Kit-bashing an aerotech g-force long version - doable?

[meep]

I bought an aerotech g-force kit which is 147cm and plan to extend it with another body tube / coupler to be 2m length. The plan is to fly it on G motors.

• According to OpenRocket the stability increases from 1.28 to 1.5. I guess the reason for this is that the CG goes forward because of the added body tube
• Does the stability calculation in OpenRocket consider fin size / surface? Would it be an issue to increase the rockets length and mass but keep the fins the normal size of the kit?
• Is there any reason i should not do this, in terms of stability or other factors?

I still need to validate the OpenRocket configuration since some people reported that some of the files that are available are not correct but the one i took as starting point should be pretty good.

 

[rcktnut]

It will be stabile, but you're not going to get much altitude out of it on a G. Even without the added BT it's not that high of a flyer on a G motor.

 

[mikec]

You also run the risk of exceeding 1500g GLOW and not being able to fly without an FAA waiver.

Built stock, the kit flies just fine on a G.

 

[meep]

I know its not going to break altitude records, i'm just wondering if there is anything i'm overlooking. Also pretty new to mid power rockets so still learning about RocketSim and aerodynamics.

The idea is to make the top part swappable so i can either fly it stock or with another body tube in the XL version. I will be flying in europe so the FAA limit is not an issue but i will check if there are any similar limitations here.

 

[rcktnut]

I know its not going to break altitude records, i'm just wondering if there is anything i'm overlooking. Also pretty new to mid power rockets so still learning about RocketSim and aerodynamics.

The idea is to make the top part swappable so i can either fly it stock or with another body tube in the XL version. I will be flying in europe so the FAA limit is not an issue but i will check if there are any similar limitations here.

Good way to go about it! It will be fine both ways. I built mine stock around 25 years ago, great flying rocket, but like I said not very high on a G motor. Do you have the new kit with the screw on motor retainer? If ever planning on getting into HPR, 29mm. HPR motors work great in it. Build accordingly to allow use of those motors. Wish I would have but did not consider it at time of building due to BATF regs. here.
BTW: Does the stability calculation in OpenRocket consider fin size / surface? Of course it does!!

 

[loopy]

If you want the extended section to be removable, build the upper with a coupler and bulkhead in the bottom to attach the shock cord from the booster to. Use a quick link to attach it, and have it separate there on ejection. Attach the parachute close to the top of the shock cord near the coupler so the tube/nose cone aren't swinging and hitting the booster. Use plastic rivets or a really tight fit to keep the nose cone attached to the top of that tube.

 

[rcktnut]

If you want the extended section to be removable, build the upper with a coupler and bulkhead in the bottom to attach the shock cord from the booster to. Use a quick link to attach it, and have it separate there on ejection. Attach the parachute close to the top of the shock cord near the coupler so the tube/nose cone aren't swinging and hitting the booster. Use plastic rivets or a really tight fit to keep the nose cone attached to the top of that tube.

+1
The G force (mine anyway stock built) deploys that way, mid BT, not nose cone. I've never had a problem with deployment charge provided with motor but others have. Others had problems with coupler not fully separating from booster with provided charge. OP will most likely need a larger ejection charge in long configuration, or just planning on blowing nose cone off in short configuration. Illustrations provided by OP confusing, chute placement, bulkhead placement???

Another thing is it would be wise to add a section of coupler to the rear end of the body tube and coat with a thin layer of epoxy. Helps to reinforce it and keep from burning up.

 

[meep]

Yes the plan is to deploy directly after the lower section just like in the stock kit. In another aerotech kit i built, the coupler / body tube at the separation point was holding very tight, so i sanded it off a bit, and never had any problems with seperation. Might do the same here if i feel like its necessary.

On another note i figured out that i was not checking the "velocity off rail" in the simulation, which with the biggest G motor is only 10m/s on the modified kit, and 12.3m/s with the stock kit (with weight values provided by the configuration in OpenRocket, not yet verified since the rocket is still in the box).

Which is pretty low and while it might be ok on windstill days, it might be an unsafe rocket if there is wind or the rail is too short.

So i will go ahead and build the replaceable upper section but fly it in stock version with G motors, and if i can move on to higher power motors i can go ahead and launch the bigger version.

 

[86mustang408w]

Im putting one together myself. Would you be willing to share the OR file?

 

[cwbullet]

You also run the risk of exceeding 1500g GLOW and not being able to fly without an FAA waiver.

Built stock, the kit flies just fine on a G.

That is a huge issue. The Aerotech kit over light for its size.

 

[PatD]

Build it to mission. I extended, epoxied and up motored mine for my L2 cert. Extended by adding a payload bay with a standard DD setup in the coupler. flew it on a J330. It works great but it is not a class 1 flyer.

 

[86mustang408w]

Yes the plan is to deploy directly after the lower section just like in the stock kit. In another aerotech kit i built, the coupler / body tube at the separation point was holding very tight, so i sanded it off a bit, and never had any problems with seperation. Might do the same here if i feel like its necessary.

On another note i figured out that i was not checking the "velocity off rail" in the simulation, which with the biggest G motor is only 10m/s on the modified kit, and 12.3m/s with the stock kit (with weight values provided by the configuration in OpenRocket, not yet verified since the rocket is still in the box).

Which is pretty low and while it might be ok on windstill days, it might be an unsafe rocket if there is wind or the rail is too short.

So i will go ahead and build the replaceable upper section but fly it in stock version with G motors, and if i can move on to higher power motors i can go ahead and launch the bigger version.

I've seen some stock built Aerotech G-Forces lately fly to about 1000 feet or so with G80-10s. Its seems like a fun rocket, I'm putting mine together soon but it will 38mm and DD. Do you have any pictures of it? Just curious I don't see many of them, thank you.