Aeropack on a Sumo

Many of you read about my L1 cert failure with my AT Sumo. After reviewing the cause of the failure, I will be leaving the baffle cap out on my new Sumo and adding an Aeropack retainer instead of the cheesy motor hook. However, when the rocket is built stock, the motors stick out of the motor tube about 3/4" where they are then grabbed by the motor hook. The 3/4" of space is taken up by some cardboard spacers. If I just glue my Aeropack on the end of the tube and use Aerotech's measurements as per the instructions, my motor will be recessed an additional 3/4" inside the rocket. It would seem that I need to scoot the motor tube 3/4" toward the aft end of the rocket so the back end of the motor stays where it does with the motor hook. Have any of you who have built Sumos with an Aeropack done this? The motor is pretty deep in the back of the rocket anyway, seems like it would be subject to the Krushnic effect if it were recessed any further.

Either way should work fine. I used an Aero Pack on my Arreaux, and moved the aft end of the motor tube towards the rear of the rocket so I could more easily unscrew the retaining cap. I've flown it without any issues. I could be wrong, but I think you'll only have to start worrying about the Krushnic if the aft end of the motor is recessed more then 1 body tube diameter inside the airframe (e.g. a motor can be recessed a maximum of 4 inches in a 4 inch airframe).

Hope this helps

You don't need to do it exactly like the instruction, you can move the motor tube. Today I install an Estes retainer on an Aerotech Initiator, they cost way less than Aero Pack

Okay, I'll move the motor tube back just to make sure that it's the same as if it were built stock. I have one other slight modification in mind, and that is epoxying a coupler into the tail section to reinforce it against landing damage. Have any of you done this, and has it had an adverse effect upon the rocket's stability?

Nope! Pretty standard upgrade for this one and the G-Force.

Wiley said:

Okay, I'll move the motor tube back just to make sure that it's the same as if it were built stock. I have one other slight modification in mind, and that is epoxying a coupler into the tail section to reinforce it against landing damage. Have any of you done this, and has it had an adverse effect upon the rocket's stability?

Click to expand...

It will effect your CG but not by much as will whatever motor retention you chose. Be sure to check CP/CG of the rocket in the launch ready configuration.