my rockets that seperate at a paper coupler, I soak the coupler with CA, then sand it smooth. At a launch, I can sand, or apply masking tape as needed. Ejection residue can also cause couplers to be more stubborn, so, I keep a bottle of baby powder in my range box, and spread it on if needed.

David
 
Not that I know anything, but my G-Force has never failed. It has to have at least 20 launches on it. I built it stock, which sadly means I can't put anything but AT SU motors in it (I know AT reloads fit in it, but I am a CTI man). Anyway, I have to wonder if you made sure everything was neatly packed inside the coupler: chute was between the coupler and the airframe, shock cord wasn't knotted. etc. Have you checked to see if the baffle is clear? If there is burnt propellant in the baffler, then you won't get enough airflow to pop the rocket apart.

Another option is to add a little extra BP to the ejection charge on your motor. I have never done this, but it would give you more oomph.
 
sheepdog said:
I guess my question would be...in it's current state it must not only eject the 19" upper body tube but also the attached nose cone. In the case of just seperation at the nose cone, you
would still have the same amount of space for ejection gases, but you would only need to eject the nose cone which is considerably less in weight. So for me from a logical sense
is seem like it would work. But then again Math and Science were not my strengths. I will let you know what I decide on. thanks for your feed back
Click to expand...

Yes, true...there is more mass in current config since half the bt is attached and being ejected. However unless I'm misunderstanding you, it wouldn't be the same amount of space for ejection gasses if you go nose ejection. Current config is that the ejection area is between the forward most centering ring and the Coupler tube Bulkhead, which is about 1.5 calibers from my guess...however if you remove the front bulkhead and don't use a stuffer tube, you expand that area to pressurize by 3x from what I see in the cutaway diagram in the instructions.

So if you want nose cone eject, I agree with the viking...a stuffer tube extending from the motor tube (maybe 29mm?) and one more centering ring so that the area to pressurize is moved just under the nose cone with room sufficient for chutes, etc.

Disclaimer is that I in no way claim to know more than the rocket designers who made this kit, so use advice with a healthy dose of doubt. ;)
 
sheepdog said:
I guess my question would be...in it's current state it must not only eject the 19" upper body tube but also the attached nose cone. In the case of just seperation at the nose cone, you
would still have the same amount of space for ejection gases, but you would only need to eject the nose cone which is considerably less in weight. So for me from a logical sense
is seem like it would work. But then again Math and Science were not my strengths. I will let you know what I decide on. thanks for your feed back
Click to expand...

If you built the kit stock and according to instructions the first time, then the volume that the ejection charge must pressurize is pretty small. It's the volume of the motor tube, plus the volume of the coupler that serves as the recovery bay. There is a bulkhead at the top of the coupler that keeps the ejection gasses from going into the rest of the upper tube, so that volume does not need to be pressurized to force the rocket apart.

If you leave out that forward bulkhead and you glue the upper BT to the coupler to make a continuous body tube, then the volume you must pressurize to blow out the nosecone is much bigger, because it includes the WHOLE upper BT, not just the part inside the coupler up to the bulkhead.

Another thing to be aware of, the extra mass of the upper BT attached to the NC helps it pull the parachute out of the recovery bay. Some people think that the ejection charge blows the parachute out like a shotgun. That might be true for small LPR rockets, but not so much for larger rockets like the 4" G-Force. For big rockets, you want them to separate with force, and the momentum of the upper part pulls the parachute out of the recovery bay --- it doesn't get shot out, it gets yanked out.

With the stock G-Force separating in the middle, you have two heavy halves of the rocket, and a very small recovery bay. As long as the rocket separates properly, those two heavy pieces will pull the chute out of the small bay.

If you redesign the rocket to separate at the NC, you only have the momentum of the NC, not the whole upper section. And that smaller momentum needs to pull the parachute all the way from the bottom of a much longer recovery bay. I think it will probably be less reliable to have it open at the top, at least without a few other mods.
 
Well I was going to follow your advice on the Stuffer tube until I got to your side effects....Don't want to gross anyone out at the club launch.
But it is still under consideration.

thanks
 
ThirstyBarbarian said:
If you built the kit stock and according to instructions the first time, then the volume that the ejection charge must pressurize is pretty small. It's the volume of the motor tube, plus the volume of the coupler that serves as the recovery bay. There is a bulkhead at the top of the coupler that keeps the ejection gasses from going into the rest of the upper tube, so that volume does not need to be pressurized to force the rocket apart.

If you leave out that forward bulkhead and you glue the upper BT to the coupler to make a continuous body tube, then the volume you must pressurize to blow out the nosecone is much bigger, because it includes the WHOLE upper BT, not just the part inside the coupler up to the bulkhead.

Another thing to be aware of, the extra mass of the upper BT attached to the NC helps it pull the parachute out of the recovery bay. Some people think that the ejection charge blows the parachute out like a shotgun. That might be true for small LPR rockets, but not so much for larger rockets like the 4" G-Force. For big rockets, you want them to separate with force, and the momentum of the upper part pulls the parachute out of the recovery bay --- it doesn't get shot out, it gets yanked out.

With the stock G-Force separating in the middle, you have two heavy halves of the rocket, and a very small recovery bay. As long as the rocket separates properly, those two heavy pieces will pull the chute out of the small bay.

If you redesign the rocket to separate at the NC, you only have the momentum of the NC, not the whole upper section. And that smaller momentum needs to pull the parachute all the way from the bottom of a much longer recovery bay. I think it will probably be less reliable to have it open at the top, at least without a few other mods.
Click to expand...

From all the feed back and articles I have read I may just try another one and build it stock and take extra precaution on the coupler and insure I check it before each and every launch. There really has been no other sure fire way to from what I have seen.
Thanks for your suggestion.
 
sheepdog said:
Well I was going to follow your advice on the Stuffer tube until I got to your side effects....Don't want to gross anyone out at the club launch.
But it is still under consideration.

thanks
Click to expand...

LOL! Yes, I know how you feel...sometimes you think "there must be a better way to do this!", but once you start it can become much more difficult than you anticipated. That's actually good...it shows you're understanding the situation and limitations. Trying to solve the design issue can also be like working on puzzles. Very tricky and many may shy away, but that is the challenge after all. :) One of my current ongoing projects is a break-apart fliskits ACME Spitfire...lots of fun, but also lots of trials, testing and fixing.

Also I just checked the directions...they suggest using either CA "OR" epoxy. I would strongly suggest epoxy on all the centering rings and bulkheads. Additionally I've heard that for these Aerotech rockets, you should check/shake clean the cooling mesh after every 2-3 flights since if it is clogged, that can also lessen the ejection charge getting through. Very good advice in my opinion.
 
I built mine with a blue tube coupler, dual deploy 38mn mmt aeropack kevlar shock cord and custom decals.

If i were to do today would clone it with LOC parts and order fin set from AT
 
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sheepdog said:
Well I was going to follow your advice on the Stuffer tube until I got to your side effects....Don't want to gross anyone out at the club launch.
But it is still under consideration.

thanks
Click to expand...

Want a more out-of-the-box idea? How about a piston system using a plunger in the added on stuffer tube and a bulkhead with glued coupler as the piston? Its a more elaborate "stretched" version of the Sumo system and the area to pressurize is much smaller. :)
 
KenECoyote said:
Also I just checked the directions...they suggest using either CA "OR" epoxy. I would strongly suggest epoxy on all the centering rings and bulkheads. Additionally I've heard that for these Aerotech rockets, you should check/shake clean the cooling mesh after every 2-3 flights since if it is clogged, that can also lessen the ejection charge getting through. Very good advice in my opinion.
Click to expand...

I am building my second G-Force kit. Like the first, it has been built with CA adhesive. I have only used 30 minute epoxy for the fin fillets. AeroTech kits do not need epoxy for general assenbly.
Epoxy only adds weight/mass.
 
Initiator001 said:
I am building my second G-Force kit. Like the first, it has been built with CA adhesive. I have only used 30 minute epoxy for the fin fillets. AeroTech kits do not need epoxy for general assenbly.
Epoxy only adds weight/mass.
Click to expand...

Why do you need to put fillets on it for? I never have with mine and it always flew nice. I could see internal, but external the fin has that weird shape to it. There might be a gap in some areas between the fin and airframe, but thick CA should fill it.
 
Initiator001 said:
I am building my second G-Force kit. Like the first, it has been built with CA adhesive. I have only used 30 minute epoxy for the fin fillets. AeroTech kits do not need epoxy for general assenbly.
Epoxy only adds weight/mass.
Click to expand...

I was actually suggesting epoxy only for the internal buikhead and centering rings since CA is more brittle and a crack (such as from a hard landing) can result in disaster the next time if enough ejection pressure is allowed to escape to the forward or aft sections. Chances of this are slim, but why risk it. However using more CA would be a good alternative and would definitely be lighter. I guess the best thing to do if you're worried about cratering a G-Force (which was part of the original post here) is a good pre-flight inspection...good practice in general for all our rockets. :)
 
AfterBurners said:
Why do you need to put fillets on it for? I never have with mine and it always flew nice. I could see internal, but external the fin has that weird shape to it. There might be a gap in some areas between the fin and airframe, but thick CA should fill it.
Click to expand...

I use 30 minute epoxy for fin fillets on all the models I build. It's easier to work with than CA or putty. I can smooth out the epoxy with my finger.

There is a good sized gap between the fin root and body tube on the AeroTech G-Force and Sumo kits.
I like my rockets to look pretty. :wink:
 
KenECoyote said:
I was actually suggesting epoxy only for the internal buikhead and centering rings since CA is more brittle and a crack (such as from a hard landing) can result in disaster the next time if enough ejection pressure is allowed to escape to the forward or aft sections. Chances of this are slim, but why risk it. However using more CA would be a good alternative and would definitely be lighter. I guess the best thing to do if you're worried about cratering a G-Force (which was part of the original post here) is a good pre-flight inspection...good practice in general for all our rockets. :)
Click to expand...

AeroTech kits are designed and engineered differently than other MPR rocket kits.
The CA adhesive just holds the parts in place. The internal structure bears the load.
I've built dozens of AeroTech kits (Including prototypes and catalog models) and CA is fine for all the centering rings and bulkheads.
 


G-Force Nose blow shown here:



ken_sneeze.jpg


GATCHAMAN_VOL_11-42-2.jpg


:)
 
Last edited:
Initiator001 said:
AeroTech kits are designed and engineered differently than other MPR rocket kits.
The CA adhesive just holds the parts in place. The internal structure bears the load.
I've built dozens of AeroTech kits (Including prototypes and catalog models) and CA is fine for all the centering rings and bulkheads.
Click to expand...

Yup, AeroTech G-Force instructions note to use CA; however it also notes "...OR 5 to 15 minute cure epoxy", so I don't think I was off-base suggesting using epoxy as well. Also one can build almost all of the mainstream rocket kits stock as instructed and it should be fine; however it seems many people prefer to mod them slightly with choice of glues, diff chutes, shock cord, DD, lights, hello kitty stickers, etc. (maybe not that last one). That's what makes this site so cool! :)

Bob, given your background experience, what are your thoughts on the original topic of a nose-blow G-Force? I have a kit right in front of me and I'm tempted to mod it just to see if I can get it to work, but it may be a failure and that would be $$ wasted.
 
Initiator001 said:
I use 30 minute epoxy for fin fillets on all the models I build. It's easier to work with than CA or putty. I can smooth out the epoxy with my finger.

There is a good sized gap between the fin root and body tube on the AeroTech G-Force and Sumo kits.
I like my rockets to look pretty. :wink:
Click to expand...

I agree fillets look nice, but as I said a little thick CA or epoxy on those gaps make it look good. I built one G-FORCE and I made fin fillets but they covered that hump on the lower part of the fin so they were decent size... they turned out nice, but a lot of work. Heck all this talk about G-FORCE's is making me want to get one again. I love that the kits go together so well.
 
Initiator001 said:
I use 30 minute epoxy for fin fillets on all the models I build. It's easier to work with than CA or putty. I can smooth out the epoxy with my finger.

There is a good sized gap between the fin root and body tube on the AeroTech G-Force and Sumo kits.
I like my rockets to look pretty. :wink:
Click to expand...


When you say you can smooth the epoxy with your finger, you mean with a gloved finger, of course. (For the benefit of those who have not used epoxy, don't get it on your skin.)
 

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